Anatomy and Physiology 1: Chapter 15 Part 3 (Hearing and Balance)

How are the cochlear hair cells stimulated?

(1) Auditory ossicles vibrate against the oval window, which sets up vibrations within the fluid-filled inner ear. (2) The endolymph of the cochlear duct vibrates, causing the hair cell stereocilia to move against the tectorial membrane (3) Bending the stereocilia causes depolarization of the hair cell; bending in the opposite direction closes the potassium ion channel while the cell hyperpolarizes. (4) The hair cell releases neurotransmitter during depolarization, generating an action potential to the cochlear nerve.

Motion sickness

-A common equilibrium disorder -A mismatch between visual and vestibular sensory input to brain

Presbycusis caused by:

-A consequence of old age -Exposure to loud noises which stiffen/tear cilia -Cochlear implants is a well-developed treatment.

Pitch

-Determined by the frequency of vibration. Human ears can hear up to frequencies from 20-20,000 Hz

Sensorineural deafness

-Direct damage to neural structures (from the cochlear hair cells to auditory cortical cells) -cochlear implants a well-developed treatment

Meiniere's Syndrome

-Labyrinth disorder affecting both semicircular canals and cochlea -Involves repeated attacks of vertigo (dizziness), nausea, vomiting, difficulty standing, tinnitus (ringing or clicking in the ears)

Treatment for Meiniere's Syndrome

-Mild: Antibiotic drugs -Moderate: Low salt diet/diuretics to decrease endolymph volume -Severe: Surgically drain excess endolymph

Drugs for motion sickness

-OTC drugs meclizine HCl (Bonine) -Scopolamine-containing patches These things depress vestibular inputs.

Loudness

-The perception of amplitude (intensity) of frequency

Perilymph

A fluid between the bone and membrane of the inner ear.The ionic composition of perilymph is comparable to that of plasma and cerebrospinal fluid. The major cation (positively charged ion) in perilymph is sodium.

Crista ampullaris

A mound of hair cells with supporting cells, located within the ampulla.

Hearing

A response to vibrating air molecules

What does sound do to the basilar membrane?

A sound causes a standing wave in the basilar membrane.

Basilar membrane

A supporting membrane, especially the membrane that supports the organ of Corti in the ear and aids in translating sound vibrations into electrical signals. Is within the cochlea of the inner ear is a stiff structural element that separates two liquid-filled tubes that run along the coil of the cochlea.

Outer hair cells (OHC)

Adjust the response of the cochlea to different frequencies.

External auditory canal

Also called external auditory meatus, or external acoustic meatus, passageway that leads from the outside of the head to the tympanic membrane, or eardrum membrane, of each ear.

Eardrum

Also called the tympanic membrane. Separates the outer ear from the middle ear, and is highly sensitive to pain.

Middle ear

An air-filled tympanic cavity in the temporal bone. It contains three small bones, the auditory ossicles. The primary function of the middle ear is to efficiently transfer acoustic energy from compression waves in air to fluid-membrane waves within the cochlea.

Function of the oval window

An oval opening at the head of the cochlea, connecting the middle and inner ear, through which sound vibrations of the stapes are transmitted.

What is anterior to the vestibule?

Anterior to the vestibule is the cochlea, which is the organ of hearing.

Sound

Any audible vibration of molecules

Inner hair cells (IHC)

Are within the organ of Corti, and send actual hearing impulses.

Labyrinth

Begins at a chamber called the vestibule that houses the organs of equilibrium.

Bending the sterocilia causes what?

Causes depolarization of the hair cell; bending in the opposite direction closes potassium ion channel while the cell hyperpolarizes.

What happens when the endolymph of the cochlear duct vibrates?

Causes the hair cell stereocilia to move against the tectorial membrane.

External ear (outer ear)

Consists of three parts: Helps to gather sound. -Outer auricle -Auditory canal (external auditory meatus) -Eardrum

What is loudness measured in?

Decibels (dB)

Rotational acceleration is detected by:

Detected by three endolymph-filled semicircular ducts, each of which houses an ampulla.

-Meiniere's Syndrome may result from what?

Distortion of membranous labyrinth by excessive endolymph accumulation

Auditory canal (tube)

Drains fluid from the middle ear into the throat behind the nose

The three regions of the ear

External ear. Middle ear. Internal ear (labyrinth)

Endolymph

Fills the chamber within the membranous labyrinth. More positive than perilymph in that is has more Potassium ions. It is mainly this electrical potential difference that allows potassium ions to flow into the hair cells during mechanical stimulation of the hair bundle

What is pitch measured in?

Hertz (Hz)

What do high frequency sounds do in the ear?

Higher frequency sounds are detected closer to the proximal end.

Conduction deafness

Hindrance to sound conduction, and can be caused by: -Earwax buildup -Perforated eardrum -Most common causes = otitis media and otosclerosis of ossicles

Utricular maculae respond to

Horizontal movement

Inner ear

Housed within the temporal bone. Sound detection and balance. Includes: oval window, semicircular ducts, cochlea, and auditory tube.

How is loudness expressed?

In decibels (dB), with 120-140 dB causing pain in most people.

Presbycusis

Inability to hear high-pitched sounds, often first sensorineural deafness in old age.

Static equilibrium

Involves the maculae of urticle and saccule, which respond to changes in gravity and linear acceleration

How does the brain interpret high frequencies?

It interprets a higher frequency of action potentials as a loud sound.

What happens when the auditory ossicles vibrate against the oval window?

It sets up vibration within the fluid-filled inner ear.

Ampulla

Located in each of the semicircular ducts.

What do low-frequencies do in the ear?

Low-frequency sounds cause a peak amplitude at the distal end of the organ of Corti.

What kind of ion channels do hair cells in the ear have?

Mechanically gated. Open when hair vibrates.

Tectorial membrane

One of two acellular gels in the cochlea of the inner ear, the other being the basilar membrane.

Symptoms of motion sickness

Pallor, rapid/deep breathing, profuse sweating, nausea, vomiting

Loud sounds

Produce vigorous vibrations of the organ of Corti, exciting a greater number of cells over a larger area.

What can cause permanent hearing loss?

Prolonged exposure to sounds greater than 90 dB

What are the ossicles and eardrum protected by?

Protected by the tympanic reflex in response to loud noises, but it is not effective for sudden loud noises.

What are the most sensitive frequencies?

Range from 1,500 to 4,000 Hz

What does the hair cell do during depolarization?

Releases neurotransmitter. This generates an action potential to the cochlear nerve.

Cristae

Respond to changes in velocity of rotary movements of the head.

Vestibule

Responds to gravitational force. Used in balance. Controlled by three semicircular canals.

Stapes

Situated between the incus and the inner ear, the stapes transmits sound vibrations from the incus to the oval window, a membrane-covered opening to the inner ear.

Cochlea

Snail like structure filled with fluid. Its walls have structures projecting outward called Organs of Corti which have cilia on them. In the cochlea, waves propagate from the base to the apex.

Change of sense of equilibrium in humans is divided into:

Static and dynamic equilibrium.

Incus

The anvil-shaped small bone is one of three ossicles in the middle ear. The incus receives vibrations from the malleus, to which it is connected laterally, and transmits these to the stapes, medially.

The organ of Corti

The basilar membrane supports the organ of Corti containing hair cells, each with stereocilia. It is a structure in the cochlea of the inner ear that produces nerve impulses in response to sound vibrations.

The organ of hearing is. . .

The cochlea

Organ of corti

The hair cells located in the organ of Corti transduce mechanical sound vibrations into nerve impulses. They are stimulated when the basilar membrane, on which the organ of Corti rests, vibrates.

Malleus

The malleus is one of three ossicles in the middle ear which transmit sound from the tympanic membrane (ear drum) to the inner ear. The malleus receives vibrations from the tympanic membrane and transmits this to the incus.

How does the middle ear protect against loud noises?

The middle ear muscles tighten up before you speak to protect your own ears from the volume of your own voice.

Oval window

The oval window is the intersection of the middle ear with the inner ear, and is directly contacted by the stapes. It is a reniform (kidney-shaped) opening leading from the tympanic cavity into the vestibule of the internal ear.

Remember

The process of rotational acceleration involves a fluid movement response

Round window

The round window is one of the two openings into the inner ear. It is closed off from the middle ear by the round window membrane, which vibrates with opposite phase to vibrations entering the inner ear through the oval window. It allows fluid in the cochlea to move, which in turn ensures that hair cells of the basilar membrane will be stimulated and that audition will occur.

The two kinds of equilibrium

The sense of equilibrium in humans is divided into static and dynamic equilibrium.

Tensor tympani muscle

The tensor tympani is a muscle within the ear. It is contained in the bony canal above the osseous portion of the auditory tube. Its role is to dampen sounds, such as those produced from chewing.

The auditory ossicles:

The three small bones in the middle ear. -Malleus -Incus -Stapes

Stereocilia

The tips of the stereocilia shear against an overlying tectorial membrane. Responds to fluid motion in numerous types of animals for various functions, including hearing and balance.

Tympanic membrane

The tympanic membrane, or eardrum, is a thin membrane that separates the external ear from the middle ear. Its function is to transmit sound from the air to the ossicles inside the middle ear. The malleus bone bridges the gap between the eardrum and the other ossicles.

Vestibulocochlear nerve

The vestibulocochlear nerve is responsible for both hearing and balance and brings information from the inner ear to the brain. A human's sense of equilibrium is determined by this nerve. Two special organs help the nerve function properly: the cochlea and the vestibular apparatus.

Outer auricle

The visible projection portion of the outer ear. Funnels vibrations toward the auditory canal and eardrum.

Where are hair cells located?

They are embedded in a gelatinous cupula that responds to motion, bending the stereocilia and stimulating hair cells.

Function of the auditory ossicles

To concentrate the energy from the eardrum to a smaller oval window.

How is Otosclerosis (conduction deafness) treated?

Treated surgically to remove excess bony tissue, replace one or more ossicles or the oval window.

Saccular maculae respond to

Vertical movement

Semicircular canals

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.