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Lecture 7 physiology of the nervous system



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Lecture 7 physiology of the nervous system

  1. 1. Physiology of the Nervous System <ul><li>Lecture No. 7 </li></ul>
  2. 2. The Nervous System <ul><li>The nervous system coordinates all body functions, enabling a person to adapt to changes in internal and external environment </li></ul><ul><li>The nervous system is composed mainly of the nerve cells (neurons) and supporting cells (neuroglia) </li></ul>
  3. 3. The neuron <ul><li>This is the basic conducting cell of the nervous system </li></ul><ul><li>Highly specialized but cannot reproduce itself </li></ul><ul><li>Main parts are the cell body (soma), the fibers: axon and dendrites. </li></ul>
  4. 4. The neuron <ul><li>The axon is a long process with myelin sheath. This conducts impulses away from the cell body </li></ul><ul><li>The dendrites are short, thick, diffuse branching processes that receive impulses and conduct them towards the cell body </li></ul>
  5. 6. The NEURON <ul><li>The nervous system is composed of neurons , which produce and conduct electrochemical impulses and supporting cells, which assist the functions of neurons. </li></ul>
  6. 7. The neuroglia <ul><li>The supporting cells </li></ul><ul><li>They supply nutrients to the neurons and help maintain the electrical potential </li></ul><ul><li>They also form part of the blood-brain barrier </li></ul><ul><li>They are made up of macroglia, microglia and ependymal cells </li></ul>
  7. 8. The neuroglia <ul><li>Oligodendrocytes produce myelin sheath in the CN </li></ul><ul><li>Scwhann cells or lemmocytes produce myelin sheath in the peripheral NS </li></ul>
  8. 11. The Organization of the Nervous System <ul><li>The nervous system is divided functionally and structurally into 2 parts </li></ul><ul><li>1. Central Nervous System- the Brain and the spinal cord </li></ul><ul><li>2. Peripheral Nervous System- the cranial nerves and spinal nerves </li></ul>
  9. 13. The Organization of the nervous System <ul><li>The Peripheral Nervous System is further classified into THREE Functional Divisions </li></ul><ul><li>1. The Somatic Nervous System- controls the skeletal muscles </li></ul><ul><li>2. The Autonomic Nervous System- controls the visceral organs </li></ul><ul><li>3. The Enteric Nervous System- controls the functions of the GIT </li></ul>
  10. 14. The Central Nervous System <ul><li>Composed of the brain </li></ul><ul><li>The brain consists of the gross structures: cerebrum, cerebellum, brainstem and the diencephalon. </li></ul><ul><li>Diencephalon- Thalamus. Hypothalamus and pineal body </li></ul><ul><li>Brainstem- Pons, medulla and Midbrain </li></ul>
  11. 16. Brain Cortex Corpus callosum Septum pellucidum Fornix Thalamus Hypothalamus Optic chiasma Hypophysis 3rd ventricle 4th ventricle Cerebellum Brain stem Spinal cord
  12. 17. The Cerebrum <ul><li>This is the largest part of the brain </li></ul><ul><li>Consists of right and left hemisphere connected by the corpus callosum </li></ul><ul><li>Each cerebral hemisphere is composed of different lobes- frontal, temporal, parietal and occipital </li></ul><ul><li>Embedded in the cerebrum is the BASAL ganglia </li></ul>
  13. 18. The Frontal Lobe of the cerebrum <ul><li>Influences the personality of the person </li></ul><ul><li>Also responsible for judgment, abstract reasoning, social behavior, language expression and motor movement. </li></ul>
  14. 19. The Temporal lobe of the Cerebrum <ul><li>This part of the cerebrum controls the hearing, language comprehension, storage and recall of memories </li></ul><ul><li>The LIMBIC system is deeply located in the temporal lobe. This controls the basic drives such as hunger, anger, emotion and sexual drive. </li></ul>
  15. 20. The Parietal lobe of the cerebrum <ul><li>This is the principal center for the reception and interpretation of Sensation </li></ul><ul><li>This part interprets and integrates the sensory inputs like touch, temperature and pain </li></ul><ul><li>It interprets size, shape, distance and texture </li></ul>
  16. 21. The occipital lobe of the cerebrum <ul><li>This functions mainly to interpret visual stimuli </li></ul>
  17. 22. Speech areas in the cerebrum <ul><li>1. Wernicke’s area- responsible for the sensory reception of speech. </li></ul><ul><li>2.Broca’s Area- responsible for the motor speech </li></ul>
  18. 24. The Cerebellum <ul><li>The second largest brain region </li></ul><ul><li>Has also two hemispheres </li></ul><ul><li>Functions to maintain muscle tone, coordinate muscle movement, posture and control balance/equilibrium </li></ul><ul><li>If this is damaged, muscle tone decreases and fine motor movements become very clumsy </li></ul>
  19. 26. The Brainstem <ul><li>Lies inferior to the cerebrum </li></ul><ul><li>Continuous with the cerebrum and the spinal cord </li></ul><ul><li>It is composed of the midbrain, the pons and the medulla oblongata </li></ul><ul><li>Functions: houses the center for respiration and cardiovascular system </li></ul>
  20. 27. The Midbrain <ul><li>This connects with the cerebrum </li></ul><ul><li>Contains numerous ascending and descending tracts and fibers </li></ul>
  21. 28. The Pons <ul><li>Connects the cerebellum with the cerebrum </li></ul><ul><li>Houses the respiratory center and cardiovascular center </li></ul><ul><li>Exit points for cranial nerves 5, 6 and 7 </li></ul>
  22. 29. The Medulla oblongata <ul><li>The most inferior portion of the brainstem </li></ul><ul><li>Serves as the center for autonomic reflexes to maintain homeostasis, regulating respiratory vasomotor and cardiac functions </li></ul><ul><li>Serves as exit of cranial nerves 9,10,11 and 12 </li></ul>
  23. 30. The Diencephalon <ul><li>The thalamus and the hypothalamus </li></ul><ul><li>The thalamus is the relay station of all sensory stimuli towards the brain </li></ul><ul><li>The hypothalamus controls body temperature, appetite, water balance, pituitary secretions and sleep-wake cycle </li></ul>
  24. 31. Brain circulation: The circle of Willis
  25. 32. The spinal cord <ul><li>A long cylindrical structure extending from the foramen magnum to the L1 in adult, L3/L4 in pedia </li></ul><ul><li>In the cross section of the spinal cord, we find the GRAY matter- contains neurons; and WHITE matter-consists of nerve fibers </li></ul><ul><li>There are 31 pairs of spinal nerves that exit the spinal cord </li></ul>
  26. 34. The spinal cord <ul><li>Each spinal nerve is formed by the dorsal root (sensory) and the ventral root (motor) </li></ul><ul><li>Cervical segments= 8 pairs </li></ul><ul><li>Thoracic segments=12 pairs </li></ul><ul><li>Lumbar= 5 pairs </li></ul><ul><li>Sacral=5 pairs </li></ul><ul><li>Coccygeal=1 pair </li></ul>
  27. 35. The Meninges <ul><li>These are 3 connective tissue layers surrounding the brain and spinal cord. </li></ul><ul><li>1. DURA MATER- the superficial, thickest layer. The area above the dura mater is called epidural space </li></ul><ul><li>2. ARACHNOID- second layer, thin and wispy. </li></ul><ul><li>3. PIA MATER- the deepest layer, adhered to the brain and spinal cord substance </li></ul>
  28. 37. The Meninges <ul><li>The space in between the arachnoid and pia mater is called the arachnoid space </li></ul><ul><li>This arachnoid space contains the cerebro-spinal fluid (CSF) </li></ul><ul><li>In this space, blood vessels are also found </li></ul>
  29. 38. The Ventricles <ul><li>These are CSF filled cavities in the brain </li></ul><ul><li>The lateral ventricle- found in the cerebrum </li></ul><ul><li>The third ventricle- in the center of the thalamus and hypothalamus </li></ul><ul><li>The fourth ventricle- located at the base of the cerebellum </li></ul>
  30. 39. The CSF <ul><li>This is the fluid found inside the ventricles that bathe the brain and spinal cord </li></ul><ul><li>Function: provides protective cushion around the CNS </li></ul><ul><li>Produced by the choroid plexus in the ventricles </li></ul><ul><li>Absorbed by the arachnoid granulations </li></ul>
  31. 40. Tracing the CSF pathway <ul><li>Lateral ventricle  Interventricular foramen of Monro  Third ventricle  Cerebral aqueduct of Sylvius  fourth ventricle  exits trough the median foramen of Magendie or the lateral foramen of Luscka  Subarachnoid spaces in the cisterna magna, spinal cord  subarachnoid space of the brain  superior sagittal sinus </li></ul>
  32. 42. The cranial nerves <ul><li>Are 12 pairs of nerves that exit the brain </li></ul><ul><li>Can be classified as </li></ul><ul><li>Sensory </li></ul><ul><li>Motor mixed (sensory and motor) </li></ul>
  33. 45. The Autonomic Nervous System <ul><li>The part of the peripheral nervous system that innervates cardiac muscles, smooth muscles and glands </li></ul><ul><li>Functionally divided into </li></ul><ul><li>Sympathetic Nervous System </li></ul><ul><li>Parasympathetic Nervous System </li></ul>
  34. 46. The SYMPATHETIC system <ul><li>Originates from the T1-L2/L3 segments of the spinal cord (thoracolumbar) </li></ul><ul><li>Utilized by the body for FLIGHT and FIGHT response </li></ul><ul><li>Neurotransmitter agents are Epinephrine and Norepinephrine (coming from the adrenal gland) </li></ul><ul><li>ADRENERGIC system </li></ul>
  35. 47. Sympathetic nervous system Pupils Salivary glands Heart Bronchi of lungs Liver Stomach Small intestines Adrenal gland Kidney Large intestine Rectum Bladder Genitals T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 T 1 1 T12 L1 L2 L3
  36. 48. Sympathetic responses <ul><li>Increased: </li></ul><ul><ul><li>HR </li></ul></ul><ul><ul><li>RR </li></ul></ul><ul><ul><li>BP </li></ul></ul><ul><ul><li>Visual Acuity (Pupillary Dilation) </li></ul></ul><ul><ul><li>Smooth Muscle tone  sphincters are contracted </li></ul></ul><ul><ul><li>Vasoconstriction </li></ul></ul><ul><ul><li>Metabolism  ↑ glucose, ↑ fatty acids </li></ul></ul>
  37. 49. Sympathetic responses <ul><li>Decreased </li></ul><ul><ul><li>Peristalsis </li></ul></ul><ul><ul><li>Salivary secretions </li></ul></ul><ul><li>Ejaculation </li></ul>
  38. 50. Parasympathetic System <ul><li>CHOLINERGIC system </li></ul><ul><li>The vegetative system </li></ul><ul><li>Feed and Breed responses </li></ul><ul><li>Cranio-sacral location </li></ul><ul><li>Cranial nerves- 3, 7, 9, 10 and S2-S4 </li></ul><ul><li>Neurotransmitter is Acetylcholine </li></ul>
  39. 51. Parasympathetic nervous system Pupils Salivary glands Heart Bronchi of lungs Liver Stomach Small intestines Large intestine Rectum Bladder Genitals
  40. 52. Parasympathetic Responses <ul><li>Increased </li></ul><ul><ul><li>Gastric secretions </li></ul></ul><ul><ul><li>Salivary secretions </li></ul></ul><ul><ul><li>peristalsis </li></ul></ul><ul><li>Pupillary constriction </li></ul><ul><li>Decreased </li></ul><ul><li>Smooth muscle tone  sphincters are relaxed </li></ul><ul><li>erection </li></ul>
  41. 53. Nerve Physiology <ul><li>The nerve cells are excitable cells </li></ul><ul><li>Any stimulus will change the membrane potential and cause an action potential to generate  impulse transmission or action potential </li></ul><ul><li>The myelin sheath of the nerve cell is responsible for the SALTATORY conduction  increases the nerve transmission </li></ul>
  42. 54. What is an action potential? <ul><li>The synchronized opening and closing of Na + and K + gates result in the movement of electrical charges that generates a nerve impulse or action potential. </li></ul><ul><li>Action potentials reach the end of each neuron where these electrical signals are either transmitted directly to the next cell in the sequence via gap junctions, or are responsible for activating the release of specialized neurotransmitter chemicals. </li></ul>
  43. 55. Terminologies <ul><li>Action potential – another name for “spike” potential or nerve impulse </li></ul><ul><li>Depolarization – upward oscilloscope deflection or Na + conductance is highest (hypopolarization) </li></ul><ul><li>All-or-None is when the action potential amplitude never varies </li></ul><ul><li>Repolarization – at this point, Na + conductance is falling rapidly and K + conductance has peaked. </li></ul><ul><li>Absolute refractory period – time of depolarization (Na + gates open) </li></ul><ul><li>Relative refractory period – time of depolarization (K + gates open) </li></ul><ul><li>Hyperpolarization – downward oscilloscope deflection below resting </li></ul>
  44. 58. ACTION POTENTIAL AT SYNAPSES <ul><li>Electrical synapses between excitable cells allow ions to pass directly from one cell to another, and are much faster than chemical synapses </li></ul>
  45. 59. <ul><li>An action potential at one node of Ranvier causes inwards currents that move down the axon, depolarizing the membrane and stimulating a new action potential at the next node of Ranvier. </li></ul>
  46. 60. What is saltatory conduction? An action potential at one node of Ranvier causes inwards currents that move down the action, depolarizing the membrane and stimulating a new action potential at the next node of Ranvier.
  47. 62. The SYNAPSE <ul><li>This is the region where communication occurs between 2 neurons or between a neuron and a target cell </li></ul><ul><li>A neurotransmitter is released from the nerve cell towards the other cell with receptor </li></ul>
  48. 64. Reflex Arc The reflex arc is a hard wired, unconscious rapid response to external stimulus involving spinal nerves and effector cell. A reflex is an automatic, involuntary response of an organism to a stimulus. The entire nervous system is composed of innumerable reflex arcs.
  50. 67. Stretch reflex
  51. 68. Biceps reflex & Radial-ulnar reflex
  52. 69. What is synaptic transmission ? <ul><li>Synaptic transmission is the process by which nerve cells communicate among themselves and with muscles and glands. </li></ul><ul><li>The synapse is the anatomic site where this communication occurs. </li></ul><ul><li>Most synaptic transmission is carried out by a chemical called a neurotransmitter. </li></ul>
  53. 70. The neurotransmitter is manufactured by the neuron and stored in vesicles at the axon terminals
  54. 71. When the action potential reaches the axon terminal, it causes the vesicles to release the neurotransmitter molecules into the synaptic cleft.
  55. 72. The neurotransmitter diffuses across the cleft and binds to receptors on the post-synaptic cleft cell. Then the activated receptors cause changes in the activity of the post-synaptic neuron.
  56. 73. The neurotransmitter molecules are released from the receptors and diffuse back into the synaptic cleft.
  57. 74. The neurotransmitter is reabsorbed by the post synaptic neuron. This process is known as reuptake.
  58. 75. Neurotransmitters
  59. 76. Physiology of Vision <ul><li>Light waves travel at a speed of 186,000 miles per second. Light is reflected into the eyes by objects within the field of vision. </li></ul><ul><li>In order to achieve clear vision, light reflected from objects within the visual field is focused in to the retina of both eyes. </li></ul><ul><li>The processes involved in producing a clear image are refraction of the light rays and accommodation of the eyes. </li></ul>
  60. 77. The eye and the visual pathway <ul><li>Vision is made possible by the stimulation of the photoreceptor cells in the retina </li></ul><ul><li>Receptor cells are the RODS and CONES </li></ul><ul><li>The eye is made up of three layers </li></ul><ul><ul><li>Fibrous layer- sclerae and cornea </li></ul></ul><ul><ul><li>Uvea- choroid and iris and ciliary bodies </li></ul></ul><ul><ul><li>Nervous coat- retina </li></ul></ul>
  61. 79. Functions of the Parts of the Eye <ul><li>Lens – refraction and focusing </li></ul><ul><li>Iris – regulated light entrance </li></ul><ul><li>Pupil – opening in the iris </li></ul><ul><li>Choroid – absorbs stray light </li></ul><ul><li>Sclera – for protection </li></ul><ul><li>Cornea – refraction of light </li></ul><ul><li>Ciliary body – holds lens in place </li></ul><ul><li>Retina – contains receptors (rods and cones) </li></ul><ul><li>Rods – for black and white vision </li></ul><ul><li>Cones – for color vision </li></ul><ul><li>Optic nerve – transmits impulse </li></ul><ul><li>Ciliary muscle – for accommodation </li></ul>
  62. 80. The optic nerve <ul><li>This is the collection of fibers from the cells in the retina </li></ul><ul><li>It passes through the brainstem as the optic chiasm </li></ul><ul><li>it will reach the occipital lobe for visual interpretation </li></ul>
  63. 82. EMMETROPIA <ul><li>Emmetropia is normal vision. </li></ul><ul><li>Parallel light rays from distant objects are in sharp focus on the retina when the ciliary muscle is completely relaxed. </li></ul><ul><li>This means that the eye can see all distant objects clearly, with its ciliary muscle relaxed, but to focus objects at close range it must provide various degrees of accommodation. </li></ul>
  64. 84. Myopia <ul><li>Myopia or nearsightedness results from an axial length of the eye that is too long for the refractive power of the eye. </li></ul><ul><li>In this case, the focal point is in front of the retina, thus, distant objects cannot be focused on the retina. </li></ul><ul><li>An object can be seen clearly if it is moved closer to the eye so that the image forms in the retina. </li></ul>
  65. 85. <ul><li>Hyperopia results from an axial length of the eye that is too short for the refractive power of the eye . </li></ul><ul><li>In this case, distant objects cannot be focused clearly because the focal point is at the back of the retina. </li></ul>
  66. 86. Astigmatism or “ghost vision” is when both far and near objects appear out of focus. This is because of the uneven diameter of the cornea (oblong-shaped). For light rays to focus precisely on the retina, the cornea usually needs to be more evenly round.
  67. 87. Fovea & Macula <ul><li>Fovea centralis is an oval, yellowish area with a depression where there are only cone cells. </li></ul>
  68. 91. Size of the Pupils <ul><li>Pupil size influences accommodation by controlling the amount of light entering the eye. In a bright light the pupils are constricted. In a dim light they are dilated. </li></ul><ul><li>Contraction of the circular fibers constricts the pupil, and contraction of the radiating fibers dilate it. </li></ul><ul><li>The size of the pupil is controlled by nerves of the ANS. Sympathetic stimulation dilates the pupils and parasympathetic stimulation causes constriction. </li></ul>
  69. 92. What is Rhodopsin? <ul><li>Rhodopsin or visual purple is a photosensitive pigment present only in the rods. It is bleached by bright light and when this occurs the rods can not be stimulated. </li></ul><ul><li>Rhodopsin is quickly reconstituted when an adequate supply of Vit A is available. </li></ul><ul><li>The rate at which dark adaptation takes place is dependent upon the rate of reconstitution of rhodopsin. </li></ul>
  71. 94. How are sounds heard? <ul><li>Sound waves cause movements of the tympanic membrane and these movements are both conveyed and amplified by the middle ear ossicles (malleus, incus, and stapes). </li></ul><ul><li>The vibrations transmitted to the ossicles cause the foot plate of the stapes to vibrate against the oval window thereby transmitting them to the inner ear. </li></ul><ul><li>Thus air-borne sound waves are transferred to the fluid in the inner ear. </li></ul>
  72. 95. The Vestibular apparatus <ul><li>This is the part of the ear that helps in equilibrium </li></ul><ul><li>Located in the inner ear </li></ul><ul><li>The saccule and utricle control LINEAR motion </li></ul><ul><li>The semicircular ducts control the Angular movement/ acceleration </li></ul>
  73. 97. Physiology of Smell <ul><li>The sense of smell is perceived when odorous materials in the air are carried into the nose and stimulate the olfactory cells. </li></ul><ul><li>Perception of odor decreases and eventually ceases due to smell adaptation </li></ul><ul><li>The sense of smell may affect the appetite </li></ul>
  74. 98. The Olfactory apparatus <ul><li>Stimulation from the olfactory nerves will reach the limbic system of the brain </li></ul><ul><li>Consists of the nose and the olfactory nerve </li></ul>
  75. 100. Primary Smell & Odor System <ul><li>6 primary types of </li></ul><ul><li>smell </li></ul><ul><li>Fragrant </li></ul><ul><li>Putrid </li></ul><ul><li>Spicy </li></ul><ul><li>Resinous </li></ul><ul><li>Burnt </li></ul><ul><li>Etheral </li></ul><ul><li>7 Odor System </li></ul><ul><li>Camphoraceous </li></ul><ul><li>Musky </li></ul><ul><li>Floral </li></ul><ul><li>Minty </li></ul><ul><li>Etheral </li></ul><ul><li>Pungent </li></ul><ul><li>Putrid </li></ul>
  77. 102. The Gustatory apparatus <ul><li>The receptor for taste are cells in the tongue group together called the taste buds </li></ul><ul><li>They are numerous in the vallate and fungiform papillae </li></ul>
  78. 103. The Gustatory apparatus <ul><li>Basic taste modalities </li></ul><ul><li>Sweet- tip of the tongue </li></ul><ul><li>Salty- over the dorsum of the tongue </li></ul><ul><li>Sour- sides of the tongue </li></ul><ul><li>Bitter- back of the tongue </li></ul>
  79. 105. How are taste perceived ? <ul><li>Taste buds which consist of small bundles of cells and nerve endings of cranial nerves (VII, IX and X). </li></ul><ul><li>The nerve cells are stimulated by chemical substances in solution that enter the pores. </li></ul><ul><li>The nerve impulses are transmitted to the thalamus then to the taste area in the cerebral cortex, one in each hemisphere, where taste is perceived. </li></ul><ul><li>4 fundamental sensations of taste have been described: sweet, sour, bitter and salty. </li></ul>
  80. 106. Next Meeting <ul><li>Quiz on Physiology of the Nervous System </li></ul>