Autonomic Nervous System-I بسم الله الرحمن الرحيم Autonomic Nervous System-I Dr.Mohammed Sharique Ahmed Quadri Assistant prof. Physiology Al Maarefa College

PNS: Efferent Division Communication link by which CNS controls activities of muscles and glands Two divisions of PNS Autonomic nervous system (ANS) Involuntary branch of PNS Innervates cardiac muscle, smooth muscle, most exocrine glands, some endocrine glands, and adipose tissue Somatic nervous system Subject to voluntary control Innervates skeletal muscle

Autonomic Nervous System The portion of the nervous system which controls most visceral function of the body is called as autonomic nervous system. Arterial pressure heart rate GI motility GI secretion Urinary bladder emptying Sweating Body temperature

The efferent autonomic signals are transmitted to the various organs of the body through 2 major subdivision. Sympathetic nervous system Parasympathetic nervous system

Physiologic anatomy of the ANS Sympathetic nerve fibers originate in the spinal cord along with the spinal nerve between T1-L2/L3 ( thoraco lumbar ). Parasympathetic nerve fibers originate from brain stem (midbrain, pons, and medulla) or the sacral spinal cord ( craniosacral). The preganglionic fibers originates from nuclei of cranial nerves (CN) III, IV, IX and X or from sacral spinal segments S2-S4.

ANS Preganglionic fiber (synapses with cell body of second neuron) Autonomic nerve pathway Extends from CNS to an innervated organ Two-neuron chain Preganglionic fiber (synapses with cell body of second neuron) Postganglionic fiber (innervates effector organ)

Physiologic anatomy of the sympathetic nervous system Sympathetic nerve fibers originate in the spinal cord along with the spinal nerve between T1 – L2. ( thoraco lumbar ) Length of the pre & postganglionic fibers Preganglionic fibers – are shorter Post ganglionic fibers – are longer

sympathetic nervous system Pre ganglionic sympathetic fibers always cholinergic, i.e. secretes Ach. This activates nicotinic receptors in the post ganglionic fibers. Post ganglionic fibers are adrenergic. They act on adrenoreceptors (α1, α2, β1, or β2). Only exception is post ganglionic fibers supplying thermoregulatory sweat glands that is cholinergic that acts on muscarinic receptors.

Functions of sympathetic nervous system Sympathetic system dominates in emergency or stressful (“fight-or-flight”) situations Promotes responses that prepare body for strenuous physical activity

Parasympathetic nervous system Parasympathetic system originates from brain stem (midbrain, pons, and medulla) or the sacral spinal cord ( craniosacral). The preganglionic fibers originates from nuclei of cranial nerves (CN) III, IV, IX and X or from sacral spinal segments S2-S4.

Parasympathetic nervous system Length of the pre & postganglionic fibers Preganglionic fibers –are longer Post ganglionic fibers – are shorter Pre ganglionic para sympathetic fibers always cholinergic, ie secretes Ach. This activates nicotinic receptors in the post ganglionic fibers. Post ganglionic fibers are cholinergic.

Parasympathetic nervous system e.g. parasympathetic innervation of eye muscles originates in the Edinger-Westphal nucleus in the midbarin. Like wise, X nerve (vagus) originates in the nuclei of the medulla.

ANS Parasympathetic system dominates in quiet, relaxed (“rest-and-digest”) situations Promotes body-maintenance activities such as digestion It allows the body to recover from stress

ANS Sympathetic Nervous System Parasympathetic Nervous System Fibers originate in thoracic and lumbar regions of spinal cord Fibers originate from cranial and sacral areas of CNS Most preganglionic fibers are short Preganglionic fibers are longer Long postganglionic fibers Very short postganglionic fibers Preganglionic fibers release acetylcholine (Ach) Most postganglionic fibers release noradrenaline (norepinephrine), accept in sweat gland (Ach) Postganglionic fibers release acetylcholine Autonomic ganglio is prevertebral & paravertebral Autonomic ganglia is near effector organ

ANS Most visceral organs innervated by both sympathetic and parasympathetic fibers In general produce opposite effects in a particular organ Dual innervation of organs by both branches of ANS allows precise control over organ’s activity

EFFECTS OF ANS

ANS Exceptions to general rule of dual reciprocal innervation by the two branches of autonomic nervous system Most arterioles and veins receive only sympathetic nerve fibers (arteries and capillaries are not innervated) Most sweat glands are innervated only by sympathetic nerves Salivary glands are innervated by both ANS divisions but activity is not antagonistic – both stimulate salivary secretion

Distinguishing Characteristics of Sympathetic and Parasympathetic Nervous Systems

References Human physiology by Lauralee Sherwood, seventh edition Text book physiology by Guyton &Hall,11th edition Text book of physiology by Linda .s contanzo,third edition