Cranial Nerve Pathways Flashcards
describe the optic nerve pathway
receptor cells stimulate the 1st neuron (bipolar) -> links the photoreceptor and synapses onto a ganglion cell (2nd neuron) -> the axons of ganglion cells exit the posterior part of the eye and exit as the optic nerve
describe the visual pathway
ganglionic neurons travel through the optic chiasm -> optic tract -> sensory/visual info goes to the thalamus (LGN) -> the 2nd order neuron finishes at the LGN and synapses with 3rd order neuron -> 3rd order neuron will go the the primary visual cortex (all the axons of the 3rd order neuron make up the optic radiation) -> the optic radiation extends back through part of the parietal and part of the temporal to get to the primary visual cortex on the bank of the calcarine sulcus
where does the temporal visual field project to?
medial nasal retina
where does the nasal visual field project to?
lateral temporal retina
which fibres (from nasal or temporal retinae) decussate (cross over) at the optic chiasm?
fibres from the nasal retina
where does the information from the superior visual field hit?
information from the upper visual field comes through the pupil and hits the inferior retina and maintains that inferior position to the LGN and travels through the temporal lobe
where does the information from the inferior visual field hit?
information from the lower visual field comes through the pupil and hits the superior retina and maintains superior position to the LGN and passes through the parietal lobe
what is a lesion in the optic nerve called (draw what it would look like if it happened to the right visual pathway)
monocular vision loss
what is a lesion in the optic chiasm called (draw what it would look like if it happened to the right visual pathway)
bitemporal hemianopia
what is a lesion in the optic tract called (draw what it would look like if it happened to the right visual pathway)
contralateral homonymous hemianopia
what is a lesion in the temporal part of the LGN called (draw what it would look like if it happened to the right visual pathway)
contralateral superior quadrantantopia hemianopia
what is a lesion in the parietal part of the LGN called (draw what it would look like if it happened to the right visual pathway)
contralateral inferior quadrantantopia hemianopia
what is a lesion in the optic radiation called (draw what it would look like if it happened to the right visual pathway)
contralateral homonymous hemianopia
what does the medial longitudinal fasciculus connect
interconnects oculomotor, trochlear, abducens and vestibular (3,4,6,8)
what are the two types of protective reflexes
corneal blink reflex and pupillary light reflex
what are the three types of coordination of eye movements
gaze, vestibulo-ocular reflex (VOR), accommodation
describe the corneal blink reflex
protective reflex to remove foreign particles and lubricates the eye
- ophthalmic division of trigeminal nerve CN V
- synpases in spinal trigeminal (nociception) and chief sensory (touch) nuclei
- interneurons synapse bilaterally w/ facial nucleus motor neurons
- facial nerve CN VII innervates orbicularis oculi ‘blink’
describe the pupillary light reflex
shine bright light in 1 eye (other eye shielded from light), stimulates CN II, fibres travel in both optic tracts, collaterals through brachium of superior colliculus to pretectal area, pretectal neurons project bilaterally via posterior commissure to Edinger-Westphal nuclei, CN III parasympathetic fibres to ciliary ganglion, post ganglionic neurons innervate constrictor pupillae
what are the 2 conjugate movements of gaze
saccades (fast) and smooth pursuit movements (slow)
describe the conjugate movement of saccades of gaze
redirect gaze so a different image falls on the fovea, use them when exploring the environment visually, the initiation of saccades: frontal eye field (FEF), supplementary eye field, parietal eye field= projects to contralateral PPRF (or riMLF) +/- superior colliculus (which then projects to PRFF)
describe the conjugate movement of smooth pursuit movement of gaze
used to keep an image on the fovea, due to either movement of the object or movement of self, use cortical (visual), cerebellar and vestibular feedback
describe vestibulo-ocular reflex (VOR)
photoreceptors are sensitive but slow, very fast reflex, generated fast eye movements to compensate for head movements in order to keep the fovea fixed on an object, adjust saccades, cerebellar input can cancel VOR
describe accomodation
- involves the cerebral cortex
- focusing on a near object
3 requirements: - convergence so that the object falls on both fovea
- increase curvature of the lens to increase refractive power to focus the image on the fovea
- pupillary constriction- reduces blur and increases depth of field
what happens: - CN II afferents to bilateral LGN (thalamus)
- primary visual cortex
- visual association cortex
- project to pretectal area
- oculomotor and Edwinger-Westphal nuclei
- CN III: somatic fibres to medial rectus: parasympathetic . fibres to ciliary muscles and constrictor pupillae
