Muscle Physiology Flashcards
Muscles contain bundles of fibers called _______
Myofibrils
Review the sarcomere on 6-2. Know I band, A band, Z line, M line
Always comes back to haunt us
What is an H zone?
A central region of A band where thin filaments do not overlap with thick filaments
Do thick or thin filaments change length in muscle contraciton?
No
What theory explains muscle contraction?
The Sliding Filament Hypothesis
What are thick filaments made of?
Myosin
What proteins are thin filaments made of?
Actin, Tropomyosin, and Troponin
Structure of actin in a thin filament?
Polymerized globular protein entwined in a helix
Function of troponin/tropomyosin?
regulate the interaction of myosin with the actin molecule
What does the hydrolysis of ATP bound to myosin do?
Causes the myosin head to pivot
Describe the cross-bridge cycle
- Baseline – Myosin with ATP is next to Actin
- Hydrolysis of ATP causes pivot of the myosin head
- Pivoted head binds Actin
- ADP+Pi is released, causing myosin head to un-pivot, pulling actin
- ATP binds, causing the myosin head to release the Actin
In resting muscle, what covers the myosin binding site?
Tropomyosin
Purpose of troponin?
Locks tropomyosin in position
What causes the troponin-tropomyosin complex to release actin for binding?
Ca ions
Where do the Ca ions that free up the actin come from?
Sarcoplasmic Reticulum
What triggers Sarcoplasmic Reticulum release of Ca?
AP traveling the transverse tubule system.
Linkage of calcium-induced calcium-release channels lead to channel changes.
What is the Transverse Tubule system?
Periodic infoldings of the plasma membrane
Describe the two receptors involved in Calcium release.
Voltage activated Ca channel in T Tubule activated calcium induced calcium release channel.
Main difference between skeletal and heart muscle?
Individual cardiac muscle cells are linked via gap junctions.
How does smooth muscle signalling get going
Phosphatidyl inositol cleaved to IP3
IP3 binds to calcium release channel to sarcoplasmic reticulum
Calcium release
What major player is no longer involved in smooth muscle
Troponin
How is smooth muscle myosin regulated?
Phosphorylation-dephosphorylation of myosin
Myosin Light Chain Kinase and Myosin Light Chain Phosphotase
What regulates MLCK?
Calmodulin
What determines the force of a muscle fiber?
Amount of overlap of thick and thin filaments
During a maintained contraction, how much of the muscle’s ATP is used to fuel the cross bridge? Pumping into the Sarc?
50-80%
20-30%
Two methods muscles use to generate ATP
Ox Phos and Anerobic glycolysis
Pros and Cons of Ox Phos?
Efficient, can operate continually
Slow process, cannot meet maximal ATP consumption rated
Pros and Cons on Anerobic glycolysis?
Fast
Limited by glycogen stores, inefficient
How many muscle fibers can a neuron innervate?
Many
How many neurons can innervate a muscle fiber?
One
What is the innervation ratio?
The number of fibers innervated by a single motoneuron.
Which is longer, muscle AP or twitch?
The twitch (10 to 100 ms)
What happens when repeated stimulations are happening faster than twitches are ending?
Tension developed by twitches summates
What happens if you make the muscles stimulate at their highest frequencies?
Twitches fuse – Tetanus
Three categories of motor units.
Slow, Fast Fatigue Resistant (FR), and Fast Fatiguable (FF)
Describe S units.
Contract slow, small peak force
Highly resistant to fatigue
Describe FF units
Contract fast, forcefully
Easy to fatigue
Describe FR units.
Similar to FF, but with smaller peak forces and higher fatigue resistance
Nerve properties may influence what properties of muscles.
Metabolic and contractile characteristics
How is force of contraction increased?
- Recruiting more motor units
2. Increasing firing rate of individual units
Order in which recruitment occurs.
S –> FR –> FF
FR and FF only for strenuous activities
Name for the rule about the order in which recruitment occurs.
The Size Principle
What does the size principle allow?
Higher motor centers determine the overall level of drive and not the exact combination of motor units to be recruited
What is malignant hypothermia? What do you do?
A mutation of ryanodine receptors. Provide muscle relaxants
What is myotonic dystrophy?
A disease with muscle weakness, cataracts, baldness, heart disease, and muscle failure.
