Exam 3 Week 14 ppt 3&4 optics & projections

Question 1

How does light refract in convex lens?

Answer 1

Convex lens will bend light at different angles along its curved surface & will focus light coming from a distant image at fixed point some distance from the convex lens

Question 2

focal length of a convex lens

Answer 2

-point at which the light is focused -dependent upon the shape of the convex lens

Question 3

focal length in normal eye

Answer 3

matches the distance from lens of eye and retina so image is focused on the retina

Question 4

What is myopia?

Answer 4

–Nearsightedness
–Overly curved lens & focal length falls short of retina
–Corrected with the use of a concave lens to lengthen the focal distance

Question 5

What is Hyperopia?

Answer 5

–Farsightedness
–Lens not curved enough so focal length falls behind the retina
–Corrected with the use of a convex lens to shorten the focal distance

Question 6

How does lens accomidate for near and far vision?

Answer 6

–Lens is pliable & changes shape
–The lens is held by suspensory ligaments whose tightness is controlled by the ciliary muscles.

Question 7

How do ciliary muscles respond For vision > 20 ft

Answer 7

relaxed & suspensory ligaments taut

Question 8

How is lens affected For vision > 20 ft?

Answer 8

Lessened curvature of lens to adapt to far vision

Question 9

How do ciliary muscles accommodate for close vision?

Answer 9

contract & suspensory ligaments loose

Question 10

How does lens accomidate for close vision?

Answer 10

Greater curvature of lens to adapt to close vision

Question 11

How does accommodation affect pupils? (4)

Answer 11

1. Change in pupillary diameter
2. Pupils constrict for close vision
3. Constricted pupils produce a greater depth of field so objects at different distances will still stay in focus
4. Depth of field need for reaching of close objects

Question 12

How do parasympathetics to eye come into play during accomidation?

Answer 12

1. Oculomotor nerve (CN III) from Edinger-Westphal nucleus via ciliary ganglion
2. Pupils constrict & ciliary muscle contracts

Question 13

What is presbyopia?

Answer 13

–Lens hardens with age
–Age related loss of power accommodation even though ciliary muscles can still contract
–Results in inability to focus on near objects

Question 14

Visual field

Answer 14

portion of space that can be viewed from the retina when the eye is fixated straight ahead

Question 15

Retinal field

Answer 15

the portion of retina that alters its firing rate in response to a stimulus

Question 16

Action of lens with regards to visual and retinal field

Answer 16

•reverses and inverts image so reversed & inverted relationship between the visual and retinal fields

Question 17

1° afferent pathway

Answer 17

bipolar cells

Question 18

pathway of 2° neuron with ganglion cell

Answer 18

–Axons form optic nerve
–Axons from nasal retinal field decussate in optic chiasm but temporal retinal fields stay ipsilateral
–So right visual field goes to left brain & left visual field goes to right brain via the optic tract

Question 19

Pathway of 3° neurons - Lateral geniculate nucleus of thalamus (6 points to know)

Answer 19

–Retinotopic pattern with half of LGN devoted to fovea
–Respond similar to ganglion cells with “on” or “off” center and opposing surround
–Only 10-20% synapses from optic tract
–Most input from visual cortex & brainstem reticular formation

• Cortical inputs provide feedback regulation of flow of information to cortex and is related to visual attentiveness
• Brainstem input is part of switch of attentiveness between sensory inputs

Question 20

What do neurons of the LGN project as?

Answer 20

optic radiation or geniculocalcarine tract to the occipital lobe

Question 21

Where do dorsal axons from the inferior visual field project to?

Answer 21

almost directly to the occipital lobe

Question 22

Geniculocalcerine tract: Describe the two pathways, where their axons are from in the visual field, and where they end

Answer 22

Superior visual field axons:

• –Ventral axons (from the superior visual field) project anteriorly and downward as Meyer’s loop
• –Inferior retinal (superior visual) field goes to inferior aspect of calcarine sulcus

Inferior visual field axons:

• –Dorsal axons (from the inferior visual field) project almost directly to the occipital lobe
• –Superior retinal (inferior visual) field goes to superior aspect of calcarine sulcus

Question 23

Describe the path of the superior visual field axons in the geniculocalcarine tract:

Answer 23

Superior visual field axons:

• –Ventral axons (from the superior visual field) project anteriorly and downward as Meyer’s loop
• –Inferior retinal (superior visual) field goes to inferior aspect of calcarine sulcus

Question 24

Describe the path of the inferior visual field axons in the geniculocalcarine tract:

Answer 24

Inferior visual field axons:

• –Dorsal axons (from the inferior visual field) project almost directly to the occipital lobe
• –Superior retinal (inferior visual) field goes to superior aspect of calcarine sulcus

Question 25

Geniculocalcarine tract (4)

Answer 25

1. Ventral axons (from the superior visual field) project anteriorly and downward as Meyer’s loop
2. Inferior retinal (superior visual) field goes to inferior aspect of calcarine sulcus
3. Dorsal axons (from the inferior visual field) project almost directly to the occipital lobe
4. Superior retinal (inferior visual) field goes to superior aspect of calcarine sulcus

Question 26

What is direct retinohypothalamic projection?

Answer 26

Small contingent of optic tract axons terminate in the hypothalamus – suprachiasmatic nucleus

Question 27

Role of direct retinohypothalamic projection
>

Answer 27

–entraining circadian rhythms in day–night cycle

Question 28

Where do some optic tract axons go specifically that bypass the LGN and project to in midbrain? (2)

and what is the function of projections to those areas?

Answer 28

1. Superior colliculus for visual reflexes
2. Accessory optic & pretectal area for visual light reflexes (pupillary constriction)

Question 29

Pulvinar- 3 points to know

Answer 29

1. Largest thalamic nucleus
2. Receives input from the superior colliculus, visual cortex & pretectum
3. Sends info to visual association areas in the posterior parietal lobe to supplement dorsal stream

Question 30

what specific nucleus do the retinohypothalamic projections go to?

(and what is it part of?)

Answer 30

the suprachiasmic nucleus of the hypthalamus