Final answer:
Coactivation in muscles involves simultaneous activation of agonist and antagonist motor neurons, enabling muscle contraction and feedback about muscle length to the CNS. Motor units play a crucial role in generating muscle tension, and the spinal cord coordinates neural signals that regulate muscle state and stability.
Step-by-step explanation:
Coactivation in muscle involves the simultaneous stimulation of both the agonist and antagonist motor neurons so that a muscle can contract while also providing information about its length to the CNS. This coactivation is important for maintaining balance and coordination during movements. Agonist muscles are responsible for creating movement through contraction while antagonist muscles oppose the action of agonists to provide control and resistance.
Motor units are comprised of a motor neuron and the group of muscle fibers it innervates, and they are fundamental to muscle contraction. When the motor neuron fires an action potential, it results in the contraction of all the muscle fibers in that motor unit. Additionally, muscle tension is the force generated by muscle contraction, through either isotonic contractions, where muscle length changes, or isometric contractions, where muscle length remains the same.
The spinal cord and the motor neurons that project to muscles form an essential part of the mechanism for coactivation. They are responsible for relaying the signals that determine muscle tension and the state of contraction or relaxation. In this context, the spinal cord acts as a central hub in the coordination of muscle activity dictated by the CNS.