Visual Pathways

name the pathway from the eye to the brain

Retina

Optic Nerve

Optic Chiasm

Optic Tract Lateral

Geniculate Body

Optic Radiation

Visual Cortex 

what are receptive fields

• Circular receptive field centre

• Peripheral area

what are ON-neurons

neurons that are excited by light hitting the centre and inhibited by light hitting the peripheral area

what are OFFneurons

Neurons that have the opposite reaction to the light are known

Rods contains?

rhodopsin (Opsin and retinal (Vit A aldehyde))

what sort of vision does rods have

scotopic; more sensitive

Cones have what type of vision?

photopic

What do retinal ganglion cells express?

photopigment melanopsin

what does retinal ganglion cells convey?

general level of illumination

what are the 3 neurons in the retina called?

photoreceptor, bipolar cell, and ganglion cell

what do Bodies of bipolar cells form?

 inner nuclear layer

what are dendrites in contact with in the bipolar cell layer

base of rods and cones

when are on cells activated

light hits the photoreceptor and are inhibited in the dark

when are off cells activated

dark and inhibited in light

when are bipolar cells hyperpolarized in rods

when the light hits the rods

for the 3rd neuron, what are dendrites of ganglion cells in contact with?

with ON or OFF synaptic centers via axons of bipolar cells.

what do m and p cells have to do with 3rd neuron

types of neurons in the visual pathway that relay information to the third-order neurons in the brain's visual cortex

M-cells full name?

magnocellular

P-cells full name?

parvocellular

what do M cells process

process visual information related to motion and flicker,

what do P (parvocellular) cells process

details like color and high-resolution shape

describe the characteristics of P-cells

smaller cell bodies, a less extensive dendritic tree, and a thinner axon than M-cells

name a major difference between P and M cells

P-cells respond preferentially to light with a particular wavelength. P-cells are color-specific, whereas M-cells do not have such specificity

name 2 interneurons of retina

amacrine cells and horizontal cells

what is Amacrine cells responsible

interaction between ON and OFF synaptic centres

what do amacrine cells increase

contrast and the detection of motion

what do horizontal cell regulate

transmission from the photoreceptors to the bipolar cells

what is horizontal cells responsibility

typical receptive fields of the bipolar cells and ganglion cells with central excitation and lateral inhibition

how do ganglion cells exit the eye

extending their axons through the optic disk to form the optic nerve

what is the horizontal diameter of the disc

1.7 mm

what is the vertical diameter

1.9 mm

what is a physiologic blind spot

disc contains no photoreceptor cells, light incident on the disc does not elicit a response

optic nerve length

5-6 cm

Optic Nerve Intraocular

0.7 – 1mm

Optic Nerve Intraorbital

30 mm

Optic Nerve Intracanalicular

6 – 10 mm

Optic Nerve Intracranial

10 – 16 mm

what is the Optic Chiasm surrounded by

Meningeal sheaths and cerebrospinal fluid

Optic Chiasm lies within where?

circle of Willis, a circle of blood vessels that is a common location for aneurysms

what is the Optic tract

Cylindric, slightly flattened band of fibers approximately 3.5 mm high and 5.1 mm long

where does the optic tract run from?

the posterolateral corner of the optic chiasm to the LGN

where does optic tract terminate at

LGN

where is visual information processed

Lateral Geniculate Nucleus, then is relayed to higher cortical centres

what is terminated in Lateral Geniculate Nucleus

etinal axons

name the 3 layers that LGN is structured

Magnocellular layers

parvocellular layers

koniocellular layers

what cells does magnocellular layer contain?

large

what cells does parvocellular layer contain?

medium

what cells does koniocellular layer contain?

small

where does Optic Radiation extend from

from LGN to Striate cortex

what is Optic Radiation grouped into

Temporal radiations (form the Meyer's loop)

Parietal radiations

what do Temporal radiations represent

contralateral superior field

what is contralateral superior field

upper-half of the visual field on the opposite side of the brain from a lesion

what do parietal radiations represent

contralateral inferior field

what are parietal radiations

deficit in the lower-left or lower-right quarter of one's vision, caused by damage to the opposite side of the brain

what is Visual cortex also known as

Striate cortex (V1)

how many systems are responsible for visual cortex

3

how is the first system formed

by three cortical columns

for the first system in visual cortex, what are the three cortical columns specific for?

specific for perception from left and right eye for binocular vision and depth perception

what is the second system in visual cortex composed for?

cells that receive information from identical retinal positions and have the same axes of orientation;

what does the second system in visual cortex provide?

perception of movement

how is the 3rd visual cortex organised into

into columns that form the irregular spots on the transverse sections called “blobs”.

what are the “blobs” in the 3rd visual cortex responsible for

perception of color

what are the areas between the “blobs” in the 3rd visual cortex called

“interblobs” which are localized neurons

specific for the perception of shape

NAME

left abopia

NAME

Bitemporal Hemianopia

NAME

Right Homonymous Hemianopia

NAME

Right Homonymous Superior Quadrantopia

name A

Left Anopia

name B

Bitemporal Hemianopia

name C

Right Homonymous Hemianopia

name D

Right Homonymous Superior Quadrantopia