Autonomic reflexes

Question 1

If there was no para/sympathetic control at all, your resting heart rate would be

Answer 1

about 100- 110 bpm

PNS+ SNS have a role in maintaining resting heart rate

Question 2

CO, BP, TPR equation

Answer 2

BP= CO x TPR 
CO= HR x FOC (force of contraction)

Question 3

Baroreceptor reflex at rest

slide 8, lecture 12

Answer 3

Signal sent to brain
Activation of parasympathetic nerve and inhibitory nerve leading to reduced sympathetic response→ parasympathetic= dominant
Parasympathetic= slows, sympathetic nerve= speeds

Question 4

Baroreceptor reflex at high BP

slide 9, lecture 12

Answer 4

Increased baroreceptor firing rate= bigger signal going to CNS
Result= greater negative effect on heart rate

Question 5

Baroreceptor reflex at low BP

slide 10, lecture 12

Answer 5

Reduced baroreceptor firing rate

Sympathetic nervous system becomes dominant trying to increase heart rate+ vasocontrction

Question 6

Baroreceptor reflex at change of posture

Problem?

Answer 6

Problem -
When you stand up, blood pressure maintains same level at heart (centre of gravity), higher at bottom and lower at top

Hydrostatic pressure in the blood vessels of the legs with additional pressure from gravity= Venous distension (more blood in the veins than usual) + Capillary fluid loss in limbs= ↓ venous return (Frank- Starling Mechanism) →↓ventriclular filling during diastole (end-diastolic volume) → ↓ volume of ejected blood during the resulting systolic contraction (stroke volume)+ less cardiac output= Less blood volume in arteries= lower arterial blood pressure

Question 7

Baroreceptor reflex at change of posture
Solution?
Diagram (slide 18, lecture 12)

Answer 7

Sympathetic nerve acting on heart= releasing Noradrenaline
Also adrenal gland (only one nerve innervating it), releases Adrenaline by bloodstream
Both act on adrenoreceptor
↑HR + FOC= ↑CO
Also ↑vasoconstriction= ↑TPR

Question 8

Postural hypotension problem
Identify problem on diagram from (slide 20, lecture 12)
Solution

Answer 8

During postural hypotension baroreceptor reflex doesn’t function properly (baroreceptors are sending signals but the ANS is impaired, which is why you feel dizzy
Emergency situation= to make you faint if the baroreceptor reflex doesn’t work.
Fainting= takes the gravity effect out which helps the situation

Question 9

Pupillary light reflex controlled by

Answer 9

Reflex is driven by autonomic control of the iris muscle

Question 10

Pupillary constriction

Answer 10

Oculomotor nerve (labelled)= parasympathetic nerve, preganglionic nerve that synapses in the ganglia very close to the eye which then results in a very short post ganglionic nerve that helps contraction of iris muslce
Parasympathetic nerve releases Ach to the eye= pupil constriction

Question 11

Drugs that inhibit/ stimulate pupillary light reflex

Answer 11

If you block these effects (Tropicamid) you see dialation= parasympathetic nervous system is constantly keeping the pupil constricted a bit
Pilocarpine aids pupillary constriction, stimulates PNS

Question 12

identify the pre- and post-ganglionic PNS nerves?

slide 25, lecture 12

Answer 12

Light comes in and activates the optic nerve (afferent nerve relaying information to the brain)
Received in the pretectal nucleus which kickstarts efferent response
Leads to preganglionic and post ganglionic fibres leading to constriction/relaxation of iris muslce

Question 13

Consensual (both) light reflex
slide 27, lecture 12

You achieve a direct response in the right pupil without a consensual response in the left pupil. Where is the lesion?

Answer 13

In lots of light, activates parasympathetic nervous system
In less light, leads to pupil dialation
No matter which eye is affected, both eyes respond (both parasympathetic nerves are activated)
Problem which efferent supply to the left eye