4 senses Flashcards
why are the senses important
adaptive significance
adaptation
ie/ neurons becoming less responsive over time
for example, a clock ticking in the background slowly goes away
pinna
external ear or external auditory meatus
captures, focuses and filters sound
they are directional - ears point in a specific direction which aids in localization - figuring out where the sound is coming from
highly mobile in some species
performs early sound processing - pattern of ridges inside act as a spectral filter - increasing and decreasing certain sound frequencies
directs sound waves into ears
guides them into ear canal - leading to middle ear
act as radiators - heavily vascular in some species
meatus
hole from outside to inside
middle ear
tympanum and ossicles
concentrates sound energy
breeding ground for bacteria, pressure is painful, subject to infection
tympanum
eardrum
membrane that seals the end of the ear canal + ossicles
vibrates when struck by sound waves from ear canal - converts sound energy into a form of kinetic energy
when ruptured hearing is impaired
ossicles
tiny bones - chain of them
smallest bones in your body
three of them
concentrate and amplify vibrations focusing pressure on small oval window
amplification is important for converting vibration in air into movements of fluid in the middle ear
what are the 3 ossicles
malleus (hammer), incus (anvil) and the stapes (stirrup)
form an articulated chain (leading from back of ear to cochlea (inner ear)) - mechanically coupling the vibrating tympanum to inner ear (oval window)
for the tymphanum to vibrate, air pressure must be equal on both sides - middle ear contains eustachian tube
if middle ear is tighter than ear is tighter than ear drum, sound waves can not move as freely
eustachian tube
in middle ear
localizes pressure
leads away to the oral- nasal cavity - this is how ear infections get in
connects to let air in and out
middle ear muscles
tensor tympani
stapedius
attach to the end of ossicles
contraction of the muscles alters the ability of the ossicles to move in response to a vibrating tympanum
has a modulating movement of the ossicles , reducing the amount of response to sounds
makes the bones stiffer and less sinsitive
activate just before we produce a self made sound ie/ speech, cough - hence why we do not think our own sounds are crazy loud
tensor tympani
is a tiny muscle connected to the malleus, which is the ossicle attached to the tympanum (makes this tight)
sound waves strike here and cause it to vibrate at the same frequency as the sound.
stapedius
connects the stapes to the floor of the middle ear
modulation of sound
occurs within 200 msec of a loud noise
happens with our own voice
oval window
where the stapes connects to the cochlea
sound
vibrational energy that in a series of compressions
decibel
measure of sound frequency perceived as loudness
perception of amplitude
perceived as a local increase or increase in air pressure
plotted as a sine wave
sound emitters
produce successive compressions are rarefactions in air - think of a loudspeaker cone
frequency
time from peak to peak
pitch Hz or cycles/sec
amplitude
peak height
loudness
db is relative
volume, how loud is the sound (strength)
intensity force sound exerts per unit area
harmonics
are multiples of the fundamental frequency of an emitter
fundamental frequency
predominant frequency of an auditory tone
timbre
is the unique “signature” sound of an emitter, comprised of the fundamental frequencies plus harmonics (or overtones)
character of the sound of an instruments
ie/ we know the sound of different instruments like piano/guitar (knowing they sound different)
doppler shift
occurs if the emitter is in motion
velocity (ie/ how an ambulance sounds far vs. away is added to the rarefraction-compression cycle to change
used by many species, especially bats
resonance
intensity of a vibration
pure tone
a tone with a singer frequency of vibration (frequency and amplitude)
transduction
converting from one form of energy to another
the inner ear
the organ that actually encodes the sound of elements
called a transducer
only the size of a pea
cochlea
fluid filled
converting sound waves from the world into something we can understand (neural activity)
fluids that fill is are not compressible
vibrations transmitted from the tympanum are communicated to the endolymph via the action of the stapes against the oval window
what are the gel fluids that fill the cochlear tubes
endolymph and perilymph
oval window
connection point of ossicles (stapes) to the cochlea
the fluid in the cochlea is not compressible, what does this cause?
there is movement (waves) produced in the endolymph - this propagates through the length of the cochlea
round window
bulges to accommodate the pressure that comes from the compressed fluid
lets energy out of the cochlea
organ of corti
transduces sound waves into neural energy
receptor system
the most important part of the cochlea for hearing
converts vibration from sound into neural activity
consists of auditory sensory cells (hair cells), elaborate framework of support cells, auditory nerve terminals that transmit neural signals to and from the brain
basiliar membrane and tectorial membrane
waves are created in the fluid of the scala vestibula causing the basilar membrane to ripple
vestibulocochlear nerve
fibers contact the bases of hair cells
some fibers convey sound info to the brain
where is the organ of corti located
in the scala media (middle canal of the 3 parallel
basilar membrane
middle canal
one of the membrane that divides the tubes of the cochlea
base: increased frequency, stiff
apex: decrease frequency
hair cells
rows of specialized receptors
inner hair cells
sterocilia protrude from top of hair cell
closer to central axis
base near basiliar membrane
when stimulated, release glutamate onto auditory nervefibers
stereocilia
tiny bristle
nesstles into hollows of tectorial membrane
- form mechanical bridge between two membranes
- forced to bend when sounds cause basiliar membrane to ripple
approximate the tectorial membrane
tectorial membrane
another divider
depolarization of hair cells
even a tiny bend in stereocilia causes a large depolarization of the hair cells
causes the operation of a special type of large and selective ion channels
- allows rush of potassium and calcium in at the base
causes synaptic vesicles to fuse with synaptic membrane and release neurotransmitters to stimulate adjacent nerve fibers
hair cells sway back, stereocilia shuts
the opening and shutting of channels is a way of encoding frequency
depolarization reaching the base of the hair cell causes a calcium channel to open - resulting calcium current provokes transmitter release
the transmitter acts on the auditory nerves leading from the hair cells to the brain
outer hair cells
12000
in 3 rows arranged in parallel
same arrangement of stereocilia
release ACh and are influenced by GABA (inhibatory NT)
hair cells ability to switch on and off
allows them to track the rapid oscillation of the basiliar membrane
hair cells are sensitive
how does the organ of corti work?
- ossicles transmit vibrations to the fluid of the cochlea, setting up traveling waves
- waves cause the basilar membrane to ripple - like the shaking of a carpet
- hair cells have their bases in the basilar membrane, and their stereocilia inserted into the tectorial membrane above
- for any frequency, amplitude of the traveling wave is exaggerated at one particular location of the basilar membrane, due to a prcess akin to resonance
energy is put into the base of the basiliar membrane which is at the stapes which vibrates the round window to go into the membrane
high frequency and smaller response at base
low frequency and heightened response in apex
IHC - afferent
leads to brain
carries info that we perceive as sound
activated by glutamate from the IHS
convey APs to the brain that provide perception of sound info
95 percent of fibers leading to brain
IHC - efferent
from brain to IHC
serve a modulatory function (influences how hair cells are) by inhibiting the IHC - afferent fibres. ACh
allow brain to control responsiveness of IHC’s
OHC - afferent
from OHC to brain
small diameter fibres using ACh
convey info about activity/mechanical state of basilar membrane (moment to moment state)
not thought to be involved in conscious perception of sound
OHC - efferent
from brain to OHC
using GABA, alter the responsiveness of OHC
tuning to make sharper, amplified
can change their length - can modify the stiffness of the regions of the basilar membrane - resulting in sharper tuning and amplification
what does movement of basilar membrane do to stereocilia
causes a deformation and benidng
tip link
connects hair cells
tuning
basilar membrane is tuned by virtue of its changing width but not enough to explain discrimination of 2 Hz