lecture 9 - special senses Flashcards
4 steps of sensation
stimulation
transduction
generation
integration
special sense (5)
smell, taste, vision, hearing, equilibrium
receptors for smell
olfactory epi
chemoreceptors
basal epithelial cells (below cribriform plate0
stem cells taht make new sensory neurons for smell
olfactory glands (bowmanss glands)
produce mucus to dissolve odorants
stimulated by facial nerve
non motile cilia
site of olfactory transduction
contain olfactory receptor protiens that detect chemicals
how does olfaction work (5)
- odorants bind to neurons
- stimulates G proteins which activates adenylate cyclase
- adenylate cyclase releases cAMP (second messenger protein)
- cAMP opens Na and K channels
- depolarization -> graded potential
olfacotry pathway (3)
axons from olfactory neurons form CN 1
synapse in olfactory bulb with mitral cells
form olfactory tract that synapses with primary olfacotry area in temporal lobe
note: olfactory pahtway is the only special sense that skips the thalamus and goes str8 to the cortex
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how is olfaction related to memory and association n shit
some axons within the olfactory tract reach the limbic system and hypothalamus which activates emotional/memory responses to odour. others can reach orbitofrontal cortex where odours are identified
5 classes of taste
sour, bitter, sweet, salty, umami
papillae
elevations on the tongue
4 types of papillae
vallate pappilae
fungiform
foliate
filiform
3 types of papillae that contain taste buds
vallate
fungiform
foliate - most die in childhood
vallate papillae
located at teh bakc of the tongue, contain 100-300 taste buds each
fungiform papillae
scattered over tongue, contain 5 ish taste buds. each
foliate papillae
located in lateral trenches of tonuge, has taste buds but most of them degenerate in childhood
vallate papillae appearance
fat ass ones at the bakc of the tongue
fungiform papillae appearnace
scattered dots
foliate papillae appearace
shark gills on the sides of the tongue
filiform papillae. appearance
fuckin everywhere, lil flamy ones
filiform papillae
contain tongues tactile receptors
increase friction on the tongue to make it easier for it to move food in the mouth
3 types of cells in a taste bud
gustatory receptor cells
supporting epi cells
basal epi cells
gustatory receptor cells
blue cells not touchin the bottom of the taste bud
~50 per taste bud
have a gustatory hair (microvilli) out the top
basal epi cells (taste buds0
develop into new receptor cell every 10 days
note: all primary tastes can be detected on all parts of the tongue becuase one taste bud contains all types of receptors for each tastatn
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molecule for each tastent (thing that is actually picked up by the receptors once dissolved)
salty - Na
sour - H
sweet/bitter/umami - IP3
(inositol triphosphate)
taste combos = buncha dif ones
gustatory receptor cells are (free, encasuplated, other cell)
other cell
the “other cell” is the gustatory receptor, which makes another GP to first order neurons
gustatory pathwya
first order gustatory fibres are in cranual nerves 7/9/10
then thalamus, then primary gustatoru area in insula
how does taste relate to emotion n shit
soem axons in teh gustatory pathway make it to limbic system or hypothalamus where they are connected with memmories n emotions
note: more than half of the bodys sensory receptors are in the eyes
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conjunctiva
thin mucous membrane that lines the eyelids and covers the sclera
tarsal plate
CT that gives shape to the eyelids
contains tarsal glands that lubricate
stye
bacterial infection of sebaceous ciliary gland in eyelash hair follicles
chalazion
infection/blockage of the tarsal glands
lacrimal apparatus
lac gland
excretory lac ducts
drain into lac canaliculi
lac sac
nasolacrimal duct
nasal cavity
what innervates the lacrimal glands
facial nerve
PSNS
lysozyme
enzyme in tears
nerves that innervate extrinsic eye muscles
abducens, occulomotor, trochlear
3 layers of the eyeball
fibrous layer - cornea/sclera
vascular layer - choroid, iris, ciliary body
inner layer - retina
how does the cornea receive o2
from the air
layeres of the cornea
nonkeratinized Strat squamous epi
collagen fibres / fibroblasts
simple squamous epi
superificial to deep
sclera functions
gives shape to eye
coveres whole eye except where cornea is
attachemt for eye muscles
keratoconus cornea
bulging of cornea
choroid functions
nourish retina
contain melanocytes that absorb scattered light
ciliary body consist of
melanocytes
ciliary processes
ciliary muscle (smooth, CN3)
pupil diamter is controlled by
autonomic NS
in bright light what happens to the pupil
circular muscle fibres contract to constrict pupil
done by PSNS, CN3
in dim light what happens ot the pupil
radial muscle fibres contract to dilate pupil
done by SNS, CN3
macula lutea
center of retina
fovea centralis
small dip in centre of macula lutea
layers of retina
pigmented layer - base, simple ish
neural layer - rods/cons/complex as shit
layers of the neural layer of the retina and what is in them (big one) (deep to superficial)
photoreceptor layer
- rods/cones
outer synaptic layer
- synapse between rods/cones and bipolar cells
bipolar cell layer
- where bipolar cells are located (along iwht amacrine and horizontal cells)
inner synaptic cell layer
- where bipolar cells synapse with ganglion cells
ganglion cell layer
- where ganglion cells are
CRVO
central retinal vein occlusion
CRVO
partial or complete retinal vein obsruction
no cure
systemic
retinal detachment
detachment of neural poriton of the retina from the pigmented layer, where fluid accumulated between them
causes distorted vision and blindness is corresponding area
anterior segment
contains anterior and posterior chambers
anterior chamber
between cornea and iris
filled with aqueous humor
posterior chamber
between iris and lens
filled with aqueous humor
aqueous humour
produced by ciliary body from filtering blood
continuously drained and replaces
nourishes lens and cornea
posterior segment
between lens and retina
filled with vitreous humour
vitreous humour
holds retina against choroid to maintain and even surface
formed only once
contains phagocytes
old people have vitreal floaters
intraocular pressure
produces by mainly aqueous humor and partially vtireous
maintains and supports the eyeball shape
glaucoma
abnormally high intraocular pressure form buildup of aqeous humor inside the eyeball which damages the retina
second most common cause of blindness to cataracts
lens
focuses light on retina
held in place by zonular fibres
avascular, made of clear proteins
cataracts
clouding of the lens
caused by genetics and aging
fixed by surgery
3 processes the eyes use to form a clear image on the retina
refraction of light by cornea and lens
- bend so light falls on fovea centralis
accomodation of the lens
- changes lens shape so light is focuses
constriction of pupil
- decreased light enters eye
refraction
bending of light as it passes from one substance to another with different density
75% done by cornea, rest by lens
lens changes in order to
view near or far objects
when viewing a far object;
the zonular fibres are tight, lens is flat, and ciliary muscle is relaxed
when veiwing a close object
zolunar fibres = loose
lens = rounded
ciliary muscle - contracted
pupillary constriction
contraction of circular iris muscles constricts pupil
prevents light from entering through lens edge to sharpen vission
protects retina from bright ilght
3 layers of retinal cells
photoreceptor layer
bipolar cell layer
ganglion cell layer
rods
cylindrical outer segment
- for balck and white vision in dim light
- 120 million
- along periphery of retina
cones
cone shapes outer segment
- for sharp colour vision
- 6 million
- in fovea centralis for visual acuity
photoreceptors parts
outer segment
inner segment
proximal end
outer segement of photoreceptors
rods - rod shaped stack of free floatinf discs
cones - cone shaped disc with lots of folds
site of transduction
inner segment of photoreceptors
contains cell nucleus, golgi complex, mitochondria
proximal end of photoreceptors
synaptic terminals synapse with bipolar cells here
photopigments
coloured protein that undergoes structural changes when is absorbs light
located in outer segment of photoreceptors
photopigments in rods
rhodopsin
photopigments in cones
photopsins (red bleu and green)
photopigments contain: (2)
opsin
retinal - light absorbing part
opsin
glycoprotein in photopigments
undergoes structural change when light is absorbed leading to receptors potential
wire looking
photopigment response to light cycle steps (4)
isomerization
bleaching
retinal isomerase
regeneration
cycle is much faster in cones (seconds, minutes in rods)
isomerization
first step in photopigments response to light
light causes retinal to change shape (from cis reginal (bent) to trans retinal (straight)) which results in a graded potential
retinal
key like part of photoreceptors
bleaching
second step in photopigment response to light
retinal separates from opsin, photopigment is now unresponsive to light
retinal isomerase (conversion)
third step of photopigment response to light cycle
retinal isomerase bends retinal back to its OG shape (cis retinal, bent)
regeneration
4th step in photopigment response to light cycle
retinal binds to photopigment reforming a functional photopigment
light adaption
decreases sensitivity quickly
- rods contribute little to light vision bc of slow regen
- cones predominent
dark adaption
increases sensitivity slowly
- after a few mins in dark, rods regenerate and gain responsiveness to light
- rods predominent
phototransduction
when light is coverted into a receptor potential
occurs in outer segment
NOTE: in the visual system, activation of a photoreceptors causes a hyperpolarizing receptor potential
a photoreceptor as rest in the dark is relatively depolarized
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formation of receptor potentials (5)
IN DARKNESS ONLY
- cis retinal present
- high cGMP production by guanylyl cyclase
- cGMP gated channels open
- inflow fo NA depolarizes receptor
- voltage gated Ca channels at synaptic terminals open
in complete darkness a photorecptor is:
what does this create?
always partially depolarized (-40)
this creates continuous release of inhibitory neurotransmitter (glutamate) onto bipolar cells
what do IPSPs do in the eyes?
IPSPs hyperpolarize bipolar cells and prevent them from sending signals to ganglion cells
summary of how a receptor potential is formed in complete darkness (paragraph)
cis retinal (resting state of retinal) must be present, and this causes guanylyl cyclase to release lots of cGMP. this causes cGMP-gated channels to open, where Na will flow into the photoreceptor. voltage gated Ca channels at the synaptic cleft will then open and cause NTs to be released
formation of receptor potentials (7)
IN LIGHT ONLY
- cis retinal must be converted to trans retinal
- transducin (a G protein) is activated by that switch
- cGMP phosphodiesterase is activated
- this leads to breakdown in cGMP
- cGMP channels will then close
- less inflow of Na = hyperpolarizing receptor potential
- decrease of voltage gated Ca channels, decrease of glutamate
in light, what happens in a photoreceptor (4, long ones0
retinal changes shape, which activates enzymes that will clsoe the Na channels by breaking down cGMP
a hyperpolarizing receptor potential is produced
release of NTs onto bipolar cells preventing them from sending signals to ganglion cells are stopped
bipolar cells become excited and activate ganglion cells (first order neurons, and nerve impulses will travel to the brain
summary of what happens in photoreceptors in the dark
retinal is cis, cGMP is produced, cGMP channels open, Na flows in, triggers voltage Ca gates to open, release of glutamate (inhibitory NT), inhibits bipolar cells from sending signals
summary of what happens in photoreceptors in light (
cis retinal is converted to trans, transducin is activated, cGMP phosphodiesterase activated, breakdown of cGMP, Na inflow slows, hyperpolarizes receptor potential, glutamate release is stopped, bipolar cells can now send signals toe ganglion cells
processing of visual light (7)
- light penetrates retina
- rods and cones transduce light into receptor potentials
- rods and cones excite bipolar cells
- bipolar cells excite ganglion cells
- axons of ganglion cells form the optic nerve
- optic nerves cross at teh optic chiasm
- relayed to thalamus, then primary visual cortex
convergence of neuron network in the eyes
126 mil photoreceptors converge into 1 mil ganglion cells
up to 600 robs synapse on a singel bipolar cell, increasing spatial sensitivity
one cone per bipolar cell, for visual acuity
amacrine cells
transmit laterally directed inhibitory signals at bipolar/ganglion cell synapses
where do signals about visual info travel to in the brain after the thalamus (3)
primary visual area in occipital lobe
hypothalamus - sleep patterns, circadian rhythms
brainstem - pupil size, coordination of head and eye movements (colliculi)
