22 Select the description of a motor end plate a the end of

22. Select the description of a motor end plate.

a. the end of the axon of a neuron at a junction with a muscle cell

b. the plasma membrane of a skin cell at a synapse with a neuron

c. the plasma membrane of a muscle cell at a synapse with a neuron

d. the end of the dendrites of a neuron at a junction with a skin cell

23. Muscle contraction is caused by:

a. myosin filaments pulling on actin filaments

b. actin filaments pulling on myosin filaments

c. filaments lengthening of the sarcomere

d. shortening of each actin filament

25. Why would calcium deficiency limit muscle contractions?

a. Calcium forms cross-bridges, which connect thick filaments to thin filaments during contraction.

b. Calcium is released from motor neurons, stimulating an action potential in the muscle fiber.

c. Calcium binds to the troponin–tropomyosin complex, exposing actin\\\'s myosin-binding sites.

d. Calcium hydrolyzes ATP, releasing energy to pull the thin filaments past the thick filaments.

Solution

22. A

The junction between the axon of neuron and sarcolemma of muscle fibre is called motor and plate or neuromuscular junction.The lining of muscle fibre is called sarcolemma.

23. B

As the thin filaments(actin filaments) are pulled deep into the A bands(Anisotropic bands which contains myosin) making the H bands(central part of A band without myosin) narrow, then the muscle shows the effect contraction.

25. C

In the absence of calcium the regulatory proteins prevent or block the action of actin and myosin, changes occured in the configuration of troponin and tropomyosin that limit the muscle contractions.