THE ROLE OF ANS IN THE VARIOUS SYSTEM - PowerPoint Presentation

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THE ROLE OF ANS IN THE VARIOUS SYSTEM

INTRODUCTION

Recall that the autonomic nervous system consists of sympathetic and parasympathetic divisions.

The sympathetic division also known as thoracolumbar outflow because the preganglionic neurons originate in the thoracic and lumbar level of the spinal cord, and send axons to the sympathetic ganglia, which parallel the spinal cord.

The parasympathetic division other wise known as

craniosacral

outflow because the preganglionic neurons originate in the brain and sacral level of the spinal cord, and send axons to ganglia located near the effector organs.

FUNCTIONS OF THE AUTONOMIC NERVOUS SYSTEM

The sympathetic division of the autonomic system activates the body to

fight or flight

response, largely through the release of norepinephrine from the postganglionic

fibers

and the secretion of epinephrine from the adrenal medulla. The parasympathetic division often produces antagonistic effects through the release of Ach from its postganglionic

fibers

.

Sympathetic stimulation to the heart is

cardioacceleratory

while parasympathetic stimulation is

cardioinhibitory

EFFECTOR ORGANS

Effector organs in the body are muscles or glands.

There are various organs with dual innervation and organs without dual innervation.

The organs with dual innervation are mostly visceral organs which produces antagonistic, complementary or cooperative effects.

Antagonistic effects:

Pacemaker of the heart:

Adrenergic stimulation from sympathetic fibers increases HR

Ach from parasympathetic fibers slows HR

Digestive tract

Sympathetic

stimulation

inhibits

intestinal movements and secretions

Parasympathetic stimulation increases movements and

secretions

Pupil of the eye:

Contraction

of the radial muscles which

are innervated

by sympathetic fibers causes dilation

Contraction

of the circular muscles which are innervated by parasympathetic fibers causes constriction

Complementary and Cooperative Effects

Complementary :

Sympathetic and parasympathetic stimulation produce similar effects

Cooperative or Synergistic:

Sympathetic and parasympathetic stimulation produce effects that work together to promote a single action

Complementary Effects

Sympathetic and parasympathetic stimulation in salivary gland secretion.

Parasympathetic stimulation – secretion of watery saliva and secretion of other exocrine glands in the digestive tract.

Sympathetic nerves cause constriction of blood vessels in the GIT

Resultant decrease in blood flow to salivary glands causes production of thicker more viscous saliva.

Cooperative Effects

Reproductive System

In the male:

Erection of penis is due to vasodilation as a result of parasympathetic activity

Ejaculation is as a result of sympathetic activity

In the female:

Clitoral erection and vaginal secretions as a result of parasympathetic activity

Orgasm is a sympathetic nerve response

Micturition or Urination reflex

Contraction

of urinary bladder is largely independent of nerve stimulation

However

, promoted by parasympathetic nerve activity

Reflex

also enhanced by sympathetic activity which increases tone of bladder muscles

Emotional states (extreme fear):

accompanied by extreme sympathetic activity

result in reflex urination at bladder volumes too low to trigger this reflex.

ORGANS WITHOUT DUAL INNERVATION

These organs receive sympathetic innervation only:

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 firing rate of the sympathetic fibers

Constriction of cutaneous blood vessels is produced by increased sympathetic activity that stimulates alpha adrenergic receptors.

Vasodilation results from decreased sympathetic nerve stimulation.

The

sympathoadrenal

system is required for

nonshivering

thermogenesis.

Animals deprived of their adrenals cannot withstand cold stress.

Sympathetic system required for proper thermoregulatory responses to heat.

In hot environment:

Decreased sympathetic stimulation produces dilation of blood vessels in the skin

This increases cutaneous blood flow and provides better heat radiation.

During exercise:

Sympathetic activity increases

Causes constriction of blood vessels in skin and stimulation of sweat glands in trunk

Sweat glands:

(1) Secrete watery sweat in response to cholinergic sympathetic stimulation

Evaporation

of dilute sweat helps cool the body

(2) Secrete

bradykinin

in response to sympathetic stimulation.

Bradykinin

stimulates dilation of surface blood vessels

Helps

to radiate some heat

inspite

of the fact that some vessels are constricted

At the end of exercise

Sympathetic stimulation is reduced

Causing cutaneous blood vessels to dilate

This increases blood flow to skin

Metabolic heat is eliminated.

These thermoregulatory responses are achieved without the direct involvement of the parasympathetic system.

CONTROL OF THE AUTONOMIC NERVOUS SYSTEM

Medulla Oblongata

Center for the control of cardiovascular, respiratory, renal, digestive and reproductive systems are located

Almost all autonomic responses can be elicited by experimental stimulation of the medulla

Sensory input travels in the

vagus

.

The hypothalamus

The medulla is responsive to control by the hypothalamus

Contains centers for the control of body temperature, hunger, thirst, pituitary gland and various emotional states

Because several of these functions involve appropriate activation of the ANS, the hypothalamus is considered a major regulator of the ANS.

The Limbic System

Includes:

The cingulate

gyrus

of the cerebral cortex

Hypothalamus

The fornix

The hippocampus

The

amygdaloid

nucleus

Involved in basic emotional drives such as:

Anger

Fear

Sex

Hunger

Blushing

Palor

Some of the visceral

Fainting reactions that accompany

“Cold sweat” emotions as a result of

Racing heartbeat autonomic activation

“Butterflies in the stomach”

The involvement of the limbic system with the control of the ANS is responsible for the visceral responses that are characteristic of these emotional states.

The Cerebellum

Impulses from the cerebellum to the medulla oblongata influence ANS activity

Cutting motor tracts of the cerebellum eliminates

Nausea

Sweating autonomic correlates of motion

Cardiovascular changes sickness.

The Cerebral Cortex

Frontal and temporal lobes influence lower brain as part of their involvement in emotion and personality