Physiology Central Nervous System pharma part II.pptx

Physiology, CNS 2

1. Sensory function of the cerebral cortex A. Somatic sensations: bodily s ensations conducted via somatic afferents nerves that come to conscious perceptions. B. Special Sensations : Vision, hearing and balance, taste, smell Visual sensation in the occipital lobe , auditory sensations in the temporal lobe . Somatic Sensation Include sensation from skin and deep structures and perceived in the parietal lobe . Can be fine sensations or crude sensations.

2. Cont.… Fine sensation : a sensory modality that allows a subject to sense and localize .   The Cerebral cortex is the highest center for the perception of fine sensations . E.g. Fine touch Crude sensations sensory modality that allows the subject to sense something without being able to localize it.  Perceived at cerebral cortex + at lower levels in the thalamus. E.g. Pain, temp., crude touch

3. Cont.… There are 3 somatosensory areas in the cerebral cortex The primary somatosensory areas (S I ) The secondary somatosensory areas (S II ) Somatosensory association area A. The primary somatosensory areas (S I ): Location: Post central gyrus of the parietal lobe Identified by Brodmann´s areas 3, 1 & 2

4. Cont.…. Body representation : It has crossed & inverted (head-down) representation Each half of the body represented in the contra lateral cortex Area of representation in each part is proportional to the No of receptors in the part not with its size

5. Cont.… Function : S I is important for the perception of the following sensations. Fine touch, tactile localization & discrimination. Localization of pain & temp. Texture of materials Proprioception (static & dynamic) Transmits sensory information to area S II and somatosensory association area for farther elaboration of sensory information (Eg. Stereognosis)

6. Cont.… B. The secondary somatosensory areas (S II ) Location: In the supra-marginal gyrus, behind the lower part of S I , Represented by Brodmann´s area-40 Body representation: Bilateral representation of the body with poor topographic representation . S II receives signal inputs from S I, thalamic nuclei, visual and auditory sensory areas . Function: Potentiates the function of S I , but not essential for these functions. S I can work without S II , but the other way round is not true.

7. Cont.… C . Somatosensory association area/ Somatic interpretation area: Location : posterior parietal cortex , behind S I above S II ( Brodmann´s areas 5 & 7 ). Connections : Received sensory impulse from SI, SII, thalamus , visual cortex & auditory cortex. Functions : Combines all sensory signals to give meanings to the sensory input. It is important for stereognosis. Effect of lesion to this areas : Astereognosis ; failure to identify objects by their touch, shape, weight & texture.

8. Special senses Found in the frontal, parietal, temporal and occipital lobes Visual areas Auditory areas Olfactory cortex Gustatory cortex Vestibular cortex

9. Visual areas Primary Visual Cortex (A-17) Found in the posterior and medial occipital lobe . Primary visual area responsible for vision and coordination of eye movements. Visual Association Area (A-18) Surrounds the primary visual cortex. Basically vision is the sensation of bars of light on our retinal cells. The primary visual cortex tells which cells are being stimulated and how . The association area lets us “see” what we’re looking at . The occipital eye field area (area-19)

10. Auditory areas Found in the superior margin of the temporal lobe , next to the lateral sulcus. Consists of: Primary auditory center (areas-41 & 42 ) Receive sensory fibers from cochlea. Sound waves excite cochlear receptors in the inner ear which send info to the auditory cortex . A uditory association/ Interpretation area ( A-20 , 21 & 22 ) L ets us interpret and remember sounds .

11. Olfactory areas Found in the frontal lobe just above the orbits. Receptors in the olfactory epithelium extend through the cribriform plate and are excited by the binding of odorants . They then send their info to the olfactory cortex . Very much involved in memory and emotion .

12. Gustatory and Vestibular areas Gustatory cortex is involved in taste and is in the parietal lobe just deep to the temporal lobe. Vestibular cortex is involved in balance and equilibrium and is in the posterior insula.

13. Lateralization The fact that certain activities are almost exclusively dominant on one of the 2 hemispheres. In most people, the left hemisphere has a more control over language, math, and logic . While the right hemisphere is geared towards musical, artistic and other creative endeavors. Most individuals with left cerebral dominance are right-handed.

14. Language Areas Large area for language understanding and production surrounding the lateral sulcus in the left (language-dominant) hemisphere Broca’s area  speech production Wernicke’s area  understanding oral/written words Lateral prefrontal cortex  language comprehension and complex word analysis Lateral and ventral temporal cortex  integrates visual and auditory stimulate

15. Cont.… Broca’s area: Involves articulation of speech . In damage, Broca’s aphasia/non-fluent aphasia ( articulation of speech is impaired but comprehension of speech is unimpaired ). Wernicke’s area: Involves language comprehension . In damage , Wernicke’s aphasia (ability to grasp meaning/language comprehension is destroyed) . Speech is rapid without any meaning . Angular gyrus: Center of integration of auditory and visual information. Damage produces aphasia ( inability to formulate or comprehend language ) Arcuate fasciculus: bundle of axons that connects Broca's and Wernicke's areas To speak intelligibly, words originating in Wernicke’s area must be sent to Broca’s area. Broca’s area sends fibers to the motor cortex which directly controls the musculature of speech.

16. 2. Basal Nuclei (basal ganglia) Group of subcortical nuclei found deep within cerebral hemisphere. Masses of gray matter composed of neuronal cell bodies located deep within white matter of the cerebrum. Contains: Corpus striatum Caudate nucleus . Putamen and Corpus striatum G lobus pallidus Lentiform nucleus Other nuclei which are functionally related to the BG : Sub thalamic nucleus The red nucleus and Substantia nigra . Functions in the control of voluntary movements . Doesn’t initiate movements but once movement is underway, they assist in the pattern and rhythm. 16

17. Cont.… From sensory, motor and association areas of the cortex info arrives at the caudate nucleus and the putamen. Processing and integration occurs w/in the nuclei and then info is sent from the globus pallidus to the motor cortex via the thalamus. The basal nuclei alter motor commands issued by the cerebral cortex via this feedback loop.

18. Neurotransmitters in the BG Fibers from the cortex to the corpus striatum : ACh Fibers from the Substantia nigra to corpus striatum : DA Fibers from the corpus striatum to SN : GABA(gamma aminobutric acid ) Fibers from the brainstem to the BG : NA, 5-HT (serotonin), Enkephalin. Effects: NA & Ach excitatory NTs GABA, DA, 5-HT, Enk : inhibitory NTs A balance b/n all these NTs is essential for proper functioning of the BG

19. BG and cortical neuronal connections The BG is connected with cerebral cortex through 2 circuits : The caudate circuit: Neurons from motor & sensory assoc. Area of cortex Caudate nucleus Globus pallidus Thalamus Primary motor & premotor area Function : for cognitive planning of sequential motor pattern

20. Cont.… 2 . The putamen circuit Fibers from the primary motor area and somatic area and motor assoc. area Putamen Globus pallidus Ventral nucleus of thalamus Primary motor area & Premotor area Function : Subconscious execution of learned pattern of mov’t

21. Function of the BG BG acts as the primary motor cortex in lower animals In human, BG controls muscle tone and voluntary mov'ts The role of BG in controlling muscle tone: The caudate nucleus stimulates muscle tone through stimulation of the vestibular and inferior olivatory nuclei. The Lentiform nucleus (putamen & globus pallidus) inhibits muscle tone through: a. Inhibition of the motor cortex b. Stimulation of the inhibitory RF and red nucleus of the brainstem NB: the inhibitory influence of BG is stronger than the stimulatory effect on muscle tone.

22. Function of the BG The role of BG in controlling voluntary mov'ts: Planning and programming of mov’t controlled by the BG. In conjunction with the motor cortex, the BG is responsible for: 1. Converting thoughts and ideas into plans of motor activities . This is the function of the caudate circuit . Controls the sequence pattern of mov’ts. E.g. Dressing pattern . Damage to the caudate circuit : inability to organize mov’ts to achieve a complex goals. 2. Controlling the learned pattern of motor activities E.g.:- writing letters of alphabet, passing a football Cutting a paper with scissors, vocalization Hammering nails, shooting a basket ball This is the function of the putamen circuit . Damage to this circuit results in motor apraxia ; loss of familiar skilled mov’ts .

23. Effect of lesion to the BG Lesion in the BG accompanied by: 1. Involuntary mov’ts during rest. These mov’ts disappear on sleep and increase with nervous tension . 2. Changes in muscle tone : hyper- or Hypotonia .

24. Cont.… Chorea (Gr: Chorea = dance) Cause : Lesion in the caudate nucleus . There is also degeneration of local cholinergic neurons leading to imbalance b/n DA, GABA & Ach. Manifestation : Rapid , purposeless, involuntary ``dancing´´ mov’ts during rest . Hypotonia , b/c the caudate nucleus is normally facilitatory to stretch reflex .

25. Cont.… B. Athetosis (Gr. A-thetos = not fixed) Cause : Lesion to the lentiform nucleus Manifestations : S low, continuous , i nvoluntary , spasmodic writhing movt of hands . Also called mobile spasm . Hands cannot kept at fixed position . Hypertonia

26. Cont.… Hemiballismus (Gr. Ballismus = jumping) Cause : Lesion to the subthalamus Manifestation : Involuntary , sudden, strong spasmodic movt that involves one limb or the whole one side of the body. May occur on legs during walking. Hypertonia

27. Cont.… D. Parkinson´s disease (Parkinsonism, paralysis agitons) Cause : Lesion in the substantia nigra leading to degeneration of the dopaminergic neurons that project to corpus striatum. Other factors precipitating parkinsons diseas: Aging : old age low level of DA and DA receptors Atherosclerosis : decreases DA secretion Drugs : DA-R blockers

28. Cont.… Each side of the midbrain contains a nucleus called the substantia nigra. Neurons in the substantia nigra inhibit the activity of basal nuclei by releasing dopamine , whereas neurons in the BG release Ach which is excitatory on sk /muscle. DA is involved in the regulation of gross, automatic mov'ts of sk/muscles . Degeneration of dopaminergic neurons in the SN that are projected on the BG results in Parkinson's disease .

29. Cont.…

30. Cont.… Manifestations : Tremor : involuntary, rhythmic oscillating movts due to alternating contraction of antagonistic muscles. E.g . Hand shake Muscle rigidity : due to continous contraction Akinesia : lack of movt, paralysis agitons Treatment : Medical: Anticholinergic drugs (atropin) Dopaminergic drugs (L-Dopa) Surgical : Destruction of ventrolateral nuclei of the thalamus

31. Hippocampus I s   a complex brain structure embedded deep into temporal lobe . Humans and other mammals have 2 hippocampi , 1 in each  side of the brain. It is a plastic and vulnerable structure that gets damaged by a variety of stimuli . I t also gets affected in a variety of neurological and psychiatric disorders . I s part of the limbic system

32. Cont.. Function of the hippocampus It has a major role in learning and memory . The hippocampus  helps humans process and retrieve 2 kinds of memory , declarative memories ( those related to facts and events) & spatial relationships . It is also where short-term memories are turned into long-term memories t hese are then stored elsewhere in the brain. If the hippocampus is damaged by disease or injury, it can influence a  person's memories as  well as their ability to form new memories resulting in amnesia. Hippocampus damage can particularly affect spatial memory, or the ability to remember directions , locations, and orientations . E.g., in Alzheimer disease , the hippocampus undergoes massive cell loss , which is associated with memory deficits .

33. Amygdala The is  a cluster of almond-shaped cells located near the base of the brain . 2 of these cell groups, one in each hemisphere (or side) of the brain. The amygdalae help define and regulate emotions which is also called emotional remembrances. The amygdala is part of the brain's limbic system. The amygdala helps control our fear response, but it also plays a crucial role in many other cognitive functions. Therefore , damage to the amygdala can cause serious problems, such as   poor decision-making and impaired emotional memories .