The Human Nervous System

Key Words

The Nervous System - detects and reacts to stimuli.

Stimuli - changes in the envrionment.

Receptors - cells that detect stimuli.

Effectors - respond to nervous impules and bring about a change.

Central Nervous System (CNS) - received information from the receptors and then coordinates a response.

Neurones - transmit information very quickly to and from the brain.

Sensory neurones - carry information as electrical impulses from the receptors to the CNS.

Motor Neurones - carry electrical impulses from the CNS to the effectors.

Synapse - the connection between two neurones.

Reflexes - rapid, automatic responses to certain stimuli that don't involve the conscious part of the brain.

Reflex arc - the passage of information in a reflex from receptor to effector.

Relay neurones - connect sensory neurones to motor neurones.

The brain - part of the central nervous system contains:

Cerebral cortex - responsible for things like consciousness, intelligence, memory and language.
Medulla - controls unconscious activites like breating and heartbeat.
Cerebellum - responsible for muscle coordination.

Magnetic resonance imaging (MRI) scan - produce a very detailed picture of the brain's structures.

Sclera - tough, supporting wall of the eye.

Cornea - transparent outer layer found at the front of the eye. It refracts light into the eye.

Iris - contains muscles that allow it to control the diameter of the pupil and therefore how much light enters the eye.

Lens - focuses the light onto the retina.

Retina - contains receptor cells sensitive to light intensity and colour.

Ciliary muscles & Suspensory ligaments - controls the shape of the lens.

Optic nerve - carries impulses from the receptors on the retina to the brain.

Long-sighted - people are unable to focus on near objects.

Short-sighted - people are unable to focus on distant objects.

Contact lenses - think lenses that sit on the surface of the eye and are shaped to compensate for the fault in focusing.

Laser eye surgery - corrects bad eyesight by vaporising tissue with a laser which changes the shape of the cornea.

Replacement lens surgery - the lens is replaced with a clear plastic one to correct bad eyesight.

Also see Light, Hormonal coordination, Homeostasis