Untitled Quiz

The Diaphragm

• The diaphragm is the primary mover of breathing.
• This dome-shaped muscle separates the abdominal cavity from the thoracic cavity.
• The diaphragm is responsible for bringing atmospheric air into the lungs.
• The diaphragm is under both voluntary and involuntary control.

Muscle Fibers

• Each muscle cell is an elongated fiber, known as a muscle fiber, and can be up to 12 inches (app. 30.5cm) in length.
• Muscle fibers are composed of several hundred to several thousand thread-like myofibrils.
• Muscle fibers bundle together to form a specific muscle segment.

Sarcomeres

• Sarcomeres are the functional contractile units of a muscle fiber.
• Sarcomeres are made up of two types of threadlike structures: thick myofilaments made up of myosin and thin myofilaments made up of actin.
• Z lines are made up of thin actinin and define the boundaries of sarcomeres.

Muscle Contraction

• Contraction of a muscle causes the myofilaments to slide toward each other, which shortens the sarcomere and the entire muscle.
• Muscle contraction requires the temporary connections of cross-bridges between the myosin head and the actin, pulling the sarcomere together.

ATP and Calcium

• Energy for muscle contraction and relaxation comes from ATP (adenosine triphosphate).
• ATP helps the myosin heads form and break the cross-bridges with actin.

Types of Muscles

• Muscle is a general term for all contractile tissues.
• Muscle tissue contains muscle fibers, each about the size of a human hair.
• The three major types of muscles in the body are skeletal, smooth, and cardiac.

Characteristics of Muscles

• Muscle tissues display five physiological characteristics: excitability, contractility, extensibility, elasticity, and conductivity.
• Calcium triggers contraction by reacting with regulatory proteins, which allow interaction of actin and myosin.
• During relaxation, calcium is stored away from the actin and myosin in the sarcoplasmic reticulum (SR).

ATP and Calcium (2)

• The motor neuron instructs a muscle to contract by releasing a neurotransmitter called acetylcholine (ACh).
• Acetylcholine causes the muscle fiber to open sodium ion channels.
• Sodium ions flow into the muscle fiber, exciting it and causing calcium to be released from the SR.
• When calcium is pumped back into the SR, the cross-bridge attachments are broken, and the muscle relaxes.

Muscular Fuel

• Muscles need fuel in the form of food and oxygen.
• The body stores glycogen in the muscle, where it is converted to glucose, which releases energy.
• Muscles with very high demands also store fat and use it as energy.
• Energy release causes heat production.

Muscular Fuel (2)

• Higher demand muscles have a greater blood supply to carry oxygen.
• The greater blood supply gives these muscles a darker color.

Smooth Muscle

• A special type of smooth muscle is called a sphincter.
• Sphincters are found throughout the digestive system and act as doorways to let material in and out.
• Contraction closes the door, while relaxation, opens it.

Cardiac Muscle

• Cardiac muscle is a specialized striated and involuntary muscle also called myocardium.
• It is located in the middle layer of the heart wall.
• Cells of the cardiac muscle are the cardiocytes.
• Cardiac muscle fibers are shorter and receive a richer supply of blood than any other muscle in the body.
• When cardiac muscle fibers contract, they force blood to circulate throughout the body.
• Contraction causes the heart to beat.

Cardiac Muscle (2)

• Membranes of cardiac muscle cells are interlocking and linked by gap junctions, forming intercalated discs.
• When one fiber contracts, it pulls the next one into a contraction, creating a domino effect.
• Cardiac muscle does not repair itself.
• Damage to cardiac muscle always leaves a scar.
• Scar tissue does not contract like normal tissue; it is rigid, which decreases cardiac output.