Ear Flashcards
what are the two parts of the external ear?
- auricle (pinna)
2. external acoustic meatus
where does the external acoustic meatus end?
tympanic membrane
what does the external acoustic meatus start as?
concha
what is the function of the concha?
directs sound into external acoustic meatus
what are the walls of the external acoustic meatus formed from?
external 1/3 - cartilage
inner 2/3 - temporal bone
what connects the tympanic membrane to the surrounding temporal bone?
fibrocartilaginous ring
what part of the ossicular chain connects to the tympanic membrane?
malleus
what supplies the deep aspect of the external acoustic meatus and tympanic membrane?
maxillary artery
what supplies the external ear?
branches of the external carotid artery
what innervates the deeper aspect of the auricle and external auditory meatus?
branches of facial and vagus nerves
which bone is the middle ear contained in?
temporal
where does the middle ear start and end?
start - tympanic membrane
end - lateral wall of inner ear
what is the function of the middle ear?
transmit vibrations from the tympanic membrane to the inner ear
(via auditory ossicles)
where are the auditory ossicles located?
tympanic cavity in middle ear
what are the auditory ossicles?
- malleus
- incus
- stapes
what is the function of the auditory ossicles?
transmit sound vibrations through middle ear
what does the ossicular chain connect?
tympanic membrane and oval window
how is sound transmitted through the middle ear?
- sound vibrations cause movement in tympanic membrane
- causes movement in auditory ossicles
- movement helps to transmit sound waves from tympanic membrane to oval window
what are the muscles of the middle ear?
tensor tympani
stapedius
what is the function of tensor tympani and stapedius?
acoustic reflex:
contract in response to loud noise
1. inhibits vibrations of ossicles
2. reduces transmission of sound to inner ear
what is the origin and insertion of tensor tympani?
origin - auditory tube
insertion - malleus (pulls it medially)
what are tensor tympani and stapedius innervated by?
tensor tympani - branch of mandibular nerve
stapedius - facial nerve
what does stapedius attach to?
stapes
what does the eustachian (auditory) tube connect?
middle ear and nasopharynx
what is the function of the eustachian tube?
equalises the pressure of the middle ear to that of the external auditory meatus
what are the main functions of the inner ear?
- convert mechanical signals from middle ear to electrical signals (to transfer information to auditory pathway in brain)
- maintain balance by detecting position and motion
where is the inner ear located?
petrous part of temporal bone
between middle ear and internal acoustic meatus
what are the main components of the inner ear?
- bony labyrinth
2. membranous labryinth
what does the bony labyrinth contain?
- cochlea
- vestibule
- 3 semi-circular canals
contained in perilymph
what does the membranous labyrinth contain?
- cochlear duct
- semi-circular ducts
- utricle
- saccule
contained in endolymph
where is the membranous labyrinth located?
within the bony labyrinth
what are the openings from the inner ear to the middle ear and where are they?
oval window - between middle ear and vestibule
round window - between middle ear and scala tympani (part of cochlear duct)
what does the vestibule communicate with?
anteriorly - cochlea
posteriorly - semi-circular canals
what does the vestibule contain?
saccule
utricle
what are the perilymph-filled chambers in the cochlea and where are they?
scala vestibuli - superior to cochlear duct & continuous with vestibule
scala tympani - inferior to cochlear duct & terminates at round window
what is the ampulla?
swelling at the end of the semi-circular canals
what is the organ of hearing?
cochlear duct
what are the organs of balance?
vestibular apparatus
- semi-circular ducts
- saccule
- utricle
what are the epithelial cells of hearing?
organ of corti
what do the saccule and utricle detect?
saccule - movement/acceleration of the head in the vertical plane
utricle - movement/acceleration of the head in the horizontal plane
is the utricle or saccule bigger?
utricle
how is balance information sent to the brain?
- head moves
- flow of endolymph in the semi-circular ducts changes speed and/or direction
- detected by sensory receptors in ampullae
- send signals to the brain
what innervates the inner ear?
vestibulocochlear nerve
what are the branches of the vestibulocochlear nerve and what do they supply?
vestibular - utricle, saccule, semi-circular ducts
cochlear - organ of corti
what is responsible for auditory reflexes?
inferior colliculi
How is information about the movement of the head sent to the CNS?
- Rotation of head in same plane as one of the semi-circular canals
- Endolymph moves in opposite direction
- Cupola and hair cells in ampulla bend in opposite direction
- Generates impulse to CNS about position head is moving in
How is movement detected in the CNS?
- Impulses generated by semicircular canals
- Sent via vestibulocochlear nerve to vestibular nuclei (medulla)
- Vestibular nuclei make connections with nuclei of cranial nerves III, IV and VI
- Cranial nerves send information to relevant parts of body
What is the function of the medial longitudinal fasciculus?
Communication between vestibular nuclei and nuclei of nerves controlling eye movement
What is the vestibulo-ocular reflex?
Reflex movements of the eyes in response to stimulation of the vestibular system
What is the Oculo-cephalic reflex?
Allows us to maintain gaze fixed on an object when head is moving
