How Do We Hear, Taste & Smell? Flashcards
amplitude
measured as sound pressure
loudness
frequency
measured in Hertz (Hz)
pitch
most people detect 20-20,000 Hz
mechanical energy of sound waves
transduced into neuronal electrical activity- information that goes into the brain
outer ear
pinna
sound waves propagate down the ear canal to the tympanic membrane
pinna
funnels sound waves into ear canal
enhances certain frequencies- speech
eardrum
vibrates with a certain speed- pitch
how big the vibrations are- loudness
3 ossicles
malleus, incus, stapes
vibrations in tympanic membrane causes 3 ossicles to
move
amplifies pressure
malleus->incus->stapes
contact between ossicles is controlled by two muscles in order to
reduce the movement- is more stiff- protects from loud sounds
mute self-made sounds
inner ear
oval window
cochlea
oval window
stapes is in contact with
transfer vibrations to 3 fluid-filled canals in cochlea
cochlea
is small and coiled
basilar and tectorial membranes separate the canals
organ of corti
basilar membrane
between the tympanic and middle canals
vibrates- different areas sensitive to specific frequencies
high freq at narrow, stiff base
low freq at wide, floppy apex/tip
tectorial membrane
between vestibular and middle canals
organ of corti
sits between basilar and tectorial membranes
contains inner and outer hair cells
inner hair cells
detect sound
outer hair cells
help discriminate between similar frequencies
support cells
hair cells transduce sound waves into
electrical activity
has 50-200 stereocilia (hairs)- will move
relay electrical information to auditory nerve fibers
inner hair cell transduction
vibrations bend stereocilia
tip links open ion channels
Ca2+ flows in, K+ depolarize IHC (receptor potential)
release NT onto auditory nerve (mainly glutamate)
not neurons- because they do not generate action potentials
tonotopic map
frequency
tuning curves
auditory nerves have distinctive receptive fields- frequency that it is more sensitive to/favorite frequency
What does the frequency of sound waves determine?
B. Pitch
auditory pathway to brain #1
Hair cells release neurotransmitter onto vestibulocochlear nerve (8th)
auditory pathway to brain #2
8th nerve synapses onto cochlear nucleus in brain stem
auditory pathway to brain #3
info travels to both superior olivary nuclei: mostly crosses midline
auditory pathway to brain #4
inferior colliculus (primary auditory centers of midbrain), then medical geniculate nucleus (thalamus), then auditory cortex
inferior colliculus->thalamus->auditory cortex
Why might it be important that auditory information travel to both the same side and opposite side colliculi?
to be able to tell which side the information is coming from
sound localization- bihearing
information from both ears and both sides of the brain- brain figures out where sound is coming from
inferior colliculus
tonotopic map- critical for sound localization
processes intensity, frequency and duration of sound
auditory cortex
identifies complex sounds that have many sub-parts (ex. vocalizations)
tonotopic map
older people losing hearing
floppy basilar membrane becomes less floppy
stiff base is less sensitive to low decibel high frequencies
cannot hear higher pitches- need to be louder
conduction deafness
disorders of the outer/middle ear that prevent vibrations from reaching the cochlea
sensorineural deafness
originates from cochlear or auditory nerve lesions; hereditary disease of hair cells
central deafness
hearing loss caused by brain lesions (such as stroke), with complex results
cochlear implant
electrode is implanted into the cochlea
detector turns into electrical signal
smell
olfaction
humans can discriminate over 1 trillion odorants!
any 2 people differ in their expression of different odor receptors by 30%
olfactory epithelium
inhalation brings odorants here
olfactory receptor neurons (6 million)
supporting cells
basal cells
olfactory neurons regenerated from
basal cells- adult neurogenesis
olfactory neurons have
cilia extending from the dendritic knob into the olfactory mucosa
unmyelinated axon to olfactory bulb
metabotropic receptors on cilia and knob
each olfactory neuron expresses only ____ type of olfactory receptor
one
each receptor belongs to 1 of 4 subfamilies
Given that humans can discriminate between 1 trillion odors, how
many different types of odor receptors do you think we have?
A. 4
B. 400
C. 40,000
D. 4 million
B. 400
can come in different combinations
one smell is made of a bunch of odorants
olfactory receptor signaling
transduction
olfactory transduction
odorant binds metabotropic receptor
G-protein activated
adenylyl cyclase activated and makes cAMP (2nd messenger)
transduction continued
cAMP causes cation (Ca2+, Na+) channels to open
voltage-gated Cl- channels open to further depolarize cell (receptor potential)
action potential in axon
olfactory bulb
olfactory neuron
mitral cells
glomeruli
olfactory neurons axons synapse on
mitral cells in the olfactory bulb
the mitral cells are
clustered into glomeruli (spheres of cells) in the olfactory bulb
glomerulus receives input
from olfactory neurons with same receptor type
separated function in olfactory bulb
functional localization of olfactory receptors in epithelium
piriform cortex
piriform cortex
olfactory representation goes directly into the cerebral cortex (no need to go through thalamus)
5 tastants
5 receptors (salty, sour, sweet, bitter, umami)
taste receptor cells
(50-150) are clustered into taste buds
taste buds are located
on sides of taste pores between papillae (bumps)
circumvallate papillate
located in the back
foliate papillae
located along the sides
fungiform papillae
located in the front of the tongue
taste cells
replaced every 10-14 days
transduction of taste
receptors on cilia are bound by tastants
receptor activation produces receptor potentials
receptor potential causes neurotransmitter release onto cranial nerves
thalamus
gustatory map in cortex
salty
Na+ ions flow through open ion channels in the taste cell membrane, causing depolarization
sour
we perceive acidic solutions as sour
acid-sensitive K+ ion channels are blocked, preventing K+ leaving the cell and leading to depolarization
acid
high concentration of H+
sweet
sugars bind to T1R2 and T1R3 receptors, causing them to join (dimerize)
sweet activation
tastant binding to receptor-> activation of G-protein-> second messengers-> Ca2+ flow into cell -> receptor potential-> neurotransmitter release
umami
amino acid receptor (mostly activated by L-glutamate and monosodium glutamate)
G-protein coupled metabotropic-like receptor; heterodimer of T1R1 and T1R3
umami activation
tastant binding to receptor-> activation of G-protein-> second messengers-> Ca2+ flow into cell-> receptor potential-> neurotransmitter release
bitter
T2R receptors: G-protein coupled metabotropic-like receptors
30 types, so can perceive many bitter flavors
bitter activation
tastant binding to receptor-> activation of G-protein-> second messengers-> Ca2+ flow into cell-> receptor potential-> neurotransmitter
Which is the part of the tongue that senses sweet?
everywhere