Muscle Physiology: Excitation-Contraction Coupling

The process where an action potential triggers muscle contraction.

Calcium influx initiates cross-bridge cycling.

Transverse tubules that link the muscle cell membrane to the sarcoplasmic reticulum.

Stores calcium, releasing it for muscle contraction.

Structure formed by one T-tubule and two lateral sacs of the sarcoplasmic reticulum.

Voltage-sensitive receptors in the T-tubule membrane.

Electrical signal that triggers calcium release.

Muscle cell.

The process of breaking down ATP into ADP and Pi, which provides energy for the myosin head to "re-cock" and be ready for another power stroke.

The interaction between a myosin head and actin filament during muscle contraction, forming a link.

The movement of the myosin head during muscle contraction, pulling on actin.

The binding of ATP to the myosin head releases the myosin head from actin, breaking the cross-bridge.

The duration of muscle activity (100 ms) is longer than an action potential (1-2 msec) in a muscle fiber.

A post-mortem state where muscles become stiff due to lack of ATP to break the cross-bridges.

The process of myosin pulling on actin, powered by ATP hydrolysis, which causes sliding filament motion in muscle contraction.

A motor neuron and all the muscle fibers it controls.

The time between an action potential reaching a muscle fiber and the actual beginning of muscle contraction. It involves steps like calcium release, tropomyosin shifting, and cross-bridge formation.

A brief, weak contraction of a muscle fiber caused by a single action potential. It's too weak to create a noticeable movement.

The point where a motor neuron's axon forms a connection with a muscle fiber. This is where the nerve signal is transmitted to the muscle.

Determined by how many muscle fibers are activated (recruitment) and the tension developed by each activated fiber.

The activation of all muscle fibers within a motor unit when the motor unit is stimulated. This leads to increased muscle tension as more motor units are recruited.

Muscles with smaller motor units (fewer fibers per unit) allow for finer control of movement (like fingers), while muscles with larger motor units (more fibers per unit) have less control but more power (like back muscles).

The alternating activation of different motor units to prevent fatigue and maintain muscle tension. This strategy helps avoid exhaustion by allowing some units to rest while others work.

Muscle fibers can be categorized as Type I (slow-twitch, fatigue-resistant) and Type II (fast-twitch, fatigable). Type I fibers are recruited first during weak or moderate exercise.

The nervous system determines which motor units to activate based on the intensity and duration of the movement. This allows for graded muscle contractions.

The force exerted on a muscle by an object or external resistance.

Muscle contraction without any change in muscle length. Tension increases, but the muscle stays the same length.

Muscle contraction with constant tension or load. The muscle changes length.

Muscle contraction that shortens the muscle.

Muscle contraction that lengthens the muscle.

The relationship between the force a muscle can generate and the velocity at which it contracts.

Different types of skeletal muscle fibers with different structural, functional, and metabolic characteristics.

The maximum shortening velocity of a muscle fiber when there is no load.

The optimal load and velocity combination for maximum power output.

The highest rate at which work can be done by a muscle.

Slow-twitch, fatigue-resistant, aerobic muscle fiber used for endurance activities.

Fast-twitch, fatigue-resistant, hybrid muscle fiber used for both endurance and power activities.

Fast-twitch, fatigable, anaerobic muscle fiber used for short, powerful bursts of activity.

Describes how motor units are recruited based on their size, starting with the smallest and weakest units first, and progressively activating larger, stronger units as more force is needed.

Muscle fibers that are more resistant to fatigue, typically smaller and slower twitching. These are recruited first according to the size principle.

The size principle ensures efficient and smooth muscle contraction by activating only the necessary motor units, minimizing fatigue and providing finer control over force output.

Muscle tension depends on both the number of muscle fibers contracting (motor unit recruitment) and the frequency of muscle fiber activation.

Repeated stimulation of a muscle fiber before it fully relaxes can lead to increased tension, as the individual twitches add up on top of each other.

The duration of a single twitch contraction, typically lasting around 100 milliseconds.

The rate at which a muscle fiber is stimulated, directly impacting the amount of tension it develops.

The length of the muscle fiber at the onset of contraction affects the amount of force it can generate.