Head and Cranial Nerves

Head and Cranial Nerves




Key Point



One should note the shape of the head and face, the range of motion of the cervical spine, and the intrinsic reflexes of the facial muscles. The skull and the neck vessels are auscultated, and the functions of the cranial nerves are tested.


3.3.1 Head and Cervical Spine


The examiner should first note the general appearance of the head and cervical spine (e.g., sunken temples in Steinert myotonic dystrophy) and the patient’s facial expressions (e.g., paucity of facial expression in Parkinson disease). Next, the range of motion of the cervical spine is tested: young, healthy persons should be able to turn the neck and head almost 90 degrees in either direction, so that the eye that is farther from the examiner disappears behind the root of the patient’s nose. Further, the patient should be able to incline the head laterally 45 degrees in either direction and to rotate it 60 degrees to the right or left when the neck is maximally flexed (this rotation occurs only at the atlantoaxial and atlanto-occipital joints).


Testing for meningismus is performed with the patient supine. This finding, if present, usually indicates meningeal irritation due to meningitis or subarachnoid hemorrhage, but is sometimes a reflex response to a mass lesion in the posterior fossa. Meningismus consists of isolated opposition to neck flexion, while the head can still be rotated. To test for meningismus, the examiner flexes the neck of the supine patient by passively bending the head forward. In genuine meningismus, the Lasègue sign (see section ▶ 13.1.2, Radicular Syndromes due to Intervertebral Disk Herniation) is usually positive, often with a positive Bragard sign as well. If attempted passive flexion of the neck also induces flexion of the lower limbs at the knee or hip joint, this is called a positive cervical Brudzinski sign. This sign is often accompanied by a positive Kernig sign: when the patient is in the sitting position, the knee cannot be passively extended, and when the patient is supine, passive straight leg raising induces reflex knee flexion.


Auscultation of the skull may reveal a pulse-synchronous bruit over an arteriovenous fistula or malformation. A carotid bruit may be due to stenosis.


The intrinsic reflexes of the facial musculature should always be examined. Tapping a finger placed over the lateral canthus of the patient’s eye normally induces contraction of the ipsilateral orbicularis oculi muscle. This reflex normally weakens (habituates) on repeated tapping; if it does not, or if there is excessively intense, bilateral contraction of the orbicularis oculi when the examiner taps on the patient’s glabella (the glabellar or nasopalpebral reflex), then Parkinson disease or another type of bilateral lesion of the corticobulbar pathways is probably present. Tapping on a tongue depressor held loosely on the patient’s lips may induce lip protrusion (positive snout reflex). The masseter reflex (jaw jerk reflex) is elicited by gently tapping the patient’s jaw from above when the patient’s mouth is half open. Another way to elicit this reflex is to tap on a tongue depressor laid on the patient’s mandibular teeth. Very intense contraction of the perioral musculature indicates bilateral involvement of the corticobulbar pathways; the most common cause is a microangiopathic lacunar state. The corneomandibular reflex (“winking jaw phenomenon”) consists of deviation of the slightly opened jaw when the cornea is touched. Its presence on only one side, or any marked asymmetry, implies an interruption of the ascending and descending brainstem pathways terminating in the pontomesencephalic reticular formation.


3.3.2 Cranial Nerves


Next, the cranial nerves are examined individually. ▶ Fig. 3.3 and ▶ Table 3.3 provide an overview of the anatomy and function of the 12 cranial nerves. The clinical syndromes associated with lesions of individual cranial nerves are presented systematically in Chapter ▶ 12. In the current chapter, we will describe the main examining techniques and a selection of the important abnormal findings that can be elicited with each technique.































































Table 3.3 The 12 cranial nerves, their brainstem nuclei, and their functions

Cranial nerve


Anatomic substrates (peripheral and central); innervated structures


Function


I


Olfactory nerve




  • Sensory neurons of the nasal mucosa (olfactory zone)



  • Olfactory fila



  • Olfactory bulb and tract



  • Olfactory striae



  • Amygdala




  • Perception of odors (only substances dissolved in the fluid of the nasal mucosa can be perceived)


II


Optic nerve




  • Retina



  • Optic nerve



  • Optic chiasm



  • Optic tract



  • Lateral geniculate body



  • Optic radiation



  • Primary visual cortex on the banks of the calcarine fissure




  • Visual perception


III


Oculomotor nerve




  • Nucleus of the oculomotor nerve and Edinger–Westphal nucleus (both are in the midbrain)



  • Peripheral nerve



  • Levator palpebrae muscle; superior, inferior, and medial rectus muslces; and inferior oblique muscle, as well as the constrictor pupillae muscle




  • Elevation of the upper lid



  • Most of the movements of the globe (eyeball)



  • Constriction of the pupil


IV


Trochlear nerve




  • Nucleus of the trochlear nerve (midbrain at its junction with the pons)



  • Peripheral nerve



  • Superior oblique muscle




  • Depression of the adducted globe



  • Internal rotation of the abducted globe


V


Trigeminal nerve




  • Pontine and spinal nuclei of the trigeminal nerve (sensory root)



  • Motor nucleus of the trigeminal nerve (motor root)



  • Gasserian ganglion



  • Three peripheral nerve branches (the ophthalmic, maxillary, and mandibular nerves)



  • Skin and mucosa of the head and face; muscles of mastication (temporalis, masseter, and medial and lateral pterygoid muscles)




  • Sensation on the face and external ear



  • Sensation on mucosal surfaces of the head



  • Innervation of the muscles of mastication


VI


Abducens nerve




  • Nucleus of the abducens nerve (pons), intramedullary fascicle nerve



  • Lateral rectus muscle




  • Lateral gaze (nucleus)



  • Abduction of the globe (fascicle or peripheral nerve)


VII


Facial nerve




  • Nucleus of the facial nerve (pons, motor fibers for the muscles of facial expression)



  • Superior salivatory nucleus (secretory fibers for the lacrimal, nasal, and palatal glands)



  • Nucleus of the tractus solitarius (gustatory fibers for the anterior two-thirds of the tongue)



  • Peripheral nerve




  • Innervation of the muscles of facial expression and the stapedius muscle



  • Lacrimation and salivation



  • Taste on the anterior two-thirds of the tongue


VIII


Vestibulocochlear nerve (statoacoustic nerve, auditory nerve)




  • Sensory neurons in the cochlea (cochlear root) and in the semicircular canals



  • Utricle and saccule (vestibular root)



  • Peripheral afferent nerve trunk



  • Brainstem nuclei and projecting fibers to higher regions of the CNS




  • Perception of sound and of bodily position, movement, and acceleration



  • Regulation of balance


IX


Glossopharyngeal nerve




  • Nucleus ambiguus (medulla, motor fibers for the muscles of the soft palate and pharynx)



  • Nucleus of the tractus solitarius (gustatory fibers from the posterior third of the tongue, somatosensory fibers from the palatal and pharyngeal mucosa)



  • Inferior salivatory nucleus, otic ganglion (secretory fibers for the parotid gland)



  • Peripheral nerve




  • Motor innervation of the palatal and pharyngeal muscles



  • Somatosensory innervation of the palatal and pharyngeal mucosa



  • Taste on the posterior third of the tongue



  • Control of swallowing


X


Vagus nerve




  • Nucleus ambiguus (medulla, motor fibers for the muscles of the soft palate and pharynx)



  • Dorsal nucleus of the vagus nerve, nucleus of the tractus solitarius (visceromotor and viscerosensory fibers for the thoracic and abdominal viscera)



  • Spinal nucleus of the trigeminal nerve (sensory fibers from the pharynx, larynx, and external auditory canal)



  • Nerve trunk




  • Innervation of the laryngeal musculature (speech)



  • Sensation in the external ear canal and the posterior cranial fossa



  • Autonomic fibers to the thoracic and abdominal viscera


XI


Accessory nerve




  • Nucleus ambiguus (medulla, cranial root)



  • Spinal nucleus of the accessory nerve (C1–C5, spinal root)



  • Nerve trunk



  • Sternocleidomastoid muscle and upper portion of the trapezius muscle




  • Turning the head to the opposite side



  • Shrugging the shoulders


XII


Hypoglossal nerve




  • Nucleus of the hypoglossal nerve (medulla)



  • Nerve trunk



  • Muscles of the tongue




  • Movement of the tongue


Abbreviation: CNS, central nervous system.



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Fig. 3.3 The cranial nerves: overview of their sites of exit from the brainstem, components, and areas of innervation. I = olfactory nerve, II = optic nerve, III = oculomotor nerve, IV = trochlear nerve, V = trigeminal nerve, VI = abducens nerve, VII = facial nerve, VIII = vestibulocochlear nerve, IX = glossopharyngeal nerve, X = vagus nerve, XI = accessory nerve, XII = hypoglossal nerve. (Reproduced from Bähr M., Frotscher M. Neurologisch-topische Diagnostik. 9th ed. Stuttgart: Thieme; 2009.)




Note



The first two cranial nerves (the olfactory and optic nerves) are actually not peripheral nerves at all, but rather are portions of the brain that happen to be situated in the periphery. The remaining 10 structurally and functionally resemble the other peripheral nerves of the body. They have motor, somatosensory, special sensory, and autonomic functions.


Cranial Nerve I: Olfactory Nerve




Note



For the nuclei and functions of this nerve, see ▶ Table 3.3. For a detailed discussion of olfactory disturbances, see section ▶ 12.1.


The sense of smell is tested individually in each nostril. The patient is asked to close his or her eyes and then to identify (or at least perceive) aromatic substances such as coffee, peppermint, cinnamon, or vanilla that are held under the open nostril. Three-quarters of normal individuals can correctly identify coffee grounds. If there is doubt about the patient’s ability to smell, asafetida (onion extract), a substance with an unpleasant odor, is used. Only a complete loss of the sense of smell (anosmia; see section ▶ 12.1), not a mere diminution of it, is neurologically relevant. Anosmia is most commonly a sequel of severe traumatic brain injury but may also be due to frontal tumors, particularly olfactory groove meningioma, or postinfectious abnormalities of the nasal mucosa, for example, after an upper respiratory “cold,” or in ozena.




Note



If it is unclear whether anosmia is of neurologic origin, the patient is given a dilute ammonia solution to smell. The unpleasant irritation that this produces is mediated, not by the olfactory nerve, but by the trigeminal nerve. If the patient fails to react, then he or she is probably suffering either from an acute process affecting the nasal mucosa (e.g., acute rhinitis) or from a psychogenic disturbance. The anosmia is not neurogenic in either case.


Cranial Nerve II: Optic Nerve




Note



For the nuclei and functions of this nerve, see ▶ Table 3.3. For a detailed discussion of optic nerve disturbances, see section ▶ 12.2.


Ophthalmoscopy

Inspection of the optic nerve papillae (optic discs) with the ophthalmoscope is an important technique for assessment of the optic nerve. Abnormal pallor indicates an optic nerve lesion ( ▶ Fig. 3.4b). In addition, inspection of the fundus can provide evidence of subacutely or chronically elevated intracranial pressure: in papilledema, the papillae are raised and hyperemic, and their margins are blurred. Enlarged retinal veins indicate impaired venous drainage due to intracranial hypertension (cf. ▶ Fig. 12.3). A raised papilla with blurred margins can also be a sign of an inflammatory process affecting the optic nerve (see section ▶ 12.2.2, ▶ 12.2.2.3).



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Fig. 3.4 Optic disc (papilla) of the right eye. a Normal disc. b Pale, atrophic disc. (These images are provided courtesy of the Department of Ophthalmology, University of Bern.)




Note



Intracranial hypertension causes papilledema, which can be seen by ophthalmoscopy. Papilledema may, however, be absent if the intracranial hypertension is acute.


Visual Acuity

For neurologic purposes, visual acuity is usually tested with a wallchart seen from a distance. Patients who wear eyeglasses should wear them for this test.


Perimetry

Visual field testing is of special importance in neurology. The visual fields can be roughly assessed in the neurologist’s office or at the bedside with so-called finger perimetry (or digital confrontation; ▶ Fig. 3.5). The examiner sits directly in front of the patient and the patient fixes one eye on the examiner’s nose. The examiner then moves a finger in each of the four quadrants of the visual field, testing first the right eye, then the left. The patient is asked whether he or she can see the finger. This method can reveal a major visual field defect, for example, bitemporal hemianopsia or quadrantanopsia (see section ▶ 12.2.1). If the visual acuity is impaired, the visual fields of the two eyes should be tested separately; if the visual acuity is normal, the visual fields can be tested with both eyes open, because the lesion, if any, lies behind the optic chiasm and any visual field defect will therefore be homonymous.



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Fig. 3.5 Testing the visual fields by digital confrontation. a Double simultaneous testing for the detection of visual hemineglect. b Individual testing of all four quadrants of the visual field of each eye.

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Dec 28, 2017 | Posted by in NEUROLOGY | Comments Off on Head and Cranial Nerves
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