Central Auditory Pathways (ascending/descending/reflexive) Flashcards
what are the central auditory pathways (3)
1) ascending
2) descending
3) collateral
incoming sensory signals
ascending
feedback mechanisms to reduce unwanted noise & focus attention
descending
CN reflexes
learned orientation reflexes
collateral
all structures are __________________ in the ascending auditory pathway
tonotopically organized
where does tonotopicity exist?
at all levels & within nuclei and fiber bundles (pathways)
afferents from most sites project _____ (MGN is the exception)
bilaterally
3 sites of obligatory synapse
1) cochlear nucleus
2) MGN of thalamus
3) auditory cortex
auditory fibers enter the central pathway via CCN VIII at the __________________
cerebellopointine angle; which is the boundary between medulla & pons
identify the IC and MGN of the thalamus
MGN only projects to _____________ primary auditory cortex
ipsilateral
______ are the first-order neurons of the central auditory pathways
spiral ganglion neurons (SGN)
Type I SGN
90-95%
large true bipolar
more myelinated
metabolically active
peripheral process: go to one IHC (10-20 contacts)
Type II SGN
unipolar
peripheral cross tunnel of Corti to branch and innervate 10-15 OHC
what does the organ of corti look like
mainly myelinate axons from Type I
uniform myelination –> signal transmission synchronization (CAP - which is a physio measure of nerve activity)
apex : low / basal : high
all fibers synapse –> bifurcate and send to collateral branches (AVCN/PCVN/DCN of nuclear nucleus)
cochlear nerve / auditory nerve
cochlear nucleus (AVCN, PVCN, DCN)
diverse projections such as other brainstem nuclei (dorsal middle/ventral acoustic stria - trapezoid body) and contralateral medial lemniscus and IC
________ is a site of obligatory synapse for all _____ fibers
cochlear nucleus
1) dorsal to contral lateral lemniscus
2) intermediate to contra lateral lemniscus and few to SOC
3) ventral (trapezoid body) to both ipsi and contra SOC
acoustic striae
superior olivary complex (SOC) subdivisions
1) medial superior olive
- receive ipsi & contra inputs
2) lateral superior olive
- localization of higher freq signals
3) MNTB
- input from contra CN and projects to ipsi SOC (enhance intensity and timing distinctions)
4) periolivary groups