MAVO Year 4 · Coordination and control · Section 10.5

Routes taken by nerve impulses

Conscious responses

A conscious response, such as smiling for a photograph, involves processing in the brain. Receptors detect a stimulus and sensory pathways carry information towards the brain. After processing, motor pathways carry commands to muscles. The person is aware of the situation and can choose a response.

What is a reflex?

A reflex is a rapid, automatic response to a particular stimulus. Reflexes can protect the body, maintain posture or regulate internal conditions. Examples include the knee-jerk reflex and the pupil's response to bright light. They do not require a conscious decision before the response occurs.

The reflex arc

The pathway involved is a reflex arc. A receptor detects a stimulus, a sensory neuron carries information towards the central nervous system, and a motor pathway activates a muscle or gland. Many reflexes use relay neurons in the spinal cord or brainstem. Some, including the main pathway of the knee-jerk reflex, connect a sensory neuron directly with a motor neuron.

The cerebrum does not need to initiate these reflexes, although brain activity can modify many reflex responses.

Becoming aware afterwards

During a withdrawal reflex, sensory information also travels towards the brain. You can begin withdrawing your hand from a harmful stimulus before becoming consciously aware of the pain. The protective movement and conscious perception therefore involve connected but different pathways.