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TCN A&P ch. 6
The Muscles
82
Anatomy
Professional
03/12/2012

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Term
Active tension
Definition
Can be determined by subtracting the predetermined passive tension curve from the total tension curve.
Term
Action potential
Definition
Rapid, brief (several msec in duration) changes in the membrane potential of a neuron or muscle cell.
Term
Agonists
Definition
Muscles that are responsible for a particular movement.
Term
All-or-nothing principle
Definition
Each skeletal muscle fiber either contracts maximally or not at all.
Term
Absolute refractory period
Definition
Early in the refractory period a period restimulation is effectively impossible.
Term
Actin
Definition
The thin polymerized filaments in the contractile machinery of all muscle.
Term
Acetylcholine
Definition
When acetylcholine interacts with receptors on the muscle fiber, an action potential is initiated in the muscle fiber membrane.
Term
Alpha actinin
Definition
Attaches thin filaments to Z disc and determines their spacing.
Term
Creatine phosphokinase
Definition
The enzyme that catalyzes the transfer of phosphate groups from CrP to ADP and from ATP to Cr.
Term
CapZ
Definition
Forms the Z discs.
Term
Aponeurosis
Definition
The attachment of muscle to bone may be direct, or the connective tissue may extend beyond the muscle to form a cord-like tendon or a this.
Term
Contractile proteins
Definition
Actin and myosin, protein components of the sarcomere.
Term
Ca++ release channels
Definition
The parts of the voltage sensors that face the interior of the cell make a close connection with the second component of the endfeet, the Ca++ release channels in the membrane of the sarcoplasmic reticulum. In the unexcited state the voltage sensors block block them. Excitation causes the voltage sensors to unblock them, releasing Ca++ into the surrounding myofibrils.
Term
Convergent
Definition
When the arrangement of the fascicles converge from a broad origin toward a tendon so that the muscle has a fan shape.
Term
Contractile machinery
Definition
Consists of thin filaments composed of polymerized actin and thick filaments composed of aggregations of myosin.
Term
Crossbridges
Definition
Attachments made by myosin heads to actin binding sites that generate force during muscle contraction.
Term
Dense bodies
Definition
Attaches some of the network of actin thin filaments within the interior of smooth muscle cells. These bodies are the functional equivalent of the Z disc in striated muscle.
Term
Fascicles
Definition
Bundles of fibers enclosed in connective tissue sheaths of perimysium.
Term
Epimysium
Definition
A covering that surrounds all of the fascicles.
Term
Fast twitch (Type II)
Definition
Skeletal muscle fibers. This type of muscle expresses a myosin that cycles rapidly.
Term
Disuse atrophy
Definition
A dramatic loss of muscle mass due to long-term immobilization of a muscle.
Term
Excitation-contraction coupling
Definition
A process that will result in a detectable mechanical response of the muscle, as the action potential sweeps across the muscle cell surface.
Term
First class lever
Definition
The fulcrum lies between the effort and the load so that moving the effort arm in one direction moves the load in the other direction.
Term
Endomysium
Definition
A layer of connective tissue that wraps each individual muscle fiber.
Term
Intercalated discs
Definition
Structures that make durable end-to-end connections between the plasma membranes of adjacent fibers in cardiac muscle.
Term
Isotonic contraction
Definition
The muscle is allowed to shorten and lift a load.
Term
Hypertrophy
Definition
With conditioning skeletal muscles undergo adaptive changes that are visible mainly as an increase in the size of the cells.
Term
Length-tension curve
Definition
The curve shows that the active tension is maximal when the muscle is near its rest length.
Term
Isometric contraction
Definition
The muscle is not allowed to shorten, although tension does develop in the muscle.
Term
Latent period
Definition
A measurable delay between muscle excitation and the onset of tension development or shortening in the muscle.
Term
Hyperplasia
Definition
An increase in the number of muscle cells.
Term
Graded strength principle
Definition
The force delivered by a muscle may increase in proportion to the intensity of the stimulus delivered to its motor nerve, even though each motor neuron and each muscle fiber obeys the all-or-nothing rule.
Term
Mechanical disadvantage
Definition
Leverage allowing a strong force to move a light load rapidly through distance.
Term
mechanical advantage
Definition
Leverage using a small force operating over a large distance to move a heavy load a short distance.
Term
Multiunit smooth muscle
Definition
Muscle not connected by gap junctions and typically is not spontaneously active. Such muscle is found in the iris of the eye and in the arrector pili muscles attached to individual hairs.
Term
Leverage
Definition
Effort length of effort arm = load length of load arm.
Term
Motor unit
Definition
A motor neuron, together with its muscle fibers.
Term
Muscle triad
Definition
Formed by T tubules lying between two terminal cisternae.
Term
Myosin
Definition
Protein component of the sarcomere. Aggregations of thick filaments in the contractile machinery of all muscle.
Term
Myosin light-chain kinase (MLCK
Definition
An enzyme that phosphorylates a portion of the myosin head.
Term
Neuromuscular junction
Definition
The connection between a motor neuron and a skeletal muscle fiber.
Term
Myoblasts
Definition
Stem cells that fuse to form skeletal muscle during embryonic development, with the result that the mature cells are long cylinders with multiple nuclei.
Term
Myoglobin
Definition
An intracellular oxygen carrier.
Term
Nebulin
Definition
Structural proteins associated with thin filaments; serves as a molecular yardstick that limits the length of thin filaments.
Term
Nodal fibers
Definition
Contained within heart muscle that are spontaneously active and can serve as pacemakers for the entire heart.
Term
Myofibrils
Definition
Each fiber contains a number of parallel structures that constitute the actual contractile machinery of the fiber. Each is composed of a highly orderly arrangement of macromolecular filaments organized in repeating units called sarcomeres.
Term
Oxygen debt
Definition
A sustained increase in oxygen uptake that follows exercise. In order to incur an oxygen debt, the exercise must be of such intensity that it demands significant recruitment of Type IIb fibers.
Term
Passive tension
Definition
The curve of passive tension of a muscle has a value of zero at rest length and rises as the length is made greater than rest length.
Term
Operating range
Definition
The optimal range of contractile performance created by the leverage arrangements imposed by the skeleton that restricts muscle lengths.
Term
Pacemakers
Definition
Some heart muscle fibers that are spontaneously active.
Term
Pink fibers
Definition
Slowly fatiguing Type IIa fibers that contain some myoglobin.
Term
Pharmacomechanical route
Definition
The second messages set in motion by autonomic transmitters may control release of Ca++ from the intracellular stores without involvement of a change in membrane potential.
Term
Pennate
Definition
The arrangement of the muscle looks like a feather with the fascicles (the barbs of the feather) projecting at an angle from a tendon (the shaft of the feather) that runs the whole length of the muscle.
Term
Origin
Definition
The less movable attachment of a muscle.
Term
Relative refractory period
Definition
A period during which it is more difficult to restimulate the muscle.
Term
Refractory period
Definition
Follows each action potential.
Term
Rest length
Definition
Skeletal muscles that are removed from the body assume a standard length.
Term
Red fibers
Definition
Type I fibers that are a red color due to myoglobin.
Term
Second class lever
Definition
The load is attached between the effort and the fulcrum. The closer the load is to the fulcrum relative to the position of the effort, the greater the mechanical advantage.
Term
Power stroke
Definition
A rotation of the head that applies force to the thin filament.
Term
Sarcoplasmic reticulum (SR)
Definition
The site within the cell where Ca++ is stored.
Term
Sarcomere
Definition
The basic functional unit of the contractile machinery of striated muscle.
Term
Slow twitch (Type I)
Definition
Skeletal muscle fibers. Expresses a myosin that cycles slowly.
Term
Single-unit smooth muscle
Definition
A type of smooth muscle that contains extensive gap junction connections, making it possible for a large number of neighboring cells to contract simultaneously as if they were one unit. Such muscle is found in the GI tract and in blood vessels.
Term
Skeletal muscle
Definition
One of three types of muscle, these muscles are attached to the skeleton and controlled by the somatic motor branch of the nervous system.
Term
Series elastic elements
Definition
Stretch components that are part of the contractile machinery.
Term
Somatic branch
Definition
The branch of motor system that controls skeletal muscle.
Term
Spatial summation
Definition
The force summation in muscle generated by the newly added motor units to increase force production summates with the force produced by the units already active.
Term
Shivering
Definition
Involuntary contractions of skeletal muscles initiated when the core body temperature falls below its central setpoint, resulting in an increase in heat production.
Term
Sliding filament theory
Definition
A theory of muscle contraction that states that each thick filament has one end overlapping slightly with the thin filaments of one Z disc and the other end among the thin filaments of the other Z disc. Shortening of the distance between the hairbrushes occurs as the thick filaments pull both sets of thin filaments toward the center.
Term
Third class lever
Definition
Effort is applied between the load and the fulcrum. The load is moved rapidly, but with a mechanical disadvantage—the disadvantage increases with the length of the load arm.
Term
Thin filaments
Definition
Double strands of polymerized actin.
Term
Structural proteins
Definition
A protein component of sarcomeres, consisting of nebulin, titin, CapZ, and alpha actinin.
Term
Temporal summation
Definition
A form of summation in muscle contraction: If the muscle is restimulated within a few tens of msec, the force or shortening generated in the second twitch can summate, or add on top of, the initial one, making a stepwise increase in tension or decrease in length.
Term
Striated
Definition
Muscle that has a striped appearance due to being tightly organized sarcomeres, as in skeletal muscle and cardiac muscle.
Term
Titin
Definition
Connects the ends of thick filaments to Z disc to prevent sarcomeres from falling apart; believed to be largely responsible for the series elastic properties of muscle
Term
Terminal cisterna
Definition
A vessel formed by the SR, near the Z disc of each sarcomere.
Term
Tetanus
Definition
A smooth rise in muscle tension or decrease in length resulting from the further reduction of the interval between successive impulses.
Term
White fibers
Definition
Rapidly fatiguing Type IIb fibers contain some myoglobin.
Term
Voltage sensors
Definition
The protein components of the endfeet that sense the action potential passing along the T tubule.
Term
Transverse tubules (T Tubules)
Definition
Finger-like projections of plasma membrane that project into the interior of the muscle fiber and pass close to each terminal cisterna.
Term
Z Discs
Definition
Part of the contractile machinery of the muscle to which thin filaments are attached.
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