Flashcards in Module D-12 Deck (25):
What are the Brodmann's areas for primary auditory cortex?
Areas 41 and 42
Which area of temporal lobe makes up primary auditory cortex?
the transverse temporal gyrus of Heschl on the superior surface of the temporal lobe
The organization of the primary auditory cortex is _______
What does the tonotopic map show?
the sound frequencies are mapped and distributed along a rostro-caudal axis
Where are low freq sounds represented?
rostrally and laterally
Where are high freq sounds represented?
caudally and medially
How is the columnar organization of cells in the primary auditory cortex
- Perpendicular to the tonotopic map
- there are columns with characteristic types of binaural innervation.
-grouped according to their pattern of input from both ears.
- Cells in one set of columns are excited by input from both ears (summation columns), labeled “EE”
- Cells in the alternating columns are excited by input from one ear and inhibited by input from the other ear (suppression columns), which is labeled as “EI”
In which layer does the input from the thalamocortical fibers come in?
What is the Place code of Frequency?
the place (or location) of a nerve cell encodes for a specific
stimulus feature (frequency, in this instance)
How are various frequencies distinguished?
Near the oval window, at its base, the basilar membrane is narrow and stiff, and therefore is activated most effectively deflected by high frequencies.
At the tip (apex) of the cochlea (helicotrema), the basilar membrane is wide and floppy, and therefore most effectively deflected by low frequencies.
The varied deflection causes varied activation of hair cells specific to the frequency of the sound
Which waves travel further in the cochlea?
Low frequency waves
What is Frequency code?
the frequency of action potentials in afferent fibers
increases with sound intensity
encoding method for stimulus intensity
What is Volley code?
Encoding method for sound intensity that based on number of afferent fibers activated
low intensity sound only activates low threshold fibers. Higher sound intensities result in the recruitment of additional afferent fibers with higher
How many auditory nerve fibers does each hair cell synapse with?
How is low frequency sound localized?
- interaural time differences.
- the first pressure wave arrives at different times at the
what pathway is used to detect the time delay for low freq sound localization?
the binaural pathways to the superior olive (MSO)
by a mechanism called “coincidence detection”
EPSPs produced in a neuron of the superior olive at the same time (coincidence) by signals arriving
from both ears will produce a larger signal in this neuron than EPSPs arriving at different times (no coincidence)
How is high frequency sound localized?
the differences in sound intensity in the two ears when the sound originates from positions lateral to the midline
, the ear on the side opposite to the sound source is in the
acoustic shadow produced by the head ( a diminished
sound pressure signal with
a lower intensity (amplitude)
what pathway is used to detect the time delay for high freq sound localization?
1) Fibers carrying auditory information synapse in the
ipsilateral superior olive, where they form excitatory
2) collaterals from these fibers cross the midline of the brainstem and form excitatory synapses on inhibitory interneurons in the contralateral trapezoid nucleus.
3) Neurons in the trapezoid nuclei send their axons to the superior olive on the same side, where they form inhibitory synapses.
4) The neurons in the superior olive receive direct excitatory input from the ipsilateral sensory input fibers, and indirect inhibitory input via interneurons in the
trapezoid nucleus, which had received excitatory input from the contralateral sensory input fibers.
5) excitation (depolarization) in one superior olive, which is forwarded to higher regions in the brainstem and cortex. The superior olive on the other side will be inhibited (hyperpolarized) and produce no output signals.
Localization of sound is performed in the _________ of the brainstem
The medial part of the superior olive uses __________ for interaural time differences, which is most effective for ___ frequency sounds
coincidence detection; low
The lateral part of the superior olive uses interaural _____ differences, which is most effective for ____ frequency sounds.
Weber's test for someone with _______ hearing loss in one ear, the sound lateralizes to the ipsilateral side
Weber's test with _________ hearing loss, the sound lateralizes to the contralateral side (side of normal hearing).
When performing the Rinne's test in normal subjects, __ conduction is better (and lasts longer) than ____ conduction. why?
Because in air the sound waves can be amplified by the middle ear (size difference)