Download Sense Organs and Stimuli - maps

Sense Organs and Stimuli
The nervous system enables humans to detect changes in their surroundings and react
to them.
The nervous system also sends electrical messages along neurones (nerve cells) in
order to co-ordinate behaviour.
A stimulus is a change in the environment.
Special cells in the body called receptors detect stimuli. The receptors are located in
the sense organs.
Name of sense
Sight
Hearing
Balance
Taste
Smell
Touch
Sense organ
Stimulus
Eye
Ear
Ear
Tongue
Nose
Skin
Light
Sound
Change in body position
Chemicals
Chemicals
Touch, pressure and temperature changes
Central Nervous System
The central nervous system (CNS) is made up of the brain and spinal cord.
Branching out of the CNS are nerves. Each nerve contains a bundle of neurones,
surrounded by an insulating layer.
Information is passed from receptors to the brain along sensory neurones. The brain
then coordinates a response and sends a message along a motor neurone to an
effector organ, which could be a muscle or a gland.
Reflex Actions
Some responses to stimuli are automatic and happen very fast, for example blinking or
pulling away from a hot object. These are called reflex actions and often protect the body
from danger.
In a simple reflex action, an electrical impulse travels from a receptor along a sensory
neurone to the brain or spinal cord, then along a motor neurone to a muscle or gland. The
muscle or gland brings about the response.
For example:
stimulus → receptor → sensory neurone → coordinator → motor neurone → effector →
response
bright light → in eye → sensory neurone → brain → motor neurone → iris muscle →
pupil gets smaller
The Eye
Part of eye
Retina
Lens
Suspensory
ligaments
Ciliary muscles
Iris
Pupil
Sclera
Cornea
Optic nerve
Structure and function
The light sensitive layer at the back of the eye; contains receptor cells.
Focuses light onto the retina.
Hold the lens in place.
Alter the shape of the lens during focusing. Muscles contract to focus
on near objects and relax to focus on far away objects.
Coloured part of the eye that controls the amount of light entering the
eye by changing the size of the pupil.
Hole which allows light to enter the eye.
Tough, white, outer layer of the eye.
Front part of the sclera which is transparent to let light into the eye. It
is curved so helps to focus light onto the retina.
Contains sensory neurones that carry impulses from the retina to the
brain.