autonomic reflexed Flashcards
bp =
CO/TPR
CO=
HR*force of contraction
resting heart rate
70bpm
intrinsic rate
100-110bpm
what can be inferred by the difference between resting and intrinsic heart rate
autonomic ns is controlling rate
PNS influence - because resting is lower than intrinsic and pns reduces heart rate
what does the atrial baroreceptor do
sense pressure and relay it to the brain by afferent nerve
brain determines level of autonomic activation
activates the PNS
inhibits the SNS
describe the signals in the normal baroreceptor response
signal generated in response to pressure sent to brain (afferent nerve) PNS proportionately activated SNS inhibited at rest - PNS is dominant
what happens to the baroreceptor reflex when the blood pressure increases
firing signal increases increase PNS stimulation Increase SNS inhibition greater -ve effect on the heart reduce HR bring CO down normalise bp
what happens to the baroreceptor reflex when the blood pressure decreases
reduced signal down the afferent nerve reduced PNS activation reduced SNS inhibition - becomes dominant increase HR vasoconstrict to increase TPR
what is a major daily problem for blood pressure
moving from lying to standing
what contributes to the pressure in a standing position
usual pressure from cardiac contraction
effect of gravity pushing the column of blood down
when standing what dos pressure depend on
where in the body
eg in foot 25mmHg from heart plus 80mmHg because of gravity - total of 105mmHg
ih heart bp 120/80, above is lower because the blood is pushed down, belwo is lower because trying to get blood back to heart
describe the bp when lying down
it is the same across the whole body
affect of standing on veins
increased hydrostatic pressure in bv of legs
veisn expand - distension
increased blood in the venous system
reduced blood in arteries - reduce arterial pressure (which is just bp)
this is blood pooling
what is the effect of increased hydrostatic pressure in leg vessels
more fluid forced out of the vessels and into the tissues by the additional pressure from gravity
why does standing cause a hypotensive effect
more venous distension and capillary fluid loss
so smaller venous return and by the Starling mechanism small CO because smaller EDV and so contractility of the heart
therefore drop in bp so CO reduced
how does the body attempt to increase CO
from the thoracic and lumbar spinal levels the sympathetic neurons are activated
NA is released at the NMJ as a NT
adrenaline is released from adrenal medulla - has a hormonal effect on heart - adrenoreceptors
increase heart rate an force of contraction
relationship between adrenaline and NA
similar
but NA gets about by the bloodstream
how does the body attempt to increase TPR
the sympathetic nerves from the thoracic and lumbar spinal levels innervate bv (and adrenal medulla which releases adrenaline that acts on the bv)
increase vasoconstriction
increase TPR
increases BP
summarise the baroreceptor reflex from changing posture
gravity force blood to pool in legs less venous return lower CO lower arterial pressure reduced firing by barorecepotors increased sympathetic activity reduced parasympathetic activity increase contractility and HR vasoconstriction - improves venous return, contract veins to return blood
what happens if you have postural hypotension
baroreceptor reflex normally kick in quickly - so you don’t notice the hypotesion
but in postural hypotension reflex not working properly, bp remain low, don’t get enough perfusion to the brain because autonomic doesn’t work effectively. baroreceptors respond but ANS doesn’t work
how does the body compensate for postural hypotension
if perfusion of the brain is ineffective, the brain switches off - faint
this removes the effect of gravity so the Bp can return to normal
what is in control of the iris muscle
the autonomic system
where is th postganglionic neuron in the eye
it is part of the PNS
goes around the iris and controls the pupil
affect of PNS being switched on, on the pupil
constricts
effect of pilocarpine
act like ACh
pupil constricts
effect of tropicamide
block PNS
massive dilation
what is the normal effect of the PNS on the pupil
keeps it mildly constricted
describe the papillary light reflex
light activates the optic nerve - afferent nerve
signal received in the pretectal nucleus - kick starts the efferent nerve
synapse in the Edinger Westphal nucleus to oculomotor nerve which travels into the ciliary ganglion (parasympathetic)
effect of the oculomotor nerve being activated by light
pupil constricts
effect on other eye to the one stimulated by light
both pupils constrict
optic nerve activates both parasympathetic nerves
clinical benefit of both eyes constricting
can detect lesions
what is the fact that both eyes called
consensual light reflex
if light in R eye, R eye constrict L eye doesn’t where is the problem
efferent supply to L eye
if shine in R, nothing in R AND shine in L and response in both where is the problem
r optic nerve
