Human Anatomy and Physiology - Muscle Tissue

Vocabulary flashcards for muscle tissue lecture notes.

Myo, mys, and sarco

Prefixes for muscle, such as in sarcoplasm (muscle cell cytoplasm).

Skeletal Muscle

Muscle tissue attached to bones and skin; also called voluntary muscle.

Cardiac Muscle

Muscle tissue found only in the heart; involuntary.

Smooth Muscle

Muscle tissue found in the walls of hollow organs; involuntary.

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 the entire muscle.

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

Rodlike elements that are densely packed in muscle fibers and contain sarcomeres.

Sarcomere

The smallest contractile unit (functional unit) of muscle fiber.

A bands

Dark regions of a sarcomere, including the H zone and M line.

H zone

Lighter regions in the middle of the dark A band.

M line

Line of protein (myomesin) that bisects the H zone vertically.

I bands

Lighter regions of a sarcomere, containing the Z disc (line).

Z disc (line)

Coin-shaped sheet of proteins on the midline of the light I band.

Myofilaments

Orderly arrangement of actin and myosin myofilaments within sarcomere.

Sarcoplasmic Reticulum

Network of smooth endoplasmic reticulum tubules surrounding each myofibril, storing and releasing Ca2+.

T Tubules

Tube formed by protrusion of sarcolemma deep into cell interior, allowing electrical nerve transmissions.

Triad

Area formed from terminal cistern of one sarcomere, T tubule, and terminal cistern of neighboring sarcomere.

Contraction

Activation of cross bridges to generate force.

Axons

Long, threadlike extensions of motor neurons that travel from the central nervous system to skeletal muscle.

Neuromuscular Junction or Motor End Plate

Region where the axon branches end on muscle fiber.

Synaptic Cleft

Gel-filled space separating the axon terminal and muscle fiber.

Synaptic Vesicles

Membrane-bound sacs within axon terminals that contain the neurotransmitter acetylcholine (ACh).

Junctional Folds

Infoldings of sarcolemma that contain millions of ACh receptors.

Chemically gated ion channels

ACh receptors (Na+ chemical gates) on sarcolemma.

Voltage-gated ion channels

Open or close in response to voltage changes in membrane potential.

End Plate Potential

Local depolarization of the sarcolemma caused by Na+ diffusing into the muscle fiber.

Threshold

Minimum voltage required to trigger voltage-gated Na+ channels and initiate an action potential.

Repolarization

Restoration of resting conditions after depolarization.

Refractory Period

Period during which a muscle fiber cannot be stimulated until repolarization is complete.

Excitation-Contraction (E-C) Coupling

Sequence of events by which transmission of an action potential along the sarcolemma leads to the sliding of myofilaments.

Cross bridge formation

High-energy myosin head attaches to actin thin filament active site.

Working (power) stroke

Myosin head pivots and pulls thin filament toward M line.

Cross bridge detachment

ATP attaches to myosin head, causing cross bridge to detach.

Cocking of myosin head

Energy from hydrolysis of ATP cocks myosin head into high-energy state.

Subthreshold stimulus

Stimulus not strong enough, so no contractions seen

Threshold stimulus

Stimulus is strong enough to cause first observable contraction

Maximal stimulus

Strongest stimulus that increases maximum contractile force.

Muscle Tone

Constant, slightly contracted state of all muscles

Isotonic contractions

Muscle changes in length and moves load

Concentric contractions

Muscle shortens and does work

Eccentric contractions

Muscle lengthens and generates force

Isometric contractions

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

Fatigue

Physiological inability to contract despite continued stimulation.

Hypertrophy

Muscle cells increase in size.

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.

Disuse atrophy

Degeneration and loss of mass.