Ear

Question 1

What are the two major systems of the ear?

Answer 1

auditory system: sound perception
vestibular system: balance

Question 2

What are the three divisions of the ear?

Answer 2

external ear
middle ear
internal ear

Question 3

What is the external ear made up of? What is the shape determined by?

Answer 3

auricle (pinna):
- oval appendage projecting from the head surface
- shape is determined by an internal supporting structure of elastic cartilage

hair follicles, sweat glands (ceruminous glands), sebaceous glands cover the auricle

external acoustic meatus:
- air filled tubular space following an s-shaped course to the tympanic membrane (eardrum)

elastic cartilage + skin

Question 4

State the composition of the external aucustic meatus.

Answer 4

wall of the lateral 1/3:
- cartilaginous
- continuous with the elastic cartilage of the auricle

medial 2/3:
- contained within the temporal bone

lined by skin
- continuous with auricle (pinna) skin

Question 5

How is ear wax formed? What is its real name? What is its function?

Answer 5

ear wax - cerumen

• formation: secretion of ceruminous glands mixes with secretions of sebaceous glands and desquamated cells
• function: lubricates skin, coats meatal hairs to empede the entry of foreign particles, provides antimicrobial protection from bacteria, fungi and insects)

Question 6

What is the composition of the middle ear? Location? Lining?

Answer 6

location: tympanic cavity (air-filled space in temporal bone)
lined by: simple squamous/cuboidal epithelium
contents: auditory ossicles (3 small bones + 2 movable joints), eustachian tube (auditory tube opening into the nasopharynx + muscles attaching to the ossicles).

Question 7

What seperates the external ear from the middle ear?

Answer 7

tympanic membrane

Question 8

Why is the middle ear easy to damage?

Answer 8

simple epithelial layer (1 cell thick)

Question 9

What is the function of the auditory tube?

Answer 9

equillibrate the pressure in the ear and nose

Question 10

What is the shape, function and layers of the tympanic membrane?

Answer 10

shape: irregular cone

function: barrier b/w external aucustic meatus and middle ear

layers (outside to inside):
- skin of external aucustic meatus (external ear side)
- DENSE connective tissue core with collagen fibers (radially and circularily arranged)
- mucosa (squamous/cuboidal epithelium- middle ear side)

Question 11

What is the function fo the ear ossicles?

Answer 11

amplify sound

Question 12

How many ossicles does the ear have? What are they?

Answer 12

3 ossicles:
1) malleus=hammer (tympanic membrane + incus)
2) incus=anvil (malleus + stapes)
3) stapes=stirrup (fits into the oval window)

Question 13

What is the function of the ossicles?

Answer 13

Convert sound waves to mechanical (hydraulic) vibrations in tissues and fluid filled chambers.

Question 14

What is the function of the auditory (Eustachian) tube? What is it composed of?

Answer 14

• narrow, flattened chamber
• lined with ciliated pseudostratified columnar epithelium + goblet cells
• vents the middle ear equalizing its pressure with the atmospheric pressure.

Question 15

What is the function of the internal ear?

Answer 15

makes the senses work

Question 16

What does the internal ear consist of?

Answer 16

2 labyrinthine compartments (one contained within the other)

1) BONY LABYRINTH:
- system of interconnected cavities and canals in the* temporal bone*

2) MEMBRANOUS LABYRINTH:
- inside bony labyrinth
- complex system of small sacs and tubules forming a continuous space

Question 17

What is the bony labyrinth composed of?

Answer 17

3 connected spaces:
- semicircular canals
- vestibule
- cochlea

Question 18

What is the membranous labyrinth composed of?

Answer 18

series of communicating sacs (utricle, saccule and endolymphatic sac) and ducts containing endolymph (3 semicircular ducts, cochlear duct, utriculosaccular duct, and ductus reuniens).

Question 19

What is the major difference bewteen the inner ear and the other 2 ear parts?

Answer 19

inner ear is filled with fluid, while the other parts are filled with air.

Question 20

State the location of cells in the inner ear.

Answer 20

specialized sensory cells and accessory supporting cells are located in 6 regions in the membranous labyrinth.

• 3 cristae ampullaris –> ampullae of semicircular ducts
• 2 maculae –> utricle and saccule
• spiral organ of Corti

Question 21

What is the function of cristae ampullaris?

Answer 21

receptors for angular acceleration of the head

Question 22

What is the function of maculae?

Answer 22

receptors for position of the head and its linear movements

Question 23

What is the function of spiral organ of Corti?

Answer 23

receptors for sound

Question 24

What is the function of hair cells?

Answer 24

mechanoelectric transducers (convert mechanical energy into electrical energy)

Question 25

Why are hair cells called hair cells?

Answer 25

- organized bundle of rigid projections at their apical surface, - surface holds a hair bundle formed by rows of stereocilia called sensory hairs - rows increase in height in one direction across the bundle

Question 26

What is the kinocilium?

Answer 26

in the vestibular system, each hair cell possesses a single true cilium located behind the row of the longest stereocilia

Question 27

What are both hair cell types associated with?

Answer 27

afferent and efferent nerves

Question 28

How do type I hair cells look?

Answer 28

- flask-shaped - rounded base - thin neck - surrounded by afferent nerve chalice and a few efferent nerves

Question 29

How do type II hair cells look?

Answer 29

- cylindrical - afferent and efferent bouton nerve endings at the base of the cell

Question 30

What does the utricle and saccule maculae contain? What is their function?

Answer 30

hair cells - epithelial mechanoreceptors

Question 31

State the composition of hair cells.

Answer 31

- contain **hair bundles** (on apical surfaces) formed by stereocilia with a single kinocilium - overlaid with a *gelatin-like* **otolithic membrane** which contains **otoliths** | otolith= otoconia calcium carbonate

Question 32

State the function of hair cells

Answer 32

- movement of otoliths is detected by hair bundles, - hair buncles activate mechanically gated ion channels - action potential is generated - functions as a sensor for cravity and linear acceleration

Question 33

Which part of the ear does 'acceleration power' affect most? How is it affected?

Answer 33

gelatin mass= otolithic membrane with otoliths - affected in the opposite direction

Question 34

Explain the function of the sensory receptors in cristae ampullaris.

Answer 34

- sensory receptors are covered by a gelatin mass= **CUPULA** - **no otoliths** cupula is deflected during the flow of endolymoh - movement within the cupula stimulated the generation of an action potential through the stimulation of mechanically gated ion channels

Question 35

What is the difference between the function of cristae ampullaris and otoliths of hair cells?

Answer 35

**cristae ampullaris**- sensors of **angular movements** of the head (centrifugal power) **otoliths** of hair cells- sensors for **gravity** and **linear acceleration** (acceleration power)

Question 36

What is the cochlear canal (labyrinth) divided into?

Answer 36

1) scala media / cochlear duct (middle compartment filled with endolymph + spiral organ of Corti) 2) scala vestibuli 3) scala tympani (+ perilymph)

Question 37

What is the cochlear canal in charge of?

Answer 37

sound recieving

Question 38

State the composition of the scala media.

Answer 38

- triangular space - basilar membrane (bottom) + spiral organ of Corti - vestibular membrane (top) (seperates scala media from vestibuli) - lateral wall= stria vascularis= produces endolymph

Question 39

What is the spitral organ of Corti composed of?

Answer 39

- hair cells (inner and outer rows), - supportive phalangeal cells, - pillar cells

Question 40

How is the tectorial membrane formed?

Answer 40

- radially oriented bundles of collagen fibers - lateral free edge projects over and attached to the organ of Corti by stereocilia of hair cells.

Question 41

Explain how sound is transmitted.

Answer 41

- stereocilia on hair cells move during interaction with the overlying tectorial membrane - tectorial membrane generated an electrical impulse - electrical impulse is transmitted to the cochlear nerve - sound waves are transmitted from the vibrating tympanic membrane to the oval window by ossicles - sound waves produce movement of the perilymph in the scala vestibule - movement deflect sthe basilar membrane and spiral organ of Corti to generate electrical nerve impulases (percieved by the brain as sounds)