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neuro > Visual System > Flashcards

Visual System Flashcards

1
Q

What are the major structures of the EYE?

A

Anatomy of the Eye: Major Structures

  • Sclera: Outer layer AKA “white of the eye” and continues as the Optic Nerve
  • Cornea: Anterior 1/6 of the Sclera and transparent structure
  • Choroid: Middle layer containing blood supply and includes the Ciliary Body
  • Ciliary Body: Structure that alters the shape of the Lens
  • Lens: Structure that focuses light on the Retina
  • Iris: Color of the Eye and determines Pupil Size (Constriction and Dilation)
  • Retina: Inner layer on the posterior aspect of the Eye and converts light into action potentials in CN II (Optic Nerve)
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2
Q

What are the parts of the RETINA? What do they do?

A

Parts of the Retina

  • Fovea
    • Small depression in the Retina of the eye where Visual Acuity is highest.
    • Retinal Cones are particularly concentrated here.
    • Central region of the Retina or Central Fixation point for each Eye
    • Encompasses 1% to 2% of Visual Field yet…
    • Encompasses 50% of the Optic Nerve and Primary Visual Cortex
  • Optic Disk
    • Point where neurons converge and exit the Eye AKA Blind Spot
  • Macula
    • Area surrounding the Fovea
    • Area of high Visual Acuity
    • Information ends up at most posterior aspect of Calcarine Sulcus
  • Photoreceptor Cells make up one of the layers of the Retina
    • Rods: “Where is it?” and key for Peripheral Vision, Dim Lighting
      • Responds to change in light to dark, black to white
    • Cones: “What is it?” and key for Central Vision, Bright Lighting
      • Important for Visual Acuity
      • Responds to Color, Detailed Stimuli, Visual Discrimination
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3
Q

What are the divisions of the RETINA and the VISUAL FIELDS?

A

Divisions of the Retina and Visual Fields

  • Light enters the Lens
  • Image is formed and INVERTED
  • Visual Fields AKA Receptive Fields have a relationship with Retinal Images
  • Definition of Visual Fields: The space or environment detected by the Retina
  • Configuration
    • Right Visual Field – Image on Left Retina
    • Left Visual Field – Image on Right Retina
    • Superior Visual Field – Image on Inferior Retina
    • Inferior Visual Field – Image on Superior Retina
  • Binocular Vision
    • Vision with Both Eyes
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4
Q

What are the pathways from space/environment to eye to the Primay Visual Cortex?

A

Visual Fields and Retina: Pathway to Primary Visual Cortex

  • Visual Info from Left Visual Field projects onto
    • Left (Eye) Nasal Hemiretina
    • Right (Eye) Temporal Hemiretina
  • Visual Info from the Right Visual Field projects onto
    • Right (Eye) Nasal Hemiretina
    • Left (Eye) Temporal Hemiretina
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5
Q

What are the Optic Radiations? What are the paths to the primary visual cortex?

A

Optic Radiations and Retinotopic Map:

Pathway to Primary Visual Cortex

  • Visual Info from Superior Visual Fields falls on Inferior Retinal Quadrants and projects onto Inferior Calcarine Sulcus (Primary Visual Cortex)
  • Visual Info from Inferior Visual Fields falls on Superior Retinal Quadrants and projects onto Superior Calcarine Sulcus (Primary Visual Cortex)
  • Therefore:
    • What falls on the Retina corresponds to what projects to the Calcarine Sulcus
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6
Q

What is the….

  • Visual Receptive Pathway
  • Visual Field Pathway
  • Retinogeniculostriate Pathway
  • Optic Nerve (CN II) Pathway….?
A

Optic Nerve (CN II) Pathway

  • MUST have light for Functions of VISUAL ACUITY and CONTRAST
  • Pathway:
    • Light enters the eye and stimulates Rods and Cones on Retina
    • Action Potential generated along Optic Nerve
    • Then through Optic Chiasm
    • Then through Optic Tracts
    • To Lateral Geniculate Nucleus (LGN) in the Thalamus
    • Then through Optic Radiation onto Calcarine Sulcus (Primary Visual Cortex)
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7
Q

What is the additional pathway

Additionally…Tectal Pathway?

A
  • Fibers from Retina to Superior Colliculi (SC) in the Brainstem Tectum
  • Superior Colliculi are major relay stations which communicate with LGN for Functions of Eye- Hand Coordination and Saccades
  • Major Pathway for Functions of Visual Attention and Detection of Motion in the Environment
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8
Q

What is the additional pathway…Additionally…Medial Longitudinal Fasciculus (MLF) Pathway?

A

Additionally…Medial Longitudinal Fasciculus (MLF) Pathway

  • From Superior Colliculi, fibers project to Medial Longitudinal Fasciculus
  • Involves…
    • Vestibular Nuclei in the Brainstem
    • Vestibular System
    • VESTIBULO-OCULAR REFLEX (VOR)
  • Functions…
    • Coordination between Cervical Spinal Cord Levels for control of Neck Muscles and Head and Eye Movement
    • Ex. Visual Fixation with Head Movement
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9
Q

What is the

Visual Reflex Pathway

Oculomotor Nerve (CN III) Pathway

Light ReflexPathway

Pupillary Reflex Pathway?

A

Pupillary Reflex Pathway

  • Function…
    • Reflex from both Direct Response or Consensual Response to light for Constriction of Pupil
  • Pathway…
    • Light enters eye and Information travels along Optic Nerve through Optic Chiasm through Optic Tracts
    • Then projects to Pretectum/Pretetal Area of Brainstem
    • Then to the Edinger-Westphal Nucleus AKA Accessory Oculomotor Nucleus (BILATERALLY) part of CN III Nuclei
    • Then, Preganglionic Parasympathetic Neuron synapses with Postganglionic Parasympathetic Neuron in the Ciliary Ganglion
    • Postganglionic Parasympathetic Neuron innervates smooth muscle of Pupillary Sphincter
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10
Q

What is the function of the Accommodation Reflex Pathway

Near Reflex Pathway Convergence Pathway?

A
  • Functions…
    • Adjustment of the Lens to bring objects into Focus with Near to/from Far Vision
    • Critical for Convergence (Medial Eye Movement) involving Visual Cortex
    • Therefore, role in Conscious Control of selection of objects on which to focus
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11
Q

​What is the pathway for the accomodation reflex

  • Near Reflex Pathway Convergence Pathway?
A

Near Reflex Pathway Convergence Pathway

    • Visual Receptive Pathway (CN II) to Visual Cortex
      • Axons from Visual Cortex (V19) and Frontal Cortex (Area 8) AKA Frontal Eye Fields descend to…
      • Optic Radiation and then to Superior Colliculi and Reticular Formation
      • Interneurons synapse with Preganglionic Parasympathetic Neurons of EWN (via CN III)
      • Then, synapse with Postganglionic Parasympathetic Neurons in Ciliary Ganglion
      • Postganglionic Parasympathetic Neurons innervate Ciliary Body that regulates Lens to bring objects into Near Focus (Accommodation)
      • Additionally, Postganglionic Parasympathetic Neurons cause contraction of Pupillary Sphincter causing Pupillary Constriction
      • Additionally, CN III motor innervation of Medial Recti Muscles of the Eye cause Medial Eye Movement for Convergence
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12
Q

Summarize the structures and functions of the accomodation reflex pathway?

A

Accommodation Reflex Pathway

Near Reflex Pathway Convergence Pathway

  • Summary of Structures and Functions
  • Ciliary Muscles contract and fatten Lens (AKA Accommodation) to Focus Near Images on Retina
  • Medial Recti Muscles contract for medial eye movement for Convergence on Near Objects
  • Pupillary Sphincter contracts to cause Pupillary Constriction to aid in Near Focus of Image
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13
Q

What are the functions of the Ocular Motor Control Pathway?

A

Ocular Motor Control Pathway

    • Range of Motion or Motor Control of Eyes and Visual Attention
      * Conjugate Eye Movement and Convergence
      * Visual Fixation (Gaze Stabilization): VOR
      * Saccades and Smooth Pursuits
      • Coordinates with Vestibular System and Neck Musculature for Head Control/Head Position
      • Key for Vestibulo-Ocular Reflex (VOR) that stabilizes image on retina during head movement
      • Key in activation of Frontal Eye Fields (Area 8) in Frontal Cortex for quick voluntary eye movement and directed attention called Saccades
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14
Q

What is the pathway for the Ocular Motor Pathway?

A

Ocular Motor Pathway

    • Starts in Occipital Lobes and Visual Association Areas
      • Fibers project to and controlled by Superior Colliculi and Pontine Reticular Formation (Visual Attention)
      • Fibers of Oculomotor CN III, Trochlear CN IV and Abducens CN VI in Brainstem innervate Eye Musculature
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15
Q

What are the directions of Gaze guided by?

A

Direction of Gaze Guided by…

  • Brain Stem Centers
    • Controls horizontal & vertical movements
  • Frontal Eye Fields
    • Voluntary eye movements
  • Posterior Parietal Cortex
    • Directs visual attention/spatial information
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16
Q

What are the key visual structures and their functions?

A

Visual Structures and Functions

  • Summary of KEY Visual System Processing Centers
  • Lateral Geniculate Nucleus (LGN)
    • Visual Reception and Visual Perception
  • Superior Colliculi
    • Range of Motion of the Eyes and Saccades
  • Pretectum
    • Pupillary Movement and Visual Light Reflex
17
Q

What are the sensory and visual perceptual functions?

A

Sensory and Visual Perceptual Functions

  • Visual Processing
    • Primary Visual Cortex (Area 17)
    • Visual Association Cortex (Area 18)
    • Higher Order Visual Association Cortex (Area 19)
  • Higher Order Processing Pathways
    • Parieto-Occipital Association Cortex: Dorsal Pathways or Dorsal Stream (Where and Spatial Processing)
    • Occipito-Temporal Association Cortex: : Ventral Pathways or Ventral Stream (What and Form Processing)
  • Other Parallel Processing
    • Frontal Eye Fields
    • Left Hemisphere: Visual and Verbal Processing
    • Right Hemisphere: Visual and Non-Verbal, Perceptual, and Spatial Processing
18
Q

What are the areas on the brain for the visual cortex?

A

Visual Cortex

  • Primary Visual Cortex
    • VI or Area 17
  • Association Areas
    • V2 & V3 or Areas 18 & 19
    • Inputs from Temporal Lobe & Parietal Lobe
  • Blood Supply
    • PCA & MCA
19
Q

What is the Dorsal Stream? What is the Ventral Stream?

A

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