Module 21 - Special Senses: Vision Flashcards
What is the palpebrae
Palpebrae: Refers to the eyelids, which protect the eye and help spread tears across the surface.
What is the palpebral fissure
Palpebral Fissure: The opening between the upper and lower eyelids, which can vary in size depending on factors like alertness or eye shape.
What is the canthus (or commissure)
Canthus (or Commissure): The corners where the upper and lower eyelids meet. There are two:
Medial Canthus: The inner corner, closer to the nose.
Lateral Canthus: The outer corner, closer to the temple.
What is the caruncle
Caruncle: A small, pinkish spot of tissue located at the medial canthus. It contains sweat and oil glands and can sometimes produce a small amount of discharge.
What is palpebral conjunctiva
Palpebral Conjunctiva: Lines the inner surface of the eyelids.
Covers the back side of the eyelids, ensuring a smooth surface that contacts the eye.
Helps in tear distribution and provides lubrication for the eyelids and eye.
what is bulbar conjunctiva
Bulbar Conjunctiva: Covers the anterior (front) surface of the eyeball, specifically the white part (sclera), but does not cover the cornea.
Transparent and allows the underlying white sclera to show through.
Provides protection and lubrication for the eye’s surface.
Describe the flow of tears
Also, excess tears in lacrimal sac drain into nasolacrimal duct and reaches the nose. That’s why your nose runs when you cry.
what are the 3 tunics of the eye
fibrous tunic, vascular tunic, retina
what is the fibrous tunic
Sclera – shape, protection, attachment of muscles
Continuous with the Cornea (bends light) (avascular)
what is the vascular tunic
Choroid – blood supply
Anterior – ciliary body (secretes aqueous humor and alters shape of lens for near or far vision) and iris (regulates amount of light into eyeball)
Contains melatonin to darken eye
what is the retina
Innermost layer of the eye
Contains photoreceptor cells - Cones (6-7M) and Rods (120M)
what does the vitreous humor do
The vitreous humor is a clear, gel-like substance that maintains the eye’s shape, allows light to pass through to the retina, cushions the eye against shocks, and helps keep the retina in place for proper vision.
what is the optic blindspot
The optic blind spot is a small area on the retina where the optic nerve exits the eye, lacking photoreceptors, which creates a gap in the visual field that the brain typically fills in.
what do the anterior and posterior chambers do in the eyes?
The anterior and posterior chambers of the eye, filled with aqueous humor, maintain pressure, help shape the eye, and provide nutrients to the eye’s tissues, including the cornea and lens.
what does the ciliary body do
The ciliary body produces aqueous humor (the fluid in the anterior and posterior chambers) and controls the shape of the lens for focusing by contracting and relaxing the ciliary muscles, which enables the eye to adjust for near and distant vision.
Describe the movement of action potential in retina
Describe the movement of light in retina
explain how we convert light into electrical signals in the eye. (cycle)
Starting State (Dark Configuration):
Retinal is inactive, and opsin is in its dark configuration.
Na⁺ channels are open due to high levels of cGMP.
Light Activation:
Light exposure activates retinal, changing it to an active form.
Opsin also changes to its light configuration.
Phosphodiesterase Activation:
The activated opsin triggers phosphodiesterase (PDE), which becomes active.
cGMP Breakdown:
Active phosphodiesterase converts cGMP to GMP, reducing cGMP levels.
Na⁺ Channel Closure:
With less cGMP available, Na⁺ channels close, reducing the flow of Na⁺ into the cell.
Return to Inactive State:
Retinal returns to its inactive form with energy input (ATP).
cGMP levels are restored, reopening Na⁺ channels, returning to the dark configuration.
Cycle Completes:
The system resets, ready to respond to new light stimuli.
Explain how light exposure influences the way info is transmitted.
Rod Cell in Darkness (Unstimulated):
Rhodopsin is in its dark configuration.
Na⁺ channels are open due to high levels of cGMP.
The rod cell continuously releases the neurotransmitter glutamate.
Glutamate inhibits the connected bipolar cell, preventing it from activating.
Exposure to Light (Hyperpolarization):
A light pulse changes rhodopsin to its light configuration, activating the signal cascade.
Phosphodiesterase (PDE) becomes active and converts cGMP to GMP, reducing cGMP levels.
Na⁺ channels close, causing the rod cell to hyperpolarize (membrane potential becomes more negative).
Reduction in Glutamate Release:
Hyperpolarization of the rod cell decreases the release of glutamate.
With less glutamate, the bipolar cell is no longer inhibited.
Activation of Bipolar Cell:
The bipolar cell becomes active due to the lack of inhibition.
The bipolar cell releases neurotransmitters to the next cells in the visual pathway, forwarding the signal for processing by the brain.
Describe the neural pathways for vision
