41. Neurons can work together in reflex arcs

41. Neurons can work together in reflex arcs

Reflex action

A rapid automatic response to a stimulus

Coughing, pupil reflex, knee jerk, swallowing

Four examples of reflexes:

Reflex arc

The nerve pathway involved in a reflex action

the brain is involved in initiating the action

Voluntary actions happen if:

Particles making contact with the lining of the respiratory tree

Stimulus of coughing:

Contraction of the diaphragm and internal intercostal muscles

Response to stimulus of coughing:

Prevents lungs being damaged or infected

Survival value of coughing:

Bright light falling on the retina

Stimulus of pupil reflex:

Contraction of the circular muscles of the iris

Response to stimulus of pupil reflex:

Prevents retina bleaching so that vision remains clear

Survival value of pupil reflex:

Stretching of the tendon just under the knee, holding the kneecap in place

Stimulus of knee jerk:

Contraction of the muscles of the upper thigh so that the leg straightens

Response to stimulus of knee jerk:

The leg can support the body's weight during walking

Survival value of knee jerk:

Food particles making contact with the back of the throat

Stimulus of swallowing:

Contraction of the muscle of the epiglottis to close entrance to trachea

Response to stimulus of swallowing:

Prevents food entering the respiratory pathway, so that the lungs are not damaged

Survival value of swallowing:

Receptor

A cell or organ that receives a stimulus and converts it into an electrical impulse

Carry impulse from the receptor to the central nervous system

Sensory neuron function:

Carry impulse slowly across the spinal cord

Connector function:

To give time for the action to be modified by impulses carried down the spinal cord from the brain

Why does the connector have no myelin sheath?

Carry impulse from the central nervous system to the effector

Motor neuron function:

Effector

The structure that carries out an action to deal with the initial stimulus

nerve fibers

White matter in central nervous system contains:

cell bodies of motor neurons

Grey matter in central nervous system contains:

both sensory and motor neurons so carries impulses in and out of the central nervous system

Spinal nerve has:

Galen

A surgeon who discovered that each spinal nerve has two branches

Either the person can move but cannot feel pain or he cannot move but can feel pain

What happens when one of the branches of the spinal nerve is damaged?