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The Sensory System (The Eye (Pupil (Black circle in the middle of the iris…
The Sensory System
The Eye
Iris
Coloured part of the eye
Expands or contract to control the amount of light entering the eye
Pupil
Black circle in the middle of the iris
Allows light to enter the eye
Changes size due to changes in the iris
In bright light it is small
In dim light it enlarges
No light is reflected out so the pupil appears black
Lens
Is a flexible structure
Changes shape depending on weather we are looking at a near or far object
It focuses light on the retina
If the lens does not take up the correct shape the object we are looking at will appear blurred
Retina
Is a light-sensitive layer at the back of the eye
Contains millions of cells that are sensitive to light
It absorbs light and allows us to see
Optic nerve
Carry's massages from the eye to the brain
Provides the link between the eye and the central nervous system
Cornea
A transparent section of the covering of the eye
Allows light to pass into the eye
Ciliary muscle
Surrounds the lens
Contracts or relaxes to cause the lens to change shape
Sense organs
Sight
Eyes
Hearing
Ears
Smell
Nose
Touch
Skin
Taste
Tougue
The Central nervous system
The central nervous system consists of the brain and spinal cord
The brain is a complex structure containing many millions of nerve cells. Nerve cells are also called neurons
The spinal cord contains many nerves which take messages to and from the brain
The ret of the nervous system contains nerves which run to and from the central nervous system
Responding to a stimulus
When pouring a cup of tea, the eye detects that the cup is almost full of tea. This is the stimulus. A message is sent along a nerve from the eye to the brain. The brain decides to stop pouring tea. It sends a message along another nerve, down the spinal cord and out to muscles in the arm or hand. We respond by raising the teapot
Sense organs and the central nervous system
Nerves carry messages from sense organs to the brain. In this way, the sense organs allow us to gather information from our surroundings. Messages travel along nerves as electrical impulses
When the brain receives information from the sense organs it makes sense of the message, memorises it and decides on the correct response
The brain then sends a message along different nerves to a muscle (or group of muscles). In this way, the brain causes us to respond to a stimulus
Sensory and motor nerves
Neuron
A nerve cell
Sensory
Carry messages to the brain
Carry impulses from the sense organs towards the brain
Makes our central nervous system aware of the stimulus
Motor nerves
Carry messages away from the brain
Carry messages from the brain/central nervous system to a muscle
Causes us to carry out a response
Stimulus and response
Anything in our surroundings that cause us to take an action is called a stimulus (plural stimuli)
The action we take is called a response