FINAL Flashcards
What is the purpose of the eye?
collect light + focus light onto the retina
- visible spectrum = 400-750 nm (purple to red)
What are the main functional components of the eye and what is their purpose?
- cornea: does most of the focusing
- pupil: controls how much light goes in
- lens: shape modified by ciliary fiber contraction: changing shape = “accommodation” –> allows fine focus
- rounding increase focal power + enables viewing of near objects - fovea: pit/focus point in the center of the macula of the retina where light is focused; high cone density –> high spatial contrast detection at the center of gaze
- retina: part of the CNS; composed of light detecting cells (photoreceptors) and other neurons
What are the common vision abnormalities?
- myopia (nearsightedness): light focuses in front of the retina
- hyperopia (farsightedness): light focuses behind the retina
- astigmatism: light does not focus and causes distorted vision
Explain the pupillary response.
Dilation: sympathetic
- relaxes ciliary muscles
Constriction: parasympathetic
- contracts ciliary muscles
Control of the pupils in the two eyes is “yoked” = work together, only one needs to be stimulated
What are the structures and functions of the main cells in the retina?
- Photoreceptors: rods (low light), cones (brighter light, color)
- send signals to ganglion cells which carry light responses deeper into the brain - Interneurons: horizontal, bipolar, and amacrine cells modify retinal response
- Pigment epithelium prevents light from bouncing around inside the eye
What are receptive fields?
portion of the retina innervated by a single ganglion cell
receptive fields are much larger for individual ganglion cells in the retina periphery than at the fovea (more rods/cones innervated by 1 ganglion)
What happens to photoreceptors in response to dark?
rods: depolarized, high transmitter release (glutamate)
- high cGMP concentration keeps nonselective cation channel open
What happens to photoreceptors in response to light?
rods: hyperpolarized, low transmitter release (glutamate)
- low cGMP concentration closes cation channel
Explain the visual transduction pathway.
- Rhodopsin = GPCR with retinal embedded in the membrane of PRs; cis-trans isomerization when it absorbs a photon
- Activates the G-protein called transducin (GαT); changes GDP to GTP; separates from βγ subunits
- Transducin activates phosphodiesterase (PDE) enzymes which converts cGMP to GMP
- cGMP levels drop, CNG channels close, reducing Ca2+/Na+ influx; hyperpolarizing membrane
- guanylyl cyclase generates cGMP from GTP opening channels in the dark; inhibited by Ca2+; controls adaptation
What is the basis of color vision?
differences in the primary structure of opsins
- Short cones: violet
- Medium cones: yellow-green
- Long cones: yellow-red
How are images formed from retinal signals?
- visual field is split left-right in nerves from each eye
- contralateral visual fields are sent to each half of the cortex (nasal); cross at optic chiasm
- temporal halves are ipsilateral
- relay signals to LGN of the thalamus
- V1 combines signals from both eyes
- Visutopic maps in the brain correspond to a specific spot in the retina to maintain spatial organization of the visual field
Olfaction facts
uses 350 olfactory receptors to detect various odors located on olfactory receptor cells (specialized neurons in the nasal cavity)
- each detects specific group of odor molecules
Different cells in the nasal cavity?
- olfactory-binding proteins: facilitate diffusion
- olfactory receptor cells: transducers; only expresses single type of receptor
- support cells: produce mucus
- basal cells: stem-cells that differentiate into new receptor cells
What is the cellular mechanism of odor sensation?
- odorant molecules bind to olfactory receptors (GPCR) in the nasal cavity
- produces cAMP which opens nonselective cation channels (Na+/Ca2+), Cl- channels open, depolarizes
- all receptors of the same type project to the same glomerulus in the olfactory bulb
- mitral cells receive input from glomerulus and relay signals through the olfactory tract
each odorant activates different subset of glomeruli
What are the features of hair cells? What is the mechanism of transduction?
- located in the inner ear and exposed to endolymph and perilymph
- cilia oriented in specific directions to detect mechanical stimuli
- transduction mechanism: cilia motion (caused by sound vibrations or fluid movement)
positive mechanical deformation: to the right (kinocilium) opens K+ channels, depolarization, opens V-gated Ca2+ channels, vesicle fusion and NT release
negative mechanical deformation: to the left closes K+ channels, hyperpolarization
mechanosensitive channels exhibit K+ leak into the cell to allow for electrical response to movement
What is the anatomy of the ear?
outer ear: pinna and ear canal collect sound
middle ear: malleus, incus, and stapes convert transmission medium from air to fluid
inner ear: cochlea converts sound pressure into electrical (neural) signals; vestibular system for balance
How does the middle ear transform air into fluid?
- tympanic membrane moves inward pushed by compression of a sound wave
- pushes malleus (longer) into incus
- pushes fluid inward
- tympanic membrane pulled by the rarefaction phase of a sound wave
- pulls malleus + incus back
- pulls fluid out
How are inner hair cells stimulated by a drop of pressure in the outer ear?
- Air pressure wave travels down ear canal; rarefaction portion of pressure wave strikes
tympanic membrane causes movement of malleus, incus and stapes to pull oval window
outward - Pressure drops in scala vestibuli (below scala tympani) round window moves inward
- Basilar membrane bows upward
- Outer hair cells deflect toward longer stereocilia
- Transduction channels open in outer hair cells (Organ of Corti) and depolarize cells
- Outer hair cells contract (shorten), amplifying movement
of basilar membrane - Endolymph flows out of the inner sulcus
- Inner hair cells move toward longer stereocilia and open transduction channels, depolarizes inner hair cells
- Depolarization opens calcium channels and causes glutamate release from inner hair cells
What is the anatomy of the vestibular system and its functions?
maintains balance; part of the inner ear
saccule and utricle detect linear acceleration, gravity, and head position based on the movements of stereocilia stuck in otolithic membrane
- saccule = vertical movement
- utricle = horizontal movement
hair cells oriented oppositely = push-pull (active/inhibit)
- positioned to cover all angles
3 semi-circular canals detect head rotation (angular acc) through fluid movement that bends hair cells
- ampulla at base of each canal have hair cells that are oriented in the same direction
What are the general features of sensory systems?
- sensory cells detect a stimulus and convert it into a receptor potential (voltage change)
- amplification
- NT release to convey signal to neurons
- adaptation to adjust sensitivity based on stimulus intensity/duration
Describe sensory field and its importance in touch sensation.
the “region” of stimulus space that can stimulate a sensory neuron
- smaller allow for greater spatial resolution (fingers)
- larger allow for general detection (back)
- overlapping fields enhance touch sensitivity
Describe the design of sensory neurons.
unipolar neurons with cell bodies in a peripheral ganglion (i.e. dorsal root ganglion)
- have rapidly adapting, intermediate adapting, and slow adapting responses to mechanical stimuli
2 projections: one to sensory receptors in tissues; other connect to spinal cord
- nerve endings contain ion channels that respond to mechanical stimuli by opening cation channels
What is the difference between rapidly adapting and slowly adapting receptors?
RA: detect transient stimuli (higher frequency vibrations)
SA: detect sustained stimuli (constant pressure); prolonged firing for duration of stimulus
What is the role of Piezo2 and TRP channels in mechanoreception?
Piezo2: channels detect mechanical force, triggering receptor potentials in touch-sensitive cells
TRP channels: nonselective cation channels that respond to specific stimuli like pressure, temperature, or chemicals