Muscle contractions

Question 1

What is the myofibril

Answer 1

a unit of a muscle made up of the sarcomere

Question 2

What is the sarcomere

Answer 2

A structure made up of Actin and myosin filaments

Question 3

Explain the sliding filament theory

Answer 3

when an action potential reaches a muscle, ca2+ ions enter the muscle via the L type Chanel. This causes. More Ca2+ to be released from the sarcoplasmic reticulum, ca2+ binds to troponin c on tropomyosin on the actin filament. This uncovers the actin binding site which the myosin head binds to.the myosin head cocks forward creating tension which shortens the myofibril causing a contraction. ADP is released from the myosin head. ATP binds to the myosin head and Ca2+ is removed from the cell by reverting the SR via a CA2+ ATPase pump. ATPase catalyses the hydrolysis of ATP releasing energy whihc causes the myosin head to return to its original position and the sarcomere return to its original length.

Question 4

Explain the how an action potential travels across a neuromuscular junction

Answer 4

Action potential depolarises the synaptic knob. This causes voltage gated ca2+ Chanel proteins to open causing an influx of ca2+ via diffusion. This causes vesicles contain ACh to release ACh into the synaptic cleft via exocytosis. The ACh binds to nicotinic ACh receptors on the motor end plate. This causes the na+ Chanel’s to open and influx of na+ enter depolarising then end plate. This causes A cascade that leads to a muscle contraction

Question 5

Physical features of the end plate and synaptic knob making it suitable for its function

Answer 5

Synaptic knob is swollen contain a lot of ACh.
Motor end plate folds to increase surface area for more ACh receptors and also contain AChesterase that breaks down ACh.