cardiac reflexes

Question 1

explain the difference between a depressor reflex and a pressor reflex

Answer 1

• depressor - a variable is restored back to its original value eg arterial bp
• pressor - variable is raised rather than stabilised eg arterial chemoreceptors

Question 2

What are the different cardiac receptors (also include lung)?

Answer 2

• veo-atrial myelinated mechanoreceptors
• muscle work receptors
• atrial chemoreceptors
• lung stretch receptor

Question 3

what part of the brain is important for relaying information to elicit a cardiac reflex?

Answer 3

the **medulla oblongata **
* the NTS receives all the sensory info from afferent fibres
* info is integrated in the NTS and relayed to other regions to modulate the activity of the medulla and elicit some reflex

Question 4

what is the difference between high and low pressure receptors?

Answer 4

• high pressure receptors - atrial baroreceptors located in the carotid sinus & aortic arch
• low pressure - veno-atrial mechanoreceptors located in the atrias

Question 5

what is the role of veno-atrial mechanoreceptors?

Answer 5

• they are sensitive to changes in central venous pressure
• the activation/excitation of these receptors increases the sympathetic activity which increases the heart rate and diuresis

Question 6

Describe the role of** lung stretch receptors**

Answer 6

• lung stretch receptors are activated during inspiration - the lung inhalation reflex
• their input to the brain stem inhibits the cardiac vagal parasympathetic neurons and therefore causes tachycardia
• the inhibitory inputs also cause sinus arrhythmia

Question 7

what is sinus arrhythmia?

Answer 7

an increase in HR during respiration

Question 8

Describe the role of atrial chemoreceptors

Answer 8

• atrial chemoreceptors are stimulated by acidosis and hyperkalaemia and hypoxaemia (low blood oxygen)
• they are located in the carotid bodies (not the sinus)
• during hypoxaemia, the reflex involing the ac’s causes vasoconstriction and increase in blood pressure due to the increase in symp activity

Question 9

What are the 2 types of muscle work receptor?

Answer 9

• mechanoreceptor
• metaboreceptor

Question 10

what are the roles of the muscle work receptors?

Answer 10

• they contibute to **exercise associated increase in HR and blood pressure **
• the muscle **mechanoreceptors **cause a reflex inhibition of cardiac vagal tone and therefore cause an increase in HR
• the muscle metaboreceptors cause a reflex that causes an increase in sympathetic outflow which causes tachycardia and increased cardiac contracitility