Ear

Question 1

What are the main divisions of the ear and their function?

Answer 1

External ear - collects sounds waves and directs them towards the middle ear, tympanic membrane converts sound waves into mechanical vibrations

Middle Ear (Tympanic cavity) - amplifies mechanical vibration and transmits vibrations to fluid in internal ear

Internal Ear - Converts fluid vibration to nerve impulse to detect sound, orientation, and acceleration of head, vestibulocochlear nerve (CN VIII)

Question 2

What are the parts of the external ear?

Answer 2

Auricle

External Acoustic Meatus

Tympanic Membrane

Question 3

What is the auricle?

Answer 3

Lined by thin skin with hair follicles, sweat and sebaceous glands

Overlies a core of elastic cartilage

Question 4

What is the external acoustic meatus?

Answer 4

Lateral 1/3 elastic cartilage and medial 2/3 is temporal bone

Line with thin skin but lacks sweat glands

Ceruminous glands present - modified sweat glands that secrete cerumen (wax)

Question 5

What is the tympanic membrane?

Answer 5

Lined externally by skin from ectoderm and continuous with that of external acoustic meatus

Lined internally by simple cuboidal epithelium and continuous with mucous membrane of the middle ear cavity. Derived endoderm

Question 6

What are the parts of the middle ear?

Answer 6

Ossicles:
Malleus
Incus
Stapes

Epithelium

Question 7

What is the malleus?

Answer 7

Hammer

Attached to tympanic membrane

Tensor tympani muscle pulls on malleus to increase tension of the tympanic membrane, preventing vibration

Question 8

What is the incus?

Answer 8

Anvil

Question 9

What is the stapes?

Answer 9

Stirrup

Smallest of the ear ossicles

Transmits mechanical vibration to oval window, causing vibrations in fluid of internal ear

Staepedius muscle - dampens movement of the stapes on the oval window

Question 10

What is the attenuation reflex?

Answer 10

Staepedius and tensor tympani limit movement of ossicles to protect the internal ear from damaging loud sounds

Question 11

Describe the epithelium of the middle ear

Answer 11

Lined with simple cuboidal to pseudostratified columnar epithelium

Mucous glands (goblet cells) are present deep within the tympanic cavity in the vicinity of the auditory tube

Auditory tube allows communication between tympanic cavity and nasopharynx

Question 12

What are the parts of the internal ear?

Answer 12

Bony Labyrinth - space within temporal bone and filled with perilymph, semicircular canals, vestibule, cochlea

Membranous Labyrinth - sacs suspended within bony labyrinth, filled with endolymph, vestibular labyrinth, cochlear labyrinth

Question 13

What is in the vestibular labyrinth of the membranous labyrinth?

Answer 13

Saccule and utricle - sensory organ the macula

Semicircular ducts - sensory organ is crista ampullaris

Sensory cells

Question 14

What are the characteristics and functions of the macula?

Answer 14

Detects linear acceleration - horizontal and vertical movements

Within utricle and saccule

Macula of utricle (horizontal acceleration) and saccule (vertical acceleration) are at right angles with each other

Structure - hair cells with sterocilia embedded within otolithic membrane and surrounded by supporting cells

Otolithic membrane - gelatinous sheet with small crystals (otoconia) lining surface and inertia of otoconia causes lag between movement of head and otolithic membrane, deflecting stereocilia

Question 15

What is the crista ampullaris in the semicircular ducts?

Answer 15

Located in the ampulla of semicircular ducts

Sense angular/rotational movements of the head

Orientated 90 degrees to long axis of the semicircular canal

Structure: Stereocilia of hair cells embedded in cupula, which is gelatinous cap over sensory epithelium.

Hair cells surrounded by supporting cells

Rotational movement of head in the plane of a particular semicircular canal causes deflection of the cupula and stereocilia in the opposite direction of movement

Question 16

What are the sensory cells within the vestibular labyrinth?

Answer 16

Vestibular hair cells consist of a single true cilium (kinocilium) and many sterocilia

stereocilia are asymmetrical with longest adjacent to kinocilium to sense directionality and directionality of movement indicated by deflection towards or away from kinocilium

Type I hair cells - rounded base, surrounded by afferent nerve

Type II hair cells - cylindrical base, afferent nerve does not surround base

Question 17

What is the cochlear labyrinth of the membranous labyrinth?

Answer 17

Cochlear duct divides the cochlea into 3 chambers:

1. Scala Vestibuli
2. Scala tympani
3. Scala Media

Question 18

What is the Scala Vestibuli of the cochlear labyrinth?

Answer 18

Separated from cochlear duct by the vestibular membrane

Communicates with tympanic cavity through oval window

Filled with perilymph

Question 19

What is the scala tympani of the cochlear labyrinth?

Answer 19

Separated from cochlear duct by basilar membrane

Basilar membrane - attaches to osseous spiral lamina, supports spiral organ of corti

Ends at the round window on medial wall of the tympanic cavity

Filled with perilymph

Question 20

Scala vestibuli and scala tympani are continuous at the ____

Answer 20

Helicotrema (apex of the cochlea)

Question 21

What is the scala media?

Answer 21

Within the cochlear duct itself

Filled with endolymph

Stria vascularis in outer wall produces endolymph

Spiral ligament attaches cochlear duct to outer wall of cochlea and supports basilar membrane

Tectorial membrane overlies spiral organ of corti, hair cells embedded within it, and spiral limbus secretes and anchors tectorial membrane to medial wall of cochlea

Ends at the helicotrema - tip of spiral cochlea

Question 22

What is the Spiral Organ of Corti, the sensory organ of the scala media?

Answer 22

Organ of hearing

Contains sensory cells:
Hair cells - inner and outer with stereocilia embedded within tectorial membrane, no kinocilium, do not detect directionality

Inner hair cells - form one row and completely surrounded by inner phalangeal cells

Outer hair cells - form 3-4 rows, only partially surrounded by outer phalangeal cells

Supporting cells:
Phalangeal cells - inner and outer, support hair cells

Pillar cells - inner and outer, form tunnel of Corti

Question 23

How is sound perceived?

Answer 23

1. Sound waves vibrate tympanic membrane
2. Tympanic membrane moves ossicles and amplifies vibrations
3. Movement of stapes in oval window produces waves in perilymph of scala vestibuli
4. Fluid waves vibrate basilar membrane deflecting stereocilia of hair cells - pitch detected based on width of basilar membrane
5. Vibrations dissipate through round window into tympanic cavity

Question 24

What is vertigo?

Answer 24

Otoconia usually from utricle, become dislodged and falls into the ampulla of a semicircular canal

Stimulates hair cells of crista ampullaris when head is moved

Produces erroneous sensation of spinning with movements of the head