Honors Anatomy Unit 6 Muscular System Notes

Skeletal Muscle

Voluntary, striated muscle attached to the skeleton.

Cardiac Muscle

Involuntary, striated muscle found in the heart.

Smooth Muscle

Involuntary, non-striated muscle lining hollow organs and blood vessels.

Produce body movement

Function of muscle tissue that includes walking, running, grasping a pencil, and nodding head.

Stabilizing body position

Function of muscle tissue where postural muscles continually contract to maintain position.

Storing and moving substances

Function of muscle tissue exemplified by sphincters and smooth muscle contractions.

Produce Heat

Function of muscle tissue used to maintain normal body temperature, with involuntary shivering increasing heat production.

Point of Origin

Attachment of a muscle's tendon to the stationary bone.

Point of Insertion

Attachment of a muscle's tendon to the moveable bone.

Antagonistic pair

A pair of muscles working at the same joint that cause opposite movements.

Flexor

Muscle that reduces the joint angle.

Extensor

Muscle that increases the joint angle.

Skeletal muscle

Groups of fascicles bundled together.

Fascicle

A bundle of muscle fibers.

Epimysium

Connective tissue that surrounds the skeletal muscle.

Muscle fiber

Many cells fused together to form one long, multinucleated, elongated cell.

Perimysium

Connective tissue that surrounds individual fascicles.

Endomysium

Connective tissue that surrounds individual muscle fibers.

Sarcolemma

Plasma membrane surrounding a muscle fiber.

Transverse tubules (T tubules)

Tunnel-like extensions of the sarcolemma that pass through the muscle fiber side-to-side.

Sarcoplasm

Cytoplasm of a muscle fiber; contains many mitochondria that produce large amounts of ATP.

Sarcoplasmic Reticulum

Network of membranous tubules that store calcium ions required for muscular contraction.

Myoglobin

Molecule found within the sarcoplasm that stores oxygen until needed by the mitochondria.

Myofibrils

Cylindrical structures that extend the length of the muscle fibers, composed of repeating units called sarcomeres.

Sarcomeres

Compartments composed of thick and thin protein filaments; basic structural units of a myofibril.

Z discs/line

Dense material that separates one sarcomere from the next.

A band

Extends the entire length of the thick filaments.

H zone

Narrow zone in the center of the A band, contains only thick filaments.

Zone of overlap

Ends of the A-band; thick and thin filaments overlap.

M line

Middle of the sarcomere; supporting proteins that hold the thick filaments together.

I band

Lighter, less dense; contains only thin filaments.

Contraction of Sarcomere

The process by which the sarcomere shortens and generates force.

Relaxation of Sarcomere

The process by which the sarcomere lengthens and reduces force.

Change in Sarcomere Length

The alteration in the length of the sarcomere during contraction and relaxation.

Change in Myosin Length

The alteration in the length of myosin filaments during muscle contraction.

Change in Actin Length

The alteration in the length of actin filaments during muscle contraction.

Change in H Zone Width

The variation in the width of the H zone during contraction and relaxation.

Change in Zone of Overlap

The variation in the extent of overlap between thick and thin filaments during contraction.

Transduction

The process by which mechanoreceptors, photoreceptors, thermoreceptors, chemoreceptors, and nociceptors convert stimuli into electrical signals.

Resting Neuron/Resting Potential

The state of a neuron when it is not transmitting an impulse, characterized by a potential difference across the membrane.

Action Potential/Nerve Impulse

A rapid change in membrane potential that propagates along the axon, resulting from the movement of ions.

Threshold Potential

The level of depolarization that must be reached for an action potential to occur.

All or Nothing Response

The principle that a neuron either fires completely or not at all when stimulated beyond threshold.

Refractory Period

The time following an action potential during which a neuron cannot fire another action potential.

Neuromuscular Junction (NMJ)

The synapse between a motor neuron and a muscle fiber where neurotransmitter release occurs.

Acetylcholine

A neurotransmitter that binds to receptors on the muscle membrane, causing depolarization and muscle contraction.

Muscle Action Potential

The electrical signal that triggers muscle contraction, initiated by the binding of acetylcholine.

Ca2+ Release

The release of calcium ions from the sarcoplasmic reticulum into the cytosol, initiating muscle contraction.

Thick filaments

Bundles of myosin

Thin filaments

Primarily actin

Actin filament

Contains primarily actin, tropomyosin, and the troponin complex.

Tropomyosin

Prevents actin from attaching to the myosin by masking the binding sites at resting state.

Calcium ions (Ca2+)

Released from the sarcoplasmic reticulum and picked up by the calcium binding sites of the troponin complex.

Troponin complex

Binding of Ca2+ causes a shift in position of the tropomyosin, allowing actin to bind with myosin.

Sliding-Filament Theory

Describes the contraction cycle where myosin heads attach to actin, forming cross-bridges.

Power stroke

The bending of cross-bridges that pulls the thin (actin) filaments toward the H zone.

ATP breakdown

Converts ATP to ADP and P, causing the myosin heads to become 'cocked' for the next power stroke.

Relaxation

Occurs when nerve impulses cease, acetylcholine is broken down, and Ca2+ ions are transported back into the sarcoplasmic reticulum.

Frequency of Stimulation

Period of time before the next action potential stimulates the muscle fiber.

Size of the Stimulus

Muscle contractions intensify when more motor neurons stimulate more muscle fibers/motor units.

Recruitment

Some muscle fibers held in tetanus while others are stimulated, resulting in smooth but steady increase in muscle tension.

Muscle Tone

Constant tension produced by muscles of the body over long periods of time.

Muscle Fatigue

Muscle fibers stop contracting when inadequate amounts of ATP are available.

Atrophy

Wasting away of muscles; decrease in size of muscle due to loss of myofibrils.

Hypertrophy

Increase in diameter of muscle fibers owing to the production of more myofibrils, mitochondria, and sarcoplasmic reticulum.

Motor Unit

Made up of a motor neuron and all of the skeletal muscle fibers innervated by the neuron's axon terminals.

Fast Twitch

Larger in diameter, white in color, generate ATP anaerobically, contract strongly/rapidly, and fatigue quickly.

Slow Twitch

Smaller in diameter, dark red in color, generate ATP aerobically, capable of sustained contractions, and very resistant to fatigue.