Chapter 8 - Specialized Senses Flashcards
Receptors
- photoreceptors
- mechanoreceptors
- chemoreceptors
Receptor Potentials
- sensory receptors have receptor potentials
- used to signal to CNS
Sensory Adaptation
- sensory receptors become less sensitive in continued presence of stimulus
Sensory Coding
- signals received by receptors are transduced to be understood by brain
Visible Spectrum
the wavelengths of light than can be detected by the human eye (400-700 nm)
Accessory structures of the eye
- eyebrow/eyelashes
- eyelids
Function of eyebrows/eyelashes
protect the eye from sunlight and foreign objects
Function of eyelids
spread oil, mucus, and saline across the conjunctiva to moisten and avoid friction
Sclera
white part of the eye
Iris
color
Pupil
central opening; allows light to enter
Lens
helps focus light on retina; must be transparent to let light pass through, and must be curved to refract light
Choroid
part of the vascular layer
Retina
contains photoreceptor cells that capture light
Macula
central point of the retina
Fovea
center of FOV; contains highest density of rods and cones
Optic Nerve
carries visual information to visual cortex
Refraction of light in general
change of light speed from one medium to another causes it to bend
Refraction of light in the eye
Convex lens refracts light so it converges on a focal point (retina)
What allows proper focusing of light?
Accommodation
Photons
individual energy particles of light
Wavelength
the distance between the peaks of two successive waves
refraction
light bending
Convex lenses
- thicker in the middle
- allow light to refract and converge at a focal point
- cause the actual image to be focused upside down and reversed from left to right
Concave lenses
- thinner in the middle
- cause light to be dispersed
- useless for focusing images on the retina
Fovea
- aka fovea centralis
- has high density of CONES
Cones
- specialized receptor cells responsible for responding to light
- tapered shape compared to rods
- responsible for processing images w/ the highest visual acuity (resolution)
Accommodation for near sight
adjustment of the shape of the lens to adjust to the distance of the image; controlled by ciliary muscles
- ciliary muscles contract, causing them to loosen the tension of the zonular fibers, causing the lens to relax into a spherical, thicker shape, crating increased REFRACTIVE POWER (see images closer to you CLEARER)
Accommodation for far sight
- ciliary muscles relax
- zonular fibers remain taut and the lens is pulled into a flatter position decreasing the lens’ refractive power
- allows you to see objects further in FOV
What controls the ciliary muscles?
parasympathetic inputs
Myopia
nearsightedness
- refract light too strongly or the eyeball length is too long
- image is focused IN FRONT of the retina
- corrected with concave lens
Hyperopia
Farsightedness
- caused by too little cornea or lens light refraction, or by an eyeball that is too short
- image is focused BEHIND the retina
- corrected by convex lens that refracts light before it reaches the eye
Order of cells from posterior to anterior
- retinal pigment epithelial cells (RPE)
- photoreceptor cells (rods/cones)
- horizontal cells
- bipolar cells
- amacrine cells
- ganglion cells (axons leading to brain)
Retinal pigment epithelial cells (RPE)
lie at the most posterior region of the eyeball, behind the photoreceptor cells and have melanin (traps light)
- also store and recycle vitamin A to photoreceptor cells
Photoreceptor Layer
contains rod and cone cells (photoreceptor cells)
- have specialized regions called OUTER SEGMENTS that capture light and initiate a second messenger cascade into electrical signal.
