UNIVERSITY OF CALIFORNIA, BARKLEY SCHOOL OF MEDICINE • PHYSIOLOGY • About: Autonomic Nervous System • Lecturer: Dr Arafad Ismail Due date: 12/01/2017 Objectives: 1. After the end of this presentation, you should be able to: Identify the location of the cell bodies and axonal trajectories of preganglionic and postganglionic sympathetic and parasympathetic neurons. 2. Identify the neurotransmitters and receptor types involved in neurotransmission within the ANS and its target organs. 3. Describe the ways that the autonomic nervous system contributes to homeostasis. Describe the ways that the autonomic nervous system contributes to homeostasis. NERVOUS SYSTEM Divisions of nervous system • Nervous system controls all the activities of the body. It is quicker than other control system in the body, namely endocrine system. Primarily, nervous system is divided into two parts: 1. Central nervous system (CNS) 2. Peripheral nervous system (PNS) Cont... • CNS is composed of the brain (located in the cranial cavity)and the spinal cord (located in the vertebral cavity), whichserve as the main control centers for all body activities. • PNS is composed of nerves arises from the brain and spinalcord (12 pairs of cranial nerves and 31 pairs of spinalnerves) which serve as linkage between the CNS and thebody. Prepheral Nervous System (PNS) • Sensory (afferent) nerves which carry nerve impulse from the sensory receptors to CNS. • Motor (efferent) nerves which carry motor response from CNS to affector organs. they’re divided into two: 1. Somatic nervous system (SNS) which regulates the voluntary contraction of the skeletal muscles, and 2. Autonomic nervous system (ANS) which regulates the involuntary control of smooth, cardiac muscles and glands. Somatic Nervous System (SNS) Autonomic Nervous System (ANS) Subdivision None Sympathetic, parasympathethic and entric Control Voluntary control Involuntary control Number of motor neurons One motor neuron (Alpha motor neuron) in b/w C.N.S and effector organs Two neurons connected by snapse b/w CNS and effector organs Neurotranmitters Acetylcholin Either acetylcholin, norepinephrine, Or norepinephrine Effector organs Skeletal muscles Supply glands, smooth and cardiac muscles Effect Contraction Either excitation or inhibition Autonomic Nervous System (ANS) • Definition: is a part of the peripheral nervous system that regulates involuntary physiologic processes including heart rate, blood pressure, respiration, digestion, and sexual arousal. To maintain homeostasis • It contains three anatomically distinct divisions: sympathetic, parasympathetic, and enteric. Divisions & Origin of the ANS AUTONOMIC GANGLIA • Definition: It is the site of physiological contact between pre and post ganglionic fibers. • Ganglia: Is a collections of neurons outside the CNS Consists of: Cell bodies of postganglionic neurons & Axon terminals of pregangionic neurons Sympathetic System • Sympathetic nervous system is called the thoracolumbar division of the ANS. B/c Sympathetic preganglionic neurons leave the spinal cord at the level of first thoracic to the third or fourth lumbar spinal segments. With its ganglions located near spinal nerve Length of pre-and postganglions neurons: Preganglion: short or small & mylinated (found near the CNS) Postganglion: long, usually un mylinated (to reach peripheral effector organs) Autonomic nerve pathway Extends from CNS to an effector organ (innervated organ) Two-neuron chain: • Preganglionic fiber: synapse with the cell body of the second neuron • Postganglionic fiber: innervated the the effector organ Adrenal Medulla Is specialized ganglion of the sympathetic nervous system. • Preganglionic fibers synapse directly on chromaffin cells in the adrenal medulla. • The chromaffin cells secrete epinephrine (80%) and norepinephrine (20%) • Receptor is nicotinic and transmitter is Ach. Organs supplied by sympathetic only : • • • • • Ventricles (vagal escape). Skin structures Skeletal Blood Vessels. Dilator pupillary muscles . Adrenal medulla Parasympathetic Systems The parasympathetic nervous system is called the craniosacral division of the ANS, because of the location of its preganglionic neurons within several cranial nerve nuclei (III, VII, IX, and X) and the IML of the sacral spinal cord. Divisions of Parasympathetic system: • Cranial division; cranial nerves that arise from (brainstem) and • Sacral division; spinal cord segments that arise(S2-S4). Cont... Length of pre-and post ganglion: • Pre-ganglion: long • Post-ganglionic neurons: short ( found in parasympathetic ganglia or near or actually in the walls of the target organs). Cranial Nerves with Parasympathetic outflow 1. Oculomotor nerve (III) Innervates smooth muscles of eye, causing it to constrict. 2. Facial nerve (VII) Stimulates the secretary activity of glands in the head. Ex. Nasal glands, lacrimal gland, submandibular, salivary, & parotid glands. 3. Glossopharyngeal never (IX) Activates the parotid, and salivary glands. Cont... 4. Vagus nerve (X) Major portion of parasympathetic cranial outflow is via vagus nerve. • mixed nerve containing both sensory and motor fibers. • sensory input from medulla to cardiovascular, pulmonary, urinary, reproductive, and digestive system travels in the afferent fibers of the vagus nerve Effects of autonomic Stimulation Skin: Apocrine gland (S): secretion Eccrine gland (P): no Action Special senses: • Iris of eye (S): Dilation & (P): constriction • Tear gland (S): Inhibitory & (P): secretion Endocrine system: • Adrenal cortex (S): secretion • And medulla (P): no Action Cont... Digestive system: • Intestine: (s): decrease peristalsis (p): Increase peristalsis • Smooth muscle: (s): relaxes (p): Contracts • Sphincters: (s): constricts (p): Relaxes • Secretion: (s): increase (p): decrease Cont... Respiratory System: • (s): dilate bronchioles • (p): constrict bronchioles Cardivadcular System: Heart Muscle: • (s): increase heart rate • (p): decrease heart rate Blood vessels: (S): constriction (P): dilation Cont... Genitourinary system: • Bladder (S): Relaxation & (P): contraction • Urinary sphincter (S): contraction & (P): relaxation penis: (S): causes erection (P): causes ejaculation Vagina: (S): causes erection of clitoris (P): causes contraction of vagina ANS: Neurotransmitters Acetylcholine and norepinephrine are the principal neurotransmitters synthesized and released by autonomic neurons. The cholinergic autonomic neurons (ie, release acetylcholine) are: (1) All preganglionic neurons, (2) All parasympathetic postganglionic neurons, (3) Sympathetic postganglionic neurons that innervate sweat glands, (4) Sympathetic postganglionic neurons that end on blood vessels in some skeletal muscles and produce vasodilation when stimulated (sympathetic vasodilator nerves). Cont... The remaining sympathetic postganglionic neurons are noradrenergic ( release norepinephrine): Adrenal medulla is essentially a sympathetic ganglion in which the postganglionic cells have lost their axons and secrete both norepinephrine and epinephrine directly into the bloodstream. The neurotransmitters are synthesized, stored in the nerve endings, and released near the neurons, muscle cells, or gland cells. ANS: Types of Receptors 1. Adrenergic receptors : alpha – receptors beta - receptors • In General, NE or epinephrine binding to alphareceptors are stimulatory while their binding to beta receptors are inhibitory. • Both and receptors have distinct subtypes (alpha 1 , 2 , & beta 1, 2,3 ). Cont... 2. Cholinergic receptor: nicotinic receptors muscarinic receptors • Nicotinic receptors: are all excitatory, and heir response is rapid (milliseconds). • Muscarinic receptors: either excitatory or inhibitory , depending on the target organ . have distinct subtypes (M1, M2, M3) Decrease heart activity. Increase motility in G.I. tract. Clinical Correlates Horner's Sydrome Horner’s syndrome, also known as oculosympathetic palsy or Bernard-Horner syndrome, It occurs due to a disruption of the pathway of the sympathetic nerves that connect your brainstem to your eyes and face. These nerves control involuntary functions, such as sweating (perspiration) and the dilation and constriction of the pupils of your eyes. Cont... Usually, symptoms of Horner’s syndrome affect only one side of the face and it occurs ipsilateral to the lesion. They include: • Drooping of your upper eyelid (ptosis). as result of loss of sympathetic activation of Muller’s muscle of the eyelid • Constricted pupil (miosis), resulting in mismatched sizes of your pupils. • Decrease in sweating or lack of sweating on your face (anhidrosis). as a result of the lack of sympathetic activation of the facial muscle sweat glands. Reference: 1. Ganong's review of medical physiology (26th edition) 2. Vander's Human Physiology (15th edition) 3. Essentials of Medical Physiology (6th edition) 4. Guyton and Hall Medical Physiology (13th edition) 5. clevelandclinic.org (horners-syndrome)
