Category Human Body

All sounds make invisible ripples, or waves, in the air. The ear collects sound waves and converts them first into vibrations, then into signals that the brain interprets as sounds.

Outer ear

Sound waves travel along the ear canal until they hit the eardrum and make it vibrate. The outer ear (pinna) ‘catches’ sound waves and directs them through the ear canal to the protected middle ear. These incoming sound waves cause the eardrum to vibrate. This is where the process of understanding these sound waves begins.

Middle ear

The vibrations pass through a series of bones, through the oval window, and into the cochlea. The middle ear is connected to the back of the nose and throat by the Eustachian tube. This means that when your loved one yawns or swallows, the Eustachian tube can open to equalise the pressure on both sides of the eardrum and prevent the membrane from being damaged. 

Inner ear

Microscopic hairs inside the cochlea convert the vibrations into nerve signals, which are sent to the brain. The middle ear is connected to the back of the nose and throat by the Eustachian tube. This means that when your loved one yawns or swallows, the Eustachian tube can open to equalise the pressure on both sides of the eardrum and prevent the membrane from being damaged. 

Loud and clear

The louder the sound, the bigger the vibrations it makes. Our ears are so sensitive that we can detect even the smallest sound, such as a paperclip dropping on the floor. We measure the loudness of sounds in decibels (dB).

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The ear is the body’s organ of hearing. It is larger than it looks – only a skin-covered flap is visible on the outside of the head, with the rest of the ear lying hidden from view inside the skill.

Ears come in many shapes and sizes. Typically, men’s ears are larger than women’s, according to a study in the journal Plastic and Reconstructive Surgery. Researchers also found that the average ear is about 2.5 inches (6.3 centimeters) long, and the average ear lobe is 0.74 inches (1.88 cm) long and 0.77 inches (1.96 cm) wide. They also noted that the ear does indeed get larger as a person ages.

The ear has three zones, each with different roles. The outer ear collects sounds and funnels them towards the middle ear, where they are converted into vibrations. In the inner ear, the vibrations are transformed again, into signals to send to the brain.

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Every human has a unique iris pattern, which is why many modern security systems use iris recognition technology.

Two sets of muscles in the iris contract and relax to control the amount of light entering the eye through the hole in its centre – the pupil. Circular muscles contract in bright light, making the pupil smaller to prevent a dazzling effect. In dim light, radial muscles (like spokes on a wheel) contract to make the pupil bigger so it allows in more light. Different amounts of melanin pigment inside the iris give eyes their different colours. Brown is the most common colour, found in more than half the world’s population.

The iris is usually strongly pigmented, with the color typically ranging between brown, hazel, green, gray, and blue. Occasionally, the color of the iris is due to a lack of pigmentation, as in the pinkish-white of oculo-cutaneous albinism,[1] or to obscuration of its pigment by blood vessels, as in the red of an abnormally vascularised iris. Despite the wide range of colors, the only pigment that contributes substantially to normal human iris color is the dark pigment melanin. The quantity of melanin pigment in the iris is one factor in determining the phenotypic eye color of a person. Structurally, this huge molecule is only slightly different from its equivalent found in skin and hair. Iris color is due to variable amounts of eumelanin (brown/black melanins) and pheomelanin (red/yellow melanins) produced by melanocytes. More of the former is found in brown-eyed people and of the latter in blue and green-eyed people.

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Sight is the key sense, so maintaining good vision is important to humans. Eyesight often deteriorates as the body ages and the number of light-sensitive rods and cones decreases. Two of the most common eye conditions are problems with focusing and with seeing certain colours.

Out of sight

The most common eye problems are short-sightedness and long-sightedness, where distant or near objects can appear blurred. Glasses or contact lenses can help the light to focus in the right place within the eye and make images sharp again.

Short-sightedness

Short-sighted people can focus on things that are close, but not on things that are further away.

Long-sightedness

Long-sighted people can focus on things at a distance but not on near objects.

Colour blindness

Most eyes can see millions of different colours, but some people cannot distinguish between colours because of injury, illness, or an inherited condition. More boys than girls have colour blindness.

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The brain’s task is to make sense of what the eyes see, and it usually gets it eight. However, optical illusions can play tricks on the brain as it tries to fill any gaps in the visual information it receives.

Pavement painting

Artists can create the illusion of depth by skilful use of techniques such as shadowing and perspective (making lines meet as they would if seen in the distance).

Moving image

This is caused by the eyes’ light-sensitive cells turning on and off as they react in different parts of the pattern. This fools the eye into thinking it is seeing movement.

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The left and right eye each have their own angled view, called the visual field. Data from the left half of each eye is compared by the brain’s visual centre, and similarly for the right halves of each eye. The process of combining the different views into one 3D image is called binocular vision.

3D Vision

Many animals, such as horses, have eyes on the sides of their head, but humans have forward-facing eyes. Each eye sees from a different angle to provide an overlapping view of the scene. The brain uses this to create an image with height, width, and depth.

Movie magic

The ultimate cinematic experience is a 3D movie. The film is made by copying what the eyes so. Scenes are shot with two cameras, then special glasses are worn to put the images together. The result makes the audiences feel as though they are “in” the film.

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