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CH.10 Muscle Function

Terms in this set (101)

Identify the 3 types of muscle tissue and cite their major functions.
-Skeletal
-Cardiac
-Smooth Muscle
Skeletal muscle tissue moves the body by pulling on our bones, cardiac muscle tissue pumps blood through the cardiovascular system, and smooth muscle tissue pushes fluids and solids along the digestive tract and other internal organs, and regulates the diameters of small arteries.
Identify the common properties shared by muscle tissues.
-Excitability (ability to receive and respond to stimulus)
-Contractility (ability of a muscle cell to shorten when it is stimulated)
-Extensibility (Stretching movement of a muscle)
-Elasticity (ability of a muscle to recoil to its resting length)
Identify the primary functions of skeletal muscle tissue.
-Producing Movement
-Maintaining Posture & Body Posture (tension)
-Supporting Soft Tissues (abdominal wall, ,pelvic floor cavity)
-Guarding Body Entrances & Exists (Sphincters, swallowing, defecating, urinating)
-Maintaining Body Temp
-Storing Nutrients (too few kcals, the contractile proteins are broken down, amino acid released, liver synthesizes glucose form amino acids or provide energy)
Skeletal muscle contains ...
-muscle tissue
-connective tissues
-blood vessels
-nerves
Each cell in skeletal muscle tissue is....
a single muscle fiber (cell).
Epimysium
dense layer of collagen fibers that surrounds the entire muscle & is continuous w/the tendons/aponeuroses of the muscle & w/ the perimysium
-separates the muscle from nearby tissues and organs
-connected to the deep fascia
Fascia
a dense connective tissue layer
Perimysium
connective tissue partition that separates adjacent fasciculi in a skeletal muscle; divides the skeletal muscle into a series of compartments
-each compartment contains a bundle of muscle called fascicle
-contains collagen , elastic fiber, blood vessels, nerves that supply the muscle fiber w/in the fascicles.
capillary networks
smallest blood vessels
myosatellite cells
stem cells that help repair damaged muscle tissue
Tendon
a collagenous band that connects a skeletal muscle to an element of the skeleton
Aponeurosis/aponeuroses
broad tendinous sheet(s) that may serve as the origin or insertion of a skeletal muscle
Describe the 3 connective tissue layers associated w/skeletal muscle tissue.
The epimysium is a dense layer of collagen fibers that surrounds the entire muscle; the perimysium divides the skeletal muscle into a series of compartments, each containing a bundle of muscle fibers called a fascicle; and the endomysium surrounds individual skeletal muscle cells (muscle fibers). The collagen fibers of the epimysium, perimysium, and endomysium come together to form either bundles known as tendons, or broad sheets called aponeuroses. Tendons and aponeuroses generally attach skeletal muscles to bones.
How would severing the tendon attached to a muscle affect the muscle's ability to move a body part?
b/c tendons attach muscles to bones, severing the tendon would disconnect the muscle from the bone, and the muscle could not move a body part
multinucleate
-skeletal muscle fiber
-each contain hundreds of nuclei just internal to the plasma membrane
sarcolemma
plasma membrane of a muscle fiber
sarcoplasma
cytoplasm of a muscle cell
The terminal cisternae that form a triad along with a T tubule are part of what organelle?
the terminal cisternae are part of the sarcoplasmic reticulum
transverse tubules (T tubules)
...
sarcoplasmic reticulum
membrane complex
triad
combination of a pair of terminal cristernae plus a T tubule
-tightly bound togetherr
-fluid contents are separate and distinct
myofibril
organized collections of myofilaments in skeletal and cardiac muscle cells
-1-2 micrometer diameter
-as long as the entire muscle fiber
-the active shortening of myofibrils is responsible for a skeletal muscle fiber contration
-also contain titin
-scattered among is mitochondria and granules of glycogen (storage) --> provide energy for short-duration, max intesisty muscular contractions
Myofilaments
fine protein filaments composed primarily of the proteins actin (thin filaments) and myosin (thick filaments)
sarcomeres
the smallest contractile unit of a striated muscle cell
A band
-dark band
-overlap of thick and thin
-3 subdivision (The M line, The H band, The zone of overlap)
I band
-light bands
- thin filaments
Sarcomeres contain
1. thin filaments
2. thick filaments
3. proteins that stabilize the positions of the thick and thin filaments
4. proteins that regulate the interactions between thick and thin filaments
thin filament
-a cytoskeletal filament in a skeletal or cardiac muscle cell; consists of F-actin, troponin, nebulin, tropomyosin
5-6 nm in diameter and 1 um long
tropomyosin
fibrous muscle protein that covers active sites on G actin and prevents actin-myosin interactions
troponin
globular muscle protein that binds to tropomyosin
troponin-tropomyosin
-contraction can occur only when this complex changes position
-takes place when calcium ions bind to their receptors on the troponin molecules
Thick filaments
a cytoskeletal filament in a skeletal or cardiac muscle cell; composed of 300 myosin, with a core of titin
-10-12 m diameter
-1.6 um long
myosin
the protein component of thick filaments
titin
molecular spring
elastic properties
recoil after stretching
tense with external force stretches the sarcomere
The Sliding-Filament Theory of Muscle Contraction
the concept that a sarcomere shortens as the thick and thin filaments slide past one another
(1) the H bands and I bands of the sarcomeres narrow,
(2) the zones of overlap widen,
(3) the Z lines move closer together, and
(4) the width of the A band remains constant.
Where would expect to find the greatest concentration of Ca2+ in a resting skeletal muscle fiber?
you would expect the greatest concentration of calcium ions in a resting skeletal muscle fiber to be in the terminal cisternae of the sarcoplasmic reticulum
action potential OR electrical impulse
a propagated change in the membrane potential of excitable cells, initiated by a change in the membrane permeability to sodium ions
-produced by the depolarization and repolarization in neurons and skeletal muscle fibers
neuromuscular junction (NMJ)
a synapse between a neuron and a muscle cell
-made up of an axon terminal (synaptic terminal) of a neuron, a specialized region of the sarcolemma called the motor end plate, and, in between, a narrow space called the synaptic cleft.
Excitation-contraction coupling
The link between the generation of an action potential in the sarcolemma and the start of a muscle contraction
-coupling occurs at the triad
cross-bridges
the binding of a myosin head that projects from the surface of a thick filament at the active site of a thin filament in the presence of calcium ions
Describe the neuromuscular junction
The neuromuscular junction, is the synapse between a motor neuron and a skeletal muscle cell (fiber). This connection enables communication between the nervous system and a skeletal muscle fiber.
How would a drug that blocks acetylcholine release affect muscle contraction?
Acetylcholine (ACh) release from the axon terminal is necessary for skeletal muscle contraction, because it serves as the first step in the process that leads to the formation of cross-bridges in the sarcomeres. A muscle's ability to contract depends on the formation of cross-bridges between the myosin heads and actin myofilaments. A drug that blocks ACh release would interfere with this cross-bridge formation and prevent muscle contraction.
What would happen to a resting skeletal muscle if the sarcolemma suddenly became very permeable to calcium ions?
If the sarcolemma of a resting skeletal muscle suddenly became permeable to Ca2+, the cytosolic concentration of Ca2+ would increase, and the muscle would contract. Also, because the amount of calcium ions in the cytosol must decrease for the relaxation to occur, the increased permeability of the sarcolemma to Ca2+ might prevent the muscle from relaxing completely
Predict what would happen to a muscle if the motor end plate lacked acetylcholinesterase (AChE).
Without acetylcholinesterase (AChE), the motor end plate would be stimulated continuously by acetylcholine, locking the muscle in a state of contraction.
What happens to sarcomere length if the zone of overlap is decreased?
If the zone of overlap is decreased, the sarcomere length is increased.
Twitch
a single stimulus-contraction-relaxation cycle in a skeletal muscle fiber
-type of muscle
-location
-internal/external environmental conditions
-etc.
latent period
the time between the stimulation of a muscle and the start of the contraction (2msec)
contraction phase
tension increases to a peak
-calcium ions are binding to troponin
-active sites on thin filaments are being exposed
-cross-bridge interactions are occurring
-ends after 15 msec after stimulation
relaxation phase
-25 msec
-the period after a contraction when the tension in the muscle fiber returns to resting levels
-Ca2+ levels decrease as ca2+ are pumped back into SR
-active sites are being covered by tropomyosin
-# of active cross-bridges is declining as they detach
treppe
-staircase in german
-pushing a swing
-gradual increase in the concentration of Ca2+ in the cytosol, in part because the calcium ion pumps in the SR have too little time to recapture the ions between stimulations.
-phenomenon in cardiac muscle
wave summation
the addition of one twitch to another
incomplete tetanus
muscle producing almost maximum tension during rapid cycles of contraction and relaxation
complete tension
higher stimulation frequency eliminates the relaxation phase
Why does a muscle that has been overstretched produce minimal tension?
A muscle's ability to contract depends on the formation of cross-bridges between the myosin and actin myofilaments in the muscle. In a muscle that is overstretched, the myofilaments would overlap very little, so very few cross-bridges between myosin and actin could form and, thus, the contraction would be weak. If the myofilaments did not overlap at all, then no cross-bridges would form and the muscle could not contract.
motor unit
all the muscle cells controlled by a single motor neuron
-size of a motor unit indicated how fine or precise a movement can be
fasciculation
"muscle twitch" under the skin; involves more than one muscle fiber; synchronous contraction of a motor unit
recruitment
The smooth but steady increase in muscular tension produced by increasing the number of active motor units
muscle tone
Normal state of balanced muscle tension
-some motor units are always active, even when the entire muscle is not contracting. Their contractions do not produce enough tension to cause movement, but they do tense and firm the muscle.
-helps prevent sudden, uncontrolled changes in the positions of bones and joints
-maintain body position
-act as shock absorber; bumps or shocks
-Strong muscle tone also makes skeletal muscles appear firm and well defined, even at rest.
Can a skeletal muscle contract without shortening? Explain.
Yes, a skeletal muscle can contract without shortening. The muscle can shorten (isotonic concentric contraction), elongate (isotonic eccentric contraction), or remain the same length (isometric contraction), depending on the relationship between the load (resistance) and the tension produced by actin-myosin interactions.
Normal muscle function requires
1. substantial intracellular energy reserves
2. a normal circulatory supply
3. a normal blood oxygen level
4. a blood pH within normal limits
ATP is generated by
-direct phosphorylation of ADP by creatine phosphate (CP)
-anaerobic metabolism (glycolysis)
-aerobic metabolism (citric acid cycle and electron transport chain)
Creatine
a nitrogenous compound, synthesized in the body, that can form a high-energy bond by connecting to a phosphate group and that serves as an energy reserve.
-a small molecule that muscle cells assemble from fragments of amino acids
creatine phosphate
a high-energy compound in muscle cells; during muscle activity, the phosphate group is donated to ADP, regenerating ATP; also called phosphoylcreatine
Creatine Kinase (CK)
When muscle cells are damaged, CK leaks across the plasma membranes and into the bloodstream. For this reason, a high blood concentration of CK usually indicates serious muscle damage.
glycolysis
anaerobic breakdown of glucose to pyruvate in the cytosol of a cell
net 2 ATP; 2 pyruvate molecules
aerobic metabolism
-provides 95% of the ATP demands of a resting cell
-mitochondria absorb oxygen, ADP, phosphate ions, and organic substrates (such as pyruvate) from the surrounding cytoplasm
-krebs cycle/citric acid cycle; breaks down organic molecules
-15 ATP molecules
oxygen debt
-oxygen demand of the body's cells remains elevated above the normal resting level
-the amount of oxygen required after physical exercise to convert accumulated lactic acid to glucose
-the amount of oxygen required to restore normal, preexertion conditions in muscle tissue.
How do muscle fibers continuously synthesize ATP?
Muscle fibers synthesize ATP continuously by utilizing creatine phosphate (CP) and metabolizing glycogen and fatty acids. Most cells generate ATP only through aerobic metabolism in the mitochondria and through glycolysis in the cytosol.
Types of Skeletal Muscle Fibers
-fast fibers
-slow fibers
-intermediate fibers
Fast Fibers (white muscles)
-most of the skeletal muscle fibers in the body
-large in diameter
-peak tension in 0.01 sec or less after stimulation
-contain densely packed myofibrils
-large glycogen reserves
-relatively few mitochondria to generate ATP
-fatigue rapidly
-use ATP in massive amounts
-pale color
-CHO
-fast-twitch glycolytic fibers, Type II-B fibers,
Slow Fibers (red muscles)
-half the diameter of fast fibers
-3x as long to peak tension
-surrounded by a more extensive network of capillaries
-contain the red pigment myoglobin
-dark color pigment
-less dependent on anaerobic metabolism
-Lipids CHO Proteins
-slowtwitch oxidative fibers, Type I fibers
myoglobin
an oxygen-binding pigment that is especially common in slow skeletal muscle fibers and cardiac muscle cells
Intermediate Fibers
-more closely resemble fast fibers,
-contain little myoglobin
-relatively pale; pink
-more capillaries and more fatigue resistant than fast fibers
-CHO
-fast-twitch oxidative fibers, Type II-A fibers, fast resistant fibers
Hypertrophy
an increase in tissue size without cell division
-enlargement of the stimulated muscle
-#of muscle fibers does not change sig. but the muscle as a whole enlarges bc each muscle fiber increases in diameter
-e.g.: body builder
atrophy
the wasting away of tissue from a lack of use, ischemia, or nutritional abnormalities
-soft, smaller, weaker,
-reduction in muscle size, tone, and power
-Muscle atrophy is reversible at first, but dying muscle fibers are not replaced.
As we age
-Skeletal Muscle Fibers Become Smaller in Diameter
-Skeletal Muscles Become Less Elastic
-Tolerance for Exercise Decreases
-The Ability to Recover from Muscular Injuries Decreases
Fibrosis
-the thickening and scarring of connective tissue, usually as a result of injury.
-increasing amounts of fibrous connective tissue
-collagen
muscle fatigue has been correlated with
(1) depletion of metabolic reserves within the muscle fibers; (2) damage to the sarcolemma and sarcoplasmic reticulum; (3) a decline in pH within the muscle fibers and the muscle as a whole, which decreases calcium ion binding to troponin and alters enzyme activities; and
(4) a sense of weariness and a reduction in the desire to continue the activity, due to the effects of low blood pH and sensations of pain.
Describe muscle fatigue.
Muscle fatigue is a muscle's reduced ability to contract due to low pH (hydrogen ion buildup), low ATP levels, or other problems.
Anaerobic endurance
the length of time muscle contractions can continue to be supported by the existing energy reserves of ATP and CP and by glycolysis
-limited by: (1) the amount of ATP and CP available, (2) the amount of glycogen available for breakdown, and (3) the ability of the muscle to tolerate lactate and the buildup of hydrogen ions generated during the period of anaerobic metabolism
-fast fibers
-muscle hypertrophy
Aerobic endurance
length of time a muscle can continue to contract while supported by mitochondrial activities.
-longer periods of time
-breaking down CHO, lipids, protein
Which activity would be more likely to create an oxygen debt: swimming laps or lifting weights?
Activities that require short periods of strenuous activity produce a greater oxygen debt, because such activities rely heavily on energy production by anaerobic metabolism. Because lifting weights is more strenuous over the short term than swimming laps, which is an aerobic activity, weight lifting would likely produce a greater oxygen debt than would swimming laps.
Which type of muscle fibers would you expect to predominate in the leg muscles of someone who excels at endurance activities, such as cycling or long-distance running?
People who excel at endurance activities have a higher than normal percentage of slow fibers. Slow fibers are physiologically better adapted to this type of activity than are fast fibers, which are less vascular and fatigue faster.
Cardiac muscle cell
contain organized myofibrils, and the presence of many aligned sarcomeres gives the cells a striated appearance.
-muscle cell small
-generally single centrally nucleus
-cells typically branched
-no triad
-t tubules are short and broad
-SR lack terminal cisternae
-stores fewer calcium
-aerobic metabolism
-glycogen and lipid
-lg # of mitochondria, reserves of myoglobin
-intercalated
intercalated discs
regions where adjacent cardiac muscle cells interlock and where gap junctions permit electrical coupling between the cells
-allows ions to move form one cell to another so that cardiac muscle cells beat in rhythm
automaticity
The spontaneous depolarization to threshold, characteristic of cardiac pacemaker cells.
pacemaker cells
cells of the sinoatrial node that set the pace of cardiac contraction
Compare and contrast skeletal muscle tissue and cardiac muscle tissue.
Compared to skeletal muscle tissue, cardiac muscle tissue (1) has relatively small cells; (2) has cells with a centrally located nucleus (some may contain two or more nuclei); (3) has T tubules that are short and broad and do not form triads; (4) has an SR that lacks terminal cisternae and has tubules that contact the plasma membrane as well as the T tubules; (5) has cells that are nearly totally dependent on aerobic metabolism as an energy source; and (6) contains intercalated discs that assist in stabilizing tissue structure and spreading action potentials.
What feature of cardiac muscle tissue allows the heart to act as a functional syncytium?
Cardiac muscle cells are joined by gap junctions, which allow ions and small molecules to flow directly between cells. As a result, action potentials generated in one cell spread rapidly to adjacent cells. Thus, all the cells contract simultaneously, as if they were a single unit (a syncytium).
Smooth muscle tissue
muscle tissue in the walls of many visceral organs; characterized as nonstriated, involuntary muscle
-contain actin and myosin as well
smooth muscle cell
-long and slender
-spindle shaped
-single nucleus
-no t tubules
-SR forms a loose network through the sarcoplasm
-lack myofibrils and sarcomeres --> nonstriated
-thick filaments are scattered throughout the sarcoplasm
-more myosin heads
-dense bodies; desmin
-twist like a corkscrew
-collagen fibers never unite to form tendons or aponeuroses
Smooth muscle tissue differ from other muscle tissue
(1) excitation-contraction coupling
(2) length-tension relationships
(3) control of contractions
(4) smooth muscle tone.
Excitation-Contraction Coupling (smooth)
trigger for smooth muscle contraction is the appearance of free calcium ions in the cytoplasm.
-calcium ions interact with calmodulin (a calcium-binding proteins)
- Calmodulin then activates the enzyme myosin light chain kinase, which in turn enables myosin heads to attach to actin.
Length-Tension Relationships (smooth)
- tension development and resting length are not directly related.
-plasticity (digestive organs)
Control of Contractions (smooth)
-categorize smooth muscle cells as either multiunit or visceral
Multiunit smooth muscle cells
a smooth muscle tissue whose muscle cells are innervated in motor units
-contract more slowly
-have more excitable plasma membrane
-iris of the eye
-do not typically occur in digestive tract
Visceral smooth muscle
a smooth muscle tissue that forms sheets or layers in the walls of visceral organs; the cells may not be innervated, and the layers often show automaticity (rhythmic contractions)
-connected y gap-junctions
-lack a direct contact with any motor neuron
-spreads in a wave that soon involves every smooth muscle cell in the layer.
-rhythmic cycles of activity in the absence of neural stimulation.
-wall of the digestive tract, gallbladder, urinary bladder, internal organs
-pacesetter cells
smooth muscle tone
-Both multiunit and visceral smooth muscle tissues have a normal background level of activity, or smooth muscle tone.
-Neural, hormonal, or chemical factors can also stimulate smooth muscle relaxation, producing a decrease in muscle tone
-tissue becomes starved for oxygen, the smooth muscle cells relax, allowing blood flow to increase and, hence, delivering additional oxygen
Identify the structural characteristics of smooth muscle tissue.
Smooth muscle cells lack sarcomeres, and thus smooth muscle tissue is nonstriated. Additionally, the thin filaments are anchored to dense bodies.
which type of muscle tissue is least affected by changes in ectracellular Ca2+ concentration during contraction?
Skeletal muscle contractions are least affected by changes in extracellular Ca2+ concentrations. In skeletal muscle, most of the Ca2+ come from the SR. Most of the Ca2+ that trigger a contraction in cardiac and smooth muscles come from the extracellular fluid.
Why can smooth muscle contract over a wider range of resting lengths than skeletal muscle can?
The looser organization of actin and myosin filaments in smooth muscle allows smooth muscle to contract over a wider range of resting lengths than skeletal muscle.
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