Cranial Nerves Part 1 Flashcards
What can cranial nerves carry?
Can carry motor, sensory, parasympathetic, special sensory fibres or a combination
What are the 12 cranial nerves?
o I Olfactory o II Optic o III Oculomotor o IV Trochlear o V Trigeminal o VI Abducent o VII Facial o VIII Vestibulochoclear o IX Glossopharyngeal o X Vagus o XI Accessory o XII Hypoglossal
Where are cranial nerves derived from?
- All derived from the brainstem or just above it
What are the positions of the cranial nerves?
See diagram in lecture notes
Where is the the olfactory nerve (I) and what does it do?
- The olfactory nerves run inferiorly from the olfactory bulb, though the perforated cribiform plate of the ethmoid bone to enter the nasal cavity.
- Special sensory fibres, conveying smell.
Where is the the optic nerve (II) and what does it do?
- The optic nerve traverses the optic canal to enter the orbit.
- The optic nerve is made entirely of special sensory fibres conveying vision.
What do lesions to the optic nerve and surrounding area cause?
- Lesion to optic nerve itself = monocular vision loss (blind in one eye)
- Lesion to optic chiasm = bitemporal hemianopia/loss of temporal vision/tunnel vision (as this is where temporal information crosses over)
- Lesion to optic tract = homonymous hemianopia/loss of left or right half of vision in both eyes
Where are the the occulomotor (III), trochlear (IV) and abducens (VI) nerves and what do they do?
o The oculomotor nerve emerges from the midbrain
o The trochlear nerve emerges from the posterior surface of the midbrain
o The abducent nerve emerges from the pons
- All 3 cranial nerves traverse the superior orbital fissure to enter the orbit.
What is the orbit and what does it house?
- Houses the eyeball, extraocular muscles and all of the nerves associated with the eye
- Pyramid shaped rather than cylindrical – medial walls parallel to each other either side of nasal cavity, but lateral wall is not parallel, thus giving pyramidal shape
- All muscles attach to both the common tendinous ring and then the eyeball – eyes look straight ahead, but muscles attach at an angle, thus making the movements of these muscles very complex
What are the 6 extraocular muscles?
- There are 6 extra ocular muscles
- 4 Rectus (straight) muscles
o Superior rectus
o Inferior rectus
o Medial rectus
o Lateral rectus - 2 oblique muscles
o Superior oblique
o Inferior oblique
How do each of the extraocular muscles move the eye?
See lecture notes
How do you clinically test an individual eye muscle?
- To clinically test an individual muscle, the muscle must be isolated – the eye is aligned with the angle of muscle pull
- Abduct eye to test rectus muscles, and adduct eye to test obliques
See picture in lecture notes
What does the oculomotor nerve do?
- Oculomotor nerve carries motor fibres to supply superior rectus, inferior rectus, medial rectus, inferior oblique and levator palpabrae superioris.
- Also parasympathetic fibres for innervating constrictor pupillae and ciliary body.
- Constrictor pupillae muscle constricts the pupil, dilator pupillae muscle dilates the pupil
See lecture notes
What does the trochlear nerve do?
- Trochlear nerve carries motor fibres to supply superior oblique. (and nothing else – very small nerve!)
- Trochlear nerve palsy hardest to identify
- Diplopia (double vision) on looking downwards
- Head tilt away to compensate for misalignment of the eyes
See lecture notes
What does the abducent nerve do?
- Abducent nerve carries motor fibres to supply lateral rectus.
See lecture notes
