Name the ion responsible for unmasking of active sites for myosin for cross-bridge activity during muscle contraction.

(1)  Calcium              

(2)  Magnesium

(3)  Sodium              

(4)  Potassium.

A motor unit is best described as:

(1) All the nerve fibres and muscle fibres in a single muscle bundle

(2) One muscle fibre and its single nerve fibre

(3) A single motor neuron and all the muscle fibres that it innervates

(4) It is the neuron which carries the message from muscle to CNS

Go through the following diagram describing muscle contraction:

Now identify A to E:
(1) A - Cross bridge, B - Cross bridge formation, C - Breaking of cross bridge, D - Sliding (rotation), E - ATP

(2) A - Cross bridge, B - Cross bridge formation, C - Sliding / rotation, D - Breaking of cross bridge, E - ATP

(3) A - Cross bridge, B - Breaking of Cross bridge, C - sliding / rotation, D - Cross bridge formation, E - AMP

(4) A - Cross bridge, B - Cross bridge formation, C - Sliding / rotation, D - ADP, E - Breaking of cross bridge

Sliding Filament Theory states that

1. Contraction of muscle fibre takes place by the sliding of thin filaments over the thick filaments

2. Contraction of muscle fibre takes place by the sliding of thick filament over thin Filaments

3. Relaxation of muscle fibre takes place by the sliding of thick filament over thin filaments

4. Relaxation of muscle fibre takes place by the sliding of thin filament over thick filament

The cross-bridge formation actually involves

1. ATP hydrolysis

2. Binding of Myosin head to the exposed active sites for myosin

3. Both A and B

4. None of these