9- autonomic reflexes

Question 1

How is CO controlled

Answer 1

The ANS affects both cardiac output AND total peripheral resistance
• CO=SVxHR
• Sympathetic stimulation of the heart causes:
Inotropic Effect (increased SV) Chronotropic Effect (increased HR)

• noradrenaline binds to the adrenergic receptors in the cardiac muscle causes an increase in the force of contraction
• Sympathetic nerves release noradrenaline to the adrenergic receptors in the SAN which causes an increase in heart rate
• The sympathetic nervous system tends to cause mass vasoconstriction
• This causes an increase in total peripheral resistance

Question 2

Describe the barorecceptor reflex

Answer 2

re is a DECREASE in blood pressure:
Firing rate from the baroreceptors decreases There is less stimulus to the brain
You get a decrease in the INHIBITION of the SNS Sympathetic activity increases

Question 3

What is the cardiovascular response to standing

Answer 3

When you stand up you are bringing GRAVITY into play - gravity tries to push the blood down to your feet
• As the veins are distensible, you can get blood pooling in the lower limbs
• If you have more blood pooling in the veins, then there is reduced venous return so a lower blood pressure
Decreased cardiac output therefore decreased arterial blood pressure
(STARLING’S LAW)
• This decrease in blood pressure causes activation of the baroreceptor reflex
• Decreases stimulation of the baroreceptors means that less stimulus is
delivered to the brain to switch off the sympathetic nervous system so there is an increase in activity of the sympathetic nervous system and so blood pressure increases (due to an increase in SV, HR and vasoconstriction)

Question 4

What is postural HT

Answer 4

Autonomic (sympathetic) impairment:
• Acute reduced sympathetic response
• Postural Hypotension
Blood flow to the brain is impaired resulting in loss of consciousness Once body is supine:
• Blood flow to the brain is restored
• Consciousness is (usually) regained

Question 5

What is the consensual reflex

Answer 5

Consensual Reflex - if you shine light in one eye, both pupils will contract
• This happens because the afferent information CONVERGES on the pretectal nucleus

Question 6

How are the pupils controlled

Answer 6

Sympathetic:
1. Pupil dilation
By innervation of radial muscle

Parasympathetic:
1. Pupil constriction
By innervation of circular muscle/sphincter pupillae

2. Accomodation for near vision, lens thickening
   By innervation of ciliary muscle

Pilocarpine stimulates Parasympathetic
Tropicamide inhibits parasympathetic

Question 7

Describe control of the bladder

Answer 7

Sympathetic nervous system (stop peeing)

1. Relaxes detrussor
2. Contracts internal sphincter

Parasympathetic nervous system (start peeing)

1. Contracts detrussor
2. Relaxes internal sphincter

Somatic nervous system
1. Controls external sphincter

Question 8

Describe innervation of the lungs

Answer 8

Lungs

Sympathetic nervous system
Pre-ganglionic neurone to adrenal medulla
Release of 80% adrenaline and 20% noradrenaline
1. Dilates bronchi and bronchioles

Parasympathetic nervous system
Pre-ganglionic neurone to ganglia near lungs
Release of ACh
1. Constriction of bronchi and bronchioles

Question 9

Describe control of the GIT

Answer 9

Sympathetic nervous system

1. Motility/Tone: decreased
2. Sphincter: contracted
3. Secretions: inhibited

Parasympathetic nervous system

1. Motility/Tone: increased
2. Sphincter: relaxation
3. Secretions: stimulated