Category Zoology

As well as providing our sense of hearing, the ears help us to keep our balance and send vital information to the brain when we move.

The inner ear is the part deepest inside the head. It contains three fluid-filled tubes called semicircular canals. As we move, the fluid inside the canals moves, sending messages to the brain to help us keep our balance. Also in the inner ear is the cochlea, which converts sounds to hearing.

Information coming from the vestibular system is processed in the brain and then sent on to other organs that need this information, such as the eyes, joints or muscles. This allows us to keep our balance and know what position our body is in.

In some situations, for example on a ship or airplane, different sensory organs (e.g. the eyes and the organ of balance) send contradictory messages to the brain. This can cause us to feel unwell, dizzy or nauseous.

The vestibular system is especially sensitive in children, and reacts more slowly to movements as we grow older. Inner ear infections and other problems may also affect how well our sense of balance works.

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Pinna (outer ear)

The pinna is the only visible part of the ear (the auricle) with its special helical shape. It is the first part of the ear that reacts with sound. The function of the pinna is to act as a kind of funnel which assists in directing the sound further into the ear. This flap channels sounds into the ear canal.

Ear canal

The ear canal, also called the external acoustic meatus, is a passage comprised of bone and skin leading to the eardrum. The ear is comprised of the ear canal (also known as the outer ear), the middle ear, and the inner ear.

Eardrum

The eardrum is a thin, film, about 9 mm (0.4 in) wide, which sits at the entrance to the middle ear and vibrates when sound waves hit it. The eardrum also helps to stop debris from getting inside the ear and damaging it.

Hammer (malleus)

Vibrations from the eardrum are picked up by this bone. The malleus is a bone situated in the middle ear. It is the first of the three ossicles, and attached to the tympanic membrane. The head of the malleus is the large protruding section, which attaches to the incus. The head connects to the neck of malleus, and the bone continues as the handle of malleus, which connects to the tympanic membrane. Between the neck and handle of the malleus, lateral and anterior processes emerge from the bone.[2

Stirrup (stapes)

The tiny stirrup bone vibrates and moves the oval window in the cochlea. If the stapes becomes damaged, such as from severe head trauma, a person may lose some or all of their ability to hear. Because the ossicles are a chain of bones, this also holds true for the incus and malleus.

Semicircular canals

These three fluid-filled tubes contain sensors that detect movement. Your semicircular canals are three tiny, fluid-filled tubes in your inner ear that help you keep your balance. When your head moves around, the liquid inside the semicircular canals sloshes around and moves the tiny hairs that line each canal

Cochlea

The snail-shaped cochlea is filled with liquid and lined with tiny hair cells that detect vibrations. The cochlea interacts with the middle ear via two holes that are closed by membranes: the oval window, which is located at the base of the scala vestibuli and which undergoes pressure from the stapes (see ‘middle ear’), and the round window, which seals the base of the tympanic membrane and is used to relieve pressure.

Hair cells

Each hair cell in the cochlea is topped by groups of microscopic hairs. Incoming vibrations bend the hairs by different amounts. These vibration patterns are turned into nerve messages and sent to the brain.

Anvil (incus)

The incus lays at the center of the ossicles, connecting the malleus to the stapes. It is shaped like an anvil, which is why ‘the anvil’ is a widely used alternative name for the bone. Vibrations from the hammer to the stirrup are transmitted through the anvil.

Smallest bones

The ear contains three of the tiniest bones in the human body. The stirrup bone is the smallest of all, at about the size of a grain of rice.

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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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