CHAPTER Xb PDL 101 HUMAN ANATOMY & PHYSIOLOGY

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1 CHAPTER Xb PDL 101 HUMAN ANATOMY & PHYSIOLOGY Ms. K. GOWRI. M.Pharm., Lecturer.

2 AUTONOMIC NERVOUS SYSTEM The autonomic or involuntary part of the nervous system controls the functions of the body carried out automatically i.e initiated in the brain below the level of the cerebrum. Effect of autonomic control are rapid and essential for homeostasis Effector organs are smooth muscle cardiac muscle glands Effect of autonomic stimulation include changes in rate and force of heartbeat stimulation or depression of secretion of glands vasoconstriction or vasodilation bronchoconstriction or bronchodilation changes in size of the pupils of the eyes. Divisions of ANS ANS is divided into two divisions sympathetic (thoracolumbar outflow) parasympathetic (craniosacral outflow) These two divisions have both structural and functional differences. Each division has two efferent neurons in its peripheral pathways between the CNS and effector organs. These are : Preganglionic neurons Postganglionic nervous system

3 SYMPATHETIC NERVOUS SYSTEM: Neurons convey impulses from their origin in the hypothalamus, reticular formation and medulla oblongata to effetcor organs and tissues. PREGANGLIONIC NEURONS: Has its cell body in lateral column of gry matter in the spinal cord between the levels of the 1 st thoracic and 2 nd or 3 rd lumbar vertebrae. Acetylcholine is the neurotransmitter. POSTGANGLIONIC NEURONS: Has its cell body in a ganglion and terminates in the organ or tissue supplied. SYMPATHETIC GANGLIA: THE LATERAL CHAINS OF SYMPATHETIC GANGLIA: The lateral chains of ganglia extend from upper cervical level to the sacrum, one chain lying on each side of the body vertebrae. Ganglia are attached to each other by nerve fibres. Preganglionic neurons emerge from cord may synapse with the cell body of postganglionic neuron. EX: Nerve which dilates the pupil of the eye leaves the cord at the level of 1 st thoracic vertebrae and passes the chain to the cervical ganglion before it synapses with cell body of post synaptic neuron PREVERTEBRAL GANGLION These are three prevertebral ganglia situated in the abdominal cavity close to the origin of arteries of the same names Coelaic ganglion Superior mesenteric ganglion Inferior mesenteric ganglion Ganglia consists of nerve cell bodies rather diffusely

4 distributed among a network of nerve fibres from plexuses. PARASYMPATHETIC NERVOUS SYSTEM: Two neurons ( preganglionic and postganglionic are involved in the transistion of impulses from their source to the effector organ. PEGANGLIONIC NEURON: This has its cell body either in the brain or in the spinal cord. Originating in the brain are cranial nerves III,VII,IX and X. Fibres leaves the cord in sacral segments 2, 3 & 4 and synapse with postganglionis neurons in the walls of pelvic organ. POSTGANGLIONIC NEURON: This has its cell body either in ganglion or in the wall of the organ supplied. MOTOR PATHWAYS: Neurons which transmit nerve impulses away from the brain are motor neurons Motor stimulation results in contraction of skeletal muscle and smooth muscle, cardiac muscle and the secretion by glands controlled by nerves of the ANS Voluntary muscle movement: Contraction of the muscle which move the joints is,in the main under conscious control,whicl means that the stimulus to contract originates the level of consciousness in the cerebrum. Efferent nerve impulses are transmitted from the brain to the body via bundles of nerve fibres or tracts in the spinal cord. Motor pathways from the brain to the muscles are made up of two neurons Pyramidal Extrapyramidal Motor fibres form the pyramidal tracts travel through the internal capsule and are the main pathway for impulses to voluntary muscles.

5 Motor fibres that do not pass through internal capsule form the extrapyramidal tracts and have connection with many parts of the brain including basal nuclei and thalamus. UPPER MOTOR NEURON: This has its cell body in the precentral sulcus area of the cerebrum. In case of spinal cord, they form lateral corticospinal tracts of white matter LOWER MOTOR NEURON: Has its cell body in the anterior horn of grey matter in the spinal cord. Lower motor neuron described as the final common pathway for the transmission of nerve impulses to skeletal muscles. Outcome of these influences is smooth, coordinated muscle movement, some of which is voluntary and some are involuntary INVOLUNTARY MUSCLE MOVEMENT: Upper motor neurons: These have their cell bodies in the brain at a level below the cerebrum i.e in the midbrain, brain stem, cerebellum or spinal cord. Influences muscle activity in relation to the maintenance of posture and balance, the coordination of muscle movement and the control of muscle tone SPINAL REFLEXES: Consists of 3 elements: Sensory neurons Connector neurons in the spinal cord Lower motor neurons A reflex action is an immediate motor response to a sensory stimulus These stimulate many connector and lower motor neurons in the cord which results in the contraction of many skeletal muscles of the hand, arm and shoulder. Reflex action takes place very quickly

6 EX: if it is a precious plate that is very hot when lifted every effort will be made to overcome the pain to prevent dropping it. STRETCH REFLEXES: Only two neurons are involved. Cell body of the lower motor neuron is stimulated by sensory neuron EX: knee jerk- This type of reflex can be demonstrated at any point where a stretched tendon crosses a joint. Used as a test of the integrity of the reflex arc. This type of reflex has a protective function it prevents excessive joint movement that may damage tendons, ligaments and muscles. SENSORY PATHWAYS: Two main sources of sensation transmitted to brain via the spinal cord 1. The skin: Sensory receptors in the skin called cutaneous receptors are stimulated by pain, heat, cold and touch Nerve impulses generated are conducted by three neurons to the sensory area in the opp hemispheres of the cerebrum where the sensation and its location are perceived Decussation occurs either at the level of entry into cord or in the medulla 2. The tendons, muscles and joints: sensory receptors are nerve endings in these structures called propriceptors and are stimulated by stretch. Nerve impulses have two destinations : (i) by a three- neuron system, the impulses reach the sensoty area of the opposite hemisphere of the cerebrum. (ii) by a two- neuron system the nerve impulses rach the cerebellar hemisphere on the same side.

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