Lecture 6

Question 1

Describe the ON mechanisms for calcium

Answer 1

Voltage gated calcium channels/L-type channels brings in trigger calcium, Type 2 RyR in SR membrane which cause CICR.

Question 2

Where does trigger calcium come from?

Answer 2

Extracellular matrix through VOC.

Question 3

Where does the calcium released in CICR come from?

Answer 3

the SR

Question 4

Describe some OFF mechanisms

Answer 4

SERCA pump regulated by phospholambam, PMCA, Na/Ca exchanger which needs an inwards sodium gradient which is maintained by Na/K ATPase.

Question 5

What are beta-1 receptors coupled with?

Answer 5

Adenyl cyclase which generates cAMP from ATP which activates PKA.

Question 6

What are some PKA substrates?

Answer 6

Phospholambam, VOCC, RyR.

Question 7

Where does the heart beat initiate?

Answer 7

The SA node

Question 8

Where does the depolarisation spread rapidly to?

Answer 8

The AV valve. there is a delay where while the atrial muscular tissue is depolarised more slowly

Question 9

Describe the SA node

Answer 9

Autorhythmic, set own rate of depolarisation, frequency sets the heart beat. pacemaker tissue constantly firing action potentials to heart muscle.

Question 10

Describe phase 0 of ventricle muscle action potential

Answer 10

Rapid depolarisation due to inward sodium current

Question 11

Describe phase 1

Answer 11

Overshoot due to small outward potassium movement starting to repolarise

Question 12

Describe phase 2

Answer 12

Plateau phase where calcium/trigger calcium is coming in which keeps membrane potential high.

Question 13

Describe phase 3

Answer 13

Repolarisation due to outward potassium current

Question 14

Describe phase 4

Answer 14

resting

Question 15

How long does the action potential in ventricular muscle last?

Answer 15

300ms (compared to 4ms in neuronal AP).

Question 16

What is the key difference between muscle cell AP and neuronal AP?

Answer 16

Muscle cell has inward calcium which creates plateau phase.

Question 17

At what point of the cycle does peak contraction occur?

Answer 17

Just before repolarisation.

Question 18

What part of the cycle is the absolute refractory period?

Answer 18

From the start of the depolarisation to the end of repolarisation.

Question 19

What prevents tetany?

Answer 19

The long refractory period.

Question 20

How does atrial plateau phase differ?

Answer 20

Not as pronounced because there are fewer VOC channels as the atria do not need as strong a contraction as the ventricles.

Question 21

How does the SA node AP differ?

Answer 21

Slower rate of depolarisation, reduced overshoot, no plateau because no calcium and no contraction. smaller amplitude

Question 22

Why is the SA node a slower response?

Answer 22

The resting membrane is less negative because there is less potassium channels. Progressive spontaneous depolarisation of the cell to threshold occurs due to slow inward movement of sodium. depolarisation occurs due to inward calcium current which is slower than sodium.