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Anat 1012 - 2 neuro > CRANIAL NERVE PATHWAYS & REFLEXES > Flashcards

CRANIAL NERVE PATHWAYS & REFLEXES Flashcards

1
Q

Protective reflexes

A
  • Corneal blink reflex

* Pupillary light reflex

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2
Q

Co-ordination of eye movement

A
  • Gaze
  • Vestibulo-ocular reflex (VOR)
  • Accommodation
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3
Q

Optic nerve CN II

A

Receptor = rods & cones
1st neuron = bipolar cell (special sense)
2nd neuron = ganglion cell
Axons of ganglion cells = optic nerve

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4
Q

The visual pathway

A
  • Ganglion cells synapse in the Lateral Geniculate Nucleus (thalamus)
  • 3rd neuron travels via optic radiation to the
  • Calcerine sulcus = primary visual cortex, occipital lobe
  • Collaterals to midbrain
    > superior colliculus >pretectal area
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5
Q

Lateralisation of the visual field at the optic chiasm

A
  • The lateral (temporal) visual field projects onto the medial (nasal) retina
  • Fibres from the nasal retinae decussate at the optic chiasm
  • The optic tract carries information from the contralateral visual field
  • lat. neurons of optic nerve remain ipsilateral while medial are contralateral
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6
Q

Superior–inferior retinotopy

A
  • Lower visual field travels through the parietal optic radiation
  • Upper visual field travels via the Meyer loop through the temporal lobe
    left nasal retina > right visual cortex
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7
Q

binocular vision

A

each eye sees different part of environment

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8
Q

LESIONS OF THE OPTIC PATHWAY:

A 
Named according to visual field lost! 
Circles = visual field
of each eye 
Dark = lost visual field
Test 1 eye at a time (other eye covered)
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9
Q

Medial longitudinal fasciculus (MLF)

A 
Interconnects nuclei of:
midbrain
1. Oculomotor 
2. Trochlear
pons
3. Abducens 
medulla oblongata
4. Vestibular
• Heavily myelinated
• Near midline tegmentum
• Anterior to 4th ventricle & PAG /cerebral aqueduct
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10
Q

3 Cranial nerves control the muscles of the eyes

A

oculomotor CN3, trochlear 4, abducens 6

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11
Q

oculomotor CN3,

A
  1. Levator palpebrae superioris
  2. Superior rectus
  3. Inferior rectus
  4. Medial rectus
  5. Inferior oblique
  6. Parasympathetic CN III fibres travel to the ciliary ganglion in the orbit
    – synapse with ciliary nerves that innervate the:
    * Constrictor pupillae: controls amount of light entering the eye
    * Ciliary muscle: rounding of lens for near vision
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12
Q

trochlear CN4

A

Superior oblique

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13
Q

abducens CN6

A

lateral rectus

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14
Q

Oculomotor - somatic motor nucleus

A
  • tegmentum of rostral midbrain
  • near midline
  • anterior to cerebral aqueduct & PAG
  • rostral end of medial longitudinal fasciculus (MLF)
  • fibres travel anteriorly to emerge in interpeduncular fossa
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15
Q

Oculomotor - Parasympathetic nucleus = Edinger-Westphal nucleus

A

• posterior to somatic nucleus
• in periaqueductal grey (PAG)
• preganglionic axons travel with somatic axons, exit @ ciliary ganglion
The parasympathetic axons are located superficially in the CN III nerve - more susceptible to compression
- dilated pupil is an early sign of CN III compression
(Pretectal area = rostral to superior colliculus @ midbrain/diencephalon junction)

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16
Q

Trochlear CN IV nucleus

A
  • Midbrain @ level of the inferior colliculus
  • near midline
  • axons exit dorsally
17
Q

Abducens CN VI nucleus

A

• caudal pons @ level of the facial colliculus
• near midline
• Contains:
Somatic motor nucleus – neurons innervate lateral rectus Interneurons – coordination of horizontal eye movements
+ cell bodies of interneurons

18
Q

Trigeminal nerve CN V

A

The trigeminal (semilunar) ganglion is homologue to the dorsal root ganglia as it contains cell bodies of (pseudo)unipolar sensory neurons
3 major branches:
- ophthalmic nerve (V1) = sensory forehead, eyelids, eye upper nasal
- maxillary nerve (V2) = sensory midface, upper teeth, lower nasal cavity, paranasal sinuses - mandibular nerve (V3) = sensory lower face + motor muscles of mastication

19
Q

Trigeminal nucleus: 4 parts

A

mesencephalic
spinal trigeminal
chief sensory
motor trigeminal

20
Q

Facial - CN7

A

Large motor component to all muscles of facial expression •Small sensory component = taste anterior 2/3 tongue
•NOTE biting tongue pain = trigeminal nerve
•Into internal acoustic meatus, out through stylomastoid forame

21
Q

Facial - CN7 parasympathetic

A
  • Lacrimal gland (tears)

* Submandibular & sublingual salivary glands

22
Q

CORNEAL BLINK REFLEX: (brainstem)

A

Protective reflex to remove foreign particles & lubricate the eye
1. Ophthalmic division of trigeminal nerve CN V
2. Synapse in spinal trigeminal (nociception) & chief sensory (touch)
nuclei
3. Interneurons synapse bilaterally with facial nucleus motor neurons
4. Facial nerve CN VII innervates orbicularis oculià“blink”

23
Q

pupillary light reflex

A

-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
-postganglionic neurons innervate constrictor pupillae
Should be direct & consensual (both eyes affected)

24
Q

gaze

A
  • photoreceptors are sensitive but slow!
  • binocular vision
    • coordinatedmovement of 2 eyes
    • each with 6 extrinsic eye muscles
    • controlled by 3 pairs of cranial nuclei
    1. Conjugate movements (eyes move together)
    2. Vergence movements (eyes opposite - both move in)
25
Q

Saccades

A
  • types of gaze
    conjugate
    fast
    • Redirect gaze so a different image falls on the fovea
    • Use them when exploring the environment visually
26
Q

Smooth pursuit movements

A

conjugate gaze
slower
• Used to keep an image on the fovea
• Due to either movement of the object or movement of self
• Use cortical (visual), cerebellar & vestibular feedback
• 2 eyes = 2 fovea ie. Both cerebral hemispheres involved.
eg - looking at something and following it

27
Q

Coordination of horizontal conjugate eye movements

A

Left PPRF controls both eyes looking to left

28
Q

the initiation of saccades

A 
• frontaleyefield(FEF)
• supplementaryeyefield 
• parietaleyefield
project to contralateral PPRF (or riMLF)
\+/- superior colliculus (which then projects to PPRF)
PPRF = controls abducens and oculomotor
29
Q

Damage to the FEF

A
  • Temporary inability to look voluntarily to the contralateral side (despite normal muscles)
30
Q

Damage to FEF & superior colliculus

A
  • Longer & more severe deficit
31
Q

VESTIBULO-OCULAR REFLEX (VOR)

A
  • photoreceptors are sensitive but slow
  • very fast reflex
  • generates 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
32
Q

VESTIBULO-OCULAR REFLEX:

A

• Vestibular apparatus detects head movement (e.ghorizontal)
• Vestibular nerve CN VIII
• Ipsilateral vestibular nuclei at pons /
medulla junction
• Project to contralateral Abducens nucleus (pons)
• Projects to
• ipsilateral CN VI (lateral rectus)
• contralateral oculomotor nucleus, midbrain, via the MLF
• CN III (medial rectus)
eg. moving at figure while moving head

33
Q

Smooth pursuit

A

Used to keep an image on the fovea when the object is moving relative to the background

  1. interest
  2. detect motion
  3. VOR cancellation
34
Q

ACCOMMODATION: involves the cerebral cortex

A

Focusing on a near object
3 requirements:
1. Convergence so that the object falls on both foveae
2. Increase curvature of the lens to increase refractive power to focus the image on the fovea
3. Pupillary constriction – reduces blur & increases depth of field

35
Q

accomodation process

A 
CN II afferents to bilateral LGN (thalamus)
• Primary visual cortex
• Visual association cortex
• Project to pretectal area
• Oculomotor & Edinger-Westphal nuclei
• CNIII
• somatic fibres to medial rectus
• parasympathetic fibres to
• ciliary muscle
• constrictor pupillae

Anat 1012 - 2 neuro (15 decks)

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