LO 10

Learning Objectives for Chapter 16 (Bio 241)

1. Layers of the Neural Tunic of the Eye Wall

  • Photoreceptor Cell Layer:

    • Outermost neural layer of the retina.

      • Contain rods + cones

  • Bipolar Cell Layer:

    • Middle layer: dendrites receive synaptic input from rods + cones.

  • Ganglion Cell Layer:

    • Innermost neural layer

2. Structures of the Three Tunics of the Eye

  • Fibrous Tunic:

    • Tough outer layer

    • Sclera:

      • White part of eye

      • Composed of dense irregular CT    

    • Cornea:

      • Convex, transparent structure at front of the eye.

  • Vascular Tunic:

    • Middle layer w/ many blood vessels.

    • Composed of three regions:

    • Choroid, ciliary body, Iris:

      • iris:

        • Colored part of the eye.

        • Contains smooth muscle, melanocytes (pigment cells), blood vessels, and neural structures.

  • Retina:

    • Internal or neural tunic

    • Divided into:

    • Pigmented Layer

    • Neural Layer: houses photoreceptors (rods and cones) and associated neurons.

3. Diabetic Retinopathy

  • Definition:

    • A serious eye condition caused by long-term high blood sugar levels damaging the blood vessels in the retina.

  • Implications:

    • It is one of the leading causes of vision loss in adults.

4. Optic Discs

  • Definition:

    • contain no photoreceptor— 2blind spot.

    • where ganglion axons exit toward the brain

5. Definitions

  • Glaucoma:

    • when pressure within the eye increases to dangerous levels, compressing retina + optic nerve

    • can lead to blindness if untreated

  • Astigmatism:

    • A vision problem caused by an irregular curvature of the cornea or lens, preventing light from focusing on a single point on the retina.

6. Steps of Photoreception

  • Photoreception occurs when light hits the retina, causing visual pigments in rods and cones to change shape.

  • This activates a G-protein pathway (opsin → transducin → PDE) that decreases cGMP levels.

  • Low cGMP closes Na⁺/Ca²⁺ channels, hyperpolarizing the photoreceptor.

  • Hyperpolarization reduces neurotransmitter release, allowing the signal to be sent to bipolar and ganglion cells, then to the brain.

7. Cerumen and its Function

  • Definition:

    • Cerumen is a yellow-brown waxy substance known as earwax.

  • Function:

    • Serves as a sticky trap for foreign bodies entering the ear and repels insects.

8. Auditory Ossicles

  • Definition:

    • Three tiny bones of middle ear.

      • Malleus

      • incus

      • stapes

9. Structures of the Inner Ear

  • Cochlea:

    • houses membranous cochlear duct

  • Vestibule:

    • Contains two sac-like structures:

      • utricle and saccule; interconnected and positioned at right angles

  • Semicircular Canals:

    • contain memrbanous semicircular canals

10. Structures Responsible for Equilibrium
1. Vestibular Nuclei (Brainstem)

  • Receive input from visual and proprioceptive sensors (especially neck muscles).

  • Send commands to eye and neck muscles.

  • Maintain balance and stable vision.

2. Cerebellum

  • Integrates eye and body signals.

  • Coordinates muscle activity and tone.

  • Maintains posture, head position, and balance.



11. Process of Hearing

  • Sound vibrations hit the tympanic membrane → move the ossicles (malleus, incus, stapes).

  • Ossicle movement transmits vibrations to cochlear fluid.

  • Fluid movement bends hair cells against the tectorial membrane, opening ion channels → action potentials.

  • Signals travel via the cochlear nerve → auditory cortex → auditory association cortex for interpretation.