Category Human Body

The chest, or thorax, lies between the neck and the abdomen. Inside the thorax lie the heart, lungs, and major blood vessels. The ribcage surrounding them is formed by the backbone, ribs, costal cartilages, and sternum (breastbone).

The ribcage is strong enough to protect the vital organs, but flexible enough to expand and contract for breathing. Attached to the ribcage are the muscles of the chest. Together with the diaphragm, many of these muscles help with breathing.

They move superiorly, inferiorly, anteriorly and posteriorly to facilitate breathing (their flexibility in their movement increases/decreases the size of the thoracic cavity; assisting the lungs in respiration. Control of these movements is via the diaphragm, external intercostals, and the intercartilaginous portion of the internal intercostals). They play a role in erythropoiesis during development (at birth, the erythropoiesis sites change, it recedes in long bones and persists in flat bones, like ribs).

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The chest houses the two powerhouse organs that keep the body running – the heart and lungs. All the body’s cells are supplied with essential blood and oxygen thanks to these vital organs. The backbone supports the body and protects the spinal column, which carries messages to and from the brain.

The chest wall is comprised of skin, fat, muscles, and the thoracic skeleton. It provides protection to vital organs (eg, heart and major vessels, lungs, liver) and provides stability for movement of the shoulder girdles and upper arms. 

One important organ in the chest is the thymus, a small butterfly-shaped organ located between the heart and the sternum, or breastbone. This organ belongs to the immune system, and its job is to produce T cells, a type of white blood cell. These are formally known as T lymphocytes; the “T” stands for thymus, where the cells originate.

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Different body systems work to keep you balanced. Signals from the inner ear combine with visual signals from the eyes, pressure sensors in the skin, and stretch sensors in the muscles to reveal the body’s position. The brain processes this and makes any adjustments to stop the body falling over.

Utricle and saccule

Inside the inner ear are two tiny organs that sense movements of the head in a straight line. The utricle detects forward and backward movement, and the saccule detects up-and-down movement.

Forward and backward movement, such as travelling in a car, is detected by the utricle. Up-and-down motion, such as riding in a lift, is sensed by the saccule.

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Inner ear shows the semicircular canals and the cochlea. The three fluid-filled canals sit at right angles to each other. When you move your head, the fluid swishes around and causes tiny hairs to bend. This sends nerve signals to the brain, which works out the direction in which you are moving. The snail-shaped cochlea converts sounds into nerve impulses.

Inner ear

The semicircular canals and cochlea are part of the inner ear. They sit within a hollow in the temporal bone of the skull.

Inside a semicircular canal

Bulb-shaped areas called ampullae sit at the base of each semicircular canal. In the middle of each ampulla is the cupula, which houses the bundle of movement-sensing hairs. The brain co-ordinates feedback from the ampullae to maintain a constant fix on the body’s position so the body can keep it balanced.

Utricle

The utricle is a small membranous sac (part of the membranous labyrinth) and paired with the saccule lies within the vestibule of the inner ear. It has an important role in orientation and static balance, particularly in horizontal tilt. The utricle is sensitive to forward and backward movements.

Saccule

The saccule is a small membranous sac, paired with the utricle, within the vestibule of the inner ear. It is part of the membranous labyrinth and has an important role in orientation and balance, particularly in vertical tilt. The saccule senses vertical movements of the head.

Oval window

The stapes, or stirrup bone, fits here to pass sound waves to the cochlea. Sound waves cause vibration of the tympanic membrane and the ossicles transmit those vibrations to the oval window, which leads to movement of fluid within the cochlea and activation of receptors for hearing.

Cochlea

The cochlea contains the spiral organ of Corti, which is the receptor organ for hearing. It consists of tiny hair cells that translate the fluid vibration of sounds from its surrounding ducts into electrical impulses that are carried to the brain by sensory nerves. This snail-shaped organ turns vibrations into audible sounds.

Auditory nerve

This nerve carries signals from the ear to the brain.  It is one of the many pieces that make up the auditory system, which enables effective hearing.

Organ of Corti

Running through the middle of the cochlea is the organ of Corti, the main receptor for hearing. Sound waves create vibrations that make wave-like movements in the fluid inside the organ of Corti. These bend the hairs, producing nerve signals, which are sent to the brain to be registered as sounds.

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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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