Chapter 15 – Neurological system assessment

Introduction to Cranial Nerves

In total, 12 paired cranial nerves originate within the brain and brainstem and extend into multiple branches (see Figure 6).

The 12 cranial nerves are related to sensory and/or motor functions (see Table 4). Sensory refers to senses such as seeing, hearing, tasting, smelling, and touching, while motor refers to movement. Innervation and associated responsibilities of the nerves can be affected when the nerve is damaged from a physical trauma (e.g., an accident), a surgical intervention, a (related to a stroke, cerebral inflammation, tumour, aneurysm), or a condition resulting in (e.g., multiple sclerosis).

The next section explores some of the most common approaches that nurses use to examine the 12 pairs of cranial nerves. Keep in mind that there are many ways to assess cranial nerves, and an abnormal finding may indicate damage to the nerve. These findings should be considered in the context of the complete neurological examination.

Figure 6: Cranial nerves.

(This image is licensed under the Creative Commons Attribution 2.5 Generic license and taken from https://commons.wikimedia.org/w/index.php?curid=15108118)

 

Table 4: Cranial nerves.

 

Nerves

  

Neurological signs and symptoms (when CN is damaged)
 

CN I (1) Olfactory nerves

Sensory nerves related to smell.

  

  • Hyposmia (partial loss of the sense of smell) or anosmia (complete loss of the sense of smell).
 

CN II (2) Optic nerves

Sensory nerves related to visual acuity (how well a person’s eyes can identify shapes and details of an object at a specific distance) and visual fields (periphery of vision). This nerve is also responsible for sending a message to the brain when light is introduced to the eye when assessing pupillary light reflex to evaluate CN III.

  

  • Partial or complete loss of central or peripheral vision.
 

CN III (3) Oculomotor nerves

Sensory nerves related to pupil innervation (pupillary constriction) and lens shape.

Motor nerves related to upper eyelid movement and eye muscle movement specific to four muscles (superior rectus, inferior rectus, medial rectus, and inferior oblique) controlling eye movements: diagonal upward (both inward and outward); diagonal downward-outward; horizontal inward.

  

  • Loss of reactivity to light and pupillary dilation.
  • Inability to track an object (follow with eyes).
  • Inability to open eyelid or ptosis (drooping of the eyelid).
  • Double vision.
 

CN IV (4) Trochlear nerves

Motor nerves related to eye muscle movement specific to one set of muscles (superior oblique) controlling the diagonal downward-inward movement of the eye.

  

  • Inability to track an object downward and inward.
  • Double vision.
 

CN V (5) Trigeminal nerves

Sensory nerves related to the sense of touch on facial (forehead, maxillary, mandible) and the cornea.

Motor nerve related to the innervation of the temporal and masseter muscles of the face.

  

  • Asymmetrical, decreased, or no sensation/feeling to forehead, cheeks, and jaw region.
  • Delayed or absent .
  • Asymmetry in jaw clenching movement and decreased strength.
 

CN VI (6) Abducens nerves

Motor nerves related to eye muscle movement specific to one set of muscles (lateral rectus) controlling the horizontal outward movement of the eye.

  

  • Inability to track an object outward on a horizontal plane.
  • Double vision.
 

CN VII (7) Facial nerves

Sensory nerves related to taste on the dorsal side of the tongue on the anterior two-thirds (at the front of the tongue).

Motor nerves related to movement of the facial muscles (i.e., facial expressions).

  

  • Alteration in taste (decreased or absent).
  • Asymmetry of facial muscles such as flattening of the nasolabial fold or flattening of forehead wrinkles.
  • Inability to close eyes.
  • Decreased or inability to smile or show teeth.
 

CN VIII (8) Vestibulocochlear nerves

Sensory nerves related to balance (vestibular) and hearing (cochlear). This is a set of two nerves including the vestibular nerves and the cochlear nerves (with some motor function).

  

  • Issues with proprioceptive sensation, balance issues, dizziness, and nausea.
  • Difficulty or absent ability to hear sounds or voices.
 

CN IX (9) Glossopharyngeal and CN X (10) Vagus nerves

These nerves work together: CN IX carries afferent messages to the brain and CN X carries efferent messages to the affected area.

Sensory nerves (CN IX) related to taste on the dorsal side of the tongue on the posterior third (toward the back of the tongue) 

Motor nerves related to movement of the soft palate, uvula, and pharynx, and some muscles of the tonsillar pillars, swallowing, and speech. 

  

  • Decreased or absent taste (CN IX).
  • Diminished or absent gag reflex.
  • Asymmetrical or lack of movement of palate and uvula.
  • Dysphagia.
  • Dysphasia.
  • Hoarseness.
 

CN XI (11) Spinal accessory nerves

Motor nerves that innervates and controls the sternocleidomastoid and trapezius muscles.

  

  • Asymmetry and atrophy of neck muscles.
  • Misaligned levelling of shoulders.
  • Decreased range of motion of neck or shoulders on one or both sides
  • Decreased muscle resistance of neck or shoulders on one or both sides.
 

CN XII (12) Hypoglossal nerves

Motor nerves related to tongue movement and strength.

  

  • Inability to stick tongue out midline and tremor of tongue.
  • Decreased or inability to move tongue.
  • Decreased or no tongue strength.

Prioritizing Care

All abnormal findings related to cranial nerve testing should be documented and reported to the physician or nurse practitioner. These findings should be considered in the context of the full neurological exam. For example, you should refer a client to an eye specialist when their visual acuity is worse than 20/30. However, some abnormal findings require immediate action. For example, a sudden change in vision (e.g., partial or complete loss) and are a priority of care and you should immediately notify the physician or nurse practitioner.

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