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BIO 304 . Human Anatomy & Physiology . American River College

Vision

Module 8 . Special Senses

Eye anatomy, accommodation, and photoreceptor function. Watch the video, then complete the retrieval check below to unlock your spaced-recall cards.

How to use this sheet Toggle the toolbar above. Notes prints the full reference for review. Study prints as a fill-in-the-blank worksheet, print it, then write each definition while you watch the video or read your book. Quiz me is on-screen typing practice; type the term, click Reveal to check yourself.

Open spaced recall
By the end
  1. Trace a ray of light from cornea to optic nerve and name every structure it passes through.
  2. Explain accommodation: how the ciliary muscle and lens change shape for near and far vision.
  3. Compare rods and cones (location, sensitivity, color, acuity).

Eye anatomy

  • CorneaTransparent dome on the front. Provides about two-thirds of the eye's refractive power. Avascular.
  • Iris & pupilIris muscle controls pupil diameter: more light in or less. Sphincter pupillae (parasympathetic) constricts, dilator pupillae (sympathetic) dilates.
  • LensAdjustable focus via ciliary muscle. Shape changes for accommodation.
  • Aqueous humorWatery fluid in anterior chamber. Produced by ciliary body, drained at the canal of Schlemm. Pressure regulator.
  • Vitreous humorGelatinous fluid in posterior chamber. Maintains eye shape.
  • RetinaPosterior neural layer. Contains photoreceptors, bipolar cells, ganglion cells.
  • Fovea centralisCones only. Highest visual acuity. What you focus on lands here.
  • Optic discWhere axons exit the eye as the optic nerve. No photoreceptors, hence the blind spot.

Accommodation

  • Distance visionCiliary muscle relaxed. Suspensory ligaments taut. Lens flattens. Light from far objects converges on the retina.
  • Near visionCiliary muscle contracts. Suspensory ligaments slacken. Lens rounds up (more refractive power). Light from close objects converges on the retina.
  • PresbyopiaLens stiffens with age and cannot round up. Reading glasses needed.

Phototransduction

  • Rods~120 million per eye. Outside the fovea. Rhodopsin. Sensitive to low light, no color, low acuity.
  • Cones~6 million per eye. Concentrated at fovea. Three types: S (blue), M (green), L (red). Color and high acuity, needs bright light.
  • Signal pathPhotoreceptor → bipolar cell → ganglion cell → optic nerve → thalamus (LGN) → primary visual cortex (occipital lobe).
Dr. Sharilyn Rennie BIO 304 . Module 8 . Special Senses