Ch 3 - Auditory Flashcards
Sound is measured in
Decibels (dB)
Sound frequency is measured in
Hertz (Hz)
Greatest Sensitivity to sound frequency is
between 2000 & 5000 Hz
Able to discriminate between the intensity of
1 dB & 2 dB
Range of sound frequency
20 Hz - 20,000 Hz
Human speech range frequency
300 Hz - 3000 Hz
As one ages we have a decrease in
High frequency tone
Sound is understood by which CN?
CN VIII
Components of Outer Ear
- Auricle/pinna
- External auditory meatus
Function of Outer Ear
Collection of sound waves & conduction to tympanic membrane
Components of Middle Ear
- Tympanic Membrane
- Middle ear ossicles: Malleus, Incus, & Stapes
- Tensor tympani & stapedius muscles
Tensor tympani is innervated by
Trigeminal Nerve
Stapedius muscle is innerved by
CN VII Facial Nerve
Function of Tensor tympani & Stapedius muscle
Dampen sound
Functions of Middle Ear
Sound amplifier
The Middle Ear communicates w/ nasopharynx via
Auditory tube
Middle Ear cavity is innervated by
CN 9 (Glossopharyngeal Nerve)
Pathology of middle ear cavity results in
Conduction Hearing Loss
Function of Inner Ear
Sound transduction
Components of Inner Ear
- Cochlear & organ of Corti
- Semicircular canals
• lateral
• posterior
• superior
Perilymph
- Similar to ECF
- The fluid within vestibuli & tympani
- High sodium, low potassium concentrations
Endolymph
- Similar to ICF
- The fluid within media
- High potassium, low sodium
Similar to ICF, this fluid is found within media
Endolymph
Similar to ECF, this fluid is found within vestibule & tympani
Perilymph
Perilymph or Endolymph: Which contains high sodium & low potassium concentrations?
Perilymph
Perilymph or Endolymph: Which contains high potassium & low sodium concentrations?
Endolymph
The cochlea is
The sensory apparatus of transduction. It contains the organ of corti
Separates vestibuli & media
Reissner’s membrane
Separates media & tympani
Basilar membrane
Organ of corgi lies on ____ within the _______ and is surrounded by _____
Organ of corti lies on basilar membrane within the scala media and is surrounded by endolymph
Auditory receptors are innervated by
CN VIII (Vestibulocochlear Nerve)
Inner hair cells are arranged
In single rows
Outer hair cells are arranged
In parallel rows; greater quantity
Bending of the cilia hair cells in one direction results in increased K+ conduction (______) and decreased K+ conduction (______) in the other direction
Depolarization & Repolarization
Depolarization of the cilia hair cells
Opens Ca2+ channels in the presynaptic terminal of hair cells releasing excitatory NT increasing the firing of CN VIII (Vestibulocochlear)
Hyperpolarization of the cili hair cells
Decreases the release of excitatory NT w/ resultant intermittent firing of CN VIII (Vestibulocochlear)
Mechanism of Auditory Transduction Starting from Sound Waves, Ending in APs in afferent cochlear nerves
Sound Waves -> Vibration of organ of Corti -> Bending of cilia on hair cells -> Change in K+ conductance of hair cell membrane -> Oscillating receptor potential (cochlear microphonic) -> Intermittent glutamate release -> Intermittent APs in afferent cochlear nerves
Mechanical deformation of stereocilia toward the kinocilium causes
K+ channels to open in the stereocilia, leading to depolarization, leading to Ca2+ to enter the cell, allowing vesicle fusion & the release of NT
Mechanical deformation of stereocilia away from the kinocilium causes
The K+ channels to close and Hyperpolarization or Repolarization occurs
Base of Basilar Membrane
- towards the oval window
- narrow and stiff
- Responds best to HIGH FREQUENCIES
Apex of Basilar Membrane
- towards helicotrema
- wide and compliant
- Responds best to LOW FREQUENCIES
Function of the Vestibular System
- Equilibrium or balance
- Works in conduction w/ the visual system
Semicircular Canals
- Arranged perpendicularly to each other
- Detects angular/rotational acceleration of the head
- Ampulla at end of each canal contains the sensory receptor
Gelatinous mass
Cupula
During Horizontal Rotation what happens?
You have horizontal angular acceleration which is sensed by lateral semicircular canal. When head moves horizontally, the endolymph moves in the opposite direction (b/c cupula moves faster than the endolymph) pushing the stereocilia towards the kinocilium ipsilaterally causing depolarization (excitation) and away from the kinocilium contralaterally (hyperpolarization = inhibition). When the endolymph catches up, the cilia will return to their original position, hence point of neither depolarization or hyperpolarization. When the movement stops, the opposite occurs. This excitatory or inhibition is then sent via CN VIII to the CNS.
Otolith Organs
Sensitive to linear acceleration/deceleration of the head due to gravitational forces
Composed of Utricle & Saccule
Utricle
Sensitive to forward-backward movements
Saccule
Sensitive to movements in all directions Sensitive to: - backward-forward movement - lateral displacements - up-down - most sensitive to lateral displacement
Nystagmus
- Occurs in response to angular or rotational acceleration of the head
- Head rotates and eyes initially move in the opposite direction of the rotation in an attempt to maintain a constant gaze = slow component of nystagmus
- When the eyes reach their maximum lateral stretch, there is a rapid return to align w/ the head as it turns = rapid component of nystagmus
- IT IS DEFINED BY THE DIRECTION OF THE RAPID COMPONENT
Postrotatory Nystagmus
If the rotation is stopped abruptly, the eyes will move in the direction opposite that of the original rotation. During the postrotatory period, the person tends to fall in the direction of the original rotation (due to stimulation of contralateral extensor muscles) b/c the person “thinks” he or she is spinning in the opposite direction
Caloric Test
Pour cold water in ear & Nystagmus to opposite side of treated ear
Pour warm water in ear & Nystagmus to same side of treated ear
Remember Acronym COWS
It is an indication that brain stem is intact
