Ear, Hearing, and Balance

Lecture:5/5

Ear, Hearing & Balance

I. External Ear

• What is the auricle (pinna)?

  • What is the function of the auricle?

• The visible portion of the ear

  • It funnels sound into the external acoustic meatus

1. What is the external acoustic meatus?

2. What glands line the external acoustic meatus?

1. A tube that extends from the auricle to the eardrum, or tympanic membrane.

2. Ceruminous glands

II. Middle Ear

1. What is the middle ear also called?

• What flanks the middle ear laterally?

  • What flanks the middle ear medially?

1. The tympanic cavity

• The tympanic membrane

  • A bony wall with two openings: the oval window and round window

Auditory Ossicles

1. What are the three auditory ossicles?

2. What is the malleus also called?

3. What is the malleus attached to?

4. What is the incus also called?

1. Malleus, incus, and stapes

2. The hammer

3. The tympanic membrane

4. The anvil

• Where is the incus located?

  • What is the stapes also called?

    • Where does the stapes fit?

• Between the malleus and stapes

  • The stirrup

    • Into the oval window

Two Primary Roles

• What is the first primary role of the auditory ossicles?

  • What is the second primary role of the auditory ossicles?

• They amplify vibrations

  • They transfer vibrations from the tympanic membrane to the oval window

What is a third role of the auditory ossicles involving muscles?

The tensor tympani and stapedius muscles contract in response to loud sounds, providing protection

III. Pharyngotympanic Tube

1. What connects the middle ear to the nasopharynx?

2. What is the pharyngotympanic tube continuous with?

• What may result from an ascending infection through the pharyngotympanic tube?

1. The pharyngotympanic tube

2. The lining of the pharynx

• Otitis media

1. What is one function of the pharyngotympanic tube?

2. What actions can cause the pharyngotympanic tube to open?

• What sensation can occur when pressure is equalized through the pharyngotympanic tube?

1. It opens to maintain equal pressure with the environment

2. Yawning and swallowing

• The ears may "pop”

IV. Protective Muscles

1. What are the two protective muscles of the middle ear?

2. When do the tensor tympani and stapedius muscles contract?

1. Tensor tympani and stapedius

2. In response to loud sounds

V. Internal Ear — Labyrinth

Bony Labyrinth

1. What is the bony labyrinth filled with?

2. What is perilymph continuous with?

• What are the three regions of the bony labyrinth?

1. Perilymph

2. CSF

• Vestibule, semicircular canals, and cochlea

Membranous Labyrinth

1. Where is the membranous labyrinth located?

2. What does the membranous labyrinth do?

• What is the membranous labyrinth filled with?

1. Inside the bony labyrinth

2. It follows the contours of the bony labyrinth

• Endolymph

VI. Vestibule & Equilibrium

• Where is the vestibule located?

  • What two smaller sacs are found in the vestibule?

    • Where is the saccule located?

      • Where is the utricle located?

• Between the cochlea and semicircular canals

  • The saccule and utricle

    • Near the cochlea

      • Near the semicircular canal

1. What equilibrium receptors are found in the saccule and utricle?

2. What do the maculae respond to?

• What type of movement does the saccule's macula respond to?

• What type of movement does the utricle's macula respond to?

1. Maculae

2. Gravity and head position

• Forward and back tilting

• Side-to-side movement

VII. Semicircular Canals

1. How many planes do the semicircular canals have?

2. What is the swelling at one end of each semicircular canal called?

3. What does each ampulla contain?

1. Three: anterior, posterior, and lateral

2. An ampulla

3. A crista ampullaris

• What do the crista ampullares respond to?

  • What happens to the endolymph during rotational movement of the head?

    • What bends in response to the movement of the endolymph?

• Angular movements of the head

  • The endolymph moves

    • The cupula

VIII. Macula vs. Crista Ampullaris

1. Where are maculae located?

• What do maculae detect?

1. In the saccule and utricle

• Gravity and head position

How are maculae activated according to the lecture?

They respond to movements such as side-to-side movement and forward/back tilting

1. Where are crista ampullares located?

2. What do crista ampullares detect?

1. In the ampullae of the semicircular canals

2. Angular movements of the head

How are crista ampullares activated?

Rotational movement of the head causes movement of the endolymph, which causes the cupula to bend

IX. Cochlea

1. What is the cochlea?

• What are the three chambers of the cochlea?

1. A spiral structure containing three separate parallel chambers

• Scala vestibuli

• scala media

• scala tympani

Scala Vestibuli

• What does the scala vestibuli contain?

  • What is the scala vestibuli continuous with?

• Perilymph

  • The vestibule

Scala Media

• What is another name for the scala media?

  • What does the scala media contain?

• Cochlear duct

  • The spiral organ and endolymph

Scala Tympani

• What does the scala tympani contain?

• What are the scala vestibuli and scala tympani continuous with?

  • What is the helicotrema?

• Perilymph

• They are continuous, running from the oval window to the round window

  • A U-turn

X. Spiral Organ & Hearing

1. What does the spiral organ contain?

2. Where are the cochlear hair cells located?

1. Rows of cochlear hair cells with stereocilia

2. Between the basilar and tectorial membranes

1. What are the cochlear hair cells attached to?

2. What coils around the base of the hair cells?

• What nerve is formed by the cochlear nerve fibers?

1. Both the basilar and tectorial membranes

2. Cochlear nerve fibers

• The vestibulocochlear nerve

XI. Basilar Membrane & Pitch

1. What happens to the basilar membrane when suprathreshold sounds occur?

2. Where does the basilar membrane respond to high-pitch frequencies?

1. A pressure wave causes the basilar membrane to vibrate

2. Near the oval window

• Where does the basilar membrane respond to low-pitch frequencies?

  • What happens when the hair cells bend?

• Near the helicotrema

  • Ion channels open and action potentials are generated

XII. Hearing — Sound Transmission

• What happens to the tympanic membrane when it receives sound?

  • What do the auditory ossicles do with the vibrations?

• It vibrates at the same intensity as the sound it receives

  • They amplify and transfer the vibrations from the tympanic membrane to the oval window

What happens when the stapes vibrates?

It creates a pressure wave in the perilymph of the scala vestibuli

What is the sequence of sound transmission from the external ear to the bending of stereocilia?

Sound wave → auricle → external acoustic meatus → tympanic membrane → malleus → incus → stapes → oval window → pressure wave in perilymph → basilar membrane vibrates → hair cells bend → stereocilia bend → ion channels open → action potentials generated

Short version to memorize:

Auricle → Meatus → Tympanic membrane → Malleus → Incus → Stapes → Oval window → Cochlea → Basilar membrane → Hair cells/stereocilia

XIV. Auditory Pathway

Where are sound signals processed?

In the primary auditory cortex of the temporal lobe

XV. Disorders — Deafness

Conductive Deafness

What is conductive deafness associated with?

Problems with sound conduction, including impacted ear wax, hole/tear eardrum, and otosclerosis (abnormal) of the ossicles

Sensorineural Deafness

What can cause sensorineural deafness?

Loss of hair cells/stereocilia, degeneration of the cochlear nerve, stroke, or tumors of the auditory cortex