1
Q
What are the functions of Muscles
A
1) Movement
2) Stability –> Prevent unwanted movement (posture and holding bones in place)
3) Control of body openings and passages –> Sphincter muscles around the eyelids (control admission of light to eyes) and regulating waste elimination
4) Heat Generation
5) Glycemic Control
2
Q
How much of Body heat is generated by muscles at rest?
A
20-30%
3
Q
What are the 3 types of muscular tissue?
A
Skeletal, Cardiac and Smooth
4
Q
What is a skeletal muscle?
A
- A voluntary striated muscle that is usually attached to one or more bones. It is called voluntary because it is usually subject to conscious control and striated because it has alternating light and dark transverse bands that reflect the overlapping arrangement of the internal proteins that enable it to contract.
- Considered the most internally complex, tightly organized of all human cells.
5
Q
What are skeletal muscle cells called?
A
Muscle Fibers –> Called this because of long slender shape
6
Q
What are Myofibrils?
A
Thick Bundles of contractile proteins in the deeper part of the cell
7
Q
What is packed between the Myofibrills?
A
- Mitochondria, Smooth ER, Carbohydrate Glycogen, Myoglobin (red oxygen-storing pigment)
8
Q
What is the plasma membrane in Skeletal Muscle Fiber?
A
Sarcolemma
9
Q
What are Transverse Tubules?
A
Tunnel-like infoldings that penetrate through the fiber and emerge on the other side.
10
Q
What is the Function of the Transverse (T) Tubules?
A
Carry an electrical current from the surface of the cell to the interior when the cell is stimulated.
11
Q
What is the Smooth ER of a muscle Fiber called?
A
Sarcoplasmic reticulum
- Forms web around myofibrils
- releases calcium into cytosol when muscle fiber is stimulated
- Has dilated sacs around T Tubules called “terminal cisternae”
12
Q
What are the 2 types of Myofilaments?
A
Thick - Made of several hundred myosin proteins; has shaft-like tail and double globular head; heads directed outward around bundle
Thin - half as wide as the thick filaments and are composed mainly of 2 intertwined strands of actin like a bead necklace. Has 50 molecules of regulatory protein tropomyosin which has a small calcium-binding protein called troponin attached to it.
13
Q
What is Titin?
A
protein which makes up the springy elastic filaments with hold thick and thin filaments in line.
14
Q
What are A bands?
A
Regions in which thick and thin filaments overlap. Middle part composed of myosin only
15
Q
What are I Bands?
A
Consists only of thin filaments
16
Q
What is the Z-Disc?
A
- Bisects the I-Band
- Plaque of protein that provides anchorage for the thin filaments
17
Q
What is the Sarcomere?
A
- Each segment of a myofibril from one Z-Disc to the next
- Function unit of the muscle fiber
18
Q
A typical Sarcomere 3 cm long has about how many sarcromeres?
A
10,000
19
Q
What is dystrophin?
A
Huge protein which links the thin filaments to the inner surface of the sarcolemma. It shortens cell when sarcomeres shorten.
20
Q
What are Motor Neurons?
A
Nerve Cells that stimulate skeletal muscles. Their bodies are located in brainstem and spinal cord
21
Q
What are Motor Nerve Fibers?
A
- Axons of Motor Neurons leading to muscles
- Branch to multiple fibers. Each fiber with only 1 nerve fiber.
22
Q
What is a Motor Unit?
A
- One Motor and all muscle fibers supplied by it
- All contract at once
23
Q
What is the difference between the very small and very large motor units?
A
The very large motor units such as ones in the thigh produce power, not fine motor control, whereas the very small motor units are not strong, but with fine motor control for such purposes as eye and hand movements
24
Q
What are some advantages of having multiple motor units in a muscle?
A
- nervous system can generate variable muscle contractions by activating a variable number of motor units - more motor units for a stronger contraction.
- They can work in shifts to prevent fatigue
25
What is the Neuromuscluar Junction (NMJ)?
Where nerve meets muscle fiber; AKA the Motor end plate
26
What is the synapse?
When nerve fiber meets any cell type
27
What is the synaptic knob?
Bulbous swelling at end of nerve fiber, nestled in a depression on the muscle fiber
28
The NMJ is separated by a tiny gap called the _____?
Synaptic cleft
29
What are synaptic vesicles?
- Membrane-bound sacs in synaptic knob
- Contain Acetylcholine (Ach) --> chemical messenger that carries out the communication that is released by nerve fiber, diffuses across the synaptic cleft, and binds to ACh receptors on the syrface of the muscle fiber. The binding stimulates the muscle fiber to contract
30
What is Acetylcholinesterase?
Enzyme found on muscle fiber and synaptic cleft. IT breaks down ACh to stop muscle stimulation
31
What causes muscle paralysis?
servered nerve or interference with ACh
32
What is Excitation?
The process of converting an electrical nerve signal to an electrical signal in the muscle fiber. At rest a muscle fiber has a voltage or electrical charge difference across its sarcolemma.
33
A muscle fiber has a voltage of what?
-70 millivolts, with the inside of the sarcolemma being negative
34
What are the steps of excitation?
1) Nerve signal arriving at synapse --> Stimulates synaptic vesicles and releasing ACh into cleft.
2) Diffusion of ACh across cleft --> Binds ACh receptors in sarcolemma, Let IN Na+ ions diffusing into fiber, and let OUT K+ ions diffusing out
3) Excitement of Sarcolemma from Ions --> initiates wave of voltage changes (Action potentials), spread in all directions away from neuromuscular junction, pass into T Tubules
EXCITATION-CONTRACTION COUPLING:
4) Excitement of T Tubules Membrane --> Opens Ca+ channels in Sarcoplasmic Reticulum, and flooding of cytosol of muscle fibers by Ca2
5) Binding of Ca2 to troponin molecules on thin filaments
6) With Binding, changing shape of tropomyosin --> reveals active sites on actin of thin filament
CONTRACTION:
7) Binding of ATP by Myosin heads --> Split into ADP and and phosphate group; causes head to cock.
8) Binding of Myosin head to thin filament
9) Release of ADP and phosphate by myosin --> Flexis into original position; tugs thin filament in power stroke
10) Release of actin by myosin head --> Occurs when binding more ATP; head now ready to repeat process
RELAXATION:
11) No more ACh released when nerve signal ceases
12) ACh already in synapse --> Broken down by ACh and cessation of muscle fiber stimulation
13) Ca2+ reabsorbed by SR --> Done by Active Transport Pumps
14) Troponin - Tropomyosin complex --> Returns to resting positions, blocks myosin binding to actin, and relaxation of muscle
35
Describe the Muscle Twitch
- Minimum contraction established by muscle
| - Single cycle of contraction and relaxation
36
What is Summation?
The addition of multiple twitches which occurs when multiple nervous stimuli arrive in rapid succession. Useful work depends on this
37
What is Treppe?
When Stimuli arrive 10-20 per second, each twitch is stronger than the one before. SR is lacking time to reabsorb Ca.
38
What causes variations in muscle tension?
increased frequency of stimulation or increased number of motor units
39
What is Muscle Tone (tons)?
- Partial contraction of relaxed muscles
- Due to low level of stimulation from nervous system
- Helps stabilize joints
- Ensures thick and thin fillaments overlap enough
40
What happens if muscle is overly shortened?
Myosin cannot slide far along actin
41
What is the length-tendon relationship?
The relationship between resting length and the ability to generate tension.
42
describe the 2 types of contraction
1) Isometric Contraction --> Contraction without change in length, muscle producing tension but not shortening, phase of normal muscular action, important in muscles stabilizing joints, and important in maintaining posture
2) Isotonic Contraction --> muscle shortening or lengthening with tension.
43
Isotonic Contraction is further divided into 2 forms, what are they?
1) Concentric Contraction --> muscle shortens as it maintains tension (e.g. when biceps brachii contracts and flexes the elbow such as during biceps curls).
2) Eccentric Contraction --> Muscle maintains tension as it lengthens (e.g. when you lower a weight to the floor but maintain enough control not to let it drop).
44
What are the 2 mechanisms for generating ATP
1) Anaerobic Fermentation --> Pathway in which glucose is ultimately converted to lactic acid. For each glucose consumed, this pathway produces a net yield of 2 ATP; Does NOT use Oxygen and is therefore a way for a muscle to produce ATP during times when demand is high but Oxygen cannot be delivered fast enough to meet the needs. It's disadvantage is the the yield is low
2) Aerobic Respiration --> Intermediate product of glucose oxidized; yields 30 ATP; produces CO2 and H20; requires Oxygen
45
What happens during intense exercise?
- ATP is made aerobically from O2 stored in Myoglobin
- Some ATP regenerated by phosphagen system
- When exhausted shifts to anaerobic respiration
- Shifts back to aerobic
46
What is Muscle Fatigue?
The progressive weakness that results from prolonged use of the muscles.
47
What are some causes of Muscle Fatigue?
- Depletion of ATP and acetylcholine
- Increasingly uncontrolled leakage of calcium from the SR
- Accumulation of K+ in the extracellular fluid, which reduces the excitability of the muscle fiber.
48
What is Endurance?
Tolerance of prolonged exercise.
49
What are the factors on which Endurance depends?
1) Muscle's supply of myoglobin and glycogen
2) Density of blood capillaries
3) Supply of organic nutrients such as fatty acids and amino acids
4) Number of Mitochondria
5) maximal Rate of Oxygen uptake
6) Simple will power and other psychological factors
50
What is Oxygen Debt?
The difference between the resting rate of oxygen consumption and the elevated rate following an exercise
51
How much Oxygen does the body typically consumer after after a strenuous exercise is over?
11 Liters
52
What are some reasons for which extra oxygen is needed?
1) Rebuild oxygen in myoglobin, hemoglobin, and plasma
2) Replenish ATP and creatine phosphate
3) Oxidize and dispose of Lactic Acid
4) Meet elevated metabolic demand
53
What are the 2 primary FIber types?
1) Slow Twitch Fibers --> exhibit relatively long, slow twitches (Up to 100 ms), so they are not well adapted for quick responses. They are, however, well adapted for aerobic respiration and do not fatigue easily. Abundant mitochondria, myoglobin, and capillaries and they give tissue red color.
2) Fast Twitch Fibers --> Well adapted for quick responses (twitches as fast as 7.5 ms), but not for fatigue resistance. Especially important in Basketball. Rich in enzymes for anaerobic fermentation and for regenerating ATP from creatine phosphate; relatively pale; more glycogen
54
What are the 2 types of exercise that improve muscle performance?
1) Resistance Exercise --> (e.g. weight lifting) the contraction of muscles against a load that resists movement.
2) Endurance Exercise (e.g. running and swimming) improves fatigue resistance. In slow-twitch fibers especially it results in increased stores of glycogen, greater numbers of mitochondria, and a greater density of blood capillaries, all of which promote faster ATP production and therefore greater fatigue resistance. Also increases the oxygen-transport capacity of the blood and enhances the efficiency of the cardiovascular, respiratory and nervous system.
55
When you have a mixture of Resistance and Endurance exercise, what is it called?
Cross Training
56
Cardiac Muscle is found where?
- Only in the Heart
57
What is the function of cardiac muscle?
Pump blood
58
What are the special properties of cardiac muscle?
1) It must contract with a regular rhythm
2) the muscle cells of a given heart chamber must be well synchronized so the chamber can effectively expel blood
3) Each contraction must last long enough to expel blood from the chamber
4) It must function in sleep and wakefulness, w/o fail and w/o need of conscious attention.
5) Must be highly resistant to fatigue
59
Is Cardiac Muscle voluntary or involuntary
INVOLUNTARY and Striated
60
What does it mean that the heart is auto rhythmic?
It has a self-maintained rhythm of contraction
61
What are the cells of cardiac muscle?
Cardiomyocytes --> shorter and appear roughly rectangular in tissue sections.
62
What are functions of Smooth Muscle?
1) Able to relax and stretch -- as they fill w/ food, urine or growing fetus.
2) Not subject to length-tension relationship
3) Keep walls of organs firm -- Maintain state of contraction (Smooth Muscle Tone)
63
Is Smooth muscle voluntary or Involuntary
INVOLUNTARY and lacks striations
64
Where does Smooth Muscle Occur?
1) Walls of blood vessels
2) Respiratory, digestive and reproductive organs
3) iris of eyes
4) hair follicles
65
What are the cells of smooth muscle?
Myocytes
66
What are the properties of Smooth Muscle?
1) Thin and Thick Myofilaments
2) No Sarcomeres or Z-discs
3) Contract with a twisting motion
4) Contracts in response to nervous stimulation, stretch stimuli, Hormones, CO2, O2 and pH
5) Contraction triggered by calcium ions -- energized by ATP
6) No T Tubules and little SR
7) Contracts slowly
8) Extremely resistant to fatigue
9) capable of mitosis unlike other muscle types
67
What are the connective tissue layers in muscle?
1) Endomysium --> Thin layer enclosing each muscle fiber; allows room for blood capillaries and nerve fibers, prevents electrical stimulation between muscle fibers.
2) Perimysium --> Layer of thick connective tissue; surrounds fascicles
3) Epimysium --> Layer surrounding muscle as a whole
4) Fasciae --> Fibrous Sheets separating muscles from each other; may separate functionally related muscles into compartments
Bio 112
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