Lecture 11 - Auditory System (Part 2) - Central Processing and Perception Flashcards
Once and electrical signal is transduced via the cochlear nerve how many synaptic pit stops are there? leading to the auditory cortex or A1
-four obligatory pit stops and one optional pitstop
- cochlear nucleus (brainstem)
- superior olive (optional)
- inferior colliculus (midbrain)
4.Medial Geniculate Body (thalamus) - Primary auditory cortex (temporal lobe)
(after reaching A1 there are association areas surrounding Heschl’s gyrus where A1 is found where further auditory processing occurs)
In the first obligatory synapse the cochlear nucleus where is it located and how many divisions does it have?
-located between the medulla and pons
-two divisions - dorsal cochlear nucleus and the anterior ventral cochlear nucleus
What does the DCN or the dorsal cochlear nucleus division do?
primary auditory processing and projects directly to the inferior colliculus in the midbrain (skips the superior olive)
What does the AVCN or the anterior ventral cochlear nucleus do?
responsible for sound localization and binaural processing which includes Bushy cells which project to the medial and lateral superior olive
-these cells also receive direct input from the cochlear nerve via unique synaptic terminal known as the end bulb of held
AVCN fibers project to the superior olive which is the second overall synaptic pit stop first optional pit stop and what are the two response types and two divisions of the superior olive?
Response Types - EE and EI
Divisions - Medial Superior Olive MSO and Lateral Superior Olive LSO
-EE is a subset of neurons which respond to auditory stimuli from both ears
-EI subset of neurons which respond to auditory stimuli from contralateral ear
-MSO - send outgoing efferent fibers to the OHCs in the cochlea to adjust the tension of the tectorial membrane
-LSO - receive incoming afferent fibers from the IHCs in the cochlea
overall - MSO OHCs
LSO - IHCs
Where is the inferior colliculus synaptic pitstop found and how many divisions does it have?
-found in midbrain
-divisions: central nucleus, dorsal cortex, lateral cortex
What does the inferior colliculus do?
sound localization and has a tonotopic map from the cochlea
What does the central nucleus of the inferior colliculus do?
-it is tonotopically organized and it serves as the core nucleus of the inferior colliculus
What does the dorsal cortex of the inferior colliculus do and how many layers does it have?
-it has four cortical layers and it is polymodal meaning it receives info from the spinal cord to participate in auditory and somatosensory processing
What does the lateral cortex of the inferior colliculus do and how many cortical layers does it have?
three layers; involved in visual and auditory processing by receiving info from the superior colliculus
What does the medial geniculate body or MGB form and how many independent divisions does it have?
-forms the auditory thalamus
-has four independent divisions - ventral MGB, dorsal MGB, medial MGB, and suprageniculate MGB
What is the ventral MGB involved in?
tonotopically organized and involved in only auditory processing
What is the dorsal MGB involved in?
involved in auditory and somatosensory processing
What is the medial MGB involved in?
auditory and limbic processing because it is close to the amygdala
What is the suprageniculate MGB involved in?
auditory and higher cognitive processing
Where is the primary auditory cortex found?
in Heschl’s gyrus of the temporal lobes
Where do the efferent projections of the primary auditory cortex target?
they target the secondary auditory cortex or A2
What is the tonotopic representation of A1?
high frequencies are caudal
low frequencies are rostral
What is the columnar organization of the primary auditory cortex?
each row represent binaural preference and each column represents frequency preference
Where and what do the higher order association areas that receive auditory information are and do?
-they are beyond the primary and secondary cortex and they receive auditory information
What are some if the association cortical targets from A1 and A2?
the limbic cortex - parietal lobes, amygdala, insula, cingulate cortex
language network - broca’s and wernicke’s area
-hippocampus - auditory memory
-motor cortex - responding to auditory stimuli through motor movement
What are the two mechanisms used by the superior olive for sound processing?
ITD - interaural time difference
ILD - interaural Intersity Level Difference
In what type of animals is ITD more effective?
-animals with larger heads meaning greater distance between ears
What do delay lines do?
they extend from bushy cells in the AVC and they must travel different distances to reach each ear creating a time difference between the ears
What part of the superior olive is involved in ILD?
lateral superior olive and in bats the medial nucleus of the trapezoid body
What type of sound is ILD most effective with and why?
high frequency sounds since they are affected by an acoustic shadow in which the ipsilateral ear experiences a greater intensity of sound that the contralateral ear
What is a cochlear implant?
replaces the organ of corti and has a tonotopic map
