Chapter 8: Muscular System

Explain how a motor nerve impulse can trigger a muscle contraction.

1. Acetylcholine released from the distal end of a motor neuron fiber stimulates a skeletal muscle fiber. 2. Acetylcholine causes the muscle fiber to conduct an impulse over the surface of the fiber that reaches deep within the fiber through the transverse tubules. 3. A muscle impulse signals the sarcoplasmic reticulum to release calcium ions. 4. Linkages form between actin and myosin, and the myosin cross-bridges pull on actin filaments, shortening the fiber. 5. The muscle fiber relaxes when cross-bridges from actin and calcium ions are transported back to the sarcoplasmic reticulum

Describe how connective tissue is part of a skeletal muscle

1. Layers of fibrous connective tissue is called fascia separate an individual skeletal muscle from adjacent muscles hold it in position. 2. The connective tissue forms broad fibrous sheets called aponeuroses, which may attach to the coverings of adjacent muscles. 3. The layer of connective tissue that closely surrounds a skeletal muscle is called epimysium. 4. Other layers of connective tissue, called perimysium, extend tissue into small compartments. 5. Those compartments contain bundles of skeletal muscle fibers called fascicles. 6. Each muscle fiber within a fascicle lies within a layer of connective tissue in the form of a thin covering called endomysium.

How is cardiac muscle similar to skeletal muscle?

Cardiac muscle is composed of striated cells joined end to end, forming fibers. These fibers interconnect in branching, three-dimensional networks. Each cell contains many filaments of actin and myosin, similar to those in skeletal muscle.

How is cardiac muscle similar to smooth muscle?

Cardiac muscle is found only in the heart. Its mechanism of contraction is essentially the same as that of skeletal and smooth muscle.

How is muscle tone maintained?

Even when a muscle appears to be at rest, a certain amount of sustained contraction is occurring in its fibers. This is called a muscle tone (tonus).

How are lactic acid, oxygen debt, and muscle fatigue related?

Fatigue is most likely to arise from accumulation of lactic acid in the muscle as a result from aerobic respiration. As lactic acid accumulates, a person develops an oxygen debt that must be repaid. Oxygen debt equals the amount of oxygen liver cells require to convert the accumulated lactic acid into glucose

Describe two major types of smooth muscle.

In multiunit smooth muscle, the muscle fibers are separate rather than organized into sheets. Smooth muscle of this type is found in the irises of the eyes and the walls of blood vessels. Visceral is composed of sheets of spindle shaped cells in close contact with one another

What is the function of a synergist? An antagonist?

Muscles that contract and assist the prime mover are called synergists. Still other muscles act as antagonists to prime movers. These muscles can resist the prime mover's action and cause movement in the opposite direction.

Explain why skeletal muscle fibers appear striated.

Myofibrils play a fundamental role in muscle contraction. They contain two kinds of protein filaments—thick ones composed of the protein myosin and thin ones mainly composed of the protein actin. The organization of these filaments produces the characteristic alternating light and dark striations, or bands, of a skeletal muscle fiber.

What is the function of intercalated disks?

The disks help to join cells and to transmit the force of contraction from cell to cell. Intercalated disks also allow muscle impulses to pass freely so that they travel rapidly from cell to cell.

Define threshold stimulus.

The minimal strength required to cause a contraction is called a thresh hold stimulus.

Explain how the filaments of a myofibril interact during muscle contraction.

A muscle fiber contraction is a complex interaction of cell components and biochemical. The final result is a movement within the myofibrils in which the filaments of actin and myosin slide past one another, shortening the muscle fiber and pulling on its attachments.

What is an all-or-none response?

A skeletal muscle fiber exposed to a stimulus of threshold strength (or above) responds to its fullest extent. Increasing the strength of the stimulus does not affect the fiber's degree of contraction. This phenomenon is called an all-or-none response.

Distinguish between a twitch and a sustained contraction.

A twitch is the contractile response of a single muscle fiber to a muscle response. During a sustained contraction, many action potentials are triggered in a motor neuron resulting in a contraction of increasing strength.

What characteristic of cardiac muscle causes contraction of the heart as a unit?

When one portion of the cardiac muscle network is stimulated, the resulting impulse passes to the other fibers of the network, and the whole structure contracts as a unit; that is, the network responds to stimulation in an all-or-none manner.