Flashcards in Neuro - auditory system 1 + 2 Deck (62)
Which cells do afferent fibers of the spiral ganglion cells synapse?
How do these afferent fibers synapse?
95% Inner hair cells (multiple fibers per inner hair cell)
5% outer hair cells (one fiber synapses on multiple outer hair cells)
What is the fluid in the scala tympani called? What is it made of?
Made of: low K+, 0 mV
What is the fluid in the Scala media called? What is it made of?
made of: High K+, 80 mV
What is the fluid in the inner hair cells made of?
Low K+ and -45 mV
How is fluid seperated between the inner hair cells and scala media?
How does a downward wave defection effect the stereocilia? (3)
1) Deflects stereocilia towards the modiolus (away from taller stereocilia)
2) Tip links closes pores
3) K+ can't get in and hair cells are hyperpolorized
How does an upward wave effect the stereocilia?
1) stereocilia deflected away from mediolos (towards taller stereocilia)
2) Tiplinks open pores and positive K+ ions from endolymph flow into hair cells
3) hair cells depolarize and release neurotransmitter
What is an audiogram?
Hearing level in patients is plotted to determine what they can hear.
Softest sound that can be detected at each frequency is plotted. Anything below line (and thus louder at each frequency) can be heard
What are the types of hearing loss?
What is conducive hearing loss?
Something blocking the external or middle ear
Treatments: surgery, medication, sometiems can't be treated
What is sensorineural hearing loss?
Involves structures of inner ear and cochlea.
Causes: Congenital, Noise exposure/trauma, Medication, age
Treatment: permanent, not much can be done to cure, can't restore structures
Where do auditory nerves synapse?
What are the functions of the two pathways that originate in the cochlear nucleus?
1) Recognition of sound patterns
2) Localizing sounds
What is the pathway for recognition of sound patterns starting from the cochlear nucleus?
Dorsal + Ventral coclear nucleus (DCN and VCN) --> Contralateral Inferior colliculus --> medial geniculate nucleus (MGN) --> primary auditory cortex
What is the pathway for localizing sounds starting from the cochlear nucleus?
Ventral cochlear nucleus (VCN) --> Superior olivary complex (SOC on both sides) --> Inferior colliculus (IC) --> Medial geniculate nucleus (MGN) --> primary auditory cortex
What is the lateral lemniscus?
carries sound pattern information from Dorsal and Ventral cochlear nuclei to contra-lateral inferior colliculus
Where is the first place for binaural convergence?
Superior olivary complex
Where is the superior olivary complex (SOC)?
In the pons
Where is the medial geniculate nucleus?
In the thalamus
Where is the auditory cortex?
Area of brain?
Broadmans area: 41
Area of brain: superior temporal lobe - Heschel's gyrus
Why is topography and laterality of limited use for diagnosis of pathology? (2)
1) Because the only place in the brain NOT binaural is cochlear nucleus
2) duplication of pathways makes it difficult to selectively cut afferents from one ear alone (unless at periphery or from cochlear nucleus)
Where is Wernicke's area and what does it do?
Where: left hemisphere in superior gyrus of temporal lobe
Purpose: speech interpretation
What is the characteristic frequency of a cell?
It is the frequency in which a cell maximally responds
What is a frequency tuning curve?
A graph that describes how well a cell responds to higher and lower frequencies
What is the result of an INCREASE in sound intensity in regards to a tuning curve?
the curve broadens
What is the result of an DECREASE in sound intensity in regards to a tuning curve?
the curve narrows
What is the purpose of broca's region?
Important for speech production (the motor aspect of speech)
Where is area 41/A1 (auditory cortex)?
buried in the lateral sulcus
What is unique about cells in the auditory cortex relative to cells in other parts of the auditory pathways?
Cells in auditory cortex can be selectively responsive to complex features of sounds
Example: some cells are selective for speech components (dynamic beginning followed by sustained tone)