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Autonomic nervous system
Autonomic: an independent system that runs on its own
The ANS is a visceral and involuntary sensory and motorsystem
The visceral motor fibers in the autonomic nerves areaccompanied by visceral afferent fibers. Most of afferent fiberssupply information that originates from sensory receptors in theviscera. Activity of these receptors may not reaches the level ofconsciousness.
Visceral afferent fibers that mediate sensation include nociceptors that travel in sympathetic nerves, such as the splanchnic nerves.
K e y n o t e s
Housekeeping and vegetative function of ANS are slow, lastlonging & less focused.
The ANS has central integrative components in thehypothalamus and brainstem autonomic nuclei that receiveinput from visceral and somatic afferents as well as from morerostral brain regions.
Example of ANS function: Response of circulation to changein body position
Functions of the ANS• Maintenance of homeostasis in response to the
normal fluctuations of controlled variables (e.g., the negative feedback regulation of blood pressure).
• Integration of the stress response, including the response to exercise and the classic “fight or flight” response.
• Integration of visceral function (e.g., coordination of organs in the digestive system after the ingestion of food).
Disorders of ANS
AsthmaConstipationDiarrheaUlcersHypertentionHeart deseaseStroke……………..
Three subdivision of ANS
Sympathetic
Parasympathetic
Enteric nervous system
The efferent path of the ANS as contrasted with the somatic motor system
Anatomical organization of sympathetic nervous system
Sympathetic nervous system
Typically activated under condition of fight, fright, & flight and duringextensive exercise
Each preganglionic sympathetic fiber synapses with many postganglionic neurons across several ganglia, producing widespread generalized effects.
Sympathetic innervation of the adrenal medulla
Preganglionic sympathetic axons terminate on the chromaffin cells. When stimulated, the chromaffin cells release epinephrine into the circulation
Parasympathetic nervous system
Anatomical organization
Parasympathetic nervous system
Parasympathetic N.S. is more focused in its activity Cranial and sacral division
Dorsal motor nucleus (DMV) is largely secretomotor, Nucleus ambiguus is visceromotor.
The DMV supplies visceral organs:-Neck (pharynx, larynx), -Thoracic cavity (trachea, bronchi, lungs, heart, esophagus)-Abdominal cavity (including much of the GI tract, liver, pancreas)
The nucleus ambigus contains two groups of neurons:(1) Dorsal group (branchiomotor) that activates striated muscle in
the soft palate, pharynx, larynx, and esophagus.(2) Ventrolateral group that innervates and slows the heart .
Acetyl-CoA + Choline transferase Acetylcholine
Tyrosine hydroxylase DOPA Decarboxylase Dopamine hydroxylation Norepinephrine
methylation Epinephrine
Cholinergic and adrenergic fibers : Ach & Norepinephrine
Chemical Transmission
Chemical Transmission
• Co-release of multiple neurotransmitter from nerve endings
• Modulatory action of autonomic transmitter
• VIP, NO: nonadrenergic, noncholinergic (NANC) e.g. in salivary gland
• Sympathetic axons innervating sweat glands and blood vessels in skeletal muscle secret Ach
1- Reuptake (50-80%)
2- Diffusion
3- Destruction (MAO & COMT)
Mechanism of transmitter removal at postganglionic ending
Receptors on the effector organCholinergic receptors:
Nicotinic: Ion conductance, Ganglion, Skeletal muscle
Muscarinic (M1,M2,M3): IP3/DAG, cAMP, gk, NO(EDRF)
Adrenergic receptors:
Alpha (α1, α2): IP3/DAG, cAMP
Beta (β1, β2, β3): cAMP
Responses of effector organs to ANS impulses
Table Continued
Sympathetic and parasympathetic tone• Tone caused by basal secretion of adrenal medullae
• Effect of sympathetic and parasympathetic denervation
• Denervation supersensitivity
Stimuli that enhance the secretion of catecholamines
Brain stem control of ANSModularly, pontine and mesencephalic control of ANS
Hypothalamus: “Head ganglion of the ANS”
Couple emotion to autonomic responseControl integrative autonomic function:
Body temperature
Appetite
Water intake
Heart rate
Arterial pressure
Sexual activity
Lactation
Growth ………
Higher brain areas control brain stem autonomic center
Medial prefrontal areas
Insular
Amygdala
Psychosomatic disease