Autonomic Nervous System

Question 1

What is the main fibre Composition of the ANS?

Answer 1

• GVM fibres
• purely motor
• That part of the NS is supplying the visceral system (gut, stomach, heart other organs)
• These organs also have sensory information, can detect pain (e.g. colic). So BOTH together will form this visceral system. So the visceral division of the NS is not quite the same as the ANS since the ANS is purely motor
• Sometimes texts and others will consider these the same. We need to think of it as purely motor fibres and therefore not exactly the true visceral division of NS

Question 2

What is the looser term or description for the ANS?

Answer 2

• “visceral division of Nervous System”
  *

Question 3

What is supplied by the ANS?

Answer 3

• smooth muscle
• cardiac muscle
• glandular tissue
• The only 3 tissues in the body that receive innervation by ANS. Only tissues supplied by autonomic fibres

Question 4

The 2 Major Divisions of the ANS

Answer 4

• Sympathetic (fight or flight) - mobilises body resources
• Parasympathetic (rest and digest) -conserves bodies resources
• Most are innervated by both: opposing actions
• exception: blood vessels in skin innervated only by sympathetic fibres

Question 5

3 Possibilities upon entry into the Sympathetic Trunk

Answer 5

• Immediate synpase in sympathetic trunk-return via grey rami communicantes
• Run up or down sympathetic trunk prior to synapse
• Leave sympathetic trunk without synapsing- run to collateral ganglia close to abdominal organs

Question 6

Cranial Nerves involved in Parasympathetic Innervation

Answer 6

• III, VII, IX, X
• Oculomotor, Facial, Glossopharyngeal, and Vagus

Question 7

Parasympathetic Division

Answer 7

• Cranial Nerves III, VII, IX, X
• Sacral Spinal Nerves
• Preganglionic neurone relatively long
• Preganglionic CB’s in cranial nerve nuclei or lateral horn grey matter of sacral spinal cord segments
• Postganglionic neurone relatively or VERY short
• Postganglionic CBs in ganglia close to or within wall of organ innervated

Question 8

Composition ANS

Answer 8

General visceral motor fibres (GVM)- purely motor

• Not the same as the “visceral division of nervous system”

Question 9

ANS supplies

Answer 9

3 tissues only:

• Smooth muscle
• Cardiac muscle
• Glandular Tissue

Question 10

General Arrangement ANS

Answer 10

• 2-neurone chain: Only ever 2 neurones involved from beginning of path in CNS (preganglionic neurone) to end in the tissue/ organ in the PNS (postganglionic neurone)
• Autonomic ganglia: cell bodies of postganglionic neurones
• Ganglion= collection of nerve cell bodies in PNS
• Nucleus= collection of nerve cell bodies in CNS

Question 11

Divisions of ANS

Answer 11

• Sympathetic- Mobilises body resources, “fight or flight”
• Parasympathetic- Conserves body resources “rest and digest”
• Most organs innervated by both - opposing actions

Question 12

Sympathetic NS

Answer 12

• Thoracolumbar outflow- restricted, only at the thoracic & cranial lumbar segments of SC is there outflow of sympathetic pathways from the CNS–> periphery
• Preganglionic CBs are located in the lateral horn of the grey matter in these segments
• Preganglionic neurone relatively short compared to postganglionic
• Axons exit SC via ventral roots of spinal nerves–> sympathetic trunk via white rami communicantes (heavily myelinated)

Question 13

On entry into the Sympathetic trunk

Answer 13

3 possibilities:

1. Preganglionic neurone undergoes an immediate synapse in sympathetic trunk & returns via grey rami communicates (lightly/nonmyelinated) to re-join the spinal nerve for distribution to either the dorsal or ventral ramus–> periphery
2. Run up/ down sympathetic trunk prior to synapse – at the cranial limit of the sympathetic trunk- cranial cervical ganglion, it synapses with the postganglionic neurone for distribution to head (or tail end of body)
3. Leave sympathetic trunk without synapsing -run to collateral ganglia close to abdominal organs i.e. coeliac, cranial mesenteric, caudal mesenteric ganglia. Postganglionic fibres distribute to abdominal/pelvic organs (preganglionic neurone is relatively longer in this case

Question 14

Parasympathetic NS

Answer 14

• Craniosacral outflow- outflow restricted, comes from brain & sacral segments of SC only
• Cranial nerves III, VII, IX and X and Sacral spinal nerves
• Preganglionic neurone= relatively long
• Preganglionic CBs are in cranial nerve nuclei or lateral horn grey matter of sacral spinal cord segments
• Postganglionic neurone relatively or very short because these neurones have their postganglionic CBs in
• ganglia close to or sometimes even within wall of organ innervated

Question 15

Autonomic Innervation of the Head

Answer 15

Parasympathetic

• cranial nerves IX, VII, III supply structures in the head with parasympathetic innervation
• Cranial nerve X supplies the thorax & abdomen with parasympathetic innervation (preganglionic fibres are extremely long in this case)