Physiology of Muscle and Levers

Muscles that are attached to bones and are responsible for voluntary movements. These muscles are striated, meaning they have a banded appearance under a microscope.

Found in the heart, this type of muscle is responsible for pumping blood throughout the body. It is also striated but functions involuntarily.

Found in the walls of hollow organs like blood vessels, intestines, and the bladder. It is non-striated and operates involuntarily, controlling movements like peristalsis and vasoconstriction.

A system where a rigid bar (bone) moves around a fixed point (joint) by the force of a muscle. The effectiveness of the lever system depends on the relative positions of the fulcrum, effort, and load.

The fixed point around which a lever rotates. In the body, this is usually a joint.

The force applied by a muscle to move a load.

The resistance that a muscle needs to overcome.

A type of lever where the fulcrum is located between the effort and the load. An example is the head resting on the atlas vertebrae.

The functional unit of a muscle fiber, defined by the area between two Z discs.

A protein that forms the backbone of the thin filament, providing binding sites for myosin heads during contraction.

The protein responsible for muscle contraction, forming cross-bridges with actin.

The process by which myosin heads bind to actin, pull the thin filaments towards the center of the sarcomere, release, and reset, leading to muscle contraction.

The release of calcium ions (Ca²⁺) from the sarcoplasmic reticulum into the cytoplasm, triggered by an action potential.

A protein that blocks myosin-binding sites on actin when the muscle is relaxed.

A complex of three proteins (troponin C, I, and T) that regulates the interaction between actin and myosin by controlling the position of tropomyosin.

A type of muscle contraction where muscle tension increases without a change in muscle length.

Muscle tension remains constant while muscle length changes. Isotonic contractions can be classified into concentric (muscle shortens) and eccentric (muscle lengthens).

A single, brief contraction resulting from a single action potential in a muscle fiber.

Increased force of contraction due to rapid succession of action potentials, preventing the muscle from fully relaxing.

Muscle fibers do not completely relax before the next stimulus, leading to higher tension with each successive stimulus.

Muscle fibers are stimulated at a very high frequency, resulting in sustained contraction with no relaxation.

Creatine phosphate quickly donates a phosphate group to ADP to regenerate ATP, providing energy for the first few seconds of intense activity.

Glucose is broken down into pyruvate, producing a small amount of ATP. In the absence of oxygen, pyruvate is converted to lactate, leading to muscle fatigue.

Glucose, fatty acids, and amino acids are oxidized in the presence of oxygen to produce a large amount of ATP. This pathway is sustainable for prolonged, lower-intensity activities.

These muscle fibers are specialized for sustained, low-intensity activities that rely on oxygen for energy production. They are highly resistant to fatigue.

These muscle fibers contract relatively quickly and can use both aerobic and anaerobic metabolism. Ideal for activities that combine endurance and power.

These fibers are designed for brief, intense bursts of power, relying mainly on anaerobic metabolism. They fatigue quickly.

The ability of cardiac muscle cells to initiate their own contractions without external signals.

The rhythmic, coordinated contraction of cardiac muscle cells, crucial for efficient blood pumping.

The fulcrum is located between the load and the effort. This lever is designed for speed and distance, such as a fishing rod.

An action potential reaching the T-tubules of a muscle fiber triggers the release of calcium ions (Ca2+) from the sarcoplasmic reticulum (SR). This process is crucial for muscle contraction, as it allows for the binding of myosin to actin.

Cardiac muscles are striated, involuntary muscles that are found only in the heart. They contain intercalated discs, which allow for rapid communication between cells and synchronized contractions. Cardiac muscles are also multinucleated.

Aerobic respiration is the process that produces the most ATP during prolonged muscle activity. This process uses oxygen to break down glucose and generate energy. The other options are less efficient for long-lasting activity.

Muscle fatigue during endurance events is linked to energy depletion and the build-up of metabolic byproducts. Type I muscle fibers, which rely on aerobic metabolism, are more resistant to fatigue. As exercise intensity increases, reliance on Type II fibers increases, leading to a build-up of lactic acid from anaerobic metabolism and fatigue.

Delayed onset muscle soreness, or DOMS, is a common phenomenon experienced after unaccustomed or intensive exercise, particularly eccentric contractions. It is thought to be caused by microscopic tears in muscle fibers and inflammation.