LECTURE 6 Flashcards
(25 cards)
3 MAIN PARTS OF THE EAR
Tympanic membrane, ossicle and cochlea
TYMPANIC MEMBRANE
- Better known as the ear drum
- Air pressure pushes against the
membrane
OSSICLES
- Tiny bones connected to the ear
drum - Help to amplify sound and transfer
it to the cochlea
COCHLEA
- Fluid-filled spiral structure
connected to the ossicles - Contains membrane that responds
selectively to different frequencies
BASILAR MEMBRANE
- Inside the cochlea (?)
- Translates vibrations by responding selectively to different frequencies
- Far end is called the “apex” - Responds to low frequencies. Low frequency vibrations can travel further, hitting the apex
- Near end is called the “base” - Responds to high frequencies. High frequency vibrations require less energy and don’t travel as far, hitting the base
Place Code
Different frequencies of sound are represented by the brain according to where along the basilar membrane is stimulated
Rate Code
Different intensities (amplitude) of. sounds are represented by the brain by the firing rate of auditory nerve neurons
Hearing Loss
- High frequencies get lost first as we age
- All sounds travel through the base, not all sounds make it to the apex
- More use over lifetime -> more wear and tear/damage
TINNITUS
Stereocilia can become damaged from excessive noise - can be reversible or irreversible
RECAP OF AUDITION BEFORE IT REACHES BRAIN
- Air molecules become pressurized
- That pressure vibrates the tympanic membrane
- The tympanic membrane vibrates the ossicles
- The ossicles vibrate the fluid-filled cochlea, which contains the basilar membrane
- Basilar membrane, which is lined with hair cells
- Hair cells have stereocilia (smaller hairs) on top of them
- Pressure on those hairs (exerted by the vibration) sends a signal through the auditory nerve
MEMORIZE FROM EAR TO CORTEX SLIDE
FROM EAR TO CORTEX
Ear -> Cochlea -> Basilar membrane -> Hair cells ->
5. Auditory nerve fibers -> Superior olive (brainstem,
pons) -> Cochlear nuclei -> Inferior colliculus (midbrain) -> Medial geniculate nucleus (MGN) (in thalamus) -> Auditory cortex (temporal lobe)
Auditory brainstem response
- Auditory signals in the brainstem are triggered mechanically
- No conscious experience required to observe these signals
- EEGs can pick up signals coming from the brainstem and related areas
- Simple electrode setup can be used to test hearing in infants and
patients who can’t respond verbally - Test involves playing tones and then observing the peaks of activity
(ERPs) as the signal travels from brainstem to auditory cortex - If peaks of activity match normal firing pattern, the patient’s auditory pathway is functioning!
Tonotopic Mapping in A1
Different cells have different “tuning curves” meaning they respond to different frequencies and frequency ranges
AUDITORY TRASNDUCTION
A sound source creates movement of air molecules and waves of air pressure
* Air pressure waves vibrate the tympanic membrane, which then vibrates the ossicles, which connect to the cochlea via the oval window
* Different frequencies of vibration of the fluid inside the cochlea distort different parts of the basilar membrane, causing hair cells to mechanically open ion channels. This is how vibration is converted to an electrical signal
* Hair cells trigger the neurons of the auditory nerve which then synapse onto brainstem structures, then the medial geniculate nucleus of the thalamus, then to primary auditory cortex.
* In primary auditory cortex (A1), similar pitches are represented near each other, pitch increasing along the rostro-caudal axis. This is called tonotopy
How do we infer spatial location
- Interaural timing difference (ITD): the difference in when a signal arrives to each ear
- Interaural intensity difference (IID): the difference in the intensity of a signal at each ear [Works well for high frequency sounds, not as well for low frequency sounds]
Interaural timing difference
the difference in when a signal arrives to each ear
* Medial superior olive (part of brainstem)
* Integrates signals from each ear
* Cells a, b, and c send signals to each other (horizontally)
Cells only “activate” when they receive signals from
both left and right at the same time
* If signals reach b at the same time, sound comes from straight ahead
Types of somatosensation
mechanoreceptors, nociceptors, thermoreceptors, proprioceptors
Mechanoreceptors
cells that detect touch/pressure/vibration of the skin
Nociceptors
pain receptors, cells that detect tissue damage/extreme temperature
Thermoreceptors
cells that detect ranges of temperature
Proprioceptors
cells that detect how much different muscles in the body are stretched/relaxe
Olfactory system
- Pathway begins in the nose
- Neural cells dangle into the nasal cavity
- Olfactory receptor cells connect to glomeruli in the olfactory bulb
Taste
- Taste receptors are not neuronal cells
- Synapse with sensory neurons
