Human`s nervous System


The nervous system is made up of the brain, the spinal cord and the network of nerves. It is responsible for detecting and processing information from inside and outside of body and produce and controls movement by stimulating the muscles.
Among other things, the brain is the site of 12 pairs of nerves which look after the senses of seeing, hearing, taste and smell, while the spinal cord provides 31 pairs of nerves for the trunk and limbs.





Human`s Five Senses

A sense is a physiological capacity of organisms that provides data for perception. The nervous system has a specific sensory system or organ, dedicated to each sense. Humans have a multitude of senses.
1. Sight (ophthalmoception),
2. Hearing (audioception),
3. Taste (gustaoception),
4. Smell (olfacoception or olfacception), and
5. Touch (tactioception)

These are the five traditionally recognized senses. The ability to detect other stimuli beyond those governed by these most broadly recognized senses also exists, and these sensory modalities include,
-temperature (thermoception),
-kinesthetic sense (proprioception),
-pain (nociception),
-balance (equilibrioception),
-vibration (mechanoreception), and various internal stimuli.






How do we taste and smell?

Taste is sometimes confused with smell. It is easy to mistake a smell for a taste. An onion, for example, has no taste. Anyone with a heavy cold may complain of losing his taste, when, in fact, he has lost his smell. Quite what sort of smell or taste we get from anything depends upon its physical and chemical properties. So before we know what the smell or taste is like, some small amount of the substance must come into contact with the sensory receptors- the nerve cells which will give the brain its message. The human tongue has about 3,000 taste buds to distinguish one taste from another. The four basic tastes- sweet, sour, salt and bitter are detected by different parts of the tongue. The taste buds are connected to a nerve which takes ‘taste’ messages to the brain.

Smell is detected by the nose. Nerve cells that deal with smells (the olfactory nerve cells) are on the upper and inner surface of the nose. There are long, hair-like lashes at the lower end of these cells which are covered by a layer of mucous. The minute particles of a substance, which we have already mentioned, must be dissolved in the layer of mucous before the nerve cells can detect them. The olfactory nerves are connected to the olfactory bulb. Here, there are more nerve cells to transmit ‘smell’ messages to the brain.









How do we hear?

Sound is caused by pressure waves that vibrate. These vibrations are funnelled by the outer ear to the ear drum. The ear drum is extremely sensitive, and it, in turn, vibrates. The vibrations of the ear drum are then transmitted to the three bones of the middle ear, the hammer, which touches the inner surface of the drum, the anvil and the stirrup. These tiny bones are joined together and the stirrup touches the inner ear or cochlea, so that it, in turn, receives the vibrations from the ear drum. The cochlea contains fluid-filled tubes which are linked to the auditory, or hearing, nerve. The vibrations cause tiny pressure changes in the fluid which act on the auditory nerve. The auditory nerve sends messages to the brain which interprets them as sound.






What is the structure of the eye? How does it work?

The light entering the eye then passes through the lens. The Eye lens acts in the same way as the lens in a camera. The muscles attached to its rim alter its shape so that the light rays are focused on the retina. The eye cavity (the space between the lens and the retina) is filled with a sticky jelly like fluid called vitreous humour. The retina is like a photographic film and it has three layers of nerve cells with the light receptors (the rods and cones) on the outside. The rods and cones convert light into nerve impulses which travel via the optic nerve to the brain. The ‘picture’ on the retina is much smaller than the original, of course, and is upside down. The brain interprets the ‘picture’ correctly, so that what we see is not distorted.









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