Neuromuscular and Nervous Systems
Upper versus lower motor neuron signs
Upper motor neuron lesions (stroke, multiple sclerosis, spinal cord injury above the reflex arc) produce hypertonia, hyperreflexia, clonus, a Babinski response and loss of fine dexterity. Lower motor neuron lesions (radiculopathy, peripheral nerve injury) produce flaccidity, atrophy, fasciculations and hyporeflexia. Recognizing which pattern is present tells you whether to expect spasticity management or joint protection and splinting.
Localization tools
Memorize the reflex arcs: biceps and brachioradialis C5–C6, triceps C7, patellar L4, Achilles S1. Dermatomes follow a similar ladder. The ASIA examination grades strength 0–5, tests light touch and pinprick, and defines the neurologic level; sacral sparing (anal contraction, sensation) predicts a better prognosis.
Tone, positioning and training
Flaccid limbs need positioning, support and passive range of motion to prevent subluxation and contracture, especially at the shoulder after stroke. Spastic limbs respond best to slow sustained stretch, weight bearing and rotation rather than quick bouncing. Neuroplasticity is driven by task-specific, repetitive, meaningful practice with enough challenge; massed practice of a functional task beats passive modalities.
Common traps
Mixing up reflex levels, labeling all weakness as upper motor neuron, and forgetting that heat can transiently worsen symptoms in multiple sclerosis. In Guillain-Barré syndrome, weakness is ascending and reflexes are lost; in Parkinson disease, amplitude and cueing matter more than stretching.
Rule of thumb: protect a flaccid limb before you strengthen it, and slow down when you treat a spastic one.