Sensory Physiology (vision) Flashcards
Vision (what it is, use, steps)
Process of light reflecting off of objects → mental image
Use: determine shape, color, and movement of objects
Steps
Light enters eye, focused by lens → retina
Retinal photoreceptors transduce light energy → electrical signal
Electrical signals processed via neural pathway
Light energy
Electromagnetic wave
Particle: photon
Visible spectrum
Wavelengths that the retina can detect
400-700 nm
The eye
Lens: focuses light on the retina
Pupil: adjustable opening to control amount of entering light
Light waves
Reflection: can strike and bounce off surfaces
Refraction: bend when traveling through objects of different densities
Concave lens: causes light waves to diverge
Convex lens: causes light waves to converge
Optics of vision
As light enters, cornea refracts light
Lens focuses light on the retina
How?
Accommodation: lens changes shape
Eye accommodation (close objects)
Light wave enters diverged → increased accommodation Increase lens curvature (more round) Mechanism Parasympathetic control Ciliary muscle contract Decreased tension on zonular fibers Lens is rounder → greater refraction
Eye accommodation (distant objects)
Distant objects Light waves enter nearly parallel → little accomodation Decrease in lens curvature (more flat) Mechanism No parasympathetic control Ciliary muscles relaxed Tension in zonular fibers Lens is flat → less refraction
Regulation of light entering the eye
Iris 2 sets of smooth muscle Circular Parasympathetic stimulation → contract muscle Pupillary constriction Radial Sympathetic stimulation → contract muscle Pupillary dilation
Retina layers
Photoreceptors (outermost) Generate graded potentials Bipolar cells (middle) Generate graded potentials Ganglion cells (innermost) Generate action potentials
Photoreceptors
Location: retina
Types:
Rods
Cones
Rods
Express rhodopsin pigment protein (opsin and retinal)
Retinal: light absorbing
Opsin: protein portion
Sensitive to light → night vision use, black and white
Many rods can bind to one bipolar cell → low resolution during low illumination
Distribution: high periphery of fovea
Cones
Express 3 opsins pigment protein attached to retinal
S cones: blue
M cones: green
L: red
Less sensitive to light → high illumination use, color
One cone binds to one bipolar cell → high resolution
Distribution: high at fovea
Signal Transduction Process
vision
Light absorbed by photopigment
Retinal and opsin dissociate
Series of chemical reaction → transduction cascade
Causes photoreceptor to hyperpolarize
Decreases amount of NT in synapse to bipolar cell
NT normally inhibit bipolar cells
Causes bipolar cell to produce graded potentials
If excited, bipolar → released NT to ganglion cell → AP
AP travels through visual pathway to brain
