Cranial Nerve Pathways

Question 1

describe the optic nerve pathway

Answer 1

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

Question 2

describe the visual pathway

Answer 2

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

Question 3

where does the temporal visual field project to?

Answer 3

medial nasal retina

Question 4

where does the nasal visual field project to?

Answer 4

lateral temporal retina

Question 5

which fibres (from nasal or temporal retinae) decussate (cross over) at the optic chiasm?

Answer 5

fibres from the nasal retina

Question 6

where does the information from the superior visual field hit?

Answer 6

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

Question 7

where does the information from the inferior visual field hit?

Answer 7

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

Question 8

what is a lesion in the optic nerve called (draw what it would look like if it happened to the right visual pathway)

Answer 8

monocular vision loss

Question 9

what is a lesion in the optic chiasm called (draw what it would look like if it happened to the right visual pathway)

Answer 9

bitemporal hemianopia

Question 10

what is a lesion in the optic tract called (draw what it would look like if it happened to the right visual pathway)

Answer 10

contralateral homonymous hemianopia

Question 11

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)

Answer 11

contralateral superior quadrantantopia hemianopia

Question 12

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)

Answer 12

contralateral inferior quadrantantopia hemianopia

Question 13

what is a lesion in the optic radiation called (draw what it would look like if it happened to the right visual pathway)

Answer 13

contralateral homonymous hemianopia

Question 14

what does the medial longitudinal fasciculus connect

Answer 14

interconnects oculomotor, trochlear, abducens and vestibular (3,4,6,8)

Question 15

what are the two types of protective reflexes

Answer 15

corneal blink reflex and pupillary light reflex

Question 16

what are the three types of coordination of eye movements

Answer 16

gaze, vestibulo-ocular reflex (VOR), accommodation

Question 17

describe the corneal blink reflex

Answer 17

protective reflex to remove foreign particles and lubricates the eye

1. ophthalmic division of trigeminal nerve CN V
2. synpases in spinal trigeminal (nociception) and chief sensory (touch) nuclei
3. interneurons synapse bilaterally w/ facial nucleus motor neurons
4. facial nerve CN VII innervates orbicularis oculi ‘blink’

Question 18

describe the pupillary light reflex

Answer 18

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

Question 19

what are the 2 conjugate movements of gaze

Answer 19

saccades (fast) and smooth pursuit movements (slow)

Question 20

describe the conjugate movement of saccades of gaze

Answer 20

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)

Question 21

describe the conjugate movement of smooth pursuit movement of gaze

Answer 21

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

Question 22

describe vestibulo-ocular reflex (VOR)

Answer 22

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

Question 23

describe accomodation

Answer 23

• 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