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The Twelve Cranial Nerves: Classification, Functions, and Bedside Testing

Roman numerals, sensory/motor classification, functions, and standard clinical tests for the twelve cranial nerves in neuroanatomy.

12 cards· by GuruOwl

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  1. 01
    Cranial nerve (CN) I (Olfactory) is tested by having the patient identify non-irritating odors with each nostril separately.
    Irritating odors may stimulate CN V (trigeminal) nociceptors, leading to a false positive.
    Flashify::Medical::Neurology::Anatomy
  2. 02
    The afferent limb of the pupillary light reflex is mediated by CN II (Optic nerve).
    The efferent limb is mediated by CN III (Oculomotor nerve).
    Flashify::Medical::Neurology::Physiology
  3. 03
    CN III (Oculomotor) palsy presents with a "down-and-out" eye, ptosis, and mydriasis (dilated pupil).
    Mydriasis occurs because CN III carries parasympathetic fibers to the pupillary constrictor.
    Flashify::Medical::Neurology::Pathology
  4. 04
    CN IV (Trochlear) innervates the superior oblique muscle, which performs depression and intorsion of the eye.
    Palsy causes vertical diplopia that improves with head tilt away from the lesion.
    Flashify::Medical::Neurology::Anatomy
  5. 05
    CN VI (Abducens) innervates the lateral rectus muscle; a palsy results in medial deviation (esotropia).
    This results in horizontal diplopia that is worse when looking toward the side of the lesion.
    Flashify::Medical::Neurology::Pathology
  6. 06
    The motor component of CN V (Trigeminal) innervates the muscles of mastication; a lesion causes the jaw to deviate toward the weak side.
    This is due to the unopposed action of the contralateral pterygoid muscles.
    Flashify::Medical::Neurology::Pathology
  7. 07
    An Upper Motor Neuron (UMN) lesion of CN VII (Facial) spares the forehead due to bilateral innervation.
    In contrast, a Lower Motor Neuron (LMN) lesion like Bell's Palsy affects the entire half of the face, including the forehead.
    Flashify::Medical::Neurology::Pathology
  8. 08
    CN VII (Facial) provides taste to the anterior 2/3 of the tongue via the chorda tympani.
    CN IX provides taste to the posterior 1/3.
    Flashify::Medical::Neurology::Anatomy
  9. 09
    The gag reflex consists of an afferent limb via CN IX (Glossopharyngeal) and an efferent limb via CN X (Vagus).
    Testing the gag reflex evaluates the integrity of both the brainstem and these specific nerves.
    Flashify::Medical::Neurology::Physiology
  10. 10
    A lesion of CN X (Vagus) causes the uvula to deviate away from the side of the lesion.
    The uvula deviates toward the strong side as the weak side of the palate fails to elevate.
    Flashify::Medical::Neurology::Pathology
  11. 11
    CN XI (Accessory) innervates the sternocleidomastoid and trapezius muscles.
    Tested by head turning against resistance and shoulder shrugging.
    Flashify::Medical::Neurology::Anatomy
  12. 12
    A lesion of CN XII (Hypoglossal) causes the tongue to deviate toward the side of the lesion upon protrusion.
    The tongue "licks the wound" because the contralateral genioglossus muscle is unopposed.
    Flashify::Medical::Neurology::Pathology