LEC-2 Skeletal Muscle Physiology Flashcards
Skeletal muscle makes up __% of one’s body mass.
40%
Smooth muscle makes up __% of one’s body mass.
~5%
Cardiac muscle makes up __% of one’s body mass.
~5%
(T/F) Skeletal muscle is able to be controlled via hormones.
False. Skeletal muscle is not able to be controlled via hormones.
(T/F) Smooth muscle is able to be controlled via hormones.
True.
(T/F) Cardiac muscle is able to be controlled via hormones.
True.
A(n) _____________ is a structural myofibril unit and also the distance between two Z discs.
Sarcomere
What are the three components of a troponin molecule?
- Troponin C - Binds to calcium ions to produce a conformational change in Troponin I
- Troponin T - Binds to tropomyosin, interlocking them to form a troponin-tropomyosin complex
- Troponin I - Binds to actin in thin myofilaments to hold the troponin-tropomyosin complex in place
Troponin (I/C/T) binds to tropomyosin, interlocking them to form a troponin-tropomyosin complex.
Troponin T
Troponin (I/C/T) binds to actin in thin myofilaments to hold the troponin-tropomyosin complex in place. It also serves to inhibit the association of actin and myosin.
Troponin I
Troponin (I/C/T) binds to calcium ions to produce a conformational change in the troponin complex.
Troponin C
Myosin exists as a hexamer consisting of __ heavy chains and __ light chains.
- 2 heavy chains
- 4 light chains
There are __ thin filaments surrounding each thick filament
6
(T/F) F-actin molecules exist as single globular proteins that polymerize to form G-actin.
False. G-actin molecules exist as single globular proteins that polymerize to form F-actin (filamentous actin).
What is the shape of F-actin?
Double helix
What polymerizes to cover the active sites of F-actin?
Tropomyosin
__________ serves to attach F-actin to the Z-line.
α-actinin
__________ serves to terminate G-actin polymerization
β-actinin
__________ is a structural protein that imparts elasticity to the sarcomere.
Titin
Describe the general mechanism of muscle contraction.
- An action potential travels along a motor neuron to a group of muscle fibers.
- At the neuromuscular junction the nerve releases a small amount of ACh.
- ACh binds to its receptors and opens local cation channels.
- Large quantities of Na+ ions diffuse inside the muscle fiber, causing local depolarization and opening of additional Na+ channels.
- The AP travels along the muscle fiber membrane and travels to the center of the muscle through T-tubules. Upon reaching the sarcoplasmic reticulum, it releases large amounts of calcium ions.
- Calcium ions initiate attractive forces between actin and myosin filaments, causing them to slide in the contractile process.
- After a fraction of a second, the calcium ions are pumped back into the SR by a Ca2+ membrane pump and remain there until a new AP.
Removal of calcium ions from myofibrils causes the muscle contraction to (speed up/slow down/cease)
Cease
What is an isometric contraction?
A contraction that results when tension on the muscle is allowed to increase, but the muscle length remains constant throughout. For example, trying to lift a car or push against a door frame.
What is an isotonic contraction?
A contraction that results when tension placed upon the muscle remains constant throughout the motion, but the muscle length changes. For example, a weight lifter performing a bicep curl with a 25lb. weight.
___________ tension is tension that develops in muscle while stretching the muscle to different lengths.
Passive
__________ tension is tension caused by stimulating the muscle to contract at differing lengths.
Total
(T/F) You may calculate active tension by adding passive and total tension together.
False. Active tension is the difference between total and passive tension.
The denervation/re-innervation of a motor unit by another motor neuron (increases/decreases) the subsequent size of the new motor unit.
Increases
Motor units for a motion are recruited in order of size from (largest/smallest) to (largest/smallest).
Recruited in order of size from smallest (first) to largest (last)
What are the two mechanisms of increased tension development in skeletal muscle?
- Multiple fiber summation or recruitment of additional motor units
- Wave summation (increased firing frequency of a single motor neuron)
The amount of ATP consumed by contracting muscle depends on what two factors?
- The load placed on the muscle
- The rate at which the muscle contracts
Short-term regeneration of ATP may be accomplished by transferring a phosphate from a phosphocreatine molecule to an ADP molecule. This process is done by the enzyme _________________.
Creatine kinase
Short-term regeneration of ATP may be accomplished by transferring a phosphate group from a single ADP molecule to another ADP molecule, resulting in AMP + ATP. This process is done by the enzyme ______________.
Adenylate kinase
What are the three methods of long-term regeneration of ATP within muscle?
- Aerobic glycolysis
- TCA cycle and oxidative phosphorylation
- β-oxidation of fats and ketone bodies
Type (I/IIA/IIB) skeletal muscle fiber is defined as red and fast oxidative.
IIa (best for running an intermediate sprint)
Type (I/IIA/IIB) skeletal muscle fiber is defined as red and slow oxidative.
I (best for running a marathon)
Type (I/IIA/IIB) skeletal muscle fiber is defined as white and fast glycolytic.
IIb (best for running a short sprint)
What are the three determinants of muscle fiber type?
- Genetics
- Training
- Motor nerve innervation
_____ is a member of the TGF-β superfamily that functions as a negative regulator of muscle growth.
Myostatin (GDF8)
_____________________ are members of a family of proteins called ligand-gated ion channels that are found in skeletal muscle and synapse between pre- and post-ganglionic fibers in SNS.
Nicotinic acetylcholine receptors
The nicotinic acetylcholine receptor is comprised of ___ subunits.
5
Which subunits of the ACh receptor bind to ACh?
The two α-subunits
The ________________ is the membrane potential generated on the postsynaptic side of the neuromuscular junction.
Endplate potential
The ____________ receptor is a voltage-dependent channel located within the T-tubule. It is in close relation to the __________ receptor located on the sarcoplasmic reticulum. Together, these receptors propagate calcium release from the SR.
- Dihydropyridine receptor is a voltage-dependent channel.
- Ryanodine receptor is located on SR
What are the immediate effects of a motor nerve section?
- Paralysis; loss of voluntary and reflex contractions
- Muscle fasciculations due to irregular release of ACh
What are the effects 2 hours after a motor nerve section?
- Failure of distal end of motor neuron to elicit muscle contraction (despite presence of ACh vesicles)
- Disappearance of MEPPs, followed by a return 1 week later
What are the effects 2 weeks after a motor nerve section?
- Muscle becomes increasingly sensitive to ACh
- ACh receptors appear outside neuromuscular junction again
- Spontaneous fibrillations in response to circulating ACh
- Eventually re-innervation and restoration of the severed NMJ will occur
__________ and __________ are used to inhibit AChE which increases ACh levels within the synaptic cleft. These are used to treat glaucoma and myasthenia gravis.
Pyridostigmine and neostigmine
__________ are chemicals that irreversibly inhibit AChE. They are present in nerve gases and insecticides.
Organophosphates
__________ are CNS depressants that decrease activity of the reticular formation through manipulation of GABA receptors. They function by increasing the frequency of opening for the inhibitory GABA receptor.
Benzodiazepines
_________ is a drug that inhibits Ca2+ release by the sarcoplasmic reticulum.
Dantrolene
Complete the following table.
Complete the following table.
Complete the following table:
Complete the following table.
