stimulation and contraction of single skeletal muscle cells excitability (also called responsiveness...
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Stimulation and Contraction of Single Skeletal Muscle Cells
• Excitability (also called responsiveness or irritability)—ability to receive and respond to a stimulus
• Contractility—ability to shorten when an adequate stimulus is received
• Extensibility—ability of muscle cells to be stretched
• Elasticity—ability to recoil and resume resting length after stretching
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The Nerve Stimulus and Action Potential
• Skeletal muscles must be stimulated by a motor neuron (nerve cell) to contract
• Motor unit—one motor neuron and all the skeletal muscle cells stimulated by that neuron
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Figure 6.4a
The Nerve Stimulus and Action Potential
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The Nerve Stimulus and Action Potential
Figure 6.4b
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The Nerve Stimulus and Action Potential
• Neuromuscular junction– Association site of axon terminal of the motor
neuron and muscle
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The Nerve Stimulus and Action Potential
Figure 6.5a
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The Nerve Stimulus and Action Potential
• Synaptic cleft – Gap between nerve and muscle– Nerve and muscle do not make contact– Area between nerve and muscle is filled with
interstitial fluid
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The Nerve Stimulus and Action Potential
Figure 6.5b
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Transmission of Nerve Impulse to Muscle
• Neurotransmitter—chemical released by nerve upon arrival of nerve impulse– The neurotransmitter for skeletal muscle is
acetylcholine (ACh)• Acetylcholine attaches to receptors on the
sarcolemma• Sarcolemma becomes permeable to sodium
(Na+)
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Transmission of Nerve Impulse to Muscle
Figure 6.5c
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Transmission of Nerve Impulse to Muscle
• Sodium rushes into the cell generating an action potential
• Once started, muscle contraction cannot be stopped
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Transmission of Nerve Impulse to Muscle
Figure 6.6
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The Sliding Filament Theory of Muscle Contraction
• Activation by nerve causes myosin heads (cross bridges) to attach to binding sites on the thin filament
• Myosin heads then bind to the next site of the thin filament and pull them toward the center of the sarcomere
• This continued action causes a sliding of the myosin along the actin
• The result is that the muscle is shortened (contracted)
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The Sliding Filament Theory of Muscle Contraction
Figure 6.7a–b
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The Sliding Filament Theory
Figure 6.8a
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The Sliding Filament Theory
Figure 6.8b
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The Sliding Filament Theory
Figure 6.8c