muscle contraction

Question 1

what are the types of muscles

Answer 1

• skeletal
• cardiac
• smooth

Question 2

Cardiac Muscle

Answer 2

• Make up the muscular walls of the heart (myocardium). It is ‘involuntary’ because its contractions are not under your control.
• Has a similar structural organisation to skeletal muscle. Including striation.

Question 3

Smooth Muscle

Answer 3

• Found in the walls of most blood vessels and tubular organs such as the intestine. It is also ‘involuntary’.
• Does not have a stripy appearance as it does not have repeating sarcomeres. More randomly arranged than in skeletal or cardiac muscle.

Question 4

skeletal muscle

Answer 4

striated

voluntary contractions

Question 5

a. explain skeletal muscle contraction

Answer 5

• each skeletal muscle consists of a collection of motor units - 1 motor neurone controls number of muscle fibres
• single branch of motor axon supplies a single muscle fibre
• action potential - calcium ions flow in - acetyl choline released - sodium enters muscle fibres = depolarisation in neurone which is propagated = known as excitation = contraction coupling
• Depolarisation of the membrane during the muscle action potential spreads along the T tubules
• This causes voltage-gated Ca2+ channels in the sarcoplasmic reticulum to open. Releasing the Ca2+ into the sarcoplasm.
• Ca2+ binds to troponin and changes its position on the actin molecule permitting actin and myosin head groups to attach

Question 6

Sliding filament theory - cross bridge cycle

Answer 6

• Depolarisation of the membrane during the muscle action potential spreads along the T tubules
• This causes voltage-gated Ca2+ channels in the sarcoplasmic reticulum to open. Releasing the Ca2+ into the sarcoplasm.
• Ca2+ binds to troponin and changes its position on the actin molecule permitting actin and myosin head groups to attach
• thick myosin filaments have 2 globular heads - forms cross- bridges with the neighbouring thin actin molecules.
• ATP is bound by the myosin causing actin and myosin to dissociate. This causes a change in the angle of the head region of the myosin
• The myosin head binds again ith the next actin-myosin binding site. This process is called cross-bridge cycle.

Question 7

b. plot a classical experimental length-tension curve for a single muscle fibre, and interpret it in terms of the sliding filament theory

Answer 7

look at pcs bible

The sarcomeres were a fixed length at rest, but during muscle contraction the size decreases as the filaments contract and slide together

maximal tension when the muscle is at its resting state, if you stretch the muscle the tension is much lower

resting = maximum overlap between the head groups of the myosin and the actin filaments

Question 8

c. describe the role of calcium in muscle contraction, including triggering of contraction, release and re-uptake