special senses Flashcards
What is aguesia?
loss of taste
What is anosmia?
loss of smell sensation
What taste papillae are in the posterior part of tongue
Circumvallate and foliate
taste papillae in anterior part of tongue
fungiform
what do the sensory cells in taste buds project
microvilli into outer taste pore
what are the properties of basal cells in taste buds
like stem cells
what junctions are present in taste buds
tight junctions between apical membranes
where are most taste receptors and channels
apical membrane of sensory cells
what are on the basolat membrane of taste buds
calcium channels, stores and transmitter vesicles
what are sweet, bitter and umami detected by
g protein coupled receptors
what is salt detected by
Na+ entering cells leading to depolarisation
what is sour detected by
H+ entering cells leading to depol
what are the receptors involed in sweet and umami?
T1R
what receptors for umami?
T1R1 and T1R3
receptors for sweet
T1R2 and T1R3
receptor for sweetener
T1R3
what is the family of receptors in bitter
T2R
why is it important to have many bitter receptors
tells us if it is poisonous
what do T1R and T2R act via
TRP channel M5 which allows entry of cations leading to depolarisation
What is the aqueous solubility of an odorant increased by?
OBPs (odorant binding proteins)
do olfactory receptor neurones have cilia?
yes, project into mucus
where are receptors for odorants located
cilia of the ORN
what is the function of the supporting cells in the ORN
determine the composition of the mucus
how many ORNs per nostril
6 million
each ORN has how many non motile cilia
8-20
how is an odour molecule transported to a receptor
dissolves in olfactory mucus, OBP transports it
what is the process in olfactory transduction
olfactory G protein activated - adenylyl cyclase activated - cAMP increases- opens ion channels - influx Ca 2+ and Na+ - opens calcium dependent Cl- channels - depol of ORN - travels up cilia, summation - increases AP firing - olfactory bulb
where do ORNs synapse, what happens here
in the glomerulus, meet dendrites of mitral cells
how many types of neurone does each glomerulus receive input from?
one
what cells are involved in the sharpening of information of smell
periglomerular cells
what cells axons form the lateral olfactory tract
mitral cell axons
where do efferent fibres from higher brain centres synapse
granule cells
how many olfactory axons per glomerulus
25000
what is the convergence of ORNs to mitral cells
1000:1
what makes up the primary olfactory cortex
piriform cortex and entorhinal cortex
what makes up the secondary olfactory cortex
orbitofrontal cortex
what does smell have an subconscious effect via?
limbic system
what is the range for human hearing
20 Hz- 20kHz
what does the wall of the external auditory meatus contain
ceruminous glands (secrete cerumen- earwax)
properties of earwax
antibacterial, anti fungal
what angle does the tympanic membrane lie at
55 degrees. due to the handle of malleus draws it into a peak
what is the middle ear lined with
ciliated epithelium
what does the external auditory meatus end in
tympanic membrane- vibrates
role of the Eustachian tube
pressure equalisation, route for infection. connects middle ear and nasopharynx
what are the ossicles
malleus, stapes, incus
what is the role of the ossicles
impedance matching
what happens in impendance matching
tympanic membrane is a large surface area so weak force by the vibrations, concentrate onto a smaller area (1/20)
what is the area that concentrates the force in impedance matching
oval window (foramen ovale)
how much does the oval window increase sensitivity by
1000x
what regulates the movement of the ossicles
stapedius and tensor tympani
what bulges to allow vibrations to move from the inner ear to the cochlea
round window (fenestra rotunda)
what happens if there is trouble with the draining of the Eustachian tube
otitis media
what can lead to reduced acuity of hearing
anything restricting the movement of the ossicles- mucus in the inner ear, ossification of joints between ossicles
what range is the human ear most sensitive
1.5-3 kHz
what are the openings of the bony/ osseous labyrinth
central opening and round window
what arises on either side of the vestibule
semicircular canals on one side, spiral cochlea on the other side
what is the membranous membrane filled with
endolymph, rich in K+
where is endolymph secreted from
stria vascularis. endolymphatic sac regulates it
what fills the space between the outer wall of the membranous labyrinth and the bony
perilymph
what happens in the cochlea and how many turns
detection of vibrations. 2 3/4 turns
what is contained in the 2 outer chambers and the middle chamber
outer- NaCl, inner- Kcl
what does the central core of the cochlea contain
auditory fibres (CN8)
what forms the floor of the scala media
basilar membrane
how is the basilar membrane at the base and apex
base- narrow and taut, apex- broader
how far do high frequencies travel
not very far, they die out when they reach the floppy membrane
how far can low frequencies travel
the full length as the floppy membrane can sustain slower oscillations
what is tonotopy
pitch mapped by position. basilar membrane splits the complex sounds into component frequencies
what detects the vibrations running along the basilar membrane
organ of corti
how many rows compose the organ of corti
4 hair cells. 3 outer layers, 1 inner layer
what are the hair cells embedded in
tectorial membrane
what happens with the basilar membrane moves up and down
the hair cells move from side to side which is picked up by the tectorial membrane. release glutamate, stimulate dendrites of spiral ganglion
what is the function of inner hair cells
pitch determination. send freq info to the CNS
how many inner hair cells are there
3,500 (400 cells per octave)
what is the function of the outer hair cells
cochlear amplifier. increase sensitivity
how do outer hair cells work as a cochlear amplifier
contract when excited by waves along the basilar membrane. oscillate in phase with the bm, so amplifies the travelling wave
how many outer hair cells
12000
what happens if the ear is damaged
hair cells may oscillate without external sound so the basilar membrane vibrates and emits sound- humming.
what happens with difference tones (Tartini’s)
2 tones present to the ear and hair cells move to produce a new peak
what is the frequency of a new tone in difference tones
difference between the two tones
what are difference tones used to diagnose
cochlear deafness show hair cell damage (distortion product otoacoustic emissions)
when can cochlear implants be used
if lost cochlear hair cell function but sensory neurones of spiral ganglion still functional
how do cochlear implants work
processor breaks down sound into frequency components. transmitted to implant receiver. conduct along wires to electrodes in the cochlea. stimulate nerve cells under the basilar membrane
what are part of the auditory pathway
superior olivary nucleus (MEDULLA); inferior colliculi (MIDBRAIN); medial geniculate nucleus (THALAMUS); auditory cortex
what is involved in sound source localisation
superior olivary nucleus
at what point in the pathway is the auditory reflex and what happens
inferior colliculi (turn head and eyes in response to a stimulus)
what tract is involved in the auditory pathway
lateral lemniscus
what is found in the primary auditory cortex
Heschl’s gyrus. tonotopically mapped
what side is language processing on
left
what side is music, prosody and inflection of speech
right
what does the secondary cortex surrounding heschl’s gyrus include
wernickes area
what is wernickes aphasia?
language fluent but meaningless words
what is brocas aphasia
language halting and non grammatical (as language produced in brocas)
what protects the ear from sound
stapedius muscle as limits the amount of movement of stapes
what happens in the stapedius reflex
if damaging levels it contracts to limit the movement of the ossicle chain and decrease the intensity of pressure pulses
is the ear better at protecting against low or high frequency sounds ?
better at blocking low frequency
what do low freq sounds mask
the higher sounds. so if intense low freq will perceive this as the low freq but if less low freq will perceive as a high freq
what happens when the stapedius is active
the higher frequencies are unmasked by the low frequencies and the perceived sound is quieter
what happens before we speak
stapedius reflex is initiated, so low frequencies can be attenuated
what is the threshold of human hearing
0dB
how much of an increase in energy carried by sound is there with each increase of 20bD
10x energy
what can exposure to very high levels lead to
at first temporary increase in hearing threshold, disturbances in hearing ringing and whistling. tinnitus, ear discomfort, muffled sounds
greater exposure leads to what
destruction hair cells. don’t regenerate in mammals
what happens in damage to hair cells (noise induced hearing loss)
production of free radicals, increase in Ca2+, might not be sufficient blood supply, can lead to apoptosis
what does noise induced hearing loss first appear as
insensitivity at 4kHz (harder to interpret consonants here)
what happens when the ear is exposed to hair cells
disruption to hair cells; with longer exposure the cells begin to round up and shorten; after a while the remaining hair cells clump together into a single mass.
do axons project directly or indirectly to the outer hair cells
directly to outer (indirect mechanism to the inner cells)
what is the limit tor sound exposure over an 8 hour day
87 dB
with every 3dB increase in sound what happens to the length of exposure
halves
what is the outermost layer of the eye, what does it form anteriorly
sclera. forms the cornea
what is the role of the lens
focuses the image onto the back of the eye- on the retina
where is the image most focused
fovea (surrounded by macula lutea)
what is between the retina and the sclera. whats significant about it
choroid- vascular layer
where is the blind spot
where the optic nerve enters the eye- there are no photoreceptors. optic disc
features of sclera
tough, fibrous, opaqued, vascular, gives eye its shape
features of the cornea
transparent, curved, no blood vessels, well innervated, cont. with the conjunctiva
features of choroid
pigmented, well vascularised, supplies o2 and nutrients for retina
features of the ciliary body
attachment for lens suspensory ligaments, contains ciliary muscles, secretion aqueous humour forms the iris
what is the gel in the posterior chamber
vitreous body- attracts and holds water molecules (vitrein and hyaluronic acid)
what is in the anterior chamber
aqueous humour
how many layers makes up the retina
2- neural and photoreceptive layer and pigmented layer. one over ciliary process one over iris
how are the fibres arranged in the sclera
randomly orientated- collagen and elastic fibres and fibroblasts
does the sclera have epithelium
no except for the cornea
what are the layers of the cornea (from top to bottom)
epithelium, bowmans membrane, stroma, decemets membrane, endothelium
what is inflammation of the choroid
uveitis (as choroid is uveal tract)
what does the ciliary body do
secrete aqueous humour, attachment for lens suspensory ligaments. forms iris
what does the ciliary body contain
ciliary muscle fibres (parasymp)
how does the ciliary body drain
via the iridocorneal angle into the canal of Schlemm
what does the iris contain
constrictor and dilator muscles para and symp innervation, no epithelium on anterior surface.
what is the ora serrata
junction between retina and ciliary body
are there photo receptors past the ora serrata
no
role of the pigmented layer of the retina
recycling rods and cones
what is the lens held within
elastic capsule (collagen and proteoglycans)
what is the lens held under tension by
fibres of the ciliary zonule
why do lens become less transparent and finally opaque with age
as crystallins denature
what is a cataract
clouding of the lens
why are cataracts a common cause of blindness
as opaque lens prevents light passing and focussing on the retina at the back of the eye
what can cause cataracts
age related degenerative changes, diabetes, enzyme deficiencies, toxic side effects. treat remove lens replace with plastic lens
what is dry macular degeneration (90%)
tiny deposits of drusen on retina, few symptoms at first can get small dark spot in central vision as more drusen accumulate. can progress to worse
what is wet macular degeneration (10%)
rarer but worse. abnormal vessels beneath retina, may bleed and leak fluid building up beneath retina so bulges up damaging the eye. central vision blurry and distorted, progresses to severe vision loss
what happens in short focus of accomodation
ciliary muscle CONTRACTS and the body is brought forward; suspensory ligaments relax; lens becomes FATTER
what happens in long focus of accomodation
ciliary muscle relaxes; suspensory ligaments are under tension; lens becomes FLATTER
what is the term for long sighted and how is the eyeball
hypermetropia. too short light focuses behind the eyeball
what is the term for short sighted and how is the eyeball
myopia. too long the light focuses in front of the eyeball
what is required in long sighted and how to treat it
additional refractive power. converging corrective lens
what is requires in short sighted and how to treat it
negative refractive power. diverging corrective lens
why is presbyopia
lens thickens becomes harder with age. cant accomodate
what is astigmatism
lens or cornea not smoothly spherical
what happens in focussing
lens moves backwards and eyes inwards (convergence)
what is the cornea constantly doing
swelling- collagen fibres exert high osmotic swelling pressure
what are the endothelial and epithelial pumps on the cornea for
maintaining correct level of hydration
does the lens swell
yes has high swelling pressure. counteracted by epithelial fluid transport
what leads to cataracts
swelling of lens, also by UV light
what happens in light to dark light reflex what is it called
dilator pupillae muscle contracts. MYDRIASIS (symp)
what happens in dark to light light reflex what is it called
constrictor pupillae muscle contracts. MIOSIS (para)
what do rod and cone cells synapse with
bipolar cells, send info to ganglion cells
what cells perform lateral inhibition at the level of the photoreceptors and what is this process for
horizontal cells. sharpen the image and decrease input from neighbouring cells
amacrine cells perform lateral inhibition at the level of what cells
ganglion cells
what is the function of Muller cells
they act as light guides from the front to the back of the retina pass the light from the surface of the retina to the photoreceptor
where are most cones found
in the fovea (rods have an inverse distribution)
where are there no rods
in the fovea and blind spot
are there any photoreceptors in the blind spot
no
where is there overlap accounting for binocular vision
central area
where does the right visual field end up
on the left part of the retina of both eyes
what happens in partial decussation
at optic chiasm- all info from right visual field ends up in left visual cortex
what is cortical magnification
if stimulus in centre of visual field then large no of neurones process info from this small region however if it is seen in periphery processed by many less neurones
what happens in response to light hitting the photoreceptor
hyperpolarisation of photoreceptor
what neurotransmitter is released from the photoreceptor
glutamate
what are the 2 types of bipolar cell associated with the photoreceptor
hyperpolarising cells and depolarising cells
what happens if there is a decrease in glutamate
the hyperpolarising cells hyperpolarise (as usually it depolarises the cell) and the depolarising cells depolarise (as usually inhibits depolarisation)
what happens if it is linked to the depolarising cell
increase firing rate
what type of cells do photoreceptors synapse with
both rods and cones synapse with both- opposite responses at the retinal ganglion cells.
what happens in the dark (phototransduction)
HIGH levels cGMP. cation channels OPEN and Na+ and Ca2+ enter. ‘dark current’. photoreceptors depolarise INCREASE in glutamate
what happens in the light (phototransduction)
LOW levels of cGMP. cation channels CLOSE. hyperpolarisation of the photoreceptor leads to decrease glutamate
what are the first and second parts of visual coding
first- form (detect edge of an object). 2nd- colour
what are the 3 types of cones
red, blue, green
what is the most sensitive to light of the 3 colours
red (559nm), then green (531nm), blue (419nm)
what are the channels for the colours of cones
red/green and blue/yellow
what are the different types of ganglion cells
X,Y and W
what are the X cells
80% ganglion ells. SLOW. CONES. central fovea
what are the Y cells
10%, FAST connected to rod cells
what are the W cells
detect light levels. involved in light reflex
what allows perception of depth
fusion of 2 images in the cortex from binocular vision
what are saccades
unconsciously move eyes compensating for poor imaging as not in focus as move away from centre of vision
which have larger outer segments (rods and cones)
rods have larger outer segments so there is a greater chance of trapping photons
if light levels fall what happens to cones
they become inactive and only rods respond, so colours begin to fade
is the central disc excited or inhibited by light
excited (outer disc inhibited)
what happens if light is shone on the inner and outer discs
inner- bursts of action potentials. outer- not much change in action potential
what is the function of the receptive fields of vision
sharpen edge of the field
where is the ganglion cell receptive field smallest
at the fovea. become larger as go towards the periphery
where does information coming from nasal hemifield go
crosses to the contralateral side of the brain. (info from temporal field remains ipsiateral)
where do most retinal axons travel to
thalamic lateral geniculate nucleus
how many layers of lateral geniculate nucleus are there
6 layers
what layers of the LGN are nasal contralat
1,4,6
what layers of LGN are temporal ipsilat
2,3,5
what are the 2 types of cell in LGN
magnocellular and parvocellular
what are the features of magnocellular of LGN (1 and 2)
large cells, ROD CELLS, low acuity, fast, high contrast
what are the features of parvocellular of LGN (3-6)
small cells, CONES, high acuity, slow, low contrast
where do axons of the LGN project
internal capsule; in optic radiation; along lateral ventricle; maintains retinopic order; into primary visual occipital cortex
what does the primary visual cortex analyse
edges
what does V4 analyse
colour vision
what does v3 analyse
dynamic vision
what does v5 analyse
motion
what is achromatopia
colour perception eliminated
what is the elimination of movement perception
akinetopsia
what is the elimination of ability to distinguish faces
prosopagnosia
what is horners syndrome
compression of the sympathetic chain leads to ptosis miosis anhydrosis
