The Autonomic Nervous System

Question 1

How to calculate blood pressure and TPR?

Answer 1

Blood pressure = cardiac output/ total peripheral resistance.

TPR= 1/r^4

Question 2

Describe how the sympathetic nervous system exerts control over the trachea and bronchi.

Answer 2

The trachea and bronchi have no sympathetic nerve fibres. They are affected by the release of catecholamines from the adrenal medulla.

Question 3

Describe the response of blood vessels to skeletal muscle during a period of increased sympathetic discharge. What causes this response?

Answer 3

Blood vessels supplying the skeletal muscle dilate. This is caused by circulating catecholamines.

Question 4

Describe the role of the adrenal medulla in the sympathetic nervous system.

Answer 4

Adrenal medulla is innervated by sympathetic pre-ganglionic nerve fibres, which release acetyl choline that binds to the nicotinic acetyl choline receptors and causes release of catecholamines from the chromaffine cells.

Question 5

What is special about the sympathetic innervation of the sweat glands?

Answer 5

The sympathetic nerves to the sweat glands release acetylcholine instead of noradrenaline.

Question 6

What are the two outflows of the parasympathetic nervous system?

Answer 6

Craniosacral

Question 7

What inhibits bladder contraction>?

Answer 7

Sympathetic nervous system

Question 8

State the four cranial nerves that form part of the parasympathetic nervous system and explain their functions?

Answer 8

Oculomotor - 3
pupil constriction
Facial - 7
innervates glands that are higher up in the body e.g. tears and salivary
Glossopharyngeal - 9
influences activity in the tissues that are higher up in the body
Vagus – 10
outflow from the CNS via the vagus goes to many organs e.g. lungs, heart, stomach, pancreas, small intestine.

Question 9

Which parasympathetic nerves come out of the sacral region?

Answer 9

Pelvic spanchnic nerves

Question 10

Describe the outflow of the sympathetic nervous system. State the vertebral levels that define the limits of this outflow.

Answer 10

Thoracolumbar (T1 - L3)

-have NO cranial nerve

Question 11

Describe the relative lengths of sympathetic and parasympathetic pre-ganglionic fibres.

Answer 11

Sympathetic nerves have a short preganglionic and a long post ganglionic
Parasympathetic has a long preganglionic and a short post ganglionic

Question 12

what is a key difference between sympathetic nervous and parasympathetic nervous system?

Answer 12

in sympathetic the post ganglionic neurone is outside ( in the sympathetic chain)the organs in parasympathetic is inside the target organ

Question 13

what is ganglia?

Answer 13

where cell body exists.

Question 14

How does innervation happen in sympathetic pathways?

Answer 14

The pre-sympathetic neurone going down the spinal cord and synapsing the preganglionic neurone and then goes through he sympathetic chain and synapses the postganglionic neurone which then innervates the target organ.

Question 15

How does innervation happen in parasympathetic neurone

Answer 15

Come out of the CNS. Target and innervate the target organ, the post-ganglionic neurone is inside the target organ.
Monosynaptic connection, only 1 synapse there.

Question 16

What neurotransmitters to parasympathetic neurone mainly use/

Answer 16

is cholinergic.
releases acetylcholine at its presynpase and post synapse.
if vagus nerve in heart is stimulated leads to bradycardia

Question 17

What neurotransmitter do sympathetic use?

Answer 17

the pre-ganglionic neurone that comes down the spinal cord uses glutamate ( excitatory)
these pre-ganglionic neurone releases acetylcholine in the ganglia, and the post ganglionic neurone usually releases noradrenaline but there are differences e.g. sweat glands

Question 18

How is noradrenaline biosynthesised?

Answer 18

1. Using phenylalanine ( get this through diet )
2. converted to tyrosine
3. then DOPA: dihydroxyphenylalanine (tyrosine hydroxylase)
4. then dopamine(dopamine decarboxylase)
5. noradrenaline(Dopamine  hydroxylase)

1-4 happens in the cytoplasm and 4-5 happens on the pre-synaptic vesicles.

Question 19

how is acetylcholine synthesised and what breaks it down?

What would happen if you inhibit acetylcholinestrase

Answer 19

Add acetate and choline using choline acetyltransferase.

-acetylcholinesterase breaks it down.

Inhibiting acetylcholinesterase would result in a build up of acetylcholine in the synaptic cleft and a decrease in the responsiveness of the post synaptic neurone receptors to acetylcholine and you will become paralysed. This how botulinum toxin works.

Question 20

where do all the sympathetic nerves emanate from in the vertebrae?

Answer 20

intermediolateral cell column

Question 21

How does the ANS control blood pressure

Answer 21

In the heart there are baroreceptors ( mechanoreceptors, respond to physical distention)
There is 1 aortic baroreceptors and 2 carotid baroreceptors which are in the neck.

These aortic baroreceptors communicate to the brain via the afferent vagus nerve (10th cranial nerve)
Carotids communicate via glossopharyngeal nerves. (9th cranial nerve)
These communicate the pressure.
Once the baroreceptors are activated due to blood pressure increasing, this is communicated back to the heart via the vagus nerve (efferent) which cause parasympathetic activity to innervate the heart and reduce stroke volume, reduce cardiac output and via inhibition of sympathetic nervous system you increase the blood vessels diameter so blood pressure decreases.

Question 22

What is the relationship between the baroreceptor firing and the
blood pressure?

Baroreflex

Answer 22

It is a S phase. The baroreceptor firing is the number of action potentials being fired as a result of blood pressure changes.
We have a set point, and it is controlled by the brain.
A slight increase in blood pressure is met by increased baroreceptor firing to move the blood pressure back to normal.

Question 23

How is this relationship in hypertension patients?

Baroreflex

Answer 23

The S shape graph is shifted to the right, so the set point is higher, therefore the brain thinks it should be defended at a higher blood pressure.

Question 24

How is the GI function regulated and what type of response is this?

Answer 24

It is regulated by the vagus nerve.
Even before ingestion, stimuli’s such as smell can stimulate the release of enzymes in your intestine.
All of these sensory input enter the hypothalamus, enter the spinal cord which regulate these responses.

This is the cephalic response: pancreas primes the body by releasing insulin into the blood even before ingestion.
2nd phase of insulin spike is glucose mediated.
This is mediated by the 10th cranial nerve.

Question 25

how is the cephalic response in type 2 diabetics different?

Answer 25

Usually the cephalic response is the first thing to go.

Question 26

What type of receptors are found in the GI tract and what part of the brain to they communicate to?

Answer 26

Mechanoreceptors.
The receptors detect that you’ve eaten and via the vagus nerve, it goes to the brain stem.
once the food ends up in the small intestine, the GI tract releases hormones which then feeds to the brain stem to tell you to stop eating, these are chemoreceptors as chemicals are released from the GI tract which has mechanoreceptors.

Question 27

what is special about vagus nerves?

Answer 27

It has afferent and efferent

Question 28

what are the 3 centres in the regulation of respiration?

Answer 28

Central respiratory centre:

Poutine respiratory centre: coordinates rate and pattern of breathing

Medullary respiratory centre:
Ventral group: coordinates rhythmicity
Dorsal group: responsible for inspiration and control of diaphragm, so initiates breathing.

All these communicate with each other.

Question 29

What influences these respiratory centres?

Answer 29

• aortic chemoreceptors
• carotid chemoreceptors, they respond to drop in oxygen, decrease in pH and increase in carbon dioxide, these feedback to the brain stem.

There are also central chemoreceptors that respond to a drop in pH and an increase in carbon dioxide.

Question 30

What type of receptors are found in the lungs

Answer 30

Mechanoreceptors are found in the lungs.

These transmit via the vagus nerves.

Question 31

How does the respiratory centre influence the respiratory rate?

Answer 31

The respiratory centre sends signals via the spinal cord.
c1-c3 innervates the accessory muscles.
c3-c5: diaphragm

therefore if you damage below c5 you don’t die as diaphragm still works.

T1-T11 : intercostal muscles, allows the ribcage to expand
T6-L1: abdominal muscles

Question 32

Describe the structure of the bladder and what are each of it controlled by?

Answer 32

The outside area of the bladder is the Detrusor muscle.
It then narrows, the tip is called the Internal sphincter and the bottom bit which you pee through is called the external sphincter (.

Question 33

Describe which nerves innervate which bladder structure ?

Answer 33

Parasympathetic innervation from sacral spinal cord ( S2-4), innervates the detrusor muscle.
Sympathetic innervates of the internal sphincter from thoracic spinal cord (T10-12).
Motor nerves (voluntary) sacral spinal cord ( S2-4) innervate the external sphincter.

The parasympathetic nervous system controls the muscles of the bladder wall
The sympathetic nervous system controls the internal sphincter
There is somatic motor control of the external sphincter

Question 34

What happens when the bladder is full?

Answer 34

You also have afferent mechanoreceptors on the distention of the bladder walls via S2-S4, this information goes to the brain and activates the PSN and inhibits the SNS, this contracts the detrusor muscle and relaxes the internal sphincter. The voiding is governed by voluntary control of external sphincter.

Question 35

What can cause vasodilation in various tissues?

Answer 35

Vasodilation can be caused by local mediators such as nitric oxide and histamines
Vasodilation in the penis is caused by increased parasympathetic stimulation
Vasodilation in the blood vessels supplying skeletal muscle is due to increased sympathetic activity (by circulating catecholamines)

Question 36

What is the capacity of the bladder?

Answer 36

450-500 mL

Question 37

State the three nerves involved in micturition.

Answer 37

Pelvic - sensory input from the stretch receptors in the wall of the bladder
Hypogastric - sympathetic input to the internal sphincter
Pudendal - voluntary control of the external sphincter

Question 38

Describe the effect of the SNS on the heart.

Answer 38

The SNS has an inotropic (increase force of contraction) and chronotropic (increase heart rate) effect

Question 39

Describe the effect of increased sympathetic firing on the blood vessels

Answer 39

Increased sympathetic firing causes constriction of most blood vessels (except those supplying the skeletal muscle, which dilate)

Question 40

How does the SNS affect arterial blood pressure?

Answer 40

SNS increase cardiac output via the chronotropic and inotropic effects and it increases TPR by causing vasoconstriction so it increases blood pressure

Question 41

Describe how the SNS affects the GI tract.

Answer 41

SNS decreases gut motility and tone
SNS stimulates contraction of sphincter
SNS generally inhibits secretory activity

Question 42

Describe the effects of increased sympathetic activity on the lungs and airways.

Answer 42

Increased sympathetic activity dilates the airways

Question 43

What are catecholamines derived from?

Answer 43

Tyrosine

Question 44

What structure is common to all catecholamines?

Answer 44

Hydroxylated phenyl ring

Question 45

If you block acetylcholine action in autonomic ganglia, how would it affect heart rate?

Answer 45

The effect on heart rate would be dependent on which branch of the autonomic nervous system was more dominant at the time. Because all autonomic ganglia have acetyl choline so blocking it would affect both sympathetic and parasympathetic pathways.

Question 46

What can happen to the noradrenaline after it has had its effect?

Answer 46

It is taken up into pre-synaptic neurones and into extraneuronal tissue
In the pre-synaptic neurones it is broken down by MAO (monoamine oxidase). In extraneuronal tissue it is broken down by COMT (Catechol-o-methyl transferase)

Question 47

Which cells in the adrenal medulla produce catecholamines?

Answer 47

Chromaffin cells

Question 48

Describe the effect of cortisol on adrenaline secretion.

Answer 48

Cortisol increases adrenaline secretion by upregulating PNMT (Phenylethanolamine N-methyltransferase).