L3: Muscle Cell Function Flashcards
• Describe the basic structure of cardiac, skeletal and smooth muscle. • Describe how the membrane potential changes in different muscle types and it’s role in triggering contraction. • Recognise the central role of Ca in muscle contraction. Describe the process by which changes in membrane potential elevate Ca and trigger contraction in cardiac, skeletal and smooth muscle – the process of excitation-contraction coupling.
What is a myocyte?
‘The Muscle Cell’
- Smallest subunit of muscular tissues & organs throughout the body
Structure of the cardiac muscle
Striated, branched & contains many mitochondria, involuntary contraction
Function of the muscle myocyte
Contraction
What are sarcomeres?
Basic unit of muscle fibre composed of actin + myosin
Structure skeletal muscle
Unbranched, striated, voluntary contraction
Structure of smooth muscle?
Spindle shaped, involuntary contraction
What does smooth muscle consists of?
Thick & thin filaments that are not arranged into sarcomeres; resulting in a non-striated pattern
What is a sarcomere?
Basic unit of muscle fibre; composed of actin & myosin
Length of sarcomere?
Distance between 2 adjacent Z lines
Which filaments are thin?
ACTIN
Which filaments are thick?
MYOSIN
What are T-tubules?
Voltage-gated calcium channels
What is a sarcolemma?
Plasma membrane of muscle cell
What happens in neuronal action potential?
Na+ moves into the cell causing depolarisation, K+ moves out of cell causing repolarisation
What happens during a refractory period?
Period where ion channels have not returned to closed state, so another AP cannot be initiated
What is a relative refractory period?
Na+ channels are ready to go, but the membrane potential is too negative, so a bigger depolarisation is needed
When would the cardiac action potential be triggered?
If theres a wave of excitation that spreads across the heart from the sino-atrial (SA) node
What do long refractory periods prevent?
Tetany (involuntary muscle contractions)
Define temporal summation
One heartbeat builds on another beat
Why is the ability to tetanise skeletal muscle important?
Allows us to maintain a contraction, allow the heart to fill with blood & contract again
Benefit of the twitch in cardiac muscle?
Forces the heart to contract & relax as it cannot tetanise
2 important purposes of long duration AP
1) prevents tetany
2) prevents us getting extra beats where we don’t want them
How is an action potential triggered in a skeletal muscle?
Triggered by activation of motor neurone, excitation initiated in the neuromuscular junction
What channels drive the action potential in smooth muscle excitation?
Time-dependent channels
