2.85 describe the structure and functioning of a simple reflex arc illustrated by the withdrawalof a finger from a hot object

Notes


Let us observe the flowchart of co-ordination in a reflex system:

Stimulus -> Receptor -> Sensory neurone ->  relay neurone in CNS -> motor neurone -> effector -> Response

Here we see that the brain has no function in the reflex system, thereby eliminating a stage in the response system in order to reduce time (i.e. no conscious decision).

Example of hot surface reaction:
Sensory organs contain receptors which, when stimulated by the intense heat, fire electrical impulses down through the spinal nerve. These impulses enter the CNS and are directly connected to the motor nerve by means of a relay nerve (this dramatically reduces response time and always produces the same response from the effector organs -> these are predetermined from DNA). This electrical impulse stimulates a response from the effector organ which in this case, would be to remove the sensory organ from the hot surface.

Note that reflexes are unconscious, always produce the same response, and are very rapid so as to reduce likelihood of organ or tissue damage.