Human A&PBIO 304 · American River College ← Week 05 pre-work

BIO 304 · Week 05 · Interactive Workbook

Vision

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Part 1 of 4 · Recall

Fill in the blanks

Type the term that completes each statement, using the word bank. Pull it from memory first.

Word bank

Vitreous humorFovea centralisNear visionDistance visionSignal pathRodsAqueous humorIris & pupilLensConesOptic discCorneaRetinaPresbyopia

  1. Transparent dome on the front. Provides about two-thirds of the eye's refractive power. Avascular.
  2. Iris muscle controls pupil diameter: more light in or less. Sphincter pupillae (parasympathetic) constricts, dilator pupillae (sympathetic) dilates.
  3. Adjustable focus via ciliary muscle. Shape changes for accommodation.
  4. Watery fluid in anterior chamber. Produced by ciliary body, drained at the canal of Schlemm. Pressure regulator.
  5. Gelatinous fluid in posterior chamber. Maintains eye shape.
  6. Posterior neural layer. Contains photoreceptors, bipolar cells, ganglion cells.
  7. Cones only. Highest visual acuity. What you focus on lands here.
  8. Where axons exit the eye as the optic nerve. No photoreceptors, hence the blind spot.
  9. Ciliary muscle relaxed. Suspensory ligaments taut. Lens flattens. Light from far objects converges on the retina.
  10. Ciliary muscle contracts. Suspensory ligaments slacken. Lens rounds up (more refractive power). Light from close objects converges on the retina.
  11. Lens stiffens with age and cannot round up. Reading glasses needed.
  12. ~120 million per eye. Outside the fovea. Rhodopsin. Sensitive to low light, no color, low acuity.
  13. ~6 million per eye. Concentrated at fovea. Three types: S (blue), M (green), L (red). Color and high acuity, needs bright light.
  14. Photoreceptor → bipolar cell → ganglion cell → optic nerve → thalamus (LGN) → primary visual cortex (occipital lobe).

Define it: high-yield vocabulary

Write a clear definition in your own words for each term.

  1. Cornea
  2. Iris
  3. Pupil
  4. Lens
  5. Aqueous humor
  6. Vitreous humor
  7. Retina
  8. Fovea centralis
  9. Optic disc
  10. Accommodation
  11. Presbyopia
  12. Rods
  13. Cones

Part 2 of 4 · Anatomy lab

Draw and label

Box A. Eye in sagittal section

Directions

  1. Draw an eye in cross-section as viewed from the side. The front of the eye is on the LEFT, the back is on the RIGHT.
  2. Draw the cornea (transparent dome at the front).
  3. Draw the iris (colored ring) and the pupil (opening in the center). Label both.
  4. Draw the lens behind the iris. Show the ciliary body and suspensory ligaments holding the lens.
  5. Label the anterior chamber (between cornea and iris, contains aqueous humor) and the posterior chamber.
  6. Fill the rest of the eye (the large back portion) with vitreous humor. Label.
  7. Line the back of the eye with the retina. Label.
  8. Mark the fovea centralis (small pit in the central retina, point of sharpest vision).
  9. Show the optic nerve leaving the back of the eye. Label the optic disc (blind spot) where the nerve exits.
  10. Wrap the eye with sclera (white outer layer) and choroid (vascular middle layer).
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Box B. Retinal layers (light path)

Directions

  1. Draw a horizontal section of retina. The light arrives from the BOTTOM (yes, paradoxically) and the photoreceptors face the TOP (away from the light).
  2. Layer 1 (bottom): retinal ganglion cells. Their axons form the optic nerve. Label.
  3. Layer 2: bipolar cells.
  4. Layer 3 (top): photoreceptors. Draw both rods (long, dim light, peripheral vision) and cones (shorter, bright light, color vision, concentrated at the fovea).
  5. Above the photoreceptors, draw the retinal pigment epithelium (RPE, a dark layer that absorbs stray light).
  6. Add arrows showing the path of light entering at the bottom and the path of the neural signal going DOWN from photoreceptors to bipolars to ganglion cells.
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Structures to label

Label each on your drawing.

  1. Cornea
  2. Iris
  3. Pupil
  4. Lens
  5. Ciliary body
  6. Suspensory ligaments
  7. Aqueous humor
  8. Vitreous humor
  9. Retina
  10. Fovea centralis
  11. Optic disc
  12. Optic nerve
  13. Sclera
  14. Choroid
  15. Photoreceptor
  16. Rod
  17. Cone
  18. Bipolar cell
  19. Retinal ganglion cell
  20. Retinal pigment epithelium

Part 3 of 4 · Physiology lab

Reason it through

A. Trace: from photon to action potential

Explain the main structure-function relationship for this topic.

B. Synthesis

1. A patient with myopia (nearsightedness) has trouble seeing distant objects. Explain the optical defect (eyeball shape or lens shape) and how a corrective lens fixes it.
2. A patient is diagnosed with macular degeneration (loss of cone-rich foveal retina). Predict which type of vision is lost FIRST (peripheral, central, color, night) and which is preserved longest, with a one-sentence reason.
3. Why is the optic disc called the blind spot? Predict what happens when an image falls on the optic disc, and explain why we don't normally notice this gap in our visual field.

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