BIOL 221 – Muscle III

Study Notes

Fatigue is the decrease in a muscle's ability to generate force due to prolonged use, primarily under anaerobic conditions.
Causes of fatigue include the accumulation of lactic acid in muscles, leading to increased acidity, which disrupts glycolytic enzyme activity and the actin-myosin cross-bridge cycle.
Depletion of glycogen stores in both the muscle and liver contributes to fatigue; as glycogen is used up, the body shifts to fat metabolism, which produces energy at half the rate of glucose.

Oxygen debt is the amount of oxygen needed to metabolize excess lactic acid after intense exercise.
Lactic acid is converted into CO2 and H2O or can be converted to glucose in the liver.
Post-exercise, elevated temperatures in heart and skeletal muscles increase oxygen consumption.

The latent period occurs between stimulation and contraction, where the muscle does not produce force.
The contraction period is when muscle shortening begins and tension peaks.
The relaxation period starts as calcium ions re-enter the sarcoplasmic reticulum.

During the refractory period, following repolarization of the sarcolemma, the muscle cannot respond to new stimuli.
If a second stimulus occurs while calcium is still outside the sarcoplasmic reticulum, the muscle exhibits a stronger contraction.

Tetanus happens when repeated stimuli lead to a lack of relaxation between contractions, resulting in a smooth and sustained contraction.
Clostridium tetani causes a pathological state of continuous muscle contraction, known as "lock jaw," which can lead to respiratory failure.
Normal fused tetanus in skeletal muscle is distinct from the pathological condition caused by C. tetani.

A motor unit consists of a motor neuron and all muscle fibers it innervates.
Precise movements involve fewer, smaller motor units, while powerful contractions engage larger motor units.
Recruitment increases muscular force by activating more motor units.

Isometric contractions maintain muscle length while tension increases (e.g., pressing against an immovable object).
Isotonic contractions involve a change in muscle length without a change in tension (e.g., lifting a weight).
Most actions involve a combination of both contraction types, starting as isometric until enough force is generated for isotonic movement.

Cardiac muscle cells are interconnected by gap junctions, forming a functional contractile unit.
The heart's electrical impulses originate in the pacemaker region of the myocardium, leading to synchronized contractions.
Atria contract first, followed by ventricles, allowing for efficient blood circulation.
Cardiac muscle exhibits a prolonged refractory period to prevent tetany, ensuring effective heart function.