Anatomy and Physiology 2e · The Neurological Exam
The Sensory and Motor Exams
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In 30 seconds
The sensory and motor exams test the two great highways of the somatic nervous system: the pathways that carry sensation from the skin, muscles, and joints into the central nervous system, and the pathways that carry voluntary movement commands out to skeletal muscle. The sensory exam samples light touch, pain, temperature, vibration, and position sense; the motor exam checks muscle bulk, tone Background resistance of muscle to passive stretch Full entry →, strength, and reflexes. Together they answer two questions: is the pathway working, and if not, where did it break?
The exam is organized around known anatomy. Sensation follows specific tracts through the spinal cord, each body region maps to a spinal segment (dermatomes), and each reflex is anchored to a spinal level. When a finding appears, the examiner can trace it backward: a patch of numbness, a weak muscle group, or an absent reflex each names a level — peripheral nerve, nerve root, spinal cord, or brain.
Why this matters
Strength testing and reflex grading are part of nearly every neurological assessment. The standardized strength scale (0–5) and reflex scale (0–4+) let different clinicians describe the same patient consistently. dermatome The strip of skin supplied by one spinal nerve Full entry → maps guide spinal cord injury assessment — the umbilicus sits near T10, for example. Most importantly, the exam separates upper motor neuron patterns (stroke, spinal cord injury) from lower motor neuron patterns (neuropathy, nerve injury), which point to different causes and treatments. For nurses and therapists, tracking strength and sensation over time documents whether a patient is improving, stable, or worsening.
The college version
Core Concepts
The sensory exam: what each test tells you
- Light touch (a wisp of cotton): tests fine-touch receptors and the dorsal column pathway.
- Pain (sharp versus dull): tests the spinothalamic pathway.
- Temperature (cool object): also the spinothalamic pathway — pain and temperature travel together.
- Vibration (tuning fork placed on a bony prominence): tests the dorsal column pathway.
- proprioception The sense of joint and body position Full entry → (joint position sense): tests the dorsal column pathway.
- Discriminative touch: two-point discrimination, stereognosis Identifying an object by touch alone Full entry → (identifying an object by touch alone), and graphesthesia Recognizing shapes or letters traced on the skin Full entry → (recognizing letters traced on the skin) — these need intact dorsal columns and sensory cortex.
The two main sensory tracts are worth knowing cold. The dorsal column–medial lemniscus pathway carries fine touch, vibration, and proprioception; it ascends on the same side of the spinal cord and crosses over in the medulla. The spinothalamic pathway carries pain and temperature; it crosses within a segment or two of entering the cord and ascends on the opposite side. Because the two tracts cross at different places, a lesion on one side of the spinal cord can abolish fine touch on the same side while abolishing pain on the opposite side — a "dissociated" sensory loss that is a classic clue in spinal cord problems.
Dermatomes: the body's segment map
Each spinal nerve supplies a strip of skin called a dermatome. Commonly taught landmarks include: C5 at the shoulder/deltoid, C6 at the thumb, C7 at the middle finger, C8 at the little finger, T4 at the nipple line, T10 at the umbilicus, L4 near the knee cap, L5 at the big toe, and S1 at the little toe and lateral foot. These maps help localize nerve root and spinal cord problems; they are reference guides, and individual variation exists.
The motor exam: bulk, tone, strength, reflexes
- Bulk: look for atrophy (a shrunken muscle) or fasciculations (visible twitching under the skin).
- Tone: resistance to passive movement. Flaccid (limp) and spastic (stiff) tones point in opposite diagnostic directions.
- Strength: graded 0–5: 0 = no visible contraction; 1 = a trace of contraction; 2 = movement with gravity eliminated; 3 = movement against gravity; 4 = movement against some resistance; 5 = normal strength. Major muscle groups are tested and recorded with the scale.
- Deep tendon reflexes: graded 0–4+, commonly taught as 0 = absent, 1+ = hypoactive, 2+ = normal, 3+ = brisk, 4+ = hyperactive (sometimes with clonus Rhythmic beating of a muscle under sustained stretch Full entry →, a rhythmic beating of the muscle). Each reflex is anchored to a spinal level; commonly taught references are the biceps and brachioradialis (C5–C6), triceps (C7), patellar (L3–L4), and Achilles (S1).
- Plantar reflex: stroking the sole normally produces curling-down toes. If the big toe extends upward and the toes fan out (the Babinski sign Big toe extends and toes fan when the sole is stroked Full entry →), it suggests damage to the upper motor neuron pathway in an adult. A Babinski response in infants is normal.
Upper versus lower motor neuron patterns
The single most testable idea in this topic is the contrast between two lesion locations:
- Upper motor neuron (UMN) damage — anywhere from the motor cortex down to the spinal cord's anterior horn, as in stroke or spinal cord injury — produces weakness with spasticity, hyperactive reflexes, a Babinski sign, and little early muscle atrophy.
- Lower motor neuron (LMN) damage — at the anterior horn cell, nerve root, or peripheral nerve, as in neuropathy — produces weakness with flaccidity, reduced or absent reflexes, atrophy, and fasciculations.
These commonly taught patterns predict the problem's level: spastic and hyperreflexic means damage above the anterior horn; flaccid and atrophic means damage to the final pathway to the muscle.
How It Works / Step-by-Step Process
- Sensory: test light touch on the face, arms, trunk, and legs; then pain (sharp/dull), temperature, vibration, and joint position; add discriminative tests (two-point, stereognosis, graphesthesia) when fine sensation matters.
- Motor: inspect muscle bulk; test tone by moving a relaxed limb; grade strength of the major muscle groups (shoulder, elbow, wrist, grip, hip, knee, ankle) on the 0–5 scale.
- Reflexes: test the biceps, brachioradialis, triceps, patellar, and Achilles reflexes, then the plantar response.
- Synthesize: does the pattern fit a peripheral nerve, a single nerve root (dermatome + its muscles + its reflex), one side of the spinal cord (dissociated sensory loss), or a brain problem (UMN signs, face and limb together)?
Common Confusions
| Do not confuse | With | Difference |
|---|---|---|
| Light touch and vibration | pain and temperature | Different tracts (dorsal columns vs spinothalamic); a "dissociated" loss helps localize the lesion |
| Upper motor neuron weakness | lower motor neuron weakness | Spastic + hyperreflexic + Babinski vs flaccid + atrophic + hyporeflexic |
| Babinski sign in an infant | Babinski sign in an adult | Normal early in life; an upper motor neuron sign after that |
| 3+ reflex | 4+ reflex | 3+ is brisk; 4+ is hyperactive and may show clonus |
| Dermatome | peripheral nerve territory | A dermatome is a spinal segment map; a peripheral nerve usually spans several segments |
| 2 on the strength scale | 3 on the strength scale | 2 moves with gravity eliminated; 3 moves against gravity |
Eli explains
The same idea, in plain words
Explain it like I’m 10
The sensory and motor exams are like checking the phone lines of the body. The sensory tests ask, "Can you feel this?" — soft touch, sharp or dull, hot or cold, and where your joints are. The motor tests ask, "Can you move?" — how strong you are and whether your reflexes fire. The pattern of what works and what doesn't tells you which cable — the brain, the spinal cord, a nerve root, or a nerve — is broken.
Worked example
A person reports numbness and weakness in the right hand after a recent injury. The exam finds reduced light touch and vibration over the right thumb and index finger (a C6 dermatome pattern), weak elbow flexion and wrist extension, and a diminished right biceps reflex — while everything else, including the plantar responses, is normal. The findings line up on a single segment: one dermatome, its muscles, and its reflex. That pattern localizes the problem to the right C6 nerve root rather than the brain, which would more likely cause spastic weakness, hyperreflexia, and a Babinski sign. A stroke patient with left arm weakness would instead show increased tone, brisk reflexes, and an up-going toe — the upper motor neuron signature.
Key takeaways
- Two sensory tracts: dorsal columns (fine touch, vibration, proprioception; crosses in the medulla) and spinothalamic (pain, temperature; crosses in the spinal cord).
- Strength scale 0–5: know the anchors — 2 = moves with gravity eliminated, 3 = against gravity, 4 = against some resistance.
- Reflex scale 0–4+: 4+ is hyperactive and may include clonus.
- Common reflex segments: biceps/brachioradialis C5–C6, triceps C7, patellar L3–L4, Achilles S1 (commonly taught references).
- Dermatome landmarks: T4 = nipple line, T10 = umbilicus, L5 = big toe.
- Babinski sign in an adult = upper motor neuron problem; normal in infants.
- UMN pattern: spastic, hyperreflexic, Babinski positive. LMN pattern: flaccid, atrophic, hyporeflexic, fasciculations.
Check yourself
6 review questions from the chapter. Try each one, then open the answer.
Which tract carries pain and temperature, and where does it cross to the other side?
Show answer
The spinothalamic tract carries pain and temperature, and it crosses within the spinal cord shortly after entering.
A patient with a peripheral nerve injury has absent reflexes and muscle atrophy. Is this an upper or lower motor neuron pattern?
Show answer
Lower motor neuron — flaccidity, hyporeflexia, and atrophy are the LMN signature.
What does the Babinski sign suggest in an adult?
Show answer
Damage to the upper motor neuron pathway (e.g., stroke or spinal cord injury).
Which dermatome landmark is at the umbilicus? At the nipple line?
Show answer
T10 at the umbilicus; T4 at the nipple line.
On the 0–5 strength scale, what does a grade of 3 mean?
Show answer
The muscle can move the limb against gravity but not against added resistance.
Why can a spinal cord lesion abolish vibration on one side of the body but pain on the other?
Show answer
The dorsal columns (fine touch, vibration) cross in the medulla, so they carry information from the same side of the body until the brainstem; the spinothalamic tract (pain, temperature) crosses in the spinal cord. A one-sided cord lesion therefore affects each tract on a different side of the body — a dissociated sensory loss.
Study tools & related lessonsKey vocabulary · Related
Key vocabulary
- dermatome
- The strip of skin supplied by one spinal nerve
- stereognosis
- Identifying an object by touch alone
- graphesthesia
- Recognizing shapes or letters traced on the skin
- proprioception
- The sense of joint and body position
- tone
- Background resistance of muscle to passive stretch
- fasciculation
- A visible twitch of muscle fibers
- Babinski sign
- Big toe extends and toes fan when the sole is stroked
- clonus
- Rhythmic beating of a muscle under sustained stretch
Sources & references
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