Lecture 18 Flashcards
Where is acetylcholine released in the neuromuscular junction
motor end plate
What is another name for neuromuscular junction
• Also known as NMJ or
myoneural junction
where is the NMJ located
Site where an axon and
muscle fiber meet
What are the parts at NMJ
- Motor neuron
- Motor end plate
- Synapse
- Synaptic cleft
- Synaptic vesicles
- Neurotransmitters
What is the use of motor unit
• All muscle fibers controlled by motor neuron •As few as four fibers • As many as 1000’s of muscle fibers
How is the muscle stimulated to contract
• Acetylcholine (ACh) • Nerve impulse causes release of ACh from synaptic vesicles • ACh binds to ACh receptors on motor end plate • Generates a muscle impulse • Muscle impulse eventually reaches the SR and the cisternae
What are the muscle coverings
- Muscle coverings:
- Epimysium
- Perimysium
- Endomysium
Names of the muscles from the most surface layer to the smallest part of the muscle
Muscle > Fascicles > muscle fibers (cells) > myofibrills > thick and thin filaments
What are the thick and thin myofilaments made of
- Actin and myosin proteins
* Titin is an elastic myofilament
What is the triad in muscle fibers
Triad
• Cisternae of SR
• T tubule
What is sarcomere
the combination of myofilaments • I band (thin) • A band (thick and thin) • H zone (thick) • Z line (or disc) • M line
What is wrapping around the actin molecule like a DNA
tropomyosin
What is the bulb attached to the tropomyosin
troponin
What is the protruding part of the myosin
cross-bridges
What is the cross–bridges made of
the head of the myosin molecule with actin-binding site and myosin ATPase site
What is connecting the myosin head to the tail
hindges
What does troponin have
Ca2+ binding site
How does muscle impulses have an impact on calcium ions
• Muscle impulses cause SR to
release calcium ions into cytosol
• Calcium binds to troponin to
change its shape
What happens when calcium binds to tropinin
• Calcium binds to troponin to change its shape • The position of tropomyosin is altered • Binding sites on actin are now exposed • Actin and myosin molecules bind via myosin cross-bridges
how does muscle contract
Exposed binding sites on actin molecules allow the muscle contraction cycle to occur.
2. cross bridges bind actin to myosin
3. cross-bridges pull thin filament (power stroke), ADP and P released from myosin
4. New ATP binds to myosin, releasing linkages
5 ATP splits, which provides power to cock the myosin cross-bridge
Where does the Ca2+ comes from
sacroplasmic reticulum, a lateral sac
What can Ca2+ do
Ca2+ binding to troponin removes blocking action of tropomyosin
What are the Cross Bridge Cycling steps
• Myosin cross-bridge attaches to actin binding site • Myosin cross-bridge pulls thin filament • ADP and phosphate released from myosin • New ATP binds to myosin • Linkage between actin and myosin cross-bridge break • ATP splits • Myosin cross-bridge goes back to original position
What happens during relaxation of the muscle
• Acetylcholinesterase – rapidly decomposes Ach remaining in
the synapse
• Muscle impulse stops
• Stimulus to sarcolemma and muscle fiber membrane ceases
• Calcium moves back into sarcoplasmic reticulum (SR)
• Myosin and actin binding prevented
• Muscle fiber relaxes
