Cells and control III
Brain
Function
Part of the CNS
Made up of billions of interconnected neurones
Brain controls everything that we do
Different regions of the brain have different functions
Region of the Brain
Cerebral hemispheres
Largest part of brain
Divided into two halves called cerebral hemishperes
Right hemishpere controls muscles on the left side of our body and vice versa for the left hemisphere
Cerebrum is responsible for movement, intelligence, memory, langauge and vision
Cerebellum
Found at the back of the brain
Responsible for muscle coordination nad balance (precise movement)
Medulla oblongata
At the base of the brain
Controls unconscious activities like breathing and heart rate
Investigating brain function
CT scanner
Uses X-rays to produce an image of the brain
Shows the structures of the brain, but not the functions
Creates a 3D image
PET scanners
Before the scan the person is injected with a radioactive chemical called a tracer, it moves around the body and collects in different areas, including the brain
More active cells take up more tracer than less active cells
Images can show which parts of the brain are active
PET scans are very detailed, are used to investigate structure and function of the brain
Can show if areas in the brain are unusually inactive or active
Treating problems in the CNS
Hard to repair damage to the nervous system as neurones in the CNS don't repair themselves
Some parts of the nervous system aren't easily accessed, tumours in certain parts of the brain can't be removed
Treatments may also lead to further damage
The Eye
Structures
Cornea - transparent outer later found infront of the eye, it refracts light into the eye
Lens - refracts light, focusing it on the retina
Iris - contains muscels that control the diameter of the pupil and therefore how much light enters the eye
Pupil - hole in the centre of the eye, though which light enters
Retina - layer at the back of the eye that contains two types of receptor cells, rod (sensetive to light intensity) and cones (sensetive to to colour
Ciliary muscles and suspensory ligaments - control the shape of the lens
Optic nerve - information from light is converted into electrical impulses by the rods and cones, optic nerve carries impulses from these receptors to the brain, its a sensory neurone
Accomodation
Eye focuses light on the retina by changing shape
Looking at near objects
1) Ciliary muscles contract, suspensory ligaments relax
2) lense becomes thicker and more rounded
3) increases the amount by which light is refracted
Looking at far objects
1) Ciliary muscles relax, suspensory ligaments tighten
2) Lense becomes narrower, less rounded
3) Light is refracted by a smaller amount
Long and short sightedness
Long sightedness
People unable to focus on near objects
Occurs when lens is wrong shape and doesn't refract the light enough or the eyeball is too short
Image of near objects are brought into focus behind the retina
Glasses with a convex lens (curves outwards) can correct long sigtedness
Short sightedness
People unable to focus on far objects
Occurs when lens is the wrong shape and refracts light too much or the eyeball is too long
Image of distant objects are brough into focus infront of the retina
Glasses with a concave lense (curves inwards) can correct short sightedness
Other vision problems
Colour blindness
People who can't tell the difference between certain colours
Occurs when the cons in the retina don't work properly or one is missing entirely
No cure as cone cells can't be replaced
Cataracts
Cloudy patch on the lense which stops light entering the eye normally
Causes blurred vision and less vivid colours aswell as trouble seeing in bright light
Can be surgically treated by replacing the faulty lense with an artificial one
Exposes patient to higher does of radiaiton than normal
Iris
In bright light, the circular muscles contract, and make the pupil smaller
In dim light, the radial muscles contract, to make the pupil larger
Protects the rod and cone cells in bright light, and let more light in when it's dim