Skeletal Muscle Physiology- Allard Flashcards
(96 cards)
1
Q
What are the characteristics of smooth muscle?
A
- smooth
- involuntary
- stimulated by autonomic nervous system, hormones, stretch, and pacemaker cells
- slow, sustained contractions and low fatigability
2
Q
What are the characteristics of skeletal muscle?
A
- striated
- voluntary
- requires somatic nervous system
- rapid contractibility and high fatigability
3
Q
What are the characteristics of cardiac muscle?
A
- striated
- involuntary
- self-stimulated stimulation and ANS modification
- continuous contraction/ relaxation and no fatigability
4
Q
What are the connective tissue layerings of a skeletal muscle fiber from the inner to outer most?
A
endomysium
perimysium
epimysium
5
Q
What is the basic contractile unit of skeletal muscle?
A
the sacromere
6
Q
What protein stabilizes the myosin to the Z line and is responsible for elasticity of our muscles?
A
titin
7
Q
Which zones in the sacromere of skeletal muscle shorten?
A
H and I zone
“HI wave”
8
Q
T-tubule is continuous with the sarcoplasm reticulum (SR). What is the function of SR?
A
regulates calcium ion concentration in the cytoplasm of skeletal muscle
9
Q
Myosin, the thick filament, has what types of protein chains?
A
- heavy chains with ATPase activity and bind to actin
- light chains that are of two types: essential and regulatory
10
Q
Actin, the thin filament, is composed of globular actin molecules that come together to form what? These G-actin also have binding site for what?
A
- filamentous (F) actin
- each G-actin has binding site for myosin
11
Q
Troponin is a complex of 3 proteins that bind to what? What occurs when calcium binds?
A
tropomyosin
when calcium binds to troponin, troponin moves tropomyosin from myosin binding sites making them exposed
12
Q
What is the function of titin and nebulin?
A
titin (largest known protein): extends from z disc and runs through the core of the myosin filament; connects myosin to the Z-lines and is responsible for muscle flexibility
nebulin: binds with and stabilizes F-actin and attaches it to the Z-disc
they are for stabilizing filaments
13
Q
What is function of myomesin and dystrophin?
A
myomesin: binds myosin and titin to the M line
dystrophin: maintains structural integrity; anchors actin to the sacrolemma (deficiencies in this protein leads to muscular dystrophy)
14
Q
What is the cause of Duchenne muscular dystrophy and what does it cause?
A
X-linked recessive disease caused by a mutation in the dystrophin gene; causes loss of structural stability of myocytes
15
Q
During this process, the heads of the myosin filaments pull the actin filaments toward the M line, in part increasing the area of overlap between the thick myosin and thin actin filaments.
A
muscle shortening AKA contraction
16
Q
What is a motor unit?
A
- a somatic motor neuron plus all the skeletal muscle fibers it stimulates
- all of the muscle fibers in one motor unit contract in unison
- the motor neurons and all of the muscle cells that it innervates
17
Q
One muscle may have many motor units of different fiber types. True or false?
A
True!!
But a single motor unit has to have the same fibers
18
Q
Fibers of a single motor unit can be of different types. True or false?
A
FALSE!!!
Fibers of a single motor unit are all of the same type!!!
19
Q
Motor units are stimulated by what?
A
upper motor neurons
20
Q
What are the acetylcholine receptors on skeletal muscles called?
A
nicotinic receptor
21
Q
Where are the cell bodies of low motor neurons for skeletal muscle located and where do their axons exit and enter?
A
- cell bodies are located in the ventral horn of the spinal cord
- axons exit the spinal cord via the ventral root and enter in spinal nerves to innervate target muscles
SOMATIC motor neurons control skeletal muscle innervation
22
Q
What are the steps of excitation at the neuromuscular junction?
A
- action potential is generated and travels down the axon of the lower motor neuron
- voltage-gated calcium channels open and release calcium into the axon terminal of the neuron binding to synaptotagmin
- calcium entry causes the exocytosis of ACh into the synaptic cleft
- ACh binds its nicotinic receptors on the skeletal muscle
- nicotinic channel allows flow of monovalent positive ions (sodium into the cell and potassium out of the cell)
23
Q
What type of channels are nicotinic receptors?
A
ligand-gated channels
24
Q
How is the endplate membrane potential generated?
A
endplate membrane potential is a local change in the membrane potential of muscle fiber that is triggered by the opening of the nicotinic receptor (channel) that allow the flow of Na+ inside the cell and K+ outside of the cell; MORE Na+ flows in than K+ out allowing for a depolarizing current to occur
IT IS essentially depolarization at the motor end plate AKA graded potential.
25
What breaks down ACh in the synaptic cleft to prevent continual stimulation of the nicotinic receptors?
acetylcholinesterase: limits the impact of ACh in the synaptic cleft
26
In the neuromuscular junction, each axon terminal innervates ________muscle fiber. Each muscle fiber has a specialized region of ___________with junctional folds containing ACh receptors.
ONE
| sarcolemma
27
What macromolecules is the synaptic cleft rich in?
glycoprotein and collagen fibers
28
What is the difference between an end plate potential and an action potential?
- end plate potential occurs at the post-synaptic membrane (NMJ) with LIGAND-gated channels of Na+ AND K+; is a graded potential
- action potential occurs at the muscle membrane with VOLTAGE-gated channels of ONLY Na+
29
What is the mechanisms of botulinum toxin?
destroys the SNARE proteins responsible for the fusion and release of the synaptic vesicle content
30
This is an autoimmune disease of the NMJ where antibodies bind to nicotinic ACh receptors inhibiting contraction.
Myasthenia gravis
these binding antibodies destroy the ACh receptors thus decreasing the number of receptors that ACh can bind to
31
Chronic inflammation of myasthenia gravis causes structural changes of the NMJ in what ways?
- flattening out of the junctional folds of the sarcolemma
- spreading out of AChR and acetylcholinesterase
- 66% decrease in number of AChR
- an increased junctional gap
32
What are the initial symptoms of myasthenia gravis?
drooping of the eyelids, clumsiness
33
How is the AP in skeletal muscle different from AP in neurons?
- not much of a hyperpolarization due to potassium already reaching its equillbrium potential through the repolarization
- chloride channels play a much bigger role as to where the resting membrane potential is of the skeletal muscle
34
What is the relationship between the timing of the skeletal muscle AP and the timing of the force generation in the skeletal muscle?
the AP is done significantly before the force generation
-this means you can generate another AP (or more) and add to the contractile force of the skeletal muscle (increase in force generation)
35
What is consisted in a triad?
1 T-tubule and 2 terminal cisterns of the sacroplasmic reticulum
36
What is the function of calsequestrin within the terminal cisternae of sarcoplasmic reticulum?
it is a low-affinity, high capacity calcium binding protein that keeps the calcium concentration in the terminal regions of the SR high
-it creates an allusion that there is not as much calcium (hoards the calcium in the terminal regions of SR)
37
What is the voltage-activated protein embedded on the T-tubule that engages with the ryanodine receptor on the SR to allow for calcium release into the myoplasm?
dihydropyridine receptor
- AP changes the configuration of dihydropyridine receptor on T-tubule which in turn knocks open the ryanodine channel by changing its configuration.
- Calcium then flows into the cytosol (inside cell) to meet troponin whose been waiting for it.
38
What type of receptor is the ryanodine receptor?
calcium channel
39
What is the function of calcium binding to troponin?
tropomyosin is removed from the myosin binding sites on the actin allowing for the myosin heads to engage with the actin
40
Contraction of the skeletal is an active process and thus we need what?
ATP
41
What happens with the ADP and Pi during the power stroke?
they are released and thus no energy left in the myosin head
when ADP and Pi is release the myosin head pivots in turn pulling the actin filament toward the M line
42
In order for the myosin head to release from its binding site on the actin, what is required?
hydrolyze another molecule ATP; if not we stay in a contracted state--> rigor mortis
cross-bridge detachment occurs after ATP attaches to the myosin
43
List in order the AP of the neuron and skeletal muscle and the contraction of the skeletal muscle.
1. AP of the neuron
2. AP of the skeletal muscle
3. Contraction of the skeletal muscle
44
What is the muscle twitch?
Motor unit's RESPONSE to a single action potential of its motor neuron
-this is the SIMPLEST contraction observed in the lab
45
What are the 3 phases of the muscle twitch?
- latent period
- period of contraction
- period of relaxation
46
What occurs in the latent period of the muscle twitch?
- follows stimulation
- excitation-contraction coupling begins
- no measurable muscle tension developed
47
What occurs in the period of contraction of the muscle twitch?
- cross bridge formation occurs
| - tension develops
48
What occurs in the period of relaxation of the muscle twitch?
- calcium reentry into the SR
| - tension declines
49
What is the function of the SERCA pump on the sarcoplasmic reticulum?
It is a Ca2+ ATPase that transfers (removes) Ca2+ from the cytosol of the cell to the lumen of the SR at the expense of ATP hydrolysis during muscle relaxation.
50
List the following muscles in order of fast twitch to slow switch
- soleus
- extraocular muscle (lateral rectus)
- gastrocnemius
- extraocular muscle (lateral rectus) and gastrocnemius are fast twitch
- soleus is slow twitch
51
What are the 3 factors that affect the development of muscle tension (force generation)?
- frequency of stimulation
- number of motor units recruited
- degree of muscle stretch to begin with
52
The _______of AP will affect how much force is generated in the skeletal muscle.
frequency
-the more frequency of stimulation, the more force is generated
53
Muscles develop what kind of responses to action potential? What are the two examples of this type of response?
graded responses due to different muscle fibers that are recruited in a certain temporal order in order to generate the amount of force that we need
-they are NOT all or nothing
-TEMPORAL summation
motor unit recruitment
54
What is treppe?
- step wise increase in peak tension of individual twitches
- "warming" up of muscles of myosin head
The example she gave was
doing curls overtime it becomes easier as opposed to when you start initially.
55
Why does summation occurs? What has to happen in order for the skeletal muscle to relax?
summation occurs when muscle is stimulated to contract faster than SERCA can restore resting calcium concentration
- for the tension in the muscle to go away you need ATP and calcium removal from the cytosol back into the SR or EC fluid
- if you stimulate the muscle again before all that calcium is pumped out of the cytosol then you have extra leftover calcium which will allow contraction of the muscle again
- more troponin activated, more tropomyosin moving out of myosin-binding sites on actin, more myosin and actin engagement, more power strokes and stronger contractions
56
What is the difference between incomplete (unfused) and complete (fused) tetanus?
Incomplete tetanus: frequency of AP that allows for maximum contractions but slight relaxation between contraction creating a quivering effect
Complete tetanus: high frequency of AP that comes before the membrane begins to relax, all the binding sites are occupied (no matter how much calcium is given) allowing for sustained/smooth contraction
57
What is physiological tetanus?
complete tetanus: sustain contraction that allow for smooth movements
58
What is pathological tetanus?
incomplete tetanus due to a bacterial infection from animal feces that generate spores that can go into open wound and find terminal ending of
59
What is the result of tetanus caused by the bacterium Clostridium tetani?
- nerve impulses go unchecked by normal inhibitory mechanisms
- generalized muscular spasm are produced
60
What is the difference between localized and generalized tetanus?
- localized: develops when only the nerves supplying the affected muscle are involved
- generalized: develops when the toxin released at the wound spreads through the lymphatics and blood to multiple nerve terminals
61
What is the difference between cardiac and skeletal muscle in terms of the refractory period? What does this mean?
- no summation or tetanus in cardiac muscle
- longer refractory period in cardiac muscle (the AP lasts as long as the muscle contraction)
YOU DON'T WANT YOUR CARDIAC MUSCLE TO GO IN A STATE OF TETANUS
62
What is the length-tension relationship for the active tension?
The more cross bridges there are between myosin heads and actin, the more tension there is.
-Resting length is usually at optimal overlap of myosin and actin
63
The initial state of skeletal muscle affects tension. How?
- more stretch of muscle initially: decreasing interaction between myosin head and actin --> less tension
- more contracted state initially: more actin engaging with each other --> less tension
64
What is the length-tension relationship for the passive tension?
the tension due to the titin elastic molecule that prevents the muscle from being overstretched, giving us stability
as the muscle is stretched from the critical/resting length then the passive tension increases
passive tension is the force at which the titin molecule is pulling back AKA due in part to the elastic recoil force of titin molecules
65
Describe the length-tension curve for a typical skeletal muscle.
- at shortened lengths all force is generated actively
- as the muscle fiber is stretched beyond its resting length, passive tension begins to contribute to the total force
- if the muscle is further stretched, passive tension accounts for most of the total force
66
Upper motor neurons stimulate lower motor neuron which stimulate skeletal muscles.
FACTS!!!
67
The voltage stimulus that produces the initial contraction is called what?
threshold stimulus
68
Compare excitability of small motor units to large motor units.
small motor units are more excitable as they have a lower threshold stimulus than large motor neurons
69
Compare the fibers of small motor units to large motor units.
small motor units: slow oxidative fibers; slow twitch
large motor units: fast glycolytic fibers; fast twitch
70
What is the maximum stimulus?
a stimulus strength that recruits all motor units
71
Increased stimulus strength leads to excitation of more motor unit and _______motor units.
larger
smaller stimulus will lead to excitation of small motor units
72
What are the ways we need ATP in skeletal muscles for contraction?
- cross bridge attachment and detachment
- calcium pumps in the sarcoplasmic reticulum (Ca2+ ATPase)
- Na+/K+ pumps that return sarcolemma to resting conditions
73
What is the fastest way to regenerate ATP?
phosphorylation of ADP by creatine phosphate
- takes ~15 seconds
- Generates 1 ATP
- does not require oxygen
74
What is the most efficient method of regeneration of ATP?
aerobic respiration
- uses several substrates: pyruvate, fatty acid, amino acid
- generates 30-32 ATP
- slow process
- DEPENDENT on oxygen
75
Fast twitch fibers use what method for regeneration of ATP?
- phosphorylation of ADP by creatine phosphate
- glycolysis: generates 2 ATP; does not require oxygen; fast process
-fast twitch fibers are rapid fatigue
76
Slow twitch fibers use what method for regeneration of ATP?
aerobic respiration
- slow twitch fibers are low fatigue muscles
- these muscles are the ones you train for endurance
- lots of mitochondria
- lots of myoglobin and blood vessels (vasculature) because they need lots of oxygen
77
What is muscle fatigue?
physiological inability to contract despite continued stimulation
- occurs when ionic imbalances (K+, Ca2+, Pi) interfere with excitation-contraction coupling
- ATP generation via glycolysis decreases pH
78
Is is possible to switch from fast glycolytic fibers to fast oxidative fibers?
Yes
79
Is is possible to switch from slow oxidative fibers to fast oxidative fibers?
No
80
Compare the myoglobin content, glycogen stores, rate of fatigue, mitochondria, and capillaries between slow oxidative and fast glycolytic fibers.
slow oxidative fibers:
- high myoglobin content
- low glycogen stores
- slow rate of fatigue
- many mitochondria
- many capillaries
- angiogenesis
fast glycolytic fibers:
- low myoglobin content
- high glycogen stores
- fast rate of fatigue
- few mitochondria
- few capillaries
81
What is the difference between muscle tension and load?
- muscle tension is the force generated by contracting a muscle
- load is the force opposing the contracting muscle
82
Concentric and eccentric are examples of what type of contraction.
isotonic contraction
83
What occurs during isotonic contraction?
- shortening of muscle
- movement of load
- tension > load
84
What occurs during isometric contraction?
- muscle does not shorten
- load is not moved
- tension < load
85
What is the difference between concentric and eccentric isotonic contraction?
concentric: muscle shorten while moving the load
eccentric: muscle lengthen while moving the load
86
What is the effect of load on the duration and velocity of contraction?
the greater the load, the less the muscle shortens and the shorter the duration of contraction
87
The force-velocity relationship depends on the type of muscle.
FACTS!!!
| Fast-twitch fibers move with a faster velocity with the same load as a slow twitch fiber.
88
What is muscle tone and what effect does it have?
- constant, slightly contracted state of muscles
- due to the action of SPINAL REFLEXES
- responsible for balance and posture
- keeps muscle firm, healthy, and ready to respond
89
What are the adaptions to aerobic exercise?
- increased number of muscle capillaries, number of mitochondria, and myoglobin synthesis
- results in greater endurance, strength, and resistance to fatigue
90
What are the effects if resistance muscle?
typically anaerobic results in
- muscle hypertrophy (increase in fiber size)
- increased mitochondria, myofilaments, glycogen stores, and connective stores
- increased muscle strength and size
91
What is the majority of energy from muscle contraction released as?
heat
shivering is muscle contractions to generate heat
92
How is the AP generated and how does repolarization occur afterwards? These events occur after the end plate potential is generated at the NMJ.
The depolarizing current from the end plate potential spreads to the adjacent areas of the sarcolemma. This causes voltage-gated Na+ ONLY to open and allow more Na+ into the muscle fiber cell thus initiating the AP. The repolarization occurs when Na+ CHANNELS are closed or inactivated and voltage-gated K+ are open allowing for K+ to diffuse rapidly out of the muscle fiber.
93
What is excitation-contraction coupling?
E-C coupling is the sequence of events by which the initiation of an AP along the sarcolemma leads to the contraction of myofilaments.
E-C coupling involves the release of calcium
94
Each axon terminal innervates one muscle fiber. True or false?
True
95
Muscles have different twitch responses. What does the strength and duration of twitches depend on?
- metabolic properties of muscles
| - myosin ATPase activity (where it gets its ATP from)
96
What is temporal summation?
an increase in tension in skeletal muscle fiber due to an increase in the frequency of action potentials
