Chapter 9 Muscles And Muscle Tissue Flashcards
1
Q
Define Muscle Fibers:
A
Elongated Skeletal and Smooth muscle Cells
2
Q
Name the Prefixes that come before words referring to muscle
A
Myo-
Mys-
and Sarco-
3
Q
Components of Skeletal Muscle Tissue:
A
o Longest muscle cells o Striated o Voluntary muscle but also activated by the reflexes. o Responsible for overall body mobility. o Exhausts quickly. o Very Adaptable
4
Q
Components of Cardiac Muscle Tissue:
A
o Occurs only in the heart.
o Striated
o Involuntary
5
Q
Components of Smooth Muscle Tissue:
A
o Found in walls of hollow visceral organs. (Stomach, urinary bladder, and respiratory passageways.)
o Role is to force fluids and other substances through internal body channels.
o Elongated cells but NO Striations.
o Involuntary
6
Q
Special Characteristics of Muscle Tissue:
A
o Excitability (Responsiveness): Ability to receive and respond to stimulus.
o Contractility: Ability to shorten forcibly when adequately stimulated.
o Extensibility: The ability to extend or stretch
o Elasticity: The ability of a muscle cell to recoil and resume its resting length after stretching.
7
Q
Muscle Functions:
A
o Producing Movement o Maintaining Posture and Body Position o Stabilizing Joints o Generating Heat o Protect fragile internal organs
8
Q
Gross Anatomy of a Skeletal Muscle:
Nerve and Blood Supply
A
- One nerve, one artery, and one or more veins serve each muscle.
- Rich blood supply in muscle.
9
Q
Gross Anatomy of a Skeletal Muscle:
Connective Tissue Sheaths
A
-Support each cell and reinforce and hold together muscles as a whole.
• Epimysium: “Overcoat” of dense irregular connective tissue that surrounds the whole muscle.
• Perimysium: Perimysium is a fibrous connective tissue layer that surrounds each fascicle.
• Endomysium: Wispy sheath of connective tissue that surrounds each individual muscle fiber. Consists of fine areolar connective tissue.
10
Q
Gross Anatomy of a Skeletal Muscle:
Attachments
A
- Direct attachments: Epimysium of the muscle is fused to the periosteum of a bone or perichondrium of a cartilage.
- Indirect attachments: Muscle’s connective tissue wrappings extend beyond the muscle either as ropelike tendon or sheetlike aponeurosis.
11
Q
Microscopic Anatomy of Skeletal Muscle Fiber:
A
o Sarcolemma: Plasma Membrane
o Sarcoplasm: Cytoplasm of a muscle cell. Contains large amounts of glycosomes and myoglobin.
o Myofibrils: Densely packed components of a muscle fiber.
12
Q
Layers of Skeletal Muscle Large to Small:
A
o Muscle surrounded in Epimysium o Fascicles surrounded by Perimysium o Muscle Fibers surrounded by Endomysium o Myofibrils o Sarcomeres o Myofilaments
13
Q
Components of a Myofibril:
A-Bands and I-Bands
A
Perfectly aligned bands giving each myofibril it’s striated appearance.
14
Q
Components of a Myofibril:
H-Zone
A
Lighter region in the midsection of an A-Band.
15
Q
Components of a Myofibril:
M-Line
A
Dark line that vertically bisects each H-Zone.
16
Q
Components of a Myofibril:
Z-Disc
A
Dark, Midline interruption of each I-Band.
17
Q
Components of a Myofibril:
Sarcomere
A
- The region of a myofibril between two successive Z-Discs.
- Smallest contractile unit of a muscle fiber.
- The functional unit of skeletal muscle.
18
Q
Components of a Myofibril:
Thick Filaments
A
- Contain MYOSIN and extend the entire length of the A Band.
- Connected in the middle of the sarcomere at the M Line.
19
Q
Components of a Myofibril:
Thin Filaments
A
- Contain ACTIN and extend across the I band and partway into the A band.
- Anchored by the Z disc.
20
Q
Molecular Composition of Myofilaments:
Myosin
A
Protein that thick filaments of a myofilament are composed of.
21
Q
Molecular Composition of Myofilaments:
Actin
A
Protein that thin filaments of a myofilament are composed of.
22
Q
Molecular Composition of Myofilaments:
Cross Bridges
A
The process in which thick and thin filaments are linked together forming a “bridge” that swivels around the point of attachment.
23
Q
Molecular Composition of Myofilaments:
Regulatory Proteins of Thin Filaments
A
Both help control the myosin-actin interactions involved in contraction.
• Tropomyosin: rod-shaped protein that spirals about the actin core to help stiffen and stabilize it. Blocks myosin-binding sites so thick filaments can’t bind to thin filaments.
• Troponin: Globular three-polypeptide complex. Part is a inhibitory subunit that binds to actin. Second binds to tropomyosin and helps position it on actin. The last binds calcium ions.
24
Q
Molecular Composition of Myofilaments:
Elastic Filament
A
- Composed of large Protein Titin, which extends from the Z-Disc to the thick filament and runs within it forming it’s core to attach to the M-Line.
- Holds thick filaments in place, maintaining organization of the A-Band.
- Helps muscle spring back to shape after stretching.
25
Molecular Composition of Myofilaments:
Dystrophin
Links the thin filaments to the integral proteins of the sarcolemma.
26
Molecular Composition of Myofilaments:
Other Proteins
Nebulin, myomesin, and C Proteins.
27
Define Sarcoplasmic Reticulum:
- An elaborate, smooth endoplasmic reticulum.
| - Interconnecting tubules surround each myofibril loosely.
28
Define Terminal Cisterns:
Form large, perpendicular cross-channels at the A-Band and I-Band junctions and they always occur in pairs.
- Large numbers of mitochondria and glycogen granules, which are involved in producing energy during contraction.
- Regulates Intercellular levels of ionic calcium.
29
Define T-Tubules:
- Elongated tube protruding deep into the cell interior.
| - Contain a Lumen, or cavity that is continuous with the extracellular space.
30
Define Triad:
- A grouping of two terminal cisterns and a T-Tubule.
- Encircle each sarcomere.
- Provide necessary signals for contraction.
- Integral proteins of the T-Tubule act as voltage sensors.
31
What Controls Muscle Contraction?
- Nerve-initiated electrical impulses that travel along the sarcolemma.
- Conduct impulses to the deepest regions of the muscle cell and each sarcomere.
- Signal for necessary release of calcium.
32
Define Sliding Filament Model of Contraction:
o During contraction the thin filaments slide past the thick ones so that the actin and myosin filaments overlap to a greater degree.
• When the nervous system stimulates muscle fibers, the myosin heads on the thick filaments latch onto myosin-binding sites on actin in the thin filaments, and the sliding begins.
• These cross-bridge attachments form and break several times during a contraction, acting like tiny little ratchets to generate tension and propel the thin filaments toward the center of the sarcomere.
• As this event occurs simultaneously in sarcomeres throughout the cell, the muscle cell shortens.
o As a muscle cell shortens: The I-bands shorten, the distance between successive Z discs shortens, the H zones disappear, and the contiguous A bands move closer together but their length does not change.
33
4 Events That Must Occur for a Skeletal Muscle Fiber to Contract:
o 1. The fiber must be activated; stimulated by a nerve ending so that a change in membrane potential occurs.
o 2. Must generate an electrical current, called an action potential, in its sarcolemma.
o 3. The action potential is automatically propagated along the sarcolemma.
o 4. Intracellular calcium ion levels must rise briefly, providing the final trigger for contraction.
34
- The 6 Steps of Events at the Neuromuscular Junction:
Step 1: AP Arrival
Action potential arrives at axon terminal of motor neuron.
35
- The 6 Steps of Events at the Neuromuscular Junction:
Step 2: Opening of Voltage Gates
Voltage-gated Ca2+ channels open. Ca2+ enters the axon terminal moving down its electrochemical gradient.
36
- The 6 Steps of Events at the Neuromuscular Junction:
Step 3: Release of ACh
Ca2+ entry causes ACh to be released by exocytosis.
37
- The 6 Steps of Events at the Neuromuscular Junction:
Step 4: ACh Diffusion across Syn. Cleft
ACh diffuses across the synaptic cleft and binds to its receptors on the sarcolemma.
38
- The 6 Steps of Events at the Neuromuscular Junction:
Step 5: Opening of Ion Channels
- ACh binding opens ion channels in the receptors that allow simultaneous passage of Na+ into the muscle fiber and K+ out of the muscle fiber.
- More Na+ ions enter than K+ ions exit, which produces a local change in the membrane potential called the end plate potential.
39
- The 6 Steps of Events at the Neuromuscular Junction:
Step 6: Termination of ACh Effects
ACh effects are terminated by its breakdown in the synaptic cleft by acetylcholinesterase and diffusion away from the junction.
40
Summary of 4 Events in Generation and Propagation of Action Potential of Skeletal Muscle Fiber:
o 1. Generation of End Plate Potential- ACh molecules bind to receptors at NMJ and open ligand-gated channels that allow Na+ and K+ to pass. More Na+ diffuses in than K+ diffuses out.
o 2. Depolarization: Generation and Propagation of an Action Potential- Na+ enters following electrochemical gradient, and once it reaches the threshold an action potential is generated and propagated along all directions of the neuromuscular junction.
o 3. Repolarization: Restoring of sarcolemma to its initial polarized state- Na+ channels close and voltage-gated K+ channels open causing K+ to diffuse rapidly out of the muscle fiber, restoring negatively charged conditions inside.
41
Define the Refractory period:
A period during repolarization in which a cell cannot be stimulated until the process is complete.
42
Define Excitation-Contraction Coupling:
- The sequence of events by which transmission of an action potential along the sarcolemma causes myofilaments to slide.
- This Action potential is brief and ends before any signs of contraction are obvious.
43
The 4 Steps of Excitation-Contraction Coupling:
o 1. The action potential propagates along the sarcolemma and down the t tubules.
o 2. Calcium Ions are released.
o 3. Calcium binds to troponin and removes the blocking action of tropomyosin.
o 4. Contraction begins.
44
The Aftermath of Excitation-Contraction Coupling:
o Muscle action potential ceases, causing voltage-sensitive tubule proteins to return to original shape, closing the Ca2+ release channels of the SR.
o Ca2+ levels in the sarcoplasm fall as Ca2+ is continually pumped back into the SR by active transport.
o Without Ca2+ the blocking action of tropomyosin is restored, myosin-actin interaction is inhibited, and relaxation occurs.
o This process occurs whenever an action potential arrives at the NMJ.
45
The 4 Steps of the Cross Bridge Cycle:
o 1. Cross bridge formation: Energized myosin head attaches to action myofilament, forming a cross bridge.
o 2. The Power (Working) Stroke: ADP and Pi are released and the myosin head pivots and bends, changing to its bent low-energy state. As a result it pulls the actin filament toward the M line.
o 3. Cross bridge detachment: After ATP attaches to myosin, the link between myosin and actins weakens, and the myosin head detaches.
o 4. Cocking of the Myosin Head: As ATP is hydrolyzed to ADP and Pi the myosin head returns to its prestrike high-energy, or “cocked” position.
46
Define Muscle Tension:
The force exerted by a contracting muscle on an object.
47
Define Load:
The opposing force exerted on the muscle by the weight of the object to be moved.
48
Define Motor Unit:
Consists of one motor neuron and all the muscle fibers it innervates, or supplies.
49
Define Myogram:
Recording of contractile activity.
50
Define Muscle Twitch:
Motor unit’s response to a single action potential of its motor neuron.
51
The 3 Phases of Muscle Twitch Myogram:
o 1. Latent Period: The first few milliseconds following stimulation when e-c coupling is occurring. Cross bridges begins to cycle but muscle tension is not yet measurable.
o 2. Period of Contraction: Cross bridges are active, and myogram tracing peaks. Last 10-100 milliseconds. If tension becomes great enough to overcome resistance the muscle shortens.
o 3. Period or Relaxation: Last 10-100 milliseconds. Initiated by re-entry of Ca2+ into SR. Contractile force declining so muscle tension decreases to zero and tracing returns to baseline. If muscle was shortened it now returns to initial length.
52
Define Graded Muscle Responses:
Healthy muscle contractions that are relatively smooth and vary in strength as different demands are placed on them.
53
The 2 Ways Muscle Contraction Can Be Graded:
o Frequency of Stimulation
o Changing Strength of Stimulation
54
Define Wave (Temporal Summation):
Occurs because the second contraction occurs before the muscle has completely relaxed.
55
The 3 Events that lead to Unfused (Incomplete) Tetanus:
o 1. The relaxation times between twitches becomes shorter and shorter.
o 2. The concentration of Ca2+ in the cytosol rises higher and higher.
o 3. The degree of wave summation becomes greater and greater, progressing to a sustained but quivering contraction.
56
Define Fused (Complete) Tetanus:
- Stimulation frequency continues to increase, muscle tension increases until it reaches maximal tension.
- All evidence of muscle relaxation disappears and the contractions fuse into a smooth, sustained contraction plateau.
57
Define Recruitment (Multiple Motor Unit Summation):
Controls the force of contraction more precisely.
58
Define Subthreshold Stimuli:
Stimuli that produce no observable contractions.
59
Define Threshold Stimulus:
The stimulus at which the first observable contraction occurs.
60
Define Maximal Stimulus:
- Strongest stimulus that increases contractile force.
| - Represents the point at which all the muscle’s motor units are recruited.
61
The Size Principle of Muscle:
o Motor Units with smallest muscle fibers are activated first because they are controlled by the smallest, most highly excitable motor neurons.
o As motor units with larger muscle fibers begin to be excited, contractile strength increases.
o Largest motor units, containing large, coarse muscle fibers, have as 50x the contractile force of the smallest ones. Controlled by largest, least excitable neurons and activated only when most powerful contraction is necessary.
62
Define Isotonic Contraction and Name the 2 Types:
o Isotonic Contraction: “Same Tension”, muscle length changes and moves a load. Tension remains relatively constant throughout contractile period.
• Concentric Contractions: Muscle shortens and does work.
• Eccentric Contractions: Muscle generates force as it lengthens.
63
Define Isometric Contraction:
- “Same Measure”, tension may build to the muscle’s peak tension-producing capacity, but the muscle neither shortens nor lengthens.
- Occurs when muscle attempts to move a load that is greater than the force the muscle is able to develop.
64
Define and State Importance of Muscle Tone:
- Due to spinal reflexes that activate first one group of motor units and then another in response to activated stretch receptors in muscles.
- Causes muscles to always be somewhat contracted at all times.
65
State What Supplies Energy for Contraction:
ATP supplies the energy to move and detach cross bridges, operate the calcium pump in the SR, and return Na+ and K+ to the cell interior and exterior respectively after e-c coupling.
66
Name the 3 Pathways to Creating ATP in the Body:
o 1. Direct Phosphorylation
o 2. Anaerobic Glycolysis
o 3. Aerobic Respiration
67
Formula That Occurs During Direct Phosphorylation to Create ATP:
o Creatine Phosphate + ADP → Creatine + ATP
o This reaction is catalyzed by creatine kinase.
68
Important Information for Direct Phosphorylation:
o During exercise the demand for ATP peaks, and available ATP is consumed within a few twitches.
o Creatine phosphate is tapped to regenerate ATP by combining with ADP.
o This process can give you quick burst energy for about 15 seconds of activity.
69
Important Information for Anaerobic Glycolysis:
o When stored ATP and CP are exhausted, more ATP is generated by breaking down (catabolizing) glucose obtained from the blood or glycogen stored in the muscle.
o Glycolysis: Glucose breakdown. Occurs whether or not oxygen is present. Glucose is broken down to 2 pyruvic acid molecules, releasing enough energy to form small amounts of ATP.
o Most of the pyruvic acid made during this process is converted into lactic acid, then diffuses into the blood stream and are used by the liver, heart, or kidney for an energy source.
o Produces ATP about 2.5x Faster than Direct Phos.
o 30-40 seconds of strenuous muscle activity.
o Though it stores more ATP its draw back is that build-up of lactic acid is often responsible for muscle soreness during intense exercise.
70
Important Information for Aerobic Respiration:
o Amount of creatine phosphate limited; muscles metabolize nutrients to transfer energy from food to ATP.
o During Rest and Moderate exercise, 95% of ATP used comes from Aerobic Respiration.
o This process occurs in Mitochondria, requires oxygen, and involves a sequence of chemical reactions that break the bonds of fuel molecules and release energy to make ATP.
o Formula: Glucose + Oxygen → Carbon Dioxide + Water + ATP
o 32 ATP per glucose, CO2, H2O
o Can provide hours of moderate exercise with continuous intake of oxygen.
71
Define Aerobic Endurance:
The length of time a muscle can continue to contract using aerobic pathways.
72
Define Anaerobic Threshold:
The point at which muscle metabolism converts to anaerobic glycolysis.
73
Define Muscle Fatigue:
State of physiological inability to contract even though the muscle still may be receiving stimuli.
74
What Must Occur in Order to Return Muscle to Resting State?
o Oxygen reserves in myoglobin must be replenished.
o Accumulated lactic acid must be reconverted to pyruvic acid.
o Glycogen stores must be replaced.
o ATP and Creatine Phosphate reserves must be resynthesized.
75
Heat Production During Muscle Activity:
60% of the energy used during exercise is actually converted to heat in order to maintain body homeostasis.
76
The 4 Factors Behind The Force of Muscle Contraction:
o Number of muscle fibers stimulated
o Relative size of the fibers
o Frequency of stimulation
o Degree of muscle stretch
77
Define Length-Tension Relationship:
Occurs when muscle is slightly stretched and the thin and thick filaments overlap optimally, because this relationship permits sliding along nearly the entire length of thin filaments.
78
Definition and Features of Slow Oxidative Fibers:
Found in athletes accustomed to Endurance-type activities.
o Speed of Contraction: Slow
o Myosin ATPase Activity: Slow
o Primary Pathway for ATP Synthesis: Aerobic
o Myoglobin Content: High
o Glycogen Stores: Low
o Recruitment Order: First
o Rate of Fatigue: Slow (Fatigue-resistant)
79
Definition and Features of Fast Oxidative Fibers:
Found in athletes accustomed to Moderate exercise activities. Sprinting, walking.
o Speed of Contraction: Fast
o Myosin ATPase Activity: Fast
o Primary Pathway for ATP Synthesis: Aerobic (Some Anaerobic)
o Myoglobin Content: High
o Glycogen Stores: Intermediate
o Recruitment Order: Second
o Rate of Fatigue: Intermediate (Moderately Fatigue-resistant)
80
Definition and Features of Fast Glycolytic Fibers:
```
Found in athletes accustomed to short-term intense or powerful movements.
o Speed of Contraction: Fast
o Myosin ATPase Activity: Fast
o Primary Pathway for ATP Synthesis: Anaerobic Glycolysis
o Myoglobin Content: Low
o Glycogen Stores: High
o Recruitment Order: Third
o Rate of Fatigue: Fast (Fatigable)
```
81
Aerobic/Endurance Exercises Results on Skeletal Muscle Fibers:
o Number of capillaries surrounding muscle fibers increases.
o Number of mitochondria within muscle fibers increases.
o Fibers synthesize more myoglobin.
82
Resistance/Lifting Exercises Results on Skeletal Muscle Fibers:
o Increase in size of muscle fibers.
o Strength not endurance.
83
Define Overload Principle:
Forcing a muscle to work hard increases muscle strength and endurance.
84
Define Overuse Injuries:
Doing to much to soon, or ignoring the warning signs of muscle or joint pain may put you at risk for these.
85
The 2 Layers of Smooth Muscle Fibers:
o Longitudinal Layer: Muscle Fibers run parallel to long axis of the organ. When these fibers contract, the organ dilates and shortens.
o Circular Layer: The fibers run around the circumference of the organ. Contraction of this layer constricts the lumen of the organ and elongates the organ.
86
Define Peristalsis:
Alternating contraction and relaxation of the Longitudinal and Circular layers of smooth muscle that mixes substances in the lumen and squeezes them through the organ’s internal pathway.
87
Define Varicosities:
Cells in smooth muscle that release neurotransmitters into a wide synaptic cleft in the general area of the smooth muscle cells.
88
Define Diffuse Junctions:
The junctions of smooth muscle in which Neurotransmitters are released by varicosities.
89
Define Caveolae:
Pouchlike infoldings of smooth muscle that sequester bits of extracellular fluid containing a high concentration of Ca2+ close to the membrane. Ca2+ influx occurs rapidly.
90
The Proportion and Organization of Smooth Muscle Myofilaments Differ from Skeletal Muscle in the Following Ways:
o Thick filaments are fewer but have myosin heads along their entire length.
o No troponin complex in thin filaments.
o Thick and thin filaments arranged diagonally.
o Intermediate filament-dense body network.
91
Define Dense Bodies:
Cytoplasmic structures within smooth muscle that are tethered to the sarcolemma, and act as anchoring points for thin filaments and therefore correspond to Z discs of skeletal muscle.
92
Contraction in Smooth Muscle is Similar to Contraction in Skeletal Muscle in the Following Ways:
o Actin and Myosin interact by the sliding filament mechanism.
o The final trigger for contraction is a rise in the intracellular calcium ion level.
o ATP energizes the sliding process.
93
Define Calmodulin:
- Cytoplasmic calcium-binding protein a smooth muscle.
| - Myosin is activated by the binding of this protein with calcium.
94
Define Myosin kinase or myosin light chain kinase:
A kinase enzyme that phosphorylates the myosin, activating it.
95
Sequence of Events in excitation-contraction coupling of smooth muscle:
o 1. Calcium ions (Ca2+) enter the cytosol from the ECF via voltage-dependent or voltage-independent Ca2+ channels, or from the SR.
o 2. Ca2+ binds to and activates calmodulin.
o 3. Activated calmodulin activates the myosin light chain kinase enzymes.
o 4. The activated kinase enzymes catalyze transfer of phosphate to myosin, activating the ATPases.
o 5. Activated myosin forms cross bridges with actin of the thin filament. Shortening begins.
96
Define the Stress-Relaxation Response:
Allows a hollow organ to fill or expand slowly to accommodate a greater volume without causing strong contractions that would expel its contents.
97
Define Hyperplasia:
Divide to increase numbers.
98
Definition and Features of Unitary Smooth (Visceral) Muscle:
In the walls of all hollow organs except the heart, far more common.
o Arranged in opposing (longitudinal and circular) sheets.
o Are innervated by varicosities of autonomic nerve fibers and often exhibit rhythmic.
o Are electrically coupled by gap junctions and so contract as a unit. (For this reason recruitment is not an option in unitary smooth muscle.
99
Definition and Features of Multi-Unit Smooth Muscle:
o Consists of muscle fibers that are structurally independent of one another.
o Is richly supplied with nerve endings, each of which forms a motor unit with a number of muscle fibers.
o Responds to neural stimulation with graded contractions that involve recruitment.
100
The 3 Steps of Myoblasts Fusing to Form Multinucleate Skeletal Muscle Fiber:
o 1. Embryonic mesoderm cells called myoblasts undergo cell division and enlarge.
o 2. Several myoblasts fuse together to form a myotube.
o 3. Myotube matures into skeletal muscle fiber.
101
Define Satellite Cells:
- Myoblast-like cells associated with skeletal muscle, help repair injured fibers and allow limited regeneration of dead skeletal muscle.
- This capability declines with age.
102
Does Cardiac Muscle Regenerate?
Cardiac muscle was thought to have no regenerative capabilities whatsoever, but recent studies suggest that cardiac cells do divide at a modest rate. Nonetheless, injured heart muscle is repaired mostly by scar tissue.
103
Does Smooth Muscle Regenerate?
Smooth muscles have a good regenerative capacity and smooth muscle cells of blood vessels divide regularly throughout life.
104
Define Muscular Dystrophy:
- Refers to a group of inherited muscle-destroying diseases that generally appear during childhood.
- Affected muscles enlarge due to deposits of fat and connective tissue, but the muscle fibers atrophy and degenerate.
105
Define Duchenne Muscular Dystrophy:
- Most common and serious form of muscular dystrophy inherited as a sex-linked recessive disease.
- Expressed almost exclusively in males.
- Skeletal muscles weaken.
106
Define Dystrophin:
Cytoplasmic protein that links cytoskeleton to extracellular matrix that helps stabilize the sarcolemma.
107
Define Sarcopenia:
Gradual loss of muscle mass.
