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43 Cards in this Set

  • Front
  • Back

What is the route of the Visual pathway?

Optic nerve


Optic chiasma


Optic tract


Lateral geniculate nucleus


Optic radiations


Visual cortex

Label the following

Label the optic nerve cross section

What are the 4 parts to the optic nerve?

Intraocular (1mm)


Intraorbital (30mm)


Intracanicular (6-9mm)


Intracranial (10mm)

What is the intraocular part of the optic nerve?

Passes through sclera, Choroid and appears in eye as optic disc.



• It consists of 4 portions

What are the 4 portions of the intraocular part of the optic nerve?

From anterior to posterior:



a) surface nerve fibre layer.


b) prelaminar region.


c) lamina cribrosa.


d) retrolaminar region.

What is the Intraorbital part?

• Extends from back of eyeball to optic foramina.



• Surrounded 3 layers of meninges & subarachnoid space.



•Near optic foramina, optic nerve surrounded by annulus of Zinn & the origin of four recti muscles.



• Some fibres of superior & medial rectus are adherent to its sheath so painful ocular movement in retrobulbar neuritis.

Describe the Internal structure of the Intraorbital portion.

•Myelination



•20-30 mm Long



•Axons: myelin and glial cell (metabolic support)

What and Where is the intracanalicular portion?

• Medial wall of canal forms lateral wall of sphenoid



• Within canal: meninges, ophthalmic artery and sympathetic plexus.



10 mm length



Related to ophthalmic artery.

What is the intracranial part?

•Leaves the cranial end of the optic canal (medially, backwards, upwards).


•4-15 mm (depending on the position of chiasm).


•Lies above cavernous sinus & converges with its fellow to form chiasm.


•Sheathed in pia mater.


What is the optic chiasma?

Area where nerve fibres arising from nasal half of two retina decussate at the chiasm.

How big is the optic chiasm?

•12mm wide


•8mm Anterio-posteriory


•Flat structure


•4 mm thick

What is the blood supply around the chiasma?

What are the optic tracts?

• Bundles of nerve fibres running outwards and backwards from postero-lateral aspect of the optic chiasm.

What do the optic tracts consist of?

Fibres from temporal half of retina of same eye & nasal half of opposite eye.


• Posteriorly each ends in Lateral Geniculate Nucleus

What is the lateral geniculate nucleus?

Oval structures situated at termination of the optic tracts.

What does the lateral geniculate nucleus consist of?

Each consist of 6 layers of neurons (grey matter) alternating with white matter (optic fibres)

What are the 2 main layers of the lateral geniculate nucleus?

• Parvocellular layers


•Magnocellular layers

What are the Parvocellular layers ?

(Form and Colour):


small cells, color sensitive



high spatial resolution (small RF)



low temporal resolution (does not see fast flickers of light)



Receive inputs from P type Retinal cells.

What are the Magnocellular layers?

(motion):



large cells, color blind



low spatial resolution (large RF)



high temporal resolution (good for processing motion stimuli)



They receive inputs from M type retinal cells.

What is the function of the lateral geniculate nucleus?

• Relay station to relay visual information from optic tract to visual cortex.



• To gate transmission of signal to visual cortex.

What layers of the lateral geniculate nucleus, do the contralateral fibres go to?

Crossed fibers -1,4,6

What layers of the lateral geniculate nucleus, do the ipsilateral fibres go to?

Uncrossed fibers - 2,3,5

What is the posterior aspect of the lateral geniculate nucleus represent?

Posterior aspect represents central 15-20 degrees of visual field


What is the anterior aspect of the lateral geniculate nucleus represent?

Anterior aspect has 4 layers, layers 4 and 6 merge, and 3 and 5, represents the peripheral field

What are the K layers?

Between each of the M and P layers. K cells are functionally and neurochemically distinct from M and P cells and provide a third channel to the visual cortex.

What are the optic radiations?



• Extends from the LGN to the visual cortex.


• Fibres ascend before sweeping laterally as well as posteriorly


Where do the medial and lateral fibres from the LGN through the optic tracts go?

• Fibres in medial aspect travel straight to visual cortex.



(Peritial lobe)


superior retinal fibres



Fibres in lateral aspect sweep forward then loop around – Meyer’s loop.



(Temporal lobe)


inferior retinal fibres

What are the temporal lobe/radiations



Consist of inferior retinal fibres (superior visual field).



Macula splitting



Blood supply -Posterior cerebral artery but also supply visual cortex

What is the Peritial lobe/ radiations?

Consists of superior retinal fibres pass proceed directly toward the visual cortex



•Blood supply middle cerebral artery



•Fibres deep within the parietal lobe are more closely grouped.

What the 3 major parts of the Brain?

• Cerebrum - 4 lobes


• Cerebellum


• Brain stem

What is the Cerebrum?

•Largest part of the brain


•Right and left hemispheres


What is the function of the cerebrum?

Performs higher functions


touch


vision


hearing


speech


reasoning


emotion


learning


fine control of movement

Where is the cerebellum?

Located under the cerebrum


What is the function of the cerebellum?

coordinate muscle movements


maintain posture


maintain balance

What does the Brain stem consist of?

Includes the midbrain, pons, and medulla


What is the function of the Brain stem?

•Relay center connecting the cerebrum and cerebellum to the spinal cord.



•Performs many automatic functions such as breathing, heart rate, body temperature, wake and sleep cycles, digestion, sneezing, coughing, vomiting, and swallowing.

What originates from the brainstem?

10 of the 12 cranial nerves

What is the visual cortex?

•Outer 4-6 mm cerebrum


•Grey matter – large number ofnerve cells


•Underlying white matter


•Embryological development - grey matter folds


•Deep folds fissures


•Shallower folds sulci


•Cortex – two hemispheres


•Visual cortex area that receives visual input

Where is the visual cortex located?

On medial aspect of occipital lobe


• Divided into areas:


-Striate area 17


-Striate area 18 and 19

What is the primary visual cortex?

Also know as the striate cortex where the perception of the visual stimuli become what we see.

What does the primary visual cortex consist of?

•Brodmann’s area 17


• V1


•Visual cortex


• Striate cortex

What are simple cortical cells?

•Respond best to bars or edges of light in a particular location in the receptive field and in a particular orientation (e.g., 45 degrees)



All simple cells are monocular


• They also have on and off areas