Lecture #20 - NMJ Energetics

What is a muscle twitch?

Response of a muscle to a single, brief threshold stimulus; simplest contraction observable in the lab.

What are the three distinct phases of a muscle twitch?

1. Latent Period, 2. Contraction Period, 3. Relaxation Period.

What happens during the latent period of a muscle twitch?

No muscle response is detected for the first few milliseconds.

How long does the contraction period last?

The contraction period lasts between 10 to 100 milliseconds.

What initiates the relaxation period of a muscle twitch?

The re-entry of Ca2+ into the sarcoplasmic reticulum.

What is a motor unit?

A motor neuron and all the muscle fibers it supplies.

How are small motor units characterized?

Small motor units have 1 neuron supplying a few myofibers, controlling fine movements.

What is the difference between fused and unfused tetanus?

Unfused tetanus involves partial relaxations, while fused tetanus has no relaxation between stimuli.

What are isotonic contractions?

Muscle length changes and tension overcomes the load to move it.

What characterizes isometric contractions?

Tension increases but the load is not moved, keeping the muscle the same length.

What is the role of ATP in muscle contraction?

ATP is used to energize myosin, remove Ca2+ from the cytosol, and replace Na+ and K+ across the sarcolemma.

What are the three pathways for ATP regeneration in muscle cells?

1. Creatine Phosphate, 2. Anaerobic Glycolysis, 3. Aerobic Respiration.

What happens during anaerobic glycolysis?

Glucose is converted to pyruvic acid, producing 2 ATP and lactic acid.

What is the Cori cycle?

The process of recycling lactic acid into glucose in the liver.

What are slow oxidative fibers?

Aerobic fibers that contract slowly, are fatigue-resistant, and are rich in mitochondria.

What are the characteristics of fast glycolytic fibers?

Anaerobic fibers that contract quickly, fatigue rapidly, and have fewer mitochondria.

What are fast oxidative fibers?

Intermediate fibers that regenerate ATP through aerobic respiration and have characteristics of both fast and slow fibers.

What happens during oxidative phosphorylation?

Electrons are transported via NADH and FADH2 through the electron transport chain, leading to ATP production.