Autonomic Reflexes Flashcards
How to work out blood pressure?
BP= CO/TPR TPR= total peripheral resistance
How to work out cardiac output?
CO=HR X FOC
FOC= Force of contraction
What would be the heart rate if your autonomic nervous system was not working?
100-110 bpm
What receptors control blood pressure/
Arterial baroreceptor.
Sense pressure in the system, relaying it back to the brain via the afferent.
Brain determining the level of autonomic activation, and is then passed down to the heart etc.
Baroreceptor are positively linked to parasympathetic nerve and negatively to sympathetic nerve.
How does the baroreceptor reflex work at rest?
Baroreceptor firing, the parasympathetic nerve is stimulated and the inhibitory interneuron in the sympathetic is activated which inhibits the sympathetic nerve.
The parasympetheic is dominant.
what happens when blood pressure is very high?
High baroreceptor firing which activates parasympathetic, the firing rate increases so a more bigger activation of the parasympathetic nerve and a bigger inhibition of the sympathetic nerve.
— therefore even greater negative effect on the heart.
what is the relationship between the blood pressure and the baroreceptor firing?
the baroreceptor is proportional to the pressure in the blood
How does the blood pressure differ when standing and lying down?
When you are lying down, the blood pressure is the same throughout the body but when standing:
heart rate on the heart is the normal rate.
Above the heart is lower because it is working with gravity and below the heart the rate is above as it has to work against gravity.
What happens when we stand up
-increase hydrostatic pressure in the blood vessels of the legs.
Venous distension (blood pooling in your leg), veins very distensible, the veins have added gravity and pressure so will expand, therefore more blood in the vein than usual.
- the more blood volume in the vein the less will be in the arteries.
-the high hydrostatic pressure due to added pressure fro gravity means more capillary fluid loss, particular in the lower limb.
- this induces a hypotensive effect because
- this is because less blood being returned to the heart
-therefore decreased venous return ( Frank-starling mechanism)
- so reduced cardiac output
-so blood pressure decreases
How can we increase heart rate when it decreases?
Increase heart rate.
- Sympathetic nerve innervate the heart and release noradrenaline to increase heart rate.
- adrenaline: only one nerve innervating it, the sympathetic nerve, main thing produced is adrenaline, acts like noradrenaline but travelled by the blood to the heart.
- Act on the adrenoreceptor and increase heart rate
OR
- increases total peripheral resistence which will increase heart rate
- done via the sympathetic nerve.
What happens as soon as you stand?
- Pooling of blood in lower limbs
- reduced venous return
- reduced CO
- arterial pressure drops
- leads to firing by baroreceptors
- leads to more sympathetic activation due to less inhibition of the sympathetic nerve.
What is postural hypotension?
when they get up from sitting to standing;
- feel dizzy
- blood pressure drops
- baroreceptor doesn’t work properly
- so blood pressure stays low
- poor perfusion to the brain so they feel dizzy
- the baroreceptor says to increase heart rate but ANS doesn’t work properly
- so the emergency situation is to faint
- they will collapse
- blood flows to the brain: normalise pressure
How does the iris work?
-Sympathetic and parasympathetic innervate the iris.
- the papillary light reflex is driven by the autonomic control of the iris muscle
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What causes postural hypotension?
Impaired sympathetic nervous system response to transient hypotension
Describe the effects of the sympathetic and parasympathetic nervous system on the eye muscles.
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
