W7: Anatomy Of ANS

Question 1

Afferent nervous system

Answer 1

Nerves that carry information from the body to the brain (sensory). Does not split any further

Question 2

Efferent nervous system

Answer 2

Nerves that carry info from brain to body, motor system. Split into somatic and autonomic.

Question 3

Somatic nervous system

Answer 3

Under voluntary control - supplies skeletal muscles. No split, just somatic efferents

Question 4

Autonomic nervous system

Answer 4

Not under voluntary control - supplies smooth muscles, glands, and cardiac muscles. Split into sympathetic, parasympathetic, and enteric.

Question 5

General actions of the ANS

Answer 5

• establishes and maintains homeostasis or internal environment in the body - through regulation of various systems of the body: cardiovascular, respiratory, digestive, thermo-regularise apparatus. Constantly working
• promotes excretory mechanisms of the body as and when necessary and appropriate. Intermittent.

Question 6

General layout of the ANS

Answer 6

• neurone with the cell body in the CNS and neurone with the cell body in the PNS connected in series
• CNS neurone’s axon crosses the boundary of the meninges to end up being in the PNS
• in the PNS, the neurone terminates to make contact with a cell body of another neurone in the PNS
• this neurone then has an axon that comes out to supply the effector organ

Question 7

What makes up a ganglion?

Answer 7

The cell bodies collected in the PNS constitute a ganglion.

Question 8

What does pre-ganglionic mean?

Answer 8

A neurone that occurs and terminates in the ganglion. Does not supply effector organs directly.

Question 9

What does post-ganglionic mean?

Answer 9

A neurone who’s axon terminates outside the ganglion. These communicate with the effectors. Relies on pre-synaptic neurone for drive. Terminate directly on effector organs.

Question 10

Sympathetic pre and post ganglionic neurotransmitter and receptors

Answer 10

Preganglionic = ACh acting via nicotinic receptors
Postganglionic = noradrenaline or adrenaline acting via alpha or beta adrenoceptors (respectively)

Question 11

Where are sympathetic nuclei found and what do they command?

Answer 11

High brain structures. These command only spinal cord systems. Then to paravertebral chain and to the effector organs.

Question 12

What do sympathetic fibres form?

Answer 12

Paravertebral chain or pre-vertebral ganglia.

Question 13

Parasympathetic pre and postganglionic neurotransmitters

Answer 13

Preganglionic = ACh acting via nicotinic receptors
Postganglionic = ACh acting via muscarinic receptors

Question 14

Where are parasympathetic fibres found?

Answer 14

Found in walls of effector organ or near branches of CNV.

Question 15

Where are parasympathetic nuclei found and what do they command?

Answer 15

High brain structures. These command brainstem/spinal cord systems. Then to the wall of the effector organ and then to the effector organ.

Question 16

Autonomic innervation of organs

Answer 16

• most have dual innervation from the sympathetic and parasympathetic and have reciprocal actions
• autonomic tone is determined by the balance of outputs of SNS and PNS
• sweat glands receive sympathetic drive only

Question 17

Where do autonomic fibres originate from?

Answer 17

Cranial-sacral sources and thoraco-lumbar sources

Question 18

Describe the autonomic fibres originating from cranial-sacral sources

Answer 18

• parasympathetic in function
• cell bodies/somata found in specific named cranial nuclei and S2,3,4 segments of the spinal cord
• axons of cranial nuclei reach periphery by hitch-hiking on fibres of cranial nerves III, VII, IX, X

Question 19

Describe autonomic fibres originating from thoraco-lumbar sources

Answer 19

• sympathetic in function

- all neural segments of spinal cord between T1 and L2

Question 20

What might lesions of the CNS cause?

Answer 20

Imbalances of autonomic outflow to visceral organs
Unbalanced autonomic outflow leading to disturbed autonomic reflexes
Death if not managed expertly

Question 21

Output of CNIII, CNVII, IX

Answer 21

• head region only
• output of pre-ganglionic neurones terminate on discrete ganglia which are in the head region
• these ganglia occur in relation to the branches of the trigeminal nerve CNV

Question 22

Output of CNX

Answer 22

• distribution to rest of body - visceral organs excluding the head region, and some head region
• cranial nerve course: specific cranial nuclei including vagal nuclei
• spinal nerve source: S2-S4
• pre-ganglionic neurones are found in either dorsal vagal motor nucleus or spinal segmental nerves of S2-S4 segments

Question 23

Where does all sympathetic outflow originate from?

Answer 23

Thoracic level of the spinal cord. T1-L2.

Question 24

What does the dorsal horn do?

Answer 24

Largely involved in sensory processing of information in the spinal cord - SOMATIC NOT AUTONOMIC

Question 25

What does the ventral horn do?

Answer 25

Largely contains cell bodies of commands or actions which will lead to effector organs - SOMATIC NOT AUTONOMIC

Question 26

Where is lateral horn found and what is it?

Answer 26

In thoracic and lumbar segments
In the grey matter produced by collections of cell bodies or preganglionic sympathetic neurones
Seen in S2-S4

Question 27

Layout of sympathetic pre-ganglionic neurones

Answer 27

• all PNS outflow from CNS to peripheral target is entirely spinal
• T1-L2/3 innervates almost all organs of the body
• axons of all pre-ganglionic neurones either: terminate immediately in the paravertebral sympathetic chain of ganglia (sympathetic trunk) OR pass through it

Question 28

What are the 3 possible modes of termination of sympathetic pre-ganglionic neurones?

Answer 28

White rami communicans, gray rami communicans, splanchnic nerves

Question 29

Effector organs of the ANS

Answer 29

Muscles that generate their own electrical activity - smooth muscles and cardiac muscles
Secretory glands