Latissimus dorsi muscles are

Which muscle is responsible for changes in body posture?

Assertion : The phase of muscle contraction occurs when myosin binds and releases actin.
Reason : Muscle contraction is initiated by a signal sent by the peripheral nervous system via motor neuron.

The Krause membrane or $Z$-line is a structure in a myofibril that separates two adjacent:

In a relaxed muscle fibril,the $H$-zone,a lighter region of low density,can be seen in the centre of:

During muscle contraction,$(P)$ get reduced whereas $(Q)$ retain the length. Here $P$ and $Q$ are $-$