AUTONOMIC NERVOUS SYSTEM (Human Physiology)
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A motor nervous system of the peripheral division of the nervous system that controls glands, cardiac muscles and smooth muscles.
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AUTONOMIC NERVOUS SYSTEM (Human Physiology)
- 2. OVERVIEW OF THE ANS ANS is a motor nervous system that controls our glands, cardiac muscle and smooth muscle. Know as the visceral motor system It influence the activities of visceral ANS act unconsciously and regulate bodily functions
- 3. OVERVIEW It’s primary target organs are; Visceral of abdominal cavity Thoracic cavity Body wall structures Visceral effectors do not depend on the ANS to function but only to adjust their activity to the body’s changing needs.
- 4. NEURAL CONTROL OF INVOLUNTARY EFFECTORS ANS regulates the activities of glands, smooth and cardiac muscles Impulses are conducted from the CNS by axon The axon of the second neuron innervates the involuntary effector Effectors such as; These effectors are part of the visceral organs, organs in body cavities.
- 5. AUTONOMIC NEURONS These neurons are called Motor or efferent neurons Two major categories of motor neurons ๏ Somatic motor neurons ๏ Visceral motor neurons Somatic motor neurons have their cell body in the CNS Visceral motor neurons involves two neurons in the efferent pathway ๏ Preganglionic neuron ๏ Postganglionic neuron
- 6. COMPARISON OF SOMATIC AND AUTONOMIC EFFERENT PATHWAYS
- 7. CHARACTERISTI C SOMATIC NERVOUS SYSTEM AUTONOMIC NERVOUS SYSTEM Effectors Voluntary muscle Cardiac muscle glands, s. muscle General functions Adjustment to external environment Adjustment within internal environment Numbers of neurons One Two Ganglia outside the CNS None Collateral ganglia or terminal ganglia Neurotransmitter Acetylcholine Acetylcholine, adrenaline, noradrenaline Center Anterior Horn cells Lateral Horn cells
- 9. VISCERAL EFFECTOR ORGANS ANS plays an important role in regulating most of the organs within the various system Damage to somatic nerve innervating skeletal muscles results into flaccid paralysis Damage to motor nerve innervating an effector makes the organ more sensitive Denervation hypersensitivity Some autonomic nerve release neurotransmitters that can either stimulate or inhibit the activity of their effectors
- 10. DIVISION OF THE ANS ANS has two (2) subdivisions; Sympathetic Nervous System Parasympathetic Nervous System Preganglionic neurons of the sympathetic division originate in the thoracic and lumber level of the spinal cord Preganglionic neurons of the parasympathetic division originate in the brain and sacral level of the spinal cord Both subdivisions have some structural features in common
- 12. SYMPATHETIC DIVISION Also called Thoracolumbar division of the ANS Its preganglionic fibers exit the spinal cord in the ventral root of the spinal nerves Preganglionic neurons synapse with postganglionic neuron in the sympathetic ganglia (Paravertebral Ganglia) Ganglia within each row are interconnected
- 13. THE PATHWAY OF SYMPATHETIC NEURONS
- 14. Myelinated preganglionic sympathetic axons exit the spinal cord in the ventral roots of spinal nerves They diverge from the spinal nerves within short pathways called white rami communicantes The axons of the postganglionic sympathetic neurons are unmyelinated and form the gray rami communicantes as they return to the spinal nerves
- 15. SCHEMATIC OF THE SNS
- 16. COLLATERAL GANGLIA Preganglionic fibers below the level of the diaphragm form splanchnic nerves. Splanchnic nerves preganglionic fibers synapse in collateral (Prevertebral) ganglia These include; Celiac, superior mesenteric and inferior mesenteric ganglia These usually innervates organs of the digestive, urinary and reproductive systems
- 18. ADRENAL GLANDS Suprarenal glands, located above each kidney Each adrenal is composed of two parts: Cortex Medulla Adrenal medulla secretes the hormone epinephrine (adrenaline) The adrenal medulla can be likened to a modified sympathetic ganglion The adrenal medulla secretes epinephrine into the blood in response to this neural stimulation Both the sympathetic ganglion and the adrenal medulla are referred to as Sympathoadrenal System
- 19. ADRENAL GLAND
- 20. PARASYMPATHETIC NERVOUS SYSTEM Know as the Craniosacral division of the ANS Preganglionic neuron synapse in ganglia next to or within the target organ These parasympathetic ganglia are called Terminal ganglia Four of the 12 pairs of cranial nerves contain preganglionic parasympathetic fibers These are the oculomotor (III), facial (VII), glossopharyngeal (IX), and vagus (X) nerves
- 22. SCHEMATIC OF PNS
- 23. FUNCTIONS OF THE ANS ๏ Blood pressure ๏ Heart and breathing rate ๏ Body temperature ๏ Digestion ๏ Energy metabolism ๏ Urination ๏ Defecation ๏ Sexual response ๏ Balance of water and electrolyte ๏ Production of body fluid
- 24. FUNCTIONS OF ANS Sympathetic division of the ANS activates the body for “Fight or Flight” response Parasympathetic division often produce antagonistic effects through the release of Acetylcholine Both divisions of the ANS affects visceral organs in different way Sympathetic theme is “Fight or Flight” Parasympathetic is “Rest and Digest”
- 25. ADRENERGIC & CHOLINERGIC SYNAPTIC TRANSMISSION Acetylcholine is the neurotransmitter used by all preganglionic neurons (PNS & SNS) Most parasympathetic postganglionic fibers release Acetylcholine Transmission at this synapse is said to be Cholinergic (Ach) Most sympathetic postganglionic fibers release Norepinephrine Transmission at this synapse is said to be Adrenergic Numerous swelling (Varicosities) occurs when the axon of a postganglionic neuron innervate a target organ
- 27. RESPONSES TO CHOLINERGIC STIMULATION All Somatic motor neurons All preganglionic neurons (SNS & PNS) Most postganglionic neurons (PNS) are Cholinergic Ach release by somatic motor neurons or preganglionic neurons (PNS/SNS) are always Excitatory Ach released by most postganglionic neurons (PNS) are; Excitatory Inhibitory
- 28. RESPONSES TO CHOLINERGIC STIMULATION Ach effects on a target organ depend on the nature of the Cholinergic Receptor Two types of cholinergic receptors Nicotinic Muscarinic The binding of Ach to nicotinic receptors is always excitatory They are located in the neuromuscular junction of the skeletal muscles fibers Nicotinic Ach receptors are ligand-gated ion channels
- 29. RESPONSES TO CHOLINERGIC STIMULATION Muscarine as well as ACh, stimulates the Ach receptors in the visceral organs. Muscarinic receptors are thus stimulated by Ach Muscarinic ACh receptors are coupled to G-proteins Their effects can be either excitatory or inhibitory.
- 30. RESPONSES TO ADRENERGIC STIMULATION Adrenergic stimulation by the release of epinephrine (Blood) and by norepinephrine (sympathetic nerve ending) Neurotransmitters response on a specific cell depends on the characteristic of the cell The presence of different membrane Receptor Proteins Two major classes of receptor proteins Alpha Beta Adrenergic receptors
- 31. RESPONSES TO ADRENERGIC STIMULATION All adrenergic receptors act via G- proteins G- protein dissociate into Alpha subunits Beta & Gamma complex Alpha subunits or B/G complex can either Cause the opening and closing of ion channels in the plasma membrane Activate an enzyme in the membrane
- 32. OTHER AUTONOMIC NEUROTRANSMITTERS Certain postganglionic autonomic axons produce their effects through mechanisms that do not involve either norepinephrine or acetylcholine These axons, consequently, have been termed “nonadrenergic, noncholinergic fibers.” Proposed neurotransmitters for these axons include ATP, vasoactive intestinal peptide (VIP), and nitric oxide (NO) Nitric oxide appears to function as the autonomic neurotransmitter that causes vasodilation of cerebral arteries.
- 33. ORGANS WITH DUAL INNERVATION Most visceral organs receive dual innervation Organs that are stimulated by both the SNS and PSN. The effects of the two divisions of the ANS may be antagonistic, complementary, or cooperative ANTAGONISTIC EFFECTS The effect of sympathetic and parasympathetic innervation of the pacemaker region of the heart is the best example of the antagonism of these two systems
- 34. COMPLEMENTARY AND COOPERATIVE EFFECTS The effects are complementary when sympathetic and parasympathetic stimulation produce similar effects The effects are cooperative when sympathetic and parasympathetic stimulation produce different effects that work together to promote a single action The effects of sympathetic and parasympathetic stimulation on salivary gland secretion are complementary The effects of sympathetic and parasympathetic stimulation on the reproductive and urinary systems are cooperative
- 35. ORGANS WITHOUT DUAL INNERVATION Although most organs receive dual innervation, some receive only sympathetic innervation. These include; The adrenal medulla; The arrector pili muscles in the skin; The sweat glands in the skin; Most blood vessels. In these cases, regulation is achieved by increases or decreases in the tone (firing rate) of the sympathetic fibers.
- 36. CONTROL OF THE ANS BY HIGHER BRAIN CENTERS The neural centers that directly control the activity of autonomic nerves are influenced by higher brain areas, as well as by sensory input MEDULLA OBLONGATA The medulla oblongata of the brain stem controls many activities of the autonomic system centers for the control of the cardiovascular, pulmonary, urinary, reproductive, and digestive systems are located in the medulla The medulla itself is responsive to regulation by higher brain areas (hypothalamus)
- 37. LIMBIC SYSTEM The limbic system is a group of fiber tracts and nuclei that form a ring around the brain stem It includes the cingulate gyrus,the hypothalamus, the fornix, the hippocampus, and the amygdaloid nucleus The limbic system is involved in basic emotional drives Blushing, pallor, fainting, breaking out in a cold sweat, a racing heartbeat, and “butterflies in the stomach” are only some of the many visceral reactions that accompany emotions as a result of autonomic activation.
- 38. “Work doesn't kill but a lazy man will die of poverty”