Transcript Cranial nerves of vision, plus visual pathway

09c
Visual System:
Which cranial nerves are
involved?
Chapter 12
Vision:
--seeing
--moving eyes
--opening eyelids
--pupil constriction
Sensory
II (Optic)
Motor
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
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?
II: Sensory
III, IV, and VI: Motor
Visual sensory:
II
Visual motor:
III, IV, VI
Visual sensory:
II (Optic nerve)
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
• 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
• Transduction
– Absorption of electromagnetic energy by visual
pigments
– Conversion into neural impulses
• 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
Superior view
Optic nerves (c.n. II) are
in the PNS.
Optic nerves join at the
optic chiasm.
Where is the optic nerve (PNS), with reference
to the brainstem?
Ventral (frontal) view
Lateral view
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
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)
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
transduces light energy :
…from left visual hemifield?
…from right visual hemifield?
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
Muscles of visual motor system
• Move eye
• Control eyelid opening
• Control pupil dilation
Superior view, left eye
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)
Lateral view
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
+ eyelid opening
• IV, trochlear: Intorsion (item F)
+ pupil constriction
• VI, abducens: Abduction (item A)
A
B
C
D
E
F
Extorsion
Intorsion
Pathology of III, IV, VI
(p. 153 of W&A)
• IV, trochlear
• III, oculomotor
– Signs
– Eye abducted and
depresssed
– Upper eyelid droops
(ptosis)
– Pupil dilated and nonreactive
– Symptoms
– Diplopia (double vision)
– Sign: Hard to move eye
“down and in”
– Symptom: Diplopia
• VI, abducens
– Sign: Eye pulled medially
– Symptom: Diplopia
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)