09c visual system which cranial nerves are involved chapter 12
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09c Visual System: Which cranial nerves are involved? Chapter 12. Vision, as used for communication involves sight + movement of eye! Vision is an active process, not just passive. Remind yourself of relationship between vision and communication, as related to clinical practice.

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09c Visual System: Which cranial nerves are involved? Chapter 12

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09c visual system which cranial nerves are involved chapter 12

09cVisual System:Which cranial nerves are involved?Chapter 12


09c visual system which cranial nerves are involved chapter 12

Vision, as used for communication involves sight + movement of eye!

Vision is an active process, not just passive.


Remind yourself of relationship between vision and communication as related to clinical practice

Remind yourself of relationship between vision and communication, as related to clinical practice.

  • How are eyes used in expressive communication?

  • How are eyes used in receptive communication?

  • Does receptive communication using eyes involve both sensory pathways to eye, motor pathways to eye, or both?


09c visual system which cranial nerves are involved chapter 12

II: Sensory

III, IV, and VI: Motor


Visual sensory ii visual motor iii iv vi

Visual sensory: II Visual motor: III, IV, VI


Visual sensory ii optic nerve

Visual sensory: II (Optic nerve)


C n ii receptors dendrites and cell body in retina

C.N. II: Receptors, dendrites and cell body in retina

  • Bipolar cell

  • Bundles of retinal bipolar cell axons emerge from retina, and make up the two optic nerves (c.n. II)

    • One for each eye

    • Right and left optic nerves join at optic chiasm


09c visual system which cranial nerves are involved chapter 12

  • Distribution of photosensors

    • Rods- peripheral retina

    • Cones- central retina (macula lutea/fovea centralis)

  • Functions of photosensors

    • Sensitive to rays of different wavelengths

    • Cones- day vision, acuity, color vision

      • Nonfunctional in dark

    • Rods- night vision and shades of green

      • Nonfunctional in bright or daylight


09c visual system which cranial nerves are involved chapter 12

  • Transduction

    • Absorption of electromagnetic energy by visual pigments

    • Conversion into neural impulses


09c visual system which cranial nerves are involved chapter 12

  • Pupillary Aperture

    • Protective mechanism in intense light

    • Regulation of light amount entering eyes

    • Dilator & constrictor muscle fibers of iris

      • Bright light- parasympathetic constriction of pupil

        • Small amount of light in

      • Dim light- sympathetic dilation;

        • greater amount of light in


Pupillary light reflex

Pupillary light reflex


Superior view

Superior view

Optic nerves (c.n. II) are in the PNS.

Optic nerves join at the optic chiasm.


09c visual system which cranial nerves are involved chapter 12

Where is the optic nerve (PNS), with reference to the brainstem?

Ventral (frontal) view

Lateral view


09c visual system which cranial nerves are involved chapter 12

Where does the visual pathway continue after optic nerve? (Trace 1st order and 2nd order visual sensory neurons: Superior view)

  • Crossing at optic chiasm

    • Some fibers cross, but not all

  • Optic tract (in CNS)

  • Synapse at lateral geniculate body (in thalamus)

  • Optic radiation

  • End in primary visual cortex (medial occipital lobe)


Projections to cortex

Projections to cortex


Trace 1 st order and 2 nd order visual sensory neurons lateral view

Trace 1st order and 2nd order visual sensory neurons: Lateral view

  • Optic nerve

  • Optic chiasm

  • Optic tract (in CNS)

  • Synapse at lateral geniculate body/

    (nucleus in thalamus)

  • Optic radiation

  • End in primary visual cortex (medial occipital lobe)


09c visual system which cranial nerves are involved chapter 12

Optic nerve (II) coming from eyes;

optic chiasm;

optic tract coursing back to lateral geniculate body

Ventral (frontal) view

Lateral view


09c visual system which cranial nerves are involved chapter 12

Which side of the retina of each eye transduces light energy :…from left visual hemifield?…from right visual hemifield?


How is cranial nerve ii tested

How is cranial nerve II tested?

  • Testing of visual fields

    • Cut #1: blindness

    • Cut #2: bitemporal heteronymous hemianop(s)ia

    • Cut #3 homonymous hemianop(s)ia (same would happen with complete cut across 5&6)

    • Damage to primary visual cortex: cortical blindness (cortical visual impairment)

Horizontal plane

(brainstem)


Now consider the cranial nerves associated with visual motor function iii iv vi

Now, consider the cranial nerves associated with visual motor function: III, IV, VI


Muscles of visual motor system

Muscles of visual motor system

  • Move eye

  • Control eyelid opening

  • Control pupil dilation

Note: For this class, you don’t need to know the names or locations of the muscles involved. Just know the motor functions (listed on left)

Superior view, left eye

Lateral view


09c visual system which cranial nerves are involved chapter 12

Possible movements of the eye, and their associated cranial nerves (For this class, no need to know associated muscles; arrows indicate muscle pull direction)

  • III, oculomotor

    • Eye

      • Elevation (item C)

      • Depression (item D)

      • Adduction (item B)

      • Extorsion (item E)

    • Eyelid opening

    • Pupillary light reflex

  • IV, trochlear: Intorsion (item F)

  • VI, abducens: Abduction (item A)

A

B

C

D

E

F

Extorsion

Intorsion

+ eyelid opening

+ pupil constriction


Pathology of iii iv vi p 153 of w a

Pathology of III, IV, VI (p. 153 of W&A)

  • IV, trochlear

    • Sign: Hard to move eye “down and in”

    • Symptom: Diplopia

  • VI, abducens

    • Sign: Eye pulled medially

    • Symptom: Diplopia

  • III, oculomotor

    • Signs

      • Eye abducted and depresssed

      • Upper eyelid droops (ptosis)

      • Pupil dilated and non-reactive

    • Symptoms

      • Diplopia (double vision)


Sidebar for the curious

Sidebar for the curious….

  • Checking c.n. III after head injury (pupillary light reflex; autonomic)

  • Locked-in syndrome (maladie de l'emmuré vivant ‘walled-in alive disease’)

    • Complete loss of all voluntary muscles in the body except the eyes

    • (ventral part of the pons is damaged, e.g., from blockage of basilar artery)

    • Book and movie: The Diving Bell and the Butterfly

  • (locked-in syndrome,

    augmentative movie, NIH)


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