Excitation Contraction Coupling in Cardiac and Skeletal Muscle Flashcards
What is excitation contraction coupling ?
A process by which there is a conversion of an electrical signal to a mechanical process (contraction of muscle).
Briefly describe what happens at the neuromuscular junction when muscle cells are innervated
Electrical signal propagates down to the axon terminal.
Change in membrane potential opens Ca channels.
Influx of Ca enables synaptic vesicles to fuse with the membrane.
ACh diffuses across the synaptic cleft and binds to nicotinic receptors.
Change in conformation causes them to open.
K+ moves out of the muscle and Na+ moves in.
Influx of Na+ causes depolarisation of the plasma membrane.
Allows threshold potential to be reached and action potential is fired.
Describe the nicotinic receptor
Ligand gated
Change in conformation by ACh binding
Describe depolarisation of the muscle fibre
Propagation of an action potential deep into the tissue through T tubules.
Change in membrane potential, which activates the voltage gated Ca2+ channels, called the DHP receptors.
This activation causes a conformational change of the channel, which allows direct coupling between DHP receptor and type 1 ryanodine receptor.
As the DHP couples with the ryanodine receptor (located in the SR), the ryanodine receptor opens, allowing Ca2+ to flow out of the stores into the cytoplasm.
Concentration of Ca2+ reaches a critical concentration which allows it to bind to troponin C, enabling actin and myosin filaments to slide across each other, causing muscle contraction.
Describe features of skeletal muscle action potential
The action potential is very brief, Na+ flows in causing a rapid depolarisation.
There is a lag between the action potential and a change in tension (onset of response)
State a key difference between cardiac and skeletal muscle action potential
Contraction of skeletal muscle doesn’t overlap with the action potential. There is a lag period.
What is a latent period ?
The time between the peak of action potential to the onset of the contractile response (onset of tension).
Why does a latent period exist ?
As the electrical signal generated from the action potential has to be delivered deep into the tissue fibre.
What is the T tubule system ?
A membrane invagination into the tissue, which allows the depolarisation of the membrane to be delivered into the muscle fibre.
What is the role of transverse tubules in contraction ?
Allows depolarisation of membrane to be delivered deep into the tissue.
What is the function of the sarcoplasmic reticulum ?
The internal calcium store in muscle.
Major Ca2+ store.
What is the role of the terminal cistern in contraction ?
The end regions of the sarcoplasmic reticulum are called the terminal cistern.
They store Ca2+ ions.
What is a key driver of tension ?
An elevation of intracellular calcium concentration.
Calcium binds to troponin C which allows contraction to occur.
Why is there no requirement for extracellular Ca2+ during the activation of contraction ?
The direct coupling between the DHP and ryanodine receptors drives the process of excitation contraction coupling in skeletal muscle.
State the junctional foot proteins involved in mechanism of Ca2+ release
DHP (Dihydropyridine receptor)
- L-type voltage gated calcium channel in the T tubule membrane
Ryanodine receptor
- Calcium release channel in the SR
