Anatomy of the Ear and the Auditory Pathway Flashcards
Anatomy of the Ear:
parotid gland near the tragus
The External Ear is divided into 2 parts:
- cartilaginous auricle on the lateral aspect of
the head - cartilaginous and bony canal (external
acoustic meatus) that passes through the
tympanic part of the temporal bone
Function of the External Ear:
- capture sound
- transmit sound
External Ear:
insert diagram
External Ear:
external acoustic meatus is part of the tympanic part of the temporal bone
Tympanic Membrane:
- boundary
- what attaches to it?
- cone of light
function
- boundary between external and middle ear
- fibrocartilaginous ring attaches to it and the
tympanic part of the temporal bone - attached to handle of malleus-umbo
- cone of light projects anteroinferiorly = can be
used to differentiate between right and left
ears
converts sound air waves into mechanical vibration
What is shown below?
Label the diagram.
insert tympanic membrane
The middle ear comprises of 2 parts:
- tympanic cavity
- epitympanic recess
Middle Ear: Tympanic Cavity:Location:
Within the petrous part of the temporal bone that is separated from the external ear by the tympanic membrane
Function of the Middle Ear:
transmit sound through the vibrations between the ossicles
How does the middle ear communicate with the nasopharynx?
via the pharyngotympanic (eustachian) tube
naso, oro and laryngopharynx;
Middle Ear:
insert diagram
Tympanic Cavity:
lateral view having removed the tympanic membrane
just a schematic
- chordae tympani provides special sensory to
tongue
Tympanic Cavity: Boundaries:
- tegmen tympani = roof/tegmental wall
- floor/jugular wall = IJV inferiorly, tympanic
branch of CNIX enters cavity - posterior/mastoid wall = chordae tympani
enters cavity - anterior wall = pharyngotympanic tube
- medial/ labrinthine wall = cochlea, oval
window, round window
The central point of the tympanic membrane is the
umbo
What holds the tympanic membrane taut?
the handle of the malleus bone
Name the ossicles, articulations and what type of joints.
- malleus (hammer) = articulates with the
tympanic membrane - incus (anvil) = lies in the middle
- stapes (stirrup) = articulates at the oval
window with the inner ear - synovial joints
Ossicles:
just need to know basic shapes
2 main muscles of the middle ear:
- tempor tympani
- stapedius
Functions of the tensor tympani and stapedius:
- to reduce vibrations of tympanic membrane
- to reduce the vibrations of the stapes at the
oval window
Tensor Tympani:
- articulation
- action
- innervation
- articulates with the handle of the malleus
- tenses on tympanic membrane by pulling on
the handle of the malleus - mandibular division of the trigeminal nerve
CNV3
Stapedius:
- articulation
- action
- innervation
- articulates with the neck of stapes
- pulls on the stapes
- facial nerve (proper division) CNVII = motor
component
Middle Ear Muscles:
from medial looking outward
Pharyngotympanic Tube function:
to equalise pressure between the middle ear and the external environment via the nasopharynx
The pharyngotympanic Tube comprises of 2 parts:
- 1/3 bone, proximal to the tympanic cavity
- 2/3 cartilage, distal to the tympanic cavity
The inner ear is a series of
bony cavities and membranous ducts in the petrous part of the temporal bone
How does the inner ear communicate with the posterior cranial fossa?
How does sensory information to do with hearing and balance travel from the inner ear to the brainstem?
vestibulocochlear nerve CNVIII
travels to the brainstem = sensory info
enters the cranial cavity via the internal acoustic meatus into the posterior cranial fossa
Inner Ear Function (2):
- conversion of mechanical stimuli into
electrical signals - conversion of mechanical stimuli of
movement and changes in position into
electrical signals
Inner Ear:
insert diagram
The Inner ear comprises of (2):
- the bony labyrinth containing perilymph
- membranous labyrinth containing endolymph
(floating within perilymph)
(sweater = bone, body = membrane)
Inner Ear:
insert diagram
Inner Ear:
insert diagram
Inner Ear:
insert diagram
The first pathway of sound into the inner ear is called
the vestibule (the bony labyrinth)
contains perilymph (similar to CSF) and houses the membranous labyrinth
communicates with the middle ear
Which of the following are apart of the bony labyrinth of the inner ear?
- vestibule
- semicircular canals
- semicircular ducts
- utricle
- scala tympani
- cochlear duct
- vestibule
- semicircular canal
- scala tympani
The semi-circular ducts are housed within the
semi-circular canals
Inner Ear: Semi-circular Canals:
- three semi-circular ducts: horizontal, anterior
and posterior - 90 degrees to each other
- widening at the end of each canal = ampulla
- contains perilymph
The vestibule houses the
utricle and saccule
Inner Ear: Cochlea:
- central core of bone = modiolus
- scala vestibuli (duct)
- scale tympani (duct)
- helicotrema (communication between scalae)
contains perilymph
How does the sound wave/vibration pass through the cochlea?
- sound wave passes through scala vestibule
first - then helicotrema
- then scala tympani
- articulate via round window back into the
middle ear
Inner Ear: Membranous Labyrinth:
- utricle
- saccule
- 3x semicircular ducts and ampullae
- cochlear duct (scala media)
- contain endolymph
- surround by perilymph and bony labyrinth
Which nutrients are the endolymph high in?
potassium
low in sodium
Inner Ear:
insert diagram
Inner Ear:
insert diagram
Cochlea:
insert diagram
Membranous Labyrinth:
insert diagram
Label the bones:
insert diagram
What are three parts of the ear?
external, middle, inner
Innervation to Ear:
insert diagram
What is the shape of the cochlear duct/scala media?
triangular shape
Cochlear Duct:
- held in place by
- boundaries/membranes
- spiral organ
- spiral ligament holds in place to petrous
temporal bone - vestibular membrane superiorly (separates
from scala vestibule) - basilar membrane inferiorly (separates from
scala tympani) - spiral organ - organ of hearing = lies on the
basilar membrane
Cochlear Duct:
insert diagram
Sound waves hit tympanic membrane, pass through ossicles, vestibule and into cochlea, then
- vibration in perilymph
- scala vestibuli first
- scala tympani
- movement of basilar membrane
- signal induction in spiral organ by causing
interaction between tectorial membrane and
sterocillia
What is the cochlear nerve formed from?
spiral ganglion at the base of lamina of modolius across the cochlea
all unit to form the cochlear part of the vestibulocochlear nerve
The Cochlear nerve travels with the vestibular nerve through
the petrous part of temporal bone
CNVIII enters posterior cranial fossa via the internal acoustic meatus
After CNVIII enters the posterior cranial fossa, what is the path of the cochlear nerve?
- travels to the dorsal and ventral nuclei in the
medulla oblongata - neurons travel to midbrain inferior colliculus
and then thalamic medial geniculate nucleus - impulses travel to the auditory cortex in the
temporal lobe (area 41/42)
spiral organ in cochlea, cochlear nerve formed, petrous part of temporal bone, via internal acoustic meatus, into medulla oblongata to dorsal and ventral nuclei, synapse and ascend into the midbrain to the inferior colliculus, pass the thalamus and travel to the auditory cortex
The superior colliculi are involved in the
pathway of visual information
What are cristae ampullaris and where are they located?
- organs of balance
- within the semicircular DUCTS of the inner ear
In what planes are the three semicircular ducts found?
- anterior = coronal = perceive lateral flexion
- posterior = sagittal =perceive flexion extension
- horizontal = transverse = perceive rotational
movement
Where do all the semicircular ducts open?
via ampulla into utricle
What is the maculae and where is it located?
- organs of balance
- utricule and saccule
What is perceived in the utricule?
Linear acceleration = horizontal plane
What is perceived in the saccule?
Linear acceleration = vertical plane
Pathway of information through the vestibular part of CNVIII: signal generation:
- rotational movements(crista ampullaris) cause movement of the
endolymph in semicircular ducts - endolymph movements distort the cupula
- stereocilia and single kinocilium embedded
within the cupula - movement of the hair cells causes electrical
signals to fire in the vestibular nerve division
of CNVIII
orrrr
- acceleration movements cause movement of
endolymph in utricle and saccule - endolymph movements distort the otholithic
membrane in gelatinous mass - stereocilia and single kinocilium in gelatinous
mass interact - causes electrical signal to fire in the vestibular
nerve division
The cupula is a
gelatinous mass
Cupula:
insert
How is the vestibular nerve formed?
inferior and superior divisions unit
the vestibular nerve travels with
the cochlear nerve through petrous bone via the internal acoustic meatus to enter the posterior cranial fossa
After entering the posterior cranial fossa, the vestibular division of CNXIII travels to
the superior, inferior, medial and lateral nuclei in the medulla oblongata and pons
neurons travel to different pathways
Summary of how vestibular information travels
- generated through the interaction of
stereocilia and a single kinocilia in gelatinous
mass - travels through the vestibular nerves
- inferior and superior vestibular nerves join to
form the vestibular division of CNXIII - travels with the cochlear nerve through the
petrous part of the temporal bone - enters the posterior cranial fossa through the
internal acoustic meatus - travels to the medulla oblongata and pons
- synapses at the superior, inferior, medial and
lateral nuclei - then travels through various pathways eg
vestibulospinal, vestibulocerebellar,
vestibuloocular reflexes
Semicircular ducts:
insert diagram
vestibular nerve
insert diagram
Vestibular Part of CNVIII:
insert
What are the organs of rotational movement?
cristae ampullaris
in the ampulla of semicircular ducts
What are the organs of accelerational movement?
maculae
in the utricle (horizontal) and saccule (vertical)
Auditory pathway:
