Anatomy of Ear Flashcards
what is the functions of the ear
- hearing + balance –> vestibulocochlear organ
- hearing –> transformation of mechanical sound waves into nerve impulses
- balance –> changes in fluid levels within inner ear
what are the two parts of the external ear
- auricle or pinna (“ear”)
- external acoustic meatus (canal connecting base of auricle to tympanic membrane)
what is the shape of the auricle or pinna
funnel shaped –> wide distally and narrows to connection with external acoustic meatus
what is the shape of the auricle determined by
auricular cartilage –> variable stiffness
rolls to form cone shape
also annular cartilage at base of auricular cartilage (anchors auricle to skull)
name the structures of the external ear
where do the vessels of the external ear run
run on convex (outer) surface
branch from caudal auricular artery (from external carotid)
where does the external ear canal run
from “closure” of auricular cartilage to ear drum
vertical and horizontal parts (hockey stick shape)
curves ventrally then rostromedially (difficult to examine with otoscope)
what is the external ear canal lined with
skin
sebaceous and tubular ceruminous glands (secrete wax)
name the structures shown of the external ear canal
what are the 4 components of the middle ear
- tympanic cavity (contains but often referred to as tympanic bulla)
- tympanic membrane
- auditory ossicles
- auditory tube (aka eustacian tube)
where does the tympanic cavity lie
within temporal bone (lateral to petrous temporal bone)
what is the tympanic cavity
air filled
thin mucus membrane lining (drain secretions so it doesn’t fill with fluid)
how can the tympanic cavity be divided
dorsal and ventral parts
dorsal - epitympanic recess
ventral = tympanic bulla
two windows dorsomedially –> dorsal = vestibular and ventral = cochlear
name the structures of the tympanic cavity
what does the tympanic membrane divide
external acoustic meatus from middle ear
what are the surfaces of the tympanic membrane called
epidermal (outer) and mucosal (inner) covering
what does the tympanic membrane attach to
fibrous attatchment to typmanic ring of temporal bone
medial surface attachted to ossicles
what is the order of the auditory ossicles from lateral to medial
malleus (hammer)
incus (anvil)
stapes (stirrup)
what is attached to the eardrum
handle/manubrium of malleus
how do articulations of the auditory ossicles occur
malleus-incus-stapes
where does the stapes insert into
vestibular window
what do ligaments attach the ossicles to
epitympanic recess
what are the auditory ossicle muscles
tensor tympani stapedius
tense eardrum and ossicle chain –> protecting
reduces vibrations when loud noises (by contracting)
what are the structures of the auditory ossicles
how does hearing work
- sound causes vibration of tympanic membrane
- motion transmitted through ossicle chain
- causes vibration in inner ear fluid at vestibular window
- transmission via walls of tympanic cavity and cochlear window
where does the auditory tube connect
tympanic cavity to nasopharynx
–> openings in lateral wall of nasopharynx
runs in cartilage trough –> out-pouching in horses = guttural pouch
what state is the auditory tube normally in and what is its function
usually collapsed
when open allows equalization of pressure on either side of tympanic membrane
allows drainage of material from tympanic cavity –> swallowing opens canal and allows drainage of secretions
if doesnt open –> fluid buildup in inner ear
what structure is this
auditory tube
what is the function of the inner ear
- hearing –> transformation of mechanical stimuli (sound) into nerve impulses
- organs of balance
what is the inner ear enclosed in
petrous temporal bone –> osseous labyrinth
contains perilymph around membranous labyrinth
what are the system of membranous ducts and cavities in the inner ear called and what do they contain
membranous labyrinth
contains endolymph
what are the central cavities of the inner ear called
- utriculus
- sacculus
what are the 3 ducts in the inner ear
3 semicircular ducts from
- utriculus - balance
- spiral cochlear duct fom
- sacculus - hearing
what stimulates sensory hairs in the inner ear
movement of endolymph stimulates sensory hairs on receptor cells in wall of labyrinth –> nerve signal generated
what are the structures of the inner ear
what do the utriculus and sacculus contain and what are their functions
further receptors
- maculae (otolith organs)
- crystals (statoconia, otoliths) adhere to sensory hairs
determine position of head relative to gravity
where are the semicircular ducts orientated
at right angles
anterior, posterior and lateral
ampullae at one insertion into utriculus
what is the function of the semicircular ducts
fluid moves with head movement
stimulates sensory hairs and cells on the cristae ampullares (barriers present in ampullae)
fluid moves slower than head because of intera
what is this structure
what is nystagmus
flicking movement of eyes in response to movement of fluid in semicircular canals
seen after stopping rotation
dizziness
may be seen with brain disorders
what does the osseous labyrinth contain
- central chamber –> vestibule (contains ultriculus and sacculus)
- semicircular canals –> contains semicircular ducts
- cochlea –> contains cochlear duct (spiral), central osseous pyramid (modiolus) with canal running around and projecting spiral lamina (thread of screw)
what is the cochlea
membrane from spiral lamina divides into 3 channels
wall between cochlear duct and scala tympani
what are the 3 channels of the cochlea
- scala vestibuli
- cochlear duct
- scala tympani
what does the wall between cochlear duct and scala tympani contain
neuroreceptors = spiral organ (aka organ of corti)
how does the inner ear contribute to hearing
- vibrations at vestibular window (from stapes) and cochlear window
- transmitted through perilymphatic space
- causes vibration of basement membrane and movement of sensory cilia
- registered by neuroreceptors
- transmitted to vestibulocochlear nerve (VIII)
what is the nerve supply to the ear
- vestibulocochlear nerve –> divides into vestibular and cochlear parts at internal acoustic meatus (vestibular - balance, and cochlear - hearing)
- facial nerve –> stapedius m
- mandibular nerve (V) –> tensor tympani m
what is the vascular supply and venous drainage to the external ear
arterial supply from external carotid via caudal auricular
venous drainage to maxillary vein
what is the vascular supply to middle and inner ear
arterial supply from occipital artery branching from external carotid
what is a aural hematoma
hematoma under skin of pinna
swollen, painful
drain with needle
where does the facial nerve pass through in the ear
through inner and middle ears
enters at internal acoustic meatus
runs dorsal to epitympanic recess –> chorda tympani criss dorsal part of tympanic membrane
–> sympathetic supply to eye passes between tympanic bulla and petrous temporal bone
how is the ear imaged
- otoscope
- radiography (widely available, tympanic bullar superimposed on other skull structures)
- advanced imaging (CT/MRI) –> clear imaging of inner and middle ear
what is otitis
inflammation or infection of ear
otitis externa (external ear)
otitis media (middle ear)
otitis interna (inner ear)
