Test 2 - Lecture 4 (Phototransduction) Flashcards
somatosensory system reports
the body’s interactions with its immediate surrounds via touch and feel
olfactory system reports
information concerning our surrounds via detection of airborne molecules that arise from carious sources outside the body
gustatory system reports
nutritional content and quality of the foods and liquids that we ingest
visual system reports
accurately locate and identify distinct objects within our visual space
photoreceptors along the retina serve as the
visual receptors (transduce streams of arriving photons into bioelectrical signals for transmission into the brain)
intensity of light (illumination)
based upon the number of photons striking a photoreceptor per unit of time (brightness)
wavelength
perceived as color
vision is based upon the capability
to see distinct objects within our visual space is based upon detecting contrasts in illumination and color
visual space
all the outside sources of both emitted and reflected light that enters the eye
visual field
region of visual space that projects light upon the retinal surface of EACH eye
extensive overlap between the L and R monocular visual fields forms
binocular visual field (roughly the central 2/3 of the visual space)
outside the binocular visual field are the L and R
monocular crescents (lateral portions of the visual space seen by just the L or R eye)
retinotopic map
transmit sensory information from the retina into the primary visual cortex (basis for brain to perceive where objects located to our body)
actual projection of the visual field upon the surface of the retina is
inverted and left/right reversed
temporal visual field project upon the
nasal retina
nasal visual field project upon the
temporal retina
superior visual field projects upon the
inferior retina
inferior visual field projects upon the
superior retina
retina cell column order
photoreceptors (rods and cones), bipolar cells, and ganglion cells
horizontal cells
interneurons, which modulate transmission from the photoreceptor to the bipolar cell
bipolar cells
serve as relay between the photoreceptor and the ganglion cell
ganglion cells
the projection neurons that generate signals for transmission into the brain via optic nerve
rods
high sensitivity, night (scotopic) vision; are monochromatic (no color)
cones
low sensitivity, providing day (photopic) vision; are chromatic
structure of the retna
pigment epithelium, photoreceptor layer, neural network layer, ganglion cell layer
muller cells
function as channel for light photons to reach photoreceptors
ganglion cells are always stimulated by the NT released from the
bipolar cell
low intensity light… cGMP is plentiful and Na channels are
open
high intensity light, cGMP is reduced and Na channels are
closed
photoreceptor cells ______ as light intensity is reduced
depolarize
photoreceptor cells ________ as light intensity is amplified
hyperpolarize
dark (no photons): cations Na and Ca channels are
open
bright light: cations Na and Ca channels are
closed
photoreceptor adaptation that reverses the light-induced reduction in cGMP
- cGMP must be regenerated within the photoreceptor
- Ca inhibits cGMP regeneration
glutamate release is dependent upon the photoreceptor membrane potential: depolarized vs hyperpolarized
depolarized: increased NT release
hyperpolarized: decreased NT release
NT release is graded; ______ relationship with absorbed light intensity
inverse
glutamate released from bipolar cell ALWAYS triggers
EPSP in ganglion cell
glutamate released from photoreceptor may trigger
either EPSP or IPSP on bipolar cell
off retinal column
absence of light
on retinal column
presence of light
off bipolar cells have
excitatory glutamate receports
on bipolar cells have
inhibitory glutamate receptor
dark conditions: off bipolar vs on bipolar
off bipolar - depolarize (more active)
on - hyperpolarize (less active)
light conditions: off bipolar vs on bipolar
off bipolar - hyperpolarize (less active)
on bipolar - depolarize (more active)
horizontal cells function as
inhibitory interneurons (GABA NT)
signaling from the central photoreceptors to the bipolar cell is determine by two opposing influences
- illumination of the central photoreceptors
- signaling form the horizontal cells
center only light stimulation: GABA
no change in GABA release from horizontal cells
extend illumination to now include the surround: GABA
reduced stimulation of horizontal cells = reduced GABA release to center receptors (causes depolarization = increasing NT of center)
