Muscles Flashcards
Describe skeletal muscle contraction in relation to control of calcium ions.
- Nerve action potential
- Diffusion of acetylcholine across synaptic cleft and binding to acetylcholine receptors
- End-plate potential
- Muscle action potential
- T-tubules depolarise and open calcium ion channels of sarcoplasmic reticulum
- Intracellular calcium increases
- Muscle fibre contracts
- Calcium ions pumped back into sarcoplasmic reticulum and muscle fibre relaxes
What is excitation-contraction coupling?
Between t-tubules and sarcoplasmic reticulum. T-tubules are invaginations of the sarcolemma that conducts action potentials towards the centre of muscle fibre. So when t-tubules depolarise, fibre contracts.
What is the sliding filament theory?
Actin and myosin interact, causing a cross bridge and so contraction. As all the sarcomeres in the muscle shorten, the entire fibre shortens in contraction. Actin and myosin filaments slide over each other in the sliding filament theory.
How do calcium ions and ATP control muscle force?
- Increase in intracellular calcium ion concentration
- Calcium ions bind to troponin
- Conformational change in troponin complex
- Moves tropomyosin out of the way
- Actin can now bind to myosin at myosin binding sites
- ATP used to move myosin head
- cross bridge formation as actin and myosin interact
What is the length-tension relationship in skeletal muscle?
Resting muscle length is at approximately the optimal length for maximum tension in contraction. If skeletal muscle is shorter/longer than the optimal, contraction is weaker.
Name 3 examples of smooth muscle locations in the body.
- Regulates tube diameter, such as in blood vessels
- Rhythmic waves of contraction, such as peristalsis
- Piloerection in retina - controlling how much light enters the eye
What is single unit smooth muscle?
This is 99% of smooth muscle.
Has coordinated contraction as a functional unit via gap junctions. Some have spontaneous activity, auto-arrhythmic or tonic.
In GI tract, uterus and bladder.
What is multi unit smooth muscle?
Each fibre contracts independently with no gap junctions. They are stimulated by autonomic neurones, no spontaneous activity.
Ciliary and piloerector muscles, for example.
How is smooth muscle controlled?
Lacks striation, troponin and t-tubules. So, calcium ions enter cells via voltage gated channels and from the sarcoplasmic reticulum, where they bind to calmodulin (troponin calcium binding protein). This phosphorylates myosin, which forms cross bridges with actin, causing contraction.
What is electrical coupling of cardiac muscle?
Desmosomes in intercalated discs stick together to make cardiac muscle strong. Gap junctions in intercalated discs allow cells to act in functional syncytium. For contraction, a wave of depolarisation must flow through gap junction of heart cells.
What is the difference between nerve and cardiac action potentials?
Cardiac takes longer because calcium ions move in cardiac cells at phase 2 of action potential during plateau. More calcium ions are released from sarcoplasmic reticulum in calcium induced calcium release.
Describe excitation-contraction coupling in cardiac muscle.
Cardiac muscle action potential > calcium ions enter in plateau > induces calcium induced calcium release from sarcoplasmic reticulum > calcium ions bind to troponin C > cross bridges > contraction > calcium ions move back into sarcoplasmic reticulum
Compare smooth and cardiac muscles in terms of calcium ions.
Skeletal: voltage gated calcium ion release from sarcoplasmic reticulum. Calcium ATPase in sarcoplasmic reticulum to remove calcium ions from cytosol.
Cardiac: calcium induced calcium release from the sarcoplasmic reticulum. Calcium ion ATPase and sodium-calcium exchangers to remove calcium ions from cytosol.
