Hearing & Balance Flashcards
Describe the External ear (3 parts)
Function: hearing
Auricle aka pinna:
- elastic cartilage covered with skin
- funnels sound into the external auditory canal
External auditory canal:
- Lined with hairs and ceruminous glands.
- Produces cerumen (ear wax)
Tympanic membrane (Ear drum)
- Thin membrane of two layers of epithelium with connective tissue between
- Sound waves cause it to vibrate
- Border between external and middle ear
Describe the Middle ear
Function: hearing
Responsible for transmitting sound vibrations from the outer ear to the inner ear
Air-filled space containing auditory ossicles (tiny bones) that transmit vibrations
Ossicles:
- malleus (hammer)
- incus (anvil)
- stapes (stirrup): transmits vibrations to the oval window
Oval window:
- connection between middle and inner ear. Foot of the stapes rests here and is held in place by the annular ligament
Connected to the inner ear by the oval and round windows
Two passages for air
- Auditory or eustachian tube: opens into pharynx, equalizes pressure
- Passage to mastoid air cells in mastoid process
Describe the Inner ear
Function: hearing and balance
Interconnecting fluid-filled tunnels and chambers within the temporal bone
The inner ear is divided into two types of labyrinths: bony labyrinth and membranous labyrinth. These labyrinths house fluid and specialized sensory cells for hearing and balance.
Body Labyrinths (the outer, rigid structure):
– Bony chambers in the temporal bone
* Cochlea: hearing
* Vestibule: balance
* Semicircular canals: balance
Membranous Labyrinth (the inner, flexible structure):
- tunnels and chambers in the bony labyrinth, these structures house the actual sensory receptors for hearing and balance
- Lymphs
Endolymph:
This is the fluid inside the membranous labyrinth, specifically within the cochlea,
vestibule, and semicircular canals. It plays a vital role in the function of hair cells,
which are the sensory receptors that detect sound and balance stimuli.
Perilymph: Perilymph is the fluid that surrounds the membranous labyrinth. It fills the space between the membranous labyrinth and the bony labyrinth, providing support and cushioning for the structures inside.
What does the oval window communicate with in the ear?
The oval window communicates with the vestibule, which in turn communicates with the scala vestibuli of the cochlea.
What is the scala vestibuli and where does it extend?
The scala vestibuli is a chamber in the cochlea that extends from the oval window to the helicotrema at the cochlear apex.
What is the second cochlear chamber and where does it extend?
The second cochlear chamber is the scala tympani, which extends from the helicotrema to the round window.
What fills the scala vestibuli and scala tympani?
Both the scala vestibuli and scala tympani are filled with perilymph.
What is the wall of the scala vestibuli made of?
The wall of the scala vestibuli is the vestibular membrane.
What is the wall of the scala tympani made of?
The wall of the scala tympani is the basilar membrane
What is the cochlear duct (scala media) and what fills it?
The cochlear duct (scala media) is the space between the vestibular membrane and the basilar membrane. It is filled with endolymph.
What are the spiral organ (organ of Corti) and its function?
The spiral organ (organ of Corti) is located in the cochlear duct, and it contains hair cells (sensory cells) with hair-like projections called stereocilia, which are responsible for hearing.
Where are the synaptic terminals of sensory neurons located in the cochlea?
The basilar region of hair cells is covered by the synaptic terminals of sensory neurons.
Where are the cell bodies of afferent neurons in the cochlea located?
The cell bodies of afferent neurons are grouped in the cochlear (spiral) ganglion.
What do afferent fibers form in the cochlea?
The afferent fibers form the cochlear nerve.
What are the two types of hair cells in the cochlea and their functions?
The inner hair cells are responsible for hearing, while the outer hair cells regulate tension on the basilar membrane.
What is a hair bundle in the cochlea?
A hair bundle consists of the stereocilia of one inner hair cell.
What is the role of the tip link (gating spring) in the cochlea?
The tip link attaches the tip of each stereocilium in a hair bundle to the side of the next longer stereocilium, helping to open ion channels when stereocilia bend.
What happens when stereocilia bend in the cochlea?
When the stereocilia bend, they open K+ gates (mechanically gated ion channels), leading to the perception of sound.
What type of ion channels are opened when stereocilia bend?
K+ (potassium) ion channels are opened when the stereocilia bend.
