Biology

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Motor neurones

Back 1

Motor neurones carry impulses to effectors.

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Relay neurones

Back 2

Relay neurones are short neurones that are found in the spinal cord, where they link motor and sensory neurones. They also make up alot of the nerve tissue in the brain.

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Synapse

Back 3

The point at which two neurones meet, there is also a tiny gap between neurones at a synapse.

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Neurotransmitter

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A substance that is released into the gap when an impulse reaches an axon terminal.

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The reflex arc

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Reflex actions are responses that are automatic, extremely quick and protect the body.

They use neurone pathways called reflex arcs, which bypass the parts of the brain involved in processing information and so are quicker than responses that need processing.

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Retina

Back 6

The part at the back of the eye that changes energy transferred by light into nerve impulses. contains rods and cones.

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Cones

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Cones are receptor cells that are sensitive to the colour of light, they generate impulses in sensory neurones, which lead into the brain through the optic nerve.

Cones only work in bright light.

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Rods

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Rods are receptor cells that detect differences in light intensity, not colour. Rods work well in very dim light which is why your colour vision is poor in dim light.

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Pupil

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The pupil is the dark area in the middle of the eye, and is where light enters.

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Iris

Back 10

The iris is pigmented, it decides the colour of your eyes so light cannot pass through.

Its muscles can constrict the pupil (decrease size) or dilate it (make it bigger).

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Cornea

Back 11

Most focusing is done by the cornea to produce a clear image, which bends (refracts) light rays to bring them together.

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Lens

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fine-tunes the focusing.

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Ciliary muscles

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Ciliary muscles make the lens fatter to focus light from near objects and thinner to focus light from different objects.

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Optic nerve

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the optic nerve contains a bundle of neurones at the back of the eye.

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Short-sighted

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Short-sighted people can't focus properly on objects that are distant, this is caused by the eyeball being too long or the cornea is too curved and bends the rays more than it should.

Corrected by a diverging lens.

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Long-sighted

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Someone who is long-sighted can't focus properly on objects that are near.

Caused by the eyeball being short.

Corrected using a converging lens.

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Cataract

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When a protein builds up inside the lens and makes it cloudy.

Full vision can be restored by replacing the clouded lens with a plastic one.

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Colour-blindness

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People with colour-blindness have some cones that do not work properly and so have difficulty in seeing some colours.

Colour-blindness cannot be corrected.

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Central nervous system (CNS)

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The brain and spinal cord form the CNS, which controls your body.

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Stimulus

Back 20

Anything in your body is sensitive to, including changes inside your body and in your

surroundings, is called a stimulus.

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Neurotransmission

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The traveling, or transmission, of impulses is called neurotransmission and happens in

neurones.

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Sensory neurone

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A sensory neurone carries impulses from receptor cells towards the CNS. A recpetor cell

impulse passes through a tiny branch called a dendrite.

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Dendrite

Back 23

A fine extension from a neurone that carries

impulses to the cells body.

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Myelin sheath

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fatty layer surrounding the axons and dendrons. This electrically insulates a neurone from

neighbouring neurones, stopping the signal lose energy.

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Cerebral Cortex

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The cerebral cortex makes up 80% of the brain. It is used for most of our senses, language, memory, behaviour and consciousness

(our inner thoughts and feelings).

It is divided into 2 Cerebral hemispheres, the right hemisphere communicates with the left side of the body and vice versa.

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Cerebellum

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At the base of the brain is the Cerebellum, it is divided into two halves and controls balance and posture. It also coordinates the timing and fine controls of muscle activity, making sure that movements are smooth.

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Medulla Oblongata

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The medulla oblongata controls your heart rate and your breathing rate. It is also responsible for reflexes such as vomiting, sneezing and

swallowing.

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Stem cells

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Cells that can divide repeatedly over a long period of time to produce cells that then

differentiate are called stem cells.

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Adult stem cells

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The adult stem cells in human tissues allow the tissues to grow and to replace old or damaged cells, they can be found in the bone marrow.

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Risks of using stem cells

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1) If stem cells continue to divide inside the body after they have replaced damaged cells, they can cause cancer.

2) Stem cells from one person are often killed by the immune system of other people that they are put into, this is called rejection.

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Meristems

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A group of cells near the end of each shoot and root allows plants to continue growing

throughout their lives. They differentiate into specialised cells that have different functions.

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Growth

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Growth is an increase in size as a result of an

increase in number or sizes of cells.

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Differentiation

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The process that changes less specialised cells into more specialised ones is callled

differentiation.

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What is mitosis?

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Mitosis is important because when cells get damaged we need more cells to replace

damaged cells.

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Diploid

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Cells with two copies of each chromosome are diploid.

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Haploid

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Gametes (sex cells) contain one copy of each type of chromosome and are haploid.

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Interphase

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There are 23 chromosomes , the cells make sub-cellular cell parts.

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Prophase

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The chromosomes double up, the copies of the chromosomes stay attached to each other,

making an x shape.

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Metaphase

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The doubled up chromosomes align at the

middle of the cell.

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Anaphase

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The chromosomes are separated and pulled apart by spindle fibres.

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Telophase

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In telophase a membrane forms around each set of chromosomes, cell division begins.

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Cytokinesis

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Two daughter cells are formed, which are both identical to the parent cell.

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Asexual reproduction

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When an organism can reproduce using just one parent. This produces offspring that are clones, which means they are genetically identical.

Relies on mitosis.

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Asexual reproduction dis/advantage

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Advantage: Much faster than sexual

reproduction as it does not need others to

reproduce.

Disadvantage: Asexual reproduction does not produce variation.

Front 45

How do cancer tumours occur?

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Rapid cell division produces growing lumps of cells called tumours that can damage the body and result in death.