Neuroscience 10 - Autonomic reflexes

Question 1

What is the baroreceptor reflex?

Answer 1

Baroreceptors => to hypothalamus or brainstem => sympathetic ganglia => heart + Blood vessels + adrenal medulla.

Question 2

What does decreased BP do?

Answer 2

1. Decreases stretch of vessels => Lower frequency of signals from baroreceptors.
2. Inhibition of sympathetic relaxed, more firing of sympathetic.
3. Increased HR + Vasoconstriction + production of adrenaline.

Question 3

What does increased BP do?

Answer 3

1. Increased stretching of vessels => Higher frequency of signals from baroreceptors.
2. Inhibition of sympathetic.
3. Powerful parasympathetic stimulation.
4. Decreased HR + Vasodilation + no adrenaline.

Question 4

How does the baroreceptor reflex start when you stand up after sitting?

Answer 4

1. Reduced venous return because of gravity.
2. Therefore decreased CO = Decreased BP.
3. Decreased baroreceptor stimulation.
4. Increased sympathetic activity = increased CO + TPR + decreased vagal tone.

Question 5

What is postural hypotension?

Answer 5

1. Stand up = decreased venous return and decreased CO.
2. Decreased BP and decreased stimulation of baroreceptors.
3. However impaired sympathetic nerve activity and hence little change on CO and TPR.
4. May cause them to faint.

Question 6

What is the parasympathetic and sympathetic effect on the pupil?

Answer 6

1. Parasympathetic = Constrict iris muscle.

2. Sympathetic = relax iris muscle.

Question 7

What happens if you give a drug that will block muscarinic receptor in the pupil?

Answer 7

Blocks parasympathetic effect. Only sympathetic effect present = pupil dilates.

Question 8

What happens if you give a drug that will activate muscarinic receptors in the pupil?

Answer 8

Powerful effect on muscarinic receptor. Parasympathetic nerve stimulation = pupil constricts.

Question 9

What is the consensual light reflex? And why is this clinically important?

Answer 9

You only need to stimulate one eye for an effect to be seen in both eyes. By shining a light on one eye, you can work out where in the reflex a problem might be.

Question 10

Describe the pathway of the pupillary light reflex.

Answer 10

1. Light detected by the optic nerve.
2. Sensory information goes to the pretectal nucleus.
3. Sensory information relayed to the Ediger-westphal nucleus (2 of these).
4. Pre-ganglionic parasympathetic nerve (cranial nerve III) => ciliary ganglion => post-ganglionic parasympathetic nerve.
5. Constriction of pupil.