Neuroanatomy Lecture #28: The Visual System

Front 1

Def of hemianopia

Back 1

Loss of one half of the visual field

Front 2

Heteronymous anopia

Back 2

Different visual field defect in both eyes

Front 3

Organization of the Visual Field:
• Def of point of fixation
• How the extension of the visual field is measured
• Other terms for the visual hemifields, specifically for the right eye
• The generic names for the 4 quadrants of the visual field
• Describing the position of the blind spot with respect to quadrants and point of fixation

Back 3

Organization of the Visual Field:
• The center of the visual field
• It is measured in degrees of maximum deviation from the point of fixation
• For the right eye
- L visual hemifield = nasal visual hemifield
- R visual hemifield = temporal visual hemifield

• Superior (left and right), Inferior left and right)
• It is ~15 degrees to the right of the point of fixation

Front 4

The visual field and the retina:
• Describe how the visual field is projected onto the retina

Back 4

The visual field and the retina:
• It is projected inversely on to the retina
- The superior half is projected onto the inferior half
- The nasal visual hemifield is projected onto the temporal hemiretina

Front 5

Visual Pathway 1: The Left Superior Quadrant
• The location of its retinal targets (2)
• The course of the above retinal fibers and where they synapse

• After the synapse,
- the name of these new fibers
- the pathways they use and their synapse
> the relative location of this synaptic target

Back 5

Visual Pathway 1: The Left Superior Quadrant
• Its retinal targets
- The inferior portion of the nasal hemiretina of the left eye
- The inferior portion of the temporal hemiretina of the right eye

• The course after the retina
- The left inferior nasal hemiretina crosses the optic chiasm
- The right inferior temporal hemiretina stay ipsilateral
* Both will synapse at the right LGN

• After the LGN,
- the fibers emerge as the optic radiation with the
> contralateral fiber using the nasal radiation pathway and
> ipsilateral fiber using the temporal radiation pathway

- Both will synapse in the inferior portion of V1
> below the calcarine sulcus

Front 6

Visual Pathway 2: The Left Inferior Quadrant

• The location of its retinal targets (2)
• The course of the above retinal fibers and where they synapse

• After the synapse,
- the name of these new fibers
- the pathways they use and their synapse
> the relative location of this synaptic target

Back 6

Visual Pathway 2: The Left Inferior Quadrant

• Its retinal targets
- The Superior portion of the nasal hemiretina of the left eye
- The Superior portion of the temporal hemiretina of the right eye

• The course after the retina
- The left Superior nasal hemiretina crosses the optic chiasm
- The right Superior temporal hemiretina stay ipsilateral
* Both will synapse at the right LGN

• After the LGN,
- the fibers emerge as the optic radiation with the
> contralateral fiber using the nasal radiation pathway and
> ipsilateral fiber using the temporal radiation pathway
- Both will synapse in the superior portion of V1
> above the calcarine sulcus

Front 7

The Primary Visual Cortex
• Location of Brodmann's area
• Where the major portion of V1 is represented
> Side of the brain
> describe w/ respect to a sulcus

• its blood supply (branches of major source, major source and minor source)

Back 7

The Primary Visual Cortex
• 17

• The major portion of V1 is represented
> on the medial side of the brain
> along the banks of two gyri, superior & inferior to the calcarine sulcus

• its blood supply
- Major: Calcarine branches from the PCA
- Minor: MCA

Front 8

Organization of V1:

• Term used for the topographic organization present here and what it means

• Where the following halves of the visual field are represented
- left half
- right half
- inferior portions
- superior portions
- center
> also, another name for this portion of the visual field
- peripheral

Back 8

Organization of V1:

• Retinotopic - refers to positions of stimuli on the retina

• Where the following halves of the visual field are represented on V1
- left half --> right hemispheric V1
- right half --> left hemisheric V1
- inferior portions --> superior to calcarine sulcus
- superior portions --> inferior to calcarine sulcus
- center --> close to the occipital pole
> another name is the macular region
- peripheral --> closer to the parieto-occipital sulcus

Front 9

Two types of columns in V1

Back 9

Ocular dominance and Orientation columns

Front 10

Describe the wiring of Ocular dominance columns from sensory fibers of the LGN

Back 10

• Sensory fibers from one eye of the LGN do not terminate in the same area of V1 as that of the contralateral eye

• Separate areas/columns in the cortex exist as dedicated inputs to each eye

Front 11

Discuss the type of experiment performed by Hubel and Wiesel that lead to the dscovery of orientation columns.
- Include the general name of the experiment, the region of the brain and parameters measured and what was proved

Back 11

Experiment w/ single cell recording

• Using a recording electrode placed in V1, the activity of single cells were recorded by presenting the subject with different orientations of horizontal bars of light

• Cells that showed the most sensitivity to a particular orientation had the highest frequency of APs recorded

• The results concluded that:
- V1 was structured into columns, in this instance for orientation
- every cell in one cortical column has a preference for a certain orientation of a light bar.
- the preferred orientation in neighboring orientation columns is different

Front 12

Two specialized parallel pathways for visual information, where their cells originate, where they synapse, the type of stimuli they discriminate and their trajectory after synapsing (this trajectory has 3 names)

Back 12

Magnocellular Pathway
- consist of M cells in the retina that synapse in the 1st two layers of the LGN
- They discriminate for motion and depth
- After the LGN, they form a dorsal/parietal pathway (what pathway)

Parvocellular cells
- consist of P cells in the retina that synapse in the last 4 layers of the LGN
- They discriminate for form and color
- After the LGN, they form a ventral/inferior temporal pathway (where pathway)

Front 13

The Confrontation Visual Test
• what it's used
• how it's tested

Back 13

The Confrontation Visual Test
• used to test loss of vision
• each quadrant of the visual field of each eye is tested
- Patient and examiner are standing at twice the arm's length in front of one another
- patient occludes one of their eyes
- examiner moves their hand from the periphery to the center of the visual field to determine where it is seen first

Front 14

Type of lesion: Optic nerve
Visual defect produced:
Possible origin:

Back 14

Type of lesion:
Visual defect produced: Monocular blindness
Possible origin: Optic neuritis

Front 15

Type of lesion: Optic chiasm
Visual defect produced:
Possible origin:

Back 15

Type of lesion:
Visual defect produced: Bitemporal hemiopia
Possible origin: Pituitary tumor

Front 16

Type of lesion: Optic tract
Visual defect produced:
Possible origin:

Back 16

Type of lesion:
Visual defect produced: Homonymous hemianopia
Possible origin: temporal lobe tumor

Front 17

Type of lesion: Temporal radiation (Meyer's Loop)
Visual defect produced:
Possible origin:

Back 17

Type of lesion:
Visual defect produced: Homonymous
Superior quadratic anopia
Possible origin: Temporal or Occipital lobe tumor

Front 18

Type of lesion: Parietal radiation
Visual defect produced:
Possible origin:

Back 18

Type of lesion:
Visual defect produced: Homonymous inferior quadrantic anopia
Possible origin: Parietal or occipital lobe tumor

Front 19

Type of lesion: Visual cortex
Visual defect produced:
Possible origin:

Back 19

Type of lesion:
Visual defect produced: Homonymous
hemianopia
Possible origin: Posterior cerebral artery dysfxn

Front 20

Macula sparing:
• definition
• Usual etiology

Back 20

Macula sparing:
• visual field deficits not involving the macula
• The MCA, the vessel supplying the occipital pole and macular vision, is not compromised but the PCA or any of its branches are