Neuro 8 - Physiology and pharmacology of the ANS

Question 1

From where do parasympathetic nerves emerge from?

Answer 1

From the base of the brain

End of the spinal cord (sacral)

Question 2

Give 4 parasympathetic cranial nerves

Answer 2

Oculomotor (3)
Facial nerve (7)
Glossopharyngeal (9)
Vagus (10)

Question 3

What is the name of the nerve which emerges from the sacral region?

Answer 3

Splachnic nerve

Question 4

Describe the parasympathetic outflow

Answer 4

Usually 2 neurons are set up:
one is pre ganglionic, the other post ganglionic, synapse at the ganglion.
The ganglion is situated close to the targeted tissue

Question 5

What is the important neurotransmitter in the parasympathetic nervous system?

Answer 5

Acetylcholine

Question 6

From where do neurons emerge from in the sympathetic nervous system? where do they synapse?

Answer 6

Thoracolumbar (T1 - L2)
They all synapse in the sympathetic trunk (=alignment of ganglia)
Short pre ganglionic fiber, long post ganglionic

Question 7

What neurotransmitters are involved in the sympathetic nervous system?

Answer 7

ACh for preganglionic synapse.
NA for postganglionic (to produce effect on organ)
Except adrenal medulla, skin/sweat glands/ peripheral blood vessels

Question 8

What is particular about the sympathetic innervation of the adrenal medulla?

Answer 8

Adrenal medulla is innervated by sympathetic pre-ganglionic nerve fibres (so doesn’t synapse in sympathetic trunk), which release acetyl choline that binds to the nicotinic acetyl choline receptors and causes release of catecholamines (A or NA) from the chromaffine cells which will act via bloodstream on target organ.

Question 9

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

Answer 9

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

Question 10

What is different between the innervation of the sympathetic and parasympathetic systems?

Answer 10

In parasympathetic, one nerve leads to one nerve. However, in sympathetic one neuron can branch off and synapse elsewhere, divide after ganglion to have different postganglionic fibers.

Question 11

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

Answer 11

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

Question 12

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

Answer 12

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

Question 13

Describe the effect of the SNS/PNS on the heart.

Answer 13

The SNS has an inotropic (increase force of contraction) and chronotropic (increase heart rate) effect.
The parasympathetic decreases HR. When baroreceptors sense a high BP, it activates parasympathetic pathway to slow down HR. ALSO stimulates inhibitory neuron that acts on sympathetic
BOTH systems are on at any time, just one dominates.
Intrinsic resting HR is 110 bpm however normal is 70 so parasympathetic dominates at rest.

Question 14

Describe the effect of increased sympathetic firing on the blood vessels.

Answer 14

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

Question 15

How does the SNS affect arterial BP?

Answer 15

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

Question 16

Describe the effects of sympathetic and parasympathetic activity on the eye muscles.

Answer 16

Sympathetic - causes dilation of the pupil (contraction of radial muscles)
Parasympathetic - constriction of the pupil and ciliary muscle contracts (lens bulges allowing near vision)
So pupillary constriction is a parasympathetic effect.

Question 17

What can the vagus nerve do in the stomach?

Answer 17

Controls secretions like HCL/pepsin and motility

Parasympathetic action

Question 18

Describe how the SNS affects the GI tract.

Answer 18

SNS decreases gut motility and tone
SNS stimulates contraction of sphincter
SNS generally inhibits secretory activity –> tends to say “don’t need gut atm”
–> PARAsympathetic = rest and digest so logic

Question 19

How does the sympathetic nervous system increase oxygen delivery to the lungs?

Answer 19

Via NA/A from the adrenals. There is no sympathetic innervation of the lungs.

Question 20

Describe the nervous control of the bladder.

Answer 20

Has both parasympathetic and sympathetic nervous controls. 
Parasympathetic is dominant - exerts control over detrussor muscle (muscle that makes bladder contract to eject urine). 
Sympathetic has control over internal spincter. 
Motor nerves (ie voluntary control) is exerted over the  external sphincter. 

Nervous control is a reflex; pressure builds up in the bladder, this sends signal -> reflex activation of the parasympathetic activity. Detrussor muscle contracts, internal sphincter relaxes because inhibition caused.

Question 21

What is acetylcholine made from?

Answer 21

Acetic acid + choline

Question 22

What are catecholamines derived from?

Answer 22

Dopamine

Question 23

What structure is common to all catecholamines?

Answer 23

They contain a cathecole ring, ie 6 carbon ring with double hydroxyl group

Question 24

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

Answer 24

Depends if you are at rest or not
If at rest - HR increases as parasympathetic is dominant
If exercising, sympathetic dominant so heart will slow down

Question 25

What 2 receptors can recognise ACh?

Answer 25

Muscarinic and Nicotinic

Question 26

What are the differences between nicotinic and muscarinic receptors?

Answer 26

Nicotinic receptors are situated at autonomic ganglia (both symp and parasymp)

Nicotinic is an ion channel linked receptor; binding of ACh causes influx of sodium and increases cell depolarisation - very fast

Muscarinic receptor is a Gprotein coupled receptor so the effect is slower.
Situated at all effector organs innervated by post ganglionic parasympathetic fibers as well as sympathetic post ganglionic fibers that involve ACh (not NA like usual so in sweat glands for example) so wherever ACh is released that is not autonomic ganglia.

Question 27

Which receptor recognise NA at the effector organ in sympathetic NS?

Answer 27

Adrenoreceptors
G protein coupled
4 types:
alpha 1 - predominant receptor - constriction - responds well to NA
alpha 2
beta 1
beta 2 - important receptor - doesn’t respond well to NA - dilates. However, responds well to adrenaline. so wherever lots of receptors you will see vasodilation - prevalent in skeletal muscle.

Question 28

Describe the synthesis and breakdown of acetyl choline.

Answer 28

Precursors - Acetyl Co A and choline transformed into NT acetylcholine + CoA by choline acetyl transferase.
ACh put into vesicle, AP, Ca2+ influx, vesicle exocytosis.
ACh binds to receptor. Rest is transformed into Choline + Acetate by Acetylcholine esterase and taken back up into cell. Choline used to synthesise more ACh.

Question 29

What would happen if you inhibit acetylcholinesterase?

Answer 29

This would inhibit reuptake of acetylcholine into cell therefore prolong and increase effect of ACh.

Question 30

Describe the synthesis of noradrenaline

Answer 30

Multiple steps
Tyrosine taken up into cell -> converted to DOPA by tyrosine hydroxylase -> converted into dopamine by DOPA decarboxylase -> into vesicle -> DA convertes to NA by dopamine beta hydroxylase

Question 31

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

Answer 31

Can be reuptaked in 2 different ways:
1 - taken into presynaptic cell and degraded in mitochondria by monoamine oxidase A (MAO-A) which forms metabolites
2 - taken into postsynaptic cell and degraded by COMT

Question 32

Which cells in the adrenal medulla produce catecholamines?

Answer 32

Chromaffin cells

Question 33

What extra step and enzyme is involved in the synthesis of adrenaline?

Answer 33

(Adrenaline is secreted into the blood not at synapse)
Same synthesis steps as NA - gives NA but extra step is converting NA to A by Phenylethanolamine Methyl transferase (PNMT)

Question 34

Describe the effect of cortisol on adrenaline secretion

Answer 34

Cortisol increases PNMT effect so increases A secretion