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
SOC projections
axons from SOC ascend, along with fibers from contra CN
axons from SOC ascend, along with fibers from contra CN, to form a pathway called _____________
lateral lemniscus
pathway of fibers, which some synpase with neurons in nucleus of lateral lemniscus
lateral lemniscus (LL)
receives all fibers from LL
some may pass through IC to SC
2nd, 3rd, 4th, or even higher order (neurons)
2nd order fibers from contra CN
projects to ipsi and contra MGN of thalamus
inferior colliculus (IC)
thalamus is the sensory relay station for ________ sensory info headed to cerebral cortex
ALL
what is the subdivision of the thalamus responsible for auditory signals
medial geniculate nucleus / medial geniculate body
what is located on the superior surface of the TEMPORAL LOBE
primary auditory cortex
primary auditory cortex lies predominately on ____________
Heschl’s
higher frequencies are located more _______ and low frequencies more ______________ in the primary auditory cortex
posteriorly ; anteriorly
the neuronal activity at any level, and thus the information extracted, may be modified by ___________ feedback circuits
descending
OCB
feedback circuits with SOC, LL, IC to CN
contra CN to CN
cortex to lower
descending pathway
allows ascending (efferent) control over cochlea
OCB
OCB fibers run with CN VIII and arise from two populations of cells with SOC: 1) __________ and 2) ___________
LSO (small cells)
MSO (large cells)
_______ is used as the neurotransmitter to hyperpolarize OHCS by opening K+ channel
ACh
latency of response of synaptic activity of the OCB is ________ msec following the sound stimulus
10-30 msec
the _____ nature of this system allows 1 cochlea to affect responses of the other cochlea
bilateral
MOC activity decreases the active processes of OHCs (leading to freq-specific reduction of cochlear gain)
precise cochlear function (sharp tuning curves)
detection and discrimination of sounds in noise by suppression of continuous background noise
proposed functions of the OCB
another name for the stapedial reflex, ME acoustic reflex, ME muscle reflex, attenuation reflex
acoustic reflex
what does the acoustic reflex represent
true CN reflex with simple reflex arc
stimulus threshold for the reflex averages around ______ dB but ranges from _______ dB
85 ; 70 -100 dB
in humans, the reflex contracts ONLY the ________ muscle bilaterally
stapedius
contralateral response is __________ and slightly ___________
slower and weaker
what can the reflex help identify
(CN VII) facial nerve lesions or retrocochlear lesions
0 such as vestibular schwannoma
why is it beneficial for the reflex to be activated in anticipation of the onset of vocalization?
it can reduce sound intensities reaching the ear by about 20 dB
functions of the acoustic reflex (3)
1) protection from loud sounds
2) mostly dampens low freq sounds
- may inhibit masking of high freq by lower freq
3) possibly to reduce likelihood of our vocalizations interfering with normal hearing
orientation reflex:
______________ generates and controls eye and head movements based on signals from different senses
superior colliculus
orientation reflex:
some auditory fibers of the ____________ pass right through the IC to reach the superior colliculus
lateral lemniscus
orientation reflex:
inputs integrated by SC directs extraocular muscles and spinal motor neurons to allow a learned __________ orientation
reflexive
____________________ is highly synchronized, allowing the measurement of signal processing (neuronal activity) to be conducted, even non-invasively (ABR)
auditory signal transmission
the ______________ of neural activity associated with auditory signals is unmatched by other neural networks or sensory systems
fidelity / precision
