Chapter 11 - Muscular Physiology Flashcards
3 general functions of muscles
- Movement of the body as a whole or movement of its parts
- Heat production
- Posture
3 Characteristics of skeletal muscle cells
- Excitability (irritability)
- Contractility and produce body movement
- Extensibility
Characteristics of skeletal muscle cells: ability to be stimulated
Excitability (irritability)
Characteristics of skeletal muscle cells ability to contract, or shorten, and produce body movement
Contractility
Characteristics of skeletal muscle cells: ability to contract, or shorten, and produce body movement
Contractility
Muscle cells are called ___________ because of their threadlike ____________
fibers, shape
plasma membrane of muscle fibers
Sarcolemma:
Membrane of the ____________ ____________ continually pumps calcium ions from the sarcoplasm and stores the ions within its sacs for later release
Sarcoplasmic reticulum (SR)
network of tubules and sacs found within muscle fibers
T tubules
True or false
Muscle fibers contain many mitochondria and several nuclei
true
numerous fine fibers packed close together in sarcoplasm
Myofibrils
Segment of myofibril between two successive Z disks
Sarcomere
Each myofibril consists of many _____________
Sarcomeres
Contractile unit of muscle fibers
Sarcomere
Striated muscle has 2 stripes:
- light
2. dark
Light stripes called ____ bands
I
Dark stripes called ____ bands
A
light _____ zone runs across the midsection of each dark A band
H
dark _____ disk extends across the center of each light I band
Z
Transverse tubules extend across the sarcoplasm at right angles to the long axis of the muscle fiber
T tubules
Formed by inward extensions of the sarcolemma
T tubules
Membrane has ion pumps that continually transport calcium ions inward from the sarcoplasm
T tubules
Allow electrical impulses traveling along the sarcolemma to move deeper into the cell
T tubules
Triplet of tubules; a T tubule sandwiched between two sacs of SR
Triad
Allows an electrical impulse traveling along a T tubule to stimulate the membranes of adjacent sacs of the SR
Triad
Each myofibril contains thousands of thick and thin _______________
myofilaments
4 different kinds of protein molecules make up myofilaments
- Myosins
- Actin
- Tropomyosin
- Troponin
the myofilament protein molecule characterized as: Makes up almost all the thick filament
myosin
the myofilament protein molecule characterized as: the heads are chemically attracted to actin molecules
myosin
the myofilament protein molecule characterized as: the “heads” are known as cross bridges when attached to actin
myosin
the myofilament protein molecule characterized as: globular protein that forms two fibrous strands twisted around each other to form the bulk of the thin filament
Actin
the myofilament protein molecule characterized as: protein that blocks the active sites on actin molecules
Tropomyosin
the myofilament protein molecule characterized as: protein that holds tropomyosin molecules in place
Troponin
Thin filaments attach to both Z disks (Z lines) of a ____________ and extend partway toward the center
sarcomere
Thick ___________ filaments do not attach to the Z disks
myosin
3 mechanisms of muscle contraction
- excitation and contraction
- relaxation
- energy sources for muscle contraction
A skeletal muscle fiber remains at rest until mechanism of muscle contraction: stimulated by a motor neuron
excitation and contraction
this mechanism of muscle contraction involves motor neurons connecting to the sarcolemma at the motor endplate
excitation and contraction (neuromuscular junction)
this mechanism of muscle contraction involves a synapse where neurotransmitter molecules transmit signals
excitation and contraction (neuromuscular junction)
in excitation and contraction, this neurotransmitter is released into the synaptic cleft that diffuses across the gap, stimulates the receptors, and initiates an impulse in the sarcolemma
acetylcholine
in excitation and contraction, a nerve impulse travels over the _____________ and inward along the T tubules, which triggers the release of calcium ions (Ca++)
sarcolemma
in excitation and contraction, Ca++ binds to _____________, which causes tropomyosin to shift and expose active sites on actin
troponin
The 4 stages of the sliding filament model
- When active sites on actin are exposed, myosin heads bind to them
- Myosin heads bend and pull the thin filaments past them
- Each head releases, binds to the next active site, and pulls again
- The entire myofibril shortens
this phase of muscle contraction is characterized when the SR begins actively pumping it back into the sacs immediately after Ca++ is released
relaxation
in this phase of muscle contraction, Ca++ is removed from the troponin molecules, thereby shutting down the contraction
relaxation
A nerve impulse reaches the end of a motor neuron and triggers release of the neurotransmitter _______________
acetylcholine (ach)
Ach diffuses rapidly across the gap of the neuromuscular junction and binds to Ach receptors on the motor endplate of the muscle fiber is characteristic of muscle ___________ and ______________
contraction, excitation
in muscle contraction and excitation, Ca++ is released from the SR into the _______________, where it binds to troponin molecules in the thin _________________.
sarcoplasm, myofilaments
in muscle contraction and excitation, ___________ molecules in the thin myofilaments shift and thereby expose actin’s active sites.
Tropomyosin
in muscle contraction and excitation, energized ____________ cross bridges of the thick myofilaments bind to ___________ and use their energy to pull the thin myofilaments toward the center of each sarcomere. The cycle repeats itself many times per second, as long as ___________ _______________ is available.
myosin, actin, adenosine triphosphate
in muscle contraction and excitation, as the filaments slide past the thick ______________, the entire muscle fiber ________________
myofilaments, shortens
in muscle relaxation, once the impulse is over, the ____ begins actively pumping Ca++ back into its sacs
SR
In muscle relaxation, as Ca++ is stripped from troponin molecules in the thin myofilaments _____________ returns to its position and blocks actin’s active sites
tropomyosin
In muscle relaxation, Myosin cross bridges are prevented from binding to actin and thus can no longer sustain the _______________.
contraction
In muscle relaxation, because the thick and thin ______________ are no longer connected, the muscle fiber may return to its longer, _____________ length.
myofilaments, resting
In muscle relaxation, stimulation of _______________ receptors initiates an impulse that travels along the sarcolemma, through the T tubules, to the sacs of the ______________ ______________ (SR)
acetylcholine (ach), sarcoplasmic reticulum
Hydrolysis of _______________ ______________ yields the energy required for muscular contraction
adenosine triphosphate (ATP)
true or false
Muscle fibers can store large amounts of ATP
false
Muscle fibers must continually ____________ ATP since they can store only small amounts.
resynthesize
In muscle fiber only ___-___ seconds of max contraction
2-4
____________ ___________ in muscle can be broken down for energy—20 additional seconds of max muscle contratction
Creatine Phosphate
ATP binds to the ________ head and transfers its energy there to perform the work of pulling the thin ___________ during contraction
myosin, filament
ATP and CP are continually resynthesized—or re-charged –by ___________ _____________.
cellular respiration
Ultimately, energy for both ATP and CP synthesis comes from ________________ of food.
catabolism
Efficient nutrient catabolism by muscle fibers requires __________ and _____________
glucose, oxygen (O2)
Skeletal muscle contraction produces _________ ___________ that can be used to help maintain the set point body temperature
waste heat
At ___________, excess O2 in the sarcoplasm is bound to myoglobin
rest
this type of respiration occurs when adequate O2 is available from blood
Aerobic respiration
True or false
Aerobic respiration is faster than anaerobic respiration; thus supplies energy for the long term rather than the short term
false
this type of respiration is very rapid, providing energy during first minutes of maximal exercise
Anaerobic respiration
this type of respiration is may occur when low levels of O2 are available
Anaerobic respiration
this type of respiration is results in the formation of lactic acid, which requires O2 to convert back to glucose, the producing of an “oxygen debt,” or excess postexercise O2 consumption
Anaerobic respiration
Muscles are composed of bundles of _________ ___________ held together by __________ __________ tissue
muscle fibers
fibrous connective
motor neuron plus the muscle fibers to which it attaches
motor unit
Some motor units consist of only a ________ muscle fibers, whereas others consist of ___________ fibers
few
numerous
true or false
the smaller the number of fibers in a motor unit, the less precise the movements available
false
true or false
the larger the number of fibers in a motor unit, the more powerful the contraction available
true
method of graphing the changing tension of a muscle as it contracts
myography
Twitch contraction has 3 phase
- Latent phase
- Contraction phase
- Relaxation phase
This is known as a quick jerk of a muscle produced as a result of a single, brief threshold stimulus (generally occurs only in experimental situations)
Twitch contraction
the staircase phenomenon
Treppe
Gradual, steplike increase in the strength of contraction that is seen in a series of twitch contractions that occur 1 second apart
Treppe
The muscle eventually responds with less-forceful contractions, and the relaxation phase becomes shorter is characteristic of this type of contraction
If the relaxation phase disappears completely, a contracture occurs
Treppe
smooth, sustained contractions
Tetanus
Multiple wave summation: multiple twitch waves added together to sustain muscle tension for a longer time is characteristic of this type of contraction
tetanus
very short periods of relaxation between peaks of tension
Incomplete tetanus
twitch waves fuse into a single, sustained peak
Complete tetanus
Why is calcium important to tetanus contractions?
The availability of Ca++ determines whether a muscle will contract; if Ca++ is continuously available, then contraction will be sustained
Muscle tone is described as continual, partial contraction of a muscle, and is also known as this
Tonic contraction
this is achieved because at any one time, a small number of muscle fibers within a muscle contract and produce a tightness
muscle tone
Muscles with less tone than normal are
flaccid
Muscles with more tone than normal are
spastic
True or false
Muscle tone is maintained by negative feedback mechanisms
true
True or false
Skeletal muscles contract with the same degree of strength at different times
false
4 factors that contribute to the phenomenon of graded strength
- Metabolic condition of individual fibers
- Number of muscle fibers contracting simultaneously; the greater the number of fibers contracting, the stronger the contraction
- Number of motor units recruited
- Intensity and frequency of stimulation
what is length-tension relation
the maximal strength that a muscle can develop, is directly related to the initial length of its fibers
A shortened muscle’s sarcomeres are compressed, so the muscle cannot develop much tension
Length-tension relation
An overstretched muscle cannot develop much tension because the thick myofilaments are too far from the thin myofilaments
Length-tension relation
Strongest maximal contraction is possible only when the skeletal muscle has been stretched to its optimal length
Length-tension relation
The load imposed on a muscle influences the strength of a skeletal contraction
Stretch reflex
The body tries to maintain constancy of muscle length in response to increased load
Stretch reflex
Maintains a relatively constant length as load is increased up to a maximal sustainable level
Stretch reflex
2 types of graded strength contractions
- isometric
2. isotonic
Contraction in which the tone or tension within a muscle remains the same while the length of the muscle changes
Isotonic contraction
the type of isotonic contraction characterized as “muscle shortens as it contracts”
concentric
the type of isotonic contraction characterized as “muscle lengthens while contracting”
eccentric
this kind of contraction means “same tension”
isotonic
in this type of contraction, all the energy of contraction is used to pull on thin myofilaments and thereby change the length of a fiber’s sarcomeres
isotonic
Contraction in which muscle length remains the same while muscle tension increases
Isometric contraction
this kind of contraction means “same length”
isometric contraction
true or false
Most body movements occur as a result of either isometric or isotonic contractions
false
Found only in the heart; forms the bulk of the wall of each chamber
cardiac muscle
Also known as striated involuntary muscle
cardiac muscle
Contracts rhythmically and continuously to provide the pumping action needed to maintain constant blood flow
cardiac muscle
Cardiac muscle resembles skeletal muscle but has unique features related to its role in ______________ _______________ ____________
continuously pumping blood
Each cardiac muscle contains parallel ____________
myofibrils
Cardiac muscle fibers form strong, electrically coupled junctions _____________ ____________ with other fibers; individual cells also exhibit branching
intercalated disks
continuous, electrically coupled mass
Syncytium
Cardiac muscle fibers form a continuous, ___________ ____________ around the heart chambers that conducts a single impulse across a virtually continuous sarcolemma
contractile band
___ ____________ are larger and form _________ with a rather sparse SR
T tubules, diads
true or false
Cardiac muscle does not run low on ATP or experience fatigue
true
this muscle is self-stimulating
cardiac
this muscle is composed of small, tapered cells with single nuclei
Smooth
in this muscle, no T tubules are present, and only a loosely organized SR is present
smooth
in this muscle, Ca++ comes from outside the cell and binds to calmodulin instead of troponin to trigger a contraction
smooth
in this muscle, no striations because thick and thin myofilaments are arranged differently than in skeletal or cardiac muscle fibers; myofilaments are not organized into sarcomeres
smooth
2 types of smooth muscle:
- Single-unit (visceral) smooth muscle
2. Multiunit smooth muscle
in this type of smooth muscle, gap junctions join smooth muscle fibers into large, continuous sheets
Single-unit (visceral) smooth muscle
this type of smooth muscle is the most common type; forms a muscular layer in the walls of hollow structures such as the digestive, urinary, and reproductive tracts
Single-unit (visceral) smooth muscle
this type of smooth muscle exhibits autorhythmicity and produces peristalsis
Single-unit (visceral) smooth muscle
Does not act as a single unit but is composed of many independent cell units
Multi-unit smooth muscle
Each fiber responds only to nervous input
Multi-unit smooth muscle
3 major functions of skeletal muscles
Movement, heat production, and posture.
name some features of the muscle cell that are not found in other types of cells
Excitability, contractibility, and extensibility.
what causes the striations observed in skeletal muscle fibers
The striations are a result of the A bands of sarcomeres appearing as relatively wide, dark stripes under the microscope, which alternate with narrower, lighter colored stripes formed by the I bands.
why is the triad relationship between T tubules and the SR important
The triad allows an electrical impulse traveling along a T tubule to stimulate the membranes of adjacent sacs of the SR.
describe the structure of thin and thick myofilaments, and name the kinds of proteins that compose them
Thin filament (actin, troponin, and tropomyosin): molecules strung together like beads to form two fibrous strands that twist around each other. Thick filament (myosin): shaped like golf clubs, with their long shafts bundled together to form a thick filament and their “heads” sticking out from the bundle.
what is a neuromuscular junction (NMJ)? How does it work?
A neuromuscular junction is a type of connection between a neuron and a muscle characterized by a narrow gap, or synaptic cleft, across which neurotransmitter molecules transmit signals. When impulses reach the end of a motor neuron fiber, small vesicles release a neurotransmitter into the synaptic cleft. These molecules contact the sarcolemma of the adjacent muscle fiber. There they stimulate receptors and thereby initiate an electrical impulse in the sarcolemma.
What is the role of calcium ions in muscle contraction
Calcium ions released from the SR bind to troponin in the thin filament allow tropomyosin to shift from its position blocking the active sites of actin molecules, thus initiating the chemical reactions that produce contractions.
where does the energy stored in ATP come from
Catabolism of foods.
contrast aerobic respiration and anaerobic respiration in muscle fibers
Aerobic respiration is a catabolic process that produces the maximum amount of energy available from each glucose molecule. Anaerobic respiration is a catabolic process that occurs when oxygen concentration is low. Anaerobic respiration may allow the body to avoid the use of oxygen in the short term, but not in the long term. It results in the formation of lactic acid.
what si the role of myoglobin in muscle fibers
Myoglobin attracts oxygen molecules and holds them temporarily. When the oxygen concentration inside a muscle fiber decreases rapidly, it can be quickly resupplied from the myoglobin.
what are 3 phases of a twitch contraction? what molecular events occur during each of these phases?
Latent period: impulse initiated by stimulation travels through the sarcolemma and T tubules to the SR where it triggers the release of calcium ions into the sarcoplasm; contraction phase: calcium binds to troponin and sliding of myofilaments begins and a contraction is observed; and relaxation phase: forceful sliding of myofilaments ceases and relaxation begins.
what is the difference between a twitch contraction and a tetanic contraction
Twitch contraction: The muscle does not begin to contract at the instant of stimulation, but rather a fraction of a second later. The muscle then increases tension until a peak is reached, after which it gradually returns to its resting state. Tetanus: smooth, sustained contractions resulting from a series of stimuli coming in a rapid enough succession that the muscle does not have the time to relax completely before the next contraction phase.
how does the treppe effect relate to the warm-up exercise of athletes
The treppe is a gradual, steplike increase in the strength of contraction. The muscle contracts more forcefully after it has contracted a few times than when it first contracts. This principle is used by athletes during their warm-up period.
what is tetanus? is it normal?
A tetanus is a smooth, sustained contraction. Yes, tetanus is the kind of contraction exhibited by normal skeletal muscle organs most of the time.
what is meant by the term muscle tone
Muscle tone (tonic contraction) is a continual, partial contraction in a muscular organ.
name 4 influences of skeletal muscle contraction strength
Metabolic condition of individual muscle fibers, recruitment of motor units, length-tension relationship, amount of load imposed on the muscle.
what is meant by the phrase “recruitment of motor units?”
Number of muscle fibers activated.
what is the difference between isotonic and isometric contractions? Concentric and eccentric?
Isotonic: a contraction in which the tone or tension within a muscle remains the same as the length of the muscle changes. Isometric: a contraction in which the muscle length remains the same while the muscle tension increases. Concentric: a contraction in which movement results in shortening of the muscle. Eccentric: a contraction in which movement results in lengthening of the muscle being contracted.
How do slow, separate, auto-rhythmic contractions of cardiac muscle make it well suited to its role in pumping blood
Cardiac muscle does not normally run low on ATP and thus does not experience fatigue.
what produces the striations in cardiac muscle
Each myofibril comprises sarcomeres that give the whole fiber a striated appearance.
how are myofilaments arranged in a smooth muscle fiber
Thin arrangements of myofilaments crisscross the cell and attach at their ends to the cell’s plasma membrane.
what is the difference between single-unit and multi-unit smooth muscle
Single-unit: most common type of smooth muscle—gap junctions join individual smooth muscle fibers into large, continuous sheets. Multiunit: composed of many independent single-cell units. Each independent fiber does not usually generate its own impulse, but rather responds only to nervous input.
By what process would Isabel’s muscles first get their energy for contraction?
a. Anaerobic respiration b. Aerobic respiration c. Recruitment d. Breakdown of creatine phosphate
D
The creatine phosphate in muscle cells provides ATP for about 20 seconds. After that the muscles use aerobic respiration until oxygen supplies are depleted. Contraction is still possible even then, using anaerobic respiration.
What substance in her muscles may be causing the aching or burning sensation?
a. Lactase b. Glucose c. Lactic acid d. Glycogen
C
When the glucose molecule is broken down without the use of oxygen, one by-product produced is lactic acid. This “acid” tends to lower the pH of the muscle cells and causes a burning sensation.
What protein molecules are interacting to allow Isabel’s muscles to contract?
a. Myosin and troponin b. Actin and myosin c. Actin and tropomyosin d. Troponin and tropomyosin
B
While troponin and tropomyosin are involved in the contraction process (exposing binding sites), it is the interaction between actin and myosin that results in actual change in length of the sarcomere.
What was causing Isabel’s increased body temperature?
a. Contraction of cardiac muscle cells b. Her increased respirations c. Contraction of skeletal muscle cells d. Conversion of ATP to glucose
C
As is true of most chemical reactions, when glucose is converted to ATP and energy, some of that energy is in the form of heat.
To pick up a heavier shovelful of snow, Isabel will recruit more _____.
a. motor units b. myoglobin c. individual muscle fibers d. myosin
A
Each muscle is composed of several motor units, which are in turn composed of individual muscle fibers. To create more force, you have to “recruit” more muscle fibers, but you can only recruit them via their motor neuron. A motor unit is one motor neuron and all of the fibers it communicates with.
Which of the following is not a function of muscles? A. Storage B. Posture C. Heat production D. Movement
A. Storage
The muscle's ability to stretch or extend and to return to its resting length is called: A. excitability. B. irritability. C. contractibility. D. extensibility.
D. extensibility.
The contractile unit of a muscle cell is the: A. actin. B. myosin. C. myofibril. D. sarcomere.
D. sarcomere.
This structure allows the electrical signals to travel along the sarcolemma and move deeper into the cell. A. Myosin B. Actin C. Transverse tubules D. sarcoplasm
C. Transverse tubules
The four kinds of protein that make up myofilaments are myosin, actin: A. tropomyosin, and myofibril. B. troponin, and myofibril. C. troponin, and trypsin. D. tropomyosin, and troponin.
D. tropomyosin, and troponin.
According to the sliding filament theory: A. actin moves past myosin. B. myosin moves past actin. C. tropomyosin moves past actin. D. troponin moves past myosin.
A. actin moves past myosin.
The energy required for muscular contraction is obtained by hydrolysis of: A. DNA. B. RNA. C. ADP. D. ATP.
D. ATP.
Anaerobic respiration results in the formation of an incompletely catabolized molecule called: A. lactic acid. B. glucose. C. myoglobin. D. ATP.
A. lactic acid.
The minimal level of stimulation required to cause a fiber to contract is called the: A. all-or-none principle. B. summation. C. tetanus. D. threshold stimulus.
D. threshold stimulus.
Three phases of the twitch contraction are the:
A. latent period, contraction phase, and stimulation phase.
B. latent period, stimulation phase, and contraction phase.
C. latent period, contraction phase, and relaxation phase.
D. stimulation phase, contraction phase, and relaxation phase.
C. latent period, contraction phase, and relaxation phase.
Repeated stimulation of muscle in time lessens its excitability and contractibility and may result in: A. tetanus. B. summation. C. twitch contraction. D. fatigue.
D. fatigue.
Muscle tone is maintained by: A. positive feedback mechanisms. B. negative feedback mechanisms. C. both positive and negative feedback mechanisms. D. none of the above.
B. negative feedback mechanisms.
A contraction in which muscle length remains the same but muscle tension increases is called an:
A. isometric contraction.
B. isotonic contraction.
C. isokinetic contraction.
D. isometric contraction and an isotonic contraction.
A. isometric contraction.
Exercise may cause an increase in muscle size called: A. atrophy. B. hypertrophy. C. isometric. D. isotonic.
B. hypertrophy.
The more muscle fibers contracting at the same time, the stronger the contraction of the entire muscle. The number of muscle fibers contracting depends on how many motor units are: A. conducted. B. inactivated. C. recruited. D. retained.
C. recruited.
