$(a)$ What is reflex arc?
$(b)$ What are the components of reflex arc?
$(c)$ How do muscle cells move?

(N/A) The pathway taken by nerve impulses in a reflex action is called a reflex arc. It is the process of detecting a signal (stimulus) and responding to it by an output action quickly.
$(b)$ The components of a reflex arc are: $\text{Stimulus} \rightarrow \text{Receptors} \rightarrow \text{Sensory neurons} \rightarrow \text{Spinal cord (Central Nervous System)} \rightarrow \text{Motor neurons} \rightarrow \text{Effector (Muscle/Gland)}$.
$(c)$ Muscle cells contain special contractile proteins that change their shape and arrangement in the cell in response to electrical impulses received from the nervous system. This change causes the muscle cells to shorten,resulting in movement.