Cardiac mechanoreceptors

Question 1

what are mechanoreceptors sensitive to?

Answer 1

• sensitive to stretch

Question 2

By what characteristics do mechanoreceptors differ?

Answer 2

• threshold
• range
• action potential frequency
• sensitivity

Question 3

Name the different types of mechanoreceptors relating to the CV system

Answer 3

1.** arterial baroreceptors** (high pressure receptors)
* located in the aortic arch
* located in the carotid sinuses
* located in the coronary arteries
2.Cardiopulmonary mechanoreceptors (low pressure volume receptors)
* veno-atrial regions
* cardiac chambers

Question 4

RECAP - describe the arterial baroreceptors - ie where are the located and what nerves do they form etc

Answer 4

• carotid sinus baroreceptors afferent fibres form the carotid sinus nerve - which then joins to form the glossopharyngeal nerve
• aortic arch baroreceptors afferent fibres run along the vagus nerve

Question 5

RECAP - what part of the brain do the arterial baroreceptors provide information to?

Answer 5

• Nucleus tractus solitarius in the medulla oblongata

Question 6

what is baroreceptor threshold?

Answer 6

• it is the lowest pressure that triggers an action potential
• axon myelination and conduction velocity are important determinants

Question 7

what are the** 2 kinds of baroreceptors** with regards to types of fibres?

Answer 7

• A fibres
• C fibres

Question 8

Describe **A fibres **

myelination, conduction velocity and threshold

Answer 8

• they have a large diameter
• fast conduction velocity as they are myelinated
• low threshold
• active at normal blood pressure

Question 9

Describe C fibers

myelination, conduction velocity and threshold

Answer 9

• the C fibres are narrow and have small diameter
• they have a** low conduction velocity** as they are not myelinated
• they have a** higher threshold** - ie only a small amount of c fibers are active at normal pressures

Question 10

which fibers are more sensitive?

Answer 10

• The A fibres are more sensitive than the C fibers
• as the A fibres have a lower threshold than the C fibres

Question 11

where does maximal carotid sinus baroreceptor activity occur?

Answer 11

at the mean arterial pressure

Question 12

what happens to the A fibres at high pressures?

Answer 12

• they reach a maximum and become saturated
• they are not as responsive at high pressures

Question 13

what are the different types of low pressure volume recpetors in the heart/

Answer 13

• veno-atrial receptors
• cardiac chamber receptors
• pulmonary artery receptors

Question 14

How do veno-atrial receptors become stimulated?

Answer 14

• they become stimulated by an increase in cardiac blood volume
• this stimulates the V-A receptors and they increase their firing

Question 15

When can the maximum activity of veno-atrial receptors happen?

Answer 15

• can occur during atrial systole
• can also occur during the v wave of atrial filling (ie ventricular systole when ventricles push blood into atrias and into the blood vessels)

Question 16

Describe what happens** as a result of the stimulation of A-V receptors**

Answer 16

• tachycardia - due to a selective increase in sympathetic outflow
• diuresis - less sympathetic outflow to the kidneys as lots is going to the heart, so this causes renal vasodilatation

Question 17

what happens as a result of stimulation of cardiac mechanoreceptors?

Answer 17

• activation triggers a depressor effect (to bring varable back to normal levels)
• causes reflex **bradycardia and vasodilatation **