Skeletal Muscle Physiology pt.1 (Exam III) Flashcards
What organ system is the largest contributor to body weight and ICF volume in non-obese people?
In addition to fluid volume, what else does this body system store?
Skeletal Muscle System
Ions and proteins
What’s an example given in class of exceptionally fine motor control?
Voicebox Control
What organ system is the primary source of basal bodily temperature?
What is the prototypical basal body temperature?
Skeletal Muscle
37°C
What energy source is stored in skeletal muscle?
Describe the basic structure of these molecules?
Glycogen
Glycogen is essentially chains of glucose stuck together.
What type of glucose transporters do skeletal muscles use? Are these insulin-dependent or independent?
What is the relevance of this if a large dose of insulin is given?
Glut-4, Insulin Dependent transporters
↑ insulin dose = skeletal muscle absorbing excessive glucose from bloodstream.
How does the skeletal muscle contribute to body temperature when at rest?
Basal Resting Tone = Small, unnoticeable relaxations/contractions.
Describe the physiologic anatomy of a skeletal muscle all the way down to the cellular components.
- Muscle
- Fasciculous
- Muscle Fiber
- Myofibril
- Sarcomere
What are motor units?
Collection of muscle fibers that are innervated by a single A-α neuron.
verify that this is correct and a decent summary
Between small motor units and large motor units, which one is recruited for tasks first?
What does this allow for? What would be the result without this setup.
Small motor units
Precise movement and control. Without this we be clunky and do things like take notes using out biceps/triceps.
Which motor units uses smaller A-α neurons? Large A-α neurons?
Small motor units
Large motor units
Which type of skeletal muscle is characterized by increased levels of myoglobin and mitochondria?
Why is this muscle the color that it is?
How efficient is this muscle?
Type 1 - Red “slow” Muscle
Red due to the increased presence of Fe+ found in the myoglobin.
Very efficient
What type of skeletal muscle is characterized by very little myoglobin and fewer mitochondria?
Why is this muscle the color that it is?
How efficient is this muscle?
Type 2 - White “Fast-Twitch” Muscle.
Lack of myoglobin
Not as efficient, only used for short burst of movement.
Why does Myoglobin contain Fe+?
Fe+ in the myoglobin pulls O₂ from the blood into the skeletal muscle for use.
Why is red meat theorized to cause cancer?
How does this connect to men’s and women’s multivitamins?
Due to oxidizing effects of Fe+ over time.
Men’s multivitamins have no Fe+ while women’s generally do have some Fe+ due to monthly menstruation.
Give an example of a type 1 fiber muscle in humans?
Give an example of a type 2 fiber muscle in humans?
- Soleus - supports body weight during long periods of standing.
- Ocular muscles.
Between actin and myosin filaments, Which is considered “thinner”?
- Actin = thin
- Myosin = thick
What structure is denoted by 1 on the figure below?
What is this, essentially?
- Sarcolemma
- The cell wall of the muscle
What structure is denoted by 5 on the figure below?
Sarcoplasmic Reticulum
What 3 things should be known about our sarcoplasmic reticulum (SR)?
- SR replaces the ER in muscle cells
- Ca⁺⁺ storage
- ICF of cell (verify)
What structure is denoted by 6 on the figure below?
What purpose does this structure serve?
Transverse Tubule
Facilitates Action Potential Propagation
What structure is denoted by 15 on the figure below?
Myofibrils
What is the functional unit of skeletal muscle?
Sarcomere
Darker bands in the sarcomere are indicative of what cellular component?
myosin
What is the fluid inside a muscle cell called?
Sarcoplasm
What structure is denoted by 1 on the figure below?
Myosin
What structure is denoted by 2 on the figure below?
M-Line
What structure is denoted by 3 on the figure below?
What is the purpose of this structure?
Titin (made of Elastin)
Titin anchors the Myosin into the Z-disk.
What structure is denoted by 5 on the figure below?
Actin
What structure is denoted by 4 on the figure below?
Z-Disk
What comprises the I-Band?
Actin only
What comprises the A-band?
Actin and Myosin overlap
What comprises the H-band (H-zone)?
Myosin only
What demarcates the M-Line?
The very middle of the Myosin filament
What structure is denoted by 1 on the figure below?
Sarcomere
What Band is denoted by 2 on the figure below?
I-Band
What Band is denoted by 3 on the figure below?
What comprises this band?
A-Band
Myosin + Actin
What Band is denoted by 4 on the figure below?
What comprises this band?
What would the middle of this band be considered?
H-Band
Myosin Only
The M-Line
When talking about sarcomere bands, what occurs during contraction?
I-Band is pulled to A-Band
When may the I-band become unviewable?
During contraction as it is pulled into the A-Band.
What structure is by the cross-section denoted by 2 on the figure below? What makes up this cross-section?
I-Band cross-section
Actin Filaments
What structure is noted by the cross-section labeled 3 on the figure below? What makes up this cross-section?
H-Band cross-section
Myosin Filaments
What structure is by the cross-section denoted by 5 on the figure below? What makes up this cross-section?
A-Band cross-section
Myosin + Actin Filaments
Where specifically do myosin and actin bind to initiate pulling?
Myosin heads
During skeletal muscle contraction, what occurs to the following:
1. A-Band
2. I-Band
3. H-Band
4. Z-Disk
- A-Band doesn’t change in width.
- I-Band’s shrink and may become masked
- H-Bands disappear
- Z-Disks move closer together
Why do skeletal muscle cells have multiple nuclei?
Cell support for things such as mRNA protein synthesis.
Skeletal muscles are often as long as neurons, what differentiates the two in terms of cellular homeostasis?
Neurons possess axonal transport system for movement of things such as proteins. Skeletal muscles do not and therefore have multiple nuclei to accomplish the same goal.
wordy
Which two organelles does the skeletal sarcomere possess in greater quantities than most cells?
Mitochondria and Nuclei
Which type of muscle fiber exhibits more inefficiency?
White “Fast Twitch” Type 2 Muscle Fibers
What composes a myosin molecule?
Which sub-component of this molecule makes up the myosin head?
What do hundreds of these myosin molecules form when twisted together?
2 heavy chains and 4 light chains.
Myosin heads are composed of light chains.
Myosin Filament
Myosin heads possess a high affinity for active sites on _________.
F-Actin
Which part of the myosin filament cleaves ATP to do work?
Myosin heads
What two structures, twisted together, form an Actin filament?
Which of these has active sites for binding with myosin?
Tropomyosin and F-actin.
F-actin possesses the active sites.
In broad strokes, how are the active sites of an actin filament revealed for binding to myosin heads?
- Ca⁺⁺ interacts w/ Troponin C
- Troponin C → Troponin T and Troponin I to unwind Tropomyosin and F-actin.
- Binding site on F-actin revealed due to unwinding.
Which component of an Actin filament “hides” the myosin head binding sites?
Tropomyosin hides active sites of the F-actin.
Which troponin molecules is bound by Ca⁺⁺?
Which troponin molecule is bound to F-actin?
Which troponin molecule is bound to tropomyosin?
Troponin C
Troponin I
Troponin T
What conditions characterize a myosin head at rest “cocked” state?
ADP and Phosphate attached to Myosin head
No connection to Actin
What step occurs after the “cocked” state of cross-bridge cycling?
Weak Cross-Bridge State:
Myosin head with ADP and P is bound to active site of F-Actin.
What characterizes the Strong Cross-Bridge State?
ADP attached to myosin head, phosphate has been sheared off.
Contraction occurs from this state (need to verify)
When does phosphate leave the myosin head?
In-between the weak cross-bridge and the strong cross-bridge states.
What phase follows myosin contraction?
Post-powerstroke phase
What occurs between the post-powerstroke phase and the attached state?
ADP leaves the myosin head.
What characterizes the attached state of cross-bridge cycling?
What is required to “unstick” the muscle so that it’s not frozen in the contracted state?
Myosin head with no ADP/ATP or phosphate attached to F-actin.
ATP has to attach to myosin head to free it from F-Actin sites.
What occurs in the released state of cross-bridge cycling?
ATP is hydrolyzed (becoming ADP) leaving the myosin head in an at rest (stretched) state.
What are the 6 phases of Cross-Bridge Cycling?
- Cocked
- Weak Cross-Bridge
- Strong Cross-Bridge
- Post-Powerstroke
- Attached
- Released
What neurotransmitter is always used at the NMJ?
What receptor is used at NMJ’s?
ACh
Nicotinic ACh (nACh)
What is used in the post-synaptic vesicle to increase surface area for ACh receptors?
Sub-Neural Clefts = “Invaginations” ~ pockets to ↑ cell surface area
Why does a pathology like myasthenia gravis take a long time to become debilitating?
NMJ’s have excessive ACh and excessive ACh Receptors. This is a safety mechanism so we always have more neurotransmitters and receptors than necessary.
How many nACh receptors are at each NMJ?
5 million
How much of neurotransmitter and nACh capacity are typically utilized? How much does this leave in reserve?
10%
90% reserve.
What is required for conformational change of an nACh receptors?
2 Acetylcholine molecules
What are the subunits of an adult ACh receptor?
2 α subunits
1 β subunit
1 δ subunit (delta)
1 ε subunit (epsilon)
Which subunits of a nACh receptor are bound by ACh?
The 2 α subunits
Depolarization from a post-synaptic cell is called ____________.
What’s a good way to think of this depolarization?
End-Plate Depolarization
This is the depolarization needed to meet the threshold for an Action Potential.
What primary ion comes through an nACh receptor when activated?
Can any other ions come through?
Na⁺
Ca⁺⁺ (much smaller amount) and K⁺ (no real movement)
What structure helps facilitate rapid depolarization deep into muscle cells?
What type of channel is located in this structure to facilitate this effect?
Transverse “T”-Tubules
V-G Na⁺ channels
What receptors are located along transverse tubules (and the cell wall) that open up the sarcoplasmic reticulum?
Does this structure become bound?
DHP (Dihydropyridine) Ca⁺⁺ Channel Receptor
No, this receptor is not bound, only activated by action potential.
What structure is physically coupled to DHP receptors?
Where is this structure located?
Ca⁺⁺ Release Channel (RyR)
Located on Sarcoplasmic Reticulum
During an action potential, by what process and from where does Ca⁺⁺ release intracellularly?
- AP activated DHP Receptor
- DHP receptor opens RyR Channel
- Ca⁺⁺ spills from SR to the ICF.
Whats another name for the RyR receptor?
Ryanodine receptor
How is Ca⁺⁺ reabsorbed back into the sarcoplasmic reticulum?
Is this through facilitated diffusion?
SERCA (SarcoEndoplasmic Reticulum Ca⁺⁺ ATPase Pump)
No, this process requires ATP due to steep Ca⁺⁺ gradient.
By which two general methods is Ca⁺⁺ pumped across a concentration gradient?
Direct Ca⁺⁺ pump
Antiporter pump (3 Na⁺ for 1 Ca⁺⁺)
What protein makes it possible for there to be massive Ca⁺⁺ stores in the sarcoplasmic reticulum?
Calsequestrin (binds many Ca⁺⁺ pumped in by SERCA’s)
In a healthy adult how does the End-Plate Potential (EPP) generated by ACh binding, compare to the threshold needed for an action potential?
The EPP in a healthy adult is much greater than the threshold needed for an action potential.
Where is AChEsterase produced?
Post-Synaptic Skeletal Muscle Cell of the NMJ
What happens to ACh that ends up in the plasma?
Destroyed by PlasmaCholineEsterase (PlasmaChE)
What was one possible used of AChE Inhibitors discussed in lecture?
What two side effects of AChE Inhibitors were very briefly discussed in lecture?
Treatment of Dementia (↑ ACh = ↑ Awareness)
↓ HR and ↑ Mucus production
In the event of a tendon rupture (say Achilles Tendon) what would the function of this muscle be post-repair?
What type of repair would be better, suturing tendon portions back together, or pulling tendon taut and screwing it into the calcaneus?
Function would never be 100% again due to loss of optimal stretch.
Suturing would be the better option but 100% of function could not be returned to.
In the depiction below, which letter(s) would be considered “optimal stretch”?
Which letter(s) would be considered overstretch?
Which letter(s) would be considered understretched?
With which letter(s) would be a contraction be possible?
Optimal Stretch = B & C (C is slightly better)
Overstretch = D
Understretched = A & E (A being worse)
Contraction possibility = E, B, & C (E sub-optimal)
Describe in layman’s terms, the significance of the blue line below?
Blue Line = Passive tension of muscle at rest
Describe in layman’s terms, the significance of the green line below?
Green Line = Active tension of muscle during contraction
Describe in layman’s terms, the significance of the red line below?
Red Line = Active tension of muscle during contraction + passive tension of muscle at rest
What drugs are given for reversal of -curare paralytics?
Why do these drugs have unintended side effects aside from paralysis reversal?
AChE Inhibitors (-stigmines)
AChE inhibition is not specific to NMJ and happens anywhere with ACh receptors.
Describe the Load/Contraction Velocity Diagram’s basic premise
↑ Load = ↓ contraction speed.
Heavy things can’t be moved quickly.
What are the “units” of hertz (Hz) regards to skeletal muscle?
Action Potentials / sec
At what Hz would we expect to see complete recruitment of all motor units in a given area?
5 - 10 Hz
What occurs in regards to muscle tension above 10-12 Hz?
Tension increases and more power is generated.
What occurs in regards to intracellular Ca⁺⁺ around or above 10-12 Hz?
More Ca⁺⁺ is influxxing into cell than is being removed.
At what Hz does force plateau?
Why does this occur?
What is this force plateau called?
~ 40Hz
- All Troponin C’s are bound w/ trigger Ca⁺⁺
- Tetanization
Describe Quantal Summation vs Temporal Summation.
- Quantal Summation: Nervous system activates small motor units 1st and then large motor units next.
- Temporal Summation: Rapid muscle stimulation that modulates force production.
What is muscular atrophy?
- Shrinkage of the muscle myofibril size due to disuse.
How does muscular denervation atrophy differ from muscular disuse atrophy?
Give an example of denervation atrophy.
- Disuse Atrophy is technically reversible but takes work (no loss of basal resting tone).
- Denervation Atrophy is mostly irreversible and is the result of losing your basal resting tone (ex. spinal cord injury)
Can skeletal muscle denervation atrophy be avoided in the case of a spinal cord injury?
Yes with $.
- Direct muscular electrical stimulation therapy everyday can keep muscle innervated in the hopes of spinal cord therapy improving in the future.
How are new muscle cells created in muscular hypertrophy?
Trick question. Existing myofibrils grow in size, new cells are not created.
What occurs with the cardiovascular system alongside the process of hypertrophy?
Angiogenesis = ↑ blood vessel size for better blood delivery.
How does muscular hyperplasia differ from hypertrophy?
What is required for muscular hyperplasia?
- During muscular hyperplasia, new muscle cells actually develop in addition to hypertrophy.
- Hyperplasia generally requires intense exercise & probably anabolic steroids.
What general issue is noted with drugs that increase cell replication?
↑ cell replication = ↑ cancer.
