NERVOUS SYSTEM

NERVOUS SYSTEMNervous system is the chief controlling & coordinating system of the bodyIt has the special property of sensitivity & conductivityNERVOUS SYSTEM consists of:Central nervous system- which has brain & spinal cordPeripheral nervous system- which has 12 pairs of cranial nerves & 31 pairs of spinal nervesFunctionally it has Somatic ( controls voluntary) and Autonomic Nervous system (controls involuntary activities)

CELL TYPES IN NERVOUS SYSTEMThe nervous tissue is composed of 2 types of cell typesThe excitable cells are the nerve cells or neuronsThe nonexcitable cells constitute neuroglia, ependyma and Schwann cellsTHE NERVE CELL OR NEURONA cell body called Soma, with central nucleus & Nissl granules in cytoplasmThe 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.

THE TYPES OF NEURONS(acc. to number of processes)1)Unipolar2)Bipolar3) Multipolar4)Pseudounipolar

THE TYPES OF NEUROGLIAL CELLS are:

Astrocytes- ensheath capillaries of CNSOligodendrocytes- formation of CNS myelin sheathsMicroglia-appear when there is tissue damage, ingest particles of degenerating myelinEpendyma- epithelium which lines the cavities of brain and covers vascular pia mater to form choroid plexusesSchwann cells which form sheaths for axons of peripheral nerves

PERIPHERAL NERVOUS SYSTEMConsists of 12 pairs of cranial nerves and 31 pairs of spinal nervesThere 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 & abdomenThere 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 nervesThe spinal cord ends at level of vertebra L1. Below this level the spinal nerves look like horses tail & are called cauda equina

THE SPINAL NERVEThe spinal nerve is connected to the spinal cord by 2 roots: anterior & posterior rootThe 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.

THE SPINAL NERVEAt 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 backThe anterior ramus supplies skin & muscles of anterolateral body wall & limbs

DERMATOMEThe area of skin supplied by one spinal nerve is called a dermatome

Twelve pairs of nerves which originate from brain stem and cerebrumPass through foramen magnum in the skullMixed nerves and special senses; some motor nerves

I: Olfactory: sense of smellII: Optic: sense of visionIII: Oculomotor: eye movement, focusingIV: Trochlear: eye movementV: Trigeminal: mixed nerve - ophthalmic: sensory: accessory eye structures - maxillary: sensory: teeth, gum, lip, face - mandibular: sensory: scalp, jaw, teeth, lipVI: Abducens: eye movementVII: Facial: mixed: taste, facial expressionVIII: Vestibulocochlear - vestibular branch: sense of equilibrium- cochlear branch: sense of hearingIX: Glosspharyngeal: mixed: pharynxX: Vagus: mixed: speech, swallowing, ANSto visceraXI: Accessory: - cranial branch: motor to pharynx and larynx - spinal branch: motor to neck and backXII: Hypoglossal: tongue movement

NERVE PLEXUS

NERVE FIBRES Each nerve fibre is an axon with its coveringsLarger axons are covered with myelin sheath & are called myelinatedThinner axons which dont have myelin sheath are called non-myelinated axonsMyelin & neurolemmal sheaths are derived from Schwann cells

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 BrainThe 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.

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.

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.

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.

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.

PARTS OF THE BRAIN

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

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

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.

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

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

DIENCEPHALON: Thalamus & HypothalamusMIDBRAIN: 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 nigraPONS: White bulging bridge middle cerebellar peduncleMEDULLA OBLONGATA: median Fissure, pyramid olive CEREBELLUM :2 Hemispheres and median vermis

APPLIED ANATOMYIrritation 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 paralysisDamage to a sensory nerve causes anaesthesia & analgesia (loss of sensation and pain).