Special Senses Flashcards
what is an adequate stimulus?
energy that sensory endings respond to
what must an adequate stimulus be converted to?
electrochemical energy (AP or ∆Vm)
what is the conversion of an adequate stimulus to electrochemical energy called?
primary transduction process
what is the primary transduction process for vision and hearing?
vision: photon into APs
hearing: pressure waves into APs
what is a generator potential?
a non-propagated, graded potential, usually depolarizing (~EPSB)
what is the magnitude of a generator potential proportional to?
strength of the stimulus
what wavelengths of light can humans see?
390-700nm
approx. how many colours can humans detect?
2.3-7.5 million
what is the sclera?
tough, white, fibrous part of the eye
what is the cornea?
clear bulb in the front of the eye, continuous w/ sclera
what is the conjunctiva?
thin, protective membrane that covers the cornea
what is the most important part of the eye for focusing?
cornea (more than the lens)
what is the anterior chamber?
clear fluid-filled chamber behind cornea and allows it to act as a unit w/ the lens
what is the aqueous humour?
clear fluid that fills the anterior and posterior chamber (~water)
what produces vs drains the aqueous humour?
ciliary body and canal of Schlemm (back to front of iris)
where is the canal of Schlemm?
at the corneal-scleral junction
what is immediately behind the anterior chamber?
crystalline lens
what are analogs for the course and fine focus of a microscope?
fine: lens
coarse: cornea
what are 2 properties of the crystalline lens?
is convex (converges light) and elastic
what is behind the lens?
vitreous chamber
what is the vitreous chamber?
large chamber filled with gelatinous substance called vitreous (~glass) that inflates the eye
what is at the back of the eye?
retina
what is the retina?
layers of receptor (rods and cones) and processing (bipolar, amacrine and ganglion) cells
what is behind the retina?
choroid layer
what is the choroid layer?
layer of black/brown pigment cells called melanin that absorb excess light
what is the process of light passage into the eye? (7)
light strikes cornea, is partially focused, passes through anterior chamber and pupil, focused by lens, passes through vitreous chamber, strikes retina, absorbed by receptor and processing cells or pigment cells
what is the pupil?
opening of the iris
what is the posterior chamber?
clear fluid-filled chamber behind iris
what is the purpose of pigment cells?
prevent light scatter which would blur image
what is accomodation?
process wherein lens curvature is increased (anterior side most affected)
when does accomodation occur?
near-vision
what holds the lens in place behind the iris?
suspensory ligaments (aka zonule fibers)
what are suspensory/zonule fibers attached to?
sphincter-like muscle called ciliary muscle
what occurs when the ciliary muscle is relaxed vs contracted? what kind of vision does this apply to?
relaxed: incr tension in suspensory ligaments and flattens lens (distance-vision)
contracted: decr tension in suspensory ligaments and thickens lens (near-vision)
what is refraction?
deflection of light as it passes from one medium to another (difference in velocity)
what is the focal distance?
distance from refractive surface (cornea) to point of convergence
what is the diopter? (2)
reciprocal of focal distance (m) and focal power of a corrective lens
what is the refractive power of the cornea in diopters?
42-43 diopters
what does a value of 42 diopters mean?
parallel light is focused 0.024m (distance btwn cornea and retina) behind refractive surface (1/42)
what is myopia? most common cause?
nearsightedness; eye is too long and light converges before retina
what is hyperopia? most common cause?
farsightedness; eye is too short and light converges behind retina
what is presbyopia? most common cause?
decr ability to focus; stiffening of lens w/ age
what is emmetropia?
normal vision
what is astigmatism?
corneal/lens surface is more curved in one plane than the other (difference in refraction btwn 2 planes)
what does a point of light look like w/ astigmatism?
line or an oval
what kind of lens do near vs farsighted eyes require?
near: negative/concave (diverges light in front of eye)
far: positive/convex (converges light in front of eye)
what does astigmatism cause?
light unfocused at any distance
what lens is used for astigmatism?
cylindrical lens
why are cylindrical lenses used for astigmatism?
adds lens power in specific meridians of the lens
what does a prescription of -1.00 x -1.25 x 180 correspond to?
- 1.00: nearsighted by 1 diopter (+: far)
- 1.25: lens power of correction for astigmatism
180: axis of cylindrical lens power
what the difference btwn a + and - cylindrical lens?
+: 1/2 convex (flat on 1 side)
-: 1/2 concave (flat on 1 side)
where do blood vessels enter eye?
optic nerve
where is the greatest area of visual acuity?
fovea
t/f: while the retina is as transparent as possible, some light is deflected away
true
what are the first cells light strikes in the retina but the last in the common pathway?
ganglion cells
which cells in the eye conduct APs and send signals to brain?
ganglion
what do the outer vs inner segments of receptor cells face?
inner: vitreous chamber
outer: pigment cells
how are discs in bottom of outer segment of receptor cells replaced?
are shed and phagocytosed by retinal pigment epithelium (RPE)
what pigment do discs of receptive cells contain?
rhodopsin
how many rods vs cones are there per retina?
rods; 100-125 million
cones: 6 million
which receptor cells detect shades of grey vs colours?
rods: shades of grey
cones: colour
are rods or cones more sensitive?
rods: higher sensitivity
cones: lower sensitivity (require brighter light)
do the pathways of rods vs cones have high acuity or low acuity?
rods: low acuity (not sharp)
cones: high acuity (high detail)
are rods or cones better for night vs day vision?
rods: night
cones: day
is there little or high convergence (>1/bipolar cell) in retinal pathways for rods vs cones?
rods: high convergence
cones: little convergence
where are rods vs cones concentrated in retina?
rods: periphery
cones: fovea
what is the transduction process in the retina when it is dark? (3 cells, 8 steps)
receptor cell: high [cGMP], Na channels open, depol., Ca channels open, Glu release (inhibitory NT),
bipolar cells: inhibited,
ganglion cell: no AP, no activation of lateral geniculate nucleus in thalamus
what is the transduction process in the retina when it is light? (3 cells, 11 steps)
receptor cell: isomerization of retinal w/ light absorption, G protein (transducin) activation, activates phosphodiesterase, breaks down cGMP, Na channels close, hyperpol., Ca channels close, decr release of Glu (inhibitory NT)
bipolar cells: disinhibited (depol.)
ganglion cell: AP, activation of lateral geniculate nucleus in thalamus
what is retinal a derivative of?
vitamin A (retinal is aldehyde form)
what isomerization occurs in the eye w/ light absorption?
11-cis retinal to all-trans retinal
what is rhodopsin made of? (2)
retinal and opsin protein
what does the apical side of the RPE face?
outer segment of photoreceptors
what are 4 functions of the RPE?
absorbs some light not absorbed by photoreceptors, transports nutrients/ions to photoreceptors, regenerates 11-cis retinal, daily phagocytosis of photoreceptors (~10%)
what occurs after light generates all-trans retinal?
trans-retinal (aldehyde) reduced to trans-retinol (alcohol), exits rod cell and transported to RPE cell, converted to 11-cis retinol then to 11-cis retinal and returned to rod cell to rejoin w/ opsin (forms rhodopsin)
what is a receptive field?
area on retina/region in visual field that activates or inhibits bipolar or ganglion cells when stimulated by light
how do cells in the brain signal (other than ganglion cells)?
by EPSPs or IBSPs
what are 2 ways receptive fields (RF) can be arranged?
on-center or off-center
what does central vs peripheral stimulation of an on-center RF cause?
central: incr APs then decr when stimulus removed
peri: decr APs then incr when stimulus removed
what does central vs peripheral stimulation of an off-center RF cause?
central: decr APs then incr when stimulus removed
peri: incr APs then decr when stimulus removed
how many ganglion cells respond per RF?
one
what occurs during diffuse (entire) illumination of an RF?
continuous firing of APs regardless of on/off-center RF
t/f: RFs don’t overlap
false, RFs can overlap
what occurs when 2 on- or 2 off-center RFs overlap?
stimulus will inhibit one ganglion cell and activate the other
what occurs when an on-center and off-center RF overlap?
stimulus will activate or inhibit both ganglion cells
Where do ON vs OFF bipolar cells have their axon terminals?
on: inner plexiform layer
off: outer plexiform layer
What 2 Glu receptors do OFF bipolar cells express? And why?
AMPARs and kianate-type receptors (cation channels); light decr Glu release from photoreceptors (hyperpol.) so cation channels don’t open and bipolar cell hyperpolarizes and ganglion cell doesn’t generate AP
What Glu receptor do ON bipolar cells express? And why?
mGluR6 (metabotropic) that closes TRPM1 (cation channel); light decr Glu release from photoreceptors (hyperpol.) so cation channels open and bipolar cell depolarizes and ganglion cell generates AP
t/f: all optic nerve fibres cross over at the optic chiasma
False
what range of frequencies can humans hear?
20-20 000Hz
approx. how many tones can humans distinguish?
340 000
what is the concha?
deepest depression of pinna that helps funnel sound into external auditory meatus (vertical to horizontal)
what is the pinna and its function?
flaps of skin on outer ear that funnels sounds into external auditory meatus (vertical to horizontal)
what is the external auditory meatus?
ear canal
what is the tympanic memb?
ear drum
what are the 4 parts of the outer ear?
pinna, concha, external auditory meatus, tympanic memb
what are the 3 parts of the middle ear?
(tympanic memb) malleus, incus and stapes (oval window)
what are 3 function of the external ear?
protects tympanic memb (internalizes it into ear), funnels sound, gathers sound E
what is the issue with the tympanic memb being internalized?
dark, moist enviro can promote fungal infections and insects
what is cerumen and its funciton?
ear wax; anti-bacterial (reduce viability by 99%) and anti-fungal properties
what allows the cerumen to be anti-bacterial and fungal? (3)
acidic pH (6), saturated fa, and lysozymes
what is the purpose of having hair in the external auditory meatus?
can detect individual of insects to be removed
what are the 2 protective features of the external ear?
cerumen and hairs
what is the function of the external auditory meatus?
gathers sound E (incr by 30-100x) and focuses it on tympanic memb
what is the function of the Eustachian tube?
connects middle ear with pharynx to balance internal and external Ps on tympanic memb
what fills the middle ear?
air (not fluid)
what is the major function of the middle ear?
matches low-impedance airborne sounds to higher impedance sounds in fluid-filled inner ear
what is impedance?
a medium’s resistance to movement
approx. what % of sound E is lost in transition from air to water?
99.9% (signals importance of middle ear)
what 2 processes in middle ear incr sound E by 200x?
- decr in diameter from tymp. memb. to oval window (20x)
2. lever action of ossicles (33%)
what are the 2 middle ear muscles?
tensor tympani and stapedius (more important)
what is the tensor tympani muscle connected to?
malleus and Eustachian tube
what is the stapedius muscle attached to?
wall of middle ear and neck of stapes near junction w/ incus
what is the purpose of the middle ear muscles?
noise reduction (contractions dampen ossicle vibrations)
t/f: the middle ear muscles can adapt to very loud, sudden noises
false, were not adapted for this
what is the main structure of the inner ear?
cochlea (snail shell)
what are the 3 tubes of the cochlea?
scala vestibuli and scala tympani (1 tube-2 parts), scala media (cochlear duct)
what joins the scala vestibuli and scala tympani?
helicotrema (corner)
what separates the scala vestibuli and scala media (cochlear duct)?
Reissner’s/vestibular memb
what fills the scala vestibuli and scala tympani?
perilymph
what fills the scala media (cochlear duct)?
endolymph
what duct funnels from the oval window?
scala vestibuli
what duct funnels into the round window?
scala tympani
t/f: the scala media is connected to the scala vestibuli and scala tympani
false, scala media is a closed chamber
what separates the scala tympani and scala media (cochlear duct)?
Basilar memb
what is the Basilar memb?
memb composed of fibres
how do the fibers of the basilar memb change from the oval to round window (apex)?
more narrow and stiff to broader and more flexible
what is the purpose of having different fibres on the basilar memb?
can detect high or low frequency sounds (and signal accordingly)
what does the organ of corti rest on?
basilar memb (in scala media/cochlear duct)
what is the organ of corti composed of?
single row of inner and outer hair cells that the tectorial memb rests on
what is the functions of the inner vs outer hair cells in organ of corti?
inner: sensory (encode sound)
outer: motor (sound f analysis)
how are Pwaves in air converted to Pwaves in fluid in ear? (6)
sound waves funneled into external auditory meatus and vibrates tympanic memb, ossicles vibrate and stapes pushes on oval window, perilymph is compressed, basilar+Reissner’s memb vibrate, organ of corti moves up and down, hair cells shear against tectorial memb
what is shearing?
force btwn 2 parts as they slide opposite to each other parallel w/ their plane of contact
hair cells have ____________ that align _________ in the front and ________ in the back
stereocilia, shortest, tallest
what are stereocilia of hair cells attached to?
tectorial memb
when is a response observed in inner hair cells?
when they move in the direction of the tallest stereocilia
what is the ion composition of endolymph?
high [K+], low [Na+] (V across hair cells is largest in body)
what is the ionic composition of perilymph comparable to?
plasma and cerebrospinal fluid
what occurs in hair cells (to brain) when stereocilia shear toward the tallest one? (5)
K-channels open (tip-links), K from endolymph flows into cell and depolarizes it, graded potential changes, rate of APs in auditory nerve changes, stimulation of auditory cortex (temporal lobe)
what separates the stereocilia from the body of the hair cell?
reticular lamina (body of cell not in endolymph)
how do we determine whether a sound is high or low pitched? (process)
Pwaves in perilymph propagate from base to apex of basilar memb, growing in A but decr in velocity until it reaches a max. displacement which correlates to its frequency
where in the cochlea are high vs low frequency sounds detected and why? (place principle)
high f: base; has stiffer, shorter stereocilia
low f: apex; has longer, floppier stereocilia
what is the purpose of the round window?
dissipates E (no sound perception)
what does it mean to say mGluR6 is “sign inverting”?
activation of mGluR6 on ON-bipolar cells by Glu (dark) causes CLOSURE of TRPM1 cation channels and thus hyperpolarization of bipolar cell (ganglion not activation)
