Hearing and Equillibrium

External (Outer) Ear

hearing

Middle ear

also hearing

Internal (inner) ear

hearing and equillibrium

Auricle (Pinna)

Outer ear; catches sound waves

Helix

Cartilage

Lobule

Flexible fleshy ear lobe

External Acoustic meatus (auditory canal)

Short, curved tube; houses the tympanic membrane (eardrum) and is lined with hairs, sebaceous glands, and ceruminous glands

What divides the external and middle ear

The tympanic membrane (eardrum)

How does sound travel through the acoustic meatus to the eardrum

The eardrum vibrates at the same frequency as the sound waves hit it, and it transmits those vibrations to the bone of the middle ear via the malleus

Tympanic membrane

Lateral end of the middle ear; transmits sound waves in

Oval Window

Medial end of the middle ear; transmits sound waves out

Pharyngotympanic tube

Inferior end of the middle ear; usually closed (but can be opened by swallowing/yawning) to equalize pressure

Auditory ossicles

malleus, incus, stapes

Malleus

connected to tympanic membrane

Incus

Anvil-shaped bone connecting malleus and stapes.

Stapes

Connected to oval window

Auditory ossicles are all suspended by

ligaments

Loud sounds stimulate ___________ and __________ to contract in order to prevent damage to downstream sensory cells

Tensor tympani and stapedius muscles

Tensor tympani

A small skeletal muscle which limits movement of ossicles and increases tension of the tympanic membrane to prevent damage in response to loud, prolonged noises.

Stapedius muscles

a middle-ear muscle that is attached to the stapes. This muscle contracts in response to intense sound.

Semicircular canals

Equilibrium

Cochlea

Hearing; extends off of vestibule

Cochlear duct

Houses spiral organ (organ of corti)

Spiral organ

the hearing receptor, which is located in the cochlea of the inner ear

Vestibular nerve

CN VIII, nerve that conducts impulses related to maintaining balance to the brain

Cochlear nerve

Transmits auditory information to the brain.

Vestibule

where stirrup attaches

Sensory cells of cochlea

Sensory cells (hair cells)

Inner hair cells

Primarily send sound signals to the brain

Outer hair cells

Amplify vibrations and protect hair cells by altering stiffness of basilar membrane

Short stiff fibers

Proximal to oval window

Long flexible fibers

Distal

What frequency can not move the short stiff fibers, and continue to the longer fibers

Low frequency sounds

What frequency vibrates the basilar membrane near its middle

Medium frequency

What frequency vibrates the basilar membrane on its base

High frequency

Pathway of sound to inner ear

Outer ear, external acoustic meatus, tympanic membrane, malleus, incus, stapes, oval window, cochlear duct, organ of corti

Frequency

Shorter wavelengths = higher frequency

Pitch

Perception of different frequencies (signals from different hair cells)

Quality

Sound characteristics like tone

Amplitude

volume

Loudness

Perception of different amplitudes

Humans can generally hear between what hertz

20-20000 hertz

Humans are most sensitive to what hertz

1500 to 4000 hertz

What is the threshold for pain (decibels)

120 decibels

Anything above 90 decibels and above can cause what if prolonged

Hearing loss

Pathway of sound info to brain

Hair cell, bipolar cell, medulla, thalamus, auditory cortex

Equilibrium

Combo of inputs from inner ear, eyes, and stretch receptors

Static equilibrium - Vestibular apparatus

Linear acceleration, position of head with respect to gravity, and helps maintain stationary balance

Dynamic equilibrium - semicircular canals

Changes in head rotation

Saccule

Cochlear duct (vertical movement)

Utricle

Semicircular canals (horizontal movements / head tilts, moving walkway)

Maculae

Equilibrium receptors located in these sacs (hair cells, different structure / otoliths)

Semicircular canals

Anterior, Lateral, Posterior (all connected to utricle sac)

Ampulla

Swollen areas of each canal, where the equilibrium receptors are

Crista ampullaris

Hair cells again, different structure

Impulses from semicircular canals are linked to

reflex eye movements

Nystagmus

Strange eye movements during and after rotation

Process of nystagmus

Rotation begins, eye drifts in opposite direction, CNS compensation causes rapid jump towards direction of rotation, rotation ends, eyes continue in direction of spin and then jerk rapidly in the opposite direction

Conduction deafness

hearing loss due to problems with the bones of the middle ear

Sensorineural deafness

A permanent lack of hearing caused by a lesion or damage of the inner ear.

Cochlear implants

Transmitter translates sound to code, then electrically stimulates vestibulocochlear nerve