Muscles Flashcards
Three types of muscles
Smooth
Skeletal
Cardiac
Striated Voluntary Muscle type
Skeletal Muscle
Striated involuntary muscle type
Cardiac Muscle
Unstriated involuntary muscle type
Smooth muscle
Connective tissue anchoring muscle at each end
Tendon
Each muscle consists of?
Muscle fibers
Each muscle fiber is composed of?
Myofibrils
Myofibrils consist of?
Myofilaments:
Thin (Actin) and Thick (Myosin)
What is the functional unit of a striated muscle?
Sarcomere
Boundaries of a sarcomere.
Z-Line
Term for the dark bands
A-bands
Term for the light bands that have the z-line in the middle. This is also considered the distance between thick filaments
I-band
Line visible in the middle of the a-band
M-line
Area that contains the M-line
H-Zone
Densest portion of the sarcomere
A-Band
Lighter portion of the a band
H-zone
Portion between a-bands
I-Band
Middle of H-Zone
M-line
Projection outward of thick filament (myosin) that makes contact with the actin during contraction
Cross Bridges
In a myofibril, each thin filament is surrounded by how many thick filaments?
3
Two sites on the globular heads of myosin molecules that form the cross bridges
Actin-Binding site and Myosin ATPase site
Main structural components of skeletal thin filaments
Actin molecules, Troponin (Globular) and Tropomyosin (thread-like)
What is the function and mechanism of tropomyosin and troponin
Actin molecules have binding sites for myosin crossbridge. Troponin attached to tropomyosin wrap around the actin molecules to cover these binding sites.
How does cross-bridge interaction between actin and myosin bring about muscle contraction? What is this called?
During contraction of striated muscle, thin filaments on each side of a sarcomere slide inward toward the A band’s center.
They pull closer together the Z discs to which they are attached, so the sarcomere shortens and the entire fiber becomes shorter.
Sliding Filament Theory
What is the role of Calcium 2+ Ion in cross bridge activity
Calcium binds to troponin causing troponin to slide the tropomyosin away allowing for binding of actin and myosin at the now unblocked cross-bridge binding sites.
This is triggered by the binding of actin and myosin
Power stroke
T/F A-band gets shorter during muscle contraction
False, I-band and H-zone become shorter
During muscle contraction, what happens to A band? Shorten,
lengthen?
It stays the same
Bending of the crossbridge upon contact with actin
Power stroke
This is needed to achieve desired extent of muscle shortening
Repeated power stroke
4 steps of the crossbridge cycle
Binding
Power Stroke
Detachment
Repeat
T/F All cross-bridge strokes are directed toward the center of the thin filament
F. All towards thick filament
T/F Cross bridges are asynchronously cycling leading to some holding on while others are letting go causing the “ladder-like” climb
True
extensions of the surface membrane that dip deep into the muscle fiber at the junctions between the A and I bands
Transverse (T) Tubules
runs longitudinally and surrounds each myofibril, with separate segments encircling each A band and I band
Sarcoplasmic Reticulum
saclike regions at the end of each sarcoplasmic reticulum segment
Lateral Sacs (Terminal Cisternae)
T tubule membrane allows spread of _______ from surface membrane transmitting surface electric activity
Action Potential
Action potential triggers what?
Release of Ca2+ from the lateral sacs
What are the effects of Ca2+ movement to the musccle?
Release: Contraction
Re-uptake: Relaxation
Type of voltage-gated calcium channel, meaning they open in response to changes in membrane potential.
These channels allow the influx of calcium ions (Ca2+) into cells
Long-lasting currents
L-type calcium channels or Ryanodine receptors
Steps in excitation-contraction coupling and muscle relaxation (8)
- Action potential triggers acetylcholine release and muscle fiber action potential.
- T tubule action potential releases Ca2+ from sarcoplasmic reticulum.
- Ca2+ binds to troponin on thin filaments.
- Ca2+ on troponin alters tropomyosin shape, exposing actin binding sites.
- Myosin cross bridges attach to exposed actin binding sites.
- Cross bridge binding initiates power stroke, pulling thin filament.
- After power stroke, cross bridge detaches from actin.
- Action potential cessation leads to Ca2+ uptake, tropomyosin blocks actin binding sites.
Tension in cardiac muscle depends on?
The amount of calcium ions in the myoplasm
What is the difference in appearance of smooth muscle and skeletal muscle
Smooth muscle cells are nucleated
T/F Contraction and relaxation occurs slowly in smooth muscle compared to skeletal muscle leading to more contractions
True
T/F Calcium Binds to Troponin in smooth muscle cells to cause the myosin cross bridge
False, Calcium binds to calmodulin due to absence of troponin
What are the steps in the calcium activation in smooth muscle cells
Ca2+ binds with calmodulin -> activates
Myosin Light Chain Kinase -> myosin light chain phosphorylation -> Phosphorylated myosin cross bridge can bind with actin
Read the summary on the final 3 pages of the Muscle and movement pdf
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