Lecture 5: Muscular System

Question-and-answer flashcards covering major concepts, structures, and vocabulary from Lecture 5 on the Muscular System.

How many skeletal muscles are found in the human body?

Over 600.

List four key functions performed by skeletal muscles.

Moving the body, chewing, digesting food, and circulating blood.

What is a muscle fiber?

A single muscle cell packed with myofibrils composed of actin and myosin filaments.

What are sarcomeres?

Repeating structural units of actin and myosin filaments within a myofibril.

Which connective tissue layer surrounds an individual muscle fiber?

Endomysium.

Which connective tissue sheath encloses a fascicle?

Perimysium.

Which connective tissue layer covers the entire muscle?

Epimysium.

What is a tendon and what is it made from?

A tough cord that anchors muscle to bone; it is formed by extensions of the epimysium.

Define fascia in relation to muscle.

Fibrous connective tissue that surrounds a muscle and merges into its tendon.

Which contractile protein forms the thick filaments?

Myosin.

Which contractile protein forms the thin filaments?

Actin.

Where does acetylcholine act to initiate muscle contraction?

At the neuromuscular junction, diffusing across the synaptic cleft to bind receptors on the muscle fiber membrane.

Which enzyme rapidly breaks down excess acetylcholine?

Acetylcholinesterase.

What event triggers the release of Ca²⁺ from the sarcoplasmic (endoplasmic) reticulum?

Depolarization traveling down the T-tubules.

Which ion binds to the actin filament to expose myosin-binding sites?

Calcium ions (Ca²⁺).

What is meant by the muscle contraction "power stroke"?

Flexing of the myosin cross-bridge that pulls the actin filament toward the center of the sarcomere.

What causes myosin to detach from actin during the contraction cycle?

Binding of a new ATP molecule to the myosin head.

What is the immediate energy source for muscle contraction?

ATP.

Name the molecule that serves as a rapid back-up energy store for regenerating ATP in muscle.

Creatine phosphate.

When ATP and creatine phosphate are depleted, which stored polysaccharide is broken down for further energy?

Glycogen.

Which metabolic by-product accumulates during anaerobic respiration and contributes to fatigue?

Lactic acid.

Define "oxygen debt."

The extra oxygen required after intense exercise to metabolize lactic acid and restore energy reserves.

What is muscle fatigue?

Reduction in a muscle’s ability to contract forcefully because of depleted ATP and other substrates.

What is muscle tone?

A state of continuous partial contraction that keeps muscles ready for action.

What happens to muscle tone when the motor nerve is severed?

The muscle loses tone and becomes limp.

Which type of contraction shortens and thickens the muscle?

Isotonic contraction.

Which type of contraction increases tension without changing muscle length?

Isometric contraction.

In muscular attachment terminology, what is the "origin"?

The attachment of a muscle to the less movable bone.

What is the "insertion" of a muscle?

The attachment of a muscle to the more movable bone.

What do we call the prime mover responsible for a particular action?

Agonist.

What term describes the muscle that produces the opposite movement to the prime mover?

Antagonist.

What are synergists?

Muscles that assist the prime mover by reducing unnecessary movement and stabilizing joints.

What are fixators?

Muscles that stabilize the origin of the prime mover so force is directed to its insertion.

Provide an example of an agonist-antagonist pair in the arm.

Biceps brachii (agonist for flexion) and triceps brachii (antagonist for extension).

Name two major posterior muscles of the back.

Trapezius and latissimus dorsi.

What are T-tubules?

Inward extensions of the muscle fiber plasma membrane that conduct action potentials into the cell.

Why do skeletal muscle fibers contain many nuclei and abundant mitochondria?

To support high energy demands and protein synthesis required for contraction.