AUTONOMIC NERVOUS SYSTEM

Dr Mohamad Aris Mohd Moklas (PhD)Department of Human AnatomyFPSK UPMaris@medic.upm.edu.my03 89472783

Autonomic nervous system:

It is the part of the nervous system concerned with the innervation of involuntary structures such as the heart, smooth muscle and glands.

It is distributed throughout the central and peripheral nervous system.

It may be divided into two parts.

Sympathetic nervous system

Parasympathetic nervous system

Preganglionic neurone

Postganglionic neurone

Ganglion

Cell body in CNS

Target organ

Basic organization of the autonomic nervous system

Sympathetic nervous system:

The activity of the sympathetic nervous system is to prepare the body for an emergency.

It accelerates the heart rate,causes constriction of peripheral blood vessels and raises the blood pressure.

Sympathetic nervous system:

It inhibits peristalsis of the intestinal tract.

It closes the sphincters.

Preganglionic neurones in thoracic segments of spinal cord & L1, L2; Thoraco-lumbar outflow

Sympathetic system:

Efferent sympathetic fibres:

The gray matter of spinal cord from T1 – L2 segment possesses a lateral horn in which are located the cell bodies of sympathetic connector neurons.

AutonomicSomatic

General arrangement of somatic & autonomic part of the nervous system.

Efferent sympathetic fibres:

The myelinated axons leave the spinal cord in anterior nerve roots and pass via white ramus communicantes to the sympathetic trunk.

The connector nerve fibres are called preganglionic sympathetic fibres.

AutonomicSomatic

General arrangement of somatic & autonomic part of the nervous system.

These preganglionic fibres enter the ganglion and form synapse.

Synapse

AutonomicSomatic

General arrangement of somatic & autonomic part of the nervous system.

What is synapse? Synapse can be defined as the site where two neurons come into close proximity but not into anatomic continuity. The gap between two neurons is bridged by a neurotransmitter substance, acetylcholine.

Postganglionic fibres pass to the thoracic spinal nerves as gray rami communicantes and are distributed in the branches of the spinal nerves to the smooth muscle in the walls of blood vessels, sweat glands and the arrector pili muscles.

Afferent sympathetic fibres:

Travel from viscera through the sympathetic ganglia without synapsing.

They enter the spinal nerve via the white rami communicantes and reach their cell bodies in the posterior root ganglion.

AutonomicSomatic

General arrangement of somatic & autonomic part of the nervous system.

Parasympathetic nervous system:

Slow the heart rate

Increase the peristalsis of the intestine and glandular activity.

Parasympathetic nervous system:

Open the sphincters.

Preganglionic neurones in the brain stem & S1, 2, 3; Cranio-sacral outflow

Efferent parasympathetic fibres:

The connector cells of this part of the system are located in the brain and sacral segments of spinal cord.

Those in the brain form parts of nuclei of origin of cranial nerves 3,7, 9 and 10 and the axons emerge in the corresponding cranial nerves.

Efferent parasympathetic fibres:

The sacral connector cells are found in the gray matter of the S2,3,4 segments of the spinal cord.

They leave the spinal cord in the anterior root of the spinal nerve.

Then they leave the sacral nerves and form the pelvic splanchnic nerves.

These fibres are preganglionic.

They synapse with cells in peripheral ganglia.

The cranial preganglionic fibres relay in the Ciliary, pterygopalatine, submandibular and otic ganglia.

The preganglionic fibres in the pelvic splanchnic nerves relay in the ganglia in the hypogastric plexus.

Parasympathetic part of the autonomic division of PNS

Efferent parasympathetic fibres:

Afferent parasympathetic fibres:

Travel from the viscera to the sensory ganglia of cranial nerves.

From pelvic nerves the afferent fibres travel to the posterior root ganglia of the sacral spinal nerves.

CLINICAL CORRELATES:

1. Neuralgia – Severe pain along the distribution of a nerve is called neuralgia.

2. Inflammation of a nerve is called neuritis.

3. Damage to a motor nerve causes muscular paralysis, whereas damage to a sensory nerve causes localised anaesthesia and analgesia.

4. Irritation of a motor nerve causes muscular spasm.

5. Regeneration of a damaged nerve depends on the degree of injury.