What is the role of acetylcholinesterase in muscle contraction?
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It decomposes acetylcholine (Ach) and prevents continuous stimulation of the muscle fiber.
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What is the role of acetylcholinesterase in muscle contraction?
It decomposes acetylcholine (Ach) and prevents continuous stimulation of the muscle fiber.
What is the contraction type of skeletal muscle?
Neurogenic, meaning it depends on nerve supply.
What is another name for longitudinal tubules?
Sarcoplasmic reticulum.
What is found in the I band of a myofibril?
Actin only.
What are the two chains that make up each actin filament?
Two chains of F-actin twisted in a spiral manner.
What happens to calcium ions during muscle relaxation?
Calcium ions are pumped back into the sarcoplasmic reticulum by a Ca++ pump.
What is a fascicle in skeletal muscle?
A bundle of muscle fibers.
What type of movement do the thin filaments undergo during muscle contraction?
They move in a ratchet-like manner, causing forward movements.
What happens to calcium ions (Ca++) during muscle contraction?
They are actively pumped back to the cisternae of the sarcoplasmic reticulum.
What enzymes are involved in the contraction and relaxation of smooth muscle?
Phosphorylase for contraction and phosphatase for relaxation.
What are the functions of the two heads of myosin?
One binds with actin and the other binds to ATP.
What holds the light bands in a myofibril?
Z lines.
How do the T tubules of cardiac muscle compare to those of skeletal muscle?
They have a diameter 5 times and volume 25 times greater than those of skeletal muscle tubules.
What is released from the myosin head after the power stroke?
ADP and Pi.
What are the sources of calcium ions for muscle contraction?
Extracellular fluid, poorly developed sarcoplasmic reticulum, and mitochondria.
What are the two types of sarcoplasmic tubules?
Longitudinal tubules and transverse tubules (T-tubules).
What does the A band represent in a myofibril?
The region where actin and myosin overlap.
What is the local depolarization at the motor end plate called?
End Plate Potential (EPP).
What does the Z line do in a myofibril?
Bisects the I band.
What do transverse tubules contain?
Extracellular fluid (ECF).
What is the result of the interaction between activated actin and the head of myosin?
ATPase activity of the myosin head splits ATP into ADP, Pi, and energy.
What are the three types of muscles?
Skeletal muscle, smooth muscle, and cardiac muscle.
What is a myofibril?
A long, thread-like structure within a muscle fiber that contains myofilaments.
What binds to the myosin head after ADP and Pi are released?
A new ATP molecule.
What do nicotinic receptors do when acetylcholine binds to them?
They lead to increased Na+ influx.
How do autonomic nerves affect smooth muscle contraction?
They only stimulate or inhibit the contraction.
Do smooth muscle fibers have T tubules?
No, they do not have T tubules.
Is cardiac muscle voluntary or involuntary?
Cardiac muscle is involuntary.
What is the role of tropomyosin in muscle contraction?
It inhibits the active sites of actin.
What type of muscle is voluntary and controlled?
Skeletal muscle.
What type of control do smooth muscles have?
Involuntary control.
What do the ends of longitudinal tubules form?
Cisternae that contain a high concentration of Ca++.
What is a key structural characteristic of smooth muscle?
Smooth muscle is not striated.
What type of muscle is cardiac muscle similar to?
Skeletal muscle, as it is striated.
What is troponin?
A globular protein attached to tropomyosin that regulates muscle contraction.
What is the role of the light chains in myosin?
They control the head function during contraction.
What are the basic structural units of skeletal muscle?
Skeletal muscle fibers.
What happens to the new ATP molecule during muscle contraction?
It is cleaved, allowing the myosin head to bind with a new active site.
What are the two types of filaments contained in each myofibril?
Thick filament and thin filament.
How are longitudinal tubules characterized?
They are parallel to the myofibrils and contain intracellular fluid (ICF).
What is the H zone in a myofibril?
The region containing myosin only.
What are the sources of calcium ions in cardiac muscle?
Cisternae of the sarcoplasmic reticulum and extracellular fluid.
What is a unique feature of cardiac muscle fibers?
They branch and have a single nucleus per cell.
How can cardiac muscle contraction be modulated?
Via the autonomic nervous system.
What characteristic gives skeletal muscle its striated appearance?
The alternating dark and light areas due to interdigitating thin (actin) and thick (myosin) filaments.
What neurotransmitter is released at the motor end plate during nerve stimulation?
Acetylcholine (Ach).
What does it mean that smooth muscle contraction is myogenic?
Smooth muscles can contract in the absence of their nerve supply.
How many polypeptide chains make up each myosin molecule?
Six polypeptide chains.
What opens voltage-gated Ca++ channels?
The propagation of the action potential.
How does the sarcoplasmic reticulum of cardiac muscle compare to that of skeletal muscle?
It is less well developed and does not store enough calcium for full contraction.
What allows cardiac muscle to contract rhythmically without external innervation?
The presence of pacemaker cells that discharge spontaneously.
What are the two main types of myofilaments in skeletal muscle?
Actin and myosin.
What effect does ATP binding have on the myosin head?
It causes detachment of the head from actin.
What is the composition of thin filaments?
They are composed of actin and regulatory proteins.
What happens when the end plate potential reaches firing level?
It propagates as an action potential (AP) along the sarcolemma and T-tubules.
What is a sarcomere?
The contractile unit of the muscle, extending from Z line to Z line.
What is the function of transverse tubules?
They transmit action potentials from the sarcolemma to the interior of the muscle fiber, releasing Ca++ from cisternae.
What does Troponin-C bind with to initiate contraction?
Calcium ions (Ca++).
What happens when the myosin head attaches to actin?
It leads to tilting of the head towards the arm.
What are the two classifications of muscle based on structure?
Striated and non-striated.
What is the primary regulatory protein in smooth muscle?
Calmodulin.
What is the function of the active site on G-actin?
It allows the head of myosin to bind, causing muscle contraction.
How many light chains are associated with each myosin head?
Two light chains are attached to each head.
What is the term for the action that pulls actin filament towards the center of the A-band?
Power stroke.
What are myofibrils composed of?
Bundles of myofilaments (contractile proteins: actin & myosin).
What structural changes occur in the sarcomere during contraction?
The sarcomere shortens, along with the I band and H zone, while the A band does not shorten.
What are G-actin subunits?
Globular subunits that form F-actin.
What are the two hinge systems in a myosin molecule?
One between the arm and head, and the other between the arm and tail.
What holds the dark bands in a myofibril?
Z lines and titin (a large protein).
What are the two classifications of muscle based on function?
Voluntary and involuntary.
What is the composition of the thick filament?
It is composed of myosin molecules.
What are the two types of heavy chains in myosin?
They twist around each other to form a double helix.
What are transverse tubules (T-tubules) characterized by?
They are infolds of the sarcolemma and parallel to the Z-line.
What does the binding of Ca++ to troponin-C cause?
It pulls tropomyosin away from the active site of actin.
What are the three subunits of troponin?
Troponin-T, Troponin-I, and Troponin-C.
How much can the active Ca++ pump concentrate Ca++ in longitudinal tubules?
1000 folds.
What does Ca++ bind to in order to activate actin?
Troponin-C.
What does the strength of contraction in cardiac muscle depend on?
The concentration of calcium ions in extracellular fluid.
What is the function of Troponin-I?
It inhibits the interaction of actin with myosin.
