Neuro 9 - Autonomic reflexes

Question 1

What is the equation for mean arterial blood pressure (MABP)?

Answer 1

MAPB = CO x TPR

where CO = SV x HR

Question 2

What are the main effects of the sympathetic nervous system on the MABP = TPR x CO equation?

Answer 2

Sympathetic stimulation increase HR
Also increases SV - inotropic effect
So CO increases
Also, sympathetic nervous system causes vasoconstriction so increased TPR
So BP increases

Question 3

Describe the response to a decrease in blood pressure.

Answer 3

Decrease in blood pressure causes a decrease in baroreceptor firing so there is a decrease in the inhibition of the SNS. The SNS activity increases so you get an increase in CO and TPR

Question 4

Where are baroreceptors?

Answer 4

Carotid sinus and aortic arch

Question 5

Describe the changes that take place when you stand up.

Answer 5

Gravity pushes a column of blood towards your toes so the blood pools in the distensible veins. This means that there is less venous return to the heart and so a lower force of contraction (Starling’s Law). This means that there is a drop in blood pressure when you stand up.
This is immediately sensed by baroreceptors -> increase/preserve baroreceptors

Question 6

What causes postural hypotension?

Answer 6

Impaired sympathetic nervous system response to transient hypotension

Question 7

Describe the effects of the sympathetic and parasympathetic nervous system on the eye muscles.

Answer 7

Sympathetic - contracts radial muscles and dilates the pupil
Parasympathetic - contracts circular muscle and contracts ciliary muscles so you get pupil constriction and lens thickening to allow near vision

Question 8

State two drugs that affect the eye muscles and how they work.

Answer 8

Pilocarpine - acetyl choline drug; activates muscarinic receptor - causes MIOSIS (constriction)
Atropine - blocks the parasympathetic nervous system; inhibits muscarinic receptor - causes MYDRIASIS (dilation)