The nervous system, with its central and peripheral divisions, maintains and controls all body functions by its voluntary and autonomic responses. The evaluation of motor, sensory, autonomic, cognitive, and behavioral elements makes neurologic assessment one of the most complex portions of the physical examination. This chapter focuses on assessment of the cranial nerves, cerebellar function and proprioception, sensory function, and the superficial and deep tendon reflexes. Assessment of mental status (cognitive function, communication, and behavior) is addressed in Chapter 7 . Muscle strength assessment is addressed in Chapter 22 .
- 1.
Test cranial nerves I through XII.
- 2.
Evaluate coordination and fine motor skills by:
- •
Rapid rhythmic alternating movements
- •
Accuracy of upper and lower extremity movements
- •
- 3.
Evaluate balance using the Romberg test.
- 4.
Observe the patient’s gait for:
- •
Posture
- •
Rhythm and sequence of stride and arm movements
- •
- 5.
Test primary sensory responses to:
- •
Superficial touch
- •
Superficial pain
- •
- 6.
Test cortical sensory response to:
- •
Vibration with a tuning fork over joints or bony prominences on upper and lower extremities
- •
Position sense with movement of the great toes or a finger on each hand
- •
Identification of familiar object by touch and manipulation
- •
Two-point discrimination
- •
Identification of letter or number “drawn” on palm of hand
- •
Identification of body area when touched
- •
- 7.
Assess superficial and deep tendon reflexes
- •
Plantar reflex
- •
Abdominal reflexes
- •
Cremasteric reflex in male patients
- •
Biceps, brachioradialis, triceps, patellar, and Achilles deep tendon reflexes
- •
Ankle clonus
- •
Anatomy and Physiology
The central nervous system (brain and spinal cord) is the main network of coordination and control for the body. The peripheral nervous system, comprising the cranial and spinal nerves and the ascending and descending pathways, carries information to and from the central nervous system. The autonomic nervous system coordinates and regulates the internal organs of the body, such as cardiac muscle and smooth muscle. It has two divisions, each tending to balance the impulses of the other. The sympathetic division prods the body into action during times of physiologic and psychologic stress; the parasympathetic division functions in a complementary and a counterbalancing manner to conserve body resources and maintain day-to-day body functions such as digestion and elimination.
The intricate interrelationship of the nervous system divisions permits the body to perform the following:
- •
Receive sensory stimuli from the environment
- •
Identify and integrate the adaptive processes needed to maintain body functions
- •
Orchestrate body function changes required for adaptation and survival
- •
Integrate the rapid responsiveness of the central nervous system with the more gradual responsiveness of the endocrine system
- •
Control cognitive and voluntary behavioral processes (see Chapter 5 )
- •
Control subconscious and involuntary body functions
The brain and spinal cord are protected by the skull and vertebrae, the meninges, and the cerebrospinal fluid. Three layers of meninges surround the brain and spinal cord, assisting in the production and drainage of cerebrospinal fluid ( Fig. 23.1 ). Cerebrospinal fluid circulates between an interconnecting system of ventricles in the brain and around the brain and spinal cord, serving as a shock absorber.
Brain
The brain receives its blood supply (approximately 20% of the total cardiac output) from the two internal carotid arteries and two vertebral arteries ( Fig. 23.2 ). Blood drains from the brain through venous plexuses and dural sinuses that empty into the internal jugular veins. The three major units of the brain are the cerebrum, the cerebellum, and the brainstem.
Cerebrum
Two cerebral hemispheres (right and left), each divided into lobes, form the cerebrum. The gray outer layer, the cerebral cortex, houses the higher mental functions and is responsible for general movement, visceral functions, perception, behavior, and the integration of these functions. The hemispheres control the contralateral (opposite) side of the body. Commissural fibers (corpus callosum) interconnect the counterpart areas in each hemisphere, permitting the coordination of activities between the hemispheres ( Fig. 23.3 ; see also Fig. 7.1 ). The frontal lobe contains the motor cortex associated with voluntary skeletal movement and fine repetitive motor movements, as well as the control of eye movements. Specific areas in the primary motor area are associated with the movement of specific parts of the body. The corticospinal tracts extend from the primary motor area into the spinal cord.
The parietal lobe is primarily responsible for processing sensory data as it is received. It assists with the interpretation of tactile sensations (i.e., temperature, pressure, pain, size, shape, texture, and two-point discrimination), as well as visual, taste, smell, and hearing sensations. Recognition of body parts and awareness of body position (proprioception) are dependent on the parietal lobe. Association fibers provide communication between the sensory and motor areas of the brain.
The occipital lobe contains the primary vision center and provides interpretation of visual data.
The temporal lobe is responsible for the perception and interpretation of sounds and determination of their source. It is also involved in the integration of taste, smell, and balance. The reception and interpretation of speech is located in the Wernicke area. The medial temporal lobes include the hippocampi, which are essential for memory storage.
The basal ganglia system functions as the extrapyramidal pathway and processing station between the cerebral motor cortex and the upper brainstem. Through its interconnections with the thalamus, motor cortex, reticular formation, and spinal cord, the basal ganglia refine motor movements.
Cerebellum
The cerebellum aids the motor cortex of the cerebrum in the integration of voluntary movement. It processes sensory information from the eyes, ears, touch receptors, and musculoskeletal system. In concert with the vestibular system, the cerebellum uses the sensory data for reflexive control of muscle tone, balance, and posture to produce steady and precise movements. The cerebellum’s hemispheres have ipsilateral (same side) control of the body.
Brainstem
The brainstem is the pathway between the cerebral cortex and the spinal cord, and it controls many involuntary functions ( Table 23.1 ). Its structures include the medulla oblongata, pons, midbrain, and diencephalon. The nuclei of the 12 cranial nerves arise from these structures. The thalamus is the major integrating center for perception of various sensations such as pain and temperature (along with the cortical processing for interpretation). The thalamus also relays sensory aspects of motor information between the basal ganglia and cerebellum. The pons transmits information between the brainstem and the cerebellum, where motor information from the cerebral cortex is relayed to the contralateral cerebellar hemisphere. The medulla oblongata is the site where the descending corticospinal tracts decussate (cross to the contralateral side).
| STRUCTURE | FUNCTION |
|---|---|
| Medulla oblongata CN IX to XII |
|
| Pons CN V to VIII |
|
| Midbrain CN III and IV |
|
| Diencephalon CN I and II Thalamus |
|
| Epithalamus |
|
| Hypothalamus |
|
| Pituitary gland | Hormonal control of growth, lactation, vasoconstriction, and metabolism |
Cranial Nerves
Cranial nerves are peripheral nerves that arise from the brain rather than the spinal cord. Each nerve has motor or sensory functions, and four cranial nerves have parasympathetic functions ( Table 23.2 ).
| CRANIAL NERVES | FUNCTION |
|---|---|
| Olfactory (I) | Sensory: smell reception and interpretation |
| Optic (II) | Sensory: visual acuity and visual fields |
| Oculomotor (III) |
|
| Trochlear (IV) | Motor: downward, inward eye movement |
| Trigeminal (V) |
|
| Abducens (VI) | Motor: lateral eye movement |
| Facial (VII) |
|
| Acoustic (VIII) | Sensory: hearing and equilibrium |
| Glossopharyngeal (IX) |
|
| Vagus (X) |
|
| Spinal accessory (XI) | Motor: turn head, shrug shoulders, some actions for phonation |
| Hypoglossal (XII) | Motor: tongue movement for speech sound articulation (l, t, d, n) and swallowing |
Spinal Cord and Spinal Tracts
The spinal cord, 40 to 50 cm long, begins at the foramen magnum as a continuation of the medulla oblongata and terminates at L1 or L2 of the vertebral column. Fibers, grouped into tracts, run through the spinal cord carrying sensory, motor, and autonomic impulses between higher centers in the brain and the body. The gray matter, arranged in a butterfly shape with anterior and posterior horns, contains the nerve cell bodies associated with sensory pathways and the autonomic nervous system. The white matter of the spinal cord contains the ascending and descending spinal tracts ( Fig. 23.4 ).
The ascending spinal tracts (e.g., spinothalamic, spinocerebellar) mediate various sensations. These spinal tracts manage the sensory signals necessary to perform complex discrimination tasks. They are capable of transmitting precise information about the type of stimulus and its location. The posterior (dorsal) column spinal tract (fasciculus gracilis and fasciculus cuneatus) carries the fibers for the sensations of fine touch, two-point discrimination, and proprioception. The spinothalamic tracts carry the fibers for the sensations of light and crude touch, pressure, temperature, and pain.
The descending spinal tracts (corticospinal, reticulospinal, vestibulospinal) convey impulses from the brain to various muscle groups by inhibiting or exciting spinal activity. They also have a role in the control of muscle tone, posture, and precise motor movements. The corticospinal (pyramidal) tract permits skilled, delicate, and purposeful movements. The vestibulospinal tract causes the extensor muscles of the body to suddenly contract when an individual starts to fall. The corticobulbar tract arising from the brainstem innervates the motor functions of the cranial nerves.
Upper motor neurons are nerve cell bodies for the motor pathways that all begin and end within the central nervous system. They comprise the descending pathways from the brain to the spinal cord. Their primary role is influencing, directing, and modifying spinal reflex arcs and circuits. The upper motor neurons can affect movement only through the lower motor neurons. The lower motor neurons, cranial and spinal motor neurons, originate in the anterior horn of the spinal cord and extend into the peripheral nervous system. They transmit neural signals directly to the muscles to permit movement. Injury to the upper motor neurons results in initial paralysis followed by partial recovery over an extended period. Injury to the lower motor neurons often results in permanent paralysis.
Spinal Nerves
Thirty-one pairs of spinal nerves arise from the spinal cord and exit at each intervertebral foramen ( Fig. 23.5 ). The sensory and motor fibers of each spinal nerve supply and receive information in a specific body distribution of cutaneous innervation called a dermatome ( Fig. 23.6 ). The anterior branches of several spinal nerves combine to form a nerve plexus (network of nerve fibers), so that a spinal nerve may lose its individuality to some extent. The spinal nerve may complement the effort of an anatomically related nerve or even help compensate for some loss of function. A multitude of peripheral nerves originates from each nerve plexus.
Within the spinal cord, each spinal nerve separates into anterior and posterior roots. The motor or efferent fibers of the anterior root carry impulses from the spinal cord to the muscles and glands of the body. The sensory or afferent fibers of the posterior root carry impulses from sensory receptors of the body to the spinal cord, and then on to the brain for interpretation by the cerebral sensory cortex.
A spinal afferent (sensory) neuron may initiate a reflex arc response when it receives an impulse stimulus such as a tap on a stretched muscle tendon. In this case, the response is transmitted outward by the efferent (motor) neuron in the anterior horn of the spinal cord via the spinal nerve and peripheral nerve of the skeletal muscle, stimulating a brisk contraction ( Fig. 23.7 ). Such a reflex is dependent on intact afferent neurons, functional synapses in the spinal cord, intact efferent neurons, functional neuromuscular junctions, and competent muscle fibers.
Infants and Children
The major portion of brain growth occurs in the first year of life, along with myelinization of the brain and nervous system. Any event that disrupts brain development and growth during this period (e.g., infection, biochemical imbalance, or trauma) can have profound effects on eventual brain function. At birth, the neurologic impulses are primarily handled by the brainstem and spinal cord, such as the following reflexes: sucking, rooting, yawn, sneeze, hiccup, blink at bright light, and withdrawal from painful stimuli. Some primitive reflexes are present at birth (e.g., Moro, stepping, palmar and plantar grasp), and as the brain develops, these reflexes are inhibited as more advanced cortical functions and voluntary control take over.
Motor maturation proceeds in a cephalocaudal direction. Motor control of the head and neck develops first, followed by the trunk and extremities. Motor development progresses, enabling more complex and independent functioning (see the table “Expected Motor Development Sequence in Children” in Chapter 22 ). Development occurs in an orderly sequence, but the timing varies considerably among children. Many capabilities may develop simultaneously in a child.
Pregnant Patients
Hypothalamic-pituitary neurohormonal changes occur with pregnancy; however, specific alterations in the neurologic system are not well identified. During the first trimester, individuals have increased sleep needs, but they may not feel rested, even with increased sleep. Late in pregnancy, sleep can be affected due to multiple discomforts, such as back pain, frequent urination, leg cramps, and restless leg syndrome.
Older Adults
The number of cerebral neurons decreases with aging, along with decreased brain size. The vast number of reserve neurons inhibits the appearance of clinical signs in many cases. Sensory functions such as taste, smell, and vision may be diminished. The velocity of nerve impulse conduction declines, so responses to various stimuli may be diminished, such as deep tendon reflexes. Sleep disturbances also occur. See Chapter 7 for changes in mental functioning.
Review of Related History
For each of the symptoms or conditions discussed in this section, particular topics to include in the history of the present illness are listed. Responses to questions about these topics provide clues for individualizing the physical examination and the development of a diagnostic evaluation appropriate for the particular patient. Questions regarding medication use (prescription and over-the-counter preparations) as well as complementary and alternative therapies are relevant for each area.
History of Present Illness
Seizures or Convulsions
- •
Independent observer’s report: fall to ground, shrill cry, motor activity, transition phase, change in color of face or lips, pupil changes or eye deviations, loss of consciousness, loss of bowel or bladder control
- •
Aura (perceptual sensation that may signal a seizure): irritability, tension, confusion, blurred vision, mood changes, initial focal motor seizure activity, gastrointestinal distress
- •
Level of consciousness: loss, impairment, duration
- •
Automatism: eyelid fluttering, chewing, lip smacking, swallowing
- •
Muscle tone: flaccid, stiff, tense, twitching; where spasm began and moved through the body; change in character of motor activity during seizure
- •
Postictal phase: weakness, transient paralysis, confusion, drowsiness, headaches, muscle aching, sleeping after seizure; any lateralization of signs
- •
Relationship of seizure to time of day, meals, fatigue, emotional stress, excitement, menses, and discontinuing medications or poor medication adherence; activity before episode
- •
Frequency of seizures; total length of seizure activity; age at first seizure
- •
Medications: antiepileptic; initiation of medication or complementary or alternative therapy, potential for herb or product used that interacts with prescribed antiepileptic medication
Pain
- •
See Chapter 6 for general topics but consider “neurologic-specific” pain such as headaches associated with meningitis or encephalitis, space-occupying lesions, neck pain, sciatica, trigeminal neuralgia, or diabetic neuropathy.
- •
Onset: sudden or progressive, associated with fever or injury
- •
Quality and intensity: deep or superficial; aching, boring, throbbing, sharp or stabbing, burning, pressing, stinging, cramping, gnawing, prickling, shooting; duration and constancy
- •
Location or path: along distribution of one or more peripheral nerves, the feet, or a more general distribution; radiating from one part to another
- •
Associated manifestations: crying, change in activity or energy level, sweating, muscle rigidity, tremor, impaired mental processes or concentration, weakness
- •
Efforts to treat and impact on life
- •
Medications: opioids or nonsteroidal antiinflammatory drugs; prescription, nonprescription
Gait Coordination
- •
Balance: sensation of leaning when walking to doorway; unsteadiness when walking
- •
Vertigo: see Chapter 13 , History of Present Illness, for more information
- •
Falling: fall one way, backward, forward, consistent direction; associated with looking up; legs simply give way; stiffness of limbs
- •
Associated problems: arthritis of cervical spine or in knees, ataxia, stroke, seizure, arrhythmias, sensory changes
- •
Medications: phenytoin, pyrimethamine, etoposide, vinblastine; prescription, nonprescription
Weakness or Paresthesia
- •
Onset: sudden, with activity initiation or following sustained activity, time before symptoms begin; rapid or slow
- •
Character: generalized or specific body area affected (face, extremity); progressively ascending or transient; proximal or distal extremities, unilateral, bilateral, or asymmetric; difficulty walking; loss of balance or coordination; hypersensitivity to touch or burning sensation
- •
Associated symptoms: tingling or numbness; confusion, trouble speaking or understanding speech; severe headache; impaired vision in one or both eyes; limb feels encased in tight bandage, pain, shortness of breath, stiffness of joints, spasms, muscle tension, sensory deficits; loss of urinary or bowel control; personality change
- •
Concurrent chronic illness such as human immunodeficiency virus (HIV) infection, diabetes, nutritional or vitamin deficiency, or recent acute illness
- •
Medications: zidovudine, chemotherapy, HIV medications, amphotericin B
- •
Hypertension
- •
Obesity
- •
Sedentary lifestyle
- •
Smoking tobacco products
- •
Stress
- •
Increased levels of serum cholesterol, lipoproteins, and triglycerides
- •
Use of oral contraceptives, sickle cell disease
- •
Family history of diabetes mellitus, cardiovascular disease, hypertension, and increased serum cholesterol levels
- •
Congenital cerebrovascular anomalies
Tremor
- •
Onset: sudden or gradual
- •
Character: worse with rest, intentional movement, or anxiety; unilateral or bilateral; body location (distal extremities, head); interference with daily activities and impact on life
- •
Associated problems: hyperthyroidism, familial tremor, liver or kidney disorder, consumption of alcohol, multiple sclerosis
- •
Relieved by: rest, activity, alcohol
- •
Medications: neuroleptics, valproate, phenytoin, albuterol, pseudoephedrine, antiarrhythmics, corticosteroids, caffeine (all may cause essential tremor)
Past Medical History
- •
Trauma: concussion or brain injury, spinal cord injury, or localized injury; central nervous system insult; birth trauma; stroke
- •
Meningitis, encephalitis, lead poisoning, poliomyelitis
- •
Deformities, congenital anomalies, genetic syndromes
- •
Cardiovascular, circulatory problems: hypertension, aneurysm, peripheral vascular disease
- •
Neurologic disorder, brain surgery, residual effects
- •
Headaches (e.g., migraines)
Family History
- •
Hereditary disorders: neurofibromatosis, Huntington chorea, muscular dystrophy, diabetes, pernicious anemia
- •
Alcoholism
- •
Intellectual disability
- •
Epilepsy or seizure disorder, headaches
- •
Alzheimer disease or other dementia, Parkinson disease
- •
Learning disorders
- •
Weakness or gait disorders, cerebral palsy
- •
Medical or metabolic disorder: thyroid disease, hypertension, diabetes mellitus
Personal and Social History
- •
Environmental or occupational hazards: exposure to lead, arsenic, insecticides, organic solvents, other chemicals; operate farm or other dangerous equipment or work at heights or in water (neurologic disorder may impact employment or personal safety)
- •
Hand, eye, and foot dominance; family patterns of dexterity and dominance
- •
Ability to care for self: hygiene, activities of daily living, finances, communication, shopping; ability to fulfill work expectations
- •
Sleeping or eating patterns; weight loss or gain; anxiety
- •
Use of alcohol or recreational drugs, especially mood-altering drugs
Infants
- •
Prenatal history: pregnant person’s health, medications taken, intrauterine infections such as toxoplasmosis, syphilis, tuberculosis, rubella, cytomegalovirus, herpes, fetal movement, prior history of hypertension, preeclampsia, bleeding, history of trauma or stress, persistent vomiting, hypertension, drug or alcohol use
- •
Birth history: Apgar score, gestational age, prematurity, birth weight, presentation, use of instruments to assist in delivery, prolonged or precipitate labor, fetal distress
- •
Respiratory status at birth: resuscitation needed, apnea, cyanosis, need for oxygen or mechanical ventilation
- •
Neonatal health: jaundice (from ABO blood type incompatibility, breast-feeding, or other causes), perinatal infections, seizures, irritability, poorly coordinated sucking and swallowing, need for intensive care, ototoxic medication exposure
- •
Congenital anomalies, congenital heart disease, or other physical disabilities
- •
Hypotonia or hypertonia in infancy, developmental delay
Children
- •
Developmental milestones
- •
Age attained: smiling, head control in prone position, grasping, transferring objects between hands, rolling over, sitting, crawling, independent walking, toilet-trained, says words other than “mama” and “dada”
- •
Pattern of development: similar to other children; always slower than others; loss of previously achieved function; change in the child’s rate of development; (progress occurred as expected until a certain age with slow progress afterward)
- •
- •
Performance of self-care activities: dressing, toileting, feeding
- •
Hyperactive or impulsive behavior; problems with schedule changes, sitting for entire meal; poor organizational skills, unable to handle more than one instruction at a time, uncontrolled anger, poor social skills; school problems
- •
Health problems:
- •
Headaches, unexplained vomiting, lethargy, personality changes
- •
Seizure activity: association with fever, frequency, duration, character of movement
- •
Any clumsiness, unsteady gait, progressive muscular weakness, unexplained falling, problems going up and down stairs, problems getting up after lying down on floor
- •
Pregnant Patients
- •
Weeks of gestation or estimated date of delivery
- •
Seizure activity: past history of seizures or pregnancy-induced hypertension; frequency, duration, character of movement
- •
Headache: onset, character, frequency, association with hypertension; visual changes
- •
Nutritional status: dietary supplements such as prenatal vitamins, calcium; salt depletion
Older Adults
- •
Pattern of increased stumbling, falls, unsteadiness, or decreased agility; worse in the dark; safety modifications used in home
- •
Interference with performance of daily living tasks, social withdrawal, personality change, feelings about symptoms
- •
Hearing loss, vision deficit, anosmia—transient or persistent
- •
Urinary or fecal incontinence
- •
Transient neurologic deficits (may indicate transient ischemic attacks)
Ask these three screening questions to assess fall risk:
- •
Have you fallen in the past year?
- •
Do you feel unsteady when standing or walking?
- •
Do you worry about falling?
A positive answer to any of the questions indicates a need for further assessment because fall risk is higher ( Centers for Disease Control and Prevention, 2016b ). Other risk factors for falls include the following:
- •
Past history of a stroke
- •
Neurologic condition such as Parkinson disease, dementia, or peripheral neuropathy
- •
Disorder of gait, balance, or vertigo
- •
Lower extremity weakness or sensory loss
- •
Impaired vision
- •
Use of an assistive device (e.g., walker or cane)
Examination and Findings
Equipment
- •
Penlight
- •
Tongue blade, paper clip, cotton-tipped applicator
- •
Tuning forks, 200 to 400 Hz and 500 to 1000 Hz
- •
Familiar objects: coins, keys, paper clip
- •
Cotton wisp
- •
5.07 monofilament
- •
Reflex hammer
- •
Additional items for a comprehensive diagnostic neurologic examination
- •
Vials of aromatic substances: coffee, orange, peppermint extract, oil of cloves
- •
Vials of solutions: glucose, salt, lemon or vinegar, and quinine—with applicators for taste testing
- •
Test tubes of hot and cold water for temperature sensation testing
Because the neurologic examination is complex, the discussion is divided into four sections for an organized approach. These sections include cranial nerves, proprioception and cerebellar function, sensory function, and reflex function. Assessment of mental status is detailed in Chapter 7 . Evaluation of muscle tone and strength, an integral part of the neurologic examination, is detailed in Chapter 22 .
The neurologic system is assessed during the entire patient visit. When the patient enters the room, his or her response to your suggestion about where to sit provides information about the functioning of the neurologic system. For example, you can observe balance, coordination and smoothness of gait, and ability to follow directions, all providing clues about the neurologic system. The musculoskeletal examination, particularly muscle tone and strength, provides important information about the neurologic examination because the systems are interdependent. When the history and examination findings have not yet revealed a potential neurologic problem, a neurologic screening examination may be performed ( Box 23.1 ).
The shorter screening examination is commonly used for health visits when no known neurologic problem is apparent.
Cranial Nerves
Cranial nerves II through XII are routinely tested; however, taste is not tested unless some aberration is found.
Proprioception and Cerebellar Function
One test is administered for each of the following: rapid rhythmic alternating movements, accuracy of movements, balance (Romberg test is given), and gait and heel-toe walking.
Sensory Function
Superficial pain and touch at a distal point in each extremity are tested; vibration and position senses are assessed by testing the great toe.
Deep Tendon Reflexes
All deep tendon reflexes are tested, excluding the plantar reflex and the test for clonus.
Cranial Nerves
Evaluating the cranial nerves is an integral part of the neurologic examination. Ordinarily, taste and smell are not evaluated unless a problem is suspected. A patient may not recognize that some hearing, certain taste sensations, or some vision has been lost. When a sensory loss is suspected, be compulsive about determining the extent of loss when testing the relevant cranial nerve.
Examination of some cranial nerves is described in detail in other chapters, associated with the body system in which they are most commonly evaluated. Testing of the optic (II), oculomotor (III), trochlear (IV), and abducens (VI) nerves are described in Chapter 12 ; the acoustic (VIII) and hypoglossal (XII) nerves in Chapter 13 ; and the spinal accessory nerve (XI) in Chapter 22 . Table 23.3 describes a review of all cranial nerve examination procedures. Unexpected findings (focal deficits) indicate trauma or a lesion in the cerebral hemisphere or local injury to the nerve. See Clinical Pearl, “Mnemonic for Cranial Nerve Names.”
One way to remember the cranial nerves is the mnemonic for the first letter of each nerve: On Old Olympus Towering Tops A Finn and German Viewed Some Hops. Classification of each cranial nerves by function—Sensory (S), Motor (M), or Both (B) can be remembered by the mnemonic: Some Say Marry Money But My Brother Says Bad Business Marry Money.
| CRANIAL NERVE (CN) | PROCEDURE |
|---|---|
| CN I (olfactory) | Test ability to identify familiar aromatic odors, one naris at a time with eyes closed |
| CN II (optic) |
|
| CN III (oculomotor), CN IV (trochlear), and CN VI (abducens) |
|
| CN V (trigeminal) |
|
| CN VII (facial) |
|
| CN VIII (acoustic) |
|
| CN IX (glossopharyngeal), and X (vagus) |
|
| CN XI (spinal accessory) |
|
| CN XII (hypoglossal) |
|
Olfactory (I)
The olfactory nerve is tested when a concern exists with the patient’s ability to discriminate odors. Have available two or three vials of familiar aromatic odors. Use the least irritating aromatic substance (e.g., orange or peppermint extract) first so that the patient’s perception of weaker odors is not impaired. Before starting the assessment make sure the patient’s nasal passages are patent. Occlude one naris at a time and ask the patient to breathe in and out.
Ask the patient to close his or her eyes and to occlude one naris. Hold an opened vial under the nose. Ask the patient to inspire deeply (so the odor reaches the upper nose and swirls around the olfactory mucosa) and to identify the odor ( Fig. 23.8 ). Use a different odor to test the other side. Continue the assessment, alternating between sides with two or three odors, comparing the patient’s ability to identify and discriminate between odors. Avoid offering multiple odors too quickly as this may confuse the olfactory sense.
Patients are expected to perceive an odor on each side, and usually to identify it. Inflammation of the mucous membranes, allergic rhinitis, and excessive tobacco smoking may all interfere with the ability to distinguish odors. The sense of smell may diminish with age. Anosmia, the loss of sense of smell or an inability to discriminate odors, can be caused by trauma to the cribriform plate or by an olfactory tract lesion.
Optic (II)
Visual acuity and visual fields are evaluated as described in Chapter 12 .
Oculomotor, Trochlear, and Abducens (III, IV, and VI)
Movement of the eyes through the six cardinal points of gaze, pupil size, shape, response to light and accommodation, and opening of the upper eyelids are described in Chapter 12 .
When assessing patients with severe, unremitting headaches, the experienced examiner evaluates movement of the eyes for the presence or absence of lateral (temporal) gaze. The sixth cranial nerve is commonly one of the first to lose function in the presence of increased intracranial pressure.
Trigeminal (V)
Evaluate motor function by observing the face for muscle atrophy, deviation of the jaw to one side, and fasciculation (muscle twitches). Have the patient tightly clench the teeth as you palpate the muscles over the jaw, evaluating tone ( Fig. 23.9 ). Muscle tone over the face should be symmetric, without fasciculation.
The three divisions of the trigeminal nerve are evaluated for sharp, dull, and light touch sensation ( Fig. 23.10 ). With the patient’s eyes closed, touch each side of the face at the scalp, cheek, and chin areas, alternately using the sharp and smooth edges of a broken tongue blade or a paper clip. Avoid using a predictable pattern. Ask the patient to report whether each sensation is sharp or dull. Then stroke the face in the same six areas with a cotton wisp, brush, or lightly with a fingerpad, asking the patient to tell when the stimulus is felt. A wooden applicator is used to test sensation over the buccal mucosa. Discrimination of all stimuli is expected over all areas of the face.
If sensation is impaired, use test tubes filled with hot and cold water to evaluate temperature sensation. Ask the patient to tell you if hot or cold is felt as you touch the same six areas of the face. Contrast the discrimination of temperature with the other sensations.
When assessment of the corneal reflex is clinically indicated, have the patient look up and away from you as you approach from the side (contact lenses, if used, should be removed). Avoiding the eyelashes and the conjunctiva, lightly touch the cornea of one eye with a cotton wisp. Repeat the procedure on the other cornea. A symmetric blink reflex to corneal stimulation is expected. Patients who wear contact lenses may have a diminished or absent reflex.
Facial (VII)
Evaluate motor function by observing a series of expressions you ask the patient to make: Raise the eyebrows, squeeze the eyes shut, wrinkle the forehead, frown, smile, show the teeth, purse the lips to whistle, and puff out the cheeks ( Fig. 23.11 ). Observe for tics, unusual facial movements, and asymmetry of expression. Listen as the patient speaks and note any difficulties with labial speech sounds (b, m, and p). Drooping of one side of the mouth, a flattened nasolabial fold, and a sagging lower eyelid are signs of muscle weakness. See the discussion of Bell palsy later in the chapter and Clinical Pearl, “Upper and Lower Neuron Disease.”
To distinguish between upper and lower neuron disease affecting the face, observe the patient’s face when laughing or crying. When the upper motor neurons are affected, as in a stroke or brain attack, voluntary movements are paralyzed, but emotional movements are spared. In a lower motor neuron disorder, such as Bell palsy, all facial movements on the affected side are paralyzed.
To evaluate taste, a sensory function of cranial nerves VII and IX, have available the four solutions, applicators, and a card listing the tastes (bitter, sour, salty, sweet). Make sure the patient cannot see the labels on the vials. Ask the patient to keep the tongue protruded and to point out the taste perceived on the card. Apply one solution at a time to the lateral side of the tongue in the appropriate taste bud region ( Fig. 23.12 ). Alternate the solutions, using a different applicator for each. Offer a sip of water after each stimulus. Each solution is used on both sides of the tongue to identify taste discrimination. The patient should identify each taste bilaterally when placed correctly on the tongue surface (see Clinical Pearl, “Evaluating Taste Sensation” ).
Taste is rarely evaluated in the routine neurologic examination. Taste acuity decreases with advanced aging, but the extent of decline varies for the four different tastes—salty, sweet, sour, and bitter—that are tested. Most individuals who describe a loss of taste sensation actually have a dysfunction of olfactory sensation ( Doty, 2012 ).
Acoustic (VIII)
Hearing is evaluated with the screening tests described in Chapter 13 or with an audiometer. Vestibular function is tested by the Romberg test (described later in the chapter). Other vestibular function tests are not routinely performed.
Glossopharyngeal (IX)
The sensory function of taste over the posterior third of the tongue may be tested during cranial nerve VII evaluation. The glossopharyngeal nerve is simultaneously tested during evaluation of the vagus nerve for nasopharyngeal sensation (gag reflex) and the motor function of swallowing.
Vagus (X)
To evaluate nasopharyngeal sensation, tell the patient you will be testing the gag reflex. Touch the posterior wall of the patient’s pharynx with an applicator as you observe for upward movement of the palate and contraction of the pharyngeal muscles. Expect the uvula to remain in the midline. Drooping or absence of an arch on either side of the soft palate is unexpected.
Evaluate motor function by inspection of the soft palate for symmetry. Have the patient say “ah,” and observe the movement of the soft palate and uvula for asymmetry. If the vagus or glossopharyngeal nerve is damaged and the palate fails to rise, the uvula will deviate from the midline.
Have the patient sip and swallow water. You can do this while examining the thyroid gland (see Chapter 11 ). The patient should swallow easily. No retrograde passage of water through the nose after the nasopharynx has closed off or aspiration should occur.
Listen to the patient’s speech, noting any hoarseness, nasal quality, or difficulty with guttural sounds.
Spinal Accessory (XI)
Evaluation of the size, shape, and strength of the trapezius and sternocleidomastoid muscles is described in Chapter 22 .
Hypoglossal (XII)
Inspect the patient’s tongue while at rest on the floor of the mouth and while protruded from the mouth ( Fig. 23.13 ). Ask the patient to move the tongue in and out of the mouth, from side to side, curled upward as if to touch the nose, and curled downward as if to lick the chin. Test the tongue’s muscle strength by asking the patient to push the tongue against the cheek as you apply resistance with an index finger. When listening to the patient’s speech, expect no problems with lingual speech sounds (l, t, d, n). Any tongue fasciculation, asymmetry, atrophy, or deviation from the midline is unexpected.
