A single muscle cell that increases its tension when activated by a nerve is called a ...

• A. Neuron
• B. Dendrites
• C. Myelin sheath
• D. Muscle fiber

Answer: (D)

A muscle fiber is the basic contractile unit of skeletal muscle. When a nerve signal reaches a muscle, it releases chemical neurotransmitters at the neuromuscular junction, causing the muscle fiber membrane to depolarize. This leads to calcium release inside the fiber, enabling the myofilaments (actin and myosin) to slide past each other and shorten the sarcomere, producing tension. So, a single muscle cell that increases its tension when activated by a nerve is a muscle fiber.

The other terms describe parts of neurons rather than the muscle cell itself: a neuron is the nerve cell that transmits signals; dendrites are tree-like extensions that receive signals on a neuron; the myelin sheath insulates axons to speed up signal transmission.