Category Zoology

What are nerve impulses like?

            A nerve impulse is like a very simple message: either ‘on’ or ‘off’. Because there are so many neurones which are connected to one another, this simple signal is enough to carry the most complicated messages throughout the whole of the body’s nervous system.

Are nerves insulated?

            A nerve impulse is an electrical signal and so it needs to be insulated if it not to leak away. Most nerve fibres are covered with a fatty layer of insulation to stop the signal from leaking away. In diseases such as multiple sclerosis, some of this insulation disappears and the nerves do not have his insulation. Although these smaller nerves can still pass a message, it travels much slower than in an insulated neurone.

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What are nerve cells?

                    Nerve cells, or neurones, make up the nerves that carry messages around your body. They have a star-shaped body containing the cell nucleus, with a long thread-like fibre called the axon. The tip of the axon is branched and touches other neurones, to which it delivers messages or nerve impulses. Neurones have many smaller threads and branches called dendrites, which receive messages from other neurones.

Are there different types of nerve cell?

                 There are three types of neurone with different functions. Motor neurones control the way your muscles work. Sensory neurones carry messages from your sense organs. Connector neurones pass messages between different parts of the nervous system.

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What is acne?

                      Acne is a common skin condition causing pimples and blackheads. These appear during adolescence when the skin produces large amounts of an oily liquid called sebum. The skin’s pores can become blocked, and the sebum builds up to produce a pimple or a blackhead. Sometimes the trapped sebum becomes infected and causes an inflamed spot, which is acne.

What is a bruise?

Bleeding under the skin after a knock causes bruises. The blood spreads in the tissues beneath the skin, and at first look purplish. As the red blood cells break down and become absorbed into the bloodstream, the bruise changes colour before disappearing.

Why do I have nails?

                      You need nails to provide a firm support for the sensitive skin on the fingertips. If you cut your fingernails too short you will notice how difficult it is to pick up small objects. Nails grow continuously from an area called the nail bed, or quick. Because your nails are transparent, you can see right into the tissue below the nail, which is always pink because it contains blood. Nails grow at a rate of about 0.1 mm per day. They are made of keratin, the same material as hair. Because nails are  not living material, they do not hurt when you cut them.

What are freckles?

                    Freckles are patches of melanin that are concentrated together instead of being spread evenly throughout the skin. Some people with very fair skin and lots of freckles do not tan evenly. They are particularly likely to develop sunburn unless they protect themselves from the Sun.

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Why do I have hair?

                           Hair originally helped prevent heat loss from the body. It no longer has that function although it does help to protect your head. Each hair grows from a pit in the skin called a follicle. The hair itself is made of a tough material called keratin, and it grows continuously from the follicle. The hair shaft contains pigment that gives the hair its colour. In older people, air may enter the hollow hair shaft, making it look grey.

Why is some hair curly?

                   Hair is straight or curly depending on the shape of the follicle from which it grows. Straight hair grows from completely round follicles, while wavy hair comes from oval follicles. Very curly hair grows from flattened follicles.

Why do some people go bald?

                       A substance called testosterone affects hair growth in men. It is responsible for the tough facial beard grown by men. Changes in testosterone levels affect the amount of hair growing on a man’s head.

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 How does skin tan?

                       Skin develops extra melanin when it is exposed to strong sunlight. Tiny grains of melanin are produced in the skin cells and spread to produce an even suntan, which helps to protect against Sun damage. This even happens in people with naturally dark skin. You can get sunburn if you are exposed to the Sun’s rays for too long, because the damage will be done before the protective melanin can develop. You should always use protective sun cream and limit the amount of time you spend in the sunshine.

How do cuts and grazes heal?

When you cut or graze yourself, the blood clots to prevent bleeding. Clotting is caused by substances in the blood. Together with small particles called platelets, these substances produce masses of fine fibres when they are exposed to air. They block the wound and prevent more blood loss. New cells grow rapidly into the wound, replacing the damaged tissue. Soon the clotted material, called a scab, falls off and clean, new skin is revealed underneath.