Read the following statements carefully and select the appropriate option given below.
(i) Muscle contraction is initiated by a signal sent by the central nervous system via a motor neuron.
(ii) A complex protein troponin is distributed at regular intervals on the tropomyosin.
(iii) Mechanism of muscle contraction states that contraction of thick filaments
takes place over the thin filaments.
(iv) The Z line attached to actins are pulled outward thereby causing a shortening of sarcomere during contraction.
(v) Red muscles contain plenty of mitochondria which can utilise the large amount of haemoglobin for ATP production.

Mechanism of muscle contraction is best explained by the sliding filament theory which states that contraction of a muscle fibre takes place by the sliding of the thin filaments over the thick filaments. The 'Z' line attached to these actins are also pulled inwards thereby causing a shortening of the sarcomere, i.e., contraction. Muscle contains a red coloured oxygen storing pigment called myoglobin. Myoglobin content is high in some of the muscles which gives a reddish appearance. Such muscles are called the Red fibres. These muscles also contain plenty of mitochondria which can utilise the large amount of oxygen stored in them for ATP production. These muscles, therefore, can also be called aerobic muscles.