Ear Flashcards
What can the ear be divided into
External
Middle
Inner
What can the external ear be divided into
Both functionally and structurally
Auricle (pinna)
External acoustic meatus
Ends at the tympanic membrane
What is the auricle
Paired structure found on either side of the head
Function is to capture and direct sound waves towards external acoustic meatus
What type of structure is the auricle
Mostly cartilaginous
What is the only part of the auricle not supported by cartilage
Lobule
What does the cartilaginous part of the auricle form
Outer curvature - helix
What is the second innermost curvature running parallel with the helix
Antihelix
What does the antihelix divide into
Two crura
Inferoanterior crus
Superoposterior crus
What is the hollow depression in the middle of the auricle
Concha
What does the concha continue into
Into the skull as the external acoustic meatus
What shape is the external acoustic meatus
Sigmoid shape tube
Where does the external acoustic meatus run
Deep part of concha - tympanic membrane
What is the external 1/3 of the external acoustic meatus compromised of
Cartillage
What is the inner 2/3 of the external acoustic meatus compromised of
Temporal bone
What path does the external acoustic meatus take
S-shape
- superior anterior direction
- superior posteriorly
- inferior anterior
Describe the tympanic membrane
Lies at distal end of the external acoustic meatus
Connective tissue structure
- skin on outside
- mucous membrane on inside
Membrane connected to the surrounding temporal bone by a fibrocartilaginous ring
What is the vasculature of the external ear
Branches of the external carotid artery
What innervates the skin of auricle
Greater auricular nerve (branch of the cervical plexus)
Lesser occipital nerve (branch of the cervical plexus)
What innervates the skin of the auricle and external auditory meatus
Auriculotemporal nerve (branch of the mandibular nerve)
What innervates the deeper aspect of the auricle and external auditory meatus
Branches of the facial and vagus nerves
Where does the middle ear lie
Within the temporal bone
Extends from the tympanic membrane to the lateral wall of the inner ear
What are the main functions of the middle ear
Transmit vibrations from the tympanic membrane to the inner ear via the auditory ossicles
What can the middle ear be divided into
Tympanic cavity
Epitympanic recess
Describe the tympanic cavity
Located medially to tympanic membrane
Contains auditory ossicles
- malleus
- incus
- stapes
Transmit vibrations through to the middle ear
What are the bones of the auditory ossicles
Malleus
Incus
Stapes
What is the role of the auditory ossicle
s
Sound vibrations cause a movement in the tympanic membrane which then creates movement (ossification) in the auditory ossicles
Link tympanic membrane to the oval window of the internal ear
What is the largest and most lateral of the ear bones
Malleus
Describe incus
Consists of body and two limbs
What is the smallest bone in the human body
Stapes - joins the incus to the oval window
What is the role of mastoid air cells
Act as buffer system of air
Release air into the tympanic cavity when the pressure is too low
What are the two muscles of the middle ear
Tensor tympani
Stapedius
What is the role of the tensor tympani and stapedius
Protective function
Contract in response to loud noise - inhibit vibrations to the malleus, incus and stapes = reduce sound to the inner ear
Known as - acoustic reflex
Describe tensor tympani
Originates from the auditory tube
Attaches to handle of malleus - pulling it medially when contracting
Innervated by tensor tympani nerve - branch of the mandibular nerve
Describe the stapedius muscle
Attaches to the stapes
Innervated by facial nerve
Describe the eustachian tube
Cartilaginous and bony tube
Connects the middle ear to the nasopharynx
Acts to equalise the pressure of the middle ear to that of the external auditory meatus
What are the two main functions of the inner ear
Convert mechanical signals from the middle ear into electrical signals - which can transfer information to the auditory pathways in the brain
Maintain balance by detecting position and motion
Where is the inner ear located
Within petrous part of temporal bone
Lies between middle ear and internal acoustic meatus
What are the two components of the inner ear
Bony labyrinth
Membranous labyrinth
Describe the bony labyrinth
Composed of cochlea, vestibule and three semi-circular canals
Structures lined internally with periosteum and contain perilymph (a fluid)
Describe membranous labyrinth
Lies within the body labyrinth
Consists of cochlear duct, semi-circular ducts, utricle and saccule
Fille with endolymph (fluid)
Describe oval window
Lies between the middle ear and vestibule
Describe the round window
Separates the middle ear from the scala tympani (part of the cochlear duct)
Describe vestibule
Central part of the bony labyrinth
Separated from middle ear by oval window
Communicates anteriorly with cochlea
Posteriorly with semi-circular canals
Saccule and utricle - located within
Describe the cochlea
Auditory part of the inner ear
Twists upon itself around a central portion of the bone = modiolus
Cone shape which points in anterolateral direction
Where are branches of the cochlear portion of the vestibulocochlear nerve found
Base of the modiolus
Describe semi-circular canals
Three
- anterior
- lateral
- posterior
Contain semi-circular ducts = responsible for balance (along with utricle and saccule)
Right angles to each other
Swelling at one end = ampulla
What is the range of human hearing
20Hz-20kHz
Is the outer ear air or fluid
Air
Is the middle ear air or fluid
Air
Is the inner ear air or fluid
Fluid
When does the pinna form
Between 10th - 18th week in utero
What is the size of the tympanic membrane
8x10mm diameter
14mg
84mm2 - 55mm2
How much energy is lost from transferring air to fluid
99.9%
What is the role of the middle ear
Amplification of the airborne vibration e.g. make it louder
What type of control is the tensor tympani
Voluntary and involuntary control
What is the role of the eustachian tube
Ventilation to middle ear space
Drainage of secretions
What is the vestibulocochlear apparatus
Set of fluid filled sacs, encased in bone
What is the cochlear responsible for
Hearing
What is the labyrinth responsible for
Balance
What is the innervation of the vestibulocochlear apparatus
Vestibulocochlear nerve
Describe the cochlea
2.5 turns fluid filled bony tube
2 openings - round and oval window
3 compartments - scala tympani, scala media and scala vestibuli
2 ionic fluids
Cochlear fluids
What ions are in
Endolymph
High K+
Cochlear fluids
What ions are in
Perilymph
Like ECF and CSF
Na+ rich
What are the cochlear fluids gradients maintained by
Na, K-ATPase
NKCC1 CIC-K chlorine channels
What would ion channel abnormalities in the cochlear result in
Deafness
Where are frequencies detected in the cochlear - basilar membrane
High frequencies - at base (narrow)
Low frequencies - at apex (wide)
What is the role of inner hair cells in the basilar membrane
Mechanical transduction
What is the role of outer hair cells in the basilar membrane
Fine tuning
Can alter stiffness of the basilar membrane to ensure maximal stimulation at one site and dampened at another = increased resolution
What does displacement of the basilar membrane cause
Movement of the specialised mechanical transducing cells
How is frequency (pitch) encoded
In nerves by location along the basilar membrane
How is intensity (loudness) encoded
In nerves by numbers responding and firing rate
How is sound transduction encoded
Inner hair cells (and OHCs)
How is amplification encoded
Outer hair cells
What is the central auditory pathway
8th nerve
Cochlear nucleus
Olive
Lateral lemniscus
Inferior colliculus
