Skeletal Muscle & Muscle Fibers

Flashcards for skeletal muscle and muscle fiber types.

Where are skeletal muscles found?

Attached to the bones of the skeleton throughout the body.

Describe the microscopic structure of skeletal muscle.

Long, cylindrical fibres arranged in bundles, multinucleated (nuclei at the periphery), striated (actin and myosin filaments within sarcomeres).

How is skeletal muscle controlled by the nervous system?

Nerves in the somatic nervous system send signals to make muscles function; every muscle fibre is supplied by the axon branch of a somatic motor neuron.

What is the neuromuscular junction (NMJ)?

The site where a motor neuron's terminal meets the muscle fibre.

What are the main functions of skeletal muscle?

Producing voluntary movements, maintaining posture, and stabilizing the body.

What are myofibrils?

Thread-like structures within muscle fibres that contain myofilaments.

What do myofilaments contain?

Myosin (thick filaments) and actin (thin filaments).

What is a sarcomere?

Basic contractile unit of muscle fibre, made of repeating sections of actin and myosin filaments.

What is the sliding filament theory?

Muscles contract as actin and myosin filaments slide over one another.

What is the role of calcium ions in muscle contraction?

They trigger muscle contraction by binding to troponin, exposing myosin-binding sites on actin.

What is cellular respiration?

Process cells use to produce ATP (energy), occurring in aerobic (with oxygen) and anaerobic (without oxygen) forms.

Explain how ATP is used in muscle contraction.

ATP binds to myosin (cross-bridge detachment), hydrolysed to re-cock the myosin head, and powers calcium pumps for reuptake.

What happens to the sarcomere during contraction?

The sarcomere shortens, Z-lines move closer, I bands narrow, H zone shrinks, A band stays the same.

What are the key characteristics of slow-twitch fibres?

Red, slow contraction, low force, high fatigue resistance, aerobic energy system, endurance activities.

How do slow-twitch fibers generate energy?

Via aerobic respiration, using glucose and fatty acids.

Give some examples of muscles with high slow-twitch fibre content.

Calf muscles, diaphragm, external obliques, trapezius.

What are the two main types of fast-twitch fibres?

Type IIa (fast oxidative-glycolytic) and Type IIb (fast glycolytic).

How do fast-twitch fibers generate energy differently from slow-twitch fibers?

Fast-twitch fibres rely mainly on anaerobic glycolysis, breaking down glucose quickly without oxygen.

What is the power output and fatigue-resistance of fast-twitch fibres?

High power output, low fatigue resistance, appear white due to low myoglobin content.

Give some examples of muscles with high fast-twitch fibre content.

Gastrocnemius, biceps brachii, quadriceps, triceps brachii, deltoids.

What percentage of slow-twitch vs fast-twitch fibers would you expect in their primary working muscles?

Eliud Kipchoge: estimated 80% slow twitch fibres, Usain bolt: estimated 70-80%fast twitch fibres

Which specific muscles are most important for their sport?

Eliud Kipchoge (marathon runner): quadriceps, hamstrings, gastrocnemius, gluteal muscles, Usain Bolt (sprinter): quadriceps, hamstrings, gluteal muscles, calves

How does their fiber composition give them an advantage in their sport?

Eliud Kipchoge (marathon runner): Slow twitch fibres support endurance, resist fatigue and use oxygen efficiently for sustained effort, Usain Bolt (sprinter): Fast twitch fibres generate rapid, high-power contractions ideal for explosive movements such as sprinting

Which energy system(s) do they primarily use during competition?

Eliud Kipchoge (marathon runner): Aerobic system – sustained oxygen-based energy production, Usain Bolt (sprinter): ATP-PC system, followed by anaerobic system

What are the limiting factors for their performance?

Eliud Kipchoge (marathon runner): Glycogen depletion, dehydration, thermoregulation issues, Usain Bolt (sprinter): rapid depletion of phosphocreatine, lactate accumulation