Muscle Slides

​Motor Unit

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​Motor neurons are the nerve cells that stimulate muscle cells.

One motor neuron may stimulate a few muscle cells or hundreds​

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​Neuromuscular Junction

​​3: synaptic vesicles containing neurotransmitter acetylcholine

4: neurotransmitter receptors on sarcolemma of muscle cell

5: mitochondrion; supply energy for contraction

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​Synapse

​•Acetylcholine, ACh, molecules are represented by small blue circles in this diagram.

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​Acetylcholine

​•ACh transporter is a molecule involved in the packaging and release of ACh in vesicles

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​Membrane At Rest

​•Although sodium and potassium ions are both positively charged, there are more positive ions outside the cell than inside when the membrane is at rest.

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​Electrical Current

​•Notice that the membrane’s resting potential is restored almost immediately after an action potential passes.

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​Calcium Ions Released

​•When calcium ions are present, they will bind with troponin and change its shape and, therefore, moves the attached tropomyosin away from the myosin binding sites on actin.

•Once the binding sites are exposed, myosin heads bind to actin forming crossbridges.

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​Crossbridges

​•When myosin heads attach to actin, they are in a “cocked” position.

•The head then pulls the actin towards the center of the sarcomere.

•ATP allows the head to release from actin and reset to the “cocked” position.

•Because several myosin heads are attached to actin at any one time, the actin filaments do not slide back to their original position, but are continuously pulled toward the center of the sarcomere.

•The filaments themselves do not shorten, but the sliding of the thin and thick filaments past each other results in shortening of the sarcomere.

•There are some good animations online that will further illustrate the sliding filament theory to your students.

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​Sliding Filament Theory

​•Notice that the myofilaments do not get shorter.

•The actin filaments are pulled closer to each other, toward the center of the sarcomere.

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​Sliding Filament Theory

​•Notice that the myofilaments do not get shorter.

•The actin filaments are pulled closer to each other, toward the center of the sarcomere.

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