Unit 3 Lecture Flashcards
1
Q
What are the three types of muscle?
A
- Skeletal muscle
- Cardiac muscle
- Smooth muscle
2
Q
What is the basic function of all muscles?
A
Generate tension
3
Q
What are the four functions of skeletal muscles?
A
- Locomotion
- Facial expression
- Posture and body position
- Regulation of body temperature
4
Q
Is skeletal muscle contraction voluntary?
A
Yes; can be automatic but we have the ability to change skeletal muscle activity
5
Q
What does skeletal muscle contraction always require?
A
Always requires nervous system input
6
Q
What is an example of a muscle that can be automatic or voluntary action?
A
Contraction of the diaphragm is usually automatic, but you can take a deep breath or hold your breath whenever you choose
7
Q
Define origin
A
Where the muscle starts on a bone (stays stationary)
8
Q
Define insertion
A
Where the muscle ends on a bone (moves towards origin)
9
Q
How do the origin and insertion work together?
A
The insertion moves towards the origin
10
Q
How do you name a movement?
A
Include the action and the name of the segment that moves:
- Flexion of the forearm
- Adduction of the thigh
11
Q
Define flexion
A
This is the movement to reduce the angle between articulating bones at a joint
12
Q
Define extension
A
This is the movement to increase the angle between articulating bones at a joint
13
Q
What is common about both flexion and extension movements?
A
Motions typically in a sagittal plane (anterior/posterior)
14
Q
Define abduction
A
Movement away from the longitudinal axis (midline)
15
Q
Define adduction
A
Movement toward the longitudinal axis (midline)…you ADD something back to your midline
16
Q
Define Reverse Muscle Action (RMA)
A
When the insertion is anchored, the origin moves toward insertion
17
Q
Classify a Muscle based on action:
- Action: Leg extension (increasing the angle at the knee)
- Origin: femur
- Insertion: tibial tuberosity
A
Muscle group: quadriceps
18
Q
Define agonist
A
Muscle primarily responsible for movement
19
Q
Define antagonist
A
Muscle which opposes the action of the agonist
20
Q
Define synergist
A
Assists the agonist in making the action more efficient
21
Q
Define fixator
A
Special synergists which help to prevent movement at muscle origin
22
Q
Example of classification of muscle by action:
Flexion of forearm
A
- Agonist: brachialis
- Antagonist: triceps brachii
- Synergist: biceps brachii
- Fixator: pectoralis minor
23
Q
Example of classification of muscle by action:
Abduction of the arm
A
- Agonist: deltoid
- Antagonist: latissimus dorsi
- Synergist: supraspinatus
- Fixator: trapezius
24
Q
What is a first class lever (EFL)?
A
Balanced level system like the human skull on the neck
25
What does E, F, and L stand for in class levers?
E= Effort
F= Fulcrum
L= Load
26
What is a second class lever (FLE)?
Sacrifices speed and range of motion for force
27
What is a third class lever (FEL)?
Favors speed and range of motion over force
28
What are groups of muscles covered by?
Deep Fascia
29
What are each individual (not a group of) muscles covered by?
Epimysium
30
What are fascicles in muscles covered by?
Perimysium
31
What are individual muscle fibers (cells) in fascicles covered by?
Endomysium
32
What are the four structural levels of skeletal muscle?
1. Organ level: muscle
2. Tissue level: Fascicles
3. Cellular level: muscle fibers (cells)
4. Chemical (subcellular) level: myofibrils
33
Two facts about muscle fibers
1. Muscle cells are called fibers
2. Muscle fibers are typically 'multinucleate' due to the fact that they develop from the fusion of myoblasts
34
Define hypertrophy
Growth of muscle due to an increase in muscle cell size (think body building)
35
Define hyperplasia
Growth of muscle due to an increase in muscle cell number (think little kids)
36
How do muscle fibers grow after birth?
After birth, growth of muscle fibers happen by hypertrophy, muscle fibers cannot undergo mitosis
37
How can satellite myoblasts grow after birth?
Satellite cells have the ability to undergo mitosis after birth to aid in muscle regeneration
38
What are the three C's of skeletal muscle physiology
1. Conduction of electrical signals
2. Control of muscle contraction
3. Contraction of muscle
39
Discuss the conduction of electrical signals
* It is the result of excitation of a muscle fiber
* Occurs along the sarcolemma (the plasma membrane of skeletal muscle fibers)
40
Discuss the control of muscle contraction
* Is accomplished by regulation of the activities of the smooth ER of skeletal muscle fibers (in muscle fibers, the smooth ER is called the 'sarcoplasmic reticulum' or 'SR'):
1. Ca2+ release (by E-C COUPLING) from the SR starts contraction
2. Ca2+ recovery later by the SR stops contraction
41
Discuss contraction of muscle
* Is carried out by the CROSS BRIDGE CYCLE
* Results from the shortening of organelles called myofibrils in the cytoplasm of skeletal muscle fibers
42
Define excitation
The events that transmit an electrical signal from a motor neuron to a muscle fiber
43
What does the arrival of the motor neuron AP result in in excitation?
Results in the generation of an AP in the skeletal muscle fiber membrane (sarcolemma)
44
Define excitation-contraction (EC) coupling
The events that connect excitation to contraction
45
What does skeletal muscle AP trigger?
Triggers release of Ca2+ from the sarcoplasmic reticulum (SR) into the sarcoplasm of the skeletal muscle fiber
46
Define contraction in the terms of physiological events of skeletal muscle fiber contraction
The events that cause the sarcomeres of the muscle fiber to shorten
47
When enables the contraction cycle to begin?
Ca2+ binds to torponin
48
Define relaxation
The events that cause the sarcomeres of the muscle fiber to return to resting length
49
What triggers the end of the contraction cycle
Removal of Ca2+ from the sarcoplasm
50
Since the activation of skeletal muscle is voluntary, what is required?
Requires an action potential to be sent from the central nervous system (CNS)
51
What does the arrival of the motor neuron AP at the neuromuscular junction always result in?
Always results in the generation of an AP in the skeletal muscle fiber's sarcolemma. This is called neuromusclar transmission
52
Difference between the endomysium and sarcolemma
Endomysium is the external covering of the muscle fibers and the sarcolemma is the internal membrane covering of the muscle fiber
53
What does the neuromuscular junction look like and what is its function?
It governs the muscle fiber to contract and without it the muscle fiber dies
54
What do somatic motor neurons synapse with?
Skeletal muscle
55
What is a critically important fact about neuromuscular junction?
There is only one connection (one NMJ) between any skeletal muscle and the alpha-motor neuron that triggers its contractions
56
What is an alpha (a)-motor neuron also called?
Axon collateral of somatic motor neuron
57
Where does neuron send the nerve impulse?
Down each axon branch to the end of all the axon terminals where the NMJs are
58
What is the first event in neuromuscular transmission?
Action potential arrives at the synaptic end bulb of motor neuron and causes opening of voltage gated Ca2+ channels
59
What is the second event in neuromuscular transmission?
Synaptic vesicles containing the neurotransmitter acetylcholine (ACh) undergo exocytosis
60
What is the third event in neuromuscular transmission?
ACh is released into the synaptic cleft and rapidly diffuses across to bind to ACh receptors on the sarcolemma (motor end plate).
61
What is the fourth event in neuromuscular transmission?
ACh receptors open and allow Na+ to enter into the muscle sarcoplasm, generating an action potential along the sarcolemma
62
What is the fifth event in neuromuscular transmission?
ACh is quickly broken down to acetate and choline by Acetylcholine Esterase (AChE) for recycling. (ACh also diffuses away)
63
Summarize the Neuromuscular Transmission (Excitation)
64
What is step 1 in EC Coupling?
Skeletal muscle sarcoleema forms tunnels (T-tubules) which travel into the cell.
65
What do T-tubules do in EC Coupling?
T-tubules travel between 'terminal cisternae' of the SR
66
What is the second step of EC Coupling
AP runs along the sarcolemma and T-tubules
67
What is step 3 of EC Coupling?
AP Triggers release of Ca2+ from SR. Ca2+ diffuses into sarcoplasm and myofibrils
68
What is the fourth step of EC Coupling?
Ca2+ binds to troponin, which changes shape and pushes tropomyosin over on thin filament to reveal myosin binding sites
69
What happens at the end of the EC Coupling?
Contraction cycle starts and SR Ca2+ recovery starts
70
Summarize Exitation-Contraction coupling
1) AP Runs along sarcolemma, continues into T-tubules
2) Triggers release of Ca2+ from SR
3) Ca2+ diffuses into sarcoplasm and myofibrils
4) Ca2+ binds to troponin on thin filament
- Myosin binding sites on actin are exposed
5) Crossbriges form -\> tension is generated
(Starts contraction cycle)
71
What is the first step of relaxation
When APs stop arriving at the NMJ, the repeating 'trigegrs' to release Ca2+ from the SR stop
72
What is the second step of relaxation
Active Ca2+ transporters in the SR membrane pump Ca+ back into the SR
73
What is the third step of relaxation?
Cytoplasmic Ca2+ decrease
74
What is the fourth step of relaxation?
As Ca2+ falls, Ca2+ comes off troponin - the myosin binding sites on actin are re-covered by tropomyosin.
75
What is the fifth step of relaxation
Crossbridge cycling stops and tension drops
76
What is the final step of relaxation?
Titin brings the sarcomere back to resting position
77
What is the main anatomical part of the muscle fiber that is involved in conduction?
'Sarcolemma' (plasma membrane)
* Surrounds 'sarcoplasm' (cytoplasm)
* Forms 'transvers tubules' (T-tubules) that tunnel through the muscle fiber
78
What is the main anatomical structure involved in control (second C in muscle physiology) and what are its functions?
'Sarcoplasmic Reticulum' (Smooth ER) - stores Ca2+
* Close proximity to T-tubules
* Surrounds myofibrils
79
What are some primary functions of skeletal muscle?
* Does what we tell it to
* Eat when we tell it to
* Contract when we tell it to
* Relax when we tell it to
80
What is the purpose of an action potential?
To open a calcium channel where acetoholine is then released
81
What causes an action potential to start?
Sodium ions rush into the structure
82
What is the immediate source of energy to support development of tension?
ATP
83
What does hydrolysis by myosin head group fuel?
Fuels tension generation using ATP
84
What does hydrolysis by the Ca2+ pump of the SR support?
Supports relaxation using ATP
85
What two processes make up energy metabolism in the cell?
Anaerobic (glycolysis) and aerobic (glycolysis and oxidative phosphorylation)
86
Does aerobic or anaerobic metabolism make more energy?
Aerobic metabolism
87
Where are the 4 places ATP come from?
1. Cell 'pool' of ATP
2. Creatine phosphate (CP) 'pool'
3. Anaerobic Glycolysis (glucose breakdown)
4. Aerobic metabolism
1. Glucose (from glycogen)
2. Fatty Acids (from lipids)
3. Amino Acids (from proteins
88
Is ATP 'stored'?
No, ATP is not stored. There is only enough to support a person for 2 seconds of maximal forc at a time in the cell 'pool' of ATP
89
What does Creatine phosphate do?
Creatine phosphate stores 'high energy phosphate. Thid pool had enough phosphate to support 15 seconds of maximal contractions
90
What is the reaction of CP and ATP after a meal vs during exercise
After a meal
: ATP + C -\> ADP + CP
During and excersciencee
: ADP + CP -\> ATP + C
91
What is creatine?
A small amino acid-like molecule that is synthesized in the liver kidney snd psncrease and transported to muscle fibers
92
What happens in a relaxed muscle fiber?
Creatine phosphate is 3-6 times more plentiful in ATP
93
Discuss glycogen
* Occurs in the cytoplasm
* Occurs rapidly
* Cans support for roughly 2 min of contraction
* Used anaerobically - glycolysis
94
Discuss aerobic metabolism
* Occurs in glycogen, fat, and protein
* Can support 40 min to several hours of contraction (intensity dependent)
95
Discuss resting, moderate, and peak activity and aerobic production of ATP
1. Resting - aerobic production of ATP
1. Supports activity and buildup of CP pool
2. Moderate - aerobic production of ATP increases
1. Supports activity, but no CP buildup
3. Peak - aerobic production of ATP maximal; as O2 becomes limiting, anaerobic metabolism fills need
1. CP depleted - lactic acid builds up (increase of H+)
96
What are three sources of fatigue?
Psychological -\> Nervous system -\> Muscle
97
What is the major cause of fatigue?
Failure of EC coupling because of increase in [Pi]cell
* Due to breakdown of creatine phosphate
* Inhibits Ca2+ release from SR
98
What are other factors that increase fatigue?
Includes insufficient oxygen, depletion of glycogen, ADP and lactate build up
99
What is the Cori Cycle?
The contribution of lactic acid from the muscles to the liver that converts to glucose in the liver that fules the muscles.
* Aerobic cellular respiration in the heart, kidneys, and skeletal muscle also contributes to the elimination of lactate
100
What is the cost of resetting the system after exercise?
O2 debt aka. excess post-exercise oxygen consumption
Two things that happen:
1. Metabolizing lactic acid
2. Repair of tissue
101
What are some reasons for elevated O2 consumption after exercise?
1. Lactic acid conversion back to glycogen in the liver (cori cycle)
2. Resynthesize creatine phosphate
3. Replace oxygen remobed from myoglobin
4. Repair
5. Other reasons...
102
Define muscle twitch
Contraction arising from a single electrical stimulus. Ex. an action potential
103
What are the three periods of a muscle twitch?
1. Latent
2. Contraction
3. Relaxation
104
What happens during the latent period and how long does it last?
* 2 msec or less
* Action potential sweeps over the sarcolemma
* Ca2+ is released from the sarcoplasmic reticulum
* No change in tension
105
What happens during the contraction period and how long does it take?
* 10-100 msec
* Ca2+ binds to troponin
* Myosin-bindinh sites on actin are exposed
* Crossbridge cycle begins and continues
* Peak tension develops
106
What happens during the relaxation period and how long is it?
* 10-100 msec
* Ca2+ transported back into sarcoplasmic reticulum
* Myosin-binding sites on actin are covered by tropomyosin
* Crossbridge cycle ends (Myosin can no longer to sites on actin)
* Tension decrease
107
Observe tension vs time chart for different anatomical parts
108
Define tetanus
* 'Summation over time (Temporal summation) of individual twitches
* Tetanus (temporal summation) is a mechanism for increasing tension
* Each hump in the charts show that more and mpre Ca2+
109
Define motor unit
A motor neuron and all the muscle fibers (cells) it innervates
110
How can summation be spatial?
By activating (aka recruitinhg) increasing numbers of motor units, tension can be increased.... "spatial summation"
111
Discuss motor units and the 'Size Principle'
* The first motor units recruited are small (innervate few fibers)
* The result is fine, carefully controlled increase in tension
* As more force is required, larger motor units are recruited
112
Analyze the size principle graph for standing to jumping
113
Define isometric contractions
'Same length'
* Muscle generates tension but does not shorten
* every contraction begins isometrically...
114
Define isotonic contraction
* 'same tension'
* after sufficient tension is generated to move the 'load' the muscle shortens
* Two types: 1) concentric; 2) eccentric
115
Define concentric contraction
When developed tension is sufficient to move the load, the muscle shortens
Effort \> Load
116
Define eccentric contraction
As tension decreases and the load exceeds tension, the muscle lengthens
Load \> effort
117
What are three strategies to increase force?
1. Increase motor unit recruitment = spatial summation
2. Increase frequency of stimulation = temporal summation
3. Optimal muscle length as start of contraction
1. Peak tension is developed at an intermediate muscle (or sarcomere) length. This is due to the length-tension relationship
118
Look at the length-tension relationship
119
Isometric vs isotonic concentration
120
Discuss conduction
* Is the result of excitation of a muscle fiber
* Sarcolemma (plasma membrane)
* Surrounds 'sarcoplasm' (cytoplasm)
* Forms 'transverse tubules' ('T-tubules') that tunnel through the muscle fiber
121
Discuss control of skeletal muscle physiology
* by Ca2+ (released by EC Coupling and later recovered)
* Sarcoplsmic reticulum
* Close proximity to T-tubules
* Surrounds myofibirils
*
122
Look at the relationship between SR and myofibrils
123
Discuss contraction
* Thanks to the cross bridge cycle
* Myofibrils
* Longitudinal bundles of protein filaments (primarily made of the proteins actin and myosin) inside muscle fibers
* Each myofibril has repeating units called 'sarcomeres'
124
What is the cause of the striated appearance?
The banding (striated) appearance of a muscle fiber is due to the alignment of all sarcomeres in all myofibrils inside the sarcoplasm
125
Three muscle proteins
* Contractile proteins
* Actin and myosin
* Regulatory proteins
* Troponin and tropomyosin
* Structural proteins
* Titin, dystrophin, a-actinin, myomesin, nebulin
126
Discuss Actin in contractile proteins
1. Actin
1. Found in thin filaments
2. Has myosin binding sites for crossbridge formation with myosin
127
Discuss myosin in contractile proteins
1. Myosin
1. Motor protein found in thick filaments
2. Has myosin head that binds to the myosin binding site on actin and forms crossbridge during muscle contraction
128
Discuss tropomyosin and troponin in regulatory proteins
1. Tropomyosin
1. Found in thin filaments
2. Covers the myosin binding sites on actin when muscle is relaxed
2. Troponin
1. Found in thin filaments
2. Holds tropomyosin in place when muscle is relaxed
3. During contraction, calcium binds to troponin and causes a conformational change that shifts tropomyosin away from the myosin binding sites on actin -\> exposes the binding sites to allow crossbridge formation
129
Discuss titin in structural proteins
* Spans half of each sarcomere from Z disc to M line
* Stabilizes the position of the thick filament; gives muscle its elasticity and extensibility; and helps the sarcomere return to resting length after contraction
130
What is strong evidence for exercise benefits?
* Lower risk of early death
* Lower risk of coronary heart disease,
stroke, high blood pressure, adverse
blood lipid profile
* Lower risk of type 2 diabetes
* Lower risk of metabolic syndrome
* Lower risk of colon and breast cancer
* Prevention of weight gain
* Weight loss, particularly when
combined with reduced calorie intake
• Improved cardiorespiratory and
muscular fitness
* Prevention of falls
* Reduced depression and better
cognitive function (for older adults
131
What is moderate to strong evidence for exercise benefits?
* Better functional health (for older
adults)
• Reduced abdominal obesity
132
What is moderate evidence for exercise benefits?
* Lower risk of hip fracture
* Increased bone density
* Lower risk of lung and
endometrial cancer
• Weight maintenance after weight
loss
• Improved sleep quality
133
What does exercise affect?
* Natural pain relievers
134
What are some CDC Physical activity recomendations for adults?
Aerobic activity
- 150 min/week at moderate intensity
- Split into \>10 min block
Muscle strengthening activity
- At least one set of 8-12 repetitions
- 2 days/week at moderate to high intensity working major muscle groups
Balance activities for older adults
-3 or more days per week
135
What is the basic principle of exercise and response of muscle:
Muscle will change in response to the stresses it encounters
136
What two things does exercise require?
1. Increase energy utilization (endurance training)
2. Increased force production (strength training)
137
Look at the exercise effects on muscles
Increased angiogenesis (development of new blood vessels)
138
What are some effects of exercise on muscle?
- Increased angiogenesis
- Higher density of mitochondria
- Increased cross sectional area
139
What is muscle hypertrophy?
Each muscle fiber increases in diameter -\> increased # of myofibrils
More sarcomeres in parallel = more cross bridges = more force
140
What is the role of satellite cells in muscle hypertrophy?
141
What factors activate the satellite cells?
* Strength training causes micro tears in the myofilaments, z-lines and connective tissues
* Damage attracts macrophages
* Macrophages release cytokines and growth factors
* Cytokines and growth factors stimulate proliferation and differentiation of satellite cells
142
Who does Nicy waub?
Da Kayee
143
What are muscle changes in strength vs endurance training?
144
Speed (velocity) X strength (force) =
= Power regarding muscle performance
145
What is endurance?
Sustained activity: Type of metabolism (aerobic vs anaerobic)
146
What are three different fiber (skeletal muscle) types?
1. Slow fiber: slowly contracting; aerobic metabolism
2. Fast fibers: rapidly contracting; anaerobic metabolism
3. Intermediate fibers: relatively fast contracting; primarily anaerobic
\*\*\*Within a motor unit, all fibers are the same type
147
Discuss slow fibers
(called SO for slow oxidattive or type I)
1. Low speed - slow myosin ATPase
2. High resistance to fatigue - relies on aerobic metabolism
1. High aerobic capacity
1. Many mitochondria
1. High myoglobin content
1. Dense capillary supply (for O2 delivery)
148
Discuss fast fibers
(Called FG for fast-glycolytic or type IIX)
1. High speed - fast myosin ATPase
2. Low resistance to fatigue - relies on anaerobic glycolysis
1. Low aerobic capacity
1. Few mitochondria
1. Low myoglobin content
149
What is myoglobin and what is it responsible for?
* 152 amino acid protein containing a heme (iron containing) prosthetic group for O2 binding
* Binds or releases on molecule of oxygen at a time
* Responsible for muscle's red color
* Abundant in diving mammals
150
Discuss intermediate fibers
(called FOG for fast-oxidative/glycolytic or Type IIA)
1. Moderate speed - intermediate myosin ATPase
2. Intermediate resistance to fatigue
1. Primarily relies on glycolysis, but has much high aerobic capacity than FG fibers
151
What are slow oxidative fiber characterists?
152
What are fast oxidative glycolystic fiber characteristics?
153
What are fast glycolytic fiber characteristics?
154
What is a common muscle composition for humans?
* Most muscles are mixtures of fast and slow motor units
* In humans a 50:50 mix is common with much individual variability
* The proportion of fast vs slow motor units is determined genetically
155
What is muscle hypertrophy? what is hyperplasia?
* Muscles become stronger when the muscle fibers in them add more myofibrils, a process called hypertrophy
* To grow a muscle by adding cells (mitosis) is called hyperplasia. Skeletal muscle does not grow/strengthen through hyperplasia
156
What is muscle atrophy?
With disuse, muscles become weaker as muscle fibers lose myofibrils, decreasing in diameter. This is called atrophy
157
What type of muscle generates tension?
ALL MUSCLE (skeletal, cardia, and smooth)
158
What are the two common themes that are underlying mechanisms that all three muscle types rely on?
1. Sliding filaments (actin and myosin)
2. Regulation of cytoplasmic [Ca2+]
1. Needed for contractions
159
What does the heart muscle do?
Pumps blood
160
What type of muscle function involves contraction of muscle around a confined volume, increasing the pressure so the fluid can be pushed through the circulatory system
Cardiac muscle
161
What are some cardia muscle structural features? (compared to skeletal muscle)
* Smaller cells (branched)
* Less extensive T-tubule and SR system
* Myofibrils also organized into sarcomeres
* Extensive cell-to-cell interactions called interecalated discs, and they contain
* Sarcoplasm-sarcoplasm channels called gap junctions
* Desmosomes
162
What does the microscopic anatomy of cardiac muscle look like?
163
What does a sarcomere on a myofibril in a microscopic cardiac muscle picture look like?
164
What are some cardiac muscle functional issues? (similarities to skeletal muscle) regarding sliding filament and Ca2+ release
* The sliding filament model still applies
* Crossbride cycling occurs
* Ca2+ interacts with regulatory proteins on the thin filament
* Ca2+ release by the SR is NOT sufficient to support cardiac muscle concentration!
* There is an obligatory need for extracellular Ca2+
* Entry of extracellular Ca2+ is required on a beat-to-beat basis
165
What are some cardia muscle functional issues (differences with skeletal muscles)?
* Contraction is NOT initiated by an electrical signal from the nervous system
* Cardiac cells show 'authorhythmicity'
* Electrical (and contractile) activity is stated by 'pacemaker cells' -\> spontaneous generation of APs
* There are no motor units, and every cardiac cell contracts with every heartbeat
* The electrical signal (the cardiac muscle action potential) moves from cell-to-cell through gap junctions
* Every contraction is a twitch (no cardiac tetanus)
* Nervous inpit influences the rate and strength of contraction
* Rate change is changed by acting on pacemaker cells
* Strength is changed by altering Ca2+ delivert from the extracellular fluid into the sarcoplasn
* The single twitch of cardia muscle have a very long time course (hundreds of milliseconds)
* This reflects the characteristics of the 'cardiac action potential' which lasts 300 milliseconds (more than 30 times longer than a skeletal muscle action
166
what does smooth muscle do?
* Smooth muscle fibers control the diameter of 'tissue tubes' such as blood vessels, the intestines
* There are many types of smooth muscle, and they have common structural features
* One small, single nucleus
* Lack of a clearly-organized structure
* Smooth muscle fibers do NOT contrain sarcomeres
* Smooth muscle fibers do NOT have an extensice T-tubule/SR system
167
Even though smooth doesnt have sarcomeres...
There are think (myosin) and then (actin) filaments with a rudimentary overlapping organization
168
What is the key to generation of tension in smooth muscle?
* Regulation of cytoplasmic Ca2+
* BUTTT that regulation is very different from that in skeletal and cardia muscle
* Ca2+ does not interatc with regulatory proreins on the thin filament to permit myosin head groups to bind
