Key Takeaways
- The central nervous system (CNS) consists of the brain and spinal cord; the peripheral nervous system (PNS) includes all nerves outside the CNS
- Upper motor neuron (UMN) lesions present with spasticity, hyperreflexia, clonus, positive Babinski sign, and no muscle atrophy initially
- Lower motor neuron (LMN) lesions present with flaccidity, hyporeflexia/areflexia, fasciculations, and rapid muscle atrophy
- Dermatomes are areas of skin supplied by a single spinal nerve root: C5 (lateral arm), C6 (thumb), C7 (middle finger), T4 (nipple line), T10 (umbilicus), L4 (medial leg), L5 (dorsal foot), S1 (lateral foot)
- Myotomes represent the muscles innervated by a single nerve root: C5 (deltoid), C6 (biceps/wrist extensors), C7 (triceps/wrist flexors), L3 (quadriceps), L4 (tibialis anterior), L5 (extensor hallucis longus), S1 (gastrocnemius)
- The corticospinal tract (lateral) is the primary motor pathway; damage causes contralateral UMN signs below the level of lesion
- The dorsal columns (posterior) carry proprioception, vibration, and fine touch; damage causes ipsilateral loss of these sensations
- The spinothalamic tract carries pain and temperature; damage causes contralateral loss of pain and temperature sensation
Neuroanatomy & Neurophysiology
Understanding the structure and function of the nervous system is essential for the NPTE neuromuscular domain. Physical therapists must be able to localize neurological lesions, predict functional deficits, and select appropriate interventions.
CNS vs. PNS Overview
| Feature | Central Nervous System (CNS) | Peripheral Nervous System (PNS) |
|---|---|---|
| Components | Brain and spinal cord | Cranial nerves, spinal nerves, peripheral nerves |
| Protection | Skull, vertebrae, meninges, CSF | Epineurium, perineurium, endoneurium |
| Regeneration | Very limited (glial scarring inhibits regrowth) | Can regenerate at ~1 mm/day (1 inch/month) |
| Myelination | Oligodendrocytes | Schwann cells |
Upper Motor Neuron (UMN) vs. Lower Motor Neuron (LMN) Lesions
This is one of the most tested concepts on the NPTE. UMN and LMN lesions produce opposite clinical presentations:
| Feature | UMN Lesion | LMN Lesion |
|---|---|---|
| Muscle tone | Spasticity (increased) | Flaccidity (decreased) |
| Deep tendon reflexes | Hyperreflexia (increased) | Hyporeflexia or areflexia (decreased/absent) |
| Babinski sign | Positive (toes fan, great toe extends) | Negative (normal flexor response) |
| Clonus | May be present | Absent |
| Muscle atrophy | Minimal initially (disuse atrophy over time) | Rapid, significant atrophy (denervation) |
| Fasciculations | Absent | Present (visible muscle twitching) |
| Distribution | Affects groups of muscles (patterns) | Affects individual muscles (segmental) |
| Examples | Stroke, TBI, MS, SCI (above conus) | Peripheral neuropathy, radiculopathy, Guillain-Barre, SCI (at level of injury) |
Key UMN Spasticity Pattern:
- Upper extremity: Flexor pattern (shoulder adduction/IR, elbow flexion, forearm pronation, wrist/finger flexion)
- Lower extremity: Extensor pattern (hip extension/adduction/IR, knee extension, ankle plantarflexion/inversion)
Spinal Cord Tracts
Understanding the major ascending (sensory) and descending (motor) tracts allows localization of spinal cord lesions:
Major Ascending (Sensory) Tracts
| Tract | Location | Modality | Crosses (Decussation) |
|---|---|---|---|
| Dorsal columns (posterior) | Posterior spinal cord | Proprioception, vibration, fine/discriminative touch | Medulla (crosses high) |
| Spinothalamic (lateral) | Anterolateral spinal cord | Pain and temperature | Spinal cord level (crosses at entry) |
| Anterior spinothalamic | Anterior spinal cord | Crude touch, pressure | Spinal cord level |
Major Descending (Motor) Tract
| Tract | Location | Function | Crosses |
|---|---|---|---|
| Lateral corticospinal | Lateral spinal cord | Voluntary motor control (skilled movements) | Medulla (pyramidal decussation) |
Clinical Significance of Decussation:
- Dorsal columns cross in the medulla → Damage in the spinal cord causes ipsilateral loss of proprioception and vibration
- Spinothalamic tract crosses at spinal cord level → Damage in the spinal cord causes contralateral loss of pain and temperature
- Corticospinal tract crosses in the medulla → Damage above the decussation (brain) causes contralateral motor deficits; damage below (spinal cord) causes ipsilateral motor deficits
Dermatomes and Myotomes
Key Dermatome Landmarks
| Nerve Root | Sensory Area |
|---|---|
| C5 | Lateral arm (deltoid patch) |
| C6 | Lateral forearm, thumb, index finger |
| C7 | Middle finger |
| C8 | Ring finger, little finger, medial forearm |
| T4 | Nipple line |
| T10 | Umbilicus |
| L1 | Inguinal ligament region |
| L3 | Anterior thigh above knee |
| L4 | Medial leg |
| L5 | Dorsum of foot, first web space |
| S1 | Lateral foot, small toe |
| S2-S4 | Saddle region (perianal area) |
Key Myotome Testing
| Nerve Root | Primary Muscle/Action |
|---|---|
| C5 | Deltoid — shoulder abduction |
| C6 | Biceps — elbow flexion; wrist extensors |
| C7 | Triceps — elbow extension; wrist flexors |
| C8 | Finger flexors — grip strength |
| T1 | Hand intrinsics — finger abduction |
| L2 | Iliopsoas — hip flexion |
| L3 | Quadriceps — knee extension |
| L4 | Tibialis anterior — ankle dorsiflexion |
| L5 | Extensor hallucis longus — great toe extension |
| S1 | Gastrocnemius/soleus — ankle plantarflexion |
| S2 | Hamstrings — knee flexion |
A patient presents with spasticity, hyperreflexia, and a positive Babinski sign. This presentation is MOST consistent with:
Damage to the dorsal columns of the spinal cord at T6 would result in loss of which sensation BELOW the level of injury?
Match each dermatome to its corresponding sensory area.
Match each item on the left with the correct item on the right
The L4 myotome is best tested by assessing which muscle action?
Peripheral nerves can regenerate at a rate of approximately _____ per day (or about 1 inch per month).
Type your answer below
A patient with an UMN lesion would typically exhibit which posture in the affected upper extremity?