Nervous System (autonomic)

Question 1

Describe the autonomic nervous system.

Answer 1

Is a network of nerves and ganglia that provide involuntary
(i.e., unconscious) control of the physiological actions that maintain internal homeostasis and respond to stress.

Question 2

What structures does the ANS innervates?

Answer 2

The ANS innervates structures within the:
• cardiovascular
• pulmonary
• endocrine
• exocrine
• gastrointestinal
• genitourinary
• skeletal muscle
• central nervous systems (CNS)
• can influence metabolism and
thermal regulation.

Question 3

Describe the division of the ANS.

Answer 3

Sympathetic nervous system (SNS)
• Predominates in in stressful situations.

Parasympathetic nervous system (PNS)
• Predominates at rest.

Enteric nervous system (ENS)
• governs the function of the GI tract, is the largest component of the ANS, and can function independent of the CNS.

Question 4

Describe the anatomy of the sympathetic nervous system.

Answer 4

• Preganglionic sympathetic neurons originate from the spinal cord (T1–L2).
• These myelinated fibers exit (via the ventral root of) the spinal nerve (travel into the sympathetic chain), and synapse with three types of ganglia (postganglionic fibers):

1- Paravertebral sympathetic ganglia: A chain of paired ganglia located lateral to the vertebral column, which runs from the skull to the coccyx forming the sympathetic trunk.

2- Prevertebral sympathetic ganglia: Unpaired ganglia that are located anterior to the vertebral column.

3- Adrenal medulla: A modified ganglia located within the adrenal gland. Although other ganglia function as
relay stations (retransmit signals) with long postganglionic fibers that innervate specific organs, the adrenal medulla directly secretes catecholamines into the venous blood stream.

Question 5

Describe the synapses of preganglionic and postganglionic fibers on the sympathetic nervous system.

Answer 5

• Preganglionic sympathetic fibers release acetylcholine at their synapse to stimulate nicotinic cholinergic postganglionic neurons (or chromaffin cells of the adrenal medulla).

• Postganglionic adrenergic neurons synapse at target organs and release norepinephrine.

Except
• In the adrenal medulla the postganglionic adrenergic neurons synapse and
NE and epinephrine are produced.

• In the sweat glands the postganglionic adrenergic neurons synapse and acetylcholine is released by the target organ (sweat glands).

Question 6

List examples of specific sympathetic ganglia that are often used as a target for interventional pain management.

Answer 6

•

Question 7

Describe the anatomy of the parasympathetic nervous system.

Answer 7

Preganglionic parasympathetic neurons originate from:
• cranial nerves III, VII, IX, and X
• sacral segments S2 - S4

Of these, the vagus nerve accommodates approximately 75% of PNS traffic.

Question 8

Describe the synapses of preganglionic and postganglionic fibers on the parasympathetic nervous system.

Answer 8

• Preganglionic parasympathetic neurons (as opposed to preganglionic sympathetic neurons) synapse with postganglionic neurons close to the target end-organ facilitating fine, discrete physiological effect.

• Both preganglionic and postganglionic parasympathetic neurons release acetylcholine;

• These cholinergic receptors are subclassified as either nicotinic
or muscarinic.

Question 9

What are the adrenergic receptors and what is their response to agonism?

Answer 9

• alpha-1 (α1), alpha-2 (α2), beta-1 (β1), and beta-2 (β2) adrenergic receptors

• α1, β1, and β2 receptors are postsynaptic and are stimulated by the neurotransmitter NE.

• The α2 receptors are presynaptic and are also stimulated by NE.

• Stimulation of α2 receptors inhibits the presynaptic release of NE, reducing overall sympathetic response.

Question 10

Describe the effects of autonomic stimulation on specific organs (including their receptors).