Chapter 41: Vision Flashcards
What is happening in the eyes?
o Photons are being transduced into electrical activities (action potentials)
Transform the image to the brain through action potential using sensory cells
o Eye is an optical portion; contains a lens
What is the liquid part of the eye found in the cornea?
Aqueous humor
What are the three layers of the eye?
Fibrous (protection), Vascular (Blood), and Neural (Brain)
What makes up the Fibrous layer of the eye?
Sclera and cornea
What is the sclera?
• Thick layer that serves a protection and muscle attachment
o Muscles need to be precisely aligned
• White part of the eye
What is the cornea?
-Front part of the eye • Anterior part of the eye • Thick, transparent membrane • Covers the colored part of the eye • Curved (convex) o Facilitates the travel of light waves in the proper direction • The first thing light hits
What makes up the vascular layer of the eye?
Choroid, Iris, Lens, and Ciliary muscles
What is the choroid?
Pigmented layer that contain blood vessels
• Dark part
What is the iris?
(colored part of the eye)
• Smooth muscle; involuntary
• Not continuous, has a hole in the middle called the pupil
o Pupil is used to get light through from the cornea to the neural layer
• Determines the size of the pupil
o Dim light: Radial smooth muscles contract, pupils dilate
o Bright light: circular smooth muscles contract, pupil constricts
What is the lens?
• Made of connective tissue.
• Convex curve. Can change shape
• Focus point
o Stretches/thickens to accommodate focus (elongate or shorten. Accommodation)
What are the ciliary muscles
• Smooth muscles
• Terminate with tiny fibers called zonular fibers
o Allows for accommodation in focus
What is accommodation?
- Object is far: ciliary muscles are relaxed, the zonular fibers become tight, causing the lens to flatten
- Object is near: ciliary muscles are contracted, the zonular fibers are loose, causing the lens to rounded (thick)
What makes up the neural layer of the eye?
Retina
What is the retina?
Where tranduction occurs
Contains neurons and photoreceptors
What are photoreceptors?
o Photoreceptors are scattered all over the retina
Concentrated in the fovea centralis
• Where you can see the most details
o Photoreceptors (Excitable cells. Contain pigments)
When photoreceptors are on, we don’t send signals to the brain
What two things do photoreceptors contain?
Rods and cones
What are rods?
Rods: Sensitive to light, any small amount of light will activate them
• Pigment called Rhodopsin (contain retina)
o S: blue light
o M: Green light
o L: Red light
What happens to the rods in the light?
o Light hits the retinal and rhodopsin
o Changes conformation, and so does rhodospin
o Transducin (Alpha, beta, gamma)
o Alpha subunit moves and causes phosphodiesterase
Breaks down cyclic cGMP
Causes sodium channels to close. HYPERPOLARIZATION
No neurotransmitter release
No graded potential
What happens to the rods in the dark?
o Are depolarized (not needed at the time) Due to Na+ channels
cGMP dependent
o Triggers receptor potential
o Do not fire action potential
o VGCC activated and neurotransmitter released
What are cones?
Cones: form synapses with bipolar cells and multipolar cells (ganglion cells). Less sensitive to light
• Pigment called Photopsin (contain retina)
• S (blue), M (green), L(Red)
• Helper cells: amacrine cells and horizontal cells
What are the five kinds of cells that photoreceptors contain?
Ganglion, Amacrine, horizontal, bipolar, rods/cones
Neural Pathway of vision
o Binocular vision: visual feel
We see things part with our left eye and part with our right eye
• Depth perception
o Information travels from the eyes to the optic nerve to the optic chiasm to the optic tract to the lateral geniculate nucleus to the visual cortex
o Central vision: perceived by BOTH eyes
Macula lutea
o Peripheral vision: only seen by one eye
Right/Left peripheral vision
What is Strabismus?
When the muscles of the eye are not properly attached
