Lecture 11: Smell and Hearing Flashcards
olfaction
specialized for identifying special molecules called odorants
what kind of receptors detects smell?
metabotropic g protein-coupled receptors
how do receptors detect smell?
Metabotropic g protein-coupled receptors transduce ions into a change in membrane potential
how many odorant receptors are there per odorant molecule?
1
are odorant molecules lipid soluble?
yes
are odorant molecules organic (made from life)?
yes
Olfactory epithelium
the tissue of the nasal sinus that sits underneath the skull (the cribriform plate) and contains olfactory receptor cells
how many types of receptor proteins does each olfactory cell express?
1
Glomeruli
located in the olfactory bulb. Where olfactory receptor cells synapse, which in turn sends axons to the brain
each glomerulus processes information about ____ types of olfactory receptor cells
1
what process allows us to recognize smells?
combinational processing
how many smells can humans recognize
tens of thousands
how is smell perception developed?
through learned assocaitions
is smell innate?
no
where does olfactory information go?
to the primary olfactory cortex in the temporal lobe, then to the amygdala
sound waves
fluctuations in air pressure that are caused by the molecules of air surrounding a vibrating object condensing and rarefying (pulling apart)
how fast do sound waves travel?
~700 MPH
what length of soundwaves can humans detect?
1.7 cm-17 m
what sound wave frequencies can humans detect?
20-20,000 times per second
3 dimensions of sound
loudness, pitch, and timbre
loudness
corresponds to the amplitude or intensity of the molecular vibrations
how is loudness determined?
by the total number of hair cells that are active and their overall activity levels
pitch
corresponds to the frequency of the molecular vibrations
how is pitch measured?
in hertz (Hz) or cycles per second
what is another word for pitch
tone
how is pitch determined?
place coding for moderate to high frequencies
rate coding for low frequencies
timbre
corresponds to the complexity of the sound
why do we use timbre
to determine the source of sound waves
how is timbre determined
Perceived by assessing the precise mixture of hair cells that are active throughout the entire cochlea
pinna
outer ear; receives sound from the external environment
typanic membrane
vibrates in response to sound waves and transfers them to the middle ear
middle ear
composed of three ossicles (small bones)
three ossicles
malleus, incus, stapes
oval windows
receives the vibrations from the ossicles and transmits them to the cochlea
cochlea
inner ear; a long, fluid-filled, coiled tube-like structure that contains sensory neurons. divided into three longitudinal divisions
three longitudinal divisions of the cochlea
Scala vestibuli
Scala media
Scala tympani
basilar membrane
encodes high notes on the end closest to the oval window. Like a xylophone, the low notes correspond to the longest (widest) section.
effect of sound waves on the basilar membrane
Sound waves cause the basilar membrane to move relative to the tectorial membrane, which causes hair cell cilia to stretch and bend`
organ of corti
Receptive organ that consists of the Basilar membrane on the bottom, the tectorial membrane on the top, and auditory hair cells in the middle
cilia
hair-like extension cells that transduce sound
outer hair cells
have cilia that are physically attached to the rigid tectorial membrane
inner hair cells
are not attached to anything. They sway back and forth with the movement of the solution
what does the movement of cilia do?
pulls open ion channels, which changes the membrane potential of hair cells.
there are ____ outer hair cells than inner hair cells
3 times
what type of hair cells transmit auditory information to the brain?
inner hair cells
people without _____ hair cells are deaf but people without _______ hair cells aren’t
inner; outer
how do outer hair cells adjust the sensitivity of the tectorial membrane
they contract like muscles to adjust the sensitivity of the tectorial membrane to vibrations
how do outer hair cells affect inner hair cells
they influence the sensitivity of inner hair cells to specific frequencies of sound
tip links
elastic filaments that attach the tip of one cilium to the side of the adjacent cilium
intersertional plaque
the point of attachment of a tip link to a cilium
what kind of protein do interserional plaques contain?
Each intersertional plaque has a single ion channel in it that opens and closes according to the amount of stretch exerted by the tip link
how do hair cells release neurotransmitters
they don’t have axons or action potentials so they continuously release neurotransmitters based on the amount of the stimulus
what is the effect of loud noises on the ear?
they can easily break tip links that interconnect each cilium. if broken, the tip links cannot transmit auditory information
can tip links grow back
yes, they grow back within a few hours and hearing comes back to normal
why does tip link breakage occur
as a protective measure against permanent damage
effect of glutamate on the ear
too much glutamate can release onto the cochlear nerve causing permanent cell death (excitotoxicity)
what percentage of 20 year olds have nose-induced hearing loss?
20%
place coding
The place where the cell is most active in the cochlea indicates the fundamental frequency (the pitch) of the sound wave
what types of frequencies are encoded by place coding?
moderate and high frequencies
rate coding
the rate of neurotransmitter release from the hair cells deepest in the cochlea determines the animal’s perception
what types of frequencies are encoded by rate coding?
very low frequencies
basilar membrane and place coding
Higher frequencies cause the bending of the basilar membrane, resulting in more hair cell activity in that area
tuning cures
indicate the sensitivity of individual inner hair cells, as is shown by their response threshold to pure tones of varying frequency. low points of the solid points indicate that the individual cells will respond to a faint sound only if it is a specific frequency. for louder sounds, cells will respond to frequencies above and below their preferred frequencies
Fundamental frequency:
the lowest frequency in a sound wave
overtone
sound wave frequencies that occur at integer multiples of the fundamental frequency
timbre
the specific mixture of frequencies (fundamental frequency + overtones) that different instruments emit when the same note is played
cochlear implant
- Typically 20-24 electrodes are positioned along the length of the cochlea
- By delivering electricity to distinct parts of the cochlea, we can cause actions potentials that correspond to different notes
- We can’t recreate this entire system, but we can create many different tones
fundamental frequency of human speech
85-180 Hz for men and 165-355 Hz for women
spatial location and phase differences and low-frequency sounds
innate method of detecting the source of continuous low-pitches sounds by means of phase differences
spatial location and loudness and high-frequency sounds
innate method of detecting the source of high-pitched sounds by analyzing the difference in loudness between ears
spatial location and timbre
- Sound waves bounce off the folds and ridges of the pinna before entering the ear canal
- Depending on the angle at which sound waves strike these folds and ridges, different frequencies of sounds can be enhanced or attenuated
sound pathway (steps)
- The organ of Corti sends auditory information to the brain via the cochlear nerve.
- These axons synapse in the cochlear nuclei of the medulla, where copies of the signal are made to be analyzed in parallel ascending paths.
- Axons from the cochlear nuclei synapse in the superior olivary nuclei in the medulla and the inferior colliculi in the midbrain, both of which help localize the source of sounds.
- Axons from the inferior colliculi synapse in the medial geniculate nucleus of the thalamus, which in turn relays the information to the primary auditory cortex in the temporal lobe
tonotropic represenation
The organization where different frequencies of sound are analyzed in different places of the auditory context
primary auditory cortex
the upper section of the temporal lobe, mostly hidden in the lateral fissure
auditory association cortex
the belt and parabelt regions
two streams of the auditory cortex
posterior and anterior pathways
posterior auditory pathway
where/ dorsal pathway
involved in spatial localization
meets up with the where vision pathway in the parietal lobe
anterior pathway
what/ ventral pathway
goes to the frontal lobe where the analysis of complex sounds occurs
auditory agnosia
various forms of auditory processing issues
amusia
The inability to perceive or produce melodic music
vestibular system
Detects gravity and angular acceleration of the head. maintains your upright head position, organizes your balance and corrects eye movements to compensate for head movements
Semicircular sacs
three ring-like, fluid-filled strictures that detect changes in head rotation (angular acceleration)
Cupula
gelatinous mass found in the ampulla of the semicircular canals; movies in response to the flow of fluid in canals
Vestibular sacs
a set of two receptor organs in each inner ear (utricle & saccule) that detect changes in the tilt of the head. Otoconia moves with gravity, depolarizing the hair cells it sits on
odorants
volatile substances that activate olfactory receptors
olfaction receptor cells
located in the olfactory epithelium
where do olfaction receptor cells synapse
in the glomeruli
how many types of receptors do olfaction receptor cells activate
1
loudness
the number of hair cells that are active
phase difference
Timing difference between the ears
level difference
Loudness difference between ears
how is the auditory cortex organized?
tonographically (by frequency)
