Control Of Cardiac Function

Question 0

What causes the pacemaker potential (funny (If) current) ?

Answer 0

Sodium moves into the cell and a small amount of potassium

Question 1

Why do pacemaker cells spontaneously depolarise?

Answer 1

Because they have a pacemaker current (funny current)

Question 2

How is the funny channel unusual?

Answer 2

Funny channel opens when membrane is hyperpolarised (more -Ve)

Question 3

When is the funny channel open?

Answer 3

When the membrane is hyperpolarised (more -Ve)

Question 5

When the funny channel is open sodium moves into the cell, this causes what to happen to the membrane?

Answer 5

Starts to Depolarise

Question 6

As the membrane depolarises the inward rectifier current is reduced how does this affect the membrane?

Answer 6

Funny current dominates increasing depolarisation

Question 7

There are 2 types of calcium channels what are these known as?

Answer 7

L-type (long lasting) T-type (transient)

Question 8

The opening of T-type calcium channels has what effect on the membrane and how?

Answer 8

Increased depolarisation caused by influx of calcium into the cell

Question 9

When the funny channel is open what enters the cell?

Answer 9

Sodium

Question 10

What does the inward rectifier current do?

Answer 10

Allows potassium to leave the cell

Question 11

What causes repolarisation of the membrane?

Answer 11

Acetylcholine activates voltage gated potassium Channels; efflux of potassium re-polarises membrane

Question 12

What causes the membrane to become hyperpolarised?

Answer 12

Calcium channels inactivate

Question 13

How is the pacemaker potential initiated?

Answer 13

1. funny current (If) - sodium enters (depolarisation)
2. Inward rectifier (Ik) reduced - less potassium leaves -funny current dominates
3. t-type calcium channel opens - Inc depolarisation - calcium influx
4. L-type calcium channels open at threshold - Huge calcium influx - depolarisation (phase 0)
5. Repolarisation - Ach activated voltage gated potassium channels open - potassium efflux repolarises membrane

Question 14

Is the response time to ANS stimulation quicker for vagal stimulation or for sympathetic stimulation?

Answer 14

Vagal stimulation is fastest

Question 15

Cardiac response to vagal stimulation is rapid. How fast is the change in the heart rate seen?

Answer 15

3 seconds

Question 16

Cardiac response to sympathetic stimulation is slow. How long does it take for the heart rate to change?

Answer 16

About 13 seconds

Question 17

Why is the cardiac response to vagal stimulation faster than for sympathetic stimulation?

Answer 17

Because of the 2nd messenger system - (ACh - direct coupling of MAChr to G protein)
- ACh hydrolyses rapidly

Question 18

What is the sequence of events in the 2nd messenger system when ACh binds to a receptor during parasympathetic stimulation of the cardiac system?

Answer 18

• Ach Binds to receptor
• G protein moves across membrane
• potassium channels open - hyperpolarisation
• calcium channels close - prevents pacemaker potential - HR slows

Question 19

Why is the cardiac response to sympathetic slower than that for parasympatheic stimulation?

Answer 19

slower because more steps required for activation.

• Activation of adenylate cyclase, converts ATP to cAMP,
• cAMP activates protein kinase
• protein kinase then phosphorylates the funny channel and t-type calcium channel

Question 20

why does it take longer for heart rate to return to baseline after sympathetic stimulation of the cardiac sycle than parasympathetic stimulation?

Answer 20

Noradrenaline metabolism and reuptake is slower than hydrolysis of acetylcholine.

Question 21

Which ANS system is responsible for beat to beat changes in heart rate ?

Answer 21

Parasympathetic nervous system