Muscle physiology Flashcards
3 types of muscle cell
cardiac (cardiomyocyte), skeletal, smooth
How can muscle cells be classified?
Striated vs smooth or voluntary vs involuntary
Which muscle cells are striated?
Skeletal and cardiac
Why are skeletal muscle cells also known as fibres?
Due to varying length
Where is smooth muscle found?
Blood vessels, tracts, GIT, bladder, lungs
Which muscle cells are classed as involuntary?
Cardiac and smooth
Despite being involuntary, how can smooth muscle be indirectly controlled?
Exercising can bronchodilation and vasodilation of blood vessels supplying the active skeletal muscles and vasoconstriction of blood vessels supplying the viscera. Or eating a big meal
How can cardiac cells be controlled indirectly?
Exercising increases contraction
Function of muscle
contract and relax to create movement
Which part of the nervous system controls skeletal muscle?
Somatic NS
Which part of the nervous system controls cardiac and smooth muscle?
Autonomic NS
How is cardiac muscle contraction controlled?
By SAN in right atrium; however, can be altered by nervous input from ANS.
What does an electrochemical gradient refer to?
The difference in concentration and difference in charge (usually concentration difference (chemical gradient) has a greater influence than the electrical gradient).
What is the resting membrane potential (Em)?
The potential difference between the inside and outside of the cell (inside - outside)
What is the resting membrane potential (Em) in muscle?
-90mV
How is the resting membrane potential of muscle -90mV?
Na+/K+ ATPase pumps out 3 Na+ and 2 K+ in. Creates a net transfer of + charge out of the cell which makes the inside negative.
Why does Na+/K+ ATPase require ATP?
Because it moves Na+ and K+ against their concentration gradients
Name of channels that allow a continual small outflux of K+ and influx of Na+
passive leak channels
3 types of gated channels important for AP generation
Chemically regulated channels (e.g. ligand-gated at synapse), voltage-gated channels, mechanically regulated channels (e.g. stretch-mediated)
Stages of an AP
- Graded potential reaches threshold
- voltage-gated Na+ channels open causing depolarisation
- Once +40mV is reached, voltage-gated Na+ channels close and voltage-gated K+ channels open
- K+ ions move out of the cell causing repolarisation
- K+ overshoot causes hyperpolarisation
- resting membrane potential is restored.
Why is the AP described as being an all-or-nothing event?
Once threshold has been reached and voltage-gated Na+ channels open, there is no stopping the AP
How long does the refractory period last?
From the time the AP begins until resting potential is restored
What causes the static contraction of skeletal muscle?
Constant firing of APs
How do the duration of APs differ between muscle cells?
Cardiac muscle cells have a longer AP (200ms) than skeletal muscle cells (5ms) because there is a delay in the opening of voltage-gated K+ channels in cardiac muscle. This leads to longer, less frequent contractions.