Muscle Physiology Flashcards
What kind of muscle is striated?
Skeletal and heart
Smooth muscle has what kind of control?
Involuntary
What is responsible for the contraction of muscles?
The action potential.
In striated muscle, what are the contractile units called?
Sarcomeres
In striated muscle what do the contractile units consist of?
Actin and myosin
How does smooth muscle contract?
Bands across the transverse and longitudinal section contract.
What is the charge of intracellular fluid?
Negative
Why is intracellular fluid negative?
Passive leak.
3 Na move out (whilst 2 k in) net loss of positively charged ions.
What opens a chemical gated channel?
e.g. neurotransmitter
What opens a voltage gated channel?
Membrane potential reaches a critical level.
What opens a mechanical gated channel?
A stretch/pressure applied.
Explain the action potential mechanism.
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.
Explain exitation-contraction coupling in smooth muscle.
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)
What is the effect of Ca in skeletal and heart muscle?
Ca in the cytoplasm binds to troponin on the surface of actin. Causes a conformational change that exposes the myosin binding sites.
What is the resting potential of muscles?
-90mv
In cardiac muscle what ensure ventricular filling?
Plateau phase
What is the name of the membrane receptor opened by calcium?
ryanodine
What are the ways Ca can leave the myofilaments?
Through the CERCA channels-require ATP.
Plasma membrane calcium ATPases.
Sodium calcium exchanger.
Describe the function of troponin and tropomyosin.
In a relaxed muscle tropomyosin prevents the myosin head from binding to actin.
What is troponin? What are its 3 subunits?
Troponin is the groove on actin that myosin binds to.
subunits are:
TnT
TnL
TnC
Explain the process of Ca binding to actin.
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.
What does smooth muscle lack?
(Has actin and myosin) Doesn’t have troponin and tropomyosin.
In smooth muscle explain the process of Ca and binding of myosin.
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.
What is required to relieve contraction?
ATP. Ca exit via CERCA requires ATP.
List abnormalities leading to disease (heart and skeletal muscle).
Calcium sparks: RyR opens when it shouldn’t, releasing small amounts of calcium.
Arrhythmia: RyR open and closes more frequently and uncontrollably.
How can failure of RyR be treated?
Gene therapy to enhance CERCA uptake.
Physical activity also increases CERCA uptake.
