EAR Flashcards
What are the three parts of the ear
Outer ear
Inner ear
Middle ear
What is the outer ear comprised of and its function
- Pinna- hearing O
collects sound waves and channels them into the ear canal - External acoustic meatus
- tympanic membrane
What is the middle ear comprised of and its function
air-filled tympanic cavity, three auditory ossicles, and tympanic membrane
What is the inner ear and its function
cochlea (the organ of hearing) and the vestibular system (the organ of balance).
How does mechanically gated transduction work
Movements affect stretch-sensitive ion channels at the tip of the sensory hairs
Tip links connecting cilia open the K+ channels
Leads to depolarisation
Voltage-gated Ca2+ channels open
Influx of Ca2+ causes release of neurotransmitter by exocytosis
How do you know if have vestibular problem
Head tilt towards lesion
What are the two parts of the vestibular organ
Semicircular canals- give dynamic information, fluid filled and say how head it moving
Otolith organs- static information.
What are the two otolith organs
Utricle
Saccule
What does the saccule sense
gathers sensory information to orient the body in space. It primarily gathers information about linear movement in the vertical plane, including the force due to gravity.
Stationary
How do the otolith organs
Each organ has a sheet of hair cells, the macula, whose cilia are embedded in a gelatinous mass, just like the semicircular canals. Unlike the canals, however, this gel has small crystals of calcium carbonate embedded in it, called otoliths. The otoliths provide the inertia, so that when movement to one side occurs, the otolith–gel mass causes the hair cells to deviate
What does the utricle do
linear accelerations and head-tilts in the horizontal plane
Detects horizontal movement
What are the semicircular canals filled with
Endolymph
How do the canals determine head movement
There are 3 canals, each one is in a different plane
Flow within the endolymph matches head rotation in the same plane as the canal.
Movement of endolymph causes cilla to move, which results in release of neurotransmitters
Why do you get a head and body tilt with vestibular problems
On side of lesion:
The excitatory impulse to the extensor muscles is failed
So you just get flexor
Also muscle isn’t functioning as anti gravity
What is the floccunolodular lobe
Part of the cerebellum
receives input from, and functions in conjunction with, the vestibular system to regulate equilibrium/balance and posture
What does the floccunolodular lobe structure look like
Ipselateral projection
What is hearing
Hearing is the neural perception of sound energy
How is sound generated
All objects vibrating in air or water generate sound
Causes compression and rarefaction of molecules in the environment, creating areas of increased and decreased pressure
What is the wavelength of sound
Distance between areas with maximal pressure
What is sound frequency
Pitch
What is sound pressure
Volume/ amplitude
What is the pinna made from
Elastic cartilage and skin
What CN innervates the muscle of the pinna
CN 7
What is the structure of the external acoustic meatus like
L shapes tube ending in tympanic membrane
Contains sebaceous glands that produce earwax, and hairs to act as a barrier to dust, insects etc.
What is the structure of the tympanic membrane lie,
Covered by epithelium on the outside
Covered by mucus membrane on the inside
What is the function of the pinna and external acoustic meatus
Pinna and external auditory meatus act as funnel to collect sound wave vibrations and direct to the eardrum
What is the function of the tympanic membrane
When sound waves reach your eardrum, they cause the membrane to vibrate, which then travels to the middle ear
Also acts as barrier to bacteria getting into the inner ear
What is the function of the middle ear
The middle ear is an air-filled cavity in the temporal bone containing ossicles transferring tympanic membrane vibrations to the inner ear
What are the three ossicles
malleus, incus, and stapes
What is the function of ossicles
Acts as a series of levers to transmit sound wave vibrations
The stapes is attached to the membrane covering the oval window of the cochlear
What does the middle ear consist of
Ossicles
Tympanic bulla
What is the Eustachian tube/ guttural pouch and its function
Auditory tube
Connects middle ear to pharynx
Narrow and normally closed
Purpose is to equalise the air pressure on the two sides of the tympanic membrane
How is sound waves transmitted to inner ear
To achieve this, it increases pressure and reduces amplitude of vibrations through the ossicles
Stapes pushes on fluid in inner ear
How many canals are there in the cochlear and what are they called
3
Outer, middle, inner
What is each canal filled with
Upper and lower canals- perilymph
Middle canal- endolymph
What is the difference between peri lymph and endolymph
Endolymph is higher in K+ and more positive electro potential
Where are the sensory cells on the cochlear
Basilar membrane
How does the cochlear work
When the oval window is compressed by the ossicles it creates wave that travel through the fluid of the cochlear
These waves cause the basilar membrane to move too
Causes hair cells and stereocilia to move for transduction of stimulus
How is frequency of sound discriminated
High frequency waves have maximum amplitudes near round window
Low frequency cause membrane to vibrate with maximum amplitude near tip of cochlear
How is the vestibular cochlear nerve connected to organ
Communicates with hair cells and enters brainstem just under cerebellum
Afferent from organ of Corti
Efferent to organ of Corti (tensions membrane)
What is the caudal colliculus
4 bumps that form of the root of the midbrain
What does the caudal colliculus do
Auditory information co-ordinates head/ear/neck muscles to orientate the animal’s head towards sound source
How does the brain determine the direction of sound
based on differences in arrival time between both ears
Lower sound pressure at furthest ear (sound shadow)
Mobile external ears help with location of sound from behind/infront
What are the two different types of hearing loss
Conduction
Sensation
What are the causes of conduction hearing loss
Otitis externa (wax in ear canal)- sound waves can’t get down
Otitis media (pus/ fluid in ear)- oscilles cant vibrate
Rupture of tympanic membrane
What are some problems with sensation hearing loss
Damaged hair cells – loud or continuous sound
Ototoxic drugs (e.g. streptomycin)
Inherited conditions
Where does conduction hearing loss occur
External to internal acoustic meatus
Where does sensation hearing loss occur
Inner ear
How does BAER work
Each ear is stimulated separately by a click stimuli
Accumulated action potential from the cochlea via the cochlear nerve can be measured as auditory evoked potential
Sedation or anaesthesia required to avoid artefacts
Can be used to determine brain health in a coma
