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┬á 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