13.2 Neurological Examination: Cranial Nerves, Motor, Sensory, and Reflexes
Key Takeaways
The neurological exam covers mental status, cranial nerves I-XII, motor bulk, tone and strength (0-5), sensation by pathway and dermatome, and reflexes (0-4+).
Upper motor neuron lesions cause spasticity, hyperreflexia, clonus, and a positive Babinski sign; lower motor neuron lesions cause flaccidity, hyporeflexia, fasciculations, and atrophy.
Pain and temperature travel in the spinothalamic tract, while vibration and proprioception travel in the dorsal columns, so the pattern of loss localizes the lesion.
Bell's palsy weakens the whole half of the face including the forehead, whereas a stroke spares the forehead because the upper face has bilateral cortical supply.
New focal weakness, facial droop, or speech disturbance with UMN signs is a stroke until proven otherwise and requires 911.
13.2 Neurological Examination: Cranial Nerves, Motor, Sensory, and Reflexes
Quick Answer: The clinical neurological examination evaluates cranial nerves (CN I–XII), motor bulk, tone, and power (graded 0 to 5 on the Medical Research Council scale), sensory pathways (spinothalamic pain/temperature vs dorsal column vibration/proprioception), deep tendon reflexes (graded 0 to 4+), and pathological reflexes (Babinski, Hoffman). Differentiating Upper Motor Neuron (UMN: stroke, spinal cord compression) from Lower Motor Neuron (LMN: radiculopathy, peripheral neuropathy) lesions hinges on tone (spasticity vs flaccidity), reflexes (hyperreflexia vs hyporeflexia/areflexia), and pathological signs (Babinski positive vs negative). The 2026 BIOM outline lists the neurological examination techniques explicitly: assessment of cognitive function, cranial nerves, sensory and motor function, dermatomal testing, and deep tendon reflexes. Orthopedic tests follow in Section 13.3.
Assessing Cognitive Function (Mental Status)
The neurological examination begins with mental status:
- Level of consciousness: alert, drowsy, stuporous, or unresponsive.
- Orientation: to person, place, time, and situation.
- Attention and memory: repeating digits, recalling three words after a few minutes.
- Language: fluency, comprehension, naming, and repetition (problems suggest aphasia).
Brief screening tools include the Mini-Cog (three-word recall plus clock drawing; a low score suggests impairment), the Montreal Cognitive Assessment (MoCA) (30 points; 26 or more is generally considered normal), and the Mini-Mental State Examination (MMSE) (30 points). A screening test does not diagnose dementia. Sudden confusion or fluctuating attention suggests delirium, which needs prompt medical evaluation (Section 12.6).
The Cranial Nerve Examination Protocol (CN I through XII)
The cranial nerve examination evaluates the brainstem, cranial base, and peripheral cranial pathways. Examiners must know the specific testing procedures, normal responses, and classic pathological signs for each pair:
| Nerve | Name | Primary Function | Clinical Testing Technique | Common Pathological Manifestations |
|---|---|---|---|---|
| CN I | Olfactory | Sensory: Smell | Present non-irritating odors (coffee, vanilla) to each nostril with opposite nostril occluded and eyes closed | Anosmia (loss of smell: cribriform plate fracture, frontal meningioma, Parkinson's early sign, viral rhinitis) |
| CN II | Optic | Sensory: Vision, afferent pupil reflex | Snellen visual acuity chart, confrontation visual field testing, funduscopic exam, direct/consensual pupillary light reflexes | Monocular blindness, bitemporal hemianopsia (pituitary adenoma at optic chiasm), optic neuritis (multiple sclerosis) |
| CN III | Oculomotor | Motor: Superior, inferior, medial recti, inferior oblique, levator palpebrae; Parasympathetic: pupil constriction | Extraocular eye movements (H-pattern), pupillary light reflex (efferent limb), observe eyelid position | Ptosis (eyelid droop), eye displaced downward and outward ("down and out"), dilated non-reactive pupil (mydriasis) |
| CN IV | Trochlear | Motor: Superior oblique (depresses and intorts adducted eye) | Instruct patient to look downward and inward (toward the tip of the nose) | Vertical diplopia worsening with downward gaze (e.g., walking down stairs); compensatory head tilt to opposite shoulder |
| CN V | Trigeminal | Sensory: Facial sensation (V1 ophthalmic, V2 maxillary, V3 mandibular); Motor: Muscles of mastication | Pinprick/light touch across three facial zones; corneal reflex (V1 afferent); palpate temporalis/masseter contraction | Facial numbness; loss of corneal reflex; weakness of jaw clench; Trigeminal neuralgia (paroxysmal electric shocks in V2/V3) |
| CN VI | Abducens | Motor: Lateral rectus (abducts eye) | Instruct patient to look laterally toward the periphery | Inability to abduct the eye past midline; horizontal diplopia on lateral gaze; vulnerability to elevated ICP (long intracranial course) |
| CN VII | Facial | Motor: Facial expression; Sensory: Taste anterior 2/3 tongue; Parasympathetic: Lacrimal/salivary glands | Raise eyebrows, frown, close eyes tightly against resistance, show teeth, puff cheeks, whistle | Facial asymmetry; Bell's palsy (complete hemifacial paralysis including forehead); Central stroke (forehead spared) |
| CN VIII | Vestibulocochlear | Sensory: Hearing (cochlear) and balance (vestibular) | Finger rub or whisper test; Weber test (tuning fork on vertex); Rinne test (air vs bone conduction on mastoid); Romberg | Sensorineural deafness vs conductive hearing loss; vertigo, nystagmus; Vestibular schwannoma / acoustic neuroma |
| CN IX | Glossopharyngeal | Sensory: Posterior 1/3 tongue taste, pharynx, carotid body; Motor: Stylopharyngeus | Gag reflex (afferent limb via CN IX; touched with tongue depressor); swallow coordination | Loss of gag reflex; dysphagia; glossopharyngeal neuralgia (throat and ear pain triggered by swallowing) |
| CN X | Vagus | Motor: Pharynx, larynx (vocal cords), palate; Parasympathetic: Viscera; Sensory: External ear | Observe soft palate elevation during "ah"; gag reflex (efferent limb); phonation / voice quality | Asymmetrical palate elevation (uvula deviates away from side of lesion); hoarseness (recurrent laryngeal nerve injury) |
| CN XI | Spinal Accessory | Motor: Sternocleidomastoid (SCM) and Trapezius | Patient shrugs shoulders against downward resistance; turns head forcefully to each side against examiner's hand | Trapezius atrophy, shoulder drop, inability to shrug affected shoulder; weakness turning head to opposite side |
| CN XII | Hypoglossal | Motor: Intrinsic and extrinsic muscles of tongue | Instruct patient to protrude tongue along midline; push tongue into cheek against resistance | Protruded tongue deviates toward the side of the lesion (in LMN weakness of genioglossus muscle); tongue fasciculations |
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| FACIAL NERVE (CN VII) DEFICIT DIFFERENTIATION |
+----------------------------------------------------------------------------+
| LOWER MOTOR NEURON (Bell's Palsy) UPPER MOTOR NEURON (CVA Stroke) |
| Lesion at Facial Nucleus / Peripheral Lesion at Contralateral Cortex |
| - Complete ipsilateral facial drop - Contralateral lower face drop |
| - CANNOT wrinkle forehead - CAN wrinkle forehead firmly |
| - CANNOT close eye tightly (lagophthalmos)- CAN close eye firmly |
| - Loss of nasolabial fold - Loss of nasolabial fold |
| - Drooping mouth corner - Drooping mouth corner |
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The Motor System: Bulk, Tone, and Strength Grading
The motor examination methodically investigates three parameters:
- Muscle Bulk: Visual inspection for symmetrical contour, disuse atrophy, or focal denervation muscle wasting (such as thenar eminence atrophy in advanced carpal tunnel syndrome, or intrinsic hand wasting in cervical radiculopathy).
- Muscle Tone: Evaluated by passively moving the patient's limbs through their normal range of motion:
- Spasticity: Velocity-dependent increase in muscle tone, characteristically resistance that peaks early and gives way ("clasp-knife" phenomenon), typical of corticospinal Upper Motor Neuron (UMN) lesions.
- Rigidity: Velocity-independent resistance throughout the entire range of motion, categorized as "lead-pipe" (continuous resistance) or "cogwheel" (rhythmic interruption of resistance seen in Parkinson's disease).
- Flaccidity / Hypotonia: Complete absence of resistance or limpness, typical of Lower Motor Neuron (LMN) lesions, spinal shock, or acute cerebellar lesions.
- Motor Strength Grading: Quantified using the internationally standardized Medical Research Council (MRC) Scale (0 to 5):
| MRC Grade | Operational Clinical Definition |
|---|---|
| Grade 0 | Complete paralysis: no visible or palpable muscle contraction whatsoever. |
| Grade 1 | Trace movement: barely perceptible flicker or trace contraction of the muscle, but no joint movement. |
| Grade 2 | Movement with gravity eliminated: active movement through complete range of motion only when the limb is supported so that gravity is neutralized (e.g., sliding arm across a smooth table). |
| Grade 3 | Movement against gravity only: active movement through complete range of motion against gravity, but unable to overcome any added external resistance applied by the examiner. |
| Grade 4 | Movement against gravity and some resistance: active movement against moderate examiner resistance, but strength is visibly diminished compared to the unaffected contralateral side. |
| Grade 5 | Normal active strength: complete range of motion against full, unyielding resistance appropriate for the patient's age and physical conditioning. |
Sensory System Pathways & Proprioception
Sensory testing isolates the two major ascending spinal tracts:
- Spinothalamic Tract: Mediates pain (pinprick testing with a sterile disposable neurological pin) and temperature sensation. Decussates within 1–2 spinal segments of entry in the anterior white commissure.
- Dorsal Column-Medial Lemniscal (DCML) Pathway: Mediates vibration sensation (tested with a low-frequency 128 Hz tuning fork over distal bony prominences: interphalangeal joint of big toe, medial malleolus, distal radius) and conscious joint position sense (proprioception: grasping the lateral borders of the distal phalanx of the toe/finger and moving it up or down by 1–2 mm with patient's eyes closed). Ascends uncrossed in the gracile and cuneate fasciculi to decussate in the medulla.
- The Romberg Test: Assesses sensory vs. cerebellar ataxia. The patient stands with feet together, arms at sides or crossed, eyes open (normal balance maintained by visual, vestibular, and proprioceptive inputs). The patient then closes their eyes for 30 seconds. A positive Romberg sign occurs if the patient maintains balance with eyes open but begins swaying violently or falls when eyes are closed. This confirms sensory ataxia due to dorsal column proprioceptive impairment (e.g., tabes dorsalis, subacute combined degeneration from B12 deficiency, diabetic polyneuropathy). In contrast, a patient with a primary cerebellar lesion is unsteady and ataxic whether their eyes are open or closed.
Deep Tendon Reflexes (DTR) & Pathological Reflexes
Deep tendon reflexes assess the integrity of both the sensory afferent arc and motor efferent arc at specific spinal segments:
| Reflex | Primary Spinal Roots | Normal Response |
|---|---|---|
| Biceps Reflex | C5, C6 | Forearm flexion and contraction of biceps brachii muscle |
| Brachioradialis Reflex | C6 | Forearm flexion and slight pronation |
| Triceps Reflex | C7 | Forearm extension and contraction of triceps brachii muscle |
| Patellar (Knee Jerk) | L4 (L2–L4) | Leg extension and contraction of quadriceps femoris muscle |
| Achilles (Ankle Jerk) | S1 (S1–S2) | Plantarflexion of the foot and gastrocnemius/soleus contraction |
DTR Grading Scale
- Grade 0: Absent reflex, even with reinforcement maneuvers (Jendrassik maneuver).
- Grade 1+: Hypoactive, diminished reflex; requires reinforcement to elicit.
- Grade 2+: Normal, brisk physiological response.
- Grade 3+: Hyperactive, exaggerated response; may indicate an upper motor neuron lesion or physiological anxiety.
- Grade 4+: Severely hyperactive with clonus (repetitive, rhythmic, involuntary muscular contractions elicited by sudden, sustained passive dorsiflexion of the ankle). Clonus of 3 or more sustained beats is unequivocally pathological.
Pathological Reflexes (Signs of Corticospinal Tract / UMN Disruption)
- Babinski Sign (Extensor Plantar Response): The lateral plantar aspect of the foot is stroked firmly with a blunt instrument from the heel forward across the ball of the foot toward the base of the great toe. A normal adult response is flexor plantar response (toes curl downward). A positive Babinski sign is slow, rhythmic dorsiflexion of the great toe accompanied by fanning (abduction) of the other four toes. This indicates corticospinal tract disruption (UMN lesion) anywhere between the motor cortex and the spinal cord.
- Chaddock Sign: Stroking the lateral foot around the lateral malleolus elicits the same extensor great toe response as Babinski.
- Hoffman Sign: The examiner stabilizes the patient's proximal interphalangeal joint of the middle finger and sharply flicks the distal phalanx downward using their thumb. A positive response is involuntary reflex flexion and adduction of the ipsilateral thumb and index finger, indicating cervical cord compression, cervical myelopathy, or hyperreflexia.
Upper Motor Neuron (UMN) vs. Lower Motor Neuron (LMN) Comparison
| Diagnostic Parameter | Upper Motor Neuron (UMN) Lesion | Lower Motor Neuron (LMN) Lesion |
|---|---|---|
| Anatomical Site of Lesion | Brain (cortex, internal capsule, brainstem) or descending spinal cord tracts (corticospinal tract) | Anterior horn cells (spinal cord), cranial nerve motor nuclei, nerve roots, peripheral nerves |
| Muscle Tone | Hypertonia: velocity-dependent spasticity; "clasp-knife" resistance | Hypotonia / Flaccidity: loose, limp, reduced resistance to passive movement |
| Deep Tendon Reflexes (DTR) | Hyperreflexia (graded 3+ to 4+); clonus present | Hyporeflexia or Areflexia (graded 0 to 1+) |
| Pathological Reflexes | Present: positive Babinski, Chaddock, and Hoffman signs | Absent: normal flexor plantar response; negative Hoffman |
| Muscle Bulk / Atrophy | Mild atrophy secondary to disuse only (late onset) | Severe, rapid denervation muscle atrophy (early onset) |
| Fasciculations | Absent | Present: visible fine involuntary twitching of muscle fascicles |
| Prototypical Clinical Conditions | Ischemic stroke, intracranial hemorrhage, traumatic brain injury, spinal cord compression, Multiple Sclerosis | Herniated disc radiculopathy, Bell's palsy, Cauda Equina syndrome, Guillain-Barré syndrome, ALS (mixed) |
A 58-year-old patient presents with progressive weakness and stiffness in the right lower extremity following a cerebrovascular event 4 months ago. Physical examination reveals velocity-dependent hypertonia ("clasp-knife" spasticity), a patellar reflex graded 3+, five beats of ankle clonus, and an upward (extensor) response of the great toe upon stroking the lateral plantar aspect of the foot. Which pathophysiological entity and classification are demonstrated by these findings?
Lower Motor Neuron (LMN) lesion characterized by flaccid paraparesis and denervation atrophy
Upper Motor Neuron (UMN) lesion characterized by loss of descending corticospinal tract inhibition
Peripheral polyneuropathy affecting large myelinated sensory fibers within the dorsal columns
Extrapyramidal Parkinsonian rigidity characterized by velocity-independent "cogwheel" tone
A 38-year-old female presents with sudden onset of right-sided facial weakness that began this morning. On physical examination, she is unable to wrinkle her right forehead, cannot close her right eye completely, demonstrates flattening of the right nasolabial fold, and exhibits drooping of the right corner of her mouth with inability to smile on the right side. Extraocular movements, extremity strength, and sensory examinations are completely intact. How does this clinical presentation distinguish between a peripheral Lower Motor Neuron (LMN) facial nerve lesion (Bell's palsy) and a central Upper Motor Neuron (UMN) stroke?
Inability to wrinkle the forehead and close the eye shows all branches of CN VII are involved, indicating a peripheral lesion (Bell's palsy); a stroke spares the forehead.
Involvement of the forehead confirms an acute ischemic stroke in the contralateral middle cerebral artery territory, which selectively paralyzes only the upper facial branch.
Inability to close the eye proves an oculomotor nerve (CN III) transection, whereas the facial nerve controls only the lower third of the face.
Sparing of extremity strength rules out any cranial nerve pathology, indicating functional conversion disorder.
When testing deep tendon reflexes, the examiner records the patient's biceps reflex as 3+ with a few beats of clonus at the ankle. How should this be interpreted?
Normal reflexes in an anxious patient who is tensing the limb
Hyperreflexia with clonus, suggesting an upper motor neuron lesion
Hyporeflexia consistent with peripheral neuropathy
A lower motor neuron lesion at the C5-C6 nerve root level with atrophy
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