Chapter 41: Vision

Question 1

What is happening in the eyes?

Answer 1

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

Question 2

What is the liquid part of the eye found in the cornea?

Answer 2

Aqueous humor

Question 3

What are the three layers of the eye?

Answer 3

Fibrous (protection), Vascular (Blood), and Neural (Brain)

Question 4

What makes up the Fibrous layer of the eye?

Answer 4

Sclera and cornea

Question 5

What is the sclera?

Answer 5

• Thick layer that serves a protection and muscle attachment
o Muscles need to be precisely aligned
• White part of the eye

Question 6

What is the cornea?

Answer 6

-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

Question 7

What makes up the vascular layer of the eye?

Answer 7

Choroid, Iris, Lens, and Ciliary muscles

Question 8

What is the choroid?

Answer 8

Pigmented layer that contain blood vessels

• Dark part

Question 9

What is the iris?

Answer 9

(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

Question 10

What is the lens?

Answer 10

• Made of connective tissue.
• Convex curve. Can change shape
• Focus point
o Stretches/thickens to accommodate focus (elongate or shorten. Accommodation)

Question 11

What are the ciliary muscles

Answer 11

• Smooth muscles
• Terminate with tiny fibers called zonular fibers
o Allows for accommodation in focus

Question 12

What is accommodation?

Answer 12

• 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)

Question 13

What makes up the neural layer of the eye?

Answer 13

Retina

Question 14

What is the retina?

Answer 14

Where tranduction occurs

Contains neurons and photoreceptors

Question 15

What are photoreceptors?

Answer 15

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

Question 16

What two things do photoreceptors contain?

Answer 16

Rods and cones

Question 17

What are rods?

Answer 17

 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

Question 18

What happens to the rods in the light?

Answer 18

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

Question 19

What happens to the rods in the dark?

Answer 19

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

Question 20

What are cones?

Answer 20

 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

Question 21

What are the five kinds of cells that photoreceptors contain?

Answer 21

Ganglion, Amacrine, horizontal, bipolar, rods/cones

Question 22

Neural Pathway of vision

Answer 22

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

Question 23

What is Strabismus?

Answer 23

When the muscles of the eye are not properly attached