Autonomic Reflexes Flashcards
What are the main effects of the sympathetic nervous system on the CO = MABP/TPR equation?
Sympathetic has an inotropic and chronotropic effect thus SV and HR are increased so CO is increased. Sympathetic firing also causes generalised vasoconstriction so TPR increases.
Describe the response to a decrease in blood pressure.
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.
Describe the changes that take place when you stand up.
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.
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
State two drugs that affect the eye muscles and how they work.
Pilocarpine - acetyl choline drug - causes MIOSIS (constriction)
Atropine - blocks the parasympathetic nervous system - causes MYDRIASIS (dilation)
Describe the pupillary light reflex.
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.
What is the consensual reflex and what causes it?
When you shine a light in one eye, both eyes constrict.
This is caused by the afferent information converging on the pretectal nucleus.
If you achieve a direct response in the right eye with no consensual response in the left eye, where does the problem lie?
There is a problem with the parasympathetic nerves in the left eye.
