09c09cVisual System:Visual System:

Which cranial nerves are Which cranial nerves are involved?involved?

Chapter 12Chapter 12

Sensory Motor

Vision: --seeing--moving eyes --opening eyelids--pupil constriction

II (Optic) III (Oculomotor)IV (Trochlear)VI (Abducens)

Vision, as used for communication involves sight + movement of eye! Vision is an active process, not just passive.

Remind yourself of relationship Remind yourself of relationship between vision and between vision and communication, as related to communication, as related to clinical practice.clinical practice.• How are eyes used in expressive How are eyes used in expressive

communication?communication?

• How are eyes used in receptive How are eyes used in receptive communication?communication?

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

II: SensoryIII, IV, and VI: Motor

Visual sensory: Visual sensory:

II II

Visual motor: Visual motor: III, IV, VIIII, IV, VI

Visual sensory: Visual sensory: II (Optic nerve)II (Optic nerve)

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

• Bipolar cellBipolar cell

• Bundles of retinal bipolar Bundles of retinal bipolar cell axons emerge from cell axons emerge from retina, and make up the retina, and make up the two optic nerves (c.n. II)two optic nerves (c.n. II)– One for each eyeOne for each eye– Right and left optic nerves Right and left optic nerves

join at optic chiasmjoin at optic chiasm

• Distribution of Distribution of photosensorsphotosensors– Rods- peripheral Rods- peripheral

retinaretina– Cones- central Cones- central

retina (macula retina (macula lutea/fovea lutea/fovea centralis)centralis)

• Functions of Functions of photosensorsphotosensors– Sensitive to rays of Sensitive to rays of

different different wavelengths wavelengths

– Cones- day vision, Cones- day vision, acuity, color visionacuity, color vision•Nonfunctional in Nonfunctional in

darkdark– RodsRods- - night vision night vision

and shades of and shades of greengreen•Nonfunctional in Nonfunctional in

bright or bright or daylightdaylight

• TransductionTransduction

– Absorption of electromagnetic energy by Absorption of electromagnetic energy by visual pigments visual pigments

– Conversion into neural impulses Conversion into neural impulses

•Pupillary AperturePupillary Aperture– Protective mechanism in intense lightProtective mechanism in intense light– Regulation of light amount entering eyesRegulation of light amount entering eyes– Dilator & constrictor muscle fibers of irisDilator & constrictor muscle fibers of iris

•Bright light- parasympathetic constriction of Bright light- parasympathetic constriction of pupilpupil

– Small amount of light inSmall amount of light in

•Dim light- sympathetic dilation; Dim light- sympathetic dilation; – greater amount of light in greater amount of light in

Pupillary light reflexPupillary light reflex

Superior viewSuperior view

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

Optic nerves join at Optic nerves join at the optic chiasm.the optic chiasm.

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

Ventral (frontal) view Lateral view

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

• Crossing at Crossing at optic chiasm optic chiasm – Some fibers cross, but Some fibers cross, but

not allnot all

• Optic tract (in CNS)Optic tract (in CNS)

• Synapse at Synapse at lateral lateral geniculate body geniculate body (in (in thalamus)thalamus)

• Optic radiationOptic radiation

• End in End in primary visual primary visual cortex cortex (medial occipital (medial occipital lobe)lobe)

Projections to cortexProjections to cortex

Trace 1Trace 1stst order and 2 order and 2ndnd order visual order visual sensory neurons: Lateral viewsensory neurons: Lateral view

• Optic nerveOptic nerve

• Optic chiasm Optic chiasm

• Optic tract (in CNS)Optic tract (in CNS)

• Synapse at Synapse at lateral lateral geniculate body/geniculate body/

(nucleus in thalamus)(nucleus in thalamus)

• Optic radiationOptic radiation

• End in End in primary visual primary visual cortex cortex (medial (medial occipital lobe)occipital lobe)

Optic nerve (II) coming from eyes; optic chiasm; optic tract coursing back to lateral geniculate body

Ventral (frontal) view Lateral view

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

How is cranial nerve II How is cranial nerve II tested? tested? • Testing of visual Testing of visual

fieldsfields– Cut #1Cut #1: blindness: blindness– Cut #2Cut #2: bitemporal : bitemporal

heteronymous heteronymous hemianop(s)iahemianop(s)ia

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

– Damage to primary Damage to primary visual cortexvisual cortex: : cortical blindness cortical blindness (cortical visual (cortical visual impairment)impairment)

(brainstem)

Horizontal plane

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

III, IV, VIIII, IV, VI

Muscles of visual motor Muscles of visual motor systemsystem

• Move eyeMove eye

• Control eyelid openingControl eyelid opening

• Control pupil dilationControl pupil dilation

Superior view, left eye Lateral view

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)

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

+ eyelid opening + pupil constriction

• III, oculomotorIII, oculomotor

• EyeEye

• Elevation (item C)Elevation (item C)

• Depression (item D)Depression (item D)

• Adduction (item B)Adduction (item B)

• Extorsion (item E)Extorsion (item E)

• Eyelid openingEyelid opening

• Pupillary light reflexPupillary light reflex

• IV, trochlear: Intorsion (item IV, trochlear: Intorsion (item F)F)

• VI, abducens: Abduction (item VI, abducens: Abduction (item A)A)

Extorsion Intorsion

F

DC

BA

E

• IV, trochlearIV, trochlear– Sign: Hard to move Sign: Hard to move

eye “down and in”eye “down and in”– Symptom: DiplopiaSymptom: Diplopia

• VI, abducensVI, abducens– Sign: Eye pulled Sign: Eye pulled

mediallymedially– Symptom: DiplopiaSymptom: Diplopia

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

• III, oculomotorIII, oculomotor– SignsSigns

– Eye abducted and Eye abducted and depressseddepresssed

– Upper eyelid droops Upper eyelid droops ((ptosisptosis))

– Pupil dilated and Pupil dilated and non-reactivenon-reactive

– SymptomsSymptoms– DiplopiaDiplopia (double (double

vision)vision)

Sidebar for the curious….Sidebar for the curious….• Checking c.n. III after head injury Checking c.n. III after head injury (pupillary light reflex; (pupillary light reflex;

autonomic)autonomic)

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

– Complete loss of all voluntary muscles in the body Complete loss of all voluntary muscles in the body except the eyesexcept the eyes

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

– Book and movie: Book and movie: The Diving Bell and the ButterflyThe Diving Bell and the Butterfly

• (locked-in syndrome,(locked-in syndrome,

augmentative movie, NIH) augmentative movie, NIH)