What is a spinal reflex arc?

An unconscious motor response to a sensory stimulus.

Sensory stimulus: An external factor that has stimulated and started an impulse (Action potential) in sensory nerves.

There are lots of different types of sensory nerves in the skin that respond to external signals such as heat, vibration, pressure.

The sensory nerve is activated (Depolarised).

The action potential transmits the sensory signal to the spinal cord, via afferent sensory nerves

 

Afferent sensory nerve (Afferent = Away from stimulus)

 

The signal is carried to the grey matter of the spinal cord

 

Unconscious motor response (Unconscious = bypassing the brain)

The signal from the sensory nerves is transmitted via synapses to interneurones

Interneurones connect to efferent somatic motor neurones.

The motor neurone sends signal to an effector muscle  which acts to move away from the stimulus.

This completes the spinal reflex arc!

Example: Your hand moving away from something hot.

Your hand moves before your brain can decide to do it voluntarily.

This saves time, removing your hand from the heat source faster than you could normally.

When it comes to burns every millisecond counts!

Note: You know you about the heat/pain as signals from the sensory nerves also travel up to your brain too (In the white matter). This takes a bit longer.