Three main divisions of the terrestrial mammalian ear:
External (outer) ear, Middle ear, Inner ear
External ear
- auricle (pinna): collects sound waves from environment
- ear canal: vertical and horizontal parts
Middle ear
- housed in tympanic part of temporal bone
- tympanic membrane (ear drum)
- tympanic bulla (tympanic cavity)
- auditory ossicles e/ associated muscles and ligaments
- communicates w/ nasopharynx via the auditory tube
Inner ear
- responsible for balance(semicircular canal)
- Housed in petrous part of temporal bone
- osseous labyrinth
- membranous labyrinth (organs of inner ear)
Three divisions of ear allow for transformation of sound pressure waves into electrical energy
- external ear captures sound waves & transmits energy to the middle ear via tympanic membrane
- ossicles of middle ear convert these pressure waves into mechanical energy
- vibrations at oval window by the stapes produces pressure waves e/in perilymph of inner ear
- movement of perilymph displaces the tectorial and basement membranes, stimulating firing of electrical impulses by cochlear neurons
The external ear is necessary for sound collection and sound localization
- visible portion of external ear is supported by irregularly shaped auricular cartilage
- proximal end of this cartilage forms a canal (vertical and horizontal ear canals)
- distal end of this cartilage forms pinna, funnel to concentrate waves
Shape of pinna is dependent upon
- the composition of the fibroelastic auricular cartilage
- the collagen/elastin composition varies among species and breeds
- non-erect, erect, semi-erect
- size & shape determines which sound frequencies are collected optimally and also many reduce noise
- vasculature helps cool body
What gland produces ear wax?
ceruminous gland
adenomoas in cats
Where do ticks like to collect?
cutaneous marginal pouch
Annular cartilage
holds ear to skull
-connects cartilagenous meatus of horizontal canal w/ bony external acoustic meatus
Scutiform cartilage
“sesmoid bone” attachment for auricular muscles and tendons
- flat, boot-shaped cartilage
- located medial & rostral to base of auricle
- aids in redirection
Auricular muscle groups that allow auricle of each ear to move towards a sound source
- rostral auricular group
- caudal auricular group
The middle ear is located in the air-filled tympanic cavity of the
temporal bone
Only connection to external environment occurs through the
auditory tube
What is the expanded ventral portion of the tympanic cavity?
tympanic bulla
What is the bony promontory?
expansion of the petrous temporal bone
-protrudes into dorsal region of tympanic cavity
Manubrium of the malleus is embedded in the
tympanic membrane
Vibrations of the tympanic membrane move to the
malleus
Contraction of ______ dampens the movement of the malleus
tensor tympani muscle
Diarthrotic (synovial) joints connect the middle ear ossicles. Movement of the malleus will result in the movement of
the incus and stapes
Contraction of the ________ dampens the movement of the stapes at the oval window
stapedial muscle
