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