NEUROANATOMY - I

1. NEUROANATOMY - I BY ADESEJI WASIU A. ALABI ADEOLA ADIGUN OLANIYI DEPARTMENT OF ANATOMY, UNIVERSITY OF ILORIN .

2. Divisions of the Nervous System 2 main subdivisions: Central Nervous System the brain & spinal cord Peripheral Nervous System - groups of neurons called ganglia and peripheral nerves provides pathways to & from the central nervous system for electrochemical signals (impulses) 2

3. The Peripheral Nervous System Composed of 2 divisions: Somatic Provides sensory information (voluntary) Transmits impulses to and from skeletal muscles - usually conscious actions Autonomic motor system for viscera (smooth muscles & glands-involuntary) Autonomic is further divided into 2 subdivisions 3

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5. The Autonomic Nervous System 2 subdivisions of Autonomic: Sympathetic participates in body’s response to stress; fight or flight Parasympathetic returns body to resting state & conserves resources 5

6. Orientation of the PNS Dorsal roots carry sensory info to the spinal cord Ventral roots carry outgoing motor axons Peripheral nerves formed from dorsal & ventral roots Symmetry of PNS Arranged on 2 axis: longitudinal: rostral to caudal ( head to tail) dorsal to ventral (back to front) Segmented: 31 pairs of spinal nerves 12 pairs of cranial nerves 6

7. Neurons The basic and functional unit of the nervous system. Consist of a cell body ( perikaryon ) and processes arising from it. The processes arising from the cell body of a neuron are called neurites . Several short branching processes called Dendrites One longer process called an Axon 7

8. Types of Neuron 8

9. Synapse Synapses are sites of junction between neurons . Types axosomatic synapse axoaxonal synapse dendro-axonic or dendro -dendritic somato -dendritic 9

10. Supporting cells of nervous system Non conducting cells of the nervous systems. Collectively referred to as Neuroglia Astrocyte Microglia Schwann cells Oligodentrocytes They provide mechanical support to neurons S erve as insulators and prevent neuronal impulses from spreading in unwanted directions. 10

11. The Central Nervous System Consists of following Regions : Spinal Cord Brain Cerebrum Cerebellum Diencephalon: the caudal (posterior) part of the forebrain, containing the epithalamus , thalamus, hypothalamus, and ventral thalamus and the third ventricle. Brain Stem Midbrain Medulla Pons 11

12. Protection of the Brain & CNS The skull & spinal column The Meninges 3 layers of tissue protecting brain Dura mater outer tough layer Subdural space – normally small Arachnoid membrane next to dura mater Subarachnoid space - spongy layer filled with cerebrospinal fluid and blood vessels Pia mater membrane that covers the brain Cerebrospinal fluid (CSF) - cushions brain; circulates around the brain & spinal cord 12

13. The Spinal Cord- gross anatomy and internal structure   The spinal cord is roughly cylindrical in shape.   It begins superiorly at the foramen magnum in the skull.   It terminates inferiorly in the adult at the level of the lower border of the L1.    In the young child, it usually ends at the upper border of L3. 13

14. Spinal Cord (cont’d) ENLARGEMENTS  Cervical & lumbar enlargements In the cervical region, it gives origin to the  brachial plexus  In the lower thoracic and lumbar regions, it gives origin to the  lumbosacral plexus CONUS MEDULLARIS: Inferiorly, the spinal cord tapers off into the conus medullaris . 14

15. FILUM TERMINALE: From the apex of conus medullaris Prolongation of the pia mater, descends to be attached to the posterior surface of coccyx. FISSURE & SULCI In the midline anteriorly , the anterior median fissure.  On the posterior surface, a shallow furrow, the posterior median sulcus . 15

16. SPINAL NERVES    Along the entire length of the spinal cord are attached 31 pairs of spinal nerves Cervical …… 8 Thoracic …… 12 Lumbar …… 5 Sacral …… 5 Coccygeal …..1 Each connects to the spinal cord by 2 roots – dorsal and ventral. Each root forms from a series of rootlets that attach along the whole length of the spinal cord segment. Ventral roots are motor  while  dorsal roots are sensory. The 2 roots join to form a spinal nerve prior to exiting the vertebral column. Almost immediately after emerging from its intervertebral foramen, a spinal nerve will divide into a dorsal ramus , a ventral ramus , and a meningeal branch that re-enters and innervates the meninges and associated blood vessels. Each ramus is mixed. Joined to the base of the ventral rami of spinal nerves in the thoracic region are the rami communicantes . These are sympathetic fibers. Dorsal rami supply the posterior body trunk whereas the thicker ventral rami supply the rest of the body trunk and the limbs. 16

17. Plexuses Except for T2 to T12, all ventral rami branch extensively and join one another lateral to the vertebral column forming complicated nerve plexuses. Within a plexus, fibers from different rami criss cross each other and become redistributed. Internal Structure: The spinal cord is composed of an inner core of gray matter, which is surrounded by an outer covering of white matter. GRAY MATTER On cross section; the gray matter is seen as an H-shaped pillar with anterior and posterior gray columns, or horns, united by a thin gray commissure containing the small central canal. A small lateral gray column or horn is present in the thoracic and upper lumbar segments of the cord. The amount of gray matter present at any given level of the spinal cord is related to the amount of muscle innervated at that level. Thus, its size is greatest within the cervical and lumbosacral enlargements of the cord. 17

18. Grey and White Matter of Spinal Cord 18 WHITE MATTER The white matter, may be divided into anterior, lateral, and posterior white columns or funiculi .    The anterior column on each side lies between the midline and the anterior nerve roots;    The lateral column lies between the anterior and the  posterior nerve roots;     The posterior column lies between the posterior nerve roots and the midline.

19. Spinal Cord Nuclei and laminae 19

20. Ascending and descending tracts of spinal cord ↑ Sensory Gracile tract Leg position & vibration Cuneate tract Arm position & vibration Dorsal spinocerebellar tract Strength & muscle speed Ventral spinocerebellar tract Modulation; interneurons Lateral spinothalamic tract Pain & temperature Anterior spinothalamic tract Light touch Spinocervical thalamic tract Kinesthetic movement & discriminative touch ↓ Motor Corticospinal tract Speed & agility Reticulospinal tract Differential facilitation of motor neurons Rubrospinal tract Fix movement errors Lateral vestibulospinal tract Extensor & posture Medial vestibulospinal tract Flexor & head position Tectospinal tract Head turning 20

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22. Clinical Anatomy of spinal cord 22

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25. 25 Epidural injections   – Lumbar epidural   • (for anaesthetic /analgesic injections)   – Caudal epidural – Cervical/thoracic epidural  

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27. The Brain Remaining 6 areas of the CNS are part of the brain The control center of the body Regulates body activity; enables you to think  Surface is gray matter - 6 x 10 6 cell bodies / cc Under gray matter is white matter - formed of myelinated axons.  Surface of the brain ( neocortex ) is convoluted Increases surface area ridges = gyri grooves = sulci 27

28. Forebrain, Midbrain, Hindbrain 28

29. The Cerebral Hemispheres Largest region of brain; 7/8 by weight - Includes: Cerebral cortex – outer surface of gray matter underlying white matter 3 nuclei (clusters of related neurons): the basal ganglia the hippocampal formation the amygdala these are masses of gray matter at the base of the cerebrum that serve the motor cortex paired cavities =   lateral ventricles Divided into 2 ‘half spheres’ = hemisheres 29

30. The Cerebral Cortex The convoluted outer surface grooves = sulci elevated regions = gyri Composed of gray matter 2-5 mm thick Contains ~ 12 billion neurons Most of the cerebral cortex is concerned with processing sensory information or motor commands 2 bands of tissue – one sensory, one motor Divided into primary, secondary, & tertiary 30

31. The Forebrain Telencephalon Olfactory bulb Cerebral cortex Basal telencephalon (basal ganglia) Corpus callosum commissure between cerebral hemispheres Internal capsule connections with brain stem Lateral ventricles 31

32. Lobes of the Cerebrum 2 sides called hemispheres Joined by a bridge = Corpus Callosum Separated by a deep fissure front to back Like 2 mirror images (but not quite) Divided into 4 lobes 1. Frontal 2. Parietal 3. T emporal 4. O ccipital 32

33. Lobes of the Cerebrum Parietal Lobe Temporal Lobe Frontal Lobe Limbic Lobe Occipital Lobe 33

34. The Frontal Lobe I ntellectual functioning R easoning Aggression Sexual behavior Speech Smell Voluntary movements 34

35. The Parietal Lobe Body sensory awareness (including taste) Language Abstract thought , especially math Body imaging 35

36. The Temporal Lobe Includes part of limbic system* Emotion* Interpretation of language Hearing Memory 36

37. The Occipital Lobe Receiving, interpreting, & discriminating visual stimuli Association of visual stimuli with memory 37

38. Ventral View 38

39. Sagittal Section 39

40. Superolateral surface 40

41. Superolateral surface 41

42. Medial surface 42

43. Medial surface 43

44. Inferior surface 44

45. White matter of Cerebral hemisphere The surface of the cerebral hemisphere is covered by a thin layer of grey matter called the cerebral cortex. The greater part of the cerebral hemisphere deep to the cortex is occupied by white matter within which are embedded certain important masses of grey matter . These fibres may be : Association fibres that interconnect different regions of the cerebral cortex. Projection fibres that connect the cerebral cortex with other masses of grey matter; and vice versa . Commissural fibres that interconnect identical areas in the two hemispheres. 45

46. Internal capsule The internal capsule may be divided into the following parts. The anterior limb lies between the caudate nucleus medially, and the anterior part of the lentiform nucleus laterally. The posterior limb lies between the thalamus medially, and the posterior part of the lentiform nucleus on the lateral side. In transverse sections through the cerebral hemisphere the anterior and posterior limbs of the internal capsule are seen to meet at an angle open outwards. This angle is called the genu ( genu = bend). Some fibres of the internal capsule lie behind the posterior end of the lentiform nucleus . They constitute its retrolentiform part. Some other fibres pass below the lentiform nucleus (and not medial to it). These fibres constitute the sublentiform part of the internal capsule 46

47. Functional areas 47

48. The Primary Sensory & Motor Cortex Primary Motor Cortex: controls voluntary movements of limbs & trunk contains neurons that project directly to spinal cord to activate somatic motor neurons Primary Sensory Areas receive information from peripheral receptors with only a few synaptic relays interposed 48

49. Brodmann Areas Cytoarchitectural areas of neocortex Regions with similar cell structure Numbered each represents a functionally distinct area Examples: Area 17 is the primary visual cortex at the caudal pole of the occipital lobe Area 4 is the primary motor cortex primary auditory cortex on left side of temporal lobe near language center 49

50. Secondary & Tertiary Areas Surrounding primary areas are higher order ( secondary & tertiary ) sensory & motor areas Process & integrate info coming from the primary sensory areas. Higher order motor areas send complex info required for motor actions to primary motor areas   50

51. Association Areas Three other large regions of cortex surround the primary, secondary & tertiary areas Called association areas In primates, association areas are majority of cortex 51

52. Localization of Cortical Functions 52

53. Lobes of the Brain & Associated Regions 53

54. Integration of Brain Functions Interactions of all areas sensory, motor & motivational systems is essential for behavior . Example: throw a ball - info about motion of ball, impact of ball, position of arms, legs, hands, etc. - sensory, motor, motivational systems Anatomical organization of each major functional system (sensory, motor, motivational) follows 4 principles 54

55. Principles of Anatomical Organization Each system contains relay centers These don’t just transmit info; also modify it Most important relay center is the thalamus almost all sensory info to cerebral cortex processed by thalamus Each system is composed of several distinct pathways Example: touch & pain 55

56. Principles of Anatomical Organization (Cont.) Each pathway is topographically organized neural map - clustered functions Most pathways cross the body’s midline Thus each hemisphere controls the actions/sensations of the opposite side . Left side dominates language; right side -spatial perception, musical ability 56

57. Diencephalon Thalamus & hypothalamus taken together Important structures found in the cerebrum Between the midbrain & cerebral hemispheres Thalamus Hypothalamus Third ventricle Retina and optic nerves develop from optic vesicle that pouches off from diencephalon during development 57

58. The Thalamus & Hypothalamus Thalamus relay center - processes & distributes almost all sensory & motor info going to the cerebral cortex links nervous & endocrine system emotional control Hypothalamus under the thalamus regulates autonomic nervous system connects to thalamus, midbrain & some cortical areas Controls body temperature, thirst, hunger, emotional behavior 58

59. Cerebellum The cerebellum consists of a part lying near the midline called the vermis , and of two lateral hemispheres. two surfaces, superior and inferior Dorsal to the pons & medulla Mostly white matter covered with a thin layer of gray matter Pleated surface; divided into several lobes Receives sensory input from the spinal cord, motor info from the cerebral cortex & input about balance from receptors in the inner ear Therefore, can coordinate planning & timing of voluntary muscle movement & maintain balance 59

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62. The Medulla Oblongata & Pons Medulla Oblongata Bottom (rostral) region of the brainstem Regulates blood pressure and respiration; controls breathing, swallowing, digestion, heart & blood vessels. Pons Above medulla links cerebellum to cerebrum; relays info from cerebral hemispheres to cerebellum 62

63. The Midbrain Mesencephalon Tectum (roof) superior colliculus + inferior colliculus Tegmentum (floor) Cerebral aqueduct Controls responses to sight (e.g. eye movements) Relay station of auditory & visual signals Motor control of some skeletal muscles 63

64. The Brainstem Anatomically, from the bottom up: Medulla Oblongata Pons Midbrain Taken together = brainstem Contains all the nerves that connect the spinal cord with the cerebrum Receives sensory info from head, face, & neck Motor neurons control muscles of head & neck 12 pairs of cranial nerves carry input & output Also involved in hearing, taste & balance 64

65. The Limbic System A functional & evolutionary division, rather than anatomical Group of structures in center of the brain above the brainstem: hypothalamus pituitary hippocampus important role in memory hippocampal gyrus amygdala coordinates actions of the autonomic & endocrine systems involved in emotions 65

66. Functions of the Limbic System Sometimes called the “mammalian brain because most highly developed in mammals One of the oldest areas of brain from an evolutionary standpoint Maintains homeostasis: e.g. helps maintain temperature, blood pressure, heart rate, blood sugar Also involved in emotional reactions needed for survival 4 F’s: fleeing, fighting, feeding. 66

67. Visualizing the Limbic System 67

68. Clinical Anatomy of Brain 68

69. Ipsilateral/Contralateral The cerebral hemispheres are involved with inputs and outputs from the contralateral side of the body Damage to neocortex causes problems on the opposite side In patients with epilepsy, surgeons occasionally cut corpus callosum to relieve seizures. Flash different pictures in each eye, patients could describe what they saw with right eye, but not left, but could pick out object - example: Heart = ART. The cerebellum is involved with the control of movement on the ipsilateral side of the body. Damage to the cerebellum causes motor deficits on the same side. 69

70. Injury Mechanisms The brain is a complex and delicate organ, and one that is vulnerable to injury from a variety of different traumas. These include: Frontal Lobe Injury Occipital Lobe Injury Temporal Lobe Injury Side Impact Injury Coup/ Contre -coup Injury Diffuse Axonal Injury Epidural Hematoma Subdural Hematoma 70

71. Frontal Lobe Injury The frontal lobe of the brain can be injured from direct impact on the front of the head. During impact, the brain tissue is accelerated forward into the bony skull. This can cause bruising of the brain tissue and tearing of blood vessels. Frontal lobe injuries can cause changes in personality, as well as many different kinds of disturbances in cognition and memory. 71

72. Occipital Lobe Injury Occipital lobe injuries occur from blows to the back of the head. This can cause bruising of the brain tissue and tearing of blood vessels. These injuries can result in vision problems or even blindness. 72

73. Temporal Lobe Injury The temporal lobe of the brain is vulnerable to injury from impacts of the front of the head. The temporal lobe lies upon the bony ridges of the inside of the skull, and rapid acceleration can cause the brain tissue to smash into the bone, causing tissue damage or bleeding. 73

74. Side Impact Injury Injuries to the right or left side of the brain can occur from injuries to the side of the head. Injuries to this part of the brain can result in language or speech difficulties, and sensory or motor problems. 74

75. Coup/Contre-coup Injury A French phrase that describes bruises that occur at two sites in the brain. When the head is struck, the impact causes the brain to bump the opposite side of the skull. Damage occurs at the area of impact and on the opposite side of the brain. 75

76. Diffuse Axonal Injury Brain injury does not require a direct head impact. During rapid acceleration of the head, some parts of the brain can move separately from other parts. This type of motion creates shear forces that can destroy axons necessary for brain functioning. These shear forces can stretch the nerve bundles of the brain . 76

77. Diffuse Axonal Injury The brain is a complex network of interconnections. Critical nerve tracts can be sheared and stressed during an acceleration-type of injury. Diffuse axonal injury is a very serious injury, as it directly impacts the major pathways of the brain. 77

78. Epidural Hematoma An epidural hematoma is a blood clot that forms between the skull and the top lining of the brain ( dura ). This blood clot can cause fast changes in the pressure inside the brain. When the brain tissue is compressed, it can quickly result in compromised blood flow and neuron damage. 78

79. Subdural Hematoma A subdural hematoma is a blood clot that forms between the dura and the brain tissue. The clot may cause increased pressure and may need to be removed surgically. When the brain tissue is compressed, it can quickly result in compromised blood flow and tissue damage. 79

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