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Special somatic afferent nerve Transection leads to blindness and no direct

pupillary light reflex

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Optic chiasma has decussating fibers from twonasal hemiretinas

Non crossing fibers from two temporal

hemiretinas Projects fibers to suprachiasmatic nucleus of

hypothalamus Midsagittal transection or pressure leads to

BITEMPORAL HEMIANOPIA Binasal hemianopia by bilateral lateral

compression(calcified ICAS)

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It contains fibers of contralateral nasalhemiretina and ipsilateral temporal

hemiretina It projects to ipsilateral lateral geniculate

body,pretectal nuclei and superior colliculus Transection causes CONTRALATERAL

HEMIANOPIA

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Six layered nucleus Layers 1,4 and 6 receive crossed fibers;layers

2,3 and 5 receive uncrossed fibers Receives input from layer VI(multiform) of

striate cortex (area 17) Receives fibers from contralateral nasal

hemiretina and ipsilateral temporalhemiretina It projects to layer IV of striate cortex through

geniculocalcarine tract

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It projects to visual cortex through twodivisions upper and lower

Upper division Projects to upper bank ofcalcarine sulcus(cuneus)

It contains fibers from superior retinalquadrants (inferior visual field quadrants)

Transection causes contralateral lowerquadrantanopia Bilateral destruction of cunei will lead to

lower altitudinal hemianopia

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Loops from lateral geniculate bodyanteriorly(Meyers loop),then posteriorly toend in lower bank of calcarine sulcus(lingualgyrus)

It contains fibers from inferior retinalquadrants (superior visual field quadrants)

Transection causes contralateral upperquadrantanopia(pie in the sky) Bilateral destruction of lingual gyri will lead to

upper altitudinal hemianopia

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It consists of upper bank(cuneus) and lowerbank(lingual gyrus)

Lesions cause CONTRALATERALHEMIANOPIA with macular sparing Posterior area receives macular input(central

vision) Intermediate area receives paramacular

input(peripheral input) Anterior area receives monocular input

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Retina the deepest tunic Composed of two layers

Pigmented layer single layer of melanocytes Neural layer sheet of nervous tissue

Contains three main types of neurons

Photoreceptor cells

Bipolar cells

Ganglion cells

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Two main types

Rod cells more sensitive to light

Allow vision in dim light Cone cells operate best in bright light

Enable high-acuity, color vision

Considered neurons

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Structures in the eye bend light rays Light rays converge on the retina at a single

focal point Light bending structures (refractory media)

The lens, cornea, and humors

Accommodation curvature of the lens isadjustable

Allows for focusing on nearby objects

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Most visual information travels to thecerebral cortex

Responsible for conscious seeing Other pathways travel to nuclei in the

midbrain and diencephalon

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Pathway begins at the retina

Light activates photoreceptors

Photoreceptors signal bipolar cells Bipolar cells signal ganglion cells

Axons of ganglion cells exit eye as the optic nerve

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Optic tracts send axons to:

Lateral geniculate nucleus of the thalamus

Synapse with thalamic neurons Fibers of the optic radiation reach the primary visual

cortex

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Some axons from the optic tracts

Branch to midbrain

Superior colliculi Pretectal nuclei

Other branches from the optic tracts

Branch to the suprachiasmatic nucleus

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The pupillary light reflex is a reflex thatcontrols the diameter of the pupil, inresponse to the intensity (luminance) of lightthat falls on the retina of the eye. Greaterintensity light causes the pupil to becomesmaller (allowing less light in), whereas lower

intensity light causes the pupil to becomelarger (allowing more light in). Thus, thepupillary light reflex regulates the intensity oflight entering the eye

http://en.wikipedia.org/wiki/Reflexhttp://en.wikipedia.org/wiki/Pupilhttp://en.wikipedia.org/wiki/Luminancehttp://en.wikipedia.org/wiki/Retinahttp://en.wikipedia.org/wiki/Eyehttp://en.wikipedia.org/wiki/Eyehttp://en.wikipedia.org/wiki/Retinahttp://en.wikipedia.org/wiki/Luminancehttp://en.wikipedia.org/wiki/Pupilhttp://en.wikipedia.org/wiki/Reflex

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Visible colored part of the eye Attached to the ciliary body

Composed of smooth muscle Pupil the round, central opening

Sphincter pupillae muscle (constrictor or circular)

Dilator pupillae muscle (dilator or radial)

Act to vary the size of the pupil

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The optic nerve is responsible for the afferent limb of the pupillary reflex - it senses the

incoming light. The oculomotor nerve is responsible for the efferent limb of the pupillary

reflex - it drives the muscles that constrict the pupil. Neuron 1

The pupillary reflex pathway begins with retinal ganglion cells, which convey information

from photoreceptors to the optic nerve (via the optic disc).

The optic nerve connects to the pretectal nucleus of the upper midbrain, bypassingthe lateral geniculate nucleusand the primary visual cortex.

Neuron 2

From the pretectal nucleus, axons connect to neurons in the Edinger-Westphal

nucleus,(crossed and uncrossed fibers) whose axons run along both the left and

right oculomotor nerves.

Neuron 3

Oculomotor nerve axons (preganglionic parasympathetic fibers) synapse on ciliaryganglion neurons.

Neuron 4

Ciliary ganglion gives rise to post ganglionic parasympathetic fibers which innervate the

constrictor muscle of the iris.

http://en.wikipedia.org/wiki/Afferenthttp://en.wikipedia.org/wiki/Efferenthttp://en.wikipedia.org/wiki/Ganglion_cellhttp://en.wikipedia.org/wiki/Photoreceptorhttp://en.wikipedia.org/wiki/Optic_nervehttp://en.wikipedia.org/wiki/Optic_dischttp://en.wikipedia.org/wiki/Pretectumhttp://en.wikipedia.org/wiki/Midbrainhttp://en.wikipedia.org/wiki/Lateral_geniculate_nucleushttp://en.wikipedia.org/wiki/Primary_visual_cortexhttp://en.wikipedia.org/wiki/Axonhttp://en.wikipedia.org/wiki/Edinger-Westphal_nucleushttp://en.wikipedia.org/wiki/Edinger-Westphal_nucleushttp://en.wikipedia.org/wiki/Oculomotor_nervehttp://en.wikipedia.org/wiki/Synapsehttp://en.wikipedia.org/wiki/Ciliary_ganglionhttp://en.wikipedia.org/wiki/Ciliary_ganglionhttp://en.wikipedia.org/wiki/Iris_(anatomy)http://en.wikipedia.org/wiki/Iris_(anatomy)http://en.wikipedia.org/wiki/Ciliary_ganglionhttp://en.wikipedia.org/wiki/Ciliary_ganglionhttp://en.wikipedia.org/wiki/Synapsehttp://en.wikipedia.org/wiki/Oculomotor_nervehttp://en.wikipedia.org/wiki/Edinger-Westphal_nucleushttp://en.wikipedia.org/wiki/Edinger-Westphal_nucleushttp://en.wikipedia.org/wiki/Edinger-Westphal_nucleushttp://en.wikipedia.org/wiki/Edinger-Westphal_nucleushttp://en.wikipedia.org/wiki/Axonhttp://en.wikipedia.org/wiki/Primary_visual_cortexhttp://en.wikipedia.org/wiki/Lateral_geniculate_nucleushttp://en.wikipedia.org/wiki/Midbrainhttp://en.wikipedia.org/wiki/Pretectumhttp://en.wikipedia.org/wiki/Optic_dischttp://en.wikipedia.org/wiki/Optic_nervehttp://en.wikipedia.org/wiki/Photoreceptorhttp://en.wikipedia.org/wiki/Ganglion_cellhttp://en.wikipedia.org/wiki/Efferenthttp://en.wikipedia.org/wiki/Afferent

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First Order Retina to Pretectal Nucleus inB/S

(at level of Superior colliculus) Second Order Pretectal nucleus to E/W

nucleus(bilateral innervation!)

Third Order E/W nucleus to Ciliary Ganglion Fourth Order Ciliary Ganglion to Sphincter

pupillae (via short ciliary nerves)

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Constricted (mioisis)

Sympathetic(pupillodilator)

denervation

Drugs

Pilocarpine

Morphine

Dilated (mydriasis)Parasympathetic (pupilloconstrictor)denervationLesion of the third CNDrugs

AtropineCocaine

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Oculosympathetic paresis

Ptosis

Miosis Ipsilateral anhidrosis

Does not dilate with cocaine4%

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First Order Posterior (paraventricularnuclei)Hypothalamus to ciliospinal centre of

Budge (C8-T2)(Uncrossed in Brainstem) Second Order Ciliospinal centre of Budge to

Superior Cervical Ganaglion Third Order Superior Cervical Ganglion to

dilator pupillae muscle. (Close toICA and joins V1 intracranially)

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Central B/S lesions (tumours, vascular andMS ) Syringomyelia,

Preganglionic Pancoast tumour, Carotid &Aortic aneurysms, Neck lesions/trauma,calung

Postganglionic Cluster headaches,

Nasopharyngeal tumours, Otitis media,Cavernous sinus mass and ICA disease. Miscellaneous Congenital (brachial plexus

injury) Idiopathic.

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Argyll-Robertson pupil

Small, irreg

Does not react to light

Reacts toaccommodation

Causes

syphilis diabetes

Miotonic pupil (Adies syndrome)

DilatedPoor response to light andconvergence.

Constricts with weakPilocarpineHolmes-Adie syndrome

Reduced tendon reflexes(Knee, ankle)

- Orthostatic hypotension

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Defective adduction of the ipsilateraleye

Nystagmus of the contralateral(abducting) eye

NORMAL CONVERGENCE

Causes Young patients

Bilateral

Demyelination

Older patients

Unilateral Vascular, tumours

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Localising the lesion

Monocular visual field defects indicatelesions anterior to the optic chiasm

Bitemporal defects are the hallmark ofchiasmal lesions

Binocular homonymous hemianopia result

from lesions in the contralateralpostchiasmal region

Binocular quadrantanopias reflect optic

tract lesions

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Area 17 visual associationarea(18,19) superior colliculus and

pretectal nucleus oculomotor complexof midbrain Rostral Edinger Westphal nucleus for

pupillary constriction via ciliary ganglion caudal Edinger Westphal nucleus for ciliary

muscle contraction Medial rectus subnucleus for convergence

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Frontal eye field area in poterior part ofmiddle frontal gyrus(8) for voluntary saccadic

movements of eyes Irritative lesion contralateral

conjugate deviation of eyes Destructive lesion transient ipsilateral

deviation of eyes

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Area 18, 19 concerned with involuntary trackand persuit movements of eyes

Stimulation contralateral conjugatedeviation of eyes

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Located in abducent nuclei of pons orparamedial reticular formation of pons

Input from contralateral frontal eye field Projects to ipsilateral lateral rectus muscle

and contralateral medial rectus subnucleus ofoculomotor complex via MLF

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