Special Senses (Hearing & Balance)

Question 1

3 areas of the ear:

Answer 1

1. External ear - auricle (“funnel”) & external acoustic meatus
2. Middle ear (tympanic cavity): AIR filled, mucosa lined
3. Internal ear (labyrinth) - carved into temporal bone, hearing & equilibrium

Question 2

Tympanic membrane

Answer 2

Eardrum, divides external ear and middle ear, VIBRATES and transmits sound

Question 3

Pharyngotympanic tube

Answer 3

Aka Eustachian tube, connects nasopharynx (throat) to inner ear

Question 4

Auditory ossicles (lateral to medial)

Answer 4

1. MALLEUS (hammer) - connects to eardrum
2. INCUS (anvil) - articulates w/ malleus & stapes
3. STAPES (stirrup) - sits in *oval window

“MIS has 3 bones in her ear”

Question 5

2 parts of INTERNAL ear:

Answer 5

1. Bony labyrinth (“cave”) - continuous space in bone, filled w/ perilymph
2. Membranous labyrinth (“water balloon” lining) - continuous series of membranous sacs & ducts, filled w/ endolymph

Question 6

Perilymph

Answer 6

Similar to CSF, fills bony labyrinth

*sound waves vibrate these fluids

Question 7

Endolymph

Answer 7

Similar to INTRACELLULAR FLUID, fills Membranous labyrinth

*sound waves vibrate these fluids

Question 8

3 regions of bony labyrinth:

Answer 8

1. Vestibule (equilibrium)
2. Semicircular canals (equilibrium)
3. Cochlea (hearing)

Question 9

Vestibule

Answer 9

“Central cavity” of BONY LABYRINTH, “big open entry space”: contains saccule & utricle - each w/ equilibrium receptors

Question 10

Semicircular canals

Answer 10

“loop de loops” of BONY LABYRINTH, each ~2/3 of a circle @ right angles to each other - XYZ axis, **equilibrium

Question 11

Cochlea

Answer 11

Spiral “snail shell” conical structure of BONY LABYRINTH, **hearing

Question 12

3 chambers of the cochlea:

Answer 12

1. SCALA VESTIBULI - superior, connects to OVAL window, *perilymph
2. SCALA MEDIA - middle, aka cochlear duct, *endolymph
3. SCALA TYMPANI - inferior, connects to ROUND window, *perilymph

Scala = “ladder”

Question 13

Receptor organ of hearing:

Answer 13

Organ of Corti / spiral organ

Question 14

Higher FREQUENCY (short wavelength) =

Answer 14

higher PITCH

Question 15

Higher AMPLITUDE =

Answer 15

higher intensity/LOUDNESS

Question 16

How we hear (summary):

Answer 16

1. Sound waves are created by vibrating objects > cause a pressure disturbance in the air
2. Sound waves enter ear and strike tympanic membrane which vibrates at same frequency
3. Auditory ossicles amplify & transfer this motion
4. Stapes pushes on the oval window, generating a wave in the perilymph of the scala vestibuli.
5. Frequencies behave differently: - below 20Hz travel entire SV & ST - no vibration in SM = no sound … higher frequencies vibrate SM and excite HAIR CELLS = sound
6. Signal travels from cochlea along cochlear nerve (CN VIII) to thalamus and then auditory cortex of temporal lobe

Question 17

Equilibrium is a response to _____.

Answer 17

Various head movements

Question 18

Vestibular apparatus:

Answer 18

equilibrium sensors in “otolith organs” and semicircular canals (inner ear) that detect head movements.

Question 19

“Otolith organs” of inner ear (2):

Answer 19

1. Utricle
2. Sacule
   membranous sacs in the VESTIBULE of the inner ear that are responsible for detecting linear acceleration and head tilt, each with one MACULA

Question 20

Macula:

Answer 20

Sensory organ for LINEAR change: up/down, front/back, left/right

w/ HAIR CELLS that act as sensory receptors embedded in otolith mb (weighed down by tiny stones) - synapse with CN VIII: Vestibulocochlear

Question 21

Crista ampullaris (crista):

Answer 21

Sensory organ for ROTATIONAL change

One crista in each semicircular canal (X, Y and Z planes), each w/ many hair cells embedded in otolith mb.