CNS anatomy is a detailed lecture of brain and spinal cord

Gross of Anatomy Nervous system Prepared by : Tsegaye Mehare ( MSC,Anatomist ) 1

Objectives At the end of this session students will be able to: List dawn subdivision of cerebrum &their functional s Describe basal nuclei structure Enumerates basal nuclei connections Describe Limbic system

Organization of the nervous system: Through out the day your body perceives and responds to multiple sensations. You smell springs flowers, feel the touch of a hand on your shoulder, and perceive your limbs moving. You control multiple muscle movements in order to walk, talk to the person, sitting next to you and hold this text book. Other muscle movements occur with out your voluntary input, such as your heart beating, your stomach churning to digest your break fast, and your started reaction to the honking of a horn. All of these sensations and muscle movements are interpreted and controlled by your nervous system.

Basic Functions of the Nervous System Sensation Monitors changes/events occurring in and outside the body. Such changes are known as stimuli and the cells that monitor them are receptors . Integration The parallel processing and interpretation of sensory information to determine the appropriate response Reaction Motor output. The activation of muscles or glands (typically via the release of neurotransmitters (NTs))

NS… Structural and functional division of the Nervous system: I. Structural division A. Central nervous system (CNS ): Command center of nervous system that interprets and processes nervous information. Consist of: Brain and spinal cord. B. Peripheral nervous system (PNS) : Projects information to and receives information from CNS, mediates some reflexes. Such as nerves and ganglia

II.FUNCTIONAL DIVISION A. Sensory Input (afferent) Sensory signals picked up by sensor receptors Carried by nerve fibers of PNS to the CNS B. Motor Output (efferent) Motor signals are carried away from the CNS Innervate muscles and glands Sensory input and motor output further divided according to the region they serve Somatic body region Visceral body region Results in four main subdivisions Somatic sensory Visceral sensory Somatic motor Visceral motor

Types of Sensory and Motor Information

Nervous Tissue Cells are densely packed and intertwined(tangled) Two main cell types Neurons – transmit electrical signals Support cells ( neuroglial cells in CNS) Nonexcitable Surround and wrap neurons Human body contains billions of neurons Basic structural unit of the nervous system Specialized cells conduct electrical impulses along the plasma membrane Nerve impulse (action potential) Neurons have special characteristics Longevity – can live and function for a lifetime Do not divide – fetal neurons lose their ability to undergo mitosis; neural stem cells are an exception High metabolic rate – require abundant oxygen and glucose Neurons die after 5 minutes without oxygen

The functional and structural unit of the nervous system Specialized to conduct information from one part of the body to another There are many, many different types of neurons but most have certain structural and functional characteristics in common: Cell body (soma) One or more specialized, slender processes (axons/dendrites) An input region (dendrites/soma) A conducting component (axon) A secretory (output) region (axon terminal) Neurons….

Cell body Cell body (soma) found around nucleus Size of cell body varies from 5–140µm Contains usual organelles plus other structures Chromatophilic bodies ( Nissl bodies) Clusters of rough ER and free ribosomes Neurofibrils – bundles of intermediate filaments Form a network between chromatophilic bodies Most neuronal cell bodies located within the CNS & protected by bones of the skull and vertebral column Ganglia – clusters of cell bodies that lie along nerves in the PNS

Neuron processes Dendrites Extensively branching from the cell body Transmit electrical signals toward the cell body Chromatophilic bodies – only extend into the basal part of dendrites and to the base of the axon hillock Function as receptive sites for receiving signals from other neurons Axons Neuron has only one Impulse generator and conductor Transmits impulses away from the cell body Chromatophilic bodies are absent No protein synthesis in axon

Axons …. Neurofilaments , actin microfilaments and microtubules provide Strength along length of axon Aid in the transport of substances to and from the cell body Branches along length are infrequent Multiple branches at end of axon called axon terminals Nerve impulse Generated at the initial segment of the axon Conducted along the axon Releases neurotransmitters at axon terminals Neurotransmitters – excite or inhibit neurons Neuron receives and sends signals

Synapses Site at which neurons communicate Signals pass across synapse in one direction Presynaptic neuron Conducts signal toward a synapse Postsynaptic neuron Transmits electrical activity away from a synapse Two neurons communicating at a synapse

Classification of neurons Structural classification Multipolar – possess more than two processes Numerous dendrites and one axon Bipolar – possess two processes Rare neurons Found in some special sensory organs Unipolar ( pseudounipolar ) – possess one short, single process Start as bipolar neurons during development

Functional classification of neurons Functional classification is based on direction of nerve impulse travels Sensory (afferent) neurons Transmit impulses toward the CNS Virtually all are unipolar neurons Cell bodies in ganglia outside the CNS Short, single process divides into Central process – runs centrally into the CNS Peripheral process – extends peripherally to the receptors

Motor ( efferent ) neurons Carry impulses away from the CNS to effector organs Most motor neurons are multipolar Cell bodies are within the CNS Form junctions with effector cells Interneurons (association neurons) Most are multipolar Lie between motor and sensory neurons Confined to the CNS

Neurons classified by function

Gray and white matter in CNS Gray matter Is gray-colored and surrounds hollow central cavities of the CNS Forms H-shaped region in the spinal cord Dorsal half contains cell bodies of interneurons Ventral half contains cell bodies of motor neurons Primarily composed of neuronal cell bodies, dendrites, unmyelinated axons Surrounds white matter of CNS in cerebral cortex and cerebellum

Gray and white matter in CNS White matter Lies external to the gray matter of brain stem and spinal cord Composed of myelinated axons Consists of axons passing between specific regions of the CNS Tracts are bundles of axons traveling to similar destinations

CENTERAL NEROUS SYSTEM Brian Spinal cord

Terminology & Neuroanatomical Directions CNS PNS Clusters of cell bodies Nuclei Ganglia Bundles of axons Tracts Nerves Anterior ( rostral ) – towards the nose Posterior (caudal) – towards the tail Dorsal – towards the surface of the back or the top of the head Ventral – towards the surface of the chest or the bottom of the head Medial – towards the middle Lateral – towards the side Proximal – close Distal – far Superior – top of the primate head Inferior – bottom of the primate head

Central nervous system Meninges — connective tissue layers that surround and protect the brain and spinal cord (CNS) Dura mater (“tough mother”) Tough, fibrous outer 2 layers Dural sinus between them contains CSF Epidural space above dura of spinal cord Arachnoid (“spidery”) Subarchnoid space Cerebrospinal fluid Pia mater (“delicate mother”) Thin inner layer Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Falx cerebri – partitions the right and left cerebral hemispheres Tentorium cerebelli - separates the occipital and temporal lobe of the cerebrum from the cerebellum Falx cerebelli - partitions the right and left cerebellar hemispheres Diaphragma sellae - forms the roof of the sella turcica Spaces between the meninges of the brain 1. Epidural space- it lies b/n the duramater and bone 2. Subdural space- lies b/n the dura mater and arachinoid mater 3. Sub arachinoid space- lies b/n arachinoid mater and pia mater contains CSF, blood vessels of brain, some filaments connecting the arachinoid and pia mater

Cranial meninges Figure 8-13(a)

Spinal meninges Figure 8-13(b)

3 primary divisions: Forebrain cortex (folded stuff) limbic system, etc (stuff around brain stem) Midbrain (top of brainstem) Hindbrain (bottom of brainstem + cerebellum ) - From dorsal to ventral four main divisions Cerebrum Diencephalon Brain stem cerebellum Brain

Superior View of Brain Figure 8-16(a)

Figure 8-16(c) Mid- sagittal Section of Brain

Cerebrum Cerebrum -largest division of the brain that divided into two hemispheres Cerebral cortex – outer most layer of gray matter making up the superficial aspect of the cerebrum.

Cerebrum…. Consists of the right and left hemispheres which are incompletely separated by a longitudinal cerebral fissure. Portions of the two hemispheres communicate by a large tract of white matter. A portion of the meninges called the falx cerebri extends into the longitudinal fissure. Contain central cavity called lateral ventricle filled with CSF. Cerebral cortex is characterized by numerous folds & grooves called convolutions Elevated called cerebral gyri Grooves called cerebral sulci

Three types of fibers named according to location and the direction in which they conduct impulses. 1. Association fibers: are confined to a given cerebral hemisphere and conduct impulses b/n neurons within the hemisphere anterior to posterior or vise versa. 2.Commussural fibers: connect the neurons and gyri of right hemisphere with the left hemisphere . E.g. corpus callosum 3. Projection fibers: from the ascending and descending tracts that transmit impulses from the cerebrum to other parts of the brain & other parts of the brain to the cerebrum.

Fibers of cerebral white matter

Each cerebral hemisphere is divide into four lobes - Frontal lobe - Parietal lobe - Temporal lobe - Occipital lobe Insula

Cerebrum - Gross Anatomy Cerebral cortex is 3mm layer of gray matter with extensive folds to increase surface area ---- divided into lobes

Frontal lobe Form the anterior portion of cerebral hemisphere A prominent deep furrow called the central sulcus (fissure of rolando ) separates the frontal lobe from the parietal lobe. Lateral sulcus: separate frontal lobe from temporal lobe. Frontal Lobe - Cortical Regions Primary Motor Cortex ( Precentral Gyrus ) – Cortical site involved with controlling movements of the body. Somatic motor association area ( premotor cortex): Coordinates motor responses (learned movements)

Cerebrum Figure 8-19

… The precentral gyrus : an important motor area, is positioned immediately in front of the central sulcus. Function of frontal lobe Areas for planning, mood, smell and social judgment Initiating voluntary motor impulses for the movement of skeletal muscles.

Parietal lobe Lies internal to the parietal bone and forms the supro -posterior part of cerebral hemispheres. It terminates; anteriorly at the central sulcus. posteriorly at parieto occipital sulcus and laterally at lateral sulcus . NB: an important anatomical feature of this lobe is the postcentral gyrus. FUNCTION Primary somatosensory area(e.g. cutaneous & muscular sensations), understanding speech & formulating words to express thoughts and emotions; interpretation of textures & shapes.

Parietal Lobe - Cortical Regions Primary Somatosensory Cortex (Postcentral Gyrus) – Site involved with processing of tactile and proprioceptive information . Somatosensory Association Cortex - Assists with the integration and interpretation of sensations relative to body position and orientation in space. May assist with visuo -motor coordination Primary Gustatory Cortex – Primary site involved with the interpretation of the sensation of Taste. .

Primary Somatosensory Cortex/ Postcentral Gyrus Primary Gustatory Cortex Somatosensory Association Cortex Regions Modified from: http://www.bioon.com/book/biology/whole/image/1/1-8.tif.jpg

Temporal lobe lies inferiorly to the lateral sulcus and lies inside the temporal bone. It is separated from frontal and occipital lobe by lateral sulcus. Contain primary auditory center. FUNCTION: Interpretation of auditory sensations; storage(memory) of auditory and visual experiences.

Primary Auditory Cortex Wernike’s Area Primary Olfactory Cortex (Deep) Conducted from Olfactory Bulb Regions

Occipital lobe Not distinctly separated from parietal & temporal lobes. The occipital lobe is superior to the cerebellum & is separated from it by an in folding of the meningeal layer called the tentorium cerebelli. Contain primary visual center. Function Integration of movements in focusing the eye, correlation of visual images with pervious visual experience & conscious perception of vision.

Occipital lobe – cortical regions Primary Visual Cortex – This is the primary area of the brain responsible for sight -recognition of size, color, light, motion, dimensions, etc. Visual Association Area – Interprets information acquired through the primary visual cortex.

Primary Visual Cortex Visual Association Area Regions Modified from: http://www.bioon.com/book/biology/whole/image/1/1-8.tif.jpg

Insula Is deep lobe of the cerebrum that cannot be viewed on the surface. It is deep to the lateral sulcus & is covered by portions of the frontal, parietal & temporal lobes. Unknown function? Autonomies response to pain stimulus

Cerebrum Hemispheric Lateralization Functional differences between left and right hemispheres Functional asymmetry is termed as hemispheric lateralization. Each cerebral hemisphere performs certain functions that are not ordinarily performed by the opposite hemisphere

Cerebrum Left Hemisphere In most people, the left brain ( dominant hemisphere ) controls: Reading, writing, and math Decision making Speech and language Right Hemisphere Right cerebral hemisphere relates to: Senses (touch, smell, sight, taste, hearing) Recognition (faces, voice inflections)

Hemispheric Lateralization

Deep gray matter of the cerebrum Consists of: Basal ganglia: involved with motor control The basal forebrain nuclei: associated with memory clastrum : a nucleus of unknown function Basal forebrain Anterior and dorsal to hypothalamus Important for arousal, wakefulness, attention Lose cells in nucleus basalis  decreased attention & intellect

Basal ganglia system Group of nuclei (mass of grey matter) in the forebrain and upper part of the brain stem that have motor function of great importance. The basal ganglia are a collection of nuclei that have been grouped together on the basis of their interconnections. These nuclei play an important role in regulating movement Role in certain disorders of movement ( dyskinesias ), which include jerky movements ( chorea ) writhing movements ( athetosis ) rhythmic movements ( tremors ) Derived from telencephalon and partly diencephalon,mesencephalon

Basal n uclei…. Comprise multiple sub-cortical nuclei within each cerebral hemisphere. Comprises corpus straitum , claustrum and amygdaloid nucleus. Primary function is likely to control and regulate activities of the motor and pre-motor cortical areas so that voluntary movements can be performed smoothly.

Traditional classification Caudate nucleus Lentiform nucleus Amygdaloid body Claustrum Clinical classification Caudate nucleus Lentiform nucleus Subthalamus Substantia nigra Corpus straitum : caudate nucleus + lentiform nucleus Lentiform nucleus: putamen (L) + globus pallidus Striatum (or neostraitum): caudate + putamen Palleostraitum: globus pallidus Basal n uclei….

Basal n uclei…. Corpus straitum Lies lateral to thalamus Divided by band of nerve fibers (int capsule) into caudate and lentiform nucleus . Corpus straitum = caudate + lentiform nuclei Lentiform nucleus= globus pallidus + putamen Majority of neuron In corpus straitum are GABAergic and only few are cholinergic. Caudate + putamen VS globus pallidus (=pale) or Input Vs Output

8 Basal Ganglia menu

Basal n uclei…. St r i a tum Electron microscope indicate the striatal neurons fall into 2 categories: 1. Spiny dendrites Large nucleus with 7-8 pri . dendrites covered with spiny processes Type I – axons reach GP/ S.Nigra ; NT : GABA, Leutenkephalin Type II – stubby and less dense spiny processes ; NT ?? Substance P 2. Smooth dendrites Small varicose and recurring dendrites and short axon , no spiny processes NT : GABA

Basal n uclei…. Caudate Nucleus The caudate nucleus is a C-shaped structure that is divided into three general regions. Head Body Tail The caudate nucleus is associated with the contour of the lateral ventricles : the head lies against the frontal horn of the lateral ventricle, and the tail lies against the temporal horn . The head = continuous with the putamen where as tail = terminates in the amygdala

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Basal n uclei…. Pu t amen P utamen lies in the brain medial to Claustrum and insula bounded laterally by the external capsule and medially by the globus pallidus . As noted earlier, the putamen is continuous with the head of the caudate nucleus . Although bridges of neurons between the caudate nucleus and the putamen show the continuity of the nuclei, the two structures are separated by fibers of the anterior limb of the internal capsule.

What lies lateral to internal capsule ? What lies medial to internal capsule ? What lies lateral to lentiform nucleus ? Lentiform Caudate + thalamus Claustrum ?

cerebrum Th a lamus Straitum + GP

Glutamate Glutamate G A B A Glutamate Indirect pathway

Glutamate Glutamate Glutamate D1 D2 Role of substantia Nigra A CH

Fine tuning of muscle activity is only possible by balance between ACH and Dopamine

Direct pathway Differences in- Indirect pathway Form striatum to GP internus Pathway From striatum to GP externus Not involved Subthalamus Involved Turn up motor activity Function Turn down motor activity Turns up via D1 Effect of Dopamine Turns down via D2 Turns down Effect of acetyl c holine Turns up

Basal n uclei…. Pathways Direct pathway involves GP internus. Direct pathway is stimulatory to movement. Indirect pathway in involve GP externus and subthalamus in addition to structures of direct pathway . Indirect pathway is inhibitory to movement Dopamine stimulate direct pathway and inhibit indirect pathway; while ACH has opposite function.

Basal n uclei…. Striatal connections Afferent connections from Cerebral cortex Amygdala Thalamus Substantia nigra Dorsal nucleus of Raphe Cortico striate fibres Primary motor area Premotor area Prefrontal cortex NT : Glutamate

Basal n uclei…. 2. Amygdalo striate fibres Part of limbic sytem = behaviour Thalamostriate fibres – Intra laminar thalamic Nu. to Striatum Nigro striatal fibres Pars compacta of S.nigra to striatum NT : Dopamine Dorsal Nu. Of Raphe(Mesencephalon) Project to striatum ; inhibitory NT : 5 HT ( hydroxy tryptamine )

Basal n uclei…. Striatal connections (efferent) Effrent fibres to GP and S.Nigra Striato pallidal fibres: CN – IC – GP & SN Putamen – medially – GP & SN NT : GABA Striato Nigral fibres : Project on pars reticulata NT : GABA & Enkephelin (spiny 1), substance P(spiny2)

Globus pallidus Globus pallidus is derived from the diencephalon . Inner smaller part. Paler . Divided into 2 parts External segment. Internal segment .

Basal n uclei…. Pallidal connections Pallidal afferent fibres: From : Striatum and STN (Sub thalamic Nu.) Unlike striatum : not from c.c, thalamus,s.n Striopallidal fibres : NT : GABA(M&L) > enkephalin(L)> substance P(M) Patients with Huntington’s disease have low levels of NT in GP Subthalamopallidal fibres : NT : GABA Inhibitory action on pallidum via interneurons

Basal n uclei…. Pallidal connections (efferent) Pallidofugal fibres to different brain stem Nu. Medial pallidal seg. – Thalamic Nu., mid brain RF & S.Nigra Pallidothalamic fibres to ventral anterior and ventro lateral thalamic nuclei Lateral pallidal seg. – Subthalamic Nu & S.Nigra Pallido subthalamic projections are inhibitory to STN via GABA. Pallido Nigral fibres terminate preferentially upon dopaminergic neurons in pars compacta (unlike striatonigral fibres on pars reticulata) via GABA & substance P

Basal n uclei…. Subthalamic Nucleus The subthalamic nucleus (of Luys) is also derived from the diencephalon. Separated from thalamus by Zona inserta . The large-celled nucleus lies Dorsomedial to the posterior limb of the internal capsule Dorsal to the substantia nigra Ventral to thalamus Lateral and caudal to hypothalamus

Basal n uclei…. Subthalamic connections Afferents : Motor, premotor and prefrontal cortex Thalamus Lateral pallidal segment (major) Pedunculopontine nucleus Efferent projections: Both segments of GP (M&L) Substantia Nigra

Basal n uclei…. Substantia Nigra S ubstantia nigra is present in the midbrain between the tegmentum and the basis pedunculi mesencephalic in origin S ubstantia nigra consists of two components: Pars compacta : dorsal cell–rich portion Pigmented(neuromelanin) neurons = contain Dopamine Principal source of striatal dopamine Pars reticulata : ventral cell–sparse portion Inhibitory neurotransmitter GABA .

Basal n uclei…. Substantia nigra connections Afferents from : Striatum GP STN Dorsal Nu. Of Raphe Pedunculopontine Nu. Nucleus accumbens Efferents fibres from SN broadly classified as : Dopaminergic Pars compacta to striatum and Dorsal nu. of Raphe Non – Dopaminergic pars reticulata to thalamus, tectum, tegmentum

Input Output Substantia nigra St ri a tum P al l id um STN, PPN, DNR. Striatum (from pars compacta – DA) Subthalamic Nucleus Lateral pallidal segment, Motor cortex Globus pallidus Pars reticulata (S.N)

Functions of basal n uclei Cerebral cortex, basal ganglia, cerebellum and thalamus motor activity muscle tone Organization of movement What type ? cerebral cortex How to perform? basal ganglia+cerebellum Assist in regulation-thalamus Control of voluntary motor activity. Control of reflex muscular activity. Control of muscle tone. Role in arousal mechanism.

Functions of basal n uclei Control of voluntary motor activity Cognitive control of motor activity. Neural discharge in Basal Ganglia begins well before the movement begins. Most of the motor actions occur as a consequence of thought process in mind. So basal ganglia is involved in planning & programming of movements. It is executed through functional neuronal circuits

Functions of basal n uclei…. Timing & scaling of intensity of movements Subconscious execution of some movements.

Functions of basal n uclei…. Control of reflex muscular activity Inhibitory effect on spinal reflexes. Regulate muscle which maintains posture. Mainly visual reflexes. Control of muscle tone. Substantia nigra of basal ganglia control γ motor neuron which maintain muscle tone. Pathway – cortical inhibitory area- striatum- pallidum - substantia nigra -reticular formation- spinal cord. Lesion – Lead pipe type rigidity in Parkinsonism. Role in arousal mechanism By connections of Globus Pallidus & Red Nucleus with Reticular Formation. Lesion – drowsiness , sleep.

Does it have direct connection to motor nuclei ?? Does it affect ipsi lateral or contra lateral side of body ?

Parkinsonism Hypokinesia Rigidity Restig tremor Release of dopamine from Substantia nigra is less. Less activation of direct pathway and less inhibition of indirect pathway May be associated with heroine addiction and antipsychotic drugs

Hyperkinesia disorders Hyperkinetic diseases are – Chorea – caudate nucleus is involved Huntington’s Sydenham’s Wilson’s disease Athetosis Ballismus (hemi) – subthalamus involved

Limbic System Limbic system i s a functional grouping that: Establishes all aspects of emotional states& motivation Limbic system especially associated 4F that is feeling ,fear, fight, flying & sexual behavior Links conscious functions of cerebral cortex with autonomic functions of brain stem Facilitates memory storage and retrieval

Limbic System…. Limbic system components are Amygdaloid body: a cts as interface between the limbic system, the cerebrum, and various sensory systems Very important for emotion & store emotional memory Has complex interaction with hypothalamus, one influence the other Limbic lobe of cerebral hemisphere: Cingulate gyrus : empathy & emotion

Limbic System…. Dentate gyrus : first region where all sensory modalities merge together to form unique representations and memories that bind stimuli together, and thus, it plays a critical role in learning and memory. Parahippocampal gyrus : short memory Hippocampus : Memory, learning If there is disturbance on these region, may results amnesia Retrograde amnesia : can't remember the old one Anterograde amnesia: no new memory

Limbic System…. Fornix: its t ract of white matter Connects hippocampus with hypothalamus Anterior nucleus of the thalamus: Relays information from mamillary body to cingulate gyrus Reticular formation: Stimulation or inhibition affects emotions (rage, fear, pain, sexual arousal, pleasure)

Reticular Formation Extensive network of neurons that runs thru the medulla and projects to thalamic nuclei that influence large areas of the cerebral cortex. Midbrain portion of RAS most likely is its center Functions as a net or filter for sensory input. Filter out repetitive stimuli. Such as? Allows passage of infrequent or important stimuli to reach the cerebral cortex. Unless inhibited by other brain regions, it activates the cerebral cortex – keeping it alert and awake . How might the “sleep centers” of your brain work? Why does alcohol make you tired?

Objectives At the end of this session you should be able to: Mention components of diancephalon Describe general structure of brainstem List dawn general structure of cerebellum Mention CSF pathway Describe peripheral nerves Recognizing major parts of spinal cord

Diencephalon Part of forebrain which lies above the midbrain, between the lower parts of the 2 cerebral hemispheres. It consists of: Thalamus: large oval mass of grey matter Subthalamus : lies directly above midbrain Hypothalamus: lies infront of subthalamus Metathalamus : formed by lateral & medial geniculate body Epithalamus : formed of pineal body, 2 habenular nuclei & posterior commissure . Third ventricle lies between the 2 halves of the diencephalon.

On the medial surface diencephalon is subdivided by hypothalamic sulcus (indicated by black line) into: Dorsal part: Ventral part: Cerebral aquedu c t D o r s a l Ventral Midbrain C C Dorsal part Thalamus & Epithalamus Ventral part Subthalamus & Hypothalamus

Thalamus Form the upper 2/3 of the lateral wall of the third ventricle. Relations : Rostrally:interventricular foramen. Ventrally:hypothalamic sulcus Posteriorly:posterior commissure Medially: third ventricle Laterally: posterior limb of internal capsule

Thalamus…. Thalamus has 2 ends Anterior and posterior 4 surfaces Medial, lateral, superior (dorsal) and inferior (ventral) Interthalamic connection ( interthalamic adhesion) connect medial surface of opposite thalamus Anterior end forms a forward projection (anterior tubercle). It forms the posterior boundaries of the interventricular foramen Posterior end ( pulvinar of thalamus) lies just above the superior colliculus and medial and lateral geniculate bodies

Thalamus…. Thalamus is composed of grey matter, interrupted by 2 vertical sheaths of white matter called medullary laminae . External medullary lamina : located laterally, separates reticular nucleus from the rest of the thalamic mass . It contains thalamocortical & corticothalamic fibers Internal medullary lamina : Y shaped complex of nuclei and fibers, separates the thalamus into anterior group between the 2 limbs of Y shaped lamina and two tiers of nuclei medial and lateral group on each side of the stem of Y shaped lamina.

Thalamus….

Thalamus…. Anterior part contains anterior nuclear group between the bifurcated fibers of internal medullary lamina Medial part of the thalamus consists of dorsomedial nucleus (DM) (or mediodorsal nucleus) Lateral part of thalamus divided into 2 parts ; ventral and dorsal parts. ventral group includes; ventral anterior (VA) Ventral lateral (VL) Ventral posterior nuclei (VP) that includes ventral posterolateral and ventral posteromedial nuclei. Dorsal group includes Lateral dorsal nucleus (LD) Lateral posterior nucleus (LP) Pulvinar (P).

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Thalamus…. Anterior part of thalamus Anterior part of the thalamus contains anterior thalamic nuclei. Afferent from: 1. Mammillary nuclei through the mammillothalamic tract. 2. Hypothalamus and cingulate gyrus Efferent to: 1. S ingulate gyrus and hypothalamus. Function: anterior thalamic nuclei is closely associated with that of the limbic system and is concerned with emotional tone and the mechanisms

Thalamus…. Medial part of thalamus Contains large dorsomedial nucleus and several smaller nuclei Afferent from Olfactory cortex, amygdaloid nucleus and hypothalamic nuclei Efferent to Prefrontal cortex Function: medial part of thalamus is responsible for the integration of a large variety of sensory information including somatic, visceral, and olfactory information, and relation of this information to one's emotional feelings and subjective states. Lateral group: dorsal subgroup nuclei Includes lateral dorsal nucleus, lateral posterior nucleus and pulvinar . Receive inputs from other thalamic nuclei and integrate these inputs Project the integrated information into sensory association areas in the cerebral cortex into parietal, temporal and occipital lobes.

Thalamus…. Ventral group; v entral anterior subgroup nuclei Afferent: from reticular formation, substantia nigra , corpus striatum and other thalamic nuclei Efferent to: motor areas and premotor cortex. Function: it probably influences the activities of motor cortex. Ventral lateral nucleus. Afferent: similar to those of ventral anterior nucleus but, in addition, has a major input from the cerebellum and a minor input from the red nucleus. Efferent: to motor and premotor regions of cerebral cortex. Function: it probably influences motor activity.

Thalamus…. Ventral posterior nucleus. This nucleus is subdivided into ventral posteromedial nucleus and ventral posterolateral nucleus. Afferent: ventral posteromedial nucleus receives the ascending trigeminal and gustatory pathways, while ventral posterolateral nucleus receives the important ascending sensory tracts, medial and spinal lemnisci Efferent: thalamocortical projections from these important nuclei pass through the posterior limb of internal capsule and corona radiata to the primary somatic sensory areas of cerebral cortex in the postcentral gyrus

Thalamus…. Other nuclei of thalamus Intralaminar nuclear group are small collections of nerve cells within the internal medullary lamina one of these nuclei, centromedian nucleus. Afferent: from reticular formation, spinothalamic and trigeminothalamic tracts Efferent: to other thalamic nuclei, which in turn project to cerebral cortex, and fibers to corpus striatum. Midline group , also known as periventricular nuclei, are on medial surface of thalamus & in massa intermedia (absent in 30% of human brains) Reticular nucleus of thalamus is a thin layer of nerve cells between external medullary lamina and posterior limb of internal capsule. Afferent from cerebral cortex and reticular formation, and its efferent is mainly to other thalamic nuclei. Medial geniculate body (MGB) forms part of auditory pathway lateral geniculate body (LGB) forms part of visual pathway

Thalamus…. Thalamic nuclei process, integrate, and relay information for the sensory, motor, limbic, and motivational systems. Play a critical role in sensation and motor control. ventroanterior and the ventrolateral nuclei of the thalamus form part of the basal nuclei circuit and thus are involved in the performance of voluntary movements. Large dorsomedial nucleus has extensive connections with the frontal lobe cortex and hypothalamus. There is considerable evidence that this nucleus lies on the pathway that is concerned with subjective feeling states and the personality of the individual. Intralaminar nuclei are closely connected with the activities of the reticular formation and are able to influence the levels of consciousness and alertness in an individual. Thalamic nuclei also appear important for transferring information from one part of the cerebral cortex to another

H y p o t h al a mus Relations Above : t halamus Below: the hypothalamus merges into the tegmentum of midbrain. Laterally: internal capsule Hypothalamus is the part of the diencephalon forming the floor and the lower part of the lateral wall of the third ventricle. It extends from the region of the optic chiasma to the caudal border of the mammillary bodies.

H ypothalamus …. Structures forming the hypothalamus Structures forming h ypothalamus lie in the interpeduncular fossa which are : optic chiasma, tuber cinerum and infundibulum, and mammillary bodies. Anterior to the hypothalamus is an area that for functional reasons is often included in the hypothalamus, it is referred to as preoptic area .

Hypothalamic nuclei are divided by an imaginary parasagittal plane into medial and lateral zones. Lying within the plane are columns of fornix and mammillothalamic tract, which serve as markers. Medial Zone It includes the following nuclei arranged from anterior to posterior: Part of the preoptic nucleus Anterior nucleus Part of suprachiasmatic nucleus Paraventricular nucleus Dorsomedial nucleus Ventromedial nucleus Infundibular ( arcuate ) nucleus Posterior nucleus. Lateral Zone It includes the following nuclei arranged from anterior to posterior: Part of the preoptic nucleus Part of suprachiasmatic nucleus Supraoptic nucleus Lateral nucleus Tuberomammillary nucleus Lateral tuberal nuclei

Hypothalam us…. Hypothalamic lines of communication H ypothalamus receives information from the rest of the body through: nervous connections bloodstream cerebrospinal fluid N eurons of hypothalamic nuclei respond and exert their control via the same routes. C erebrospinal fluid may serve as a conduit between the neurosecretory cells of hypothalamus and distant sites of the brain.

Hypothalamus…. Afferent nervous connections of hypothalamus The main afferent pathways are: 1. Somatic and visceral afferents. General somatic sensation, gustatory and visceral sensations reach hypothalamus through collateral branches of lemniscal afferent fibers and tractus solitarius and through reticular formation. 2. Visual afferents leave optic chiasma & pass to suprachiasmatic nucleus. 3. Olfaction travels through the medial forebrain bundle.

Hypothalamus…. 4. Corticohypothalamic fibers arise from frontal lobe of cerebral cortex and pass directly to the hypothalamus. 5. Hippocampohypothalamic fibers pass from hippocampus through fornix to mammillary body. 6. Amygdalohypothalamic fibers pass from amygdaloid complex to hypothalamus through the stria terminalis 7. Thalamohypothalamic fibers arise from dorsomedial and midline thalamic nuclei. 8. Tegmental fibers arise from the midbrain

Connections of the hypothalamus M ajor tracts conveying input to hypothalamus .

Hypothalamus…. Efferent nervous connections of hypothalamus M ain efferent pathways are: 1. Descending fibers to the brainstem and spinal cord influence the peripheral neurons of autonomic nervous system. They descend through a series of neurons in the reticular formation. Hypothalamus is connected to parasympathetic nuclei of oculomotor , facial, glossopharyngeal , and vagus nerves in the brainstem. In similar manner, reticulospinal fibers connect the hypothalamus with sympathetic cells of origin in lateral gray horns of first thoracic segment to second lumbar segment of spinal cord and sacral parasympathetic outflow at the level of second, third, and fourth sacral segments of spinal cord.

Hypothalamus…. 2. Mammillothalamic tract arises in the mammillary body and terminates in the anterior nucleus of the thalamus. Here, the pathway is relayed to the cingulate gyrus . 3. Mammillotegmental tract arises from the mammillary body and terminates in the cells of the reticular formation in the tegmentum of the midbrain. 4. Multiple pathways to the limbic system.

The major tracts conveying output from the hypothalamus.

Hypothalamus….

Subthalamus It lies between thalamus and tegmentum of midbrain It contains 3 nuclei Subthalamic nuclei Upper end of red nucleus Upper end of substantia nigra Epithalamus Epithalamus is a dorsal posterior segments of diencephalon and covers the third ventricle. Includes habenular and interconnecting fibers called habenular commissure and pineal glands Function: secret melatonin, which induces sleep. Lateral geniculate nuclei : Relay visual information from optic tract to visual cortex and mid brain. Medial geniculate nuclei : relay auditory information from inner ear to auditory cortex.

Posterior surface

BRAIN STEM From rostal to caudal, three regions of brain stem are : Midbrain Pons Medulla oblongata N.B.: the brain stem has the same structural plan as the spinal cord, with outer white matter & inner gray matter. But there are nuclei of gray matter located in the white matter. General function It produces the rigidly programmed, automatic behaviors necessary for our survival It act for all the tracts running b/n the cerebrum & the spinal cord It is heavily involved with the innervation of the face & the head(10 of the cranial nerves attached to it).

… It contains the nuclei of the last 10 cranial nerves in mid brain nuclei of oculomotor (III) nuclei of Trochlear (IV) in the pons nuclei of trigeminal (V) nuclei of abducent (VI) nuclei of facial (VII) nuclei of vestibulocochlear (VIII) In the medulla oblongata nuclei of glossopharyngeal (IX) nuclei of vagus (X) nuclei of cranial root of accessory (XI) nuclei of hypoglossal (XII)

Mid brain The smallest part of the brain stem, found just superior to the pons Connects the pons and cerebellum to the fore brain (include the cerebrum and diencephalons) The cavity of the mid brain is represented by a narrow canal called the cerebral aqueduct. It conducts CSF from the lateral and 3 rd ventricle to the 4 th ventricles The cerebral aqueduct divides the mid brain in to anterior and posterior parts

…

Mid brain…. The anterior part is formed of two cerebral peduncles , which are separated by interpeduncular fossa Each cerebral peduncle consists of crus cerebri (basis peduncle), substantia nigra and tegmentum ( contians red nuclei) Red nuclei Receives information from the cerebellum and cerebral cortex. Form Rubrospinal tract: Neurons contribute to upper limb flexion. The posterior part is called tectum , formed of 4 eminences ( colliculi )

Mid brain…. These are Two superior colliculi -center for vision Receives visual input from retina and frontal and occipital eye fields Receives auditor input from inferior colliculus Mediates audiovisual refflexes Commissure of superior colliculus c onnects two superior colliculus Two inferior colliculi - centers for hearing large mass of grey matter lying in the tectum Forms cell station in auditory pathway.

Mid brain…. Each colliculus is laterally related to a ridge called brachium. Superior and inferior brachium arises from respective colliculi Superior brachium connects the superior colliculus to lateral geniculate body Inferior brachium connects the inferior colluculus to medial geniculate body

Blood supply of brain There are two paired arteries which are responsible for the blood supply to the brain; the vertebral arteries , and the internal carotid arteries. These arteries arise in the neck, and ascend to the cranium. Within the cranial vault, the terminal branches of these arteries form an anastomic circle, called the Circle of Willis .,from this circle, branches arise which supply the majority of the cerebrum. Other parts of the CNS, such as pons and spinal cord are supplied by smaller branches from the vertebral arteries. Internal carotid arteries (ICA) move superiorly within the carotid sheath, and enter the brain via the carotid canal of the temporal bone. They do not supply any branches to the face or neck.

Blood supply of brain…. Internal carotid arteries branches Once in the cranial cavity, internal carotids pass anteriorly through cavernous sinus and distal to the cavernous sinus, each ICA gives rise to: Ophthalmic artery – Supplies the structures of the orbit Posterior communicating artery – acts as an anastamotic ‘connecting vessel’ in the Circle of Willis (see ‘Circle of Willis’ below). Anterior cerebral artery – supplies part of the cerebellum. The internal carotids then continue as the middle cerebral artery, which supplies lateral portions of the cerebrum.

Blood supply of brain…. Vertebral arteries Right and left vertebral arteries arise from subclavian arteries and ascend througn foramen transversarium . Vertebral arteries enter the cranial cavity via the foramen magnum and within the cranial vault, some branches are given off: Meningeal branch - supplies falx cerebelli , a sheet of dura mater. Anterior and posterior spinal arteries – supplies the spinal cord, spanning its entire length. Posterior inferior cerebellar artery – supplies the cerebellum. After this, the two vertebral arteries converge to form the basilar artery . Several branches from basilar artery originate here, and go onto supply cerebellum and pons and terminates by bifurcating into the posterior cerebral arteries.

Blood supply of brain….. Circle of Willis It is an arterial circle at the base of the brain in the interpeduncular fossa . It is formed by anterior cerebral artery and internal carotid arteries: present immediately proximal to the origin of the middle cerebral arteries & posterior cerebral branches of basilar artery. To complete the circle, two ‘connecting vessels’ are also present: Anterior communicating artery: This artery connects the two anterior cerebral arteries. Posterior communicating artery: A branch of the internal carotid, this artery connects the ICA to the posterior cerebral artery.

Blood supply of brain…. There are three cerebral arteries; anterior, middle and inferior and each supply a different portion of the cerebrum. Clinically, it is important to be aware of the regional blood supply to the cerebrum – in the event of vascular disruption; a clinician must know what parts of the brain are likely to be affected. Anterior cerebral arteries supply the anteromedial portion of the cerebrum. Middle cerebral arteries are situated laterally, supplying the majority of the lateral part of the brain. Posterior cerebral arteries supply both the medial and lateral parts of the posterior cerebrum.

Venous d rainage of b rain It includes a external and internal cerebral veins External cerebral veins: . Superior cerebral veins that drain superolateral surface of cerebral hemisphere terminate into superior sagittal veins . . Superficial middle cerebral vein drains area around lateral sulcus they terminate into cavernous sinus . Internal cerebral vein . Great cerebral veins : It is formed by union of two internal cerebral veins. It terminates in the straight sinus drains the deep structures of the forebrain. Basal veins : It is formed by union of deep middle cerebral vein and anterior cerebral vein and terminates by joining great cerebral vein.

3. Dural venous sinuses D ural venous sinuses are connected to extra cranial veins via emissary (representative) veins. Cerebral damage caused by venous infarction manifests as epileptic attacks and focal paralysis of the limbs.

PONS - Housed with in the pons are sensory and motor tracts that run through the pons and connect brain and spinal cord. - The middle cerebellar peduncles are transverse fibers that connect the pons to the cerebellum. - The pons also houses two autonomic respiratory centers. 1. Pneumotaxic center II. Apneustic center - These centers regulate the rate and depth of breathing. - The pons houses sensory and motor cranial nerve nuclei for the trigeminal (CNV), abducens (CN VI), and facial (CN VII) cranial nerves. Additionally, some of the nuclei for the vestibule cochlear cranial nerve (CN VIII) are located there.

MEDULLA OBLONGATA The most inferior portion of the brain stem in the posterior cranial fossa and continous with the spinal cord at the foramen magnum Contains nuclei that regulate cardiovascular and respiratory functions Distinctive characteristics of its ventral surface are the elongated pyramids, which contain tracts from the cerebral cortex the posterior wall of medulla oblongata forms the floor of fourth ventricle and has median longitudinal sulcus

Medulla contains several autonomic nuclei, which regulate functions vital for life. The most important autonomic center in the Medulla Oblongata are : The cardiac center: regulates both the heart’s rate and it’s strength of contraction. II. The vasomotor center: controls blood pressure by regulating the contraction and relaxation of smooth muscle in the walls of the smallest arteries. Blood pressure increase when vessels walls are constricted and lowers when vessel walls are dilated. III. The Respiratory Center: regulates the respiratory rate. It is influenced by the apneustic and pneumotaxic centers of the pons . IV. Other nuclei in the medulla are involved in coughing, sneezing, salivation, swallowing, gagging and vomiting.

Diencephalon and Brain Stem

Cerebellum Trilobed structure of the brain, lying posterior to pons , medulla oblongata and fourth ventricle and inferior to occipital lobes of the cerebral hemispheres Situated in the posterior cranial fossa and covered superiorly by the tentorium cerebelli Is somewhat ovoid in shape and constricted in its median part. Responsible for the regulation and coordination of complex voluntary muscular movements and the maintenance of posture and balance

Right & left hemispheres connected by vermis Connected to posterior aspect of the brainstem by three symmetrical bundles of nerve fibers called the : Cerebellum….

Cerebellum…. C erebellum is divided into three main lobes: Anterior lobe may be seen on the superior surface of the cerebellum and is separated from the middle lobe by a wide V-shaped fissure called the primary fissure Middle lobe Sometimes called the posterior lobe), which is largest part of the cerebellum, is situated between the primary and posterolateral fissures. Flocculonodular lobe Is situated posterior to the posterolateral fissure. Formed by two flocculi and the nodule

Cerebellum…. Tonsils Are roughly spherical lobules on the inferior aspect of posterior lobe. Tonsil may be displaced down through the foramen magnum in conditions of severe raised intracranial pressure or in congenital malformations Horizontal fissure : that is found along the margin of the cerebellum separates the superior from the inferior surfaces Vermis Consists of superior and inferior part Superior vermis lies between superior medullary velum & primary fissure

L ongitudinal division Vermis (medial zone) Paravermal Region ( Intermediate zone) 3. Cerebellar Hemisphere: (Lateral zone)

Anatomically Transverse plane Longitudinal plane Anterior lobe V e r m i s Posterior lobe Flocculonodular Paravermis Hemisphere Functionally Spino- c e r e b e ll u m Cerebro- c e r e b e ll u m Vestibulo- c e r e b e l l u m P h y l og e n e t i c Paleo- c e r e b e ll u m Neo- c e r e b e ll u m Archi- c e r e b e l l u m

Cerebellum…. Functionally Vestibulocerebellum Corresponds best with the flocculonodular lobe Has reciprocal connections with vestibular and reticular nuclei and plays a role in control of body equilibrium and eye movement. Spinocerebellum Corresponds best to the anterior lobe Has reciprocal connections with the spinal cord and plays a role in control of muscle tone as well as axial and limb movements, such as those used in walking and swimming . Cerebrocerebellum or pontocerebellum Horresponds best to the posterior lobe Has reciprocal conections with the cerebral cortex and plays a role in planning and initiation of movements, as well as the regulation of discrete limb movements.

Cerebellum…. P hylogenetically Archicerebellum Oldest zone corresponds to the flocculonodular lobe. Paleocerebellum More recent phylogenetic development than the archicerebellum corresponds to the anterior lobe and a small part of the posterior lobe. Neocerebellum The most recent phylogenetically , corresponds to the posterior lobe.

Cerebellum…. Functional areas of the cerebellar cortex Cerebellar cortex is divided into three functional areas. Cortex of vermis : influences the movements of the long axis of the body namely; neck, shoulders, thorax, the abdomen, and hips. Intermediate zone of cerebellar hemisphere: this area has been shown to control the muscles of the limbs, especially the hands and feet. Lateral zone of each cerebellar hemisphere: appears to be concerned with the planning of sequential movements of the entire body and is involved with the conscious assessment of movement errors.

Fistugial nucleus Globose nucleus Emboliform nucleus Dentate nucleus 4 th Ventricle Pons

Arterial supply of cerebellum : Superior cerebellar Anterior inferior cerebellar, Posterior inferior cerebell Venous blood drain into Great cerebral vein Venous sinuses.

Ventricles and Cerebrospinal Fluid Internal chambers within the CNS lateral ventricles found inside cerebral hemispheres Connected through interventricular foramen to 3 rd ventricle third ventricle is single vertical space under corpus callosum Cerebral aqueduct found in midbrain, connects the third ventricle to the fourth ventricle Fourth ventricle-found at the base of cerebellum on the posterior surface of medulla oblongata and pons anterior to the cerebellum it continues with the central canal of the spinal cord Lined with ependymal cells and containing choroid plexus of capillaries that produce CSF

Cerebrospinal Fluid Clear liquid fills ventricles and canals & bathes its external surface (in subarachnoid space) Brain produces & absorbs about 500 ml/day filtration of blood through choroid plexus has more Na+ & Cl - but less K+ & Ca+2 than plasma Functions buoyancy -- floats brain so it neutrally buoyant protection -- cushions from hitting inside of skull chemical stability -- rinses away wastes Escapes from 4th ventricle to surround the brain Absorbed by arachnoid villi into venous sinus

Flow of Cerebrospinal Fluid

Blood-brain barrier The brain has a rich supply of capillaries that provide its nervous tissue with nutrient,02& all other vital molecules. Formed by astrocytes & stimulate endothelial cells to form tight junction However, some blood-borne molecules that can cross other capillaries of the body cannot cross the brain capillaries. E.g. urea, mild toxins from food, and bacteria toxins are prevented from entering the brain by BBB, which protect the neuron of the CNS. Blood brain barrier is markedly reduced or missing in three distinct locations in the CNS Choroid plexus Hypothalamus Pineal Gland

Cranial nerves Arise from brain 12 cranial nerves are named in superior –inferior sequence as CNI to CN XII Have three general categories of cranial nerve functions; sensory, somatic motor and parasympathetic

Oh Oh Oh To Touch And Feel Very Green Vegetables A H Olfactory Optic Oculomotor Trochlear Trigeminal Abducens Facial Vestibulococlear Glossopharangeal Vagus Accessory Hypoglossal I II III IV V VI VII VIII IX X XI XII

Cranial nerves Sensory motor parasympathetic I O lfactory yes no No II Optic Yes No No III Oculomotor No Yes Yes IV Trochlear No Yes No V Trigeminal Yes Yes No VI Abducent No Yes No VII Facial yes Yes Yes VIII Vestibulochochlear yes No No IX Glossopharyngeal Yes Yes Yes X Vagus Yes Yes yes XI Accessory No Yes No XII hypoglossal No yes No

… Olfactory. These are the sensory nerves of smell. Optic. Because it develops as an outgrowth of the vbrain , this sensory nerve of vision is not a true nerve at all. It is more correctly called a brain tract. Oculomotor . The name oculomotor means “eye mover.” This nerve innervates four of the extrinsic eye muscles —muscles that move the eyeball in the orbit. Trochlear . The name trochlear means “pulley.” This nerve innervates an extrinsic eye muscle that hooks through a pulley-shaped ligament in the orbit. Trigeminal. The name trigeminal means “threefold,” which refers to this nerve’s three major branches. The trigeminal nerve provides general sensory innervation to the face and motor innervation to the chewing muscles.

… Abducens . This nerve was so named because it innervates the muscle that abducts the eyeball (turns the eye laterally). Facial. This nerve innervates the muscles of facial expression as well as other structures. Vestibulocochlear . This sensory nerve of hearing and equilibrium was once called the auditory nerve. Glossopharyngeal . The name glossopharyngeal means “tongue and pharynx,” structures that this nerve helps to innervate. Vagus . The name vagus means “vagabond” or “wanderer.” This nerve “wanders” beyond the head into the thorax and abdomen. Accessory. The accessory nerve carries motor innervation to the trapezius and sternocleidomastoid muscles. Hypoglossal. The name hypoglossal means “below the tongue.” This nerve runs inferior to the tongue and innervates the tongue muscles.

Anatomy of the Spinal Cord Located with in the vertebral canal of the vertebral column It extends from the foramen magnum of the occipital bone to the level of the first lumbar vertebra (L1) Spinal cord develops more slowly than the associated vertebral column. Thus the spinal cord doesn’t extend through out the length of the vertebral column. Terminal part of the spinal cord is called conus medullaris . The filum terminale , a fibrous strand composed of pia mater , extends inferiorly from the conus medullaris to the coccyx

Spinal Cord….. Distal end spinal cord: Conus medullaris : is thin , conical spinal cord below lumbar enlargement Filum terminale : thin thread of fibrous tissue at end of conus medullaris & attaches to coccygeal ligament Cauda equina : nerve roots extending below conus medullaris

Spinal Cord…. Enlargements of the Spinal Cord Caused by: amount of gray matter in segment that is involved with sensory and motor nerves of limbs Cervical enlargement: Nerves of shoulders and upper limbs Lumbar enlargement: Nerves of pelvis and lower limbs

Spinal Cord…. 31 Spinal Cord Segments Based on vertebrae where spinal nerves originate Positions of spinal segment and vertebrae change with age

Spinal cord…. Gray Matter Surrounds central canal of spinal cord Contains neuron cell bodies, neuroglia , unmyelinated axons Posterior horns contain interneurons . Anterior horns contain some interneurons as well as the cell bodies of motor neurons. These cell bodies project their axons via the ventral roots of the spinal cord to the skeletal muscles. The amount of ventral gray matter at a given level of the spinal cord is proportional to the amount of skeletal muscle innervated.

Spinal cord…. Gray Matter Lateral horn neurons are sympathetic motor neurons serving visceral organs. Their axons also exit via the ventral root. Afferent sensory fibers carrying info from peripheral receptors form the dorsal roots of the spinal cord. The somata of these sensory fibers are found in an enlargement known as a dorsal root ganglion. The dorsal and ventral roots fuse to form spinal nerves.

Spinal Cord…. White matter Myelinated nerve fibers. Allows for communication between brain and spinal cord or between different regions of the spinal cord. White matter on each side of the cord is divided into columns or funiculi that contians ascending or descending tracts.

Spinal Cord…. Organization of White Matter Posterior white columns : lie between posterior gray horns and posterior median sulcus Anterior white columns : lie between anterior gray horns and anterior median fissure Anterior white commissure : area where axons cross from one side of spinal cord to the other Lateral white columns : located on each side of spinal cord between anterior and posterior columns

Spinal cord…. Figure 8-15a

Spinal Cord…. Central area of gray matter shaped like a butterfly and surrounded by white matter in 3 columns

Spinal Cord…. Conduction Bundles of fibers passing information up & down spinal cord Locomotion Repetitive, coordinated actions of several muscle groups Central pattern generators are pools of neurons providing control of flexors and extensors (walking) Reflexes Involuntary, stereotyped responses to stimuli Example , removing hand from hot stove

Factors that fix spinal cord Attachment of filum terminale to the coccyx Attachment of ligamentum denticulatum to the Dura matter Attachment of dura mater to margin of the foramen magnum.

Spinal Nerves 31 pairs spinal nerves arise from the spinal cord Are identified by a letter and number (e.g., T4) designating the order of their origin Named for point of origin from the segments of spinal cord: 8 pairs of cervical nerves ( C 1 – C 8 ) 12 pairs of thoracic nerves ( T 1 – T 12 ) 5 pairs of lumbar nerves ( L 1 – L 5 ) 5 pairs of sacral nerves ( S 1 – S 5 ) 1 pair of coccygeal nerves ( Co 1 ) 194

Spinal Nerves Posterior View 195 Cervical nerves: are named for inferior vertebra All other nerves: are named for superior vertebra

Spinal Nerves… Connect to the spinal cord by the dorsal root and ventral roots Dorsal root – contains sensory fibers - cell bodies located in the dorsal root ganglion Ventral root – contains motor fibers arising from anterior gray horn The dorsal (posterior) and ventral(anterior)nerve roots unite, within or just proximal to the intervertebral foramen , to form a mixed spinal nerve 196

Spinal Nerves… Branch into dorsal ramus and ventral ramus - Dorsal and ventral rami contain sensory and motor fibers rami communicantes (white & gray) – connect to the base of the ventral ramus to the sympathetic chain ganglia The unilateral area of skin innervated by the fibers of a single spinal nerve is called a dermatome The unilateral muscle mass receiving innervation from the fibers conveyed by a single spinal nerve is a myotome . 197

198

Innervation of the Back Dorsal rami – innervate back muscles - Follow a segmented pattern - Innervate a horizontal strip of muscle and skin (in line with emergence point from the vertebral column) Innervation of the anterior thoracic and abdominal wall Thoracic region – ventral rami arranged in simple, segmented pattern Intercostal nerves supply intercostal muscles, skin, and abdominal wall - Each gives off lateral and anterior cutaneous branches 199

Innervation of the back 200

Figure 15.1 Autonomic n ervous s ystem and visceral s ensory n eurons

Somatic Nervous System (SNS) Operates under conscious control Seldom affects long-term survival SNS controls skeletal muscles Autonomic Nervous System (ANS) Operates without conscious instruction ANS controls visceral effectors Coordinates system functions: cardiovascular, respiratory, digestive, urinary, reproductive

Somatic nervous s ystem

Autonomic nervous s ystem

Divisions of ANS ANS different from somatic motor in: Effectors Efferent pathways ( neurotransmiter ) Target organ in response to neurotransmiter Operates largely outside our awareness & has two divisions: Sympathetic division: Increases alertness, metabolic rate, and muscular abilities “Kicks in” only during exertion, stress, or emergency “Fight or flight

Parasympathetic division: Reduces metabolic rate and promotes digestion Controls during resting conditions “Rest and digest”

Sympathetic division Ganglionic n eurons occur in three locations: Sympathetic chain ganglia Collateral ganglia Suprarenal medullae Are on both sides of vertebral column Control effectors: - in body wall - inside thoracic cavity - in head - in limbs

Ganglionic neurons…. Paravertebral ganglia -found on side of vertebral column Contain ganglionic neurons that innervate tissues of H ear and lung Sympathetic innervation to head and neck region Collateral ganglia: a re anterior to vertebral bodies Contain ganglionic neurons that innervate tissues and organs in abdominopelvic cavity Suprarenal (adrenal) medullae: Very short axons When stimulated, release neurotransmitters into bloodstream (not at synapse) Function as hormones to affect target cells throughout body

Sympathetic trunk & pathways Upon entering in to sympathetic trunk ganglion on preganglion fibers may do one of the following: Synapse with ganglionic neuron with the same level of paravertebral ganglia 2. Ascend or descend sympathetic trunk to Synapse in another trunk ganglion 3. Pass through the trunk ganglion & emerge with out synapse

Sympathetic division

Sympathetic Division Figure 8-34

Parasympathetic d ivision Autonomic Nuclei Are contained in the mesencephalon , pons , and medulla oblongata: Associated with cranial nerves III, VII, IX, X In lateral gray horns of spinal segments S 2 –S 4 Ganglionic neurons in peripheral ganglia Near target organ Embedded in tissues of target organ Usually paired

Parasympathetic division

Parasympathetic division Parasympathetic Activation Centers on relaxation, food processing, and energy absorption Localized effects, last a few seconds at most

Thank you!

Reflexes Automatic responses coordinated within spinal cord Through interconnected sensory neurons, motor neurons, and interneurons Produce simple and complex reflexes

Spinal Reflexes Rapid, automatic responses to specific stimuli Basic building blocks of neural function One neural reflex produces one motor response Reflex arc: The wiring of a single reflex Beginning at receptor Ending at peripheral effector Generally opposes original stimulus (negative feedback)

Five Steps in a Spinal Reflex Step 1: Arrival of stimulus, activation of receptor ( biological transducers): Physical or chemical changes Step 2: Activation of sensory neuron: Graded depolarization Step 3: Information processing by postsynaptic cell: Triggered by neurotransmitters Step 4: Activation of motor neuron: Action potential Step 5: Response of peripheral effector : Triggered by neurotransmitters

spinal reflexes….

Monosynaptic reflexes A stretch reflex Have least delay between sensory input and motor output: For example, stretch reflex (such as patellar reflex) Completed in 20–40 msec Receptor is muscle spindle

Stretch reflex

Spinal Reflexes…. Withdrawal Reflexes Move body part away from stimulus (pain or pressure) For example, flexor reflex : pulls hand away from hot stove Strength and extent of response: depends on intensity and location of stimulus

Flexor reflex Figure 8-30

Integration and control of spinal reflexes Reflex behaviors are automatic but processing centers in brain can facilitate or inhibit reflex motor patterns based in spinal cord

Sensory & motor pathways

Major& minor ascending tracts Dorsal white column Lateral spinothalamic Anterior spinothalamic Anterior spinocerebellar Posterior spinocerebellar Spinotectal Spinoreticular Spino - olivary Cuneocerebellar Major descending tract Pyramidal tract Rubrospinal tracts Vestibulospinal tracts Tectospinal tracts Reticulospinal tracts Olivospinal tracts

There is a continuous flow of information between the brain, spinal cord, and peripheral nerves. Information is relayed by sensory (ascending) and motor (descending) ‘pathways’. Generally the pathways consists: Chain of tracts with associated nuclei for synapses (relay) Consist of two or three neurons Exhibit somatotopy (precise spatial relationships) Decussate Are paired (bilaterally and symmetrically)

Somatic s ensory pathways Monitor conditions both inside the body and in the external environment Sensation-stimulated receptor passes information to the CNS via afferent (sensory) fibers Most sensory information is processed in the spinal cord , thalamus or brain stem. Only 1% reaches the cerebral cortex and our conscious awareness Processing in the spinal cord can produce a rapid motor response (stretch reflex)

Sensory pathways Processing within the brain stem may result in complex motor activities ( positional changes in the eye, head, trunk ) Contain a sequence of three neurons from the receptor to the cerebral cortex First order neuron: Sensory neuron that delivers information from the receptor to the CNS Axon (central process) passes to the spinal cord through the dorsal root of spinal nerve gives many collaterals which take part in spinal cord reflexes runs ipsilaterally and synapses with second-order neurons in the cord and medulla oblongata

Second order neuron: Has cell body in the spinal cord or medulla oblongata Axon decussate & terminate on 3rd order neuron Third order neuron: Has cell body in thalamus(VPL) Axon terminates on cerebral cortex

White Matter: Pathway generalizations Ascending and descending fibers are organized in distinct bundles which occupy particular areas and regions in the white matter Generally long tracts are located peripherally in the white matter, while shorter tracts are found near the gray matter TRACT is a bundle of axon (within CNS) having the same origin, course, destination & function The name of the tract indicates the origin and destination of its fibers The axons within each tract are grouped according to the body region it innervated

Posterior column contain only ascending tracts Anteriolateral column contain both ascending & descending tracts

Ascending spinal tracts Transmit impulses concerned with specific sensory modalities: pain, temperature, touch, proprioception , that reach a conscious level (cerebral cortex) From tactile and stretch receptors to subconscious centers (cerebellum) Three major pathways carry sensory information Posterior column pathway ( gracile & cuneate fasciculi ) Anterolateral pathway ( spinothalamic ) Spinocerebellar pathway

Some of ascending spinal tracts Dorsal white column Lateral spinothalamic Anterior spinothalamic Anterior spinocerebellar Posterior spinocerebellar Spinotectal 7. Spinoreticular 8. Spino-olivary 9. Cuneocerebellar

Dorsal Column tract The most modern tract, high velocity sensation & highly myelinated axon Contains two tracts , Fasciculus gracilis (FG) & fasciculus cuneatus (FC) Contain the axons of primary afferent neurons that entered into spinal cord through dorsal roots of spinal nerves FG contains fibers received at sacral, lumbar and lower thoracic levels, FC contains fibers received at upper thoracic and cervical levels Carries sensations of highly localized (“fine”) touch, pressure, vibration and conscious proprioception

Fibers ascend without interruption where they terminate upon 2 nd order neurons in nucleus gracilis and nucleus cuneatus The axons of the 2 nd order neurons decussate in the medulla as internal arcuate fibers and ascend through the brain stem as medial lemniscus . Medial lemniscus terminates in the ventral posterior lateral nucleus of the thalamus & 3 rd order neurons project to the somatosensory cortex ( thalamocortical fibers)

Posterior column pathway….

Spinothalamic tracts It is primitive ,moderately myelinated axon & less developed sensation Located lateral and ventral to the ventral horn that carry impulses concerned with pain and thermal sensations (lateral tract) and also non- discriminative touch and pressure (medial tract) Fibers of the two tracts are intermingled to some extent in the brain stem, forming spinal lemniscus Fibers are highly somato -topically arranged, with those for the lower limb lying most superficially and those for the upper limb lying deeply Information is sent to the primary sensory cortex on the opposite side of the body

Lateral Spinothalamic tract Carries impulses concerned with pain and thermal sensations. Axons of 1 st order neurons terminate in the dorsal horn Axons of 2 nd order neuron (mostly in the nucleus proprius ), decussate within one segment of their origin then, pass through the ventral white commissure & ascend to terminate on 3 rd order neurons in the thalamus(VPL) Thalamic neurons(3 rd ) project to the somatosensory cortex

Anterior Spinothalamic tract Carries impulses concerned with non- discriminative touch and pressure Axons enter the spinal cord from the posterior root ganglion and proceed to the tip of the posterior gray column, where they divide into ascending and descending branches . Branches travel for a distance of one or two segments of the spinal cord contributing to posterolateral tract of Lissauer & first-order neuron terminate by synapsing with cells in the substantia gelatinosa group in the posterior gray column

Anterior Spinothalamic tract…. Axons of the second-order neuron now cross very obliquely to the opposite side in the anterior gray and white commissures within several spinal segments and ascend in the opposite side As the anterior spinothalamic tract ascends through the medulla oblongata, it accompanies the lateral spinothalamic tract and the spinotectal tract , all of which form the spinal lemniscus Spinal lemniscus terminate by synapsing with the third-order neuron in the ventral posterolateral nucleus of the thalamus Thalamic neurons project to the somatosensory cortex

Anterior spinothalamic tract

Fast pain fiber connected directly to 2 nd order neuron but slow pain fiber(c) have multiple connection each other that will diffuse stimulus, late alone, connected 2 nd order neuron which make difficult to localize this type of stimulus Fast pain fiber directly reach to VPL nucleus thalamus but slow pain fiber will diffuse in one of following nuclei: Very small amount of slow pain fiber move to VPL nuclei of thalamus Most of fiber go to intralaminar nucleus of thalamus. Intralaminar nucleus are located within white matter that found b/n parts of thalamus which can fire cerebral cortex. A little slow pain fiber & all ascending tracts have collateral attachment to reticular format so as, to fire cerebral cortex

Analgesia System Stimulation of certain areas of the brainstem can reduce or block sensations of pain. Brian has its own mechanism of decrease pain by forming analgesic system by release pain blocker in the posterior gray column Analgesic system originated from Periventricular area of the diencephalon, Periaqueductal gray matter of the midbrain Midline nuclei of the brainstem. Analgesic system can suppress both sharp pricking pain and burning pain sensations by releasing two compounds with morphine like actions, called enkephalins and endorphins.

Spinocerebellar tracts Anterior spinocerebellar : 2 nd order neuron cross to the opposite side and ascend in the spinal cord 2 nd order neuron enter into cerebellar cortex by superior cerebellar peduncle and then, it will re-cross to its original side Spinocerebellar system consists of sequence of only two neurons Two tracts: Posterior & Anterior Located near the dorsolateral and ventrolateral surfaces of the cord Contain axons of the second order neurons Carry information derived from muscle spindles, Golgi tendon organs and tactile receptors to the cerebellum for the control of posture and coordination of movements Epsilateral cerebellum Clarkes nucloes ( dorsolateral nucleos ) – cellbody 2 nd order neuron ( c 8_ s 3 ) Lower limb, trunk to cerebellum

Posterior spinocerebellar tract Axons enter into posterior root ganglion then to posterior gray column and terminate by synapsing on second-order neurons at the base of the posterior gray column . The neurons are known collectively as the nucleus dorsalis (Clarke's column). Axons of the second-order neurons enter the posterolateral part of the lateral white column on the same side and ascend as the posterior spinocerebellar tract to the medulla oblongata & joins the inferior cerebellar peduncle and terminates in the cerebellar cortex.

Posterior spinocerebellar tract…. These tract does not ascend to cerebral cortex because nucleus dorsalis (Clarke's column) extends only from the eighth cervical segment caudally to the third or fourth lumbar segment Axons entering the spinal cord from the posterior roots of the lower lumbar and sacral segments ascend in the posterior white column until they reach the third or fourth lumbar segment, where they enter the nucleus dorsalis . Posterior spinocerebellar fibers receive muscle joint information from the muscle spindles, tendon organs, and joint receptors of the trunk and lower limbs.

Information concerning tension of muscle tendons and the movements of muscles and joints is used by the cerebellum in the coordination of limb movements and the maintenance of posture.

Anterior spinocerebellar tract Axons entering into spinal cord from the posterior root ganglion & terminate by synapsing with the second-order neurons in the nucleus dorsalis at the base of the posterior gray column. Majority of the axons of the second-order neurons cross to the opposite side and ascend as the anterior spinocerebellar tract in the contralateral white column while minority of the axons ascend as the anterior spinocerebellar tract in the lateral white column of the same side . Crossed fibers ascend through the medulla oblongata and pons , enter to cerebellum through superior cerebellar peduncle and terminate in the cerebellar cortex by re-crossing back within the cerebellum. Anterior spinocerebellar tract conveys muscle joint information from the muscle spindles, tendon organs, and joint receptors of the trunk and the upper and lower limbs. It is also believed that the cerebellum receives information from the skin and superficial fascia by this tract.

Some of minor tracts 7. Spinoreticular : very important to stimulate reticular system and cerebral cortex 8. Spino-olivary : crossing of 2 nd order neuron is at the same level of spinal segment that 2 nd order neuron enter into spinal cord & ascend superiorly upto olivary nuclei Then, from olivary nucli transmit to cerebellum by inferior cerebellar penduncle Functionally similar to spinocerebellar tract 9. Cuneocerebellar : accessory nucleus of cuneatus in the spinal cord to cerebellum Information from upper limb will ascend with this tract Counter part of dorsal spinocerebellar tracts that will take sensory stimulus above c 8

Somatic m otor pathways CNS issues motor commands in response to information provided by sensory systems by the somatic nervous system (SNS) and the autonomic nervous system Conscious and subconscious motor commands control skeletal muscles by traveling over 3 integrated motor pathways Corticospinal pathway – voluntary control of motor activity Corticobulbar tracts Corticospinal tracts Inderict pathways – modify or direct skeletal muscle contractions by stimulating, facilitating, or inhibiting lower motor neurons

Motor Pathways Contain a sequence of two neurons from the cerebral cortex or brain stem to the muscles Upper motor neuron : has cell body in the cerebral cortex or brain stem, axon decussates before terminating on the lower motor neuron Lower motor neuron : has cell body in the ventral horn of the spinal cord, axon runs in the ipsilateral ventral root of the spinal nerve and supply the muscle. UMN LMN

Descending Spinal Tracts Originate from the cerebral cortex & brain stem Concerned with: Control of movements Muscle tone Spinal reflexes & equilibrium Modulation of sensory transmission to higher centers Spinal autonomic functions

The motor pathways are divided into two groups Direct pathways (voluntary motion pathways) - the pyramidal tracts Indirect pathways (postural pathways), essentially all others - the extrapyramidal pathways

Direct (pyramidal) system Regulates fast and fine (skilled) movements Originate in the pyramidal neurons in the precentral gyri Impulses are sent through the corticospinal tracts and synapse in the anterior horn Stimulation of anterior horn neurons activates skeletal muscles Part of the direct pathway, called corticobulbar tracts , innervates cranial nerve nuclei

Indirect ( extrapyramidal ) system Complex and multisynaptic pathways The system includes: Rubrospinal tracts Vestibulospinal tracts Tectospinal tracts Reticulospinal tracts Olivospinal tracts

Descending spinal tracts

Corticospinal tracts Concerned with voluntary, discrete, skilled movements, especially those of distal parts of the limbs (fractionated movements) Innervate the contralateral side of the spinal cord Provide rapid direct method for controlling skeletal muscle

Origin: motor and sensory cortices Axons pass through corona radiata , internal capsule, crus cerebri , pontine nucleus and relay into cerebellum by middle cerebellar peduncle for updating on what cerebral cortex plan to do then pyramid of medulla oblongata In the caudal medulla about 75-90% of the fibers decussate and form the lateral corticospinal tract Rest of the fibers remain ipsilateral and form anterior corticospinal tract. Anterior part also decussate before termination

Termination : Ventral horn neurons (mostly through interneurons , a few fibers terminate directly) Corticobulbar tracts end at the motor nuclei of CNs of the contralateral side

Rubrospinal Tract Controls tone of limb flexor muscles, being excitatory to motor neurons of these muscles but inhibits extensor muscle Site of cross over: immediately bellow its origin Origin : Red nucleus

Tectospinal tract Mediates reflex movements of the head and neck in response to visual stimuli Origin : Superior colliculus Site of cross over: immediately bellow its origin

Vestibulospinal tracts Vestibulospinal tracts Origin : vestibular nuclei which is situated in the pons and medulla oblongata beneath the floor of the fourth ventricle Function : Has excitatory influences upon extensor motor neurons, control extensor muscle tone in the antigravity maintenance of posture & inhibtes flexer muscle Involved in movements of the head required for maintaining equilibrium Site of cross over : uncrossed This nuclei receive affarent fibers from vestibular nerve & deep cerebellar nucleus.

Medial vestibulospinal tract

Olivospinal tracts Origin : olive nucleus Site of crossover: brain stem Function : unknown ?to influence the activity of the motor neurons in the anterior gray column

Reticulospinal tracts Origin : pontine & medullary reticular format Function: Influence voluntary movement, reflex activity and muscle tone by controlling the activity of both alpha and gamma motor neurons mediate pressor and depressor effect on the circulatory system Are involved in control of breathing

Descending autonomic fibers Origin : cerebral cortex,hypothalamus , amygdaloid complex & reticular formation Site of crossover : brainstem Fibers run in the reticulospinal tracts & terminate on the autonomic neurons in the lateral horn of thoracic & upper lumbar (sympathetic) and sacral segments (parasympathetic) levels of the spinal cord Function : Higher centers associated with the control of sympathetic & Para sympathetic activity situated mainly in the hypothalmaus

Problems of nervous system Concussion A temporary disturbance of the brain’s ability to function due to a hard blow to the head

Paralysis A loss of sensation and movement of part of the body due to an injury of the spinal cord or brain

Parkinson’s Disease The brain does not produce enough of the neurotransmitter that transmits messages from the brain to the muscles Symptoms: tremors, rigid muscles, shuffling walk, and loss of facial expression Red areas show where chemical is stored

Alzheimer’s Disease A gradual shrinking of the neurons in the cerebrum Symptoms: memory loss, emotional disturbances, inability to function on own, death

Epilepsy Abnormal transmission of messages between the neurons in the brain Symptoms: seizures

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CNS anatomy is a detailed lecture of brain and spinal cord

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CNS anatomy is a detailed lecture of brain and spinal cord

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