lecture 7: CN I-CN VI Flashcards
where do axons of olfactory receptor neurons locate?
- how many bipolar neurons are located here?
sphenoethmoid recess of nasal cavity
- ~ 3 million
Can olfactory receptor neurons renew? if so, how long does it take & how?
yes
every 30-60 days by stem cells
odorant receptors are located on the _______ which detect and bind to other molecules to activate.
once activated, chemical information gets converted into _____ ____ to help _____ and ______ odor
dendrites
electrical signals
process and identify
mainly _____ receptors but also less likely ______ receptors make up odorant receptors
G-protein coupled receptors (GPCR)
ionotropic receptors
CN ____ fibers also spread in the olfactory epithelia. It can detect _____
V
pungency
CN I:
- myelinated or non-myelinated?
- thick or thin?
- fast or slow transmission?
- what makes up the olfactory filaments?
—> where is the crossing point? synapses with?
- nonmyelinated
- thinnest axons (.2 micrometers)
- slowest transmission speed (0.1 m/sec)
- 20-30 axon bundles
—> cribriform plate; olfactory bulb
are mitral cells similar to pyramidal cells in the neocortex? why or why not?
yes
both are excitatory neurons that release glutamate.
the axons are stimulated to promote firing of an action potential
what are centrifugal fibers?
negative circuit regulating odorant detection
Takes signals from CNS to peripheral structures
* allows us to have adaptation to certain odors
the olfactory projection pathway is a _____ neuron pathway
- list them
3
1st order: olfactory receptor neuron
2nd order: mitral cell
3rd order: olfactory cortex & limbic system
what is the only sensation that doesn’t need the thalamus for relay of conscious perception?
smell (olfaction)
what makes up the primary olfactory cortex?
piriform cortex and periamygdaloid cortex
what structures do the primary olfactory cortex project to & what do each do?
- hypothalamus: drive. (you smell food, now you want it too)
- amygdala: emotional learning. (smell gas & know it’s bad)
- hippocampus: memory. (smell something familiar)
- thalamus: relay station and coordination center
although the thalamus isn’t directly correlated to olfaction, how does it indirectly play a role in olfaction?
feedback projections from olfactory cortex go to olfactory association cortex in insula near gustatory cortex (involved in perception of flavor/taste).
because it has multisensory integration, perceptions of smell and taste can overlap.
which stage of eye development is this:
protrusion of optic vesicle from diencephalon
4th week
which stage of eye development is this:
- optic vesicle folds in to form double layered optic cup
- invasion of ectoderm forms lens vesicle
5th week
which stage of eye development is this:
- optic cup inner layer: retina
- optic cup external layer: retinal pigment epithelia
- both layers: continue to grow anteriorly to form ciliary body and iris
- lens vesicle: pinch off to form lens
- leftover ectoderm to form cornea
6th week
landmarks around the eye:
- anterior end of photosensitive retina:
- circular transition zone, junction of cornea and sclera
- ora serrata
- limbus
structures in external and internal layers:
- limbus –>
- blood supply, absorb stray light –>
- ora serrata –>
- sclera and cornea
- choroid capillaries
- retina and ciliary bodies
what does the ciliary body do?
lens accommodation and aqueous humor secretion
what does the iris do?
controls the amount of light that enters the eye
_____ and ______ increase inner pressure to maintain eyeball shape
aqueous humor and vitreous humor
what is aqueous humor?
- location:
- secreted by:
- drains into:
clear, watery fluid that fills ant. and post. chambers of eye. provides nutrients
- anterior to lens
- epithelia in ciliary body
- scleral venous sinus then to venous drainage of eye
what is vitreous humor?
- location:
clear, jelly like humor in eyeball
- posterior to lens
what is glaucoma?
what other condition is it like?
increased production or blocked circulation of aqueous humor
- like hydrocephalus in the brain
how does the eye “focus”
coordinated efforts of transparent cornea and lens - refracts (bends) light
cornea:
- convexity?
- primary purpose?
- makes ____ adjustments
- convex anteriorly –> maintained by intraocular pressure
- primary refractive surface –> light passing through with the most refraction
- gross adjustments
lens:
- convexity?
- primary purpose?
- makes ____ adjustments
- biconvex (cannot be adjusted)
- accommodation (adjust focus at diff. distances)
- fine adjustments
ciliary muscle contraction ______ zonular fibers for _____ sight
loosens
near
** when focusing on a near object, ciliary muscle contracts
ciliary muscle relaxation _____ zonular fibers for ___ sight
tightens
far
** when focusing on distant objects, ciliary muscle relaxes
_______ innervates ciliary muscle. through _______ fibers, it controls the ciliary muscle which helps with accommodation
CN III
parasympathetic
what is cataract?
degeneration/clouding of lens which can result in blindness
which germ layer develops the lens?
ectoderm
what two structures help adjust brightness and image quality?
iris
retina
pupillary sphincter (constrictor pupillae):
- shape:
- _____ iris diameter/pupil ______ –> allows _____ light into eye in ______ light
- innervation/stimulation:
- circular
- decrease ; constricts –> less ; bright
- CN III (parasympathetic)
pupillary dilator/dilator pupillae:
- shape
- _____ iris diameter/pupil ______ –> allows _____ light into eye in ______ light
- innervation/stimulation:
- radiating spokes
- increase ; dilates –> more ; low
- sympathetic
what is the major role of the retina?
visual sensitivity adjustment
absorbing strayed light by pigmented epithelia
retina can be divided into _____ layers –> we only need to know the outer synaptic layer (____ types of cells) and inner synaptic layer (____ types of cells)
10
outer = 5
inner = 2
describe the flow of outer synaptic layer:
inner synaptic layer:
outer:
- rods & cones (photoreceptor cells) synapse with the bipolar neurons (converging info from photoreceptors)
inner:
- interneurons & ganglion cells
- bipolar cells form synapse w/ ganglion cells
true or false. the direction of light and the direction of information processing is the same direction.
false
opposite direction
axonal bundles of ganglion cells form the _______
optic nerve CN II
why is the optic disk also called the blind spot?
–> why do we not see a blind spot?
it is the place where the optic n. exits –>
it has no photoreceptors so it cannot detect light and contribute to visual perception
–> the brain “fills it in” by processing visual info from both sides
macula:
- location… why?
- ___ mm diameter
- blue light absorbs _____, so macula sees _____
- circular portion of retina lateral to optic disk… optic n. sits at 45 deg projection but eye sits forward. light goes directly back but we can see details due to the lateral location
- 3
- pigment ; yellow
describe the two parts that make up macula:
- fovea:
- peripheral retina:
- center of macula ; 0.35 mm diameter ; “cone only” therefore has the highest visual acuity (helps see details)
- sees visual field outside center ; many rods which see black and white (lose color in peripheral vision)
true or false. photoreceptors are neurons
false - NOT neurons
they are rods and cones cells
external segment of photoreceptors contain ________, the tip is embedded in _______ and constantly renews (____% replaced daily)
free floating discs
pigmented epithelia
10%
the free floating discs are filled with _____:
–> this is a _____ detector and activates _______
–> _____ in rods
–> ______ in cones
opsins
photon ; GPCR
rhodopsin
different types
circuitry between external and internal segments occur BUT ______
photoreceptors undergo hyperpolarization and depolarization in response to light stimuli:
- hyperpolarization with light exposure =
- depolarization without light exposure =
NO action potential is initiated
no glutamate released
glutamate released
the receptive field in photoreception is maintained all the way to ______ : _________
V1 : retinotopy
the area of synapse of photoreceptors and bipolar cells is:
_______ specific to rods
_______ specific to cones
spherule
pedicle
how are bipolar cells similar to photoreceptors?
not neurons and no AP initiation
“on” bipolar cells:
- _____ in light
- ______ by glutamate
- _______ receptor
- excited by ______
“off” bipolar cells:
- _____ in light
- ______ by glutamate
- _______ receptor
- excited by ______
- active
- inhibited
- metabotropic
- light stimuli
- inactive
- activated
- ionotropic
- reduction of light stimulus
bipolar cells are also called _____ order neurons.
they converge signals of multiple _______ to a single ________.
they share a _____:_____ relationship with cones
1st
photoreceptors ; bipolar cell
1:1
true or false. light is NOT continuous.
true
exhibit wave and particle like characteristics
ganglion cells:
- ___ order neuron
- _____ types in humans
2nd
20
X/P/beta ganglion cells:
- converge from ____
- function:
- cones
- color and finer details
Y/M/alpha ganglion cells:
- converge from ______
- function:
- rods
- motion and coarse patterns
melanopsin contains ganglion cells that can detect light. this means there is no convergence with ________
cones or rods ; bipolar cells
melanopsin contains W/K type ganglion cells, however, they are not for vision but for _______
circadian rhythm
why can the pupillary light reflex still exist in blind people with photoreceptors injured?
pupillary light reflex contains melanopsin containing ganglion cells which detect light on their own and don’t need cones or rods to detect light
horizontal cells are in the ______ layer and form synapses with _______ cells
amacrine cells are in the _____ layer and form synapses with ____ and _____ cells
both assist in modulating the ______ pathway
outer synaptic layer
photoreceptor cells
inner synaptic layer
bipolar and ganglion cells
transmission
what is the 3rd order neuron in the visual pathway?
ganglion axons project to LGN of thalamus
information from LGN further projects to ____.
V1
V1:
- only ______ detected
- macula projects to ____ and takes over ______ of V1
directional bars
posterior/occipital part ; 60%
what is Meyer’s loop?
inferior projection fibers course through temporal lobe in the superior quadrant
visual information from the left visual field of both eyes is processed in the
R hemisphere of brain
dorsal stream:
- ganglion cells:
- to parietal lobe:
- to medial temporal lobe:
- to frontal lobe:
- Y/M/alpha ganglion
- where –> retrieve memory about location/shape/motion of objects, R side dominate
- navigation
- how
ventral stream:
- ganglion cells:
- to inferior temporal lobe:
- continue to project to _______ lobe
- explain the reference to “the man who mistook his wife for a hat”
- X/P/beta ganglia
- what –> retrieve memory of object names
- medial temporal lobe
- the man’s memory is of a hat so he thought his wife was a hat
V1 sees:
V4 sees:
- lines with different directions with retinotopy maintained
- colors with retinotopy maintained
integration of _____ and _____ helps with object recognition and visual perception for the process of ______. explain what that is
visual cortex and dorsal/ventral streams
“best guess” through “fill it in” –> still see objects in the blind spot
— predictive processing which helps fill in complete missing or occluded parts of a visual scene
left visual hemifield by:
right visual hemifield by:
R temporal and L nasal retina
L temporal and R nasal retina
_______ crosses to form the optic chiasm
contralateral nasal retina axons
axons from _______ and ________ form optic tract
temporal retina and contralateral nasal retina
true or false. most of the time patients who are blind have absolutely no vision
false - spectrum of vision loss
bitemporal hemianopia can also be called:
tunnel view - pituitary gland tumor impinges chiasm
Left homonymous hemianopia can also be called:
lost visual field
where is the tectopulvinar pathway located?
— what two structures coordinate eye movement which is why we can’t separate eye movement?
in midbrain
– pretectal area and superior colliculus
what is Blindsight/Riddoch’s phenomena?
V1 function is lost so patient experiences blindness, however, they still have motion perception. When stimuli is in motion in blind visual field, they can see it.
CN III, IV, and VI all exit at _________ meninges but they cross the cranium (enter the orbit) at the _________
different
superior orbital fissure
Levator palpebrae superioris is innervated by _______.
– common tendinous ring in the _______
– function
CN III
posterior orbital wall
lifts upper eyelid –> opens eye
innervations of extra-ocular muscles:
- superior rectus:
- medial rectus:
- lateral rectus:
- inferior rectus:
- superior oblique:
- inferior oblique:
- CN III
- CN III
- CN VI
- CN III
- CN IV
- maxilla, CN III
due to distal attachment variations according to different textbooks, the function of eye muscles may be different. for example:
CN IV palsy –>
- innervates superior oblique which _______ the eye AND
—> if depress & medial, what would happen if there was injury to this muscle?
–> if depress & lateral, what would happen if there was injury to this muscle?
depresses
–> eye goes up and rotates outward
–> eye goes up and rotates inward
functions of eye muscles:
- lateral rectus:
- medial rectus:
- lateral
- medial
what is convergence?
when both eyeballs adduct at the same time –> we can do this but if born that way, that is not normal
what is strabismus? what are the 4 pathologies of it?
1. esotropia
2. exotropia
3. hypertropia
4. hypotropia
2 eyes not lined up properly to different directions
1. adducted eyeballs - convergence: CN VI palsy
2. abducted eyeballs - divergence: medial rectus strain or CN III palsy
3. elevated eyeballs - CN IV palsy
4. depressed eyeballs - inferior oblique muscle strain or CN III palsy
** some can be compensated, some cant
describe the synapse of CN III
preganglionic axons from Edinger Westphal nuclei –> synapses with 2nd cell body in ciliary ganglion –> postganglionic axons hike on short ciliary nerve
pupillary light reflex:
- afferent:
- efferent:
- effects:
- optic nerve –> ganglion cells, no photoreceptor needed
- oculomotor nerve, Vm
- constriction of pupil
CN V:
- nuclei
- location
- crossings of V1, V2, V3
- three Ss nuclei, one Sm nucleus
- middle and lateral pons
- V1: ophthalmic n, Ss only, superior orbital fissure
V2: maxillary n, Ss only, foramen rotundum
V3: mandibular n, Ss and Sm, foramen ovale
Somatosensory function of CN V:
facial sensory stimuli
chemical sensation of taste and smell
Somatic motor function of CN V:
mastication of temporalis, masseter, medial and lateral pterygoids
tensor tympani: hearing
tensor veli palatini: swallowing
diagastric anterior belly and mylohyoid: speaking, swallowing
