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39 Cards in this Set

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  • Back
Striated muscle
Muscle characterized by sarcomeres aligned in register; includes skeletal and cardiac muscle.
Smooth muscle
Muscle without sarcomeres and hence without striations, whose myofilaments are nonuniformly distributed within small, mononucleated, spindle-shaped cells.
Skeletal muscle
The striated muscle whose neurogenic contraction is responsible for moving the bodies of animals.
Cardiac muscle
Heart muscle; individual fibers differ from skeletal muscle fibers in being small, elongated, tapered, and mononucleated. Includes noncontractile conducting fibers and contractile fibers.
Muscle fibers
A skeletal muscle cell.
A longitudinal unit of a muscle fiber, made up of sarcomeres and surrounded by sarcoplasmic reticulum.
The contractile unit of a myofibril, bounded at each end by a Z disk.
Each sarcomere contains two kinds of long, thin proteins called myofilaments arranged in a precise geometric pattern.
Thin filaments
A myofilament that contains actin and regulatory proteins such as troponin and tropomyosin.
A ubiquitous protein that participates in muscle contraction and other forms of cellular motility. G-actin is the globular monomer that polymerizes to form F-actin, the backbone of the thin filaments of muscle.
Thick filaments
A myofilament made primarily of myosin.
A protein that makes up the thick filaments and cross-bridges in muscle fibers; it is also found in many other cell types and is associated with cellular motility.
Spirally arranged projections from myosin thick filaments that bind to sites on actin thin filaments during muscle contraction.
A long protein molecule located in the grooves between actin filaments of muscle; inhibits muscle contraction by blocking the binding of myosin cross-bridges to actin filaments.
A calcium-binding complex of globular proteins associated with actin and tropomyosin in the thin filaments of muscle. When troponin binds Ca2+, it undergoes a conformational change, causing propomyosin to reveal myosin-binding sites on the actin filament.
Length-tension relation
Relation between the amount of overlap between actin and myosin filaments and the tension developed by an active sarcomere; also, the relation between the initial length of a whole muscle and the maximum tension it can produce during isometric contraction.
Sliding-filament theory
The theory that muscle sarcomeres shorten when actin thin filaments are actively pulled toward the middle of myosin thick filaments by the action of myosin crossbridges.
A complex of muscle proteins formed when myosin cross-bridges bind to actin.
Isometric contraction
Contraction during which a muscle does not shorten significantly.
Isotonic contraction
Contraction in which the force generated remains constant while the muscle shortens.
Excitation-contraction coupling
In muscle fibers, the process by which electrical excitation of the plasma membrane leads to activation of the contractile process.
Transverse tubule (T tubule)
Tubules found in striated muscle fibers that are continuous with the plasma membrane, extend deep into the fiber, and are closely apposed to the terminal cisternae of the sarcoplasmic reticulum.
Sarcoplasmic reticulum (SR)
A smooth, membrane-limited network surrounding each myofibril. Calcium is stored in the SR and released as free Ca2+ during excitation-contraction coupling.
A calcium-binding protein that contributes to the regulation of [Ca2+] in muscles.
Ryanodine receptors
Ryanodine receptors are tetrameric proteins that span the SR membrane. Half of them are lined up with proteins in the T-tubule membrane, called dihydropyridine receptors for their ability to bind dihydropyridine drugs.
Dihydrophridine receptors
Ryanodine receptors are tetrameric proteins that span the SR membrane. Half of them are lined up with proteins in the T-tubule membrane, called dihydropyridine receptors for their ability to bind dihydropyridine drugs. The dihydropyridine receptors have been more precisely identified as a type of voltage-gated calcium channel, called an L-type channel, which explains how they can respond to APs traveling along the membrane of T tubules.
Active state
In muscle fibers, the condition in which myosin cross-bridges are attached to actin, causing the fibers to resist a force that would pull them apart.
Summation of contraction
The addition of muscle tension due to repeated rapid stimulation of muscle.
Tonic fibers
Muscle fibers that contract very slowly and do not produce twitches. Found in the postural muscles of amphibians, reptiles, and birds, as well as in the muscle spindles and extraocular muscles of mammals. Tonic fibers normally produce no action potentials, and action potentials are not required to spread excitation, because the innervating motor neuron runs the length of the muscle fiber and makes repeated synapses all along it.
Twitch fibers (phasic fibers)
The most common striated vertebrate skeletal muscle; produces an all-or-none twitch in response to an all-or-none action potential.
The length of time during which a transient physiological variable is at half of its maximum value or greater.
Motor pool
The collection of motor neurons that innervate a particular muscle.
Motor unit
The unit of motor activity , consisting of a motor neuron and all of the muscle fibers it innervates.
Pacemaker fibers
An excitable cell or tissue that fires spontaneously and rhythmically.
Initiated by rhythmic electrical activity within a muscle cell or cells in the absence of neuronal input.
Single-unit smooth muscles
A smooth muscle in which individual fibers are coupled through gap junctions, allowing excitation to spread through the muscle independent of neuronal activity; contraction in these muscles is often myogenic, driven by internal pacemaker cells.
Multi-unit smooth muscles
A smooth muscle in which individual muscle fibers contract only when they receive excitatory input from neurons.
A calcium-binding regulatory protein that plays a role in the “latch” mechanism of some smooth muscles.
A troponin-like calcium-binding regulatory protein found in essentially all tissues.