Autonomic nervous system

 Nervous System

1. Central nervous system


b.Spinal cord

2. Peripheral nervous system

a. Sensory or afferent division; to CNS

Receptor- CNS

b. Motor or efferent division; from CNS

CNS- muscle

b. Motor or efferent division

For an example; cold person will shivering (somatic motor system) and constriction of blood vessel ANS.

1. Somatic Nervous System; innervates skeletal muscle/ motion

2. Autonomic nervous system; involuntary motion

a. Sympathetic division; fight or flight

b. Parasympathetic division; rest and digest

Autonomic or involuntary part of nervous system control "automatic" function of body. (Initiated in brain below level of cerebrum).

Effect of autonomic cavity are rapid and effector organs are -

1. Smooth muscle of internal organ; changes in blood vessel diameter.

2. Cardiac muscle; change in rate and force of heartbeat.

3. Glands; increasing or decreasing gastrointestinal (salivary and sweat glands) secretion.

Autonomic nervous system (ANS) is visceral efferent (motor) system because it concerned with internal organs or viscera.

It's primary function is to regulate visceral activities to maintain homeostasis.

Efferent (motor) nerves autonomic nervous system arise from brain and emerge at various levels between mid brain and sacral region of spinal cord.

Division of Autonomic nervous system

1. Sympathetic nervous system

Activity- helps body adjust stressful


Originate in thoracolumbar region of spinal cord

2. Parasympathetic nervous system

Activity- during rest

Emerge from brain and sacral spinal cord (craniosacral)

Autonomic pathway

In ANS each division has two efferent neurons, in its peripheral pathway between CNS and effector organ.

The two neurons in pathway synapse in autonomic ganglia, which are outside CNS.

Ganglia containing cell bodies of neuron

1. Preganglionic neurons

2. Postganglionic neurons

Cell body of preganglionic neurons is in brain or spinal cord.

It's axon terminals synapse with cell body of postganglionic neurons in autonomic ganglion outside the CNS.

Postganglionic neurons conducts impulses to effector organ.

Sympathetic nervous system

Detects body's rapid involuntary response to dangerous or stressful situation.

Since preganglionic neurons originate in spinal cord at throcaic and lumbar level, name thoracolumbar outflow.

1. Preganglionic neuron 

It's cell body in brainbrain is in brain stem or spinal cord and it's myelinated axon courses through cranial or spinal nerve.

1st neuron= preganglionic, 2nd neuron = postganglionic 

 Acetylcholine                              Noradrenaline

Axon terminates at synapses with dendrites and cell body of one or more neurons in an autonomic ganglion.

Acetylcholine is neurotransmitter at sympathetic ganglion.

2. Postganglionic neurons 

This has its cell body in ganglion and terminates in organ or tissue supplied.

Noradrenaline (norepinephrine) is usually neurotransmitter at sympathetic efforts organs.

3. Sympathetic ganglia

1. Sympathetic chain ganglia

2. Prevertebral ganglia

Sympathetic chain ganglia

This chains extend from upper cervical level to sacrum, one chain lying on each side of vertebral bodies.

Ganglia are attached to each other by nerve fibres.

Preganglionic neurons that emerge from spinal cord may synapse with cell body of post ganglionic neurons at same level or they may pass up or down the chain through one or more ganglia before synapsing.

For example, nerve that dilates pupil of eye leaves cord at level of 1st thoracic vertebrae and passes up chain to superior cervical ganglion before it synapses with cell body of postsynaptic neurons. The postganglionic neurons then pass to eye.

Arrangement of ganglia allows excitation of nerve at multiple levels very quickly, providing a rapid and widespread sympathetic response.

As sympathetic chain ganglia are near spinal cord. Most sympathetic preganglionic axon are short and postganglionic axons are long.

Prevertebral ganglia

These three prevertebral ganglia situated in abdominal cavity close to large abdominal arteries.

1. Coeliac ganglion

2. Superior mesenteric ganglion

3. Inferior mesenteric ganglion

Preganglionic sympathetic fibers pass through the lateral chain to reach these ganglia.

2. Parasympathetic Nervous System; rest and digest system

(Conserves energy as it slow heart rate, increase intestinal and gland activity, and relax sphincter muscle in gastrointestinal track.

Two neurons preganglionic and postganglionic are involved in transmission of impulse from their sources to effector organ.

Neurotransmitter at both synapses is acetylcholine.

1. Preganglionic neurons

Arise from brain stem in brain or sacral region of spinal cord.

Those originating in brain are cranial nerves -

Oculomotor nerve III

Facial nerve VII

Glassopharyngeal nerve IX

Vagus nerve X

Arising from nuclei in mid brain and brain stem, and their nerve fibers terminate at or near effector organ.

Cranial Outflow

Oculomotor nerve III

Parasympathetic fibers of oculomotor nerves innervate smooth muscle (cillary and pupillary constrictor muscles) in eye that cause lense to bulge and pupil to constrict to close vision.

Facial nerve VII

Parasympathetic fibers of facial nerve stimulate may gland in head-

Nasal glands

Lacrimal gland of eye

Submandibular and sublingual salivary glands

Glossopharyngeal nerves IX

Parasympathetic fibres in glossopharyngeal nerve activate the parotid salivary gland anterior to ear.

Vagus Nerve X

Parasympathetic cranial outflow via vagus (X) nerve organ.

Innervate liver, gall bladder, stomach, small intestine, kidney, Pancreas, large intestine.

To neck

To thoracic organ - thorax - cardia plexus

Pulmonary plexus serving lungs and bronchi and esophageal plexus supplying esophagus.

Cardia plexus supply fibres to heart .

To abdominal cavity

In abdomen vagus nerves, enters the abdominal cavity through the esophageal hiatus.

Sacral outflow- 

Their fibers leave spinal cord in sacral segment 2,'3 and 4 and synapse with postganglionic neurons in walls of pelvic organs.

2. Postganglionic neurons

This is usually very short and has its cell body either in ganglion or more often, in wall of organ supplied.

Physiology of Autonomic Nervous System

1st neurons                     2nd neurons

Preganglionic.                 Postganglionic

ANS neurotransmitter and receptors

Integration and control of ANS (reflexes)

Effect ANS

Autonomic function


Receptor in cell membrane combination of neurotransmitter and receptor function signal to cell.

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