NOTES: The Muscular System (Ch 8, part 1) Functions, Characteristics, Types of Muscle Tissue

**Muscles can be voluntary or involuntary** Functions of Muscle: Movement Heat production (thermogenesis)- byproduct of cellular respiration (converting glucose to ATP in the mitochondria of cells) Posture & body/joint support **Muscles can be voluntary or involuntary**

4 Characteristics of Muscle Tissue Excitability (irritability): ability to respond to certain stimuli by producing electrical signals called action potentials Stimuli= neurotransmitters or hormones Click for animation

4 Characteristics of Muscle Tissue Contractility: ability to shorten & thicken Extensibility: muscle can be stretched without damage to the tissue Most muscle tissue is found in pairs: one contracts while the other is relaxed & stretching Elasticity: muscle returns to its original shape after contraction & extension Click for animation!

3 Types of Muscle Tissue: Smooth Cardiac Skeletal

1. SMOOTH MUSCLE • Walls of hollow internal organs (arteries, respiratory passages, digestive canals -Involuntary muscle • Smooth muscle fibers (cells) contain filaments of actin and myosin & 1 nucleus (no striations) • Muscle fibers (cells) are separate and organized in flattened sheets Joined by electrical junctions

 Characteristics Unique to Smooth Muscle Contraction: • Can maintain a contraction longer than skeletal muscle • Can change length without changing tension (smooth muscle lining the stomach can stretch but still maintain pressure inside the stomach)

2. CARDIAC MUSCLE • Found only in the heart • Composed of striated cells joined end to end (only 1 nucleus)

• Cells are connected by INTERCALATED DISCS (which function in transmitting the impulse of contraction from cell to cell) -Involuntary -Cells don’t get “fatigued”

• The network of cardiac cells contracts as a unit (all-or-none response!) • Cardiac muscle is SELF-EXCITING and AUTO-RHYTHMIC

3. Skeletal Muscle Attaches to skeleton & is responsible for voluntary body movements Each muscle fiber (cell) is elongated and multinucleated; has distinct transverse striations Muscle fibers are grouped in bundles (each bundle is a FASCICLE)

SKELETAL MUSCLE ACTIONS *The type of movement a skeletal muscle produces depends on the way the muscle attaches on either side of a joint. • Immovable end of a skeletal muscle is called the ORIGIN (may be more than one) • Movable end of a skeletal muscle is called the INSERTION

SKELETAL MUSCLE ACTIONS *when a muscle contracts, its insertion is pulled towards its origin.

Interaction of Skeletal Muscles: Skeletal muscles function in groups The muscle responsible for most of a movement is the: PRIME MOVER (or AGONIST)

Interaction of Skeletal Muscles: Muscles that contract and assist the prime mover are: SYNERGISTS Muscles that resist the action of the prime mover are: ANTAGONISTS

Muscles that function as joint stabilizers are called FIXATOR muscles Maintain posture or balance Most muscles function as one or more of these. A muscle that may be a prime mover during flexion may be an antagonist during extension.