Homeostasis - Maintaining a stable
internal environment
The cells in your body
need the right conditions to
function properly.
The main automatic control
systems: nervous and hormonal.
Every automatic response system is made
up of three main components: receptors,
coordination centres (the brain, spinal cord &
pancreas) and effectors
Negative feedback -
counteracts changes
The Nervous System
The Nervous System - detects and
reacts to stimuli. This helps humans
to react to their surroundings and
coordinate their behaviour.
Central Nervous System (CNS) - In vertebrates,
it consists of the brain and spinal cord only. In
mammals, it is connected to the body by
sensory neurones and motor neurones.
Sensory neurone - neurones
that carry information as
electrical impulses from the
receptors to the CNS.
Relay neurones - carry the electrical
impulses through the CNS
Motor neurones - carry the
electrical impulses from the
CNS to effectors
Effectors - muscles and glands
which respond to nervous impulses
Receptors - detects the
stimuli
The Brain
The brain is a part of the CNS. It is responsible for
complex behaviour and is made up of billions of
interconnected neurones. Each region of the brain
controls a different part which helps scientists to
work out what each part does when studying a
patient with brain damage.
The different regions and the
functions they carry out:
There are many different ways scientists use
to study the brain, here are three:
Studying patients with brain
damage: If a small part of the
brain has been damaged, the effect
this has on the patient can tell you
what that part does.
Electrically stimulating the brain: Scientists
push a tiny electrode into the tissue and give
it a small zap. This allows them to see what
the part does from the stimulation.
MRI scans - Magnetic resonance imaging scanners produce
very detailed pictures of the brain's structures. They use this to
see what part of the brain is active when the patient is doing
things e.g. listening to music or trying to recall memory.
The brain is very delicate so when
studying it there are many risks.
It can cause physical
damage to the brain.
It can cause more problems for
patients with brain damage.
It can cause increased problems
with brain function e.g. difficulties
with speech.
The Eye
Here is a labeled picture of an eye:
Sclera - the
tough, supporting
wall of the eye
Cornea - transparent outer
layer in front of the eye,
refracts light into the eye
Iris - muscles that control the
diameter of the pupil and 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 and
Suspensory Ligaments -
controls the shape of the lens
Optic Nerve - carries impulses
from the receptors on the
retina to the brain
The Iris Reflex
Bright light - a reflex forces the pupil to decrease
in size. The circular muscles in the iris contract
and the radial muscles relax. This reduces the
amount of light that can enter the eye.
Dim light - the circular muscles in the iris
relax and the radial muscles contract. The
pupil increases in size which allows more
light to enter the eye.
Focusing on near and distant objects
Near objects - the ciliary muscles contract
which slackens the suspensory ligaments.
The lens curve more which increases the
amount by which it refracts light.
Distant objects - the ciliary muscles relax
which tightens the suspensory ligaments.
The lens curve less which decreases the
amount by which it refracts light.