The Ear Flashcards
divisions of ear
middle and inner ear communicate?
The middle and inner ears communicate at the oval and round windows.
relations of ear?
external ear lies posterior to the superficial temporal vessels and auriculotemporal nerve.
The middle ear is related to the internal carotid artery and the auditory (Eustacian, pharyngotympanic) tube
The internal ear sits surrounded by bone between the middle and posterior cranial fossae.
The temporal lobes of the brain sit superior to the internal structures and the internal auditory (acoustic) meatus opens into the inner ear from inside the cranial cavity. This meatus carries the facial and vestibulocochlear nerves into the inner ear and petrous temporal bone.
features of external ear
lymph drainage?
Lymph to parotid and cervical lymph nodes
arterial supply ear
venous drainage?
from external carotid
blood drains into corresponding veins into external + internal jugular
nerve supply external ear?
external auditory meatus blood supply?
innervation?
surfaces tympanic membrane?
what runs across medial surface?
attached to inner surface?
innervation to lat surface? medial?
Outer surface = stratified squamous epithelium, inner surface covered by mucous membrane
Chorda tympani runs across the medial surface
Malleus attached to inner surface
Lateral surface = auriculotemporal nerve (CN V3) and auricular branch of vagus (CN X)
Medial surface = tympanic branches of glossopharyngeal nerve (CN IX)
tympanic cavity
ossicles found here
joints between ossicles?
plane synovial
…
mastoid infection ear?
An aditus or opening in the middle ear communicates with the mastoid air cells. This creates a potential route for infection from the middle ear into the tiny lined air cells of the mastoid process.
2 tiny muscles within the middle ear
sensory nerve supply tympanic cavity?
blood supply?
Sensory nerve supply to tympanic cavity (including medial surface of tympanic membrane) from CN IX
Blood supply mostly via tympanic branches of posterior auricular, ascending pharyngeal and maxillary arteries (caroticotympanic from internal carotid also)
facial nerve pathway summary
The facial nerve enters the temporal bone via the internal auditory meatus and travels through the petrous temporal bone until it exits at the stylomastoid foramen.
The facial nerve then passes into the parotid gland and divides into branches to supply the muscles of facial expression.
As it passes through the temporal bone it also gives off several branches.
The greater petrosal nerve passes to form the nerve of the pterygoid canal (with the deep petrosal nerve from the carotid plexus) to supply parasympathetic secretomotor fibres to the lacrimal gland and small glands of the nose and palate.
The nerve to stapedius branches from the facial nerve to supply this muscle in the tympanic cavity.
The chorda tympani branches from the facial nerve to cross the medial surface of the tympanic membrane.
chorda tympani ear?
pathway
function
Crosses the medial surface of tympanic membrane and handle of malleus
Leaves the tympanic cavity via petrotympanic fissure
Joins the lingual nerve
Parasympathetic = sub-lingual and sub-mandibular salivary glands
Special sense of taste for the anterior two-thirds of the tongue
(The chorda tympani joins the lingual nerve (CNV3) in the infratemporal fossa)
eustachian tube found
open?
function
innervation?
Connects the nasopharynx (lateral wall) with the tympanic cavity (middle ear)
Normally closed, but when tensor veli palatini contract (swallow, yawn etc) lumen opens
Equalises pressure on both sides of the tympanic membrane
Sensory via CN IX
what attach to eustachian tube?
The medial part is closest to the pharynx and provides attachment for salpingopharyngeus and tensor and levator veli palatini
middle ear arterial supply?
Anterior tympanic (Glaserian) artery from 1st part of maxillary artery
features of inner ear
Vibration from the stapes at the oval window creates waves of movement through the fluids of the bony and membranous labryrinths which reach the special sense of hearing and balance cells housed in the membranes
labyrinths of inner ear
features of cochlea
describe hearing
cochlea houses the cells that provide the special sense of hearing.
Vibration is passed from the footplate of the stapes to the membrane of the oval window.
The oval window vibrates in response, and a wave of movement passes into the perilymph of the scala vestibuli.
The cochlea forms a shell-like shape so the scala vestibuli ascends to the top of the shell shape (helicotrema) and then the wave passes down the scala tympani until it reaches the base of the cochlea again, but this time at the round window.
The round window vibrates gently into the middle ear. Nothing is attached to this round window, so the vibration wave harmlessly dissipates into the middle ear.
As the wave of vibration passes through the perilymph it presses on the membranous labyrinth (the cochlear duct). This deforms the membrane, and this deformation is detected by the special cells within the membrane.
spiral organ?
The cells in the spiral organ/organ of Corti detect movement and transform it into electrical energy (a nerve impulse) which is then passed to the cochlear nerve – part of cranial nerve VIII. This nerve carries the nerve impulses to the brain to be interpreted as different sounds by the auditory cortex
The ‘scala’ are named after stairs/steps – you ascend the vestibular stairs to the top of the cochlea and then descend via the tympanic staircase.
semicircular canals found? types? contain? swelling? function?
Lie posterior and lateral to the vestibule
Anterior, posterior and lateral
Ant and post set at right angles, lat = horizontal
Contain the semi-circular ducts (continuous with utricle)
Each duct swells at the end = ampullae
function = balance
features of semicircular canals
ampulla of semicircular canals contain?
vestibule?
what do these structures contain?
Each ampulla houses equilibrium receptor called crista ampullaris which responds to angular (rotational) movements of the head as endolymph moves
sends impulses to vestibular part of CN XIII
Vestibule = bony labyrinth that contains utricle and saccule
U + S house equilibrium receptors called maculae = respond to the pull of gravity and changes in head position
otliths?
Otoliths are teeny pieces of bone that sit on the receptor cells and move in response to the movement of the endolymph
…
vestibulocochlear nerve pathway?
inner ear arterial supply?
mainly internal auditory artery
