Test Neuromuscular and Nervous Systems 1 Flashcards
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A patient presents with spasticity, hyperreflexia, and a positive Babinski sign in both lower extremities following a stroke. These findings are most consistent with a lesion affecting which neural structure?
Answer: Upper motor neurons of the corticospinal tract
Upper motor neuron (UMN) lesions interrupt descending inhibitory control, producing the classic triad of spasticity, hyperreflexia, and a positive Babinski sign. Lower motor neuron lesions instead cause flaccidity, hyporeflexia, and muscle atrophy.
A patient with a complete T10 spinal cord injury would most likely present with which of the following functional profiles?
Answer: Paraplegia with full trunk control and intact respiratory function
The diaphragm is innervated by C3–C5 (phrenic nerve), so a T10 lesion spares respiratory function entirely. T10 injuries result in paraplegia with loss of lower extremity motor/sensory function and variable trunk control, but the upper extremities and breathing remain intact.
Which descending motor pathway carries the primary commands for fine, skilled voluntary movements of the distal upper extremities, including individual finger control?
Answer: Lateral corticospinal tract
The lateral corticospinal tract originates from primary motor cortex, decussates in the medullary pyramids, and synapses directly on anterior horn motor neurons controlling distal limb musculature. It is the dominant pathway for fine voluntary motor control, especially of the hands and fingers.
On repetitive nerve stimulation testing at 3 Hz, a patient shows a decremental response in the compound muscle action potential (CMAP) amplitude. Which disorder does this finding most strongly suggest?
Answer: Myasthenia gravis
In myasthenia gravis, postsynaptic acetylcholine receptors are reduced by autoantibodies, so successive nerve stimuli deplete the available quanta and CMAP amplitude decrements by ≥10%. Lambert-Eaton syndrome, by contrast, shows an incremental response because high-frequency stimulation mobilizes more calcium and acetylcholine release.
Selective damage to the dorsal columns of the spinal cord, as seen in the posterior cord syndrome or subacute combined degeneration, would produce ipsilateral loss of which sensory modalities below the lesion?
Answer: Proprioception and vibration sense
The dorsal columns (fasciculus gracilis and cuneatus) carry ipsilateral proprioception, vibration, and discriminative (two-point) touch. Pain and temperature travel in the contralateral anterolateral (spinothalamic) tract. Isolated dorsal column injury therefore spares pain/temperature while eliminating position sense and vibration.
A patient demonstrates resting tremor that diminishes with voluntary movement, cogwheel rigidity, and bradykinesia. The primary pathophysiology underlying this presentation involves degeneration of which neural pathway?
Answer: Dopaminergic projections from the substantia nigra pars compacta to the striatum
Parkinson disease is caused by loss of dopaminergic neurons in the substantia nigra pars compacta, which project via the nigrostriatal pathway to the striatum. Loss of dopamine disrupts basal ganglia circuitry, resulting in the hallmark motor features of resting tremor, rigidity, bradykinesia, and postural instability.