Chapter 10 Review
List six major functions of skeletal muscle.
1. Producing movement 2. Maintain posture and body position 3. Supporting soft tissue 4. Guarding body entrances and exits 5. Maintaining body temperature 6. Storing nutrients
List four factors that are required for normal muscle function.
1. Substantial intercellular energy reserves 2. A normal circulatory supply 3. Normal blood oxygen level 4. A blood pH within normal limits
What are three factors that determine how long a muscle contraction lasts?
1. The period of stimulation at neuromuscular junction 2. The presence of free calcium ions in the cytosol 3. Availability of ATP
ATP and creatine phosphate reserves are depleted in a contracting muscle in ~ __ seconds.
15
What is the function on tendons and aponeuroses?
Attach skeletal muscles to bones. Where they contact the bone, the collagen fibers extend into the bone matrix, providing a firm attachment. As a result, any contraction of the muscle pulls on the attached bone
What three structures make up the neuromuscular junction?
Axon terminal, motor end plate and synaptic cleft
List three factors that promote muscle relaxation and its return to normal resting length.
Elastic forces, opposing muscle contractions, and gravity
Which type of muscle fiber fatigues the quickest due to relatively few mitochondria?
Fast Fibers
In general, smooth muscle function is to...
Form. Sheets, bundles, or sheaths around other tissues in almost every single organ
Muscle tissue shares these common properties: excitability, contractility, extensibility, and elasticity. Describe what each property means.
- Excitability, also known as responsiveness or irritability, is the ability to receive and respond to a stimulus. - Contractility refers to the ability of a muscle cell to shorten when it is stimulated. - Extensibility is stretching movement of a muscle. - Elasticity is the ability of a muscle to recoil (spring back) to its resting length
List two mechanisms that are used to quickly return calcium levels in a muscle fiber to normal.
1. Active calcium transport into SR and 2. Active calcium transport across the sarcolemma into the extracellular fluid
The endomysium is a flexible, elastic connective tissue layer that contains three structures that are in direct contact with the individual muscle fibers. Name them and state their function.
1. Capillary networks- supply blood to the muscle fibers 2. Myosatellite cells- stem cells that help repair damaged muscle tissue 3. Nerve fibers that control the muscle NOTE: later in this chapter you will discover the importance of nerve fibers being in direct contact with muscle fibers
What size motor units are located in areas of the body which require precise movements?
4-6 muscle fibers
What is a fascicle, and what connective tissue layer surrounds it?
A bundle of fibers located within compartments the perimysium
When the power stroke occurs, the bound _____ and _______ group on the myosin head are released.
ADP, phosphate
At the beginning of the contraction cycle, the breakdown products of ATP called ___ and _________ remain bound to the myosin head.
ADP, phosphate (P)
State the difference between anaerobic and aerobic endurance.
Anaerobic endurance is the length of time muscular contraction can continue to be supported by the existing energy reserves of ATP and CP and by glycolysis. Aerobic endurance is the length of time a muscle can continue to contract while supported by mitochondrial activies
Why are skeletal muscle cells multinucleated?
As a result of the fusion of the many myoblasts that fuse to form each long muscle fiber
List difference when comparing skeletal muscle and cardiac muscle. Focus on size, number of nuclei, branching, intercalated discs.
Cardiac muscles cells are relatively small, has a single nucleus, branched, T tubules are short and broad and have no triads, encircle the sarcomeres at Z line, SR lacks terminal cisternae and stores fewer calcium ions, mostly dependent on aerobic metabolism and have intercalated discs
ACh binds to an ACh membrane channel receptor on the motor end plate of the muscle fiber. Due to this, what type of membrane channel opens?
Chemically gated Na+
What are two ways that ACh is removed from the synaptic cleft?
Diffusion and broken down by AChE into acetic acid and choline
What is muscle fiber?
Enormous compared to other cells, contain hundreds of nuclei, develop by fusion of embryonic cells (myoblasts) and known as striated muscle cells
Which transport mechanism is used to transfer acetylcholine out of the axon terminal?
Exocytosis
Thin filaments (actin) contain which four proteins?
F-actin, nebulin, tropomyosin and troponin
________ is the anaerobic breakdown of glucose to pyruvate in the cytosol of a cell and it provides a net gain of 2 ATP molecules and generates 2 pyruvate molecules from each glucose molecule.
Glycolysis NOTE: glyco- means sugar (glucose) and -lysis means to break apart. Therefore, glycolysis is the breakdown of glucose
What is the difference between muscle hypertrophy and muscle atrophy?
Hypertrophy is an enlargement of the stimulated muscle and atrophy is reduction in muscle size, tone and power
Know the difference between the composition and thickness of A bands and I bands.
I ban is thin, and light and A bands are dark NOTE: The Tips & Tools section that explains how to remember the difference between A and I bands is good. It reads: You can remember that actin occurs in thin filaments by associating the "tin" in actin with the word thin. Then remember that thIn filaments look lIght and form the I band. Similarly, the A bands are dark.
What is the difference between incomplete and complete tetanus?
Incomplete tetanus is a muscle producing almost maximum tension during rapid cycles of contraction and relaxation. Complete tetanus is when higher stimulation frequency eliminates the relaxation phase
List several organs that use the contractions of smooth muscle.
Integumentary system, cardiovascular system, respiratory system, digestive system, urinary system, and reproductive system
Scattered among the skeletal muscle myofibrils are mitochondria and granules of glycogen. What is the function for these?
Mitochondrial activity and glucose breakdown by glycolysis provide energy in the form of ATP for short-duration, maximum-intensity muscular contractions
The neurotransmitter __________ is released by the motor neuron's axon terminal into the synaptic cleft.
acetylcholine (ACh)
The enzyme ___________ breaks down ACh.
acetylcholinesterase (AChE)
Electrical impulses generated by the sarcolemma travel along the T tubules into the cell interior. These impulses, called _______________, trigger muscle fiber contraction.
action potential
Differences in the size, density, and distribution of thick filaments and thin filaments account for the _________ appearance of each myofibril.
banded
A contraction can occur only when the troponin-tropomyosin complex changes position, exposing the active sites on actin. The change in position takes place when _______ ions bind to their receptors on the troponin molecules.
calcium
A muscle contraction ends when the sarcoplasmic reticulum reabsorbs _______ ions from the cytosol of the muscle fiber.
calcium
Once in the smooth muscle sarcoplasm, the calcium ions interact with __________, a calcium-binding protein.
calmodulin
A push applied to an object called ____________ tends to force the object away from the source of the compression.
compression
In an isotonic _________ contraction, the muscle tension exceeds the load and the muscle shortens.
concentric
The sliding of actin and myosin fibers in a sarcomere allows a muscle fiber to _________.
contract.
When ATP is needed during muscle contraction, energy stored in creatine phosphate regenerates ADP to ATP using an enzyme called ____________.
creatine kinase [ADP + creatine phosphate ATP + creatine] (Remember, kinases are enzymes that phosphorylate molecules. Phosphorylates means the addition of a phosphate group)
In an isotonic _______ contraction, the peak tension developed is less than the load, and the muscle elongates due to the contraction of another muscle or the pull of gravity.
eccentric
The link between the generation of an action potential in the sarcolemma and the start of a muscle contraction is called _______________ which occurs at the triads.
excitation-contraction coupling
Axons of nerve cells are called nerve _________.
fibers.
The threshold potential for a muscle fiber is _____________________________.
from -70 to -60 mV for neurons and -85 to -55 mV for skeletal.
During muscle contraction, myofibrils get shorter, which then makes the muscle fiber ______________.
get shorter.
The glucose broken down during glycolysis comes primarily from reserves in the sarcoplasm.
glycogen
Cardiac muscle cells are found only in the ________.
heart
At a(n) ________ disc, the sarcolemmas of two adjacent cardiac muscle cells are extensively intertwined and bound together by gap junctions and desmosomes which allow ions to move from one cell to another so that the cells beat in rhythm.
intercalated
The load and the speed of contraction are ________ related.
inversely (ie: the heavier the load, the slower the contraction)
In a(n) _______ contraction, the muscle as a whole does not change length, and the tension produced never exceeds the load.
isometric
Each muscle fiber contains hundreds to thousands of cylindrical structures called ___________.
myofibrils.
The amount of oxygen required to restore muscle to normal, pre-exertion conditions is called __________.
oxygen debt.
Specialized cardiac muscle cells called _______ cells normally determine the timing of contractions.
pacemaker
This ability of smooth muscle to function over a wide range of lengths is called ___________.
plasticity
During the _______ period, the conditions in muscle fibers are returned to a normal, pre-exertion level.
recovery
An object's load (or __________) is a passive force that opposes movement. Before a movement can occur, the applied tension must overcome this passive force.
resistance
The plasma membrane of a muscle fiber is called the _______________.
sarcolemma.
The length-tension relationship relates the tension produced by the entire muscle fiber to the length of individual _________. Skeletal muscle fibers contract more forcefully when stimulated within the range of their optimal resting lengths.
sarcomeres
The cytoplasm of a muscle fiber is called ___________.
sarcoplasm.
The smallest functional unit of a muscle fiber is called a ___________.
sarcoplasm.
A muscle contraction begins when the _______________ releases stored calcium ions into the cytosol of the muscle fiber.
sarcoplasmic reticulum
In skeletal muscle fibers, a membrane complex called the _______________ forms a tubular network around each myofibril.
sarcoplasmic reticulum (SR)
The explanation of muscle contraction is known as the __________ theory.
sliding-filament
Thick filaments (myosin) consist of 300 myosin molecules, each having a long _____, and a globular ______.
tail, head
At each end of the muscle, the collagen fibers of the epimysium, perimysium, and endomysium come together to form either a bundle known as a ________, or a broad sheet called an _____________.
tendon,aponeurosis
Once that stimulus is removed from the muscle fiber, calcium channels in the SR close and calcium ion pumps pull calcium from the cytosol and store it within the____________.
terminal cisternae NOTE: Review Figure 10-13 Steps Involved in Skeletal Muscle Contraction and Relaxation. This is a great synopsis of what occurs during this series of events.
Excitable membranes seen in neuron and muscle fibers contain __________ ion channels that are activated and inactivated by changes in the membrane potential.
voltage-gated
If a second stimulus arrives before the relaxation phase has ended, a second, more powerful contraction occurs. The addition of one twitch to another in this way is called _________.
wave summation
Muscles dominated by fast fibers appear pale and are often called _____ muscles.
white
List four components of a skeletal muscle organ?
Skeletal muscle tissue, connective tissues, blood vessels and nerves NOTE: skeletal muscle tissue is different than skeletal muscle. Skeletal muscle as a whole is an organ. Remember, organs are composed of two or more tissues
Action potential propagated down a muscle fiber triggers the release of Ca2+ from the _________ of the sarcoplasmic reticulum.
T tubules
The electrical signal for muscle contraction is distributed quickly throughout the interior of the cell by structures called ___________.
T tubules.
Skeletal muscle is also called striated muscle. What two proteins give skeletal muscle it striated appearance?
Actin (thin) and myosin (thick)
What are three major differences between muscle fibers and a "typical" cell described in Chapter 3?
1. Difference of size- skeletal muscle fibers are enormous 2. Multinucleate 3. striated
List four effects of aging on the muscular system.
1. Skeletal muscle fibers become smaller in diameter 2. Skeletal muscles become less elastic 3. Tolerance for exercise decreases 4. The ability to recover from muscular injuries decreases
Aerobic metabolism normally provides __ percent of the ATP demands of a resting cell.
95
Myofibrils consist of bundles of protein filaments called myofilaments. What major protein makes up individual thin filaments and individual thick myofilament?
Actin and Myosin
Which type of muscle fiber contains numerous mitochondria and myoglobin?
Slow Fibers
List several differences when comparing smooth muscle to skeletal muscle. Focus on spindle shape, nuclei, presence of T tubules, striations.
Spindle shaped, long and slender, has no T tubules, nonstriated, single centrally located nucleus
What happens to allow cross-bridge detachment to occur?
Tropomyosin pushes the myosin head away. The displacement of tropomyosin exposes the active sites of actin, allowing cross bridges to form
A muscle ___________ is a single stimulation which produces a single contraction
Twitch
What ion is stored and released by the sarcoplasmic reticulum?
calcium
In skeletal and cardiac muscles, the trigger for contraction is the binding of calcium ions to troponin. In contrast, the trigger for smooth muscle contraction is the appearance of free in the __________ cytoplasm.
calcium ions
During strenuous exercise, oxygen cannot enter the cells fast enough to support aerobic metabolism, the pyruvate from glycolysis is converted into _______.
lactate.
Myosin _________ occurs when the free myosin head splits ATP into ADP and P. The energy released is used to recock the myosin head.
reactivation
The smooth but steady increase in muscular tension produced by increasing the number of active motor units is called __________.
recruitment.
On either side of a T tubule, the tubules of the sarcoplasmic reticulum enlarge, fuse, and form expanded chambers called ______________.
terminal cisternae.
If the stimulation continues and the muscle fiber is never allowed to relax completely, tension will increase until it reaches its maximum potential tension. This is called ________.
tetanus.
If a skeletal muscle fiber is stimulated a second time immediately after the relaxation phase of a twitch has ended, the resulting contraction will develop a slightly higher maximum tension than did the first contraction. This will occur for 30-50 stimulations. This phenomenon is called ______.
treppe.
Strands of _________ cover the active sites on G-actin and prevent actin-myosin interaction.
tropomyosin
Calcium ion binding to troponin changes its shape causing it to change its position which rolls the attached __________ strand away from the active sites on G-actin.
tropomyosin NOTE: Make sure that you review Spotlight Figure 10-11 Excitation-Contraction Coupling for a synopsis of what occurs during this event
The typical resting membrane potential for skeletal muscle fibers is _______.
-85mV NOTE: remember that there are more sodium ions outside of the cell than inside of the cell, and more potassium inside the cell that outside the cell. The negative membrane potential (-85mV) is caused by negatively charged protein molecules inside of the cell. NOTE: remember that an influx of sodium ions into the cell leads to depolarization as the membrane potential becomes less negative. It becomes less negative because sodium ions are positively charged (cations). The movement of potassium ions out of a cell leads to hyperpolarization as the membrane potential becomes more negative. A return to the resting potential is called repolarization.
Muscle tissue in a skeletal muscle is surrounded by three layers of connective tissue (CT): (1) an epimysium, (2) a perimysium, and (3) an endomysium. Where are each located?
1. The epimysium surrounds muscle, connected to deep fascia, separates muscle from surrounding tissues 2. The perimysium surrounds muscle fiber bundles and contains collagen (compartments), elastic, blood vessels and nerves 3. The endomysium surrounds individual muscle cells and contain capillary networks, myosatellite cells (stem cells) that repair damage and nerve fibers NOTE: notice that these words contain mys-. Any scientific term that has mys- or myo- means pertaining to muscle. In addition, the prefix epi- means on top of, so you can remember epimysium as the outer most CT layer. Finally, the prefix endo- means within, so you can remember endomysium as the inner most CT layer
Cocking the myosin head requires energy. What energy source is used?
Breaking down ATP; in doing so, the myosin head functions as ATPase, an enzyme that breaks down ATP
In skeletal muscle, what is a triad?
Combination of a pair of terminal cisternae plus a T tubule
Strands of the elastic protein titin extend from the tips of the thick filaments to attachment sites at the Z line. What is the function of titan?
Elastic protein, extends from tips of thick filaments to the Z line, keeps filaments in proper alignment and aids in restoring resting sarcomere length
Define force and endurance.
Force is the maximum amount of tension produced by a particular muscle or muscle group and endurance is the amount of time during which person can perform a particular activity
When muscle cells contract, they pull on the attached tendon fibers similarly to how a line of people might pull on a rope. The pull, called _________, is an active force: Energy must be expended to produce it.
Tension
__________ applied to an object tends to pull the object toward the source of the tension.
Tension
Depolarization and repolarization events of a muscle fiber's plasma membrane produce an electrical impulse called a(n) ____________ that is propagated along their plasma membranes.
action potential
Cardiac muscle tissue contracts without neural stimulation. This property is called __________.
automaticity
ATP transfers energy to creatine to create a high-energy compound called ___________.
creatine phosphate (CP, phosphocreatine) [ATP + creatine ADP + creatine phosphate]
After the active sites on G-actin are exposed, the myosin heads bind to them forming __________.
cross-bridges.
In a(n) ______ contraction, tension increases and the skeletal muscle's length changes.
isotonic
Skeletal muscle fibers cannot begin contraction until they receive instructions in the form of action potentials from ________ neurons in the nervous system.
motor
Some motor neurons control a few muscle fibers, but most control hundreds or thousands of them through multiple axon terminals. A _________ consists of a motor neuron and all the muscle fibers that it controls.
motor unit
This resting tension in a skeletal muscle is called ________.
muscle tone
During development, groups of embryonic cells called __________ fuse, forming individual multinucleated skeletal muscle fibers.
myoblasts
Branches of the T tubules and the sarcoplasmic reticulum encircle structures called ________.
myofibril Remember, one muscle fiber contains hundred of myofibrils each of which are encircled by T tubules and the sarcoplasmic reticulum. The myofibril is encircled, NOT the muscle fiber
Non-fused myoblast cells remain in adult skeletal muscle and are called _________ cells.
myosatellite
One of the structures in the endomysium are stem cells called _________ cells that function in repair of damaged muscle tissue.
myosatellite
Calmodulin activates the enzyme ____________, which in turn enables myosin heads to attach to actin.
myosin light chain kinase
The synapse between a motor neuron and the muscle fiber is called the ___________ junction.
neuromuscular
The motor neuron's axon terminal releases a chemical signal called a(n) ______________ into the synaptic cleft.
neurotransmitter
Many smooth muscle cells are not innervated by motor neurons, and the neurons that do innervate smooth muscles are ___ under ______ control.
not, voluntary
During depolarization, the inside of the plasma membrane reverses from a negative to a positive charge peaking at a membrane potential of +30 mV. Voltage-gated sodium ion channels close and repolarization of the membrane then begins as voltage-gated _________ ion channels open and positively charged ________ ions leave the cell.
potassium, potassium
When the myosin head pivots, using the energy released from the hydrolysis of ATP, the head swings toward the M line in a movement known as the ____________.
power stroke.
In a skeletal muscle fiber, the amount of tension generated during a contraction depends on the number of __________ performed by cross-bridges in each of the myofibrils.
power strokes
Once the muscle fiber plasma membrane reaches the threshold potential, voltage-gated ______ ion channels open and there is a rapid influx of positively charged ______ ions into the cell.
sodium, sodium
During the refractory period, the initial concentrations of sodium and potassium are restored in the cell by using the _______________ pump.
sodium-potassium ion
Each _________ molecule also has a binding site for calcium ions, and this site is empty when the muscle fiber is at rest.
troponin