S1: Physiology of the Sympathetic Nervous System

Question 1

The sympathetic nervous system prepares the body for ‘fear, fight and flight’

List some changes of the body that occur with ‘fear, fight and flight’

Answer 1

1. Increase in heart rate and contractility meaning increased cardiac output resulting in more blood to the muscles
2. Diversion of blood to skeletal muscle to provide more energy for movement
3. Maintains blood pressure as a result of diverting blood
4. Increase air to lungs by bronchodilation, resulting in increased O2 Uptake and CO2 removal
5. The dilation is pupils, allow more light into the eye for better vision
6. There is increased fuel for muscles to get ready for physical activity
7. Sweating is increased to regulate temperature
8. There is a decrease in non- essential functions such as GI Tract to limit amount of energy being used

Question 2

What is the role of the hypothalamus in the sympathetic system?

Answer 2

The hypothalamus releases a ‘danger’ signal which sends information to the rostral ventral lateral medulla (RVLM)

It is the higher sensors that perceive danger etc. and modulate

Question 3

What fibres travel down to the spinal cord (T1-L2/3)?

Answer 3

Excitatory bulbospinal fibres

Question 4

Where does the excitatory bulbospinal fibres synapse with preganglionic fibres?

Answer 4

The inter medio lateral point

Question 5

Compare the length of the sympathetic pre and post ganglionic fibres

Answer 5

The pre-ganglionic fibres are short

The post-ganglionic fibres are long

Question 6

Where are a2 receptors found?

Answer 6

They are primarily on the blood vessels

However, also found in:
Eye
Certain sphincters
Genitalia
GI

Question 7

Where are B1 receptors found?

Answer 7

They are found primarily in the heart and kidney

Also in GI

Question 8

Where are B2 receptors found?

Answer 8

Vascular smooth muscle of coronary arteries
Cerebral vessels
Skeletal muscles
Airways
GI tract
Smooth muscle of bladder

Question 9

Where in the heart are the B1 receptors found?

Answer 9

They are located on the sino atrial node (SAN)

Muscle cells

Question 10

What happens when noradrenaline acts in the B1- adrenoreceptors in the SAN?

Answer 10

NA causes an increase in the frequency of the pacemaker potentials which produces an increase in heart rate at the SAN

The increase in the rate of impulses through atria to ventricles helps to maintain balance between heart rate and contractions

Question 11

What happens when noradrenaline acts in the B1- adrenoreceptors in muscle cells?

Answer 11

NA binding to B1 will result in increased force of contraction of atria and ventricles resulting in increased stroke volume (SV) and they relax faster

Question 12

Sympathetic nerve stimulation increases cardiac output (CO)

What is the CO equation?

Answer 12

CO = SV x HR

Cardiac output= stroke volume x heart rate

SV is measured in (vol/best)
HR is measured in (beat/min)

Question 13

What happens when NA/A act at a1 adrenoreceptors on blood vessels?

Answer 13

When they bind, they cause contraction of arterioles (vasoconstriction) which increases total peripheral resistance.

It will also cause the construction of veins (Venoconstriction). This increases cardiac output as it brings more blood back to heart —> starlings law

Question 14

Why do we get blood flow?

Answer 14

Pressure difference- the pressure of blood leaving the heart is greater than that of blood entering the heart

Question 15

What happens when adrenaline (releases by sympathetic nerve activity on adrenal gland) acts on B2 adrenoreceptors on coronary arteries and skeletal muscle arteries?

Answer 15

It causes vessels to dilate increases blood flow through coronary arteries and skeletal muscle

Question 16

Name the key function of the kidney

Answer 16

It controls blood pressure

It also filters the blood and produces urine

Question 17

What organ secretes renin?

Answer 17

Kidney

Question 18

How does the sympathetic nervous system cause the release of renin?

Answer 18

The sympathetic nerves synapsing at granular cells which have B1 receptors which when stimulates release renin

Question 19

What receptors are found in the kidney (that are sympathetic)?

Answer 19

B1 adrenoreceptors

Question 20

Renin links the sympathetic system to a chemical called angiotensin II

Why is angiotensin important?

Answer 20

Angiotensin causes increased blood pressure and cardiac output
It causes vasoconstriction of arterioles increasing total peripheral resistance

Question 21

What happens when angiotensin stimulates the adrenal cortex?

Answer 21

It causes the adrenal gland to release aldosterone which results in increased Na+ and H2O retention from the kidney (more sodium and water is taken back into the blood).
This leads to increase blood volume

Question 22

Short summary on how sympathetic NS increases blood pressure

Answer 22

Sympathetic system - B1 receptor on granular cells in kidneys - renin - angiotensin II - vasoconstriction - aldosterone from adrenal glands - increased Na+ and H2O retention - increased blood volume = increased blood pressure

Question 23

Why is B1 blockers successful at reducing blood pressure?

Answer 23

They prevent the sympathetic nervous system from releasing renin and so angiotensin II production is stopped

Question 24

What happens when a/b receptors are stimulated by sympathetic NS in liver and skeletal muscle?

Answer 24

• breaks down glycogen into glucose (glycogenolysis)
• promotes glucose synthesis (gluconeogenesis)

Both of these help increase levels of glucose so more ATP is formed for fight or flight

Question 25

What happens when a adrenoreceptors are stimulated by sympathetic NS in pancreas?

Answer 25

Decrease of insulin from beta cells and it prevents global uptake (we want to use the glucose not store it)

This also stops insulin from inhibiting glycogenolysis, glucagenogenesis and lipolysis

Question 26

What happens when B adrenoreceptors are stimulated by sympathetic NS in adipose tissue (fat)?

Answer 26

• increased lipolysis (where triglycerides are broken down into free fatty acids + glycerol)
• free fatty acids go under beta oxidation into acetylcholine coA and enter the kerbs cycle
• glycerol is recycled into glycolysis pathway

Both of these increase ATP yields

Question 27

What happen when a1/a2 and B2 adrenoreceptors are stimulated by sympathetic NS in GI motility?

Answer 27

It induces inhibition of GI motility

Activation of a1 adrenoreceptors evokes construction of the internal bladder sphincter

B2 adrenoreceptors induces relaxation of smooth muscle allowing filling of the bladder and prevents urination

The bowel/bladder function is non essential during ‘fear,fight and flight’

Question 28

Do the lungs receive sympathetic innervation?

Answer 28

No

Question 29

What activates the B2 adrenoreceptors in the lungs?

Answer 29

The bronchioles contain B2 adrenoreceptors which are activated by circulating adrenaline in the blood. This produces bronchodilation which helps facilitate breathing

Question 30

What happen when a1 adrenoreceptors are stimulated by sympathetic NS in dilator papillae?

Answer 30

This causes dilation of pupil allowing more light into retina for more acutely sight

It does this by constricting the dilator muscle

Question 31

How does the sympathetic NS act on sweat glands?

Answer 31

Acetylcholine act at muscarinic receptors