Anatomy Neurology

12 Cranial Nerves PDF

12 Cranial Nerves

12 Cranial Nerves
Nerve
Components
Cell Bodies
Peripheral Distribution
Function
I Olfactory
SVA
Olfactory epithelial cells
Olfactory nerves
Smell
II Optic
SSA
Ganglion cells of retina
Rods and cones
Vision
III Oculomotor
GSE
Nucleus III
Levator palpebrae; recti: superior, medial, inferior; and inferior oblique
Eye movement
GVE
Edinger-Westphal nucleus
Ciliary ganglion—Ciliary body—Sphincter pupillae
Contraction of pupil and accomodation
GP
Mesencephalic nucleus V
Ocular muscles
Kinesthetic sense
IV Trochlear
GSE
Nucleus IV
Superior oblique
Ocular movement
GP
Mesencephalic nucleus V
Superior oblique
Kinesthetic sense
V Trigeminal
GSA
Trigeminal ganglion
Ophthalmic, maxillary, and mandibular divisions to mucous membranes and skin of face and head
General sensation
SVE
Motor nucleus V
Temporalis, masseter, pterygoids, anterior belly of digastric, mylohyoid, tensors palatini and tympani
Mastication
GP
Mesencephalic nucleus V
Muscles of mastication
Kinesthetic sense
VI Abducens
GSE
Nucleus VI
Lateral rectus
Eye movement
GP
Mesencephalic nucleus V
Lateral rectus
Kinesthetic sense
VII Facial
SVE
Motor nucleus VII
Muscles of facial expression, stapedius, stylohyoid, post, belly of digastric
Facial expression
GVE
Salivatory nucleus
Greater petrosal— pterygopalatine ganglion—nasal mucosa, lacrimal gland; chorda tympani—lingual nerve, submandibular ganglion—submandibular, sublingual glands
Secretomotor
SVA
Geniculate ganglion
Chorda tympani—lingual nervetaste buds anterior two-thirds tongue
Taste
GVA
Geniculate ganglion
Greater petrosal, chorda tympani
Visceral sensation
GSA
Geniculate ganglion
Auricular branch—ear and mastoid
Cutaneous sensation
VIII Vestibulocochlear
SSA
Spiral ganglion
Organ of Corti
Hearing
SP
Vestibular ganglion
Vestibular mechanism
Balance
IX Glossopharyngeal
SVA
Inferior ganglion IX
Lingual br.—taste buds posterior one-third tongue, circumvallate papillae
Taste
GVA
Inferior ganglion IX
Tympanic nerve—middle ear, pharynx, tongue, carotid sinus
Visceral sensation
GVE
Salivatory nucleus
Tympanic—lesser petrosal—otic ganglion auriculotemporal to parotid gland
Secretomotor
GSA
Inferior ganglion IX
External ear
Cutaneous sensation
SVE
Nucleus ambiguns
Stylopharyngeus
Swallowing
X Vagus
GVE
Dorsal motor nucleus X
Cardiac nerves and plexus, ganglia on heart; pulmonary plexus, ganglia respiratory tract; esophageal, gastric, celiac plexus; myenteric and submucous plexus—to transverse colon
Smooth muscle and glands
SVE
Nucleus ambiguus
Pharyngeal br., superior, inferior laryngeal nerves
Swallowing, speaking
GVA
Inferior ganglion X
All fibers in all branches
Visceral sensation
SVA
Inferior ganglion X
Br. to epiglottis, base of tongue, taste buds
Taste
GSA
Superior ganglion X
Auricular br.—ear, meatus
Cutaneous sensation
XI Accessory
SVE
Nucleus ambiguus
Communication to vagus—muscles of pharynx and larynx
Swallowing, speaking
SVE (Assuming branchiomeric origin)
Upper spinal cord—lat. column
Spinal portion—sternocleidomastoid, trapezius
Movement, head and shoulder
XII Hypoglossal
GSE
Nucleus XII
Brs. intrinsic, extrinsic muscles of tongue
Tongue movement
GP, general proprioception; GSA indicates general somatic afferent; GSE, general somatic efferent; GVA, general visceral afferent; GVE, general visceral efferent; SP, special proprioception; SSA, special somatic afferent; SVA, special visceral afferent; SVE, special visceral efferent.

 Cranial Nerves—Clinical Testing
Cranial Nerve
Modality
   Assessment Technique
Perceived Dysfunction
I Olfactory
SVA
Patient is asked to differentiate distinct odors (coffee, vanilla) with eyes covered. Test each side independently.
Damage such as an ethmoid fracture may result in anosmia (loss of sense of smell).
II Optic
SSA
Eye charts are used to assess visual acuity. Visual fields are determined by examining when patient observes an object moving from lateral to medial. Ophthalmoscope used for observing retina, optic disc, and blood vessels.
Damage to the retina usually results in blindness to the affected eye. Damage beyond the optic chiasma will present partial visual losses.
III Oculomotor
GSE
Patient is asked to follow with his or her eyes the examiner’s finger as it moves up and down vertically and medially and laterally. Watch for crossing of eyes during convergence.
Damage to this modality may cause paralysis of all extraocular muscles except the superior oblique and lateral rectus. This produces lateral strabismus and inability to look vertically. Also ptosis (eyelid drooping).
GVE
Examine patient for pupillary reflex with light shining on and off in each eye. Observe and compare contractions and dilations in affected and unaffected eyes.
Damage to this modality will produce lack of pupillary reflex, dilated pupils, and lack of changes in pupil at close focus.
IV Trochlear
GSE
Analysis of function is performed during testing of the oculomotor nerve.
Damage to this nerve causes double vision and inability to rotate the eye inferolaterally.
V Trigeminal Ophthalmic division (V1)
GSA
Test for corneal reflex with whisp of cotton. Prick forehead with pin (pain), apply warm and cold objects (temperature).
Damage to this division will inhibit the corneal reflex and will reduce or inhibit sensation over the (V1) zone.
Maxillary division (V2)
GSA
Stroke sensory zone of (V2) with eyes closed (light touch), prick with pin (pain), apply warm and cold objects (temperature).
Damage to this division will reduce or inhibit sensation over the (V2) zone.
Mandibular division (V3)
GSA
Stroke sensory zone of (V3) with eyes closed (light touch), prick with pin (pain), apply warm and cold objects (temperature).
Damage to this division will reduce or inhibit sensation over the (V3) zone.
Mandibular division (V3)
SVE
Ask patient to clench jaws, open, then move jaw side to side with resistance. Muscle strength in the temporalis and masseter should be compared from side to side by palpation.
Damage in this modality may cause paralysis of the muscles of mastication, thus causing the jaw to deviate same side as the lesion.
VI Abducens
GSE
Analysis of function is performed during testing of the oculomotor nerve.
Damage to this nerve causes double vision and paralysis of the lateral rectus muscle, thus the eye remains rotated medially on the affected side.
VII Facial
SVA
Test for taste for sweet and salty on anterior 2/3 of tongue.
Damage to this modality will reduce or inhibit the sensation of taste on the anterior 2/3 of the tongue.
GVE
Observe tearing with pungent fumes (ammonia).
Damage to this modality will reduce or inhibit the ability to secrete tears from the affected side. Mucus production in the nasal cavity and salivary gland secretions from the submandibular and sublingual glands is more difficult to evaluate.
SVE
Observe symmetry of face when asked to close eyes, frown, smile, whistle, raise eyebrows. Look for flacid sagging of face.
Damage to this modality, such as in stroke, causes a paralysis of the muscles of facial expression, which causes the face to sag and an inability to make facial expressions on the affected side.
VIII
Vestibulocochlear
Cochlear division
SSA
Test with a tuning fork by air and bone conduction.
Loss of hearing by air conduction indicates a lesion or damage to the middle ear. Loss by bone conduction indicates nerve deafness.
Vestibular division
GSA (SP)
Test walking a straight line, dizziness. Watch for rapid eye movements.
Damage to the vestibular division elicits dizziness, nausea, vomiting, and uncontrolled rapid eye movement.
IX
Glossopharyngeal
GVA
Test for gag reflex and swallowing and position of the uvula during this procedure. Test touch reception on the posterior 1/3 of the tongue.b
Damage to this modality would reduce or inhibit the gag reflex and produce difficulty in swallowing. It would also reduce or inhibit general sensation on the posterior 1/3 of the tongue.
Sensation to the carotid body and sinus would also be lost, thereby altering blood pressure and oxygen tension in the bloodstream.
SVA
Test for bitter and sour taste on the posterior 1/3 of the tongue and on circumvallate papillae.
Damage to this modality would reduce or inhibit the sense of taste over the posterior 1/3 of the tongue and on the circumvallate papillae.
GVE
Observe saliva flow from the parotid duct.
Damage to this modality would reduce or inhibit saliva secretion from the parotid gland.
X Vagusc
SVE
Have patient elevate the palate by saying “aahhhh,” swallow, and speak.
Damage to this component will prevent the palate from being elevated and will make swallowing and speech difficult.
XI Accessoryd
SVE
Have patient shrug shoulders and rotate head against resistance.
Damage to this modality would reduce or inhibit the movement of the head and shoulders.
XII Hypoglossal
GSE
Have patient protrude and retract tongue.
Damage to this nerve will cause the tongue to deviate toward the affected side on protrusion, and that side will appear shrunken and wrinkled.
GSA, general somatic afferent; GSE, general somatic afferent; GVE, general visceral efferent; SP, special proprioception; SSA, special somatic afferent; SVA indicates special visceral afferent; SVE, special visceral efferent.

  • Note that some modalities associated with certain cranial nerves are not represented in this table because some areas of the head and neck receive overlapping innervation from more than one cranial nerve, thus complicating definitive testing. For example the area about the ear/auditory meatus receives sensory innervation from several cranial nerves in addition to contributions from the cervical plexus, thereby making assessment extremely difficult.
  • Because there is close association and intermingling of nerve fibers of the glossopharyngeal, vagus, and accessory nerves, it is difficult to distinguish the affected nerve in clinical testing procedures. However, the gag reflex is generally considered the definitive test for glossopharyngeal nerve damage.
  • Although the vagus nerve serves visceral structures in the thorax and abdomen, the contents of the table are restricted to its functions in the head and neck.
  • This assumes that the SVE component of the accessory nerve that serves the sternocleidomastoid and trapezius muscles is from the cranial root of the accessory nerve. Remember that the SVE component of the vagus is also part of the cranial root of the accessory nerve. Therefore, damage to this root would affect both areas served by the vagus and the accessory nerves.

Cranial Nerve Examination Video…