Module 4 - Skeletal Muscle Physiology Flashcards
1
Q
What is the Somatic Nervous System?
A
• PNS associated with the VOLUNTARY control of body movements via skeletal muscles
• Alpha Motor Neurons and Gamma Motor Neurons
2
Q
What is the Autonomic Nervous System?
A
Sympathetic Nervous System
Parasympathetic Nervous System
3
Q
What are Upper Motor Neurons?
A
• Motor neuron signals travel from brain to spinal cord
• A neuron that extends from brain and synapses with a lower motor neuron, commonly in the lower spinal cord
• Corticospinal tract and Corticobulbar tract
4
Q
What are the Lower Motor Neurons?
A
• Motor neuron that originates (cell body) in the spinal cord/brainstem and send signals to skeletal muscles
• Anterior grey horn of spinal cord and cranial nerve nuclei
5
Q
Where does the Upper Motor Neurons originate?
A
Cerebral Cortex
6
Q
Upper Motor Neurons follow which 2 pyramidal tracts?
A
Corticospinal Tract
Corticobulbar Tract
7
Q
Where do Lower Motor Neurons originate?
A
• Spinal Cord: Anterior Grey Horn
• Brainstem: Pons and Medulla
8
Q
What are 3 types of lower motor neurons?
A
Alpha Motor Neuron
Beta Motor Neuron
Gamma Motor Neuron
9
Q
What do Alpha motor neurons innervate? What action does this motor neuron lead to?
A
Extrafusal skeletal muscle
Muscles contraction
10
Q
What do Gamma motor neurons innervate? What action does this motor neuron lead to?
A
Intrafusal muscle fibers
Function is to adjust the sensitivity of the muscles spindles
11
Q
What are extrafusal skeletal muscle fibers?
A
• Primary muscle fiber of skeletal muscle- leads to muscle contraction
• Generates contraction process- creating tension and movement
• Innervated by alpha (α) motor neurons
12
Q
What are intrafusal skeletal muscle fibers? What is the main function?
A
• Smaller muscle fibers found within muscle spindles that are
embedded within the extrafusal skeletal muscle fibers
• Has SENSORY and MOTOR innervation
• SENSORY: Basically, stretch receptors
• Detect the amount and rate of change in muscle length
• MOTOR: Allows for muscle contraction
• Of the fiber- controlling sensitivity of the sensory portion
• EFFERENT: Gamma (γ) motor neurons Provides proprioception
• AFFERENT: Group Ia and II sensory fibers
information
13
Q
How is the force of muscle contraction “controlled?”
A
The number of motor units that are stimulated
14
Q
What is the order in which motor units fire?
A
Small motor units fire first, then larger ones, then larger ones
15
Q
T or F
The ANS and UMN and LMN are part of the somatic nervous system.
A
F
16
Q
T or F
LMNs are found in the CNS and PNS.
A
T
17
Q
All of the options are true regarding intrafusal muscle fibers, except?
• A. It contains sensory and motor functions
• B. Alpha lower motor neurons innervate intrafusal muscle fibers
• C. Assists with proprioception
• D. Assists with detection of rate of muscle length
A
B
18
Q
T or F
Upper motor neurons synapse with extrafusal muscle fibers via a neuromuscular junction.
A
F
19
Q
T or F
A motor unit is all the gamma lower motor neurons and the extrafusal muscle fibers it innervates.
A
F
20
Q
What are the components of the NMJ?
A
• Axon terminal of lower motor neuron
• Neurotransmitter vesicles
• Synaptic cleft
• Sarcolemma of skeletal muscle
• Cholinergic nicotinic receptors
• Bind acetylcholine
• Ligand gated sodium (Na +) channels
**Remember, each branch of the axon terminal of the LMN will make a junction/synapse with ONE skeletal muscle fiber.
21
Q
What is the sacrolemma?
A
Plasma membrane of skeletal muscle
22
Q
What is the Motor End Plate?
A
• Indented to fit the axon terminal
• Contains cholinergic nicotinic receptors that bind acetylcholine
• Ligand gate sodium (Na +) channels
23
Q
What type of channels are found outside the motor end plate?
A
Voltage gated sodium (Na+) channels
24
Q
What are the steps of the a potential of the NMJ?
A
• 1. Action potential is propagated to axon terminal
• 2. Action potential stimulates voltage gated calcium (Ca 2+) ion channels to open
• 3. Calcium (Ca 2+) ions cause the release of acetylcholine into the synaptic cleft
• 4. Acetylcholine binds to Sodium (Na +) ion LIGAND gated channels on the skeletal muscle
• It is an excitatory stimulus- brings the membrane potential closer to threshold
• 5. If the graded potential is strong enough an action potential is generated and in travels in both directions of the plasma membrane
• Generated by activating Sodium (Na +) VOLTAGE gated ion channels
• 6. Acetylcholine is broken down in synaptic cleft and prevents action potential in skeletal muscle from continually being generated
25
Why does calcium (Ca2+) ion rush into the axon terminal?
Bind to neurotransmitter vesicles causing them to fuse with membrane
26
What happens when ACh binds to cholinergic nicotinic receptors?
Bind 2 ACh molecules
Allow for Na+ to fish into the cell
27
What potential does this cause on the motor end plate of the sarcolemma?
Graded potential
28
Where does the action potential travel along?
Along the sacrolemma and down the T-tubules
29
Why does the action potential stop? What is responsible for this?
Must break down ACh within the synaptic cleft
Enzyme break down ACh - Acetylcholinesterase
30
What makes ACh in the axon terminal?
Choline Acetytransferase
31
T or F
Voltage gated sodium channels open in the axon terminal to stimulate the release of a neurotransmitter.
F
32
Describe the characteristics and role of the cholinergic nicotinic receptors.
Ligand gated sodium channels that bind acetylcholine found in the motor end plate initiating an action potential
33
Where are sodium voltage gated channels located on the sarcolemma and what role do they have?
Located just outside of the motor end plate and once activated will generate an action potential within the muscle cell
34
What role do T-tubules have with the neuromuscular junction?
Allow for the action potential process to be transmitted deep into the skeletal muscle tissue
35
What are the muscle functions?
• 1. Body Grooving Movement
• Conscious movement of skeletal muscles- get your groove on!
• 2. Postural Stability
• Stand up straight!
• 3. Movement & control of various internal organs and fluids
• Cardiac and smooth muscle contraction
• Sphincters, blood, urine, defecation
• 4. Heat Production/Body Temperature Regulation
• Consume that ATP!
• 5. Glycemic control
• Skeletal muscles love that ATP- need a lot of glucose!
36
What are muscle characteristics?
• Excitability
• Muscle cells have the capability of responding to stimuli by changing the membrane potential
throughout the cell
• Conductivity
• Muscle cells have the capability of generating an action potential and propagating it throughout
the cell
• Contractility
• Muscle cells can shorten, yes shorten in size
• Extensibility
• Muscle cells can lengthen too, yes get longer in length
• Up to 3x the length to when they are contracted
• Most cells lyse open with any little stretch placed upon them
• Elasticity
• Muscle cells are elastic- ”snap” back their original length when stretched
37
What are the general muscle anatomy?
• Tendon
• Fascia
• Endomysium
• Fascicles
• Perimysium
• Muscle fiber/cell
38
What does the sarcoplasm contain?
• Glycogen
• Storage form of carbohydrates
• Myoglobin
• Protein that contains heme
• Red in color
• Storage device for oxygen
39
What percentage is skeletal muscle of your body weight?
40%
40
What statement is true of sarcomeres?
A. It contains thick filaments that overlap on z discs
B. The H zone is where the thick and thin filaments overlap
C. Sarcomeres are found in myofibrils
D. It extends from I band to H band
C
41
T or F
Glycogen is a storage form for oxygen in the sarcoplasm.
F
42
All of the statements are true, except?
A. A sarcomere consists of thick and think filaments
B. The triad region consists of the junction of terminal cisternaes and transverse tubules
C. Sarcoplasmic reticulum surrounds each myofilament
D. Skeletal muscle cells have multiple nuclei
C
43
What option is true regarding myofibrils?
A. The thick filament consists of tropomyosin and actin
B. The thin filament has two binding sites
C. The thick and thin filament are arranged in sarcomeres that allow for
muscle contraction
D. Calcium binds to actin to allow the thick filament to bind to the thin
filament
C
44
Describe how the thick filament binds to the thin filament.
Heavy chain of myosin’s head has an actin binding site
45
What are the contraction steps?
Step 1: Excitation
• Action potential transmission
Step 2: Excitation-Contraction Coupling
• Release of calcium ions
Step 3: Contraction
• Crossbridge of myofilaments
• Power Stroke of myofilaments
Step 4: Relaxation
• Release of the myofilaments
46
What is activated when the action potential traveling down the T-tubules?
1. Dihydropyridine receptor (DHPR)
2. Ryanodine receptor
47
What is the Digydropyridine Receptor (DHPR)? Where are they found?
• Found on the sarcolemma of the T-tubule
• Are voltage-gated calcium (Ca 2+) ion channels
• AKA: L-type calcium channel
48
What is Ryanodine Receptor? Where are they found?
• Found on the membrane of the Sarcoplasmic Reticulum
• Intracellular calcium channel
• Mediate the release of calcium ions from the sarcoplasmic reticulum
• Activated (opens) when DHPR is activated
49
If the _______ is activated - it activates (opens) the _______ receptor. Calcium ions FLOOD the sarcoplasm.
DHPR
Ryanodine
50
What is the sarcoplasm filled with?
Calcium (Ca2+) ions floods the sacroplasm
51
What happens after calcium (Ca2+) ions binds to troponin?
It causes a configurational shift which moves tropomyosin off actin’s active sites to bind the thick filament (myosin heads).
52
What is it called when actin and the myosin heads bind together?
Cross Bridge
53
What is it called when the myosin head pulls the thin filament toward the M line of the Sarcomere?
Power Stroke
54
What happens to the actin and myosin during the cross bridge process?
• Actin’s active sites must be ”open”
• Myosin’s heads must be in its HIGH ENERGY CONFIGURATION
• AKA ”Activated” position
55
What happens with the myosin head during the power stroke process?
• Myosin head (HIGH ENERGY CONFIGURATION) is bound to actin
• Myosin releases energy going from the HIGH ENERGY CONFIGURATION to the LOW ENERGY CONFIGURATION
• This pushes the thin filament toward the M line
56
What happens when the power stroke process is completed?
• Myosin head releases ADP from ATP binding site on myosin head
• For myosin head to release from Actin- IT MUST BIND A NEW ATP MOLECULE
• Then it hydrolyzes the ATP to put the myosin head in its HIGH ENERGY
CONFIGURATION
• Called the RECOVERY STROKE
• Cross Bridge – Power Stroke occurs again
57
Do we want our muscles to stay contracted indefinitely?
At some point we want the muscle to stop contracting
UMN ceases AP on LMN, no more AP releasing ACh, no more AP within sarcolemma
58
What is the SERCA?
Sarcoendoplasmic reticulum Ca 2+-
• Pumps calcium (Ca 2+) ions back into the sarcoplasmic reticulum
• Calcium (Ca2+) ions that dissociate from troponin are pumped back up into the sarcoplasmic reticulum
• Requires energy
59
What is isometric contractions?
Generate force without changing the length of the muscle
60
What is isotonic contractions?
Generate force by changing the length of the muscle and can be concentric contractions or eccentric contractions
61
What is concentric contractions?
Causes muscles to shorten, thereby generating force
62
What is eccentric contractions?
Cause muscles to elongate in response to a greater opposing force
63
T or F
The DHP receptor is activated when calcium ions enter the sarcoplasm.
F
64
What is the function of calcium ions in muscle contraction?
Calcium binds to troponin, moving tropomyosin off of actin’s binding sites allow myosin (binding site on its head) to bind to actin
65
T or F
Activation of the ryanodine receptor allows for the release of calcium ions into the sarcoplasm.
T
66
What is the role of the SERCA?
SERCA is the Sarcoendoplasmic Reticulum Calcium ATPase pump that pumps calcium ions back into the sarcoplasmic reticulum helping to stop muscles fibers from contracting
67
How does myosin’s high energy configuration work?
Once the myosin head binds ATP and it is hydrolyzed, it puts the myosin head within its high energy configuration allowing it to bind to actin’s binding site (if open)
68
What does the contraction of muscles depend on?
Depends on the production and availability of ATP and the type of muscle fiber
69
What are the 4 ways ATP is produced?
• Skeletal muscle does have minor storage of ATP
• Aerobic (Cellular respiration) (Oxidative phosphorylation)
• Anaerobic (Glycolysis) (anaerobic fermentation)
• Creatine phosphate (CP)
70
What are the 3 types of muscle fibers?
• Slow oxidative
• Fast oxidative
• Fast glycolytic
71
What breaks the myosin-actin cross-bridge?
ATP
72
What form do muscle cells store a small amount of ATP?
Glycogen
73
What is the average amount of stored ATP would provide enough energy to perform maximum exercise?
Several seconds
74
What must happen in order to perform sustained periods of muscle contraction?
ATP must be generated within the muscle cells
75
What happens in glycolysis?
Glucose catabolized into 2 pyruvate molecules and 2 ATP molecules
76
Oxygen is present to catabolize pyruvate in aerobic respiration or anaerobic respiration? Which one is without oxygen?
With oxygen aerobic respiration
Without oxygen anaerobic respiration
77
What is another name for aerobic respiration?
Cellular Respiration
78
How many ATP are generated per glucose molecule in aerobic respiration?
38 ATP
79
What is another name for Anaerobic respiration?
(Anaerobic Glycolysis) (Anaerobic Fermentation)
80
How many ATP are generated per glucose molecule in anaerobic respiration?
Only 2 ATP are generated per glucose
81
Which respiration type is required for exercise periods longer than 30 seconds?
Aerobic
82
What is pyruvate catabolized into in the absence of oxygen?
Lactate
83
What is another name for Creatine Phosphate?
Phosphocreatine, CP
84
What happens during Creatine Phosphate?
Rapidly donate a phosphate group to ADP to form ATP and creatine under anaerobic conditions
Reaction of phosphocreatine + ADP to ATP + creatine is reversible
85
What activities is creatine phosphate use for?
High intensity / Explosive Activities
• Only for a few seconds
86
T or F
Oxygen presence is necessary for Type IIb muscle fibers to contract?
F
87
T or F
Myoglobin helps to make ATP for muscle contraction?
F
88
T or F
Creatine phosphate allows for the production of ATP from ADP and provides minutes of activity
as an energy source?
F
89
What type of muscle fiber will have a red color? (Select all that apply)
A. Type I
B. Type IIa
C. Type IIb
D. Type III
A and B
90
What is myoglobin?
• Specialized protein found in skeletal muscles that stores oxygen
• Contains iron (Fe) molecule
• Importance of iron molecule in myoglobin and hemoglobin
• Provides the redness color to muscle
• Doesn’t directly make ATP; provides the oxygen
91
What determines the source of energy a muscle cell uses?
High intensity/Explosive activities?
About 30 seconds of activity?
Beyond 30 seconds to hours of activity?
Duration and intensity
• High Intensity/Explosive Activities
• ATP Storage
• Creatine Phosphate
• ~30 Seconds of Activity
• Anaerobic Respiration
• Beyond 30 Seconds to Hours of Activity
• Aerobic Respiration
92
What are the other names of Type I Muscle fibers?
Type IIa muscle fibers?
Type IIb muscle fibers?
• Slow oxidative (SO); Slow Twitch
• Type I Muscle Fibers
• Fast oxidative (FO); Glycolytic
• Type IIa Muscle Fibers
• Fast glycolytic (FG)
• Type IIb Muscle Fibers
93
What are muscle fibers classified?
Classified based on how quickly they contract and resistance to fatigue
94
What does the speed of contraction directly relate to?
Related to how long it takes to complete a Cross Bridge – Power Stroke cycle
• Dependent upon how quickly ATP can hydrolyzed
• Type II fibers have a faster ATPase
• Type II fibers pump Calcium (Ca 2+) into the sarcoplasmic reticulum much faster too
95
Slow Oxidative:
Contraction Speed?
Contraction Force?
• Slower in contraction
• Slower in releasing and up taking calcium from sarcoplasmic reticulum
• Slower ATPase hydrolyzing ATP
• Low
96
Slow Oxidative:
ATP Usage?
Aerobic respiration
97
Slow Oxidative:
Type of Exercise/Muscles?
• Endurance muscles
• Postural muscles
• Running, swimming
98
Slow Oxidative:
Cellular Characteristics?
• Dense network of capillaries
• LOTS of mitochondria
• Thinner in diameter
99
Slow Oxidative:
Muscle Color?
• RED
• High myoglobin concentration
100
Slow Oxidative:
Fatigue?
Slow to fatigue
101
Type IIa (Fast Oxidative):
Contraction Speed?
Contraction Force?
• Faster in contraction (quick responses)
• Fast release and up taking calcium from sarcoplasmic reticulum
• Fast ATPase hydrolyzing ATP
• Stronger than Type I Fibers
102
Type IIa (Fast Oxidative):
ATP Usage?
• Anaerobic and Aerobic respiration
103
Type IIa (Fast Oxidative):
Type of Exercise/Muscles?
• Sprinting 400 meters
• Power lifting
• Jumping/Sprinting
104
Type IIa (Fast Oxidative):
Cellular Characteristics?
• Limited network of capillaries
• Limited mitochondria
• Thicker in diameter
• Higher levels of creatine phosphate
105
Type IIa (Fast Oxidative):
Muscle Color?
• RED
• High myoglobin concentration
106
Type IIa (Fast Oxidative):
Fatigue?
Intermediate
107
Type IIb (Fast Glycolytic):
Contraction Speed?
Contraction Force?
Contraction Speed
• Fastest in contraction
• Faster in releasing and up taking calcium from sarcoplasmic reticulum
• Faster ATPase hydrolyzing ATP
Contraction Force
• High
108
Type IIb (Fast Glycolytic):
ATP Usage?
Anaerobic respiration
109
Type IIb (Fast Glycolytic):
Type of Exercises/Muscles?
• Power lifting
• Jumping/Sprinting
• Quick bursts of movement for short
110
Type IIb (Fast Glycolytic):
Cellular Characteristics?
• Limited network of capillaries
• Limited of mitochondria
• Thickest in diameter
111
Type IIb (Fast Glycolytic):
Muscle Color?
• WHITE
• No to low myoglobin concentration
112
Type IIb (Fast Glycolytic):
Fatigue?
Fastest to fatigue
113
Where are smooth muscle general located?
• Visceral Location (walls of hollow organs)
• GI system
• Respiratory system
• Urinary system
• Reproductive system
• Blood vessels
• Eyes
• Dermis
114
What is the histological view for smooth muscles?
• Histological view
• Smaller in length and diameter
• Spindled shape
• Single nucleus
• Unconscious control
115
What are the characteristics for smooth muscles?
• Do not have striations or sarcomeres
• Do have thick and thin filaments
• Is extremely energy efficient with its oxygen consumption
• Thick and thin filaments can be linked together for a long period of time
• Maintain force for hours, days and even weeks
• Maintain tension
• Create movement (Motility)
116
What are the two types of smooth muscles?
1. Unitary Smooth Muscle (Visceral Muscle)
2. Multi-Unit Smooth Muscle
117
Where are unitary smooth muscle located? Do they have gap junctions? Do they have varicose ties?
GI tract, Uterus, Urogenital tract
Yes
No
118
Where is the unitary smooth muscle innervation?
• ANS
• Hormones
• Stretching
119
Where are multi-unit smooth muscle located? Do they have gap junctions? Do they have varicose ties?
Tunica media, Bronchioles, Eyes, Dermis
No
Yes
120
Where is the Multi-unit smooth muscle innervation?
Innervation
• ANS
• Hormones
• Not from stretching
121
What is the Intracellular Anatomy of smooth muscle?
• Actin
• Contractile filament
• Tropomyosin
• Myosin
• Contractile filament
• NO Troponin
• Calmodulin
• Regulatory protein that initiates contraction in smooth muscle
• Like troponin
• Sarcoplasmic Reticulum
• Stores and releases calcium ions
• Myosin light chain kinase (MLCK)
• Adds a phosphate group (phosphorylation) to the myosin head to active ATPase activity
• Allows for it bind to actin
• Myosin light chain phosphatase (MLCP)
• Removes the phosphate group (dephosphorylation) from the myosin head
• Inhibits ATPase activity
• Prevents it from binding to actin
122
What are the steps for contraction for smooth muscles?
• Step 1: Stimulus
• Meets potential threshold
• Step 2: Increase of ICF of Calcium (Ca 2+) ions
• From the ECF (voltage gated Ca 2+ channels) and/or Sarcoplasmic Reticulum
• Step 3: Calcium (Ca 2+) ions bind to calmodulin activating it
• Leads to activation of myosin light chain kinase (MLCK)
• Inhibition of caldesmon and calponin
• Step 4: Activated MLCK activates the myosin light chain
• Step 5: Cross bridge and Power stroke
123
What 2 functions activates calmodulin?
1. Alters calponin and caldesmon
2. Activates the enzyme: Myosin Light Chain Kinase (MLCK)
124
What happens when the intracellular calcium (Ca2+) ions decreases?
• Stimulus is removed or no longer leads to threshold potential
• Voltage gated Calcium (Ca 2+) close
• Increase uptake of Calcium (Ca 2+) ions back into sarcoplasmic reticulum
• Remove Calcium (Ca 2+) ions from the sarcoplasm back into the ISF
• Calcium (Ca2+) ATPase pump
• Calcium (Ca2+) - Sodium (Na +) Cotransporter pump
125
What happens when activity of myosin light chain phosphatase?
• Removes the phosphate from the myosin light chain
• Opposite action of active myosin light chain kinase
• Inhibits the activity of the myosin ATPase enzyme on myosin head
• Activity increases with decreased intracellular calcium (Ca 2+) ion concentratio
126
What are some characteristics of smooth muscle contractions?
• Function for long periods without rest
• Power output is low, but contractions can continue without using large amounts of energy
• Some smooth muscle can also maintain contractions even as Calcium (Ca 2+) ions are removed and myosin kinase is inactivated/dephosphorylated
128
All of the options are true regarding smooth muscle types, except?
A. Unitary smooth muscle has gap junctions
B. Multi-unit smooth muscle cells can contract independently of each other
C. Unitary smooth muscle contract as a unit
D. Multi-unit smooth muscle cells can be stimulated to contract by stretch
D
129
T or F
Latch-bridges are a class of cross-bridges in smooth muscle that are commonly found in smooth muscle sphincters.
T
130
All the options are true regarding smooth muscle contraction, except?
A. Most of the calcium that allows for smooth muscle contraction comes from the ECF
B. The myosin light chain kinase becomes activated by calmodulin
C. When the myosin head binds calcium, it can bind with actin
D. Myosin light chain phosphatase needs to be activated for smooth muscle relaxation to occur
C
