autonomic nervous system Flashcards
autonomic reflex arc: recall an example of an autonomic reflex arc and explain pathways involved
what is the baroreceptor reflex involved in
blood pressure control
what is the equation for calculating mean arterial blood pressure
cardiac output x total peripheral distance
how do you calculate cardiac output
heart rate x force of contraction
how do you calculate total peripheral resistance
1/r^4
what branch of the motor nervous system has some influence over heart rate at rest
parasympathetic
function of baroreceptors
sense pressure in system and send signals to brain
along what nerve do signals from baroreceptors reach the brain
afferent vagus nerve
what branch of the motor nervous system do baroreceptors stimulate
parasympathetic nervous system
what branch of the motor nervous system do baroreceptors inhibit
sympathetic nervous system
how do baroreceptors cause blood pressure to be maintained at rest
constant firing rate from baroreceptor to brain (afferent vagus nerve) activates parasympathetic nerve (efferent vagus nerve) to heart and activates the inhibitory nerve to the sympathetic nerve; this reduces the sympathetic response and increases the parasympathetic response to heart, arterioles and veins, meaning heart rate is lowered and diameters of blood vessels are increased, maintaining the correct blood pressure
how do baroreceptors cause high blood pressure to be lowered
arterial baroreceptor firing rate increases so much bigger signal sent to brain, causing a much bigger activation of the parasympathetic nerve to heart and a much bigger activation of inhibitory nerve to sympathetic nerve; this causes a much bigger reduction in the sympathetic response to heart, arterioles and veins, meaning heart rate is lowered and diameters of blood vessels are increased, lowering blood pressure
how do baroreceptors cause low blood pressure to be increased
arterial baroreceptor firing rate decreases so much smaller signal sent to brain, causing a much smaller activation of parasympathetic nerve to heart and a much smaller activation of inhibitory nerve to sympathetic nerve; this causes a much bigger sympathetic response to heart, arterioles and veins, meaning heart rate is increased and diameters of blood vessels are decreased, increasing blood pressure
how does changing posture alter blood pressure
gravity
where is blood pressure neutralised when standing
at heart
where is blood pressure lower when standing
above heart
where is blood pressure higher when standing
below heart
when standing, how does increased hydrostatic pressure in leg blood vessels lead to lower arterial blood pressure
increased hydrostatic pressure in leg blood vessels → venous distension so more blood in venous system than normal → less blood in arteries → less pressure in arteries
when standing, what does increased hydrostatic pressure in leg blood vessels also cause in capillaries
extra capillary fluid loss
what is the result of venous distension and capillary fluid loss when standing
reduced venous return so lower cardiac output and less TPR so lower blood pressure in arterial system
how is cardiac output increased when standing up to increase blood pressure by noradrenaline
increase heart rate or force of contraction via sympathetic nervous system (noradrenaline)
how is cardiac output increased when standing up to increase blood pressure by adrenaline
adrenal gland sympathetic nerve produces adrenaline which travels up to heart and increases HR and FOC (also causes vasoconstriction to increase TPR)
what is postural hypotension
impaired autonomic function so less effective at increasing cardiac output, causing blood pressure to stay low especially at the brain (cerebral hypo-perfusion), causing fainting
why do people faint with postural hypotension
by lying down, gravity has no effect
what drives the pupillary light reflex
autonomic control of iris muscle
parasympathetic nerve: location of pre- and post-ganglionic fibres
longer pre-ganglionic fibre to ganglion near eye, short post-ganglionic fibre to control iris muscle
what neurotransmitter is released by the parasympathetic nerves in the pupillary light reflex
acetylcholine
what drug is also used to mimic acetylcholine
pilocarpine
what is the outcome on the pupil of parasympathetic activation
constriction
what drug can block parasympathetic activation and cause pupil dilation
tropicamide
what branch of the motor nervous system has some influence over pupil constriction at rest
parasympathetic, as pupil is mildly constricted
pupillary light reflex: when light enters, what nerve is activated
sensory optic nerve II
pupillary light reflex: where is the information sent to
pretecal nucleus in brain
pupillary light reflex: once effector response is created, what nerve is activated
pre-ganglionic ocular nerve III to ciliary ganglion, then post-ganglionic ocular nerve III to iris muscle
pupillary light reflex: what is the outcome of light presence
constriction (more light caused more constriction)
pupillary light reflex: what occurs if the stimulus is only present in one eye
both eyes respond - doesn’t matter if stimulus is only present in one eye
pupillary light reflex: if there is a response in the right eye but not left, what does this indicate
sensory optic nerve II and the right side of parasympathetic neurone is fine, but there is a problem in efferent parasympathetic supply in left eye
