Electrical and Chemical Signals

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Electrical and Chemical Signals
(Edexcel)
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The Nervous System
The CENTRAL NERVOUS SYSTEM (CNS) enables us to
react to our surroundings. It consists mainly of
the brain, the spinal chord, nerve cells
(neurones) and receptors.

• Types of receptor
• Light receptors in the eyes
• Sound receptors in the ears
• Taste receptors on the tongue
• Smell receptors in the nose
• Touch, pressure and temperature receptors in the
  skin
• Changes of position receptors in the ears
  (balance)

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Nervous Reactions
When we react to a stimulus our bodies use the
following pattern
For example, consider a man and a camel
Oh No!
What are the stimulus, receptor, coordinator,
effector and response in this situation?
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Examples of reactions
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Types of nerve cell
Nerve cells (neurones) are elongated with
branched endings to connect to many muscles
fibres.
1) Motor neurone
2) Sensory neurone
3) Relay neurone
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The Brain
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Disruption to the Brain
These are when part of the brain is starved of
oxygen. The affected part may no longer be able
to work properly. This is when the brain neurones
send random messages to each other, resulting in
uncoordinated fits. This disease is when cells
divide and grow uncontrollably. This disease
develops when the brain stops producing dopamine,
a chemical that helps brain cells to communicate.
A lack of dopamine means the brain cannot
coordinate movement properly.
Parkinsons Disease Tumours Strokes Grand mal
epilepsy
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Synapses
Neurones never ____ each other there is a small
gap between them called a _____. A signal is
sent from one _______ to the next by a _______
transmitter across the synapse. These
transmitters are then ________.
Words chemical, synapse, neurone, touch,
destroyed
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Conscious actions
A conscious action is one where the brain makes a
considered response. Heres what happens
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Reflex actions
Sometimes conscious action is too slow to prevent
harm, e.g
In situations like this the body bypasses the
brain to produce a quicker response. Heres how
it works
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Reflex actions
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The Eye
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Seeing things
Rays of light are refracted (bent) first by the
cornea and then by the lens. They focus on the
retina.
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Focussing on different distances (accomodation)
For distant objects the ciliary muscles relax and
the suspensory ligaments pull tight making the
lens pull thin the light doesnt bend as much.
For close objects the ciliary muscles contract
allowing the lens to go fat, thus bending the
light more.
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The Iris Reflex
When the light is bright the radial muscles
relax, the circular muscles contract and the
pupil increases in size.
When the light is bright the radial muscles
_____, the circular muscles _______ and the pupil
________ in size.
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The four parts of blood
1. RED BLOOD CELLS contain haemoglobin and
carry ______ around the body. They have no
_______ and a large surface area.
2. PLATELETS small bits of cells that lie
around waiting for a cut to happen so that they
can ____ (for a scab).
3. WHITE BLOOD CELLS kill invading _______ by
producing _________ or engulfing (eating) the
microbe.
These three are all carried around by the PLASMA
(a straw-coloured liquid). Plasma transports CO2
and ______ as well as taking away waste products
to the ______.
Words antibodies, clot, kidneys, oxygen,
nucleus, glucose, microbes.
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The role of haemoglobin
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Hormones
Hormones are chemical messengers produced by
endocrine _____. They control the way in which
parts of the body work and are transported to
their target organs in the _______. Some
examples...

• The pancreas produces _______
• The adrenal gland produce ________
• The pituitary gland produces FSH and LH
• Testes produce __________
• Ovaries produce progesterone

Words testosterone, glands, bloodstream,
insulin, adrenaline
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The Menstrual Cycle
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Fertility
The events that happen in a female body during
the menstrual cycle are triggered by hormones
(chemical messengers). Artificial hormones can
be used to

• Stimulate the release of eggs (fertility
  treatment)
• Inhibit the release of eggs (contraceptive pills)

In normal circumstances natural hormones are
responsible for releasing the egg and for
thickening the lining of the womb. These
hormones are produced by the pituitary gland in
the brain and in the ovaries.
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Fertility
3 hormones are involved in the menstrual cycle
oestrogen, LH and FSH. Heres how

• Artificial fertility
• To INCREASE fertility FSH is given to stimulate
  maturation of eggs.
• To DECREASE fertility oestrogen is given (The
  Pill) to inhibit FSH production stopping eggs
  from maturing.

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IVF
Some couples cannot have children naturally.
In-vitro fertilisation (IVF) can help. Heres
how it works
1. Eggs are removed from the womb and placed in a
solution of oxygen and water to keep them alive
2. Sperm is added
3. The fertlised egg is allowed to grow into an
embryo (a group of 4-8 cells)
4. Usually 3 of these embryos are transferred
back into the uterus
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Ethical issues of IVF
IVF
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Controlling Blood Sugar levels
We need glucose in our bodies to help our cells
to respire and produce energy. What happens if
we have too much glucose?
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Diabetes
Diabetes is a ________ in which a persons blood
sugar (i.e. glucose) level may rise to a _______
level. This is because the ______ doesnt
produce enough _________. Diabetes can be
treated by __________ carefully or by injecting
extra insulin when needed. Diabetics have to
test their blood sugar level before they decide
how much insulin to _______ themselves with.
Words insulin, disease, inject, dangerous,
eating, pancreas
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Genetic engineering - Insulin
Step 1 Enzymes cut out the part of the human
chromosome that is responsible for producing
insulin.
Step 2 Using another enzyme cut open a ring of
bacterial DNA (a plasmid). Other enzymes are
then used to insert the piece of human DNA into
the plasmid.
Step 3 Place the plasmid into a bacterium which
will start to divide rapidly. As it divides it
will replicate the plasmid and make millions of
them, each with the instruction to produce
insulin. Commercial quantities of insulin can
then be produced.