Ear Flashcards
What are the two major systems of the ear?
auditory system: sound perception
vestibular system: balance
What are the three divisions of the ear?
external ear
middle ear
internal ear
What is the external ear made up of? What is the shape determined by?
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
State the composition of the external aucustic meatus.
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
How is ear wax formed? What is its real name? What is its function?
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)
What is the composition of the middle ear? Location? Lining?
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).
What seperates the external ear from the middle ear?
tympanic membrane
Why is the middle ear easy to damage?
simple epithelial layer (1 cell thick)
What is the function of the auditory tube?
equillibrate the pressure in the ear and nose
What is the shape, function and layers of the tympanic membrane?
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)
What is the function fo the ear ossicles?
amplify sound
How many ossicles does the ear have? What are they?
3 ossicles:
1) malleus=hammer (tympanic membrane + incus)
2) incus=anvil (malleus + stapes)
3) stapes=stirrup (fits into the oval window)
What is the function of the ossicles?
Convert sound waves to mechanical (hydraulic) vibrations in tissues and fluid filled chambers.
What is the function of the auditory (Eustachian) tube? What is it composed of?
- narrow, flattened chamber
- lined with ciliated pseudostratified columnar epithelium + goblet cells
- vents the middle ear equalizing its pressure with the atmospheric pressure.
What is the function of the internal ear?
makes the senses work
What does the internal ear consist of?
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
What is the bony labyrinth composed of?
3 connected spaces:
- semicircular canals
- vestibule
- cochlea
What is the membranous labyrinth composed of?
series of communicating sacs (utricle, saccule and endolymphatic sac) and ducts containing endolymph (3 semicircular ducts, cochlear duct, utriculosaccular duct, and ductus reuniens).
What is the major difference bewteen the inner ear and the other 2 ear parts?
inner ear is filled with fluid, while the other parts are filled with air.
State the location of cells in the inner ear.
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
What is the function of cristae ampullaris?
receptors for angular acceleration of the head
What is the function of maculae?
receptors for position of the head and its linear movements
What is the function of spiral organ of Corti?
receptors for sound
What is the function of hair cells?
mechanoelectric transducers (convert mechanical energy into electrical energy)
Why are hair cells called hair cells?
- 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
What is the kinocilium?
in the vestibular system, each hair cell possesses a single true cilium located behind the row of the longest stereocilia
What are both hair cell types associated with?
afferent and efferent nerves
How do type I hair cells look?
- flask-shaped
- rounded base
- thin neck
- surrounded by afferent nerve chalice and a few efferent nerves
How do type II hair cells look?
- cylindrical
- afferent and efferent bouton nerve endings at the base of the cell
What does the utricle and saccule maculae contain? What is their function?
hair cells - epithelial mechanoreceptors
State the composition of hair cells.
- 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
State the function of hair cells
- 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
Which part of the ear does ‘acceleration power’ affect most? How is it affected?
gelatin mass= otolithic membrane with otoliths
- affected in the opposite direction
Explain the function of the sensory receptors in cristae ampullaris.
- 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
What is the difference between the function of cristae ampullaris and otoliths of hair cells?
cristae ampullaris- sensors of angular movements of the head (centrifugal power)
otoliths of hair cells- sensors for gravity and linear acceleration (acceleration power)
What is the cochlear canal (labyrinth) divided into?
1) scala media / cochlear duct (middle compartment filled with endolymph + spiral organ of Corti)
2) scala vestibuli
3) scala tympani (+ perilymph)
What is the cochlear canal in charge of?
sound recieving
State the composition of the scala media.
- triangular space
- basilar membrane (bottom) + spiral organ of Corti
- vestibular membrane (top) (seperates scala media from vestibuli)
- lateral wall= stria vascularis= produces endolymph
What is the spitral organ of Corti composed of?
- hair cells (inner and outer rows),
- supportive phalangeal cells,
- pillar cells
How is the tectorial membrane formed?
- radially oriented bundles of collagen fibers
- lateral free edge projects over and attached to the organ of Corti by stereocilia of hair cells.
Explain how sound is transmitted.
- 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)
