Introduction to the Autonomic Nervous System

Question 1

What are the four functional types of nerve fibers?

Answer 1

Sensory afferent, sensory efferent, visceral afferent, visceral efferent. The SA and SE have cell bodies in the dorsal root ganglion

Question 2

What is the general mode of ANS action?

Answer 2

regulates visceral functions by a two-neuron chain. Pre-ganglionic cell body and axon in the CNS, synapses with with post-ganglionic cell body in an autonomic ganglion outside the CNS

Question 3

What are the three designations of autonomic ganglia?

Answer 3

1. Sympathetic chain - Also called paravertebral or SANS - Found lateral to the vertebral bodies along entire length of vertebral column. 24-25 pairs all attached in ladder fashion by sympathetic trunk
2. Collateral - also called SANS prevertebral - found ventral to the verebral bodies, often next to major branches of abdominal aorta
3. Terminal - most are PANS, found within the wall of the viscera (only seen by histology)

Question 4

What are the exceptions to dual innervation by SANS and PANS?

Answer 4

Most viscera are dually innervated. However, only SANS innervates most blood vessels, sweat glands, and adrenal medulla

Question 5

What is the thoracolumbar outflow?

Answer 5

The location of the outflow of SANS axons from the CNS. Functions to spend energy stores throughout the body

Question 6

What is the craniosacral outflow?

Answer 6

The location of PANS axons from the CNS. They function to conserve and store energy

Question 7

What part of the ANS innervates most of the upper limb? What is the function?

Answer 7

SANS innervates the cutaneous blood vessels, sweat glands, and arrector pili muscles. Leads to smooth muscle contraction, increasing blood pressure, sweating for heat dissipation, or piloerection “goose bumps” for heat conservation

Question 8

What is the path of the SANS neuron in the upper limb?

Answer 8

Originates in nucleus in spinal cord called intermediolateral column (ILC) gray matter. Sends preganglionic neuron through white communicating ramus (WCR) of anterior root which is myelinated. Synapse occurs in sympathetic chain ganglion (SCG) of sympathetic trunk. Postganglionic axon is unmyelinated and slow moving through the gray communicating ramus (GCR), heads to target

Question 9

What are the thoracic splanchnic nerves?

Answer 9

Preganglionic neuron arises in ILC, moves through WCR but does not synapse at sympathetic chain ganglion. It moves through the posterior thoracic wall and synapses at a prevertebral SANS ganglion (collateral).

Question 10

What are the three divisions of thoracic splanchnic nerves?

Answer 10

Greater (G) - T5-T9
Lesser (L) - T10-11
Least (l) - T12
synapse in collateral ganglia

Question 11

What is the function of the thoracic splanchnic nerves?

Answer 11

After synapsing in collateral ganglia, the postganglionic SANS neurons follow the blood vessels branching from abdominal aorta to the organs, smooth muscle, and gland final targets. They function to decrease GI motility and secretions, and decrease blood supply to the viscera

Question 12

What PANS axons run with CNIII?

Answer 12

Cranial nerve 3 - Oculomotor - PANS preganglionic - innervate eye structures

Question 13

What PANS axons run with CNVII?

Answer 13

Cranial nerve 7 - Facial - PANS preganglionic - control secretion of tears and saliva

Question 14

What PANS axons run with CNIX?

Answer 14

Cranial nerve 9 - glossopharyngeal - PANS preganglionic - control secretion of tears and saliva

Question 15

What PANS axons run with CNX?

Answer 15

Cranial nerve 10 - vagus nerve - PANS preganglionic - control thoracic and abdominal viscera

Question 16

What is the function of the PANS sacral outflow (S2-4)?

Answer 16

Preganglionic axons follow pelvic splanchnic nerves to terminaal ganglion in wall of pelvic viscera. Function to empty contents of lower abdomen and pelvic viscera (defecation and urination (micturition) reflexes)

Question 17

What neurotransmitter is released by SANS and PANS preganglionic neurons?

Answer 17

Both release acetylcholine - Ach

Question 18

What neurotransmitter is released by SANS postganglionic neurons? What are the receptors called?

Answer 18

Norepinephrine - adrenergic receptors. Thus they are called adrenergic nerves

Question 19

What neurotransmitter is released by PANS postganglionic neurons? What are the receptors called?

Answer 19

Acetylcholine. They are muscarinic receptors. PANS postganglionic nerves are called cholinergic!

Question 20

What is the function of propanolol?

Answer 20

Blocks activity of norepinephrine, helps stop tachycardia caused by SANS

Question 21

What is the function of atropine?

Answer 21

Blocks Ach of muscarinic receptors. Relaxes parasympathetic contraction

Question 22

What cells of the adrenal medulla release epinephrine and norepinephrine?

Answer 22

Chromafin cells

Question 23

Where is the SANS innervation of the upper limb supplied by?

Answer 23

T2-T6 spinal levels, the preganglionic axons move through the WCR and ascent the sympathetic trunk before synapsing at the stellate ganglion (cervicothoracic or inferior cervical ganglion). Postganglionic axons meet up with C6-T1 nerve roots of the brachial plexus in ventral rami

Question 24

What is the stellate ganglion?

Answer 24

The cervicothoracic ganglion (CTG). Also called the inferior cervical ganlgion (ICG)

Question 25

What is a stellate ganglion block?

Answer 25

Treatment for Raynaud’s disease, where excessive stimulation of SANS nerves may lead to ischemia or gangrene of upper limb. This is due to excessive vasomotor tone by SANS stimulation