1. DR. ZAHOOR ALI SHAIKH LECTURE--- 12 1

2. First We Will Discuss ‘ORGANIZATION & CELLS OF NERVOUS SYSTEM’ then we will talk about ‘Overview of Central nervous system’ [CNS] 2

3. ORGANIZATION OF NERVOUS SYSTEM The Nervous system is organized into 1. Central Nervous System (CNS) -- BRAIN -- SPINAL CORD 2. Peripheral Nervous System -- Nerve fibers that carry information between CNS and other parts of body at periphery. 3

4. Organization of nervous system 4

5. CNS Central nervous system regulates body activities. CENTRAL NERVOUS SYSTEM 1) BRAIN 2) SPINAL CORD 5

6. PERIPHERAL NERVOUS SYSTEM PNS Peripheral Nervous System is sub divided into 1) Afferent Division (Sensory) – which carry information to CNS 2) Efferent Division (Motor) – which carry information from CNS to muscle and glands. 6

7. PNS [cont] Efferent (Motor) division of PNS is further divide into --Somatic Nervous System– it is under our voluntary control E.g. fibers of motor neuron that supply skeletal muscle. --Autonomic Nervous System – it is not under our control ( involuntary) and supply smooth muscle and glands. 7

8. PNS [cont] Autonomic Nervous System (ANS) ANS– supplies cardiac muscle, smooth - muscle, glands. ANS is divided into 1) Sympathetic ANS 2) Parasympathetic ANS Enteric ANS– in the wall of digestive tract 8

9. ORGANIZATION OF NERVOUS SYSTEM 9

10. PERIPHERAL NERVOUS SYSTEM Neurons in peripheral nervous system transmit signals between the central nervous system and receptors,and Effectors in the body. In Peripheral Nervous System, there are 12 pairs of cranial nerves. There are 31 pairs of spinal nerve, from spinal cord. - 31 pair of Spinal nerve exit from cervical (8 pairs), thoracic (12 pairs), lumber (5 pairs), sacral (5 pairs), and coccygeal (1 pair). 10

11. 11

12. 12 Cranial Nerves 12 pairs

13. 13 Spinal Nerves 31 pairs

14. FUNCTIONAL CLASSES OF NEURONS 14

15. FUNCTIONAL CLASSES OF NEURONS There are THREE functional types of Neurons 1) Afferent Neurons– which carry information to CNS. 2) Efferent Neurons– which carry information away from CNS (to the periphery). 3) Interneurons– They form interactive net-work between neuron. 15

16. FUNCTIONAL CLASSES OF NEURON 16

17. AFFERENT NEURON Afferent Neuron has sensory RECEPTOR, that generates action potential in response to a particular stimulus. Sensory impulse are taken by axon toward the spinal cord. 17

18. EFFERENT NEURON Efferent Neuron lies in the peripheral nervous system. It has cell body in the CNS. Efferent axon leaves the cell body and goes to innervate muscle. 18

19. INTERNEURONS Interneurons lie in the CNS. About 99% of all neurons are Interneurons. Human CNS has more than 100 billion Interneurons. 19

20. GLIAL CELLS OR NEUROGLIA 20

21. GLIAL CELLS or NEUROGLIA Glial cells are connective tissue of CNS. Glial cells support the interneurons physically, metabolically, and functionally. They do not conduct nerve impulses. Glial cells are of FOUR types. 21

22. GLIAL CELLS or NEUROGLIA (cont) There are 4 type of Glial Cells 1. Astrocytes 2. Oligodendrocytes 3. Microglia 4. Ependymal Cells 22

23. GLIAL CELLS 23

24. Important Functions Of Glial Cells 1. Astrocytes  Functions i. Formation of blood – brain – barrier ii. Formation of neural scar tissue 2. Oligodendrocytes  Functions i. Forms myelin sheath in the CNS. 24

25. Important Functions Of Glial Cells 3. Microglia  Functions i. Phagocytosis [defense cells of CNS] ii. Release nerve growth factor. 4. Ependymal Cells  Functions i. Formation of Cerebrospinal fluid [CSF]. ii. Work as Neural Stem Cell – to form new neurons and glial cells. 25

26. Protection Of The Brain 26

27. Protection Of Brain  As CNS is very delicate, it is protected by – skull bone [covers the brain] and Vertebral column [surrounds the spinal cord].  Meninges – cover brain and spinal cord. Meninges lie between bony covering [outside] and nervous tissue [inside]. Meninges are Durameter, Arachnoid and Piameter.  CSF - Cerebro Spinal Fluid is present in subarachnoid space. CSF works as cushion.  Blood - brain barrier – it selectively allows the materials to pass to brain. 27

28. MENINGES & CSF 28

29. Cerebro Spinal Fluid [CSF] It surrounds brain and spinal cord. It is present in subarachnoid space. It is formed by choroid plexuses [capillaries in the piameter] of ventricles in the brain. Volume of CSF is about 125 – 150 ml. 29

30. CSF [cont]  Clinical Note Hydrocephalus [water in the brain]. Occurs if CSF accumulates more, due to the block in its circulation or reabsorption. If hydrocephalus is untreated, increased CSF pressure can lead to brain damage and mental retardation. Treatment – surgically shunting the excess CSF to veins elsewhere in the body. 30

31. ‘Important Information’ Brain function depends on 1. Oxygen 2. Glucose Brain needs continuous supply of O2 and Glucose. Brain damage results if - brain gets no O2 supply for 4 to 5mins or - no glucose supply for 10 to 15mins. 31

32. Thank you 32