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27 Cards in this Set

  • Front
  • Back

1. Axon terminal of motor neuron forms _________ with as single muscle cell

2. Signals are passed between nerve terminal and muscle fiber by what neurotransmitter?

1. neuromuscular junction

2. ACh


1. released ACh binds to __________ on __________

2. binding triggers

3. ______________ produces motor end-plate potential

4. how are adjacent areas brought to threshold?

5. ______________ initiated and propagated throughout muscle fiber

1. receptor sites on motor end plate of muscle cell membrane

2. opening of specific channels on motor end plate

3. ion movement depolarizes motor end plate and produces motor end plate potential

4. local current flow between motor end plate and adjacent muscle cell membrane brings adjacent areas to threshold

5. action potential is initiated and propagated throughout muscle fibrr

Events at NMJ

1. action potential in motor neuron is propagated to axon terminal (terminal button)

2. local action potential triggers the opening of voltage-gated Ca channels and the entry of Ca into terminal button

3. Ca triggers release of ACh from vesicles

4. ACh diffuses across space separating the nerve and muscle cells and binds to specific receptor sites on motor end plate on muscle cell membrane

5. binding opens nonspecific cation channels (large amount of Na into muscle - small amount of K+ out)

6. result = end plat potential (localized current flow b/w depol. end plate and adjacent membrane)

7. local current flow opens voltage-gated Na channels in adjacent membrane

8. Entry of Na reduces potential to threshold -> action potential -> prop thruout muscle fiber

9. Acetylcholinesterase destroys ACh located on motor end plate and terminates muscle cell response

What does acetylcholinesterase do?

1. inactivates ACh

2. ends end-plate motor potential/action potential/ and muscle contractoin

NMJ is vulnerable to chemical agents and diseases (5)

1. black widow venom - explosive release of Ach

2. botulinum - blocks release of ACh

3. curare - blocks action of ACh at receptor sites

4. organophosphates prevent inactivation of ACh

5. myasthenia gravis - inactivates ACh receptor sites

1. 3 types of skeletal muscle are

1. skeletal - striated - voluntary

2. cardiac - striated - involuntary

3. smooth - unstriated - involuntary

1. Muscles are about _______ of total body weight

2. skeletal muscles are about ________ of total body weight in men

3. skeletal muscles are about ______ of total body weight in women

4. cardiac and smooth muscles are about ___ of total body weight in humans

1. 50%

2. 40$

3. 32%

4. 10%

Skeletal muscle

1. individual unit

2. contain abundant

3. muscle consists of a number of muscle fibers

1. muscle fiber

2. mitochondria

3. lying parallel to one another held together by connective tissue

A single skeletal muscle cell is

1. multinucleated

2. large, elongated, and cylindrically shaped

3. fibers usually extend entire length of muscle

whole muscle (organ) --> muscle fiber(a cell) --> ...

myofibril (intracellular structure) --> thick and thin filaments (cytoskeletal elements) --> myosin and actin (contractile proteins)

The contractile elements of a muscle fiber are



1. is the ______ of skeletal muscle

2. regions of sarcomere

1. functional unit

2. A band: made up of thick filament along with portions of thin filament that overlap on both ends of thick filaments

H zone: area within middle of A band where thin filaments don't reach

M line: extends vertically down middle of A band within center of H zone

I band: remaining portion of thin filaments that do no project into A band


1. makes up

2. consists of

3. structure

4. cross bridges

1. thick filament

2. consists of 2 identical subunits shaped like golfclubs

3. tails intertwined toward center, globular heads project out

4. heads form cross bridges between thick and thin fil.

- C-B has actin binding site and myosin ATPase site

Thin filament

1. primary structural component and its shape

2. consists of 2 other proteins

3. struture

1. 2 chains of spherical actin molecules twisted together (actin helix)

2. tropomyosin and tropoin

3. actin helix surrounded by tropomyosis and troponin that form a ribbon that covers binding sites for myosin cbs

Tropomyosin is

thread like molecules that cover actin sites blocking interaction that leads to muscle contraction

Troponin structure

mad of three polypeptide units

1. one binds to tropomyosin

2. one binds to actin

3. one binds to Ca2+

Effect of Ca on troponin

1. when not bound to Ca, troponin stabilizes tropomyosin position that blocks cb binding sites

2. when bound to Ca, tropomyosin moves away from blocking position -> actin and myosin bind -> contraction of muscle

Sliding filament mechanism

1. increase in Ca

2. decrease in Ca

3. describe what happens

1. starts filament sliding

2. stops sliding

3. filaments on each side of sarcomere slide inward over stationary thick fil. towards center of A band during contraction (all sarcomeres thruout muscle fiber's length shorten)

1. Cycles of cross bridge binding and bending pull

2. when myofibril contracts what parts of sarcomere becomes shorter?

3. do filaments decrease in length to shorten sarcomere?

1. thin filament inward

2. H zone, I band, Z lines come closer, A remains same

3. no

What is a power stroke?

Activated CB bends toward center of thick fil "rowing" thin filament to which it is attached

What happens during a power stroke? (4)

1. SR releases Ca into sarcoplasm

2. myosin head binds to actin

3. myosin head pulls toward center of sarcomere (power stroke)

4. ATP binds to myosin had and detaches it from actin

What is the sarcoplasmic reticulum?

1. fine network of interconnected compartments that surround each myofibril

- not continuous

- segments wrapped around each A and I band

- ends of segments expand to form lateral sacs

Transverse Tubules

1. run perpendicularly from surface of muscle cell membrane into central portions of muscle fiber

2. membrane is continuous with surface membrane

3. action potential on surface membrane runs down into t-tubule

Spread of action potential down T-tubule triggers

release of Ca from SR into cytosol

1. Relaxation depends on

2. what happens during relaxation

1. reuptake of Ca into SR

2. Acetylcholinesterase breaks down ACh at NMJ -> muscle fiber action pot. stops -> when action potential no longer present Ca moves back into SR

Ca Release in Exciatation-Contraction coupling (7)

1. ACh released by axon of motor neuron - crosses cleft and binds to motor end plate

2. action pot. generated - end-plate potential propagated across surface mem and down t-tubules

3. actions potential in t-tubules trigger release of Ca from SR

4. Ca released from lateral sacs - bind to troponin - tropomyosin moves aside

5. myosin CBs attach to actin and bend - pulling actin fil toward center of sarcomere (powered by ATP)

6. Ca actively taken up by SR when no longer local action pot

7. Ca not bound anymore - tropomyosin moves back - contractions ends (actin back in resting position)

Cross bridge activity (4)

1. Energized: ATP split by mosin ATPase: ADP and Pi remain attached to myosin - energy stored in CB

2. Ca PRESENT: Binding: enabled to bind with CB

3. Bending: power stroke at CB triggered on contact b/w myosin and actin - P released during and ADP released after power stroke

4. ATP avail: Detachment: linkage b/w actin and myosin broken as ATP binds to myosin CBs -> CB assums originals position (ATP hydrolyzed cycles starts again)

NO ATP: Rigor complex: (after death) actin and myosin remain bound in rigor complex)