Lec 06- Auditory Senses Flashcards
What is the conduction pathway sequence?
- TM
- Malleus
- incus
- Stapes
- Oval window
What is the difference between he TM SA and that of the stapes?
TM = 55 Stapes = 3.2
TM SA is 17x Stapes
What does the increased SA of the TM do?
increases force from the ossicular lever system to the cochlear fluid by 22x
Why does the TM need a greater force?
- fluid has greater inertia than air
- increase in force needed to cause vibration in the fluid
What provides the impedance matching between the air and fluid?
TM and Auditory ossicles
How would hearing sensitivity be affected in the absence of the ossicular system and the TM?
affected negatively (look up)
Which muscle pulls the handles of the malleus inward?
tensor tympani
What muscle pulls the stapes outward?
Stapedius
What effect do the Tensor Tympani muscle and the Stapedius muscle cause for the ossicular system?
-
What is the function of the attenuation reflex?
-
What effect do the Tensor Tympani muscle and Stapedius muscle have on a person’s sensitivity to his or her own speech?
- Protects a little from loud noises
- Makes you alert of your own voice
What consists of 3 side-by-side coiled tubes?
cochlea
What are the 3 coiled tubes of the cochlea?
- Scala vestibuli
- Scala media
- Scala tympani
What are the 4 major components of the cochlea?
- Scala vestibuli
- Scala media
- Scala tympani
- Reissner’s (vestibular) membrane
What does the Reissner’s membrane separate?
- Scala media
- Scala vestibuli
Why are the scala media and vestibule considered to be a single chamber as far as sound conduction is concerned?
because of the thinness of Reissner’s membrane
What does Reissner’s membrane maintain within the Scala Media?
a special fluid (secreted by Stria Vascularis)
What does the Basilar membrane separate?
- Scala Media
- Scala Tympani
What contains 20,000-30,000 fibers that project from the modiolus of the cochlea to the outer wall?
basilar membrane
The distal ends of the fibers are not fixed but are ___________ in the basilar membrane
embedded
Can the fibers in the basilar membrane vibrate?
YES
Where does the length of the basilar fibers increase?
from the oval window to the apex of the cochlea (hemicotrema)
Where does the diameter of the fibers decrease?
from the oval window to the apex of the cochlea
What is the result of the basilar fiber length increasing and the diameter decreasing?
- Stiff, short fibers near the oval window will beat at high frequency (base)
- Long, limber fibers near the apex of the cochlea will vibrate at low frequency (apex)
Where does high frequency resonance of the basilar membrane occur?
base of cochlea
Where does low frequency resonance of basilar membrane occur?
apex of cochlea (helicotrema)
What generates nerve impulses in response to vibration of basilar membrane?
Organ of Corti
What are the sensory receptors of the Organ of Corti?
- hair cells
- protruding fibrous processes
How many rows of internal hair cells are in the Organ of Corti?
single row of internal hair cells
3,500
12um diameter
How many rows of external hair cells are in the Organ of Corti?
3-4 rows of external hair cells
12,000
8um diamiter
What do the outer hair cells do with vibrations?
rise
What do hair cells stimulate?
nerve fibers that lead to the spiral ganglion of Corti
Where are stereocilia in the Organ of Corti?
stereo cilia from hair cells touch or are embedded in the overlying tectorial membrane
What happens when the hairs bend ing one direction?
they are depolarized
-hyperpolarized when they are bent in the opposite direction
What creates a rigid unit in the Organ of Corti?
Outer ends of hair cells are:
- Tightly attached to reticular lamina
- Supported by Rods of Cotri (attached to the basilar fibers)
Where do neurons in the ganglia send axons?
into the upper level of the medulla
via the cochlear nerve CN8
What causes movement of the reticular lamina?
movement of the basilar fiber
What does movement of the reticular lamina cause?
shearing forces on the hair cells against the tectorial membrane
What happens to the hair cells whenever the basilar membrane moves?
hair cells get excited
How many stereocilia does each hair cell have on its apical border?
100
Where are sterocilia longer?
on the side farther from the modiolus
What happens when cilia are bent in the direction of the longer ones?
tensile force is created on the shorter cilia
What happens as a result of the tensile force on the shorter cilia?
1- Creates a mechanical transduction
2- Opens 200-300 K+ channels
3- Depolarization of the hair cell membrane
4- Creates more (-) internal environment
5- Repolarization
What fills the Scala media?
endolymph
What fills the Scala vestibuli and Scala tympani?
perilymph
What does the endolymph contain?
High [K+]
Low [Na+]
What does the perilymph contain?
Low [K+]
High [Na+]
What is the voltage difference (Endocochlear potential) between the Endolymph and Perilymph?
+80mV (Scala media is positive)
-70 - (-150) = +80
Where do the tops of hair cells project?
through the Reticular Lamina
Bathed by Endolymph
What surrounds the lower bodies of hair cells?
Perilymph
What is the intracellular potential of hair cells with respect to the Endolymph?
-70 mV
What is the intracellular potential of hair cells with respect to the Perilymph?
-150 mV
What is the place principle?
- the nervous system detects sound frequencies by determining positions along the basilar membrane that are most stimulated
- sends impulses into the medulla
- creates auditory image of what is going on in the environment
How does the auditory system determine loudness?
-
What is a decibel?
1/10th of a bell
log system
How does the frequency range that can be heard change with age?
-
What are the 6 components of the nervous system pathway?
- Spiral organ of corgi (where AP generated)
- Dorsal/Ventral cochlear nuclei (in medulla)
- Superior olivary nucleus
- Lateral lemniscus’ nucleus
- Medial geniculate nucleus (thalamus)
- Auditory cortex
Where does decussation occur between right and left auditory nervous system pathways?
- lower medulla
- trapezoid body
What is the relationship between the auditory tracts and the RAS?
RAS = associated with arousal states
Sound affects RAS
Where is the auditory cortex located?
- Along temporal lobe below central sulcus
- Near areas that detect high and low frequency
What are the characteristics of primary auditory cortex and the auditory association areas?
Close to the Wernicke’s area
5th lobe
creates deep fold of gray matter
What happens to decibels as frequency increases?
decibels decrease
