Transcript Innervation of the Eye and Orbit

Innervation of the Eye and
Orbit
Part 1: The Optic Nerve and
its Projections
•VS112
A sensory organ with complex
mobility
Performing the basic neurological exam
of the eye isn’t difficult, but to
accurately diagnose a problem requires
knowledge of the wiring and
connections that underlie the
observable behaviors.
There are a lot of terms, anatomy and
pathways you’ll need to know.
Organization
 Optic Nerve - pathways, lesions.
 Cranial Nerves - who’s on first.
 Parasympathetic & Sympathetic.
 Nerve Damage, Growth and Development.
Background: Neurons
 What is a nerve cell?
 What is their job and how to they do
it?
 Anatomy of a cell. (Fig 5.1)
 Gather information (synaptic
input)
 encode information
 Deliver information (Fig 5.2)
•Different morphologies
for different
specialization of nerve
function.
Nerve Action
 Membrane potential
 Excitability
 Receptor potential
 Synapses
 Inhibition
 Action potentials
Synapses are communication
sites
Synapses: Cell to cell
connections: Electrical vs.
Chemical
•Fig 5-1
Lecture 1 Optic Nerve and
Optic Pathways
 Parsing out the pathways.
 Central Destinations.
 Lesions and Visual Fields.
Optic Nerve (sensory output)
 Forming the nerve - GANGLION
Cells
(5.3)
Economy of movement or flow
Geographical segregation
 Organizing the flow of information
Step 1: Nasal/Temporal
Visual Fields
Left Brain Right Right Brain (5.5)
Forming the nerve - GANGLION
Cells (5.3)
•Temporal fibers coalesce at the chiasm
Visual Fields
(5.4 draw on board)
 Nasal field = temporal retina
 Temporal (lateral) field = ??
 Superior field (sky) = inferior
retina
 E.g.: mouse or rabbit blue
cone density
 Inferior field (earth) = ??
Primary Optic
Pathway is to the
LGN and on to
striate cortex
•Contralateral visual field
•Through ipsilateral eye’s
nasal retina,
•And contralateral eye’s
temporal retina
Decussation at the Chiasm
 Information sorting begins here (Fig. 5.5)
 Partial cross-over of ganglion cell fibers
organizes the visual world into left vs.
right visual fields
 Temporal - tight (short- non crossing)
 Nasal - meandering (crosses over)
Decussation follows a pattern
related to the visual fields.
•Fig 5-5 draw on overhead
Lesions of the Optic Pathway
 Optic nerve => one entire eye (5.12)
 Split chiasm => loss of crossing fibers
(nasal retina=temporal visual fields)
 Optic tract =>Loss of contralateral
visual field
 Partial chiasm - unpredictable due to
meandering fibers (5.13)
Visual field deficits predict
location of the lesions
Projections of the optic nerve
(5.7)
 Lateral Geniculate Nucleas (main relay
to cortex)
 Superior Colliculus (eye movement)
 Pretectal Nuclei (pupillary light reflex)
 Accessory optic system
 Biological clock (suprachiasmatic n.)
Brainstem and Midbrain
(Fig5-7)
Lateral Geniculate Nuclei paired structure.
 90% of G-cell projection (fig 5.8-10)
 Distinctly layered structure (6 layers -
monkey)
 Layer specific to eye (1,4,6
contralateral)
 Layers 2,3,5 ispsilateral eye
 Retinotopic mapping
Lateral
Geniculate
nucleas is part of
the thalamus- a
paired structure,
important for
relaying
information to
cortex
The Big Picture
•LGN is a layered structure
Retino-topic mapping
•An exaggeration of the foveal input
•Fig 5.9
Central 5° of visual field (3% of retina) covers 50% of LGN and
visual cortex.
Multiple maps overlie one
another in the layers of LGN
•Layer 1,4,6
contralateral
•Layer 2,3,5
ipsilateral
•Retinotopic
maps overlie,
meaning that
common
points in
visual fields
stack in the
layers.
LGN - organization Summary
 Left LGN - right visual field
From left eye temporal retina
Right eye nasal retina
 Retinotopic mapping
2,3,5 ipsilateral
1,4,6 contralateral
(6 -copies)5.8-5.9
Layer 1 & 2 Magnocellular (large cells)
Layers 3-6 parvocellular
 Maps are in register in layers 5.10
Superior colliculus
 Largest axon bundle for non-visual
projections
 Axon collaterals create retinotopic map
Contralateral visual field (diagram on
board)
Binocular-non-segregated input
Under-represented fovea
 Input from many sites (eye movement
- related)
Projections to superior colliculi
From left eye
Fig 5-11
From right eye
X
Left eye
•ipsilateral visual field has no blind spot
Pretectal nuclei
- Grab bag of 5 nuclei receiving
G-cell inputs
 Olivary (projects to Edinger-Westphal
nuclei) and involve in pupillary light
reflex
 Nucleus of the optic tract - eye
movement controls
 Anterior, posterior and medial pretectal
nuclei (specific functions unknown).
Accessory Optic System
 Three pairs of nuclei receive small
inputs from ganglion cells
 Output to vestibular nuclei and
cerebellum
 Thought to be involved in coordinating
head/eye movements
Suprachiasmatic Nucleus
 Part of the hypothalamic
pathway
 Degeneration studies
show direct input from
the retina
 Thought to be part of
circadian clock (jet lag.
S.A.D.)
Summary
 Optic Nerve
 Formation
 Crossing at chiasm
 Projections
 LGN
 Visual field segregation
 Contra - ipsi-lateral eye separation
 Functional G-cell type separation
 Parvo and magno pathways
 SCN, AON, Sup Coll, Pretectal