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Questions and Answers
ACh stands for Acetylcholine, which is the neurotransmitter released at the NMJ.
True
The NMJ allows for direct physical contact between the motor nerve and the muscle.
False
The process of neurotransmitter release at the NMJ is a chemical synapse mechanism.
True
Alpha motor neurons are also known as upper motor neurons.
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Mitochondria are abundant in both the pre-synaptic and post-synaptic terminals of the NMJ.
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The synaptic cleft at the NMJ is about 50 micrometers wide.
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The binding of ACh to receptors on the muscle sets up a muscle action potential.
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The process of cross-bridge formation is involved in muscle relaxation.
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The sequence of events at the NMJ includes the arrival of a nerve signal and the subsequent release of neurotransmitters.
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Type I muscle fibers are also known as fast twitch fibers.
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Acetylcholine (ACh) is broken down by acetylcholinesterase (AChE) after it triggers an action potential.
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Skeletal muscle contractions occur in a unit called a sarcomere, which extends from one M line to the next.
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Type II muscle fibers have a high level of myoglobin compared to Type I fibers.
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Myosin ATPase in Type I fibers hydrolyzes ATP more quickly than in Type II fibers.
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The arrangement of actin and myosin filaments within myofibrils provides muscles with a striated appearance.
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Skeletal muscle fibers contain a well-developed sarcoplasmic reticulum for calcium storage.
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Slow twitch fibers primarily rely on glycolytic metabolism for energy.
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T-tubules are involved in the rapid transmission of the muscle action potential across the fiber.
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Troponin and tropomyosin are components of the thick filament in muscle cells.
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Study Notes
Neuromuscular Junction (NMJ)
- The NMJ is an example of a synapse where a motor nerve meets the muscle
- The NMJ is a chemical synapse
- The synaptic cleft is the space between the nerve and the muscle
- The NMJ is approximately 20 µm wide
- The neurotransmitter acetylcholine (ACh) is released into the synaptic cleft
- ACh binds to receptors on the muscle
- This triggers an end-plate potential (EPP)
- The EPP sets up an action potential in the skeletal muscle
- The muscle then contracts
Structure of the NMJ
- The motor neuron is known as a lower motor neuron, somatic motor neuron, or alpha (α) motor neuron
- The pre-synaptic nerve terminal and the post-synaptic muscle terminal both contain many mitochondria
- ACh is synthesised and stored in the pre-synaptic terminals in synaptic vesicles
- ACh is broken down by acetylcholinesterase (AChE)
Contractile Unit of Muscle
- The contractile unit of skeletal muscle is the sarcomere which extends from one Z disc to the next
- Sarcomeres are composed of:
- Actin (thin filament)
- Myosin (thick filament)
- Titin
- Troponin
- Tropomyosin
Types of Skeletal Muscle Fibers
-
Type I Slow twitch (Red) muscle fibers
- Good for posture
- Myoglobin +++ (red color)
- Mitochondria +++
- Oxidative metabolism +++
- Sarcoplasmic Reticulum (SR) Moderately Developed
- Myosin ATPase isoform hydrolyses ATP more slowly
- Fatigue resistant
-
Type II Fast twitch (White) muscle fibers
- Good for extraocular eye muscles
- Less Myoglobin
- Less Mitochondria
- Some Oxidative metabolism & More Glycolytic metabolism
- Sarcoplasmic Reticulum (SR) Highly developed
- Myosin ATPase isoform hydrolyses ATP quickly
- More Fatigue prone
Muscle Histology
- Muscle fibers are made up of myofibrils
- Myofibrils are made up of myofilaments of Actin and Myosin
- The T-tubules enable the muscle action potential to spread throughout the muscle fiber
- Muscle fibers contain many mitochondria which produce ATP
- The SR is where calcium is stored
Contraction-Relaxation Cycle
- The sequence of events that occur during a muscle contraction and relaxation is known as the cross-bridge cycle
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Description
Explore the fascinating mechanics of the neuromuscular junction (NMJ), where motor nerves meet muscle fibers. This quiz covers the structure, function, and importance of the NMJ in muscle contraction, including the roles of neurotransmitters and the contractile unit of the muscle. Test your knowledge on how signals lead to muscle movement!
