12 Cranial nerves Flashcards
basics
4 functions of the cranial nerves
- Supply motor innervation to the muscles of the face, eyes, tongue, jaw, and SCM/trapezius muscles.
- Transmit somatosensory information from the skin and muscles of the face and TMJ joint.
- Transmit ‘special’ sensory information related to visual, auditory, vestibular, taste, smell, visceral function.
- Provide parasympathetic regulation of : pupil size, curvature of the lens of the eye, HR, BP, breathing, and digestion.
Cranial Nerve 1, and testing for nerve.
Olfactory nerve, afferent for smell.
Test- smell with 1 nostril then the other such as lemon/coffee/sanitizer/scent. affected during covid.
cranial nerve 1 is inhibited by compression of
the anterior fossa (meningioma). Ipsilaterally.
Cranial nerve 2. and testing for nerve.
Optic nerve. Testings are Snellen Chart (1 eye), Visual fields assessment (hold finger in periphery), Accommodation (lens to flatten or thicken due to ciliary muscles), pupillary light reflex.
Cranial nerve 2 anatomy
So let’s go through these a little bit- we know that the axons of the retina converge at the optic disc and then pass into the optic nerve. It then goes through the optic Canal to join the optic chiasm these are myelinated by oligodendrocytes the visual pathway is such that the area of the sort of the middle cranial fossa. The optic nerves from each eye have formed the optic chiasm but at this chiasm it’s very important to note that fibers from the nasal or medial half of each retina cross; they decussate. Over To the contralateral optic tract. While fibers from temporal/lateral half remain IPSILATERAL.
Cranial nerve 2 and the lateral geniculate nucleus
fibers synapse here, at thalamus, that relay station to the optic radiations that then go to specific areas of the brains visual cortex.
Homonymous hemiopia test.
4, 8, 10, and 2 o clock to wiggle finger to assess homunculus . bilateral visual one half of field loss, on the same visual field each eye. (+) Homonymous hemiopia.
Cranial nerve 3 and anatomy
oculomotor nerve. somatic motor > oculomotor nucleus to skeletal mm of eye the superior+inferior+medial rectus (3) and inferior oblique muscle, ciliary muscle, sphincter papillae, and the levator palpebrae superioris.
Visceral motor> parasymp via EWN>eye intrinsics for accommodation (ciliary muscles) and pupil constriction (sphincter pupillae mms)
Cranial nerve 3 functions
mainly constricts pupil, lens accommodation (ciliary mms)
Moves eye up, down, medial, raises upper eyelid. Vestibulo-ocular reflex.
Cranial nerve 3 special tests
H-pattern test, ptosis check, accommodation, VOR: gaze stabilization during head mvmnts (CN 3+6+8). ***VOR = vestibulo-ocular reflex. “Dolls eyes” and light reflex constriction.
Cranial nerve 4
Trochlear nerve, motor (somatic efferent) to the superior oblique muscle. Only nerve to arises from dorsal surface of brainstem and crosses to other eye from its nucleus. Passes through trochlea (decussates), one of the longest C. nerves (vagus)
Cranial nerve 4 function
moves eye medially, inferiorly VIA the superior oblique muscle. SO4 Trochlear nerve
Cranial nerve 4 test
H-test, typically eyes move superiorly causing double vision.
Cranial nerve 5 anatomy
mixed sensory and motor. Originates from the anterolateral surface of the mid-pons as a large sensory root (portio major) and a smaller motor root (portio minor).
Cranial nerve 5 function and V1 vs V2 vs V3.
Mixed S/M. motor to muscles of mastication, sensory to face “MOM”. V1 ophthalmic branch, V2 maxillary branch, V3mandibular branch.
Cranial nerve 5 deficits
Trigeminal neuralgia Wallenberg syndrome. (V1-V2-V3)
5 muscles of the eye
superior rectus, inferior rectus, medial rectus, superior oblique, and inferior oblique. **CN 4 is affected heavily by MS!
Cranial nerve 5 tests
Cotton ball touch dermatome V1-V2-V3, tap finger on chin. Palpate muscles of mastication.
