Middle Ear Anatomy and Function

• The middle ear starts at the eardrum (tympanum) and goes to the oval and round windows.
• It is an air-filled chamber containing 3 small bones called ossicles.
• The ossicles are the malleus (hammer), incus (anvil), and stapes (stirrup).
• Sound vibrations that hit the eardrum are concentrated within the malleus, then the incus, then the stapes, and finally to the membrane covering the oval window.
• The Eustachian tube extends from the middle ear to the mouth and nose.
• The Eustachian tube allows for air pressure equalization.
• An ear infection can cause fluid build-up, creating air pressure inequalities.
• This can lead to discomfort, temporary deafness, and poor balance.
• The semicircular canals are involved with balance.
• The cochlea is connected with hearing.
• The vestibule is connected to the middle ear by the oval window.
• Fluid movement in the canals helps identify body movement (dynamic equilibrium).
• The 3 semicircular canals are arranged at different angles.
• The cochlea is shaped like a snail's shell and is fluid-filled.
• It contains rows of hair cells and the Organ of Corti, the functional unit for sound.
• The Organ of Corti identifies and responds to sound waves of different frequencies and intensities.
• Sound is a form of energy that travels through air, water, and solids.
• Hearing starts when sound waves push against the eardrum, then the malleus, incus, and stapes.
• The bones concentrate and amplify vibrations.
• The muscles and ligaments work collaboratively to stabilize and support the skeletal system, ensuring that bones maintain their correct alignment and function effectively during movement.
• Additionally, specific muscles surrounding the inner ear play a crucial role in dampening loud sounds, thereby protecting delicate structures within the ear from potential damage caused by excessive noise exposure.
• Hair cells play a crucial role in the auditory process; they convert mechanical vibrations from the basilar membrane into electrical signals that the brain interprets as sound.
• Fluid vibrations move the basilar membrane, causing hair cells to bend and stimulating sensory nerves.
• Auditory information is sent to the brain.
• The inner ear identifies both pitch and loudness.
• The basilar membrane also responds to mechanical stimulation.
• A jarring blow to the skull sets up vibrations passed on to the cochlea.
• Conductive hearing loss is deafness caused by a mechanical problem within the ear.
• Sensorineural hearing loss is deafness caused by a neural problem with the ear or brain

Additional Info

• Tinnitus is a ringing in the ear or a "phantom sound".
• Tinnitus can be caused by a malfunction of the cochlea, transmitted to the brain.
• It can be temporary, like after a rock concert.
• Tinnitus occurs when hair cells are damaged, bent, or destroyed.
• Loss of hair cells occurs as we age.

Static Equilibrium

• Involves movement along one plane such as horizontal or vertical.

• Head position is maintained by the Vestibule, which consists of 2 fluid-filled sacs: The saccule and utricle are critical components of the vestibular system, located within the inner ear. These two interconnected structures are responsible for detecting linear accelerations and the position of the head relative to gravity. Both are filled with a specialized fluid called endolymph, which helps facilitate the sensing of motion.

  Within the saccule and utricle, there are specialized sensory cells known as hair cells, which are embedded in a gelatinous matrix that contains tiny calcium carbonate crystals called otoliths. When the head moves, the otoliths shift due to inertia, bending the hair cells and triggering nerve impulses. These impulses are then transmitted to the brain, allowing us to maintain balance and orient ourselves in space.

  The saccule primarily responds to vertical movements, such as when we move from a sitting to a standing position, while the utricle is more sensitive to horizontal movements, like when we accelerate in a car. Together, they provide vital information that contributes to our sense of balance and spatial awareness, functioning as part of the overall mechanism of static equilibrium.

• There are tiny hair-like receptors within these sacs.

• Cilia from hair cells are suspended in a jellylike material.

• This material contains small rocks called otoliths.

• When the head is in a normal, upright position, the otoliths do not move.

• When the head is bent forward, gravitational force acts on the otoliths, pulling them downward.

• The otoliths cause hair receptors to bend, stimulating a sensory nerve.

• Information about head position is relayed to the brain for interpretation.

Dynamic Equilibrium

• It plays a crucial role in maintaining balance and orientation by detecting changes in position and acceleration, allowing the body to adapt to various movements.
• Balance is maintained by 3 fluid-filled semicircular canals
• Rotational stimuli cause fluid in the canals to move, bending cilia attached to hair cells.
• Once hair cells bend, they initiate nerve impulses, which are carried to the brain.
• Rapid continuous movement of fluids within semicircular canals causes motion sickness.
• Three fluid-filled semicircular canals provide information about body movement.
• Rotational stimuli cause the fluid in the canals to move, which bends the cilia.
• The bent cilia initiate nerve impulses, which are carried to the brain and interpreted as body movements.
• Static equilibrium is movement along one plane, such as the horizontal or the vertical.
• Dynamic equilibrium is the aspect of balance that provides information during movement.