NERVOUS SYSTEM

1. NERVOUS SYSTEM

2. NERVOUS SYSTEM • Nervous system is the chief controlling & coordinating system of the body • It has the special property of sensitivity & conductivity • NERVOUS SYSTEM consists of: • Central nervous system- which has brain & spinal cord • Peripheral nervous system- which has 12 pairs of cranial nerves & 31 pairs of spinal nerves • Functionally it has Somatic ( controls voluntary) and Autonomic Nervous system (controls involuntary activities)

3. CELL TYPES IN NERVOUS SYSTEM The nervous tissue is composed of 2 types of cell types • The excitable cells are the nerve cells or neurons • The nonexcitable cells constitute neuroglia, ependyma and Schwann cells THE NERVE CELL OR NEURON • A cell body called Soma, with central nucleus & Nissl granules in cytoplasm • The cell processes are called neurites, the short branching processes are called Dendrites & a single long process is called Axon-which carries impulses away from the body.

4. THE TYPES OF NEURONS(acc. to number of processes) 1)Unipolar 2)Bipolar 3) Multipolar 4)Pseudounipolar

5. THE TYPES OF NEUROGLIAL CELLS are: Astrocytes- ensheath capillaries of CNS Oligodendrocytes- formation of CNS myelin sheaths Microglia-appear when there is tissue damage, ingest particles of degenerating myelin Ependyma- epithelium which lines the cavities of brain and covers vascular pia mater to form choroid plexuses Schwann cells which form sheaths for axons of peripheral nerves

8. PERIPHERAL NERVOUS SYSTEM Consists of 12 pairs of cranial nerves and 31 pairs of spinal nerves There are 12 pairs of cranial nerves which come out from brain, leave the skull through foramina, supply the head and neck except the 10th Vagus which also supplies to thorax & abdomen There are 31 pairs of spinal nerves which leave the spinal cord & pass out through intervertebral foramina. There are 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal nerves The spinal cord ends at level of vertebra L1. Below this level the spinal nerves look like horse’s tail & are called “cauda equina”

12. THE SPINAL NERVE • The spinal nerve is connected to the spinal cord by 2 roots: anterior & posterior root • The anterior root consists of nerve fibres carrying nerve impulses away from CNS- called efferent fibres. • The posterior root consist of bundles of nerve fibres that bring impulses to the CNS, are called afferent fibres.

14. THE SPINAL NERVE • At each intervertebral foramen the anterior & posterior roots unite to form a spinal nerve. The motor & sensory fibres get mixed together so that each spinal nerve is a mixed nerve. • On coming out from the foramen, the spinal nerve divides into a large anterior ramus & a smaller posterior ramus. • The posterior ramus supplies the muscles & skin of the back • The anterior ramus supplies skin & muscles of anterolateral body wall & limbs

16. DERMATOME The area of skin supplied by one spinal nerve is called a dermatome

17. Twelve pairs of nerves which originate from brain stem and cerebrum • Pass through foramen magnum in the skull • Mixed nerves and special senses; some motor nerves

18. I: Olfactory: sense of smell • II: Optic: sense of vision • III: Oculomotor: eye movement, focusing • IV: Trochlear: eye movement • V: Trigeminal: mixed nerve - ophthalmic: sensory: accessory eye structures - maxillary: sensory: teeth, gum, lip, face - mandibular: sensory: scalp, jaw, teeth, lip • VI: Abducens: eye movement • VII: Facial: mixed: taste, facial expression • VIII: Vestibulocochlear - vestibular branch: sense of equilibrium - cochlear branch: sense of hearing • IX: Glosspharyngeal: mixed: pharynx • X: Vagus: mixed: speech, swallowing, ANSto viscera • XI: Accessory: - cranial branch: motor to pharynx and larynx - spinal branch: motor to neck and back • XII: Hypoglossal: tongue movement

19. NERVE PLEXUS

20. NERVE FIBRES • Each nerve fibre is an axon with its coverings • Larger axons are covered with myelin sheath & are called myelinated • Thinner axons which don’t have myelin sheath are called non-myelinated axons • Myelin & neurolemmal sheaths are derived from Schwann cells

23. The Meninges • The brain in the skull is surrounded by three protective membranes or meninges: the dura mater, the arachnoid mater, and the pia mater. Dura Mater of the Brain • The dura mater is described as two layers: the endosteal layer and the meningeal layer. • These are closely united except along certain lines, where they separate to form venous sinuses.

24. The meningeal layer is the dura mater proper. • It is a dense, strong, fibrous membrane covering the brain and is continuous through the foramen magnum with the dura mater of the spinal cord.

26. Arachnoid Mater of the Brain • The arachnoid mater is a delicate, impermeable membrane covering the brain and lying between the pia mater and the dura mater externally.

29. Pia Mater of the Brain • The pia mater is a vascular membrane that closely invests the brain, covering the gyri and descending into the deepest sulci. • It extends over the cranial nerves and fuses with their epineurium. • The cerebral arteries entering the substance of the brain carry a sheath of pia with them.

31. The cerebrospinal fluid • Is produced by the choroid plexuses within the lateral, third, and fourth ventricles of the brain. • It escapes from the ventricular system of the brain through the three foramina in the roof of the fourth ventricle and enters the subarachnoid space. • The spinal subarachnoid space extends down as far as the second sacral vertebra • Eventually, the fluid enters the bloodstream by passing into the arachnoid villi and diffusing through their walls.

32. PARTS OF THE BRAIN

33. Cerebrum • The cerebrum is the largest part of the brain and consists of two cerebral hemispheres connected by a mass of white matter called the corpus callosum. • Each hemisphere extends from the frontal to the occipital bones; above the anterior and middle cranial fossae and posteriorly, above the tentorium cerebelli. • The hemispheres are separated by a deep cleft, the longitudinal fissure into which projects the falx cerebri

34. Gyri (ridge) Sulci (groove) Fissure (deep groove) http://williamcalvin.com/BrainForAllSeasons/img/bonoboLH-humanLH-viaTWD.gif

35. The surface layer of each hemisphere is called the cortex and is composed of gray matter. The cerebral cortex is thrown into folds or gyri separated by fissures or sulci. By this means the surface area of the cortex is greatly increased. The large sulci subdivide the surface of each hemisphere into lobes.

36. Cerebral Cortex CerebralCortex Cerebral Cortex - The outermost layer of gray matter making up the superficial aspect of the cerebrum. http://www.bioon.com/book/biology/whole/image/1/1-6.tif.jpg

37. Lobes of the Brain (4) • Frontal • Parietal • Occipital • Temporal http://www.bioon.com/book/biology/whole/image/1/1-8.tif.jpg * Note: Occasionally, the Insula is considered the fifth lobe. It is located deep to the Temporal Lobe.

40. DIENCEPHALON: Thalamus & Hypothalamus MIDBRAIN: 1)Crura Cerebri ( broad bundles of nerve fibres from cerebral hemispheres to Pons 2) Tectum in posterior part has 4 colliculi 3) between the 2 lie tegmentum and substantia nigra PONS: White bulging bridge middle cerebellar peduncle MEDULLA OBLONGATA: median Fissure, pyramid olive CEREBELLUM :2 Hemispheres and median vermis

42. APPLIED ANATOMY • Irritation of a motor nerve causes muscular spasm. Mild irritation of a sensory nerve causes tingling & numbness. • Severe pain along the distribution of a nerve is called neuralgia. • Damage to a motor nerve causes motor paralysis • Damage to a sensory nerve causes anaesthesia & analgesia (loss of sensation and pain).