Flynn Lectures Flashcards
Ohm’s Law
V=IR
resistance of membrane (R)
ion channels act as a resistor in circuit surrounding membrane, if no ion channels are present, resistance is infinite
current (A) of membrane
measured if movement of charge across membrane
capacitance (C)
C=q/V (measures the amount of charge that can build up around the membrane
capacitor properties
can hold a charge equal to that of the input voltage (Coulomb’s Law = capacitor has a maximum voltage), charging delay
time constant (tau)
time taken to reach 63% of maximum voltage, a quality of the membrane that describes how quickly membrane potential will change when charge is introduced
how to calculate tau time constant?
t = RC (R = membrane resistance, C = membrane capacitance)
membrane capacitance is affected by:
size of conductive plates (intracellular vs extracellular fluid), distance between plates (better capacitor if plates closer together), insulator constant
membrane resistance is affected by:
number of ion channels in the membrane
length constant (lambda)
distance charges move to acquire 37% of maximum voltage
how to calculate length constant?
lambda = sqrt [ Rm / (Ri + Ro) ] (Rm = membrane resistance, Ri = axial resistance, Ro = 0) lambda = sqrt [Rm/Ri]
what is membrane resistance Rm?
due to ion channels, greater membrane resistance = less ion channels (charges can move further down axon, larger length constant)
what is axial resistance Ri?
internal resistance caused by stuff inside the axon that opposes the movement of ions/charges down the axon, larger axial resistance = harder to charges to move = lower length constant
what resistance does diameter affect?
axial resistance, larger diameter = lower axial resistance
what are passive electrical properties?
- time delayed change in membrane potential (time constant tau)
- distance degradation (length constant lambda)
- summation (temporal/spatial)
describe the structure of voltage-gated sodium channels
four domains consisting of six membrane spanning segments, fourth mss is voltage-sensitive, has 4 P loops (pore-forming loops on intracellular side)
describe the structure of voltage-gated potassium channels
one domain consisting of 6 mss, 1 P loop, selective for potassium because of position of charged amino acid residues to interact with hydration shell of K+ ion specifically
what causes relative and absolute refractory periods?
- inactivation of sodium channels
- increased potassium permeability
- decreased membrane resistance (V=IR, R decreases means more I is required to reach V)
what determines conduction velocity?
1) axon diameter (increase in diameter = greater decrease in Ri than decrease in Rm, length constant increases and thus conduction velocity increases)
2) myelination (increased Rm = increased length constant = increased conduction velocity)
3) temperature (channels change shape more easily at warmer temperatures)
what are the steps of neurotransmitter release?
1) targeting (vesicles filled up with NT are mobilized from stores and moved toward axon terminals)
2) docking (irreversible, will go through exocytosis, when vesicle first makes contact with presynaptic membrane)
3) priming (requires protein structures, formation of V-snare T-snare complex)
4) fusion/exocytosis (vesicle membrane incorporated into presynaptic membrane)
5) endocytosis (recycles membrane to create new vesicles)
classical neurotransmitter release
requires endocytosis to form new vesicles
kiss and run
vesicle barely opens and is continually re-used (involves different proteins
what types of proteins are on the vesicle?
V-snares, which are involved in fusion (e.g. synaptotagmin)
what types of proteins are on the postsynaptic membrane?
t-snares
what causes fusion/exocytosis?
V-snares and T-snares form a snare complex, calcium binds to synaptotagmin
sensory receptor cell
a cell that is specialized to transform the energy of a stimulus into an electrical signal
stimulus
a form of external energy (external to the cell) to which a sensory receptor cell can respond
sense organ
anatomical structures that are specialized for the reception of particular kinds of stimuli, usually a sense organ contains many similar receptor cells
sensory systems
sense organs and all of their associated central processing areas
sensory transduction
conversion of stimulus energy into an electrical signal
sensory receptor molecules
receptor molecules that are particularly sensitive to a sensory stimulus and initiate the transduction of stimulus by producing a receptor potential
sensory modality
the subjective nature of the sensory stimulus
what are 4 ways that sensory receptor cells can be classified?
1) sensory modality
2) form of stimulus energy that excites sensory receptor cells
3) mechanism of transduction (ionotropic/metabotropic)
4) location of the source of stimulus energy relative to body (exteroceptors/interoceptors)
what are two functional roles of sensory receptor cells?
1) transduce some form of stimulus energy and convert it to an electrical signal (receptor potential)
2) encodes info about stimulus
principle of labeled lines
the sensory modality or quality of sensation associated with a stimulus depends solely on which receptor cells are stimulated, rather than on how they are stimulated
mechanoreceptors
specialized to respond to different types of mechanical stimuli
dorsal roog ganglion (DRG) cells
touch receptor cells with cell bodies in the dorsal root ganglion, send their distal processes into the skin, and their central axons into the spinal cord
what are four types of dorsal root ganglion cells with specialized endings with epithelial cells? (touch receptors)
1) Merkel disk
2) Meissner corpuscles
3) Ruffini endings
4) Pacinian corpuscles
Merkel disk
located just below the skin epidermis, responds to indentation of the skin, slow adapting, compression/light touch, attached to skin by protein strands
what are four types of info encoded by sensory receptors?
1) modality - type of energy
2) location - set of sensory receptors that are active
3) intensity - total amount of stimulus energy delivered to the receptor
4) timing - when the stimulus energy starts and stops
Pacinian corpuscle
largest of 4 main mechanoreceptors, located deep in the dermis, responds to vibration and pressure, rapidly adapting
Ruffini endings
located deep in dermis, responds to stretch, slow adapting, indicates limb position and object shape, attached to the skin
Meissner’s corpuscle
located superficially, physiologically similar to Pacinian corpuscles, rapidly adapting, responds to fine light touch
mechanoreception is mediated by:
stretch activated ion channels
what are two types of skin?
hairy skin and glabrous skin (most tactile discrimination)
adaptation
the frequency of action potentials in response to a continuous and constant stimulation decreases over time
tonic (slowly adapting) responses
decrease slowly in frequency and generally continue for as long as the stimulus is present (eg. Merkel discs and Ruffini endings)
phasic (rapidly adapting) responses
adapt rapidly, generally signal changes in touch or pressure (e.g. Meissner corpuscles, Pacinian corpuscles)
proprioceptors
internal mechanoreceptors, associated ith the musculoskeletal system
muscle spindle
proprioceptive organ in vertebrates, monitors the length of a skeletal muscle
tensor tympani
muscle connected to auditory ossicles; pulls malleus medially, involved in chewing, helps with acoustic reflex
stapedius muscle
muscle connected to auditory ossicles; pulls on the stapes, talking, helps with acoustic reflex
acoustic reflex
activated by very loud intense sound, causes contraction of tensor tympani and stapedius muscle to reduce transmission through middle ears and reduce damage to inner ears
vestibular membrane
between scale vestibuli and scala media
basilar membrane
between scala media and scala tympani
organ of Corti
sits on top of basilar membrane, where auditory transduction occurs
utricle detects
horizontal linear head movements (otolith organ)
saccule detects
vertical linear head movements (otolith organ)
perilymph in scala vestibuli and scala tympani is similar to:
extracellular fluid
endolymph in scala media has very high concentrations of:
potassium ions; this is why when stretch-activated ion channels open on hair cells, there is an influx of cations including potassium
activation of hair cells produces:
depolarization/membrane potential which causes more neurotransmitter release onto afferent synapses, causes more action potentials to be generated by afferents
3 rows of outer hair cells:
modulate sensitivity
1 row of inner hair cells:
majority of auditory transduction occurs here
semicircular canals contains:
endolymph fluid (similar to endolymph in scala media of cochlea)
otolith
“rocks” of calcium carbonate that sit on top of the gelatinous layer, lag behind with movement and causes pulling on hair cells
convex lens
causes light rays to converge
concave lens
causes light rays to diffract
emmetropia
normal vision
a far source results in:
parallel incoming light rays
a near source results in:
diverging incoming light rays (requires more refraction to converge properly on the retina)
in emmetropia, far source;near source
far source does not require accommodation, near source requires accommodation
myopia
nearsightedness, eyeball is too long or lens too strong, focus of light rays is in front of the retina
in myopia, far source;near source
no accommodation for far source (distant image out of focus because converges in front of retina), no accommodation for near source (focus on retina)
myopia can be corrected with:
concave lens
with a concave lens in myopia, far source;near source
far source=no accommodation, slight divergence of light rays allows proper convergence of light on retina, near source=accommodation, near source focused on retina
hyperopia
farsightedness, eyeball is too short or lens too weak
in hyperopia, far source;near source
far source=accommodation, focused on retina; near source=accommodation, focused behind retina (object not in focus)
hyperopia can be corrected with:
convex lens
with a convex lens in hyperopia, far source/near source:
far source = no accommodation, focused on retina; near source = accommodation, focused on retina (converges light rays on retina)
presbyopia
“old” sighted, same effects as hyperopia, near objects are not being refracted enough because dynamic accommodation reduces with age
cornea
protective, outermost layer of the eye that is responsible for the vast majority of refraction
astigmatism
cornea is not even/symmetrical, different amounts of refraction, diverse light rays don’t all converge on the retina (requires a corrective lens that balances refraction across the surface of the cornea)
anterior chamber
chamber in front of the lens that is filled with aqueous humour, bathes cells of cornea and provides cells with nutrition
aqueous humour is produced in the:
ciliary body at the rate of 5mL/day
Canals of Schlemm
where aqueous humour is drained into the vascular system
glaucoma
increased ocular pressure most commonly caused by decreased drainage of aqueous humour, can squeeze on optic nerve and cause permanent damage to axons, will usually affect periphery of visual field first
iris
controls amount of light that actually reaches photoreceptors
parasympathetic stimulation of the iris causes:
pupil constriction to allow less light into the eye, circular constrictor muscle (inner) activated
sympathetic stimulation of the iris causes:
pupil dilation to allow more light into the eye, radial dilator muscle (outer) activated
lens
refinement of refraction, made of crystallin proteins that allow light to pass easily and are flexible (contributes to refractive ability)
sympathetic stimulation of ciliary muscle causes:
relaxation of ciliary muscle = taut suspensory ligaments = flattened, weak lens (less refraction)
parasympathetic stimulation of ciliary muscle causes:
contraction of ciliary muscle = slackened suspensory ligaments = rounded, strong lens (more refraction)
cataract
lens becomes opaque/cloudy, treatment=surgery that involves replacement with a prosthetic
fovea
macula lutea, area of greatest visual acuity, centre of retina
optic disk
where all axons of optic nerve and blood vessels collect and go through eye, located laterally to the fovea (no visual perception in this “blind spot”)
saccades
small twitches/movements of the eye that allow brain to fill in the blind spot
transduction occurs at photoreceptors and then passes to:
bipolar cells (cell body in centre, two projections in opposite directions) to ganglion cells (axons make up the optic nerve)
horizontal cells
perpendicular cells between photoreceptors and bipolar cells, modulates activity of the retina
amacrine cells
perpendicular processes in between bipolar and ganglion cells
