PHS 301 Hearing and Equilibrium

Question 1

Functions of the ear and where these functions are interpreted

Answer 1

• Hearing (interpreted in the auditory cortex of
  the temporal lobe)

– Equilibrium (balance) (interpreted in the
cerebellum)

Question 2

Regions of the ear

Answer 2

–Outer ear – functions in hearing, gathers
sound.
– Middle ear – functions in hearing; transmit
and modulate sound
– Inner ear – functions in both hearing and
equilibrium

Question 3

Structures of the external ear

Answer 3

• Auricle (pinna)
• External acoustic meatus / External auditory canal
• Tympanic membrane

Question 4

Function of Auricle (pinna)

Answer 4

collects sound and helps direct sounds. Composed of the helix (rim) and the lobule (earlobe)

Question 5

External acoustic meatus / External auditory canal characteristics and functions

Answer 5

– Lined with skin
– Contains hairs, sebaceous glands, and
ceruminous glands
– Tiny hairs called cilia aid in transmitting
sound waves inward.
– Ends at the tympanic membrane (eardrum)

Question 6

Tympanic membrane

Answer 6

Forms the boundary between / Separates
the external and middle ear

Question 7

Characteristic of middle ear

Answer 7

• Air-filled cavity within the temporal bone
• Only involved in the sense of hearing
• The tympanic cavity
• Medial wall

Question 8

The tympanic cavity

Answer 8

– A small, air-filled space
– Located within the petrous portion of the
temporal bone

Question 9

Medial wall is penetrated by

Answer 9

–Oval window
– Round window

Question 10

Describe the two tubes associated with the middle ear

Answer 10

• The opening from the auditory canal is covered by the tympanic membrane (eardrum).
• The auditory tube (also known as the
  Pharyngotympanic tube or eustachian tube) connecting the middle ear with the throat or pharynx.
• Allows for equalizing pressure during yawning or swallowing
• This tube is otherwise collapsed

Question 11

Describe the auditory ossicles

Answer 11

– Malleus (hammer)
* Resembles shape of a hammer
* Connected to tympanic membrane and
transmits sound vibrations to second auditory ossicle

– Incus (anvil)
* Resembles shape of an anvil
* Transmits sound vibrations from malleus to third auditory ossicle.

– Stapes (stirrup)
* Shaped like a tiny stirrup
* Transmits sound vibrations from incus to inner ear

Question 12

Function of the Oval window

Answer 12

• Separates middle ear from inner ear
• Base of stapes fits into oval window

Question 13

Muscles that inhibit vibration when sound is too loud

Answer 13

– Tensor tympani m. (inserts on malleus)
– Stapedius m. (inserts on stapes)

Question 14

What is the inner ear?

Answer 14

Also known as labyrinth- twisted bony tubes.
Includes sense organs for hearing and balance.

Question 15

Types of labyrinth in the inner ear

Answer 15

Bony (protective) labyrinth
Membranous labyrinth

Question 16

Describe the Bony labyrinth

Answer 16

a cavity consisting of three parts:

• Semicircular canals
• Vestibule
• Cochlea

Contains perilymph; similar composition to CSF since it is connected to the arachnoid space.

Question 17

Discuss the membranous labyrinth

Answer 17

Membranous labyrinth
- series of membrane-walled sacs and ducts
– Fit within the bony labyrinth
– Suspended in perilymph, filled with a clear fluid –endolymph.

– Consists of three main parts
* Semicircular ducts
* Utricle and saccule
* Cochlear duct

Question 18

Discuss the cochlea

Answer 18

• A spiraling chamber (Snail-shaped) in the bony labyrinth
• Contains endolymph and perilymph; auditory fluids that aid in the transmission of sound vibrations.
• Coils around a pillar of bone – the modiolus
• Spiral lamina – a spiral of bone in the modiolus that holds the cochlea in position
• The cochlear nerve ( a branch of the vestibulocochlear nerve CNVIII) runs through the core of the modiolus

Question 18

The cochlear duct (scala media) function, location and constituents

Answer 18

– contains receptors for hearing
– Lies between two chambers
* The scala vestibuli
* The scala tympani

– The vestibular membrane – the roof of the cochlear duct
– The basilar membrane – the floor of the cochlear duct

It is the auditory party of the inner ear

Question 19

Organ of Corti

Answer 19

the receptor epithelium for hearing, also called the “True organ of hearing”
* Consists of hair cells (receptor cells).
* Here, sound vibrations are converted into nerve impulses that are transmitted to the brain for interpretation as hearing

Question 20

The AUDITORY PATHWAY is divided into two subsystems

Answer 20

– The Peripheral auditory pathway (Outer, Middle and Inner ear)

– The Central auditory pathway (from the
cochlear nucleus up to the primary auditory
cortex).

Question 21

Peripheral auditory pathway

Answer 21

• The outer ear collects sound waves
• The sound waves strike the tympanic
  membrane, causing it to vibrate.
• Vibrations from the eardrum move the malleus
• These vibrations are transmitted across the middle ear by three bony ossicles.
• Stapes transfer sound through the oval
  window to the cochlea of the inner ear.
• As the stapes moves into the oval window, transmitting its vibrations, the round window membrane moves out, thus allowing movement of the fluid within the cochlea.
• The round window serves as a pressure relief valve.
• Fluid movement within the cochlear moves the basilar membrane and this leads to the bending of the hair cells (actual vibration receptors) within the organ of Corti.

Question 22

CENTRAL AUDITORY PATHWAY

Answer 22

• This moves stereocilia at the tips of the hair cells against the tectorial membrane and opens potassium channels in them.
• The influx of K+ from the endolymph depolarizes the cell.
• Depolarization of the hair cell causes the release of a neurotransmitter (probably glutamate) at its basal surface and the initiation of nerve impulses in a sensory neuron that synapses with it.
• Action potentials are sent through the hair cells to the afferent cochlear nerves to the brain.
• The cochlear branch of nerve VIII runs from the organ of Corti to the brain
• Continued stimulation can lead to adaptation (overstimulation to the brain makes it stop interpreting the sounds)

Question 23

The ascending auditory pathway

Answer 23

Transmits information from cochlear receptors to the cerebral cortex

Question 24

Types of equilibrium

Answer 24

– Static equilibrium- in the vestibule – Dynamic equilibrium- in the semicircular canals

Question 25

Discuss the vestibule Vestibule

Answer 25

* Central portion of inner ear * Located next to stapes and between cochlea and semicircular canals * Contains utricle and saccule membranous pouches or sacs that aid in maintaining balance.

Question 26

Discuss the Utricle and saccule

Answer 26

suspended in perilymph * Two egg-shaped parts of the membranous labyrinth * House the macula – a spot of sensory epithelium * Organs of balance that detect movement and acceleration Utricle - larger and receives semi-circular ducts Saccule - receives the cochlear duct

Question 27

Macula description and function

Answer 27

* Each saccule and utricle contains a macula * Each macula can therefore cover two dimensions of movement (up and down, forward and back). * Hence, keeps one vertically oriented with respect to gravity. Macula – contains receptor cells – Monitor the position of the head when the head is still – Contains columnar supporting cells – Receptor cells – called hair cells * Synapse with the vestibular nerve

Question 28

Semicircularcanals description and function

Answer 28

• Located behind the vestibule • Three bony, fluid-filled loops that help to maintain one’s balance. • Lie posterior and lateral to the vestibule • Anterior and posterior semicircular canals lie in the vertical plane at right angles • Lateral semicircular canal lies in the horizontal plane. • Semicircular duct – snakes (inserts and rotates inside) through each semicircular canal

Question 29

What is STATIC EQUILIBRIUM?

Answer 29

Maculae–receptors in the vestibule – Senses static equilibrium and linear acceleration of the head (not rotational movements) – Report on the position of the head –Send information via the vestibular nerve to the cerebellum. * Hair cells are embedded in the otolithic membrane * Otoliths (tiny stones) (carbon carbonate CaCO3) float in a gel around the hair cells. * Movements cause otoliths to bend the hair cells (gravity moves the “rocks” over and pulls the hairs) * When hair cells in the otolith organs are activated, signals reach the medial part of the ventral horn. By activating the ipsilateral pool of motor neurons innervating extensor muscles in the trunk and limbs, this pathway mediates balance and the maintenance of upright posture. * Hence, the otolith organs are also known as gravity receptors, responsible for detecting linear acceleration, or movement in a straight line.

Question 30

What is ANGULAR/DYNAMIC EQUILIBRIUM?

Answer 30

• Action of angular head movements (i.e., rotation, lateral flexion or nodding) is controlled by three semicircular canals • Have swellings, called ampullae and within each ampulla is the sense organ, called the crista. • In the cristae the hairs of the hair cells are embedded in a gelatinous mass, called the cupula, which extends across the ampulla Any rotation of the head results in fluid motion within the canals. • Movement of endolymph causes a deflection (pushing) of the cupula. • The cupula stimulates the hair cells • An impulse is sent via the vestibular nerve to the cerebellum. • A large role of the semicircular canal system is to keep the eyes still in space while the head moves around them.

Question 31

Equilibrium pathway

Answer 31

• Via vestibular nerve branch of VIII (Vestibulocochlear n.) to the brain stem • Only special sense for which most of the information goes to lower brain centers

Question 32

What do the Auditory and Vestibular Systems Have in Common (and why some disease processes can affect both hearing & balance)

Answer 32

1. Common Fluid System. The membranous labyrinth is one continuous fluid system serving both hearing and balance. If there’s something wrong with this fluid system, both hearing and balance will be affected. Example: Meniere’s Disease. 2. Hair Cell Motion Detectors. Hearing and balance both involve the detection of motion: slowly varying (i.e., low frequency) in the case of balance, higher frequency vibratory motion in the case of hearing. In both cases, the motion detectors are hair cells that operate on nearly identical principles.

Question 33

DISORDERS OF THE EAR

Answer 33

• Ménière's Disease – Chronic inner ear disease – Over accumulation of fluid in the labyrinth – Characterized by recurring episodes of vertigo, hearing loss, feeling of pressure or fullness in the affected ear, and tinnitus • Labyrinthitis – Infection or inflammation of the labyrinth or the inner ear –Specifically, the three semicircular canals in the inner ear

Question 34

Types of deafness

Answer 34

* Conductive –Hearing loss caused by breakdown of the transmission of sound waves through the middle and/or external ear. * Sensorineural –Hearing loss caused by inability of nerve stimuli delivery to brain from inner ear due to damage in auditory nerve or cochlea. * Note: Anything that deranges the vestibular signal causes vertigo, a perception of head motion when the head is still. This may be associated with visuovestibular conflict, nausea, and vomiting.

Question 35

The utricle and saccule detect motion in which planes?

Answer 35

* The utricle lies horizontally in the ear and can detect any motion in the horizontal plane. * The saccule is oriented vertically, so it can detect motion in the sagittal plane.