Anatomy of the Autonomic Nervous System

Question 1

Function of ANS?

Answer 1

Involuntary control of the viscera

Question 2

3 divisions of the ANS?

Answer 2

Sympathetic
Parasympathetic
Enteric

Question 3

Pathway of the ANS? (fibres/ganglia)

Answer 3

Consists of a pre-ganglionic neurone, a ganglion, and a post-ganglionic fibre

Question 4

Locations of sympathetic and parasympathetic ganglia?

Answer 4

Sympathetic - Paravertebral ganglia in the sympathetic trunk. Found closer to spinal cord than viscera being innervated
Parasympathetic - Ganglia found close to or in the viscera they innervate

Question 5

The two types of nerves involved and their functions?

Answer 5

Afferent - carries sensory impulses from all parts of the body to the CNS
Efferent - carries “messages/instructions” from brain to muscles/organs of the body

Question 6

Which spinal nerves do preganglionic efferent fibres originate from in sympathetic NS?

Answer 6

Thoracic nerves
Upper lumbar nerves (L1-L3)
Known as the THORACOLUMBAR outflow

Question 7

Pathway of preganglionic neurones to ganglion?

Answer 7

Emerge from spinal cord via ventral root of grey matter in spinal cord
Pass through ventral ramus to white rami communicates to ganglion

Question 8

Structural components of sympathetic nervous system?

Answer 8

Sympathetic trunks (2)
Nerve plexuses
Subsidiary ganglia

Question 9

Viscera innervated by SNS?

Answer 9

Sweat glands
Arrector muscles of hair
Smooth muscle in vessels
Heart
Lungs
Abdominal/pelvic viscera

Question 10

What happens to preganglionic neurone after it has entered ganglion?

Answer 10

Synapses within the ganglion or sends fibres up and down to other ganglia
Postganglionic fibres travel via dorsal or ventral rami to effector organ via grey rami communicantes

Question 11

What is the sympathetic trunk and why is it necessary?

Answer 11

A chain of ganglia and connecting fibres which lie next to the vertebra for the entire length of the vertebral column.
Allows dispersion of the sympathetic outflow from a relatively small region of the spinal cord (T1-L3) to peripheral regions via all spinal nerves

Question 12

What is a plexus regarding the sympathetic nervous system?

Answer 12

A network of nerve fibres originating from different levels associated with an organ

Question 13

What are the different sympathetic plexuses?

Answer 13

Cervical
- Plexus around pharynx
- Cardiac plexus
- Thyroid plexus
- Pulmonary plexus
Thoracic
- Plexus around thoracic aorta
- Splanchnic nerves

Question 14

4 divisions of splanchnic nerves and point of entry to abdomen plexus

Answer 14

Greater (T5-T9), pierce diaphragm and enter abdomen plexus around great blood vessels supplying gut
Lesser (T10-T11), pierce diaphragm and enters abdomen plexus around aorta
Least (T12), pierce diaphragm and enters abdomen plexus and around gut
Lumbar, below diaphragm and take part in all plexuses of sympathetic nerves in abdominal/pelvic regions

Question 15

Parasympathetic efferent fibres arise from?

Answer 15

Cranial nerves
Sacral nerves
Known as the CRANIO-SACRAL OUTFLOW

Question 16

How is the sacral outflow arranged?

Answer 16

Leaves via the anterior rami of S2-4
Visceral branches pass directly to pelvic viscera as pelvic splanchnic nerves
There are minute ganglia in wall of viscera giving rise to postganglionic fibres

Question 17

5 fibre types of pelvic splanchnic nerves and viscera they terminate at/in?

Answer 17

Motor fibres to rectum
Motor fibres to bladder wall
Inhibitory fibres to bladder sphincter (relaxation)
Vasodilator fibres to penis/clitoris (erection)
Visceromotor fibres to large part of the gut (superior to most of abdominal/pelvic viscera)

Question 18

What are the 4 cranial nerves comprising cranial outflow?

Answer 18

Oculomotor nerve (CN III)
Facial nerve (CN VII)
Glossopharyngeal nerve (CN IX)
Vagus nerve (CN X)

Question 19

Where is the enteric system?

Answer 19

The walls of the alimentary tract

Question 20

What two plexuses are involved in the enteric system?

Answer 20

Myenteric plexus (found between smooth muscle layers)
Submucosal plexus (found in submucosal layer of gut wall)

Question 21

Functions of enteric system?

Answer 21

Sensory - monitoring mechanical, chemical, and hormonal activity of the gut
Motor - gut motility, secretion, vessel tone