Muscle Physiology

Question 1

What kind of muscle is striated?

Answer 1

Skeletal and heart

Question 2

Smooth muscle has what kind of control?

Answer 2

Involuntary

Question 3

What is responsible for the contraction of muscles?

Answer 3

The action potential.

Question 4

In striated muscle, what are the contractile units called?

Answer 4

Sarcomeres

Question 5

In striated muscle what do the contractile units consist of?

Answer 5

Actin and myosin

Question 6

How does smooth muscle contract?

Answer 6

Bands across the transverse and longitudinal section contract.

Question 7

What is the charge of intracellular fluid?

Answer 7

Negative

Question 8

Why is intracellular fluid negative?

Answer 8

Passive leak.

3 Na move out (whilst 2 k in) net loss of positively charged ions.

Question 9

What opens a chemical gated channel?

Answer 9

e.g. neurotransmitter

Question 10

What opens a voltage gated channel?

Answer 10

Membrane potential reaches a critical level.

Question 11

What opens a mechanical gated channel?

Answer 11

A stretch/pressure applied.

Question 12

Explain the action potential mechanism.

Answer 12

Na channel originally inactivated.

Once the threshold is met, the channels open and allow depolarisation occur. = action potential.

Once action potential sent, the Na channels close.
The K channels open.

Once the K channels open, depolarisation occurs.

Question 13

Explain exitation-contraction coupling in smooth muscle.

Answer 13

Depolarisation in smooth muscle opens calcium channels in the membrane.

Ca entry induces calcium to be produced from the sarcoplasmic reticulum.
(amplifies the signal)

Ca moves into the myofilaments and causes contraction.
(relaxes once Ca is removed)

Question 14

What is the effect of Ca in skeletal and heart muscle?

Answer 14

Ca in the cytoplasm binds to troponin on the surface of actin. Causes a conformational change that exposes the myosin binding sites.

Question 15

What is the resting potential of muscles?

Answer 15

-90mv

Question 16

In cardiac muscle what ensure ventricular filling?

Answer 16

Plateau phase

Question 17

What is the name of the membrane receptor opened by calcium?

Answer 17

ryanodine

Question 18

What are the ways Ca can leave the myofilaments?

Answer 18

Through the CERCA channels-require ATP.

Plasma membrane calcium ATPases.

Sodium calcium exchanger.

Question 19

Describe the function of troponin and tropomyosin.

Answer 19

In a relaxed muscle tropomyosin prevents the myosin head from binding to actin.

Question 20

What is troponin? What are its 3 subunits?

Answer 20

Troponin is the groove on actin that myosin binds to.

subunits are:
TnT
TnL
TnC

Question 21

Explain the process of Ca binding to actin.

Answer 21

Calcium binds to the TnC subunit of troponin.

Ca binding causes a conformational change.

Conformational change pulls tropomyosin away from troponin and myosin can bind.

Question 22

What does smooth muscle lack?

Answer 22

(Has actin and myosin) Doesn’t have troponin and tropomyosin.

Question 23

In smooth muscle explain the process of Ca and binding of myosin.

Answer 23

Ca binds to calmodulin.

Conformational change occurs which activates myosin light chain kinase,

The MLCK phosphorylates the peptide on the myosin head and it binds to actin.

Question 24

What is required to relieve contraction?

Answer 24

ATP. Ca exit via CERCA requires ATP.

Question 25

List abnormalities leading to disease (heart and skeletal muscle).

Answer 25

Calcium sparks: RyR opens when it shouldn’t, releasing small amounts of calcium.

Arrhythmia: RyR open and closes more frequently and uncontrollably.

Question 26

How can failure of RyR be treated?

Answer 26

Gene therapy to enhance CERCA uptake.

Physical activity also increases CERCA uptake.