Cellular And Molecular Events

Question 1

What do action potentials trigger in cardiac myocytes?

Answer 1

Increases in cystolic calcium.

Question 2

Describe the shape of the ventricular action potential:

Answer 2

Voltage gated sodium channels open and there is sodium influx which gives a sharp peak. There is then a little drop in membrane potential due to opening of K channels. There is a small decrease as calcium influx occurs and then these channels inactivate and the membrane potential is reached after the voltage gated K+ channels open and there is K+ efflux.

Question 3

What is the name of the slow rise in membrane potential during the action potential on the sino-atrial node?

Answer 3

Funny current.

Question 4

What ion channel is responsible for the funny current?

Answer 4

Na channels.

Question 5

In the sinoatrial node action potential, state which channel is responsible for each the upstroke and the downstroke.

Answer 5

Upstroke: calcium channels, downstroke: potassium channels

Question 6

Why aren’t voltage gated Na channels responsible for the funny current? What channel opens instead?

Answer 6

These would inactivate and therefore there would not be sufficient Na influx. HCN channels.

Question 7

What is a HCN channel?

Answer 7

Hyper polarisation activated cyclic nucleotide gated channel

Question 8

What property of the sinoatrial node means that it sets the heart rate?

Answer 8

It is the fastest to depolarise

Question 9

Where are nuclei positioned In cardiac muscle?

Answer 9

They are singly and centrally located.

Question 10

Name two features which differentiate cardiac muscle from other kinds of muscle

Answer 10

Branching and gap junctions

Question 11

What is the purpose of gap junctions in cardiac muscle?

Answer 11

They allow ion move,net across them and so electrically couple the cells.

Question 12

Name the two ways in which cystolic calcium increases during the ventricular action potential.

Answer 12

L-type calcium channels in the t tubule system permit movement of calcium across the sarcolemma and CICR channels permit movement of calcium out of the SR.

Question 13

What happens to cystolic calcium after muscle contraction?

Answer 13

It is pumped back into the SR by SERCA to maintain the calcium store.

Question 14

What pumps in the membrane cause calcium efflux after contraction?

Answer 14

Na/Ca exchanger and sarcolemma Ca ATPase

Question 15

What cells are responsible for the tone of blood vessels?

Answer 15

Smooth muscle cells in the tunica media.

Question 16

Name two causes of excitation-contraction coupling in smooth muscle cells:

Answer 16

Depolarisation which allows Ca to enter the cell by voltage gated Ca channels
Noradrenaline which binds to a1 receptors and releases IP3 which acts on SR leading to increased calcium.

Question 17

How does increased calcium lead to contraction in smooth muscle cells?

Answer 17

Calcium binds to calmodulin which activates myosin light chain kinase which phosphorylates the myosin heads and means they can. Interact with actin.

Question 18

How does smooth muscle contraction stop as calcium levels decline?

Answer 18

Myosin light chain phosphotase dephosphorylates the myosin light chain so it can no longer interact with the actin filaments.

Question 19

What molecule can phosphorylate myosin light chain kinase and what does this cause?

Answer 19

Protein kinase A. Inhibits action of MLCK and so there is increased vasomotor tone.