Explain how is hand pulled away from the hot object reflexly.

Explanation

A connection between the input (sensory) nerve and output (motor) nerve along with spinal cord is called reflex arc.
It is a path of reflex action which consists of receptor, sensory neuron, relay neuron and motor neuron connected to effector organ.

Thus a neural pathway for the sensory and motor messages that pass through the spinal cord forms the reflex arc. A very rapid response is shown through it.
The following example can clarify the meaning of reflex arc:
Suppose by mistake and unknowingly one touches a hot object by one.s hand. One would withdraw the hand all of a sudden without giving a slightest thought. Here the hot object is the source of stimulus.
This stimulus activates the sensory nerve fibre in the hand and carry that impulse to the spinal cord. The sensory centres in the spinal cord receive the stimulus and transmits the response to the motor centre of the spinal cord. This motor message is transmitted through the motor nerve fibre to definite muscles of the hand, which upon contraction, withdraws the hand. The hand or its muscles act as effector organ. This entire neural path from the sensory or receptor organ, to the effector organ is a reflex arc.