AUTONOMIC NERVOUS SYSTEM

PRESENTED BY:

LAHARI PALADUGU

PHARM D (09-10)

DEFINITIONThe autonomic nervous system (ANS or visceral nervous system or involuntary nervous system) is the part of the peripheral nervous system that acts as a control system, functioning largely below the level of consciousness, and controls visceral functions.

The ANS affects heart rate, digestion, respiratory rate, salivation, perspiration, pupillary dilation, micturition, and sexual arousal.

Most autonomous functions are involuntary but a number of ANS actions can work alongside some degree of conscious control.

LOCATIONWithin in the brain, the autonomic nervous system is located in the

medulla oblongata in the medulla oblongata in the lower brainstemlower brainstem.

The hypothalamushypothalamus, just above the brain stem, acts as an integrator for autonomic functions, receiving ANS

regulatory input from the limbic limbic system system to do so.

DIVISIONS

SYMPATHETIC NERVOUS SYSTEM

It has:

-A central controlling part

-A peripheral portion which takes origin in the lateral lateral horn horn of the spinal cord from T1 to L2. The main cerebral

controlling center is the posterior hypothalamusposterior hypothalamus.

- The peripheral portions has:- Afferent fibers

- Efferent fibers

(THORACOLUMBAR) OUTFLOW OF SYMPATHETIC FIBERSConsists of cell bodies in the lateral horn of the spinal the lateral horn of the spinal cord cord (intermediolateral cell columns) from T1 to L2/3.T1 to L2/3.

Because its cells begin in the thoracic and lumbar regions of the spinal cord, the SNS is said to have a thoracolumbar outflowthoracolumbar outflow.

ORGANIZATION.

Take origin from the lateral horn cells of T1T1 to L2L2 and come out of the spinal cord spinal cord via the anterior rootanterior root.

AxonsAxons of these nerves leave the spinal cord through the anterior rootlet/rootanterior rootlet/root. They pass near the spinal spinal (sensory) ganglion(sensory) ganglion, where they enter the anterior rami anterior rami of the spinal nerves. However, unlike somatic innervation, they quickly separate out through white white rami connectors rami connectors that connect to either the paravertebralparavertebral (which lie near the vertebral column) or prevertebralprevertebral (which lie near the aortic bifurcation) gangliaganglia extending alongside the spinal column.

SYNAPTIC TRANSMISSION.To reach target organs and glands, the axons must travel long distances in the body, and, to accomplish this, many axons relay

their message to a second cell through synaptic synaptic transmissiontransmission. The ends of the axons link across a space, the

synapsesynapse, to the dendrites of the second cell. The first cell (the

presynaptic cell) sends a neurotransmitter neurotransmitter across the synaptic cleft where it activates the second cell (the postsynaptic cell). The message is then carried to the final destination.

SOME TERMS…

In the SNS and other components of the peripheral nervous

system, these synapses are made at sites called gangliaganglia.

The cell that sends its fiber is called a preganglionic cellpreganglionic cell, while the cell whose fiber leaves the ganglion is called a

postganglionic cellpostganglionic cell. As mentioned previously, the preganglionic cells of the SNS are located between the first thoracic segment and third lumbar segments of the spinal

cord. Postganglionic cells have their cell . Postganglionic cells have their cell bodies in the ganglia and send their axons bodies in the ganglia and send their axons to target organs or glands.to target organs or glands.

Presynaptic nerves' axons terminate in either the paravertebral ganglia paravertebral ganglia or prevertebral gangliaprevertebral ganglia. There are four different ways an axon can take before reaching its terminal:

The postsynaptic cell then goes on to innervate the targeted end effector (i.e. gland, smooth muscle, etc.). Because paravertebral and prevertebral ganglia are relatively close to the spinal cord, presynaptic neurons are generally much shorter than their postsynaptic counterparts, which must extend throughout the body to reach their destinations.

The ganglia include not just the sympathetic trunks but also the cervical ganglia (superior, middle, and inferior), which sends sympathetic nerve fibers to the head and thorax organs, and the celiac and mesenteric ganglia (which send sympathetic fibers to the gut).

AN EXCEPTION… THE ADRENAL MEDULLA

Specialized ganglion of the SNS.

Presynaptic neurons pass through paravertebral ganglia, on through prevertebral ganglia and then synapse directly with suprarenal tissue. This tissue consists of cells that have pseudo-neuron like qualities in that when activated by the presynaptic neuron, they will release their neurotransmitter (epinephrine) directly into the blood stream.

Preganglionic fibers synapse directly on chromaffin cells chromaffin cells in the adrenal medullaadrenal medulla.

These chromaffin cells secrete epinephrine and norepinephrine epinephrine and norepinephrine into the circulation.

MECHANISM OF ACTION.The SNS is designed for a quick immediate and massive action and in conjunction with adrenal medulla initiate reactions in

conditions of stress… Fight or flight reactionFight or flight reaction.

MECHANISM…

Its effect is mediated by catecholaminescatecholamines through three types of receptors:

•epinephrine and norepinephrine are mediated by αα--receptorsreceptors and β-receptorsβ-receptors

• αα11-receptors-receptors

• αα22-receptors-receptors

• ββ11-receptors-receptors

• ββ22-receptors-receptors

•dopamine action is mediated through D receptorsD receptors

PARASYMPATHETIC NERVOUS SYSTEM (CRANIOSACRAL SYSTEM)

The parasympathetic system is responsible for stimulation of

"rest-and-digest" "rest-and-digest" or “feed and breed”“feed and breed” activities that occur when the body is at rest, especially after eating, including sexual arousal, salivation, lacrimation, urination, digestion, and defecation

Its action is described as being complementary to complementary to the sympathetic nervous system.the sympathetic nervous system.

LOCATION.

Parasympathetic nerve fibers arise from the central nervous system with the S2, S3, and S4 S2, S3, and S4 spinal nerves spinal nerves and from third, seventh, ninth, and third, seventh, ninth, and tenth cranial nervestenth cranial nerves. Because of its location, the parasympathetic system is commonly referred to as having "craniosacral outflow", "craniosacral outflow", which stands in contrast to the sympathetic nervous system, which is said to have "thoracolumbar outflow".

The parasympathetic nerves that arise from the S2, S3, and S4 spinal nerves are commonly referred to as the pelvic splanchnic nerves or the "nervi erigentes".

PATHWAYS.

The main controlling center is present in the anterior anterior hypothalamushypothalamus. The parasympathetic nervous system also has:

1) Afferent fibers

2) Efferent fibers

The afferent fibers afferent fibers are concerned with the detection of detection of volume and pressure changes volume and pressure changes in the viscera.

The efferent fibers efferent fibers are concerned with secretomotor secretomotor activity activity of the viscera.

OUTFLOW.

The outflow has two divisions:

1) Cranial division

2) Sacral division

CRANIAL DIVISION.

The preganglionic nerve fibers preganglionic nerve fibers of these neurons synapse in the appropriate ganglia. These ganglia are present near the target organ.

Postganglionic nerve fibers Postganglionic nerve fibers starts from these ganglia and supply to the organ.

Preganglionic fibers are longer and the postganglionic fibers are shorter.

CRANIAL DIVISION.

The cranial outflow is through III, VII, IX, and X.

Occulomotor – IIIOcculomotor – III

Constrictor pupillae Ciliaris

Facial – VIIFacial – VII

Lacrimal gland Submaxillary gland and sublingual gland

Glossopharyngeal – IXGlossopharyngeal – IX

Parotid glandVagus – XVagus – X

CVS, RS, GIT, up to transverse colon.

SACRAL DIVISION

The preganglionic neurons are present in the lateral horns of the lateral horns of sacral segments (S2, S3, and S4). sacral segments (S2, S3, and S4).

Preganglionic fibers come out through the anterior root anterior root and

form nervi erigentis or pelvic nervenervi erigentis or pelvic nerve.

The postganglionic neurons are present in the target organ target organ itself.

Nervi erigentis supplies the descending colon, sigmoid descending colon, sigmoid colon, and rectumcolon, and rectum. It also supplies the urinary bladder, urinary bladder, erectile tissue of the penis and the uterus. erectile tissue of the penis and the uterus.

RECEPTORSThe parasympathetic nervous system uses chiefly acetylcholine acetylcholine (ACh) (ACh) as its neurotransmitterneurotransmitter, although peptidespeptides (such as cholecystokinincholecystokinin) may act on the PSNS as a neurotransmitter.

The ACh acts on two types of receptors, the muscarnicmuscarnic and nicotinic cholinergic nicotinic cholinergic receptors.

Most transmissions occur in two stages: When stimulated, the preganglionic nerve releases ACh at the ganglionpreganglionic nerve releases ACh at the ganglion, which acts on nicotinic receptors of postganglionic neuronsnicotinic receptors of postganglionic neurons. The postganglionic postganglionic nerve then releases ACh to stimulate the muscarinic receptors of nerve then releases ACh to stimulate the muscarinic receptors of the target organthe target organ.

NICOTINIC RECEPTORS.

MUSCARNIC RECEPTORS.

INTERACTION OF THE TWO DIVISIONS… SNS & PSNS.

Most of the organs receive dual nerve supply. Though the actions of these two systems appear to be opposed, they are in-fact complementary. Depending on the situation at one moment, the sympathetic dominates and the PSNS is inhibited and in the next moment, the PSNS dominates and the SNS is inhibited.

ENTERIC NERVOUS SYSTEM.Consists of intramural nerve plexesus:

(a) myenteric plexus(a) myenteric plexus

(b) Meissner’s plexus(b) Meissner’s plexus

These are present in the GIT and contain the sensory, motor, and sensory, motor, and interneurons. interneurons.

Their activity is modulated by the sympathetic and parasympathetic nerve fibers. Several neurotransmitters are associated with this system. They influence

-Smooth muscle: peristalsis and villi movementsSmooth muscle: peristalsis and villi movements

-Gland secretion: of enzymes, electrolytes, and the Gland secretion: of enzymes, electrolytes, and the mucousmucous

-Blood vessels: alter blood flowBlood vessels: alter blood flow

-APUD cells: release of various GIT hormonesAPUD cells: release of various GIT hormones

CENTRAL CONTROL OF THE AUTONOMIC NERVOUS SYSTEM.

DISORDERS OF THE ANS.- Autoimmune autonomic gangliopathy

- Congenital central hypoventilation syndrome

- Familial dysautonomia

- Holmes-Adie syndrome

- Horner syndrome

- Multiple system atrophy

- Neurally mediated syncope

- Orthostatic hypotension

- Postural tachycardia syndrome

- Striatonigral degeneration

- Vasovagal syncope

- Erectile dysfunction

- Etc……

DRUGS AFFECTING AUTONOMIC ACTIVITY.

REFERENCES.

1) https://en.wikipedia.org/wiki/Sympathetic_nervous_system

2) https://en.wikipedia.org/wiki/Parasympathetic_nervous_system

3) http://www.nlm.nih.gov/medlineplus/autonomicnervoussystemdisorders.html

4) http://www.dana.org/news/brainhealth/detail.aspx?id=9780

5) Fundamentals of Medical Physiology 4th Edition – LPR

6) BRS Physiology 5th edition - Costanzo