The autonomic nervous system

Question 1

What is the ANS?

Answer 1

A diffuse system innervating…
- visceral structures
- glandular myoepithelium
- fat
- vasculature

Question 2

ANS afferent, efferent and central components

Answer 2

• afferent and efferent nerves often use the same pathway
• afferent visceral axons may also travel via somatic spinal nerves to reach the CNS
• mostly; general visceral efferent innervations

Question 3

Dual innervation

Answer 3

Each organ receives impulses from sympathetic and parasympathetic nerves axons
- sympathetic dominance= Fight/Flight
- parasympathetic dominance= Rest/digest

Question 4

Neurotransmitters

Answer 4

• Adrenaline
• Noradrenaline
• Acetylcholine

Question 5

Control centres of the ANS

Answer 5

• Rostral hypothalamus; influences parasympathetic NS
• Caudal hypothalamus; influences sympathetic NS
• connected to brainstem centres that regulate cardiovascular function and respiritory

Question 6

Other areas of brain that influence ANS (not control centres)

Answer 6

• cerebrum and limbic system; fear
• olfactory stimulation; drooling

Question 7

Enteric nervous system

Answer 7

The autonomic neurons that innervate the alimentary tract, located in the…
- submucosal (Meisner) plexus
- myenteric (Auerbach) plexus

Question 8

Sympathetic pathways

Answer 8

• Originate at lateral/intermediate horn of the thoracolumbar spinal cord
• preganglionic axons; ventral root -> spinal nerve -> (white) ramus communicans -> sym. trunk
  TO BODY & LIMBS; sym. trunk -> (grey) rami communicans -> spinal nerve
  TO HEAD; sym. trunk -> ansa subclavia -> cervical sympathetic trunk
  TO ABDOMEN & PELVIS; sym. trunk -> splanchnic nerves -> various ganglia

Question 9

Sympathetic: structures of the head

Answer 9

post-synaptic neurones, originating from the cranial cervical ganglion

Question 10

Sympathetic: thoracic viscera

Answer 10

Mostly post-synaptic neurones, originating from middle cervical and cervicothoracic ganglia

Question 11

Sympathetic; abdominal viscera

Answer 11

Splanchnic nerves arising from the abdominal and thoracic sympathetic trunks and synapsing in prevertebral ganglia

Question 12

Sympathetic; pelvic viscera

Answer 12

hypogastric nerves arising from the caudal mesenteric ganglia

Question 13

Parasympathetic Pathways

Answer 13

Originates from the brainstem and sacral elements of the spinal cord
- CN III, VII, IX & X innervate the head
- Vagus nerve innervates thoracic and abdominal viscera
- Sacral PS nerves innervate pelvic viscera

Question 14

The Vagus nerve

Answer 14

CN X
- starts at brainstem and reaches the colon
- rich vagal innervation to the heart
- caudal to lung, splits into dorsal and ventral branches
- pass through diaphragm at oesophageal hiatus
- many smaller branches supply abdoninal viscera
- Vagal nerve trunks run in nerve plexuses on coeliac and cranial mesenteric vessels