Autonomic reflexes Flashcards
how is high blood pressure detected in the baroreflex?
baroreceptors in the aorta sending impulses via afferent CNX
baroreceptors in the carotid bodies send impulses via glossopharyngeal CNIX nerve
these are sent to the vasomotor centre
the lower the pressure the ______ baroreceptor firing rate
LOWER
if blood pressure is higher or lower than the set point, what happens
this is corrected by output of the vasomotor centre
what happens to the set point in people with hypertension?
it increases
this may be due to impaired cerebral bloodflow hence higher blood pressure needed to perfuse.
what controls blood pressure?
cardiac output: heart rate, stroke volume: contractility, preload, afterload.
peripheral resistance: radius of vessels
how does the baroreflex work?
afferent baroreceptor nerve is linked positively to parasympathetic nerve (stimulates it) and linked negatively to sympathetic nerves (inhibits).
this means when firing rate increases, there is more stimulation of parasympathetic hence heart rate decreases. there is also more inhibition of sympathetic hence heart rate decreases further and blood vessels dilate.
how does gravity cause hypotension?
blood pools in veins, increasing pressure in leg. more fluid lost to tissue. decreased venous return means decreased cardiac output in frank starling relationship.
how does the body combat orthostatic hypotension?
reduced BP means reduced firing rate. this means less inhibition of sympathetic nervous system. this increases heart rate, contractility leading to greater cardiac output.
venous walls also contracted meaning less pooling, increased venous return again increasing cardiac output.
peripheral resistance all increased by arteriolar constriction.
what is postural hypotension?
when body has impairment to normal corrective mechanism, ie takes longer to restore blood pressure.
this mean you faint as correct cerebral perfusion cannot be maintained.
how is pupillary contraction controlled
CNIII oculomotor nerve synapses in the ciliary body with the postganglionic neurone which releases acetyl choline at the iris muscle causing contraction.
hence when pilocarpine drug analog given it mimics Ach and causes pupil contraction.
describe the pupillary light reflex
as light levels increase impulses are sent via the optic CNII nerve to the pretectal nucleus in the midbrain. this activates the parasympathetic occulomotor nerve arising from the Edinger-westphal nucleus. the preganglionic neurone synapses in the ciliary ganglion. the postganglionic neurone then causes the iris muscles to contract hence pupil gets smaller.
this process is consensual, no matter which eye activates the reflex, both eyes will contract the same amount.
