Human Anatomy and Physiology: Muscles and Muscle Tissue

Flashcards for reviewing muscle tissue, skeletal muscle anatomy, muscle fiber microanatomy, muscle fiber contraction, and smooth muscle.

Myo, mys, sarco

Prefixes for muscle. Example: sarcoplasm: muscle cell cytoplasm

Skeletal Muscle

Attached to bones and skin; also called voluntary muscle; can be consciously controlled; contracts rapidly; tires easily; powerful

Cardiac Muscle

Found only in the heart; involuntary: cannot be controlled consciously

Smooth Muscle

Found in walls of hollow organs; involuntary: cannot be controlled consciously

Excitability (responsiveness)

Ability to receive and respond to stimuli

Contractility

Ability to shorten forcibly when stimulated

Extensibility

Ability to be stretched

Elasticity

Ability to recoil to resting length

Epimysium

Dense irregular connective tissue surrounding entire muscle; may blend with fascia

Perimysium

Fibrous connective tissue surrounding fascicles (groups of muscle fibers)

Endomysium

Fine areolar connective tissue surrounding each muscle fiber

Insertion

Attachment to movable bone

Origin

Attachment to immovable or less movable bone

Sarcolemma

Muscle fiber plasma membrane

Sarcoplasm

Muscle fiber cytoplasm

Myofibrils

Densely packed, rodlike elements; single muscle fiber can contain 1000s; accounts for ~80% of muscle cell volume

Sarcomere

Smallest contractile unit (functional unit) of muscle fiber; contains A band with half of an I band at each end

Actin myofilaments

Thin filaments; extend across I band and partway in A band; anchored to Z discs

Myosin myofilaments

Thick filaments; extend length of A band; connected at M line

Sarcoplasmic Reticulum

Network of smooth endoplasmic reticulum tubules surrounding each myofibril; stores and releases Ca2+

T Tubules

Tube formed by protrusion of sarcolemma deep into cell interior; allow electrical nerve transmissions to reach deep into interior of each muscle fiber

Sliding Filament Model of Contraction

During contraction, thin filaments slide past thick filaments, causing actin and myosin to overlap more

Acetylcholine (ACh)

Neurotransmitter that transmits AP across from neuron to muscle cell

Chemically Gated Ion Channels

Opened by chemical messengers such as neurotransmitters; Example: ACh receptors on muscle cells

Voltage-Gated Ion Channels

Open or close in response to voltage changes in membrane potential

Neuromuscular Junction (NMJ)

Consists of axon terminals, synaptic cleft, and junctional folds

End Plate Potential

Local depolarization of the sarcolemma

Depolarization

Generation and propagation of an action potential (AP)

Repolarization

Restoration of resting conditions; Na+ voltage-gated channels close, and voltage-gated K+ channels open

Refractory Period

Muscle fiber cannot be stimulated for a specific amount of time, until repolarization is complete

Cross Bridge Cycle

The series of events during which myosin heads pull thin filaments toward the center of the sarcomere

Rigor Mortis

3–4 hours after death, muscles begin to stiffen; intracellular calcium levels increase, resulting in cross bridge formation

Motor Unit

Consists of one motor neuron and all the muscle fibers it innervates

Recruitment

Stimulus is sent to more muscle fibers, leading to more precise control

Muscle Tone

Constant, slightly contracted state of all muscles

Isotonic Contractions

Muscle changes in length and moves load; can be either concentric or eccentric

Isometric Contractions

Load is greater than the maximum tension muscle can generate, so muscle neither shortens nor lengthens

Concentric Contractions

Muscle shortens and does work

Eccentric Contractions

Muscle lengthens and generates force

Muscle Fatigue

Physiological inability to contract despite continued stimulation

Hypertrophy

Muscle cells can increase in size with regular exercise

Oxidative Fibers

Use aerobic pathways

Glycolytic Fibers

Use anaerobic glycolysis

Slow Oxidative Fibers

low-intensity, endurance activities

Fast Oxidative Fibers

Medium-intensity activities

Fast Glycolytic Fibers

Short-term intense or powerful movements

Sarcopenia

Loss of muscle mass that begins by age 30