Optic Nerve and Visual System

What nervous are the retina and optic nerve part of?

CNS

What is the function of the Retina

encodes visual information in the discharge of neurons that project through the optic nerve (CN 11)

What is the function of the sclera

Attachment site for extraocular muscles

Where does the optic nerve (CN 11) emerge from?

Optic Nerve (CN 11)

What is the cornea? (Description)

Transparent portion of eye over the anterior pole

What is the optic nerve homologous with?

Spinal cord WHITE matter

T/F the Optic nerve is a peripheral nerve and is capable of regeneration

FALSE - optic nerve is NOT a peripheral nerve and therefore is NOT capable of regeneration

What is the function of the cornea

allows light to enter the eye

What nervous system controls the Iris

Autonomic nervous system (think the IRS automatically takes all your money :()

Define the optic disc

Region where retinal axons leave the eye in the optic nerve starting medial to fova

Are radial fibers parasympathetic or sympathetic

Sympathetic

What are the two types of fibers found in the Iris

Circular Fibers

Radial Fibers

What is the function of Circular fibers?

constricts pupils to reduce the amount of light falling onto the retina

What is the function of the radial fibers

Dilate pupil

What is found in the ciliary body

Ciliary muscles that alter the shape of the lens

What is the function of ciliary muscles

Alter the shape of the lens

What area is also known as the “blind spot”

Optic disc

What is the area for maximal visual acuity?

Fovea Centralis

What is found within the Fovea centralis?

ONLY cones

What is found within the macula Lutea

Mostly cones; few rods

What are the two kinds of retina

1. Non-Neural

2. Neural

What is the function of the pigment epithelium

Refracts and partially absorbs the light before it reaches the photoreceptors

What is the retina?

Inner surface of choroid; photoreceptive

What is the function of the Neural Retina

Transduce light to electrical impulses by a series of photochemical reactions and physiochemical changes

What is the neuron pathways of the neural retina?

1st order - bipolar cells in retina

2nd order- ganglion cells that form optic nerve

Inter neuron- Horizontal & amacrine cells

What is the function of Interneurons (horizontal & amacrine) in neural retina

Modulate transmission

What is the function of 2nd order ganglion cells

Generate action potentials

What is the Neural retina

Photoreceptors that interdigitate with the pigment epithelium

What is more numerous rods or cones?

Rods are 20x more numerous than cones

What are rods sensitive too?

Very sensitive to light; NOT sensitive to color

What are cones sensitive to?

Response to bright light; sensitive to color and shape

Where are cones most commonly found

Most numerous in fovea

What type of photoreceptor helps you see in the dark or dim light?

Rods!

What are the 4 functions of the Visual Association Cortex

1. Interpret visual images

2. Recognition

3. Depth perception

4. Color vision

Cause of Monocular Blindness

cataract, intraocular hemorrhage, or retinal detachment

Cause of Bitemporal Hemianopia

Compression of optic chasm by pituitary tumor

Definition of Bitemporal Hemianopia

Loss of peripheral vision/tunnel vision

Cause of Homonymous Hemianopia

Vascular or neoplastic lesions of the optic tract, optic radiation or occipital cortex

Define Homonymous Hemianopia

Loss of Contralateral visual field

List the 5 steps of the Visual Pathway

1. Retinal ganglion axons assemble at optic disc

2. Travel in the optic nerve (CN II)

3. Converge in the optic chias

   1. Medial portion decussate to contralateral side

   2. Lateral portion remain ipsilateral

4. Axons travel to thalamus

5. Thalamocortical neurons (3rd order) project to the primary visual cortex of the occipital lobe

When axons travel to the thalamus a small number bypass the thalamus and go to the ____ and ____ for mediation of the ______ reflex

Pretectal region

Superior colliculi

Pupillary light reflexes

What are the two types of Pupillary Light reflexes

1. Direct light reflex

2. Consensual light reflex

What is direct light reflex

illumination of retina causes the pupil to constrict

What is the consensual light reflex

Constriction of the non-illuminated eye

Where are Thalamocortical neurons (3rd order) primary located

Medial aspect of the occipital lobe above and below calcarine sulcus