Unit 7: Auditory System Flashcards
Function of the Auditory System
Converts sound waves from the external environments into action potentials that travel to the auditory system of the brain.
What Frequencies can ears detect?
- Frequencies ranging from 20Hz to as high as 20,000 Hz
- acute hearing occurs in the range of 1000 to 3000 Hz.
Components of the Outer Ear
- The ear (auricle)
- external auditory canal
Components of the Middle Ear
- Eardrum
- Ossicles
- Incus
- Malleus
- Staples
- Eustachian tube
Components of the Innear Ear
- Cochlea
- for processing sound
- Vestibular Apparatus
- involved with the sense of balance
Structure of the Cochlea
- Resembles snail shell
- hollow area inside is divided into 3 compartments
- scala vestibular
- middle cochlear duct
- scala tympani (lower)
- basilar membrane separates the cochlear duct from the tympanic duct
Function+Structure + Location of the Organ of Corti
- where sound waves are converted to APs by special hair cells
- Hair cells embedded in the tectorial membrane
- sound waves cause the basilar membrane to vibrate which will bend the hair cells that are fixed to the tectorial membrane.
How is sound generated?
sound is generated when the wave of air pressure hits parts of the ear (or microphone) and turns it into electrical information ( APs in the CNS) that is then interpreted as sound
Frequency and Intensity of Soundwaves
- Frequency
- # of waves or cycles per unit of time
- Intensity (loudness)
- amplitude (height) of the soundwave
How is sound vibration Transfered and Amplified?
- airwaves travel through the air and reach the outer ear
- these waves are funneled into the external auditory canal and strike the tympanic membrane causing it to flex back and forth
- levering action of the ossicles amplifies the pressure waves that strike the tympanic membrane.
What is the function of the ossicles?
- the ear ossicles cause the oval window to vibrate
- oval window:
- small membrane-covered opening directly under the stapes
By how many more times are the sound waves amplified by the ossicles?
- Waves are amplified 15 to 20 times their original amount due to
- ear ossicles amplifying the vibration of the tympanic membrane
- the oval window is much smaller than the tympanic membrane
What is the fluid inside the cochlea called?
- Perilymph
- transmits the waves to the hair cells embedded into the basilar membrane
- hairs detect the vibration then turn them into APs in the auditory nerve
Short Wavelengths: displacement of the basilar membrane….?
displacement of the basilar membrane near the oval window
Long Wavelengths: displacement of the basilar membrane?
- displacement of the basilar membrane far away from the oval window
- low frequencies will stimulate sounds at the apex of the cochlea
How do we hear different frequencies?
- the way we hear different frequencies is due to the displacement of the basilar membrane
- pressure waves in the fluid created at different regions of the membrane
- occurs because the membrane is not consistent across its length
Basilar Basement Membrane
- wide and thin at the top of the cochlea and narrow and thick at the oval window
- tension is tight at the base
- loose at the top
- depending on the part of the membrane that is vibrating only certain hair cells will be activated by certain sounds.
- length and the stiffness of the hair cells also differ slightly along the length of the membrane
How are sounds converted to APs?
- when the basilar membrane vibrates, the hair cells are bent
- triggers the opening of ion channels leading to the depolarization of cells
- depolarization causes the release of neurotransmitters from the hair cell exciting neurons of the auditory nerves which then fires APs.
- triggers the opening of ion channels leading to the depolarization of cells
- the louder the sound the stronger the vibration of the basilar membrane the more bent the hairs the more neurotransmitter released the more frequent the APs
- these signals flow to the auditory cortex located in the temporal lobe
The vestibular system (location; function 4; detects 3 things…)
- inner ear infections and colds affect balance
- Vestibular system is located in the inner ear next to the cochlea is responsible for maintaining balance, equilibrium + postural reflexes.
- detects rotational + linear motion and the position of your head relative to the rest of your body.
- also responsible for the vestibular ocular reflex (type of eye movement)
2 Primary structures of the vestibular system
semi circle canals
- detect rotational accelerations of the head - three semicircular canals in each apparatus detect movement in each plane of direction.
Otolith
- detect linear acceleration
Semicircular canals: filled w/ _______ and each canal end has a swelling called an ______, inside each ______ is the sensory region called ______ _____ that contains the sensory hair cells fixed at the base and their _____ are embedded in a gelatinous material called the _______?
- filled w/ a fluid (endolymph)
- swelling at the end of each canal (ampula)
- inside ampula is the sensory region called the crista ampullaris
- contains the sensory hair cells, fixed at the base and their cilia are embedded in a gelatinous material called the cupula.
- inside ampula is the sensory region called the crista ampullaris
Semicircular canals function.
- When the head is rotated to the left the endolymph inside the canals lags behind + seemingly moves to the right
- the endolymph hits the cupula and bends the hair cells embedded in it
- when the hair cells are bent in a particular direction they will depolarize and fire action potentials sending signals to the brain
- when bent in the opposite direction cell will hyperpolarize sending no signals to the brain
Otolith Organs
- detect linear acceleration/position of the head when tilted
two otolith organs
- utricle
- horizontal acceleration
- i.e in a car
- saccule
- detects vertical accelerations
- elevator
- Both organs together detect head tilts.
Otolith structure + function.
- Both contain many hair cells that are anchored at the base and their cilia embedded in a gelatinous membrane
- membrane contains otolith crystals embedded in it to give weight + inertia during movements
Body at Rest (Vestibular system)
- regular series of APs being produced in the vestibular nerve
- acceleration in either plane
- otolith crystals lag behind and move in the opposite direction to the acceleration
- this bends the cilia of the hair cells in the opposite direction causing them to increase the frequency of APs in the vestibular nerve.
- increasing the acceleration increases the frequency of APs
- otolith crystals lag behind and move in the opposite direction to the acceleration
Body moves at constant velocity
- hair cells return to a resting state
- as do the frequency of APs
Body begins to decelerate
hair cells bend in the other direction which causes the frequency of APs to decrease further from the resting state
Hair Cell Function
- responsible for processing sound by the auditory system
- processing information on balance + equilibrium by the vestibular system
Hair Cell at Rest
hair cell at rest releases a small resting level of neurotransmitters from their base onto the sensory nerve which fires APs.
- when smaller stereocilia bend toward the larger kinocilia during acceleration for example, the hair cell releases more neurotransmitters causing more APs in the sensory nerve
- when stereocilia bend away from the kinocilium during. deceleration the hair cell releases less neurotransmitter resulting in fever APs
