p.11
Regulatory Proteins in Muscle Contraction
What is the role of acetylcholinesterase in muscle contraction?
It decomposes acetylcholine (Ach) and prevents continuous stimulation of the muscle fiber.
p.1
Excitation-Contraction Coupling
What is the contraction type of skeletal muscle?
Neurogenic, meaning it depends on nerve supply.
p.6
Muscle Fiber Structure
What are the two chains that make up each actin filament?
Two chains of F-actin twisted in a spiral manner.
p.11
Excitation-Contraction Coupling
What happens to calcium ions during muscle relaxation?
Calcium ions are pumped back into the sarcoplasmic reticulum by a Ca++ pump.
p.3
Muscle Fiber Structure
What is a fascicle in skeletal muscle?
A bundle of muscle fibers.
p.10
Excitation-Contraction Coupling
What type of movement do the thin filaments undergo during muscle contraction?
They move in a ratchet-like manner, causing forward movements.
p.10
Role of Calcium in Muscle Contraction
What happens to calcium ions (Ca++) during muscle contraction?
They are actively pumped back to the cisternae of the sarcoplasmic reticulum.
p.12
Smooth Muscle Characteristics
What enzymes are involved in the contraction and relaxation of smooth muscle?
Phosphorylase for contraction and phosphatase for relaxation.
p.5
Role of Calcium in Muscle Contraction
What are the functions of the two heads of myosin?
One binds with actin and the other binds to ATP.
p.12
Differences in Muscle Types
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.
p.11
Role of Calcium in Muscle Contraction
What are the sources of calcium ions for muscle contraction?
Extracellular fluid, poorly developed sarcoplasmic reticulum, and mitochondria.
p.7
Muscle Fiber Structure
What are the two types of sarcoplasmic tubules?
Longitudinal tubules and transverse tubules (T-tubules).
p.4
Muscle Fiber Structure
What does the A band represent in a myofibril?
The region where actin and myosin overlap.
p.8
Excitation-Contraction Coupling
What is the local depolarization at the motor end plate called?
End Plate Potential (EPP).
p.7
Muscle Fiber Structure
What do transverse tubules contain?
Extracellular fluid (ECF).
p.8
Excitation-Contraction Coupling
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.
p.1
Differences in Muscle Types
What are the three types of muscles?
Skeletal muscle, smooth muscle, and cardiac muscle.
p.3
Myofibrils and Filaments
What is a myofibril?
A long, thread-like structure within a muscle fiber that contains myofilaments.
p.8
Excitation-Contraction Coupling
What do nicotinic receptors do when acetylcholine binds to them?
They lead to increased Na+ influx.
p.2
Smooth Muscle Characteristics
How do autonomic nerves affect smooth muscle contraction?
They only stimulate or inhibit the contraction.
p.12
Differences in Muscle Types
Do smooth muscle fibers have T tubules?
No, they do not have T tubules.
p.2
Cardiac Muscle Characteristics
Is cardiac muscle voluntary or involuntary?
Cardiac muscle is involuntary.
p.6
Regulatory Proteins in Muscle Contraction
What is the role of tropomyosin in muscle contraction?
It inhibits the active sites of actin.
p.7
Muscle Fiber Structure
What do the ends of longitudinal tubules form?
Cisternae that contain a high concentration of Ca++.
p.2
Smooth Muscle Characteristics
What is a key structural characteristic of smooth muscle?
Smooth muscle is not striated.
p.2
Cardiac Muscle Characteristics
What type of muscle is cardiac muscle similar to?
Skeletal muscle, as it is striated.
p.6
Regulatory Proteins in Muscle Contraction
What is troponin?
A globular protein attached to tropomyosin that regulates muscle contraction.
p.5
Regulatory Proteins in Muscle Contraction
What is the role of the light chains in myosin?
They control the head function during contraction.
p.10
Excitation-Contraction Coupling
What happens to the new ATP molecule during muscle contraction?
It is cleaved, allowing the myosin head to bind with a new active site.
p.5
Muscle Fiber Structure
What are the two types of filaments contained in each myofibril?
Thick filament and thin filament.
p.7
Muscle Fiber Structure
How are longitudinal tubules characterized?
They are parallel to the myofibrils and contain intracellular fluid (ICF).
p.4
Muscle Fiber Structure
What is the H zone in a myofibril?
The region containing myosin only.
p.12
Role of Calcium in Muscle Contraction
What are the sources of calcium ions in cardiac muscle?
Cisternae of the sarcoplasmic reticulum and extracellular fluid.
p.2
Cardiac Muscle Characteristics
What is a unique feature of cardiac muscle fibers?
They branch and have a single nucleus per cell.
p.2
Cardiac Muscle Characteristics
How can cardiac muscle contraction be modulated?
Via the autonomic nervous system.
p.1
Skeletal Muscle Characteristics
What characteristic gives skeletal muscle its striated appearance?
The alternating dark and light areas due to interdigitating thin (actin) and thick (myosin) filaments.
p.2
Smooth Muscle Characteristics
What does it mean that smooth muscle contraction is myogenic?
Smooth muscles can contract in the absence of their nerve supply.
p.8
Excitation-Contraction Coupling
What opens voltage-gated Ca++ channels?
The propagation of the action potential.
p.12
Skeletal Muscle Characteristics
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.
p.2
Cardiac Muscle Characteristics
What allows cardiac muscle to contract rhythmically without external innervation?
The presence of pacemaker cells that discharge spontaneously.
p.9
Regulatory Proteins in Muscle Contraction
What effect does ATP binding have on the myosin head?
It causes detachment of the head from actin.
p.6
Muscle Fiber Structure
What is the composition of thin filaments?
They are composed of actin and regulatory proteins.
p.8
Excitation-Contraction Coupling
What happens when the end plate potential reaches firing level?
It propagates as an action potential (AP) along the sarcolemma and T-tubules.
p.4
Muscle Fiber Structure
What is a sarcomere?
The contractile unit of the muscle, extending from Z line to Z line.
p.7
Excitation-Contraction Coupling
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.
p.9
Excitation-Contraction Coupling
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.
p.6
Excitation-Contraction Coupling
What is the function of the active site on G-actin?
It allows the head of myosin to bind, causing muscle contraction.
p.5
Myofibrils and Filaments
How many light chains are associated with each myosin head?
Two light chains are attached to each head.
p.4
Muscle Fiber Structure
What are myofibrils composed of?
Bundles of myofilaments (contractile proteins: actin & myosin).
p.10
Skeletal Muscle Characteristics
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.
p.6
Muscle Fiber Structure
What are G-actin subunits?
Globular subunits that form F-actin.
p.5
Myofibrils and Filaments
What are the two hinge systems in a myosin molecule?
One between the arm and head, and the other between the arm and tail.
p.4
Muscle Fiber Structure
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.
p.5
Myofibrils and Filaments
What is the composition of the thick filament?
It is composed of myosin molecules.
p.5
Myofibrils and Filaments
What are the two types of heavy chains in myosin?
They twist around each other to form a double helix.
p.7
Muscle Fiber Structure
What are transverse tubules (T-tubules) characterized by?
They are infolds of the sarcolemma and parallel to the Z-line.
p.8
Excitation-Contraction Coupling
What does the binding of Ca++ to troponin-C cause?
It pulls tropomyosin away from the active site of actin.
p.6
Regulatory Proteins in Muscle Contraction
What are the three subunits of troponin?
Troponin-T, Troponin-I, and Troponin-C.
p.12
Role of Calcium in Muscle Contraction
What does the strength of contraction in cardiac muscle depend on?
The concentration of calcium ions in extracellular fluid.
p.6
Regulatory Proteins in Muscle Contraction
What is the function of Troponin-I?
It inhibits the interaction of actin with myosin.
