Ms. K. GOWRI. M.Pharm., Lecturer.

Ms. K. GOWRI. M.Pharm., Lecturer.

CENTRAL NERVOUS SYSTEM (CNS) central nervous system consists of brain and spinal cord membrane covering the brain and spinal cord are surrounded by three membrane Meninges lying between the skull and brain and verterbrae and spinal cord

named from outside inwards they are dura mater arachnoid mater pia mater dura and arachnoid mater are separated by potential spacethe subdural space the arachnoid and pia mater are separated by subarachnoid space, containing cerebrospinal fluid.

BRAIN: brain constitutes about one fifth of the body weight and lies within the cranial cavity parts are cerebrum cerebellum medulla oblongata mid brain and pons

BLOOD SUPPLY TO THE BRAIN: the circulus arteriosus and its contributing arteris play a vital role in maintaining a constant supply of oxygen and glucose to the brain and even when contributing artery is narrowed or the head is moved brain receives about 15% of cardiac output approximately 75o ml of blood per min autoregulation keeps blood flow to the brain constant by adjusting the arterioles diameter.

CEREBELLUM: this is the largest part of the brain and it occupies the anterior and middle cranial fossae. it is divided by deep cleft, the longitudinal cerebral fissure, intro right & left cerebral hemispheres. the superficial part of the cerebrum is composed of nerve cell bodies or grey matter, forming cerebarl cortex, deeper layer consits of nerve fibres or white matter

for descriptive purpose each hemisphere of the cerebrum is divided into lobes which take the names of the bones of the cranium under which the lie frontal parietal temporal occipital

INTERIOR OF CEREBRUM: afferent and effernt fibres linking the diiferent parts of the brain and spinal cord are as follows association fibres connect different parts of a cerebral hemisphere by extending from one groups to another commissural fibres projection fibres connect the cerebral cortex with grey matter.

FUNCTIONS OF CEREBRUM: There are 3 main varieties associated with cerebral cortex 1. Mental activities involved in memory, intelligence, sense of responsibility, thinking, reasoning,etc 2. Sensory perception, including the perception of pain, temp, touch, sight, hearing 3. Initiation and control of skeletal muscle contraction.

CEREBELLUM: The cerebellum is situated behind the pons and immediately below the posterior portion of the cerebrum occupying the posterior cranial fossae It is ovoid in shape and has two hemispheres, separated by a narrow median strip called vermis. Grey matter forms the surface of the cerebellum and the white matter lies deeply.

FUNCTIONS: It is concerned with co ordination of voluntary muscular movement, posture and balance. Cerebellum controls and co ordinates the movements of various groups of muscles ensuring smooth, even, precise actions. Associated with maintenance of the balance and equilibrium of the body. Proprioceptor impulses from the muscles and joints indicate their position in relation to the body. Impulses influence the contraction of skeletal muscle so that balance and posture are maintained. Damage results is clumsy uncordinated muscular movement, staggering gait and inability to carry out smooth, steady, precise movements.

MEDULLA OBLONGATA: Medulla oblongata extends from pons and above and is continuous with the spinal cord below. It is about 2.5cm long and it lies just within the cranium above the feramen magnum. Outer aspect composed of white matter which passses between the brain and the spinal cord. Grey matter lies centrally. Vital center consisting of groups of cells associated with autonomic reflex activity, lie in deeper structure.

These are: cardiac centre respiratory centre vasomotor centre relflex centres of vomiting, coughing, sneezing and swallowing.

MEDULLA OBLANGATA HAS SEVERAL SPECIAL FEATURES: 1. Decussation of the pyramids. 2. Sensory decussation. 3. Cardiovascular centre centrols the rate & force of cardiac contraction. 4. Respiratory centre centrols rate & depth of respiration. 5. Vasomotor centre centrols the diameter of the blood vessels especially the small arteries and arterioles. 6. Reflex centres irritating substances are present in the stomach or respiratory tract, nerve impulses pass to the medulla oblongata, stimulating the reflex centres which initiate the reflex action of vomiting, coughing & sneezing.

CEREBRAL VENTRICLES: With in the brain there are four irregular shaped cavities or ventricles. they are 1. Right and left lateral ventricles. 2. Third ventricle. 3. Fourth ventricle. Lateral ventricle: These cavities lie within cerebral hemispheres, one on each side of the median plane just below the corpus callosum

Separated by a thin membrane, septum lucidum and are lined with ciliated epithelium. Communicate with third ventricle by interventricular foramina. Third ventricle: It is a cavity situated below the lateral ventricles between the two parts of the thalamus. It communicates with fourth ventricle by a canal, cerebral aqueduct or aqueduct of the midbrain.

Fourth ventricle: It is diamond shaped cavity situated below and behind the third ventricle between the cerebellum and pons.

CEREBROSPINAL FLUID: It is secreted into each ventricle of the brain by choroid plexuses. CSF passes back into blood through tiny diventricular of arachnoid mater called arachnoid villi. From the root of the 4 th ventricle CSF flows through foramina into subarachnoid space and completely surrounds brain and spinal cord. CSF is a clear, alkaline fluid with specific gravity of 1.005, consisting of water mineral salts glucose plasma proteins creatinine urea

FUNCTIONS: Supports and protects brain and spinal cord. Maintains uniform pressure. Act as cushion and shock absorber. Keeps brain and spinal cord moist and there may be interchange of substances between CSF and nerve cells, such as nutrients and waste products.

CRANIAL NERVES: 12 pairs of cranial nerves originating from nuclei in the inferior surface of the brain, some sensory some motor and some mixed. Their names and numbers are: I Olfactory : sensory II Optic : sensory III Oculamotor : motor IV Trochelar : motor V Trigeminal : mixed

VI Abducent: motor VII Facial : mixed VIII Vestibulocochlear : sensory IX Glossopharyngeal : mixed X Vagus : mixed XI Accessory : motor XII Hypoglossal : motor

I Olfactory nerves: These nerves are sense of smell. Their nerve endings and fibres originate in the upper part of the mucous membrane of the nasal cavity. II Optic nerves: These nerves are sense of sight. These fibres originate in the retinae of the eye and combine to form optic nerves. Pass through optic foramina of the sphenoid bone into the cranial cavity and join at optic chiasma.

III Oculomotor nerves: These nerves arise from nerve cells near the cerebral aqueduct. They supply four extraocular muscles intraocular muscles ciliary muscles levator palpebrae. circular muscles of the iris

IV Trochlear nerves: These nerves arise from nerve cells near the cerebral aqueduct. supply superior oblique muscles of the eyes. V Trigeminal nerves: These nerves contain motor and sensory fibres and it is the largest among the cranial nerves. 3 main branches of this nerves 1. opthalmic nerves only sensory and supply lacrimal glands, forehead. 2. maxillary nerves only sensory and supply the cheeks, upper gums. 3. mandibular nerves both sensory and motor fibres.

VI Abducent nerves: These nerves arise from a group of nerve lying under the floor of the 4 th ventricle. supply lateral rectus muscles of the eyeballs. VII Facial nerves: Composed of both sensory and motor nerve fibres. Motor fibres supply muscles of facial expression. VIII Vestibulocochlear nerves: Nerves composed of two distinct sets of fibres, vestibular nerves cochlear nerves

Vestibular nerves arise from semicircular canals of the inner ear and convey impulses to cerebellum. Cochlear nerves originate in the organ of corti in the inner ear and convey impulses to the hearing areas. IX Glossopharyngeal nerves: Nerves arise form nuclei in the medulla oblangata. motor fibres stimulate the muscles of the tongue and pharynx and the secretory cells of the parotid glands.

X Vagus nerves: Nerves have more extensive distribution them any other cranial nerves. motor fibres supply the smooth muscles and secretory glands of the pharynx, larynx, trachea, heart, etc. XI Accessory nerves: Nerves arise from cell bodies in the medulla oblongata in the spinal cord. Branches join the vagus nerves and supply the pharyngeal and laryngeal muscles.

XII Hypoglossal nerves: Nerves arise form cells in the medulla oblongata. Supply the muscles of the tongue and muscles surrounding the hyoid bone.