Autonomic Reflexes

Question 1

a. what are two equations for cardiac output?

Answer 1

CO = HR x Force of Contraction

CO = stroke volume x HR

Question 2

b. what is the equation to blood pressure?

Answer 2

BP = Cardiac Output / Total Peripheral Resistance

Question 3

c. what is the Total peripheral resistance mainly based off?

Answer 3

the radius of the blood vessel

Question 4

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

Answer 4

Sympathetic has an
- inotropic ( increased SV)
- chronotropic effect
( increased HR)

thus SV and HR are increased so CO is increased.

Sympathetic firing also causes generalised vasoconstriction so TPR increases.

Question 5

e. how does the sympathetic nervous system affect total peripheral resistance?

Answer 5

• sympathetic activity causes mass vasoconstriction

- this causes an increase in total peripheral resistance

Question 6

f. describe the effect of an increased blood pressure?

Answer 6

• the sympathetic causes baroreceptor to increase its firing rate
• there are baroreceptors in the carotid sinus and aortic arch
• the more pressure there is the faster the neurones fire
• the firing inhibits the sympathetic activity

Question 7

g. Describe the response to a decrease in blood pressure.

Answer 7

• 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 8

h. what happens to people with hypertension?

Answer 8

there is a disconnect between baroreceptors and regulation of blood pressure

Question 9

i .Describe the changes that take place when you stand up.

Answer 9

• 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.

Question 10

j. what does this decrease in blood pressure cause

Answer 10

• the decrease in blood pressure causes activation of the baroreceptor reflex
• which means the sympathetic system is activated

Question 11

k. What causes postural hypotension?

Answer 11

Impaired sympathetic nervous system response to transient hypotension

Question 12

L. how does postural hypotension work?

Answer 12

• so when you stand up the blood pools by your feet which reduces the venous return
• this decreases the cardiac output
• also decreases arterial blood pressure stimulating baroreceptors
• in people with PH there is impaired sympathetic nerve response
• this means the baroreceptor reflex has little effect on the heart and TPR so you cannot maintain blood pressure
• this leads to loss of blood to the brain which is fainting
  ( loss of consciousness)

fainting gets you on the ground so the blood flow can return to the head

Question 13

m. what parasympathetic nerve is innervating the eye?

what is the iris under control of?

what does sympathetic and parasympathetic do?

Answer 13

oculumotor nerve

• goes to ciliary ganglion
• nerve fibre goes through ciliary muscle

iris is under control of both controls of the ANS

sympathetic : pupil dilation
parasympathetic : pupil constriction

Question 14

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

Answer 14

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 15

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

Answer 15

Pilocarpine - acetylcholine drug - causes MIOSIS (constriction)
by activating the muscarinic acetlycholine receptors

Atropine - blocks the parasympathetic nervous system - causes MYDRIASIS (dilation)

Question 16

p. Describe the pupillary light reflex.

Answer 16

• Afferent information goes via the optic nerve to the pretectal nucleus.
• From here, the impulses travel to the Edinger-Westphal nucleus where there parasympathetic neurons begin.
• The preganglionic parasympathetic neuron goes to synapse in the ciliary ganglion.
• There is a short postganglionic neuron that goes to the iris which causes pupil constriction

the overall reflex = parasympathetic reflex

Question 17

q. What is the consensual reflex and what causes it?

Answer 17

• When you shine a light in one eye, both eyes constrict.
• this is because both parasympathetic nerves are activated.
• This is caused by the afferent information converging on the pretectal nucleus.

Question 18

r. If you achieve a direct response in the right eye with no consensual response in the left eye, where does the problem lie?

Answer 18

There is a problem with the parasympathetic nerves in the left eye.