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38 Cards in this Set

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What is the troponin complex/group?
it controls position of tropomyosin on actin
what makes up the thin filament
1 tropomyosin and 2 strands of actin
what is the hierachical organization of muscle tissue?
it is formed in bundles, bundles are formed of numerous muscle cells, cells are formed of myofibrils, myofibrils consist of many myofilaments
what is a myofibril formed of and what does it form/
It is formed of thick & thin filaments, the thick filaments are made of myosin with a myosin head and the thin filaments are made of 2 actin strands and 1 tropomyosin strand with troponin group/complex.
Together they form SARCOMERES
Be able to identify and understand where the A-band, I-band, M-line, and Z-lines are.
A-bands are the length of the THICK filament (red line)
I-bands are the distance between each THICK filaments
M-line is located in the center of each THICK filament
Z-line is the verticle line that conects each THIN filament
How to ID a sarcomere?
Sarcomeres are the distance between THIN filaments
Sarcomeres are identified by what color of line...?
they are alternating light-dark units, which repeat down the length of the myofibril
how can you identify a muscle contraction verses relaxed states
The sarcomeres in a myofibril lengthen when the muscle fiber is relaxed and shorten when the cell is contracted
How do muscles contract?

Describe the Sliding-Filament Theory/model
the contraction of muscles is controlled by the multiple strands of Myosin as the myosin head on the ends of each strand bind to the 2 coiled chains of actin, the thin filament, which catalyzes the hydrolysis of ATP into ADP and a phosphate ion. This suggests that the myosin was the site of active movement, NOT actin.
MOVEMENT is PRODUCED BY 4 STEPS:
1) ATP BINDS, Myosin head releases
2) ATP IS HYDROLYZED, Myosin head pivots, binds to new actin subunit, which forms a new compound of ADP + Phosphate ion
3) PHOSPHATE ION IS RELAESED, myosin head pivots, moves filament as the neck bends back to its original position, known as POWER STROKE
4) ADP IS RELEASED, cycle is ready to repeat as a new ATP molecule then binds to the myosin, causing myosin to release from actin, and the cycle starts anew
How does relaxation occur?
In addition to containing actin and myosin, thin filaments contain 2 KEY PROTEINS called TROPOMYOSIN and TROPONIN, which both work together to block myosin binding sites on actin. When both are in particular conformation, the myosin-actin interaction cannot occur, therefore the THICK & THIN filaments cannot slide past each other...
How do Tropomyosin & Troponin move out of the way to allow muscle contraction?
This begins w/the arrival of an electrical signal from a motor neuron.
This leads to an Action Potential at the Neuromuscular Junction that triggers the release of Ca2+ ions, which binds to Troponin-Tropomyosin and allows Myosin to walk along Actin.
How do Action Potentials Trigger Muscle Contraction?
List the 5 steps...
1) Action potentials trigger the release of the neurotransmitter called ACETYLCHOLINE (ACh) from the motor neuron into the synaptic cleft between the motor neuron and the muscle cell
2) ACh diffuses across the synaptic cleft and binds to ACh receptors on the plasma membrane of the muscle cell.
3) The action potentials propagate across muscle cells plasma membrane and into interior of cell via T-tubules
4) Proteins in T-tubules open Ca2+ channels in sarcoplasmic reticulum
5) Ca2+ is released from sarcoplasmic reticulum. Sarcomeres contract when troponin and tropomyosin move in response to Ca2+ ions and expose actin binding sites in the thin filaments
How to ID a T-tubules
they are intracellular structures that run vertically across the sarcoplasmic reticulum dividing one sarcomere from the next
What events, ions and NT contribute to the transmission of the AP across the neuromuscular junction?
Events: Ap arives and ACh is released, the ACh binds to ACh receptors on the muscle cell, triggering depolarization that leads to AP, which the AP propagates across muscle cells plamsa membrane and into interior of cell via T-tubule
Ions: Ca2+ channels open up in the sarcoplasmic reticulum, Ca2+ ions are released and then the troponin and tropomyosin move in response to the Ca2+ ions, which expose the actin binding sites in the thin filaments
NT: the AP triggers the release of the NT called Acetylcholine (ACh), which then binds to ACh receptors on the muscle cell, triggereing depolarization that lead to AP
what is a muscle twitch?
it is the type of muscle contraction that is stimulates by a single AP in a motor neuron
what is a motor unit?
A motor unit is a single α-motor neuron and all of the corresponding muscle fibers it innervates. Groups of motor units often work together to coordinate the contractions of a single muscle; all of the motor units that subserve a single muscle are considered a motor unit pool.
The motor unit consist of what 4 pieces?
Motor neurons, the branches leading off of the motor neuron, muscle fibers that the branches of motor neurons attach to, and the myofibrils that are located w/in the muscle fibers
what is the name of the myosin head?
Globular Head
a single muscle cell if formed of what?
many myofibrils
what is the name of the part that the Mysoin head is connected to?
Fibrous tail
what is the function of the M-line?
The M-line keeps the muscles from collapsing w/in the H-zone that is w/in the A-band
skeletal muscle tissue
attached to the bone, its function is to move the skeleton
Characteristics of cells are that it is multinecleates, unbranched, and there activity is "VOLUNTARY", meaning that a signal from motor neuron is required
Musle contractions work how?
they work in antagonistic pairs, meaning that one muscle contracts and another relaxes
how do skeletal muscles work?
Skeletal muscles work in antagonistic pairs, one muscle contracts, while the other restricts
What is a thin filament?
THIN FILAMENTS
2 strands of ACTIN (Protein)
1 strand of TROPOMYOSIN (regulatory protein)
What is a thick filament?
THICK FILAMENTS is composed of many MYOSIN (protein), that have many myofilaments
what is a myofilament composed of?
- A Band: length of thick filaments
- I Band: thin filaments only
- H-Zone: Thick filaments only
- Sarcomere: basic contractile unit of muscle cell repeat
- Z-Line: boundary between 2 sarcomeres
what is the Sliding filament theory of muscle contraction:
1) there are 2 strands of actin present and the myosin head is in low energy configeration
2) Myosin head binds ATP Molecule
3) ATP-> ADP + Pi (Pi = high energy Phosphate) Myosin binding site on actin
4) Myosin returns to low energy state, ADP + Pi is leaves
5) Actin is bound to Z-line, so sarcomere shortens
How does a muscle rest?
it rests when a long, rodlike tropomyosin molecule blocks the myosin binding sites that are instrumental in forming cross-bridges
how do muscles contract?
they contract when another protein complex, troponin, binds calcium ions, the binding sites on actin are exposed, crossbridges w/myosin can form and the muscle contracts
Describe a sarcomere, bands, lines, zones, etc...
sarcomere - smallest contractile unit of skeletal muscle
Z disc - ends of sarcomere
A band - beginning of mysoin to end of adjacent myosin held together at the M line
H zone - end of one actine myofilament to the beginning of the next actin myofilament in the same sarcomere
M line - bisects sarcomere, anchors two adjacent myosin myofilaments together (center of H zone)
I band - area in two adjacent sarcomere that only contain actin myofilaments
What happens during maximum contraction?
during maximal contraction:
Z discs come together towards A band
I band narrows
H zone disappears
CONTRACTION IS WHEN?
Different parts of the sarcomere are sliding past each other
Light area is ?
thin filaments only
the darl area is?
Thick filaments only
contraction happens when?
the myofilaments slide past each other, so they do NOT shorten
what is the regulatory protien and where is it located?
it is the Tropomyosin, and it is located in the thin filament
Describe what generally happens to one myosin head?
1) It has a crook in the head, which means that is it NOT standing straight up and it is NOT in contact w/the Actin, this is when the myosin is in its low energy state,
2) to initiate muscle contraction the myosin needs to bind w/ATP, to generate an AP, once it is bound, the myosin will hydrolize the ATP and then releases energy, which is used by the myosin (the myosin is now in its High energy state), then neck comes out and the head is now standing up, producing ADP + Pi (inorganic phosphate),
3) myosin now binds w/the actin strand, for this to happen it needs to bind in s SPECIFIC myosin binding site on the actin, thus the myosin head is standing up and it binds to the actin
4) ADP + Pi is released and this in return sends the myosin back to its low energy state, taking the energy away
5) a new ATP binds to the low energy myosin and in this process the myosin is released from the actin, then the cycle repeats back to step (2)