Auditory pathway Flashcards
What is the hardest part of the skull?
The petrous bone
What part of the ear sits on the petrous bone?
Cochlear
What runs through the internal acoustic meatus?
Facial nerve and vestibulocochlear nerve
What bone is attached to the tympanic membrane of the middle ear?
The ossicles
What are the 3 parts of the Ossicles?
Incus, Malleus and Stapes bone
Why is air allowed to go to the middle ear and via what pathway?
Via the auditory tube and ensures equilibrium in the skull
What is the course of energy/wave from the outside to the inner ear?
External ear = Sound waves
Middle ear = Sound waves g mechanical
Inner ear = Mechanical g electrical
What two structures is the middle ear attached to?
Connected to the nasopharynx and the mastoid air cells
Why is the middle ear phone to infection via auditory tube?
Due to the middle ear being connected to the nasopharynx
What is the possible negative consequence of the middle ear being connected to the mastoid air cells?
Infection may spread to middle cranial fossa
Why is there a thrombosis risk of the middle ear?
Due to the internal jugular vein lieing inferior
What is the cause of pulsatile tinnitus
?
Internal carotid artery lies anterior and the pulse nockes on the osicles
What is the middle ear at risk of being it is traversed by chorda tympani and facial canal?
Infection risk
What is the route of the middle ear to the tongue?
Chordna tympani nerve
What is the route of the middle ear to the partoid gland?
lesser petrosal nerve
What is the connection between the middle ear and facial muscles?
Via the facial nerve (7)
Where is the inner ear found?
The bony labyrinth which is the rigid, bony outer wall of the inner ear in the temporal.
What are the 3 cavities of the temporal bone?
Semicircular canals, vestibule and cochlea
What is contained within the inner ear?
Contains perilymph wich is a extra cellular fluid
What is extra cellular fluid?
Fluid which is high in sodiu and low in potassium
What structure does the Stapes bone sit on?
The oval window.
When the osicle bones are vibrated the stape vibrates the oval window.
What is the cochlear duct?
A membranous sac that runs through the cochlea
What is contained within the cochlear duct?
Contaiend with endolymph which is intracellular and has low levels of sodium and high levels of potassium.
The cochlear duct seperates the cochlea into what?
Into two chambers
Scala vestibule and the scala tympani
What is the position of the Scala vestibule and Scala tympani in the Cochlea?
Scala vestibule sits above the cochlear duct
The Scala vestibulea t the top of Cochlea duct become the Scala tympani which is underneath the duct.
Scala Vestibule and Scala tympani are continous at what point?
These two chambers are continuous at the apex of the cochlea – helicotrema
What is the movement of the perilymph in the cochlea?
Hydraulic pressure created in the perilymph, by the vibrations of the stapes pass to the apex via the Scala Vestobule.
Pass through the helicotrema and descend via the Scala Tympani to the round window.
What is the consequence of the movement of the perilymph around the Cochlea on the cochlear duct?
As the fluid moves around the cochlea it deforms the fluid, endolymph, in the cochlear duct.
What forms the roof and floor of the cochlear duct?
The roof of the cochlear duct is formed by the vestibular membrane and the floor by the basement membrane
What is the auditory receptor of the cochlea duct?
It is the Spiral organ (of Corti) on the basilar membrane.
What does the spiral organ contain and how is it stimulated?
The spiral organ contains hair cells with the tips embedded into the tectorial membrane.
The spiral organ is stimulated by the deformation of the cochlear duct by the perilymph in the surrounding SV and ST
What is the consequence of the tectorial membrane movement?
The cilia in the spiral organ open up and open up ion channels –> Get depolarization as ions move across a semipermeable membrane which cause action potential through the cochlear nerve
What is the structure of the vestibulocochlear nerve?
The vestibulocochlear nerve consists mostly of bipolar neurons and splits into two large divisions: the cochlear nerve and the vestibular nerve
How is the auditory fiber formed?
Axons of bipolar neuron in
spiral ganglion
Forms the cochlear nerve which
becomes part of vestibulocochlear nerve (CNVIII)
Enters brainstem at cerebellopontine angle
Where does the 1st auditory fibre synapse?
Synapse with 2o neurons in dorsal and ventral cochlear nuclei
What are the characteristics features of auditory pathway?
Polysynaptic
Bilateral (so sound can be localised)
It compares two inputs
Timing
Loudness
What are the auditory centres in the brain stem?
Cochlear nuclei
Superior olivary nucleus –> superior to the olive
Inferior colliculus –> invovled in hearing
Medial geniculate nucleus
of thalamus–> project to the cortex ( Heschl’s gyrus)
What is the route from the cochlea to the to the heschl’s gyrus?
Cohlea–> spiral ganglion –> cochlear nuclei –> superior olivary nucleus (pons) –> inferior colliculus (mid brain)–> medial genincualte nucleus (thalamus)–> Heschl’s gyrus ( cerebral cortex)
What is the trapezoid body?
Where some of the axons coming from the cochlear nucleus decussate, or cross over to the other side before traveling on to the superior olivary nucleus.
What is the route of superior olivary nucleus to the inferior colliculus?
Via the lateral lemniscus
What is the route of inferior colliculus to medial genicualte nucleus?
Via inferior brachium
Where is the Heschl’s gyrus found?
Foudn in the superior temporal gyrus of the temporal lobe
Does the basilar membrane of the cochlear duct respond in the same way all the time?
Different regions of the basilar membrane
respond maximally to sounds of different pitch
Where is low pitch found in the basement membrane?
Apex responds to Low pitch
What part of the Heschl’s gyrus is ative when sound information is low pitch?
Sound information of Low pitch projects to
anteroLateral part of Heschl’s gyrus
What seperates the frontal and temporal cortex?
Lateral sulcus
What aprt of the basilla membrane is more stiff and what is the consequence?
The proximal part is more stiff so needs higher frequency to vibrate that the distal part that is more fleixble.
Where is Heschl’s gyrus found?
In the primary auditory cortex buried in the lateral sulcus of the temporal cortex.
What is ts 2nd auditroy areas?
Hemispheres have specific dominant functions; the left hemisphere houses the 2o auditory
area. Specialised area for linguistic function
What are the the two ares of secondary auditory areas?
Broca’s area:
Anterior
Motor/production of words
Wernicke’s area:
Posterior
Sensory/understanding
What is aphasia?
Results from damage to the speech areas:
Broca’s (non-fluent) or Wernickes (fluent)
What artery supplies the Broca’s and Wernicke’s aras?
The middle cerebral artery
What motor actions occur at the inferior colliculus via the descending auditory pathways?
Reflex head and eye movement
via the CN III, VI and VI
What motor actions occur at the superior olivary nucleus via the descending auditory pathways?
To stapedius via CN VII and
tensor tympani via CN V3
Prevents damage during loud noise
What does stapedius attach to?
The stapes
What is the action of Tensor tympani?
It created tension in the tympanic membrane to try to dampen down the sound /frequency
Why does stapedius and tensor tympani try and reduce the frequency?
If it is too loud can damage the hair cells permanently
What is the route of the descending auditory pathway?
Heschl’s gyrus to Mediaul geniculate nucleus to inferior colliculus to superior olivary nucleus to cochlear nuclei to cochlea
What is the action of the Heschl’s gyrus ( primary projection area)?
Sensory areas – specific sensory pathways terminate here, perceived sensation
What is the role of Assoicated ara of auditory pathway?
Receives input from primary sensory area
Involved in interpretation/understanding
What is Brocas aphasia?
Broca’s aphasia knows what he or she wants to say, but is unable to accurately produce the correct word or sentence.
What is Wernicke’s aphasia?
Wernicke’s aphasia are unaware that the words they are producing are incorrect and nonsensical.
What is the route from the middle ear to the mastoid ari cell?
Via the mastoid antrum
How is the auditory pathway represented?
Tonotopic represented
What is the specific artery that supplies wernickes area?
Tempeorooccipital artery
