1) E
The brain is not involved in the REFLEX to a stimulus. Hence, E is the correct answer.

A – Sensory neurone senses a stimulus and then transmits an electrical impulse to the central nervous system. 

B – Muscle cells need to to contract in order to produce a movement 

C – The motor neurone is the neurone that signals the muscle cells in the erector muscle to take action

D – Relay neurones are like bridges which connect sensory neurones and motor neurones. They pass on the electrical impulses from the sensory neurones to the motor neurones.

E – Brain is not part of the reflex arc. Since the reflexes need to be rapid, automatic and protective (RAP), it will take too long for the electrical impulses to travel to the brain and back. The reflex arc involves the central nervous system for RAP reflexes.