21 - Autonomic Nervous System

Question 1

Tissues innervated by autonomic nervous system

Answer 1

All tissues except skeletal muscle fibres (careful: ANS innervates blood vessels within skeletal muscle)

Question 2

What does the ANS need in order to maintain homeostasis?
1
2

Answer 2

• Signalling from the periphery, i.e. specialised sensors,
visceral sensory nerves
• CNS circuits to
– ‘interpret’ the signals
– decide on the most suitable outcome
– activate the appropriate sympathetic or parasympathetic
nerves

Question 3

Anatomical distinction between sympathetic and parasympathetic nervous systems

Answer 3

Sympathetic fibres emerge from thoraco-lumbar part of spinal cord.

Parasympathetic fibres emerge from the cranio-sacral parts of the spinal cord.

Question 4

Parts of spinal cord where no autonomic pathways originate

Answer 4

Cervical spine or lumbar enlargements.

Question 5

Location of sympathetic pre-ganglionic neuron cell bodies

Answer 5

Intermediolateral cell column (T1 to L3)

Question 6

Connections of sympathetic preganglionic neurons

Answer 6

Sympathetic postganglionic neurons lie in two types of ganglia:

1) Paravertebral ganglia (sympathetic chain)
2) Prevertebral ganglia

Question 7

Function of sympathetic paravertebral ganglia

Answer 7

Primary source of vasoconstrictor muscles

Question 8

Function of sympathetic prevertebral ganglia

Answer 8

Primary source of neurons innervating non-vascular smooth muscle

Question 9

Sympathoadrenal system

Answer 9

Sympathetic preganglionic neurons innervate adrenal medulla (release of adrenaline)

Question 10

Parasympathetic brainstem nuclei
1
2
3

Answer 10

Edinger-Westphal nucleus

Salivatory nuclei

Dorsal motor nucleus of vagus
and nucleus ambiguus

Question 11

Edinger-Westphal nucleus role

Answer 11

To ciliary ganglion to control

sphincter pupillae, ciliary muscle

Question 12

Salivatory nuclei role

Answer 12

To submandibular, sphenopalatine and otic ganglia to
control lacrimal, salivary, sublingual, nasal and palatine
glands

Question 13

Dorsal motor nucleus of vagus and nucleus ambiguus role

Answer 13

To microganglia near and on outer surface of thoracic and abdominal organs: numerous functions

Question 14

Sacral spinal parasympathetic preganglionic location

Answer 14

Intermediolateral cell column (S1 to S5)

Question 15

Where do sacral postganglionic parasympathetic neurons connect?

Answer 15

Postganglionic neurons lie in pelvic plexus (inferior hypogastric plexus).

Form microganglia on target organs.

Question 16

Pelvic ganglia

Answer 16

Pelvic ganglia contain many sympathetic and parasympathetic neurons:
i.e., these are mixed ganglia =
very unusual

Question 17

Where do the sympathetic neurons which deliver sensory information to ANS travel?

Answer 17

In the same nerve bundles as motor ANS neurons.

Question 18

How do ANS neurons connect with target organs?

Answer 18

Complex networks of unmyelinated axons within organs

More than one site of transmitter release per axon (axon varicosities)

Question 19

Major CNS integrative centre of autonomic function

Answer 19

Nucleus tractus solitarius (nucleus of the solitary tract)

Question 20

Type of neurons in the nucleus tractus solitarius

Answer 20

Second-order sensory neurons, which receive input from visceral afferents.

Question 21

Functions of the nucleus tractus solitarius
1
2

Answer 21

Information received from the periphery is distributed to either:
1. Provide feedback to reflexes that control organ/tissue function

2. Provide information to higher centres to drive more complex responses (coordinated behaviour: visceral, somatic, endocrine; emotion)

Question 22

Central coordinator of autonomic output

Answer 22

Hypothalamus

Question 23

Examples of AND reflexes that don’t require the CNS

Answer 23

Enteric nervous system function.

Question 24

What often accompanies sympathetic NS activation?

Answer 24

Adrenal medulla activation (sympathoadrenal system).

Question 25

Why is sympathetic NS able to stimulate a large number of targets quickly? 1 2

Answer 25

• Catecholamine hormones spread through the bloodstream • Each preganglionic neuron activates many postganglionic neurons

Question 26

Situations where sympathetic mass activation is necessary

Answer 26

Extreme, 'fight or flight' situations

Question 27

Situations where subtle sympathetic control are necessary

Answer 27

Adjustments of blood pressure (postural), small temperature changes, reproductive, voiding

Question 28

``` Examples of parasympathetic functions 1 2 3 4 ```

Answer 28

* Decreased heart rate * Decreased contractile force of heart * Increased gut motility * Constriction of airways

Question 29

Why is the ability of the parasympathetic NS to 'mass activate' limited, compared to the sympathetic? 1 2 3

Answer 29

- Much lower ratio of pre:postganglionic neurons - No equivalent of adrenal gland, ie no circulating Ach to affect all organs at once. - Therefore coordination has to occur by brain mechanisms

Question 30

Are the sympathetic and parasympathetic NSs often antagonistic? 1 2 3

Answer 30

• There are very few cases where the two systems are genuinely antagonistic at the cellular level. • More commonly, actions are on different tissues to cause different type of actions (synergistic but not necessarily opposite). • Some tissues only have one type of innervation.

Question 31

Examples where sympathetic and parasympathetic NSs are genuinely antagonistic at the cellular level 1 2

Answer 31

1) Heart rate (S increases heart rate, P decreases, acting on SA node) 2) Airways (S relaxes, P constricts)

Question 32

Examples of functional antagonism between S and P 1 2

Answer 32

Sympathetic contract pupil dilator muscle contract base of bladder (continence) Parasympathetic contract pupil sphincter muscle contract body of bladder (voiding)

Question 33

Examples of different but not opposite actions of S and P 1 2 3

Answer 33

Sympathetic serous salivary secretion - only S innervation constriction of abdominal vasculature - only S innervation lipolysis --- ``` Parasympathetic mucous salivary secretion -- -- Tear secretion (lacrimal glands) - only P innervation ```

Question 34

Electroceuticals

Answer 34

Implanting an electrical device in the body which modulates nervous function