Coordination and Response: Reflex Arc

Vocabulary flashcards covering the components, pathways, examples, and advantages of reflex actions and reflex arcs.

Reflex action

An automatic, involuntary response to a stimulus that coordinates an effector without the need for thought or a conscious decision.

Stimulus

A change in the external or internal environment of an organism.

Reflex arc

The nervous pathway along which electrical impulses are transmitted from a receptor to an effector without involving conscious regions of the brain.

Receptor

Sensory cells or nerve endings that pick up and detect a stimulus, such as heat, light, or stretch.

Sensory neurone

A neurone that transmits electrical impulses from a sensory receptor to the central nervous system (spinal cord).

Relay neurone

Also known as an interneuron or connector neurone; a neurone located within the spinal cord that connects sensory and motor neurones.

Motor neurone

A neurone that conducts impulses out from the central nervous system to an effector.

Effector

A muscle or gland that executes a protective response against a stimulus when stimulated by a motor neurone.

Synapse

A microscopic junction between neurones across which impulses are relayed.

Fig. 5.1 Reflex Arc

A diagram depicting the withdrawal reflex arc from a flame, showing impulse transmission through a sensory neurone in a spinal nerve, a relay neurone in the spinal cord, and a motor neurone that triggers contraction of the biceps muscle.

The reflex knee jerk (Figure 14.5)

A simple reflex arc initiated by tapping the tendon below the kneecap, which activates stretch receptors and sends impulses via sensory and motor neurones through the spinal cord coordinator to contract the leg extensor muscle.

Advantages of simple reflexes

They are fast, automatic, and protective or defensive, preventing injury by rapidly removing the body from a source of danger.

Blinking reflex

An automatic reflex action that occurs unpreventably when a particle of dust touches the cornea of the eye.

Coughing reflex

An unsuppressible reflex action triggered when a particle of food touches the lining of the windpipe.

Pupil reflex

An involuntary reflex action where the pupil contracts when bright light shines into the eye, occurring without conscious awareness.