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76 Cards in this Set

  • Front
  • Back
___ is the ability to receive and respond to a stimulus, that is, any change in the environment whether inside or outside the body.
Excitability, also termed responsiveness or irritability
____ is the ability to shorten forcibly when adequately stimulated. This property sets muscle apart from all other tissue types.
_____ is the ability to be stretched or extended.
_____ is the ability of a muscle fiber to recoil and resume its resting length after being stretched.
Muscle performs four important functions for the body: what are they?
It produces movement, maintains posture, stabilizes joints, and generates heat.
skeletal muscle accounts for at least __ of body mass
a fine sheath of connective tissue consisting of areolar and reticular fibers-surrounds each individual muscle fiber
, the endomysium-wrapped muscle fibers are grouped into ____
each fascicle is a layer of fibrous connective tissue called
An “overcoat” of dense irregular connective tissue that surrounds the whole muscle.
) when a muscle contracts, the movable bone, the muscle’s ______, moves toward the immovable or less movable bone, the muscle’s ____
In _____ attachments, the epimysium of the muscle is fused to the periosteum of a bone or perichondrium of a cartilage.
direct, or fleshy,
In ____ ____, the muscle’s connective tissue wrappings extend beyond the muscle either as a ropelike tendon or as a sheetlike aponeurosis
indirect attachments
the sracoplasm contains unsusually large amounts of____ (granules of stored glycogen) , and ____, a red pigment that stores oxygen
glycosomes, myogobin
The _____ contain the contractile elements of skeletal muscle cells, and they account for about 80% of cellular volume.
A sarcomere (sar′ko-mĕr; literally, “muscle segment”) is the region of a myofibril between two successive __ ___.
Z discs
The central ___ filaments extend the entire length of the A band while The more lateral ____ filaments extend across the I band and partway into the A band.
thick, thin
The __ ___, a coin-shaped sheet composed largely of the protein alpha actinin, anchors the thin filaments.
Z disc
_____ filaments extending from the Z disc connect each myofibril to the next throughout the width of the muscle cell.
Intermediate (desmin)
The myofilaments are connected to the sarcolemma at the __ __ and the __ ___.
Z discs. M lines.
Thick filaments (about 16 nm in diameter) are composed primarily of the protein ___.
Each __ __ has a rodlike tail terminating via a flexible hinge in two globular heads.
myosin molecule
Each thick filament contains about __ myosin molecules bundled together
Besides bearing actin binding sites, the heads contain ATPase enzymes that split ___ to generate energy for muscle contraction.
The thin filaments (7–8 nm thick) are composed chiefly of the protein ___
Two strands of ____ ,a rod-shaped protein, spiral about the actin core and help stiffen it
tropomyosin (tro″po-mi′o-sin),
The other major protein in the thin filament,___, is a three-polypeptide complex
troponin (tro′po-nin),
Titin has two basic fxns, what are they?
(1) holding the thick filaments in place, thus maintaining the organization of the A band, and (2) assisting the muscle cell to spring back into shape after being stretched or shortening.
Another important structural protein is ____, which links the thin filaments to the integral proteins of the sarcolemma (which in turn are anchored to the extracellular matrix)
At each A band–I band junction, the sarcolemma of the muscle cell penetrates into the cell interior, forming an elongated tube called the _ ____
T tubule
Muscle contraction is ultimately controlled by nerve-initiated electrical impulses that travel along the ______
Because _ ___ are continuations of the sarcolemma, they can and do conduct impulses to the deepest regions of the muscle cell and to every sarcomere
T tubules
____ ends when the cross bridges become inactive and the tension generated declines, inducing relaxation of the muscle fiber.
The sliding filament theory of contraction states that during contraction the thin filaments slide past the thick ones so that the ___ and ___ filaments overlap to a greater degree
actin myosin
For a skeletal muscle fiber to contract, it must be stimulated by a nerve ending and must propagate an electrical current, or ___ ____, along its sarcolemma.
action potential
Although the axon terminal and the muscle fiber are exceedingly close (1–2 nm apart), they remain separated by a space, the __ ___
synaptic cleft
. Within the flattened moundlike axon terminal are synaptic vesicles, small membranous sacs containing the neurotransmitter ___ , or ACh.
The ___ __ ___, the troughlike part of the muscle fiber’s sarcolemma that helps form the neuromuscular junction, is highly folded. These junctional folds provide a large surface area for the millions of ACh receptors located there.
motor end plate
When a nerve impulse reaches the end of an axon, voltage-gated calcium channels in its membrane open, allowing ___ to flow in from the extracellular fluid.
Ca2+ (propelled by its electrochemical gradient)
The presence of calcium inside the axon terminal causes some of the synaptic vesicles to fuse with the axonal membrane and release ___ into the synaptic cleft by exocytosis
Like the plasma membranes of all cells, a resting sarcolemma is _____
Describe the first step of the action potential.
. First the membrane areas adjacent to the depolarized motor end plate are depolarized by local currents that spread to them from the neuromuscular junction. This opens voltage-gated sodium channels there, so Na+ enters, following its electrochemical gradient, and initiates the action potential
Describe the second step of the action potential.
During step 2, the action potential is propagated (moves along the length of the sarcolemma) as the local depolarization wave spreads to adjacent areas of the sarcolemma and opens voltage-gated sodium channels there (see Figure 9.8c). Again, sodium ions, normally restricted from entering, diffuse into the cell following their electrochemical gradient.
Describe the third step of the action potential.
Step 3 is repolarization, which restores the sarcolemma to its initial polarized state. The repolarization wave, which quickly follows the depolarization wave, is a consequence of Na+ channels closing and voltage-gated K+ channels opening. Since the potassium ion concentration is substantially higher inside the cell than in the extracellular fluid, K+ diffuses rapidly out of the muscle fiber
During repolarization, a muscle fiber is said to be in a ___ ___, because the cell cannot be stimulated again until repolarization is complete.
refractory period
__ __ __ is the sequence of events by which transmission of an action potential along the sarcolemma leads to the sliding of myofilaments.
Excitation-contraction (E-C) coupling
The events of excitation-contraction coupling occur during the __ __, between action potential initiation and the beginning of mechanical activity (shortening).
latent period
When intracellular calcium levels are low, the muscle cell is relaxed/excited?
Name the 4 steps to muscle fiber contraction.
Cross bridge formation, The power (working) stroke, Cross bridge detachment, “Cocking” of the myosin head.
The force exerted by a contracting muscle on an object is called __ ___ , and the opposing force exerted on the muscle by the weight of the object to be moved is called the ___
muscle tension load
A motor neuron and all the muscle fibers it supplies is called a ___ ___
motor unit
Define Period of relaxation.
The period of contraction is followed by the period of relaxation. This final phase, lasting 10–100 ms, is initiated by reentry of Ca2+ into the SR. Because contractile force is no longer being generated, muscle tension decreases to zero and the tracing returns to the baseline. If the muscle shortened during contraction, it now returns to its initial length.
Define Period of contraction.
The period of contraction is when cross bridges are active, from the onset to the peak of tension development, and the myogram tracing rises to a peak. This period lasts 10–100 ms. If the tension (pull) becomes great enough to overcome the resistance of a load, the muscle shortens.
Define Latent period.
The latent period is the first few milliseconds following stimulation when excitation-contraction coupling is occurring. During this period, muscle tension is beginning to increase but no response is seen on the myogram.
In general, muscle contraction can be graded in two ways. Name them.
(1) by changing the frequency of stimulation and (2) by changing the strength of the stimulus.
if two identical stimuli (electrical shocks or nerve impulses) are delivered to a muscle in rapid succession, the second twitch will be stronger than the first. What is this called?
wave summation
______ contractions are about 50% more forceful than concentric ones at the same load and more often cause delayed-onset muscle soreness
Name the two types of isotonic contractions.
Eccentric, Concentric
The force of contraction is controlled more precisely by _____, also called multiple motor unit summation
delivering shocks of increasing voltage to the muscle, calling more and more muscle fibers into play. The stimulus at which the first observable contraction occurs is called the ____ _____.
threshold stimulus.
The ____ _____ is the strongest stimulus that produces increased contractile force.
maximal stimulus
The recruitment process is not random; instead it is dictated by the ___ principle.
Fortunately, after ATP is hydrolyzed to ADP and inorganic phosphate, it is regenerated within a fraction of a second by three pathways
1) by interaction of ADP with creatine phosphate, (2) from stored glycogen via the anaerobic pathway called glycolysis, and (3) by aerobic respiration.
The initial phase of glucose respiration is ____
Under these anaerobic conditions, most of the pyruvic acid produced during glycolysis is converted into ___ ____, and the overall process is referred to as ____ _____.
lactic acid anaerobic glycolysis
During glycolysis, glucose is broken down to two pyruvic acid molecules, releasing enough energy to form small amounts of ATP. How much ATP is produced?
(2 ATPs per glucose).
The anaerobic pathway harvests only about __& as much ATP from each glucose molecule as the aerobic pathway; however, it produces ATP about__ times faster.
5%, 2 1∕2
___ ___ is a state of physiological inability to contract even though the muscle still may be receiving stimuli.
Muscle fatigue
Availability of ATP declines during contraction and a total lack of ATP results in ______, states of continuous contraction because the cross bridges are unable to detach
Oxygen debt is defined as what?
Oxygen debt is defined as the extra amount of oxygen that the body must take in for these restorative processes.
Only about __% of the energy released during muscle contraction is converted to useful work
What 4 factors affect the force of muscle contraction?
(1) the number of muscle fibers stimulated, (2) the relative size of the fibers, (3) frequency of stimulation, and (4) the degree of muscle stretch
The more rapidly a muscle is stimulated, the ____ the force it exerts.
The cells that rely mostly on the oxygen-using aerobic pathways for ATP generation are ____ fibers; those that rely more on anaerobic glycolysis are ____ fibers.
oxidative, glycolytic
The innervating nerve fibers of smooth muscle tissue, which are part of the autonomic nervous system, have numerous bulbous swellings, called _____
The varicosities release neurotransmitter into a wide synaptic cleft in the general area of the smooth muscle cells. Such junctions are called ____ ____.
diffuse junctions.