The ear Flashcards
1
Q
What are the three main sections of the ear?
A
External, middle and inner.
2
Q
What does the external ear consist of?
A
- auricle (pinna) = visible part of the ear that resides outside the head.
- external acoustic meatus (EAM) = (also known as the ear canal) tube running from outer ear to the middle ear. The ear canal extends from the pinna to the eardrum around 2.5cm in length and 0.7 cm in diameter.
3
Q
What does the middle ear consist of?
A
- It is the air-filled central cavity of the ear, behind (or internal) the eardrum.
- Auditory ossicles: the ossicles are three bones in the middle ear that are among the smallest bones in the human body. They serve to transmit sound from the air to the fluid filled labyrinth (cochlea).
4
Q
What does the inner ear consist of?
A
- the inner ear is supplied by the 8th cranial nerve in all vertebrates.
- responsible for sound detection and balance.
- it consists of the bony labyrinth, a hollow cavity in the temporal bone of the skull with a system of passages comprising two main functional parts:
- the cochlea = dedicated to hearing, converting sound pressure patterns from the outer ear into electrochemical impulses which are passed onto the brain via the auditory nerve.
- the vestibular system = dedicated to balance.
5
Q
What is the external acoustic meatus?
A
- also known as the ear canal (part of external ear).
- canal is 2-3cm in length,
- the lateral (to the side) 1/3 is catilaginous ‘S-shaped’ .
- the ceruminous and sebaceous glands produce earwax (cerumen).
- the medial (middle - close to body) 2/3 are bony and lined with thin skin continuous with the tympanic membrane.
6
Q
What is the tympanic membrane?
A
- also known as the ear drum.
- thin semi-transparent membrane.
- externally lined by thin skin.
- it functions to transmit sound from the air to the ossicles in the middle ear and then to the oval window in the fluid filled cochlea.
- it’s internally lined by mucous membrane.
- separates external ear and middle ear.
7
Q
What does the tympanic membrane consist of?
A
- umbo.
- cone of light.
- lateral process of malleus.
- handle of malleus.
8
Q
What does the middle ear consist of?
A
- 3 auditory ossicles: 3 small bones. They transmit sound from the air to the fluid filled cochlea in the inner ear. They are known as malleus, incus and stapes.
- the eardrum is merged to the malleus, which connects to the incus which in turn connects to the stapes.
- the movement of ossicles may be stiffened by two muscles.
- stapedius muscle: connects to the stapes and is controlled by the facial nerve.
- tensor tympani: connects to the base of the malleus and is under the control of the medial pterygoid nerve.
- these muscles contract in response to loud sounds, reducing the transmission of sound to the inner ear.
- known as the acoustic reflex.
9
Q
What do the auditory ossicles look like?
A
- malleus: has a head and handle (looks like a muscles arm).
- incus: has a body and limbs (thickest of the three parts, has a kink in it).
- stapes: has a body and base (looks like a circle).
10
Q
Where in the middle ear are tensor tampani and stapedius located?
A
- tensor tympani: this muscle is not as strong as stapedius. It courses through a bony canal in the wall of the anterior middle ear and attaches to the neck of the manubrium.
- stapedius: arises from the pyramidal process and the tendon attaches to the posterior neck of the stapes.
11
Q
What happens in the inner ear?
A
- Movements of the tympanic membrane (ear drum) are transmitted by the auditory ossicles to the inner ear.
12
Q
What does the inner ear consist of?
A
- vestibulochochlear organ (reception of sound and balance maintenance).
- membranous labyrinth.
- bony labyrinth.
- the bony labyrinth is the network of passages with bony walls lined with periosteum. The membranous labyrinth runs inside the bony labyrinth. There is a layer of perilymph fluid between them.
13
Q
What is the bony labyrinth?
A
- rigid bony outer wall of the inner ear.
- contained within the otic capsule of the petrous part of the temporal bone.
- consists of three parts: vestibule, semicircular canals and cochlea.
- these are cavities hollowed out of the substance of the bone and lined by periosteum.
- they contain clear fluid, the perilymph, in which the membranous labyrinth is situated.
14
Q
What is the membranous labyrinth?
A
- situated in the inner ear.
- lodged within the bony labyrinth.
- collection of fluid filled tubes and chambers which contain the receptors for the sense of equilibrium and hearing.
- separated from the walls of the bony labyrinth by perilymph.
15
Q
What is cranial nerve 8 and what is its function?
A
- vestibulocochlear - consists mostly of bipolar neurones splits into two large divisions, the cochlear nerve (of hearing) and the vestibular nerve (of balance).
- it transmits sound and equilibrium (balance) information from the inner ear to the brain (via sensory cells, the hair cells).
- it emerges from the pontomedullary junction and exits the inner skull via the internal acoustic meatus in the temporal bone.
