BIO 201 Anatomy & Physiology Lecture Schedule

Last Modified: October 19, 2000 (J. Crimando).

BIO201 Anatomy & Physiology
Lecture Outline 10: Physiology of Vision

I.Vision:
    A. Anatomy of The Eye
       1. Accessory structures
          a. palpebrae (eyelids)
          b. lacrimal apparatus
          c. extrinsic eye muscles
             i. superior/inferior obliques
             ii. lateral/medial rectus
             iii. superior/inferior rectus
       2. Eyeball structure
          a. anterior chamber behind cornea
             i. filled with aqueous humor
          b. posterior chamber behind lens
             i. filled with vitreous humor
          c. entire eyeball covered with conjunctiva
             i. thin mucous membrane
             ii. continuous with palbebral conjunctiva
             iii. dilation of conjunctival blood vessels cause "bloodshot" eyes
          d. fibrous tunic (outer coat of eyeball wall)
             i. sclera ("whites" of the eyes)
             ii. cornea - transparent cover, focuses image onto lens
             iii. canal of Schlemm at junction of sclera/cornea
                 aa. drains anterior chamber fluid (aqueous humor)
          e. vascular tunic (middle coat of eyeball wall)
             i. choroid
                 aa. dark layer (rich in melanocytes)
                 bb. prevents backscattering of light
             ii. ciliary body
                 aa. contains ciliary processes and ciliary muscle
                 bb. suspensory ligaments attach ciliary body to lens
                 cc. contraction of ciliary body draws it closer to lens
             iii. suspensory ligaments
                 aa. keeps lens stretched tight
             iv. iris ("colored" part of eye)
                 aa. pupil allows light to enter eye
                 bb. circular (constrictor) and radial (dilator) muscles control pupil diameter
          f. neuronal tunic (inner coat of eyeball)
             i. retina
                 aa. photoreceptors and neuronal layers
          g. lens
             i. fine focuses image onto retina (onto central fovea)
             ii. accomodation adjusts thickness of lens to focus light
             iii. relaxation of ciliary body for distant viewing
                 aa. suspensory ligament tension pulls, lens flattens
             iv. contraction of ciliary body for near viewing
                 aa. tension is absorbed by ciliary body, lens thickens

    A. Physiology of Vision
       1. Photoreceptor layer
          a. rods
             i. absorb light
             ii. do not differentiate color (only shades of greys)
             iii. sensitive to low light levels
             iv. more present in peripheral areas of retina (outside central fovea)
          b. cones
             i. absorb light of particular wavelengths (red, green, or blue)
             ii. less sensitive in low light levels
             iii. concentrated in central fovea
       2. Rhodopsin light-absorbing pigment (consists of opsin + retinal)
          a. rhodopsin is embedded in many membrane "discs" inside photoreceptors)
          b. opsin protein portion holds retinal molecule
          c. retinal molecule (derived from vitamin-A) absorbs light energy
       3. "Dark current" in photoreceptors
          a. Na+ stay open in photoreceptor when NO LIGHT is being absorbed
          b. constant current of Na+ into cell keeps photoreceptor MOST ACTIVE IN DARKNESS
          c. active photoreceptor (in dark) continually releases inhibitory neurotransmitters onto neuronal cells in retina
       4. Light reactions
          a. light photon absorbed by retinal
          b. opsin releases "energetic" retinal ("bleaching")
          c. opsin then activates transducin molecule
          d. active transducin activates phosphodiesterase enzymes
          e. active phosphodiesterase enzymes cause Na+ CLOSURE
          f. Na+ channel closure reduces "dark current"
          g. photoreceptor releases less of the inhibitory neurotransmitters onto neuronal retinal cells
          h. neuronal retinal cells fire action potentials, carried by optic nerve to brain... NOW YOU SEE!
       5. Structures of Visual Pathway
          a. cornea
          b. lens
          c. retina
          d. optic nerve (cranial nerve II)
          e. optic chiasma (only the lateral field of view crosses here)
          f. optic tract
          g. lateral geniculate of thalamus (visual relay)
          h. thalamus relays to visual cortex & association areas(occipital lobe)
          i. thalamus also relays to hypothalamus and midbrain
          j. hypothalamus relays info to pineal via superior cervical ganglia
          k. midbrain regulates visual reflexes

This is only a general outline.
There may be material that has been discussed in lecture that is not included in this outline
and there may be material on this outline that has not been discussed in lecture.
Any material discussed in lecture or listed in this outline is "fair game" for the test.