Sensory Systems Flashcards
The Eye
______ and _______ focus the light
______ detects the light
______ carries information to the brain
The Eye
cornea and lens focus the light
retina detects the light
optic nerve carries information to the brain
Retinal organization
Label:
Eyes are anchored to the brain by _______
Eyes are anchored to the brain by optic nerves
How did eyes become connected to the brain?
- Eyes “sprouted” off the forebrain (prosencephalon) as opposed to connecting to it secondarily
Morphogenesis of the eye
- the forebrain forms lateral evaginations, the ______
- Once these contact the overlying _______ they invaginate on themselves to become _______
Morphogenesis of the eye
- the forebrain forms lateral evaginations, the optic vesicles
- Once these contact the overlying ectoderm they invaginate on themselves to become bilayered optic cups
- The inner layer of the optic cup will become the _______
- the outer layer will become the _______ and ______
- The overlying ectoderm will invaginate to form the ______
- Remaining ectoderm will form the ______
- The inner layer of the optic cup will become the retina
- the outer layer will become the retinal pigmented epithelium and iris
- The overlying ectoderm will invaginate to form the lens
- Remaining ectoderm will form the cornea
Lens is specialized and arises from __________
Lens is specialized and arises from neurogenic placodes (ectoderm)
What is the choroid fissure?
- The choroid fissure allows vessels to grow into the eye, nourishing the developing retina and lens
- Once vessels and axons have grown, the fissure closes, ensuring circular symmetry of the eye
What is Ocular Coloboma?
- Coloboma results from a failure of the choroid fissure to close
- Defect may be in retina, iris, and/or lens
- Gap in the eye
Lens invagination:
- Lens placode separates from _____ to form ______
- Formation of the lens requires signals from _______
Lens invagination:
- Lens placode separates from ectoderm to form lens vesicle
- Formation of the lens requires signals from optic vesicle
Lens development:
- Cells on the posterior face of the lens vesicle differentiate into _______
- elongate ______
- Start to express ______, protein that makes lens transparent
Lens development:
- Cells on the posterior face of the lens vesicle differentiate into primary lens fibers
- elongate anterior-posteriorly
- Start to express crystallins, protein that makes lens transparent
________ cells remain proliferative throughout life
Newly born cells migrate _______ and form _______
anterior lens cells remain proliferative throughout life
Newly born cells migrate peripherally and form secondary lens fibers (wrap around primary lens fibres)
_______ make up 90% of protein in lens fibres
crystallins make up 90% of protein in lens fibres
What are congenital cataracts?
Dr Norman Gregg linked ______ with congenital cataracts
- Cloudly lens often caused by crystallin mutations
- Many causes, both environmental and genetic, with ~100 genes implicated
- Dr Norman Gregg linked maternal rubella with congenital cataracts at a time when we didn’t know anything crossed the placenta
The retina begins as a ________
The retina begins as a pseudostratified neuroepithelium
Cell division (mitosis) happens at the ______ of the retina
Cell division (mitosis) happens at the apical surface of the retina
The mature retina has 3 layers of cells (green) composed of ________ and separated by two ______ (red)
The mature retina has 3 layers of cells (green) composed of 6 types of neurons and 1 glia and separated by two synaptic layers (red)
How are the various cell types of the retina generated?
- Temporal organization
- All progenitors in retina can give rise to any of the 6 types of neurons and 1 glia in the retina.
- Does so in waves
What is the sequential order of retinal cell differentiation?
- Ganglion cell
- Horizontal cell
- Amacrine cells
- Cones
- Bipolar cells
- Rods
- Muller cells (glia)
The ______ are the output neurons of the eye; they bundle together and exit the eye as the ______
The retinal ganglion cells (RGCs) are the output neurons of the eye; they bundle together and exit the eye as the optic nerve
Visual pathway:
Retina → thalamus (lateral geniculate nucleus) → optic radiations → Visual cortex (occipital lobe)
What are three issues that must be overcome regarding the visual pathway?
- Segregate Left Field vs Right Field
- Preserve Map of visual field (retina → brain)
- Right vs Left eye (segregate inputs)
Some axons cross at the ______ between the eye and lateral geniculate nucleus (thalamus)
Optic Chiasm
Visual Fields:
- Left visual field is captured by _____ sides of both eyes
- Right visual field is captured by _____
Visual Fields:
- Left visual field is captured by right sides of both eyes
- Right visual field is captured by left sides of both eyes
Which axons cross at the optic chiasm and why?
- Left visual field from the left eye crosses and the right visual field from the right eye crosses
- Left side of brain gets RIGHT VISUAL FIELD
- Right side of brain gets LEFT VISUAL FIELD
Axon guidance at optic chiasm
- The axons of right and left side RGCs express different ________
- Nasal vs Temporal
- Many guidance cues surround the _____
- The axons of RGCs that view the visual field on the same side behaviour at the chiasm
- Axons of RGCs that view the visual field on the opposite side behaviour at the chiasm
Axon guidance at optic chiasm
- The axons of right and left side RGCs express different guidance cues receptors
- Nasal vs Temporal
- Many guidance cues surround the optic chiasm
- The axons of RGCs that view the visual field on the same side will cross at the chiasm (contralateral)
- Axons of RGCs that view the visual field on the opposite side will NOT cross at the chiasm (ipsalateral)
Where do ganglion cell axons synapse?
After crossing, the axons travel to the lateral geniculate nucleus (LGN) a collection of neurons in the thalamus
Topographic mapping:
Organization of the visual field inputs is maintained in _____
Topographic mapping:
Organization of the visual field inputs is maintained in lateral geniculate nucleus
Gradients of guidance cues and receptors
What creates the topographic map?
- Gradients of guidance cues and receptors
- “dif postal code”
- Axons with specific receptors match based on guidance cues
Gradients of guidance molecule receptor expression in the ______ and gradients of guidance molecule ligand expression in ______ establish topographic mapping of retinal axons
Gradients of guidance molecule receptor expression in the retina and gradients of guidance molecule ligand expression in Lateral Geniculate nucleus establish topographic mapping of retinal axons
_______ carry visual information from the LGN (thalamus) to the Primary Visual Cortex (V1)
optic radiations carry visual information from the LGN (thalamus) to the Primary Visual Cortex (V1)
Each LGN (and primary cortex) receives visual information for _____ but from _____
Each LGN (and primary cortex) receives visual information for one visual field but from both eyes
RGC axons sort into ________ in the LGN
RGC axons sort into eye-specific layers in the LGN before sending to the visual cortex
The different layers created in the LGN of left and right eye are sorted into _______ in the cortex
The different layers created in the LGN of left and right eye are sorted into ocular dominance columns in the cortex
What are two mechanisms that contribute to the sorting of Left and reight eye into ocular dominance columns
- Guidance cues
- Optic chiasm
- Gradient map in LGN
- Activity
Sorting of eye-specific inputs to LGN
- RGC axons from the left and right eyes initially overlap in the _____
- Segregation of the axons is dependent on _______
Sorting of eye-specific inputs to LGN
- RGC axons from the left and right eyes initially overlap in the LGN
- Segregation of the axons is dependent on spontaneous activity of RGC neurons
- prenatally, random firing of cells near each other help with spatial organization
- Fire together wire together
Sorting of eye specific inputs to visual cortex
- LGN neurons primarily target layer ___ of the visual cortex
- _______ overlap initially
- Eye- specific inputs segregate ______ into adjacent fields
- Requires _________
Sorting of eye-specific inputs to visual cortex
- LGN neurons primarily target layer 4 of the visual cortex
- axon branches overlap initially
- Eye- specific inputs segregate postnatally into adjacent fields
- Requires vision in both eyes as the axons compete for territory
What was the experiment that won Hubel and Wiesel the 1981 Nobel prize
- Visual cortex of cat with radioactive tracer from one eye
- Covered one eye of cat during critical period
- eye left open dominated the visual cortex
- Covered both eyes
- columns didn’t change
What are 2 key parts of the olfactory system
- Olfactory epithelium w/ primary sensory nn (olfactory receptor cells)
- Axons contact 2nd order neurons in olfactory bulb
Olfactory cell sends axons through the _____ into the ______
Olfactory cell sends axons through the ethmoid bone into the olfactory bulb
________ form near nasals and differ into olfactory epithelium
- some of the cells differentiate into sensory nn known as _____
- extend axons a short distance to synapse with _____ cells in the ______
Olfactory/nasal placodes form near nasals and differ into olfactory epithelium
- some of the cells differentiate into sensory nn known as olfactory receptor cells
- extend axons a short distance to synapse with mitral cells in the olfactory bulb
At the same time as the primary sensory neurons are differentiating in the olfactory epithelium, the brain produces an outgrowth called the ______
- Here, neuroepithelial cells differentiate into ______ called _____
At the same time as the primary sensory neurons are differentiating in the olfactory epithelium, the brain produces an outgrowth called the olfactory bulb
- Here, neuroepithelial cells differentiate into secondary neurosensory cells called mitral cells
Label
A
B
The cribriform plate (derived from ______) forms around the projections of the ______
The cribriform plate (derived from neural crest) forms around the projections of the primary neurosensory cells
As the brain and face grow, the axons of the ______ elongate to make the olfactory tracts
- Grow through ______ from _____
As the brain and face grow, the axons of the mitral cells elongate to make the olfactory tracts
- Grow through mesenchyme from neural crest & bone formed around it
Each primary olfactory neuron expresses only 1 type of _______
Each is expressed in a subset of neurons spread across the ______
These neurons converge together on the ______ of ______ forming structures called _____
Each primary olfactory neuron expresses only 1 type of odorant receptor
Each is expressed in a subset of neurons spread across the olfactory epithelium
These neurons converge together on the dendrites of specific mitral cells forming structures called glomeruli
Topographic mapping in olfactory system
- information is sorted based on the ______
Topographic mapping in olfactory system
- information is sorted based on the olfactory receptors
- receptors themselves direct the axons
Auditory system
- movement of fluid hits ____ and opens ____
Auditory system
- movement of fluid hits cilia and opens ion channels
three bones of the inner ear:
Maleus
Incus
Stapes
The _______ is what opens when your ears “pop” to equalize pressure
The pharyngotympanic tube is what opens when your ears “pop” to equalize pressure
label the ear
The otic placode forms in the _______
The otic placode forms in the inner ear
