A skeletal muscle is controlled through motor units. Each motor unit contains one lower motor neuron and the muscle fibers supplied by its axon. The CNS changes muscle force by recruiting more units and changing how frequently recruited units fire. A rough model is: $$ \text{descending + sensory input} \rightarrow \text{alpha motor-neuron spikes} \rightarrow \text{muscle-fiber […]
A TENS unit is a battery, waveform generator, current-control circuit, and a few electrodes. It sends pulsed current through the skin to recruit nearby nerve fibers. The goal is not to repair a strained muscle, realign a joint, or remove inflammation. It is to change the neural traffic associated w/ pain. A rough model is: […]
A pulse oximeter does not directly count oxygen molecules, measure the partial pressure of oxygen, or sample arterial blood. It sends red and infrared light through tissue, extracts the part of the optical signal that changes with each pulse, and maps that signal through an empirical calibration curve. A rough model is: $$ \text{red/IR transmission} […]