Motor Units Simulator

An interactive educational visualization demonstrating how motor neurons innervate muscle fibers and how continuous action potentials result in sustained muscle contraction (tetanus).

✨ Features

• Multiple Activations: Click on multiple motor units to see overlapping activations simultaneously.
• Sustained Contraction Animation: Unlike a simple twitch, the muscle fibers demonstrate a smooth, sustained contraction (tetanus) via CSS transformations.
• Action Potential Flow: Animated dashed lines represent the electrical signal traveling down the axons.
• Dynamic Legend: A clickable legend that stays synchronized with the visual state of the diagram.

📖 How to Use

• Activate a Motor Unit: Click on any of the green Neuron cell bodies (labeled A, B, C, or D) on the left side of the screen, or click their corresponding buttons in the legend below.
• Observe the Flow: Watch the action potential travel down the axon, light up the terminal bulbs (NMJs), and cause the specific muscle fibers (1-16) associated with that unit to glow and contract.
• Toggle Multiple Units: Click additional neurons to activate multiple motor units at the same time. Click an active neuron again to deactivate it.
• Reset: Click anywhere on the black background to reset the entire diagram and deactivate all units.

🧠 Biological Concepts Explained

This visualization helps illustrate several core physiological concepts:

1. The Motor Unit: A motor unit is defined as a single motor neuron and all the muscle fibers it innervates. In this app, Neuron A innervates fibers 1, 5, 9, and 13. When Neuron A fires, only those specific fibers contract.
2. Neuromuscular Junction (NMJ): The point where the axon terminal meets the muscle fiber. This is represented by the glowing bulbs that appear when a unit is active.
3. Sustained Contraction (Tetanus): When a motor neuron fires a continuous train of high-frequency action potentials, the muscle fibers do not just twitch and relax; they enter a state of smooth, sustained contraction. This is visually represented by the fibers smoothly shortening and thickening, accompanied by a continuous electrical glow.