martin chapter 8 Flashcards
auricle or pinna, what is it?
the visible external part of the ear
external auditory meatus
tubular passage found in each temporal bone
mechanical displacement of the tympanic membrane (produced by changes in sound pressure waves) is transmitted to the inner ear by?
tiny bones termed middle ear ossicles
3 tiny ossicles
1. malleus
2. incus
3. stapes
where is the inner ear transductive machinery located?
in a coiled structure within the temporal bone named cochlea
where are auditory receptors located and how are they called?
in the cochlea
they are called hair cells because they are characterized by a bundle of hair-like stereo cilia on their apical surface.
each auditory receptor is sensitive to a limited frequency range of sounds
from the base of the cochlea to the apex the sound frequency to which a hair cell is most sensitive changes. where are receptors that are most sensitive to higher frequencies located?
in the base of the cochlea
in the apex instead there are hair cells that are most sensitive to lower frequencies
who determines where a sound originates?
CNS auditory neurons based on timing, loudness and spectral characteristics of sound
hair cells are innervated by?
distal processes of bipolar sensory neurons located In the spiral ganglion
the central process of bipolar neurons in the auditory system refers to?
the central process of a bipolar neuron refers to the part of the neuron that carries information toward the central nervous system (CNS).
what do the central processes of the bipolar neurons form?
the cochlear division of the vestibulocochlear nerve (Cranial nerve VIII)
where do the axons of the cochlear division of the vestibulocochlear nerve project?
they project to the ipsilateral cochlear nuclei, located in the rostral medulla
cochlear nuclei consist of:
-dorsal cochlear nuclei
-ventral cochlear nuclei (that have an anterior and posterior subdivisions)
where does the ventral cochlear nucleus project?
it projects bilaterally into the superior olivary complex, a cluster of nuclei in the caudal pons
where do neurons in the superior olivary complex project?
to the inferior colliculus via an ascending pathway called lateral lemniscus
where does the dorsal cochlear nucleus project?
directly into the contralateral inferior colliculus (also via the lateral lemniscus) bypassing the superior olivary complex
which is the site of convergence of all lower brain stem auditory nuclei?
the inferior colliculus
what is wernicke’s area and where is it located?
is an area of the cerebral cortex involved in understanding speech. it is located in the superior temporal gyrus
where is Broca’s areas?
located in the inferior frontal gyrus
a cortical area fundamental for the production of speech
what is the thalamic auditory relay nucleus of the ascending auditory pathway?
the medial geniculate nucleus
where does the medial geniculate nucleus project?
to the primary auditory cortex, located in the sylvian fissure (also called lateral sulcus, found on the superior surface of the temporal lobe) on Heschl’s gyri
the primary auditory cortex is surrounded by?
secondary auditory areas
where are several higher order auditory areas located?
in the superior temporal gyrus and sulcus. several areas located there are important for understanding speech
where are the auditory sensory organs located?
within the membranous labyrinth
what is the membranous labyrinth made of?
it is made of the cochlea and 5 vestibular sensory organs
1. saccule
2. utricle
and 3 semicircular canals
much of the membranous labyrinth is filled with?
endolymph, which is extracellular fluid that resembles intracellular fluids due to its ionic constituents
it has high potassium conc and low sodium conc
the space between the membranous labyrinth and the temporal bone is filled by?
perilymph, a fluid resembling extracellular fluid and CSF
the cochlea is stimulated by?
the vibration of the stapes
in the cochlea we have 3 coiled channels
scala vestibuli
scala media
scala tympani
lenght of the cochlea
30 mm, from base to apex
what is the organ of corti? what does it contain?
it is a specialized portion of the cochlear duct. it contains inner and outer hair cells (depending on their position according to the axis of the coiled cochlea)
the organ of corti rests on?
the basilar membrane
hair cells of the organ of corti are covered by which membrane?
tectorial membrane
the basic auditory transductive apparatus is made of?
basilar membrane
hair cells
tectorial membrane
most of the axons of the cochlear division of cranial nerve VIII innervate which type of hair cells?
inner hair cells
each inner hair cell is innervated by at least 10 auditory nerve fibers and each auditory nerve fiber contacts only a single (max a few) inner hair cell
NB: only a small fraction of auditory nerve fibers innervated the outer hair cell population. each fiber branches to contact multiple outer hair cells
what does the organ of corti do?
transduces sounds into neural signal
hearing depends on the movement of what? produced by what?
hearing depends on the movement of the basilar membrane produced by sound
the shorter hair bundles are located in which hair cells? the longer ones?
in the hair cells positioned at the base of the cochlea because shorter bundles are tuned to high frequencies. the longer ones are on hair cells located at the apex because they are tuned to low frequencies
what is horizontal sound localization? which nucleus is important for horizontal sound localization?
Horizontal sound localization is the ability to tell where a sound is coming from on the left or right side.
the ventral cochlear nucleus is fundamental for this.
what is the principal auditory decussation?
the trapezoid body, which contains crossing axons of the ventral cochlear nucleus as they travel to the superior olivary nucleus
Where do the axons from the dorsal cochlear nucleus decussate to then project to the inferior colliculus?
in the dorsal acustic stria
where do some axons from the posterior division of the ventral cochlear nucleus decussate?
in the intermediate acoustic stria
which artery supply the cochlear nuclei?
anterior inferior cerebellar artery
unilateral occlusion of this artery can produce deafness in one hear because the cochlear nuclei get informations from one ear only
the superior olivary complex contains 3 components
- medial superior olivary nucleus
- lateral superior olivary nucleus
- nucleus of the trapezoid body
what does the inferior olivary nucleus contain?
neurons that are important in movement control
what is interaural time difference?
low frequency sound activate the two ears at slightly different times, producing an interaural time difference
what is interaural intensity difference?
For high frequency sounds the interaural time difference is very small. the head however acts as a shield and attenuates these sounds. an high frequency sound arriving to the distal ear will be more soft than the closer ear’s one->the sound energy is absorbed by the head and this results in a interaural intensity difference.
neurons in the medial superior olivary nucleus are sensitive to?
interaural time difference, they respond only to low frequency sounds
neurons in the lateral superior olivary nucleus are sensitive to?
interaural intensity differences and they are tuned to high frequency stimuli
the structure of the external ear is important for sounds localized along which axis?
the vertical axis
peripheral auditory system, what is it?
The peripheral auditory system refers to the parts of the auditory system that lie outside the central nervous system (CNS) and are responsible for capturing and transducing sound energy into neural signals. It primarily includes the structures of the ear and the auditory nerve.
what is the olivocochlear bundle?
some neurons in the superior olivary complex are not directly involved in processing horizontal location of the source of sounds. These neurons receive auditory informations from the ventral cochlear nucleus (primary the posteroventral subdivision) and give rise to axons that project back to the cochlea via the vestibulocochlear nerve. this efferent pathway is called olivocochlear bundle. this olivocochlear projection regulates the sensitivity of the peripheral auditory system.
insertion and innervation of stapedius muscle
innervated by facial nerve
insert on the stapes
insertion and innervation of tensor tympani muscle
innervated by the mandibular branch of the trigeminal nerve
inserts on the malleus
when the stapedius and the tensor tympani muscle contract, what’s the consequence at the level of the middle ear?
they limit the movements of middle ear bones and dampen the oscillations of the tympanic membrane to sounds
acustic reflexes, what are they?
involuntary muscle contraction in the middle ear (stapedius and tensor tympani muscles) in response to high-intensity sound stimuli. It’s a protective mechanism to dampen loud sounds and protect the inner ear.
what is the brain stem ascending auditory pathway?
lateral lemniscus
carrier axons primarily from the contralateral dorsal cochlear nucleus and the superior olivary complex to the inferior colliculus.
many of the axons of the lateral lemniscus (in particular those coming from part of the ventral cochlear nucleus) also send collateral branches to?
the nucleus of the lateral lemniscus. It contains mostly inhibitory neurons that project to the inferior colliculus. the nucleus of the lateral lemniscus is another site in which axons decussate
3 components parts comprise the inferior colliculus:
- central nucleus
- external nucleus
- dorsal cortex
what is the principal site of termination of the lateral lemniscus in the inferior colliculus?
the central nucleus
Is lamination used in the auditory system?
yes, it is used to pack neurons with similar functional attributes or connections
NB: the central nucleus is laminated
name of the tract through which the inferior colliculus projects to the medial geniculate nucleus of the thalamus
brachium of inferior colliculus
what is the brachium of the superior colliculus?
brings afferent informations to the superior colliculus
which division of the medial geniculate nucleus is the principal auditory relay nucleus?
the ventral division
it is laminated and tonotopically organized
each lamina contains neurons sensitive to similar frequencies
in which layer of the primary auditory cortex does the medial geniculate nucleus terminate?
layer IV of the primary auditory cortex
the primary auditory cortex is tonotopically organized along the axis of heschl’s gyri, how?
low frequencies are processed laterally while higher frequencies medially
NB: there is also a columnar organization:
neurons sensitive to similar frequencies are arranged across all 6 layers (from the pial surface to the white matter)
the primary auditory areas transmit inputs to?
the secondary auditory areas
the secondary auditory areas transmit inputs to?
higher order areas
secondary and higher order areas, in humans, respond to?
speech
