muscular system Flashcards
(87 cards)
1
Q
Functions muscle tissue
A
- Movement (movement of body parts, transport of materials)
- Stabilization (body postures, organ function)
- Thermogenesis (predominantly skeletal muscle)
2
Q
General characteristics of muscle tissue
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- Possess irritability, contractility, extensibility, and elasticity
- Composed of elongated cells
3
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Location: somatic/skeletal muscles
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upper part of esophagus, diaphragm
4
Q
A muscle is surrounded by
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epimysium (composed of dense connective tissue)
5
Q
The muscle is made up of bundles of muscle cells called
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(fascicles)
6
Q
bundles of muscle cells (fascicles), is covered by
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perimysium
composed of dense connective tissue
7
Q
fascicle is made up of numerous muscle cells/”fibers”, each covered by
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endomysium (consisting of a basal lamina)
8
Q
At the myotendinous junction, the endomysium, perimysium, and epimysium become continuous with the
A
muscle tendon, which attaches the muscle to the bone
9
Q
the cell membrane of a muscle fiber
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Sarcolemma
10
Q
continuous with the sarcolemma, extending into the interior of the fiber, surrounding the myofibrils
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Transverse tubules (aka, T tubules)
11
Q
specialized endoplasmic reticulum, forms a tubular network around the myofibrils
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Sarcoplasmic reticulum
12
Q
large chambers of sarcoplasmic reticulum encircling the myofibril, on either side of the transverse tubule; storage of calcium ions
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Cisternae
13
Q
unit of a transverse tubule and flanking cisternae encircling a myofibril
A
Triad
14
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made up of microfilaments (aka, myofilaments), arranged into sarcomeres
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Myofibril
15
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made up primarily of the contractile protein actin
i. Also contain the regulatory proteins, troponin and tropomyosin
ii. Held in place by the structural protein nebulin, which attaches the…………………. to the Z disc
A
Thin filaments
16
Q
made up primarily of the protein myosin
Held in place by the structural protein, titin, which attaches the ……………….. to the Z disc and to the M line
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Thick filaments
17
Q
Additional structural protein that makes up the M line
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Myomesin
18
Q
Additional structural protein that connects thin filaments to the sarcolemma of the cell, thus helping to transmit muscle tension to the muscle tendon
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Dystrophin
19
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the functional unit of muscle contraction
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Sarcomere
20
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dark band, primarily made up of thick filaments
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A band
21
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center of the A band, made up of the structural protein myomesin, holding the thick filaments in place
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M line
22
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lighter zone on either side of the M line, contains only thick filaments
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H zone
23
Q
overlapping zone of thin and thick filaments
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Zone of overlap
24
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light band, made up entirely of thin filaments
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I band
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boundary between two sarcomeres, made up of the structural protein actinin, which holds the thick and thin filaments in place
Z disc/line
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.....................stimulated by signals from the nervous system; this generates an action potential (i.e., an electrical impulse) which travels down the.......................
Sarcolemma
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Action potential travels through the.................. to the...........................
T tubules, myofibrils
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Action potential triggers release of
calcium ions from the cisternae
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Calcium ions (Ca2+) cause exposure of binding sites on the
actin molecules of the thin filaments
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Calcium ions bind to ......................, causing........................ to move away and uncover the binding sites on the actin molecules
troponin, tropomyosin
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What causes the thin filaments to slide past the thick filaments, toward the M line, resulting in contraction of the muscle fiber
Myosin binding to actin
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Myosin head binds to an actin molecule on the thin filament; this causes the release of
phosphate group (Pi)
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Before contraction of sarcomere begins, ........................... binds to the myosin head and immediately hydrolyzes into....................... , a .........................., and........................
adenosine triphosphate (ATP),adenosine diphosphate (ADP),phosphate group (Pi) and stored energy
34
Release of the Pi initiates the ‘power stroke,’ which pulls the thin filament
toward the center of the sarcomere
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at the end of the power stroke, the.........................is released from the myosin head
ADP molecule
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Another ATP molecule attaches to the myosin head, which causes the
myosin head to detach from the actin molecule
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due to permanent cross-bridging between actin and myosin because no ATP is available to break the bond
Rigor mortis
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Energy sources stored within the muscle (anaerobic)
Breakdown of creatine phosphate
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Energy sources stored within the muscle and in the liver (anaerobic)
Glycolysis of glycogen
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.................................... of lipids, carbohydrates, and proteins (aerobic)
Oxidative metabolism
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immediate utilization of creatine phosphate and glycogen (anaerobic)
Phase I
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aerobic breakdown of fatty acids, carbohydrates, and proteins
Phase 2
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return to glycolysis (anaerobic) of glycogen remaining within the muscle
Phase 3
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embedded within the muscle belly; monitors changes in muscle length (both shortening [i.e., contraction] and lengthening [i.e., stretch])
Muscle spindle
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Intrafusal muscle fibers (specialized skeletal muscle cells) enclosed within a spindle-shaped connective tissue capsule; no actin or myosin filaments in the central portion of each intrafusal muscle fiber, only nuclei (structure of muscle spindles)
i. Nuclear bag fibers
| ii. Nuclear chain fibers
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sensory nerve endings (type Ia) are wrapped around the center of both nuclear bag fibers and nuclear chain fibers
Primary ending
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sensory nerve endings (type II) are wrapped around the center of only the nuclear chain fibers
Secondary ending
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Gamma motor nerve fibers that predominantly innervates nuclear bag intrafusal fibers
Gamma-dynamic (gamma-d)
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Gamma motor nerve fibers that predominantly innervates nuclear chain intrafusal fibers
Gamma-static (gamma-s)
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i. Primary and secondary sensory endings fire continuously and in proportion to the degree of stretch
ii. Gamma-static motor fibers fire, proportionate to the increase or decrease in stretch
Slow, prolonged stretch: “static” response
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i. Primary sensory endings fire, only while change in length is occurring
ii. Gamma-dynamic motor fibers fire, maintaining spindle fiber length proportions, and thereby maintaining receptor sensitivity
Sudden stretch: “dynamic” response
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stretch receptor located at the myotendinous junction
Tendon organ (aka, Golgi tendon organ)
1. Small bundle of tendon collagen fibers surrounded by a connective tissue sheath, one end connected to muscle fibers, the other end merging into the tendon
2. A single type Ib sensory fiber wraps around the collagen fibers of the tendon organ
3. Tendon organ fires in response to tension on the organ, due to either muscle contraction or muscle stretch
4. Has both dynamic and static response levels
53
a. Muscle is stretched suddenly, thereby stretching the muscle spindle; primary sensory fibers are activated (“dynamic response”) and action potentials travel into the spinal cord, synapsing directly with alpha motor neurons associated with that muscle (i.e., the homonymous muscle)
b. Alpha motor neurons of the homonymous muscle are activated and cause the muscle to contract, thereby decreasing the stretch on the muscle and returning the muscle spindles to their original length and returning the firing rate of the primary sensory fibers to their baseline (“static”) level
c. At the same time, motor commands are sent from the spinal cord to contract synergistic muscles and relax antagonistic muscles
Reflex cycle
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a. Prevent the development of too much tension within the muscle, protecting the muscle and tendon from potential damage
b. Equalizes the contraction strength of muscle fibers within a muscle
Functions of the Golgi tendon
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stimulation of a body part causes contraction of flexor muscles, withdrawing the body part away from the stimulus
Flexor-withdrawal reflex
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spread the reflex signal to other associated muscles
Diverging neural circuits
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inhibiting contraction of associated antagonist muscles
Reciprocal inhibition circuits
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prolonging the contraction of the flexor muscles after the stimulus has stopped
Circuits which cause an afterdischarge
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extension of contralateral limb, 0.2 to 0.5 seconds after the beginning of the flexor-withdrawal reflex
Crossed-extensor reflex
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Cells are striated, with actin and myosin arranged into sarcomeres
Cells are short and branched, with a single nucleus
Cardiac muscle tissue
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Cardiac muscle tissue what is larger and more plentiful than in skeletal muscle cells
Mitochondria
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Cardiac muscle tissue what is more numerous and larger (in diameter) than in skeletal muscle cells
Transverse tubules
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Cardiac muscle tissue what is less well developed than in skeletal muscle cells
Sarcoplasmic reticulum
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Sources of calcium during cell contraction
a. Released from cisternae of the sarcoplasmic reticulum
b. Extracellular fluid: calcium brought into the cell via the transverse tubules and diffuses across the cell membrane into the cell’s interior
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Cardiac cells originate from
a single myoblast
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Cardiac Cells interconnected to each other via
intercalated discs
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region consisting of numerous adherent junctions (viz., desmosomes) and numerous gap junctions
Intercalated discs
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keep the cells from pulling apart as they contract
Desmosomes
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act as ‘electrical synapses,’ passing the contraction signal directly from one cell to all the others within the interconnected network
Gap junctions
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all the cells within each network contract simultaneously, as if they were a single cell
Functional syncytium
Cells within the upper heart chambers (right and left atria) are all interconnected into a single network and the cells within the lower heart chambers (right and left ventricles) are all interconnected into a single network
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1. Cells are short and fusiform in shape, with a single, centrally located nucleus
2. Cells are not striated; actin and myosin are arranged differently from the sarcomeres of skeletal and cardiac muscle cells
3. Sarcoplasmic reticulum is sparse and there are no transverse tubules
Smooth muscle Structure
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some scattered within the cell and some attached to the cell membrane
smooth muscle
Dense bodies
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some are bonded to membrane dense bodies of adjacent cells
smooth muscle
Membrane dense bodies
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In smooth muscle Actin filaments lack troponin; calcium instead binds to regulatory protein............................., associated with the myosin filaments
smooth muscle
calmodulin
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Myosin filaments interspersed in between..................
smooth muscle
actin filaments, halfway between the dense bodies
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structural proteins forming a framework for the actin and myosin filaments
smooth muscle
Intermediate filaments
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myosin heads on one side of the myosin molecule hinge (bend) in one direction, while heads on the opposite side hinge in the opposite direction
smooth muscle
‘Sidepolar’ cross-bridges between myosin and actin
Resulting cell shortening proceeds from a spiral, corkscrew-like contraction
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Little calcium is stored within the .......................; most comes from extracellular fluid, and enters the cell through .................................. in the sarcolemma
smooth muscle
sarcoplasmic reticulum,calcium channels
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Numerous cells are arranged into a single sheet of interconnected cells, which all contract simultaneously
Typically found in hollow organs (e.g., stomach, intestines, uterus, bile duct, bladder, most blood vessels)
VISCERAL (aka, unitary, syncytial, single-unit) SMOOTH MUSCLE
(Cells are connected by numerous gap junctions, which transmit action potentials (as well as ions) between cells)
(Most organs have two layers of muscles, one running longitudinally, the other running transversely; the stomach has a third layer, running obliquely to the other two)
80
Composed of individual smooth muscle cells, unconnected to nearby cells
i. Each cell is covered by a thin membrane (composed of fine collagen fibers and glycoproteins) which insulates it from nearby cells
ii. Each cell receives its own innervation
iii. Found in the constrictor and dilator muscles of the iris, arrector pili muscle, pulmonary air passages, and the walls of the largest arteries
Multi-unit smooth muscle
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Calcium-calmodulin complex binds to, and activates
myosin light chain kinase (MLCK)
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MLCK phosphorylates one of the light chains within a myosin head
allows the myosin head to bind to actin
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Myosin-actin cross-bridge cycle repeats until
available calcium is depleted; cycle is slower than in skeletal muscle (cross-bridge is intact for a longer period of time)
84
Myosin light chain is de-phosphorylated by action of
myosin phosphatase
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T/F Onset and relaxation of contraction is much slower than in skeletal and cardiac muscle
T
a. Calcium channels open much more slowly, slowing the entry of calcium into the cell; channels stay open longer as well
b. Slow removal of calcium by calcium pumps
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T/F Lengthening of the cross-bridge cycle, in combination with the slowness of contraction onset and relaxation, produces a prolonged muscle tone without excessive energy expenditure
T
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1. Nervous input: the predominant stimulus for multi-unit smooth muscle, less common for single-unit smooth muscle
2. Hormonal input
3. Muscle cell stretch
4. Nearby chemical environment of the muscle cell (e.g., lack of oxygen, excess carbon dioxide, increased hydrogen ion concentrations)
Regulation of smooth muscle contraction
