Final answer:
The reflexive withdrawal of the hand upon touching something extremely hot involves a reflex arc where sensory neurons send a signal to the spinal cord, which then triggers a motor response to the arm muscles, contracting the biceps and relaxing the triceps for a rapid withdrawal.
Step-by-step explanation:
When you touch something extremely hot and burned your fingers, such as a stove, the pathway for the reflexive withdrawal of the hand is initiated by sensory neurons detecting the high temperature. This sensory input is rapidly sent to your central nervous system, specifically the spinal cord, where it triggers a reflex arc. In response to this, an interneuron in the spinal cord sends a motor response to the skeletal muscles that control arm movement. As the biceps brachii muscle of the arm contracts to pull the hand away, the opposite muscle, the triceps brachii, must relax to allow a quick withdrawal. This is facilitated by the inhibition of the motor neuron controlling the triceps through the release of neurotransmitters from the interneuron, thus preventing any delay in response.
The sudden and automatic withdrawal action, known as the hot-stove withdrawal reflex, is a protective mechanism that occurs without the involvement of the brain, making it extremely swift to help minimize tissue damage from exposure to the painful stimulus.