The Visual Pathway Neurons
1st Order |
Photoreceptors to Bipolar Cells |
2nd Order |
Bipolar cells to Ganglion cells |
3rd Order |
Ganglion cells to Thalamus (LGN) |
4th Order |
Thalamus (LGN) to Visual Cortex |
Visual Pathway Site Lesions
Optic nerve |
Ipsilateral monocular blindness |
Optic Chiasm (lateral) |
Ipsilateral monocular nasal hemianopia |
Optic tract |
Contralateral homonymous hemianopia |
Optic radiation |
Contralateral homonymous quadrantanopia |
Occipital cortex |
Contralateral homonymous hemianopia with macular sparing |
Visual Pathway Blood Supply
Optic nerve |
Ophthalmic artery |
Optic chiasm |
Branches from: Internal carotid Posterior communicating artery Anterior cerebral artery Anterior communicating artery |
Optic tract |
Middle cerebral artery (MCA) |
Lateral geniculate nucleus |
Anterior choroidal branches of the MCA Thalamogeniculate branches of the posterior cerebral artery (PCA) |
Optic radiations |
MCA |
Calcarine sulcus |
Mostly by the PCA. The MCA also helps supply the anterior portion, which corresponds to the macula |
Accommodation Pathway
Retina --> |
Visual cortex (allows tracking of object to face) |
Visual cortex --> |
Midbrain (recruit pupillary reflex center) |
Midbrain --> Reflex Center -> |
Eye (Edinger-Westphal – constriction lens rounding) Oculomotor Nuc (convergence) |
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Taste Pathway (Ipsilateral) CN VII, IX, X
First order |
Sensory neurons to Solitary nucleus |
Second order |
Solitary nucleus to Thalamus (VPM) |
Third order |
Thalamus (VPM) to Cortex |
Olfaction Pathway (Ipsilateral; No Thalamus)
First order |
Olfactory nerves to Olfactory bulb |
Second order |
Olfactory bulb to Olfactory Temporal Cortex |
Motor Cranial Nerve (LMN) Lesions
Oculomotor |
CN III |
Extraocular muscles, levator palpebrae |
Diplopia; Loss of: pup. constriction, accommodation, medial gaze; lateral deviation (“down and out”), ptosis |
Trochlear |
Trochlear |
Superior oblique |
Diplopia; upward-inward gaze |
Trigeminal Motor |
CN V |
Muscles of mastication |
aw weakness, open jaw deviates to same side |
Nucleus Ambiguus |
CN IX,X |
Pharyngeal/laryngeal muscles |
Difficulty swallowing, loss of gag, hoarse voice, dysarthria; uvula deviates to opposite side |
Anterior horn C1-5 |
CN XI |
Sternocleidomastoid, trapezius |
Weakness in shoulder shrug and turning head to opposite side |
Hypoglossal |
CN XII |
Tongue muscles |
Tongue deviates to same side on protrusion |
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Drugs to treat Parkinson
Levodopa |
Dopamine precursor |
nausea, vomiting, hallucinations, delusions |
Carbidopa |
Dopa decarboxylase inhibitor |
nausea, vomiting, hallucinations, delusions |
Entacapone, Tolcapone |
COMT inhibitor |
nausea, vomiting, hallucinations, delusions, hepatoxicity |
Rasagiline |
MAO-B inhibitor |
nausea, hallucinations Serotonin syn, tyramine effect |
Amantadine (For dyskinesia) |
Increases dopamine release, inhibits reuptake |
ataxia, livedo reticularis |
Benztropine, Trihexyphenidyl (For tremors) |
Anti cholinergic |
dry mouth, ¯ sweating, constipation, urinary retention, blurry vision |
Eye Infections
Blepharitis |
Inflammation of the eyelid, skin, lashes |
Red, scaly or flaking eyelid skin |
Lid Hygiene |
Stye |
nfection of Zeis, Moll, Meibomian glands |
Painful swelling and redness of gland |
Warm compress, antibiotics |
Chalazion |
Obstruction of Zeis or Meibomian glands |
Painless, rubbery nodules |
Warm compress, massage, antibiotics |
Conjunctivitis |
nflammation of the conjunctiva; bacterial or viral; allergy |
Red eye with engorged vessels |
Self-limiting, antibiotics |
Keratitis |
Inflammation of cornea– bacterial, viral, fungal, parasitic |
red eye, photophobia, irritation, discharge, lacrimation, flurecein dye - ulcer |
Antibiotics/virals |
Anterior Uveitis |
Inflammation of the middle layer of the eye, infection, systemic inflammation, idiopathic |
photophobia, pain, redness of eye/limbus, WBCs in anterior chamber, hypopyon |
Pupillary dilation, anti-inflam, anti-viral, steroids |
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