Ch.6: The Muscular System Flashcards
1
Q
Muscles are responsible for all types of:
A
Body movement
2
Q
What are the three basic muscle types found in the body?
A
- Skeletal muscle
- Cardiac muscle
- Smooth muscle
3
Q
Skeletal and smooth muscle cells are:
A
- Elongated
* (muscle cell = muscle fiber)
4
Q
Contraction and shortening of muscles are due to:
A
• The movement of microfilaments
5
Q
All muscles share some terminology, such as:
A
- Prefixes myo- and mys- refer to “muscle”
* Prefix sarco- refers to “flesh”
6
Q
What is skeletal muscle and what are the properties of it?
A
- Most skeletal muscle fibers are attached by tendons to bones
- Skeletal muscle cells are large, cigar-shaped, and multinucleate
- Also known as striated muscle because of its obvious stripes
- Also known as voluntary muscle because it is the only muscle tissue subject to conscious control
7
Q
Skeletal muscle cells are surrounded and bundled by connective tissue, such as:
A
- Endomysium—encloses a single muscle fiber
- Perimysium—wraps around a fascicle (bundle) of muscle fibers
- Epimysium—covers the entire skeletal muscle
- Fascia—on the outside of the epimysium
8
Q
The epimysium of skeletal muscle blends into a:
A
Connective tissue attachment
9
Q
What are tendons?
A
• Cord-like structures
Mostly collagen fibers
Often cross a joint because of their toughness and small size
10
Q
What are aponeuroses?
A
- Sheet-like structures
* Attach muscles indirectly to bones, cartilages, or connective tissue coverings
11
Q
What are the properties of smooth muscle?
A
- No striations
- Involuntary—no conscious control
- Found mainly in the walls of hollow visceral organs (such as stomach, urinary bladder, respiratory passages)
- Spindle-shaped fibers that are uninucleate
- Contractions are slow and sustained
12
Q
What are the properties of cardiac muscle?
A
- Striations
- Involuntary
- Found only in the walls of the heart
- Uninucleate
- Branching cells joined by gap junctions called intercalated discs
- Contracts at a steady rate set by pacemaker
13
Q
Whereas all muscle types produce movement, what are the three other important roles skeletal muscle has:
A
- Maintain posture and body position
- Stabilize joints
- Generate heat
14
Q
What is a sarcolemma?
A
Specialized plasma membrane
15
Q
What are myofibrils?
A
- Long organelles inside muscle cell
* Light (I) bands and dark (A) bands give the muscle its striated (banded) appearance
16
Q
What is the banding pattern of myofibrils?
A
I band = light band • Contains only thin filaments • Z disc is a midline interruption A band = dark band • Contains the entire length of the thick filaments • H zone is a lighter central area • M line is in center of H zone
17
Q
What is a sarcomere?
A
- Contractile unit of a muscle fiber
* Structural and functional unit of skeletal muscle
18
Q
What is the organization of the sarcomere?
A
Myofilaments produce a banding (striped) pattern
• Thick filaments = myosin filaments
• Thin filaments = actin filaments
19
Q
Thick filaments =
A
- Myosin filaments
- Composed of the protein myosin
- Contain ATPase enzymes to split ATP to release energy for muscle contractions
- Possess projections known as myosin heads
- Myosin heads are known as cross bridges when they link thick and thin filaments during contraction
20
Q
Thin filaments =
A
- Actin filaments
- Composed of the contractile protein actin
- Actin is anchored to the Z disc
21
Q
At rest, within the A band there is a zone that lacks actin filaments called the:
A
H zone
22
Q
During contraction, H zones disappear as actin and myosin filaments:
A
Overlap
23
Q
What is sarcoplasmic reticulum (SR)?
A
- Specialized smooth endoplasmic reticulum
- Surrounds the myofibril
- Stores and releases calcium
24
Q
What are the special functional properties of skeletal muscles?
A
- Irritability (also called responsiveness)—ability to receive and respond to a stimulus
- Contractility—ability to forcibly shorten when an adequate stimulus is received
- Extensibility—ability of muscle cells to be stretched
- Elasticity—ability to recoil and resume resting length after stretching
25
Skeletal muscles must be stimulated by a motor neuron (nerve cell) to:
Contract
26
What is a motor unit?
One motor neuron and all the skeletal muscle cells stimulated by that neuron
27
What is a neuromuscular junction?
Association site of axon terminal of the motor neuron and sarcolemma of a muscle
28
What is a neurotransmitter?
* Chemical released by nerve upon arrival of nerve impulse in the axon terminal
* Acetylcholine (ACh) is the neurotransmitter that stimulates skeletal muscle
29
What is a synaptic cleft?
* Gap between nerve and muscle filled with interstitial fluid
* Although very close, the nerve and muscle do not make contact
30
When a nerve impulse reaches the axon terminal of the motor neuron:
• Step 1: Calcium channels open, and calcium ions enter the axon terminal
• Step 2: Calcium ion entry causes some synaptic vesicles to release acetylcholine (ACh)
• Step 3: ACh diffuses across the synaptic cleft and attaches to receptors on the sarcolemma of the muscle cell
• Step 4: If enough A C h is released, the sarcolemma becomes temporarily more permeable to sodium ions (N a+)
*Potassium ions (K+) diffuse out of the cell
*More sodium ions enter than potassium ions leave
*Establishes an imbalance in which interior has more positive ions (depolarization), thereby opening more N a+ channels
• Step 5: Depolarization opens more sodium channels that allow sodium ions to enter the cell
*An action potential is created
*Once begun, the action potential is unstoppable
*Conducts the electrical impulse from one end of the cell to the other
• Step 6: Acetylcholinesterase (AChE) breaks down acetylcholine into acetic acid and choline
*AChE ends muscle contraction
*A single nerve impulse produces only one contraction
31
A cell returns to its resting state when:
* Potassium ions (K+) diffuse out of the cell
| * Sodium-potassium pump moves sodium and potassium ions back to their original positions
32
What causes filaments to slide?
* Calcium ions (C a2+) bind regulatory proteins on thin filaments and expose myosin-binding sites, allowing the myosin heads on the thick filaments to attach
* Each cross bridge pivots, causing the thin filaments to slide toward the center of the sarcomere
* Contraction occurs, and the cell shortens
* During a contraction, a cross bridge attaches and detaches several times
* ATP provides the energy for the sliding process, which continues as long as calcium ions are present
33
What are graded responses?
* Muscle fiber contraction is “all-or-none,” meaning it will contract to its fullest when stimulated adequately
* Within a whole skeletal muscle, not all fibers may be stimulated during the same interval
* Different combinations of muscle fiber contractions may give differing responses
* Graded responses—different degrees of skeletal muscle shortening
34
Graded responses can be produced in which two ways?
1. By changing the frequency of muscle stimulation
| 2. By changing the number of muscle cells being stimulated at one time
35
What is a muscle response to increasingly rapid stimulation?
Muscle twitch
• Single, brief, jerky contraction
• Not a normal muscle function
36
In most types of muscle activity, nerve impulses are delivered at a:
* Rapid rate
| * As a result, contractions are “summed” (added) together, and one contraction is immediately followed by another
37
When stimulations become more frequent, muscle contractions get:
* Stronger and smoother
| * The muscle now exhibits unfused (incomplete) tetanus
38
Fused (complete) tetanus is achieved when the muscle is stimulated so rapidly that:
* No evidence of relaxation is seen
| * Contractions are smooth and sustained
39
What is a muscle response to stronger stimuli?
* Muscle force depends upon the number of fibers stimulated
* Contraction of more fibers results in greater muscle tension
* When all motor units are active and stimulated, the muscle contraction is as strong as it can get
40
What is ATP?
* Only energy source that can be used to directly power muscle contraction
* Stored in muscle fibers in small amounts that are quickly used up
* After this initial time, other pathways must be utilized to produce ATP
41
Concept Link
Recall that ATP can be compared to a tightly coiled spring that is ready to uncoil with tremendous energy when the “catch” is released (Chapter 2, p. 55). Remember that all bonds store energy and that the “catch” in this example is one of the characteristic high-energy phosphate bonds in ATP.
42
What are the three pathways to regenerate ATP?
1. Direct phosphorylation of ADP by creatine phosphate
2. Aerobic pathway
3. Anaerobic glycolysis and lactic acid formation
43
What is direct phosphorylation of ADP by creatine phosphate (CP)?
• Fastest of the three pathways to regenerate ATP
• Muscle cells store CP, a high-energy molecule
After ATP is depleted, ADP remains
• CP transfers a phosphate group to ADP to regenerate ATP
• CP supplies are exhausted in less than 15 seconds
• 1 ATP is produced per CP molecule
44
What is aerobic respiration?
* Supplies ATP at rest and during light/moderate exercise
* A series of metabolic pathways, called oxidative phosphorylation, use oxygen and occur in the mitochondria
* Glucose is broken down to carbon dioxide and water, releasing energy (about 32 ATP)
* This is a slower reaction that requires continuous delivery of oxygen and nutrients
45
What is anaerobic glycolysis and lactic acid formation?
* Reaction that breaks down glucose without oxygen
* Glucose is broken down to pyruvic acid to produce about 2 ATP
* Pyruvic acid is converted to lactic acid, which causes muscle soreness
* This reaction is not as efficient, but it is fast
* Huge amounts of glucose are needed
46
If muscle activity is strenuous and prolonged:
Muscle fatigue occurs
47
Suspected factors that contribute to muscle fatigue include:
* Ion imbalances (Ca2+, K+)
* Oxygen deficit and lactic acid accumulation
* Decrease in energy (ATP) supply
48
After exercise, the oxygen deficit is repaid by:
Rapid, deep breathing
49
What are isotonic contractions?
* Myofilaments are able to slide past each other during contractions
* The muscle shortens, and movement occurs
* Example: bending the knee; lifting weights; smiling
50
What are isometric contractions?
* Muscle filaments are trying to slide, but the muscle is pitted against an immovable object
* Tension increases, but muscles do not shorten
* Example: pushing your palms together in front of you
51
What is muscle tone?
* State of continuous partial contractions
* Result of different motor units being stimulated in a systematic way
* Muscle remains firm, healthy, and constantly ready for action
52
Exercise increases muscle:
Size, strength, and endurance
53
Aerobic (endurance) exercise (biking, jogging) results in:
* Stronger, more flexible muscles with greater resistance to fatigue
* Makes body metabolism more efficient
* Improves digestion, coordination
54
Resistance (isometric) exercise (weight lifting) increases muscle:
* Size and strength
| * Individual muscle fibers enlarge
55
What are the Five Golden Rules for understanding skeletal muscle activity?
1. With a few exceptions, all skeletal muscles cross at least one joint.
2. Typically, the bulk of a skeletal muscle lies proximal to the joint crossed.
3. All skeletal muscles have at least two attachments: the origin and the insertion.
4. Skeletal muscles can only pull; they never push.
5. During contraction, a skeletal muscle insertion moves toward the origin.
56
Muscles are attached to no fewer than two points, which are:
* Origin: attachment to an immovable or less movable bone
| * Insertion: attachment to a movable bone
57
When the muscle contracts, the insertion moves:
Toward the origin
58
Body movement occurs when muscles:
Contract across joints
59
What is flexion?
* Decreases the angle of the joint
* Brings two bones closer together
* Typical of bending hinge joints (e.g., knee and elbow) or ball-and-socket joints (e.g., the hip)
60
What is extension?
* Opposite of flexion
* Increases angle between two bones
* Typical of straightening the elbow or knee
* Extension beyond 180° is hyperextension
61
What is rotation?
* Movement of a bone around its longitudinal axis
* Common in ball-and-socket joints
* Example: moving the atlas around the dens of axis (i.e., shaking your head “no”)
62
What is abduction?
Movement of a limb away from the midline
63
What is adduction?
* Opposite of abduction
| * Movement of a limb toward the midline
64
What is circumduction?
* Combination of flexion, extension, abduction, and adduction
* Common in ball-and-socket joints
* Proximal end of bone is stationary, and distal end moves in a circle
65
What is dorsiflexion?
Lifting the foot so that the superior surface approaches the shin (toward the dorsum)
66
What is plantar flexion?
Pointing the toes away from the head
67
What is inversion?
Turning sole of foot medially
68
What is eversion?
Turning sole of foot laterally
69
What is supination?
* Forearm rotates laterally so palm faces anteriorly
| * Radius and ulna are parallel
70
What is pronation?
* Forearm rotates medially so palm faces posteriorly
| * Radius and ulna cross each other like an X
71
What is opposition?
Moving the thumb to touch the tips of other fingers on the same hand
72
Muscles can only pull as they:
Contract, not push
73
In general, groups of muscles that produce opposite actions lie on:
Opposite sides of a joint
74
What is a prime mover?
Muscle with the major responsibility for a certain movement
75
What is an antagonist?
Muscle that opposes or reverses a prime mover
76
What is a synergist?
Muscle that aids a prime mover in a movement or reduces undesirable movements
77
What is a fixator?
Specialized synergists that hold a bone still or stabilize the origin of a prime mover
78
Muscles are named on the basis of several criteria, such as?
```
By direction of muscle fibers
• Example: rectus (straight)
By relative size of the muscle
• Example: maximus (largest)
By location of the muscle
• Example: temporalis (temporal bone)
By number of origins
• Example: triceps (three heads)
By location of the muscle’s origin and insertion
• Example: sterno (on the sternum)
By shape of the muscle
• Example: deltoid (triangular)
By action of the muscle
• Example: flexor and extensor (flexes or extends a bone)
```
79
Increasing muscular control reflects the maturation of the:
Nervous system
80
Muscle control is achieved in a:
Superior/inferior and proximal/distal direction
81
To remain healthy, muscles must be:
Exercised regularly
82
Without exercise, muscles:
Atrophy
83
With extremely vigorous exercise:
Muscles hypertrophy
84
As we age, muscle mass decreases, and muscles become more:
Sinewy
85
Exercise helps retain muscle:
Mass and strength
