Chapter 11: Muscle Flashcards
1
Q
What are the three types of muscle tissue and where are they found?
A
Skeletal: attached to bones, voluntary, striated
Cardiac: heart wall, involuntary, striated
Smooth: walls of hollow organs, involuntary, non-striated
2
Q
skeletal muscle
A
- Attached to bones and moves parts of the skeleton
- Striated: alternating light and dark bands
- Works mainly in a voluntary manner
- Together, they compromise the muscular system
3
Q
Cardiac Muscle
A
- Only the heart contains this muscle (forms most of the heart wall)
- Striated
- Involuntary - not under conscious control
- This built-in rhythm is called autorhythmicity
4
Q
Smooth Muscle
A
- Located in the walls of hollow internal structures, such as blood vessels, the airways, stomach, intestines and uterus
- Looks nonstriated = which means smooth
- Usually involuntary
5
Q
function of muscle
1) Producing body movements
A
Walking, running and localized movements such as grasping a pencil or nodding the head
6
Q
function of muscle
2) stabilizing body positions
A
Skeletal muscle contractions stabilize joints and maintain body positions
7
Q
function of muscle
3) storing and moving substances within the body
A
- Accomplished by contractions of sphinchters: ringlike bands of smooth muscle that prevent outflow of the contents of a hollow organ
- Contraction and relaxation help adjust blood vessel diameter and regulate the rate of blood flow and return of blood to the heart
8
Q
function of muscle
4) generating heat
A
- Produces heat, a process known as thermogenesis
- Used to maintain normal body temperature
- Shivering can increase heat production
9
Q
What are the other key muscle properties
A
1) electrical excitability
2) Contractility – can shorten to produce force
3) Extensibility – can stretch without damage
4) Elasticity – can return to original shape after stretch
10
Q
Muscle fibers
A
A single muscle cell, long and multinucleated, composed of myofibrils, surrounded by connective tissue
11
Q
Fascicle
A
bundle of muscle fibers
- connective tissue surrounds groups of 10-100 muscle fibers, separating them into bundles, continuous with its tendons
12
Q
Tendon
A
cord of connective tissue that connects muscle to bone
13
Q
Sarcolemma
A
plasma membrane of a muscle fiber
14
Q
T-tubules:
A
Invaginations of sarcolemma that carry action potentials into fiber
- filled with extracellular fluid
15
Q
What is the sarcoplasm and what does it contain?
A
Cytoplasm of a muscle fiber; contains glycogen, myoglobin, mitochondria, and myofibrils
16
Q
myoglobin
A
colored, O2 binding protein that stores O2 until it is needed to generate ATP in mitochondria (only found in muscle)
17
Q
Myofibrils
A
Thick filaments (myosin) and thin filaments (actin), arranged into repeating sarcomeres
18
Q
What is a sarcomere and what are its key structures?
A
sarcomere: repeating units of myofibril
Z Disc:
- Define the boundaries of a sarcomere
- Anchor thin filaments (actin) and titin (a structural protein)
A band:
- The dark region in the middle
- Contains the entire length of thick filaments (myosin)
- Overlap with thin filaments occurs here
I band:
- The lighter region on either side of the Z disc
- Contains only thin filaments (actin)
- Gets shorter during contraction
H zone:
- Central part of the A band
- Contains only thick filaments (no overlap with actin)
- Disappears during contraction
M line:
- Located in the center of the H zone
- Formed by supporting proteins that hold thick filaments together
19
Q
thick vs thin filaments
A
Thick filaments are made of myosin, which pulls on other filaments to make muscles contract.
Thin filaments are made of actin, and they have spots where myosin can grab on during contraction.
- have two helper proteins: troponin and tropomyosin, which control when myosin can bind
20
Q
Define electrical excitability in muscles.
A
Ability to respond to stimuli by producing action potentials
Triggered by chemical stimuli and autorythmic electrical signals.
21
Q
What are muscle fibers composed of?
A
Hundreds to thousands of muscle cells arranged parallel to one another
Each fiber is surrounded by connective tissue.
22
Q
How is mature skeletal muscle fiber characterized?
A
Has multiple nuclei
The number of fibers is set before birth.
23
Q
Describe the structure of thin filaments.
A
2nm in diameter and 1-2um long, involved in contraction
Composed of actin.
24
Q
What are thick filaments made of?
A
16 nm in diameter and 1-2 um long, involved in contraction
Composed of myosin.
25
What is the role of the sarcoplasmic reticulum (SR)?
Stores Ca2+ ions
## Footnote
Essential for muscle contraction.
26
What are terminal cisternae?
Dilated end sacs of the sarcoplasmic reticulum that release Ca2+
## Footnote
Triggers muscle contraction.
27
What is a triad in muscle anatomy?
A T tubule and two terminal cisternae on either side
## Footnote
Important for excitation-contraction coupling.
28
What are contractile proteins?
Proteins that generate force during contraction
## Footnote
Includes myosin and actin.
29
What is the function of myosin?
Motor protein that converts chemical energy in ATP to mechanical energy
## Footnote
Main component of thick filaments.
30
What are G actin and F actin?
G actin: individual globular actin molecules
F actin: linked G actin molecules forming a fibrous strand
## Footnote
G actin has a myosin-binding site.
31
What is the role of tropomyosin?
Regulatory protein that covers myosin-binding sites on actin in relaxed muscle
## Footnote
Helps switch the contraction process on/off.
32
What happens when Ca2+ binds to troponin?
Tropomyosin moves away from myosin-binding sites on actin
## Footnote
Initiates muscle contraction.
33
What is the role of structural proteins in muscle?
Keep thick and thin filaments in alignment and contribute to myofibril stability
## Footnote
Includes titin.
34
What is the sliding filament mechanism?
Thick and thin filaments slide past one another during contraction
## Footnote
Causes the sarcomere to shorten.
35
What are the four major steps of the contraction cycle?
* ATP hydrolysis
* Attachment
* Power Stroke
* Detachment
## Footnote
Each step is crucial for muscle contraction.
36
What occurs during the power stroke?
Myosin head pivots and pulls thin filament toward the center of the sarcomere
## Footnote
ADP is released during this motion.
37
What happens during the detachment phase of the contraction cycle?
A new ATP binds to the myosin head, causing it to release actin
## Footnote
Prepares myosin for the next cycle.
38
What is the neuromuscular junction (NMJ)?
Synapse between a somatic motor neuron and a skeletal muscle fiber
## Footnote
Contains synaptic end bulbs, a synaptic cleft, and the motor end plate.
39
What role does acetylcholine (ACh) play in muscle contraction?
Excitatory neurotransmitter that generates end plate potential (EPP)
## Footnote
Binds to nicotinic ACh receptors on the motor end plate.
40
What are the two main phases of a skeletal muscle action potential?
* Depolarizing phase
* Repolarizing phase
## Footnote
Involves opening and closing of voltage-gated ion channels.
41
Define excitation-contraction (EC) coupling.
Sequence of events linking muscle action potential to muscle contraction
## Footnote
Occurs at the triads of skeletal muscle fibers.
42
What is the role of Ca2+ ATPase pumps?
Active transport proteins that move Ca2+ from the sarcoplasm back into the SR
## Footnote
Essential for muscle relaxation.
43
What are the three ways skeletal muscle fibers produce ATP?
* Creatine phosphate
* Anaerobic glycolysis
* Aerobic respiration
## Footnote
Each method has different energy yields and conditions.
44
What is creatine phosphate?
Energy-rich molecule found in muscle fibers
## Footnote
First source of energy during muscle contraction.
45
What is anaerobic glycolysis?
Breakdown of glucose without oxygen, producing lactic acid and 2 ATP
## Footnote
Occurs when oxygen levels are low.
46
What is aerobic respiration?
Oxygen-requiring process producing ATP, carbon dioxide, water, and heat
## Footnote
Yields about 30-32 ATP per glucose molecule.
47
What is oxygen debt?
Added oxygen taken in after exercise to restore metabolic conditions
## Footnote
Used to convert lactic acid back to glycogen and resynthesize ATP.
48
What is muscle fatigue?
Inability of a muscle to maintain force of contraction after prolonged activity
## Footnote
Results from various factors including calcium depletion and lactic acid buildup.
49
What is recovery oxygen uptake (EPOC)?
Extra oxygen taken in after exercise to restore metabolic conditions
## Footnote
Helps in the recovery process and muscle repair.
50
What is oxygen debt?
The added oxygen over and above the resting oxygen consumption that is taken into the body after exercise
## Footnote
Used to restore metabolic conditions to resting level.
51
What are the three ways oxygen debt is paid back?
* Convert lactic acid back into glycogen stores in the liver
* Resynthesize creatine phosphate and ATP in muscle fibers
* Replace the oxygen removed from myoglobin
52
What does recovery oxygen uptake refer to?
The extra oxygen your body takes in after exercise to recover and return to its resting state
## Footnote
Also known as excess post-exercise oxygen consumption (EPOC).
53
What is a motor unit?
A somatic motor neuron plus all the muscle fibers it innervates
54
What is a twitch?
A brief contraction of a group of muscle fibers within a muscle in response to a single action potential
55
What are the three phases of a twitch?
* Latent period
* Contraction period
* Relaxation period
56
What occurs during the latent period of a twitch?
A brief delay between the application of the stimulus and the beginning of contraction
## Footnote
Events of excitation-contraction coupling occur.
57
What happens during the contraction period of a twitch?
Ca 2+ binds to troponin, exposing myosin binding sites on actin, leading to peak tension development.
58
What occurs during the relaxation period of a twitch?
Ca 2+ is actively transported back into the sarcoplasmic reticulum, causing tension to decrease.
59
What are graded potentials in skeletal muscles?
Contractions that vary in strength depending on how much force is needed by the muscle.
60
What determines muscle tension?
* Frequency of stimulation
* Muscle fiber length
* Muscle fiber diameter
* Motor unit size
61
What is the refractory period?
The period of lost excitability after a muscle fiber contracts and cannot respond to a new stimulus.
62
What is wave summation?
A phenomenon where stimuli arriving at different times cause contractions with greater tension.
63
What is unfused (incomplete) tetanus?
A sustained but wavering contraction where the muscle fiber relaxes only slightly between stimuli.
64
What is fused (complete) tetanus?
A smooth, sustained contraction where individual twitches cannot be detected.
65
What is the length-tension relationship?
Indicates how the forcefulness of a muscle contraction depends on the length of the sarcomeres before contraction.
66
What is muscle tone?
Small amounts of tautness or tension in the muscle due to weak, involuntary contractions.
67
What is the difference between origin and insertion?
* Origin: attachment of a muscle tendon to the more stationary bone
* Insertion: attachment of the muscle tendon to the more movable bone
68
What is flexion?
The act of bending a limb at a joint.
69
What is extension?
The act of straightening a limb at a joint.
70
What are antagonistic muscles?
Muscles that promote opposite actions at the same joint.
71
What are the two forces that act on a lever?
* Effort (E) → causes movement
* Load (or resistance) → opposes movement
72
What is mechanical advantage?
When the load is closer to the fulcrum than the effort, requiring less effort to move a large load.
73
What is mechanical disadvantage?
When the load is farther from the fulcrum than the effort, requiring more effort to move a small load.
74
What are series elastic elements?
Parts of a muscle that are elastic and stretch slightly before transferring tension.
75
What is an isotonic contraction?
A contraction where the muscle keeps a constant level of tension but changes length.
76
What is a concentric isotonic contraction?
A contraction where the muscle shortens as it pulls.
77
What is an eccentric isotonic contraction?
A contraction where the muscle lengthens while still increasing tension.
78
What is an isometric contraction?
A contraction where the muscle stays the same length while creating tension.
79
What does the load-velocity relationship describe?
How the speed of muscle contraction changes depending on the load.
80
What are red muscle fibers?
Skeletal muscle fibers with high myoglobin content that appear darker.
81
What are white muscle fibers?
Skeletal muscle fibers with low myoglobin content that appear lighter.
82
What is the function of slow oxidative fibers?
Provide long-lasting endurance and maintain posture.
83
What is the function of fast oxidative glycolytic fibers?
Provide medium power and medium-length activity.
84
What is the function of fast glycolytic fibers?
Provide short, intense bursts of power.
85
What is unique about cardiac muscle?
Found only in the heart, striated, branched, and usually has one nucleus.
86
What are intercalated discs?
Special junctions that connect heart muscle cells together.
87
What is a functional syncytium?
A mass of interconnected muscle fibers acting as a single, coordinated unit.
88
What is autorhythmicity in cardiac muscle?
The ability of cardiac muscle to generate its own electrical signals.
89
What is excitation-contraction coupling?
The events that connect the muscle action potential to muscle contraction.
90
What is the role of calcium in cardiac muscle contraction?
Ca 2+ enters the cell and triggers the release of more Ca²⁺ from the sarcoplasmic reticulum.
91
What is smooth muscle?
Muscle found mainly in the walls of hollow organs and tubes.
92
What is the structure of smooth muscle?
Spindle-shaped, with a single nucleus and no striations.
93
What triggers smooth muscle contraction?
An increase in intracellular Ca 2+.
94
What is the latch state in smooth muscle?
A state where myosin heads stay attached to actin for longer, allowing sustained tension with low ATP use.
95
What regulates smooth muscle tone?
The autonomic nervous system (ANS).
96
What are the two forms of smooth muscle?
* Single Unit Smooth Muscle
* Multi Unit Smooth Muscle
97
What distinguishes single unit smooth muscle?
Fibers contract together as a single unit.
98
What distinguishes multi-unit smooth muscle?
Fibers act independently and must be stimulated individually by nerves.
99
What is autorhythmicity in smooth muscle?
The ability of muscle to generate its own action potentials without outside stimulation.
100
What are viscera?
Internal organs such as the stomach, intestines, urinary bladder
## Footnote
Viscera are essential components of the body's organ systems.
101
What characterizes autorhythmic muscle?
It can generate its own action potentials without outside stimulation
## Footnote
Found in single unit smooth muscle.
102
What is multi unit smooth muscle?
Fibers that act independently of each other as multiple units
## Footnote
Must be stimulated individually by nerves to contract.
103
Where is multi unit smooth muscle found?
In airway of lungs, iris, some blood vessels
## Footnote
Has a richer supply of ANS nerve endings.
104
What are autorythmic fibers?
Pacemaker cells that do not contract but spontaneously generate action potentials
## Footnote
They play a crucial role in initiating muscle contractions.
105
What are contractile fibers?
Fibers that do contract but cannot start action potentials; contract in response to signals from autorythmic cells
## Footnote
They are responsible for the actual muscle contraction.
106
What is a pacemaker potential?
Always reaches threshold leading to an action potential
## Footnote
Caused by an increase in Ca²⁺ into the cell or decrease of K⁺ out of the cell.
107
What is a slow wave potential?
Might reach threshold; action potential sometimes happens
## Footnote
Fluctuations in Na⁺ out of the cell influence this potential.
108
What factors can lead to smooth muscle contraction?
Action potentials, subthreshold depolarizations, even without membrane potential changes
## Footnote
Excitation-contraction coupling mechanisms play a vital role.
109
What are voltage gated Ca²⁺ channels?
Channels that open in response to depolarization
## Footnote
They open gradually depending on membrane potential.
110
What triggers Ca²⁺ release from the sarcoplasmic reticulum?
Ca²⁺ entering through voltage-gated channels can trigger release via Ca²⁺ release channels
## Footnote
This is essential for muscle contraction.
111
What are receptor activated channels?
Channels that open in response to neurotransmitters or hormones
## Footnote
They play a significant role in muscle regulation.
112
What is the store operated channels function?
Open when SR Ca²⁺ stores are depleted
## Footnote
They help maintain Ca²⁺ levels for contraction.
113
What is the stress relaxation response in smooth muscle?
Allows smooth muscle to undergo great changes in length while retaining the ability to contract effectively
## Footnote
Important for functions such as digestion.
114
What factors regulate smooth muscle activity?
Excitatory (promote contraction) and inhibitory (promote relaxation) factors
## Footnote
All alter the concentration of Ca²⁺ in the sacroplasm.
115
True or False: Smooth muscle is voluntary.
False
## Footnote
Smooth muscle is involuntary and controlled by the ANS.
116
Fill in the blank: Smooth muscle can be influenced by _______.
Hormones acting on specific receptors
## Footnote
Hormonal influence is significant in regulating smooth muscle function.
117
What happens when smooth muscle fibers are stretched?
They initially contract developing increased tension
## Footnote
This is part of the stress relaxation response.
