52 Questions
What are the three types of muscle tissue?
Skeletal, cardiac, and smooth
Which type of muscle tissue is subject to conscious control?
Skeletal muscle
What is the term for the plasma membrane of muscle cells?
Sarcolemma
What is the gross structure that skeletal muscle tissue is packaged into?
Skeletal muscles
What is the function of skeletal muscle tissue?
Produce movement, maintain posture, stabilize joints, and generate heat
Where is smooth muscle tissue found?
In hollow visceral organs
What are the special characteristics of muscle tissue?
Excitability, contractility, extensibility, and elasticity
What surrounds each individual muscle fiber?
Endomysium
What is the function of cardiac muscle tissue?
Occurs only in the heart and is involuntary
What does skeletal muscle consist of, in addition to muscle fibers?
Nerves, blood vessels, and connective tissues
What surrounds each fascicle?
Perimysium
Which type of muscle tissue forces fluids through body channels?
Smooth muscle tissue
What is the composition of connective tissue sheaths that support muscle tissue?
Epimysium, perimysium, and endomysium
What controls the activity of each skeletal muscle fiber?
A nerve ending
What is the function of skeletal muscle?
Exert a force from a fraction of an ounce to about 6 pounds
What is the main function of muscle tissue?
Produce movement, maintain posture, stabilize joints, and generate heat
What is the main component of thin filaments in skeletal muscle?
Actin
Which protein holds thick filaments in place and helps the muscle cell spring back into shape after stretching?
Titin
What is the function of the Sarcoplasmic Reticulum (SR) in skeletal muscle?
Regulates intracellular levels of ionic calcium
What is the role of T tubules in skeletal muscle fibers?
Increase the muscle fiber's surface area and conduct impulses to trigger the release of calcium
What is the function of dystrophin in skeletal muscle?
Links thin filaments to the integral proteins of the sarcolemma
What maintains the alignment of filaments and sarcomeres in skeletal muscle?
C proteins
What do the triad relationships between T tubules and SR provide signals for in skeletal muscle?
Muscle contraction
What happens to the length of thick and thin filaments during muscle contraction?
Neither the thick nor the thin filaments change length during contraction
Which proteins control myosin-actin interactions in skeletal muscle?
Tropomyosin and troponin
What is the main component of thick filaments in skeletal muscle?
Myosin
What do the intermediate (Desmin) filaments do in skeletal muscle?
Extend from the Z disc and connect myofibrils throughout the width of the muscle cell
What model of contraction states that during contraction, thin filaments slide past thick ones so that actin and myosin filaments overlap?
Sliding filament model of contraction
What are the three connective tissue sheaths of skeletal muscles?
Epimysium, perimysium, and endomysium
What is the average length of a sarcomere, the smallest contractile unit of a muscle fiber?
2 µm
What is the primary protein component of thick filaments in muscle cells?
Myosin
What is the function of myosin heads during muscle contraction?
Form cross bridges with actin
What is the role of T tubules in muscle cells?
Transmit action potentials to the interior of the muscle fiber
What is the function of sarcoplasmic reticulum in muscle cells?
Store and release calcium ions for muscle contraction
What is the size range of skeletal muscle fibers?
10-100 µm diameter, up to 30 cm long
What are the proteins responsible for motility and shape change in muscle fibers?
Actin and myosin
What is the main reason for the commonality of indirect muscle attachments?
Durability and small size
What type of muscle attachment involves the muscle being fused directly to bone or cartilage?
Direct attachment
What is the term for the movable bone to which a muscle is attached, moving towards the immovable bone during contraction?
Insertion
What is the primary function of the endomysium in skeletal muscles?
Surround individual muscle fibers
What is the neurotransmitter used to signal muscle contraction at the neuromuscular junction?
Acetylcholine
What triggers the release of Ca$^{2+}$ from the terminal cisterns of the SR during muscle contraction?
Action potential
What is the role of troponin during muscle contraction?
Binding to Ca$^{2+}$
What type of neurons initiate skeletal muscle contractions?
Motor neurons
What causes the local depolarization called an end plate potential (EPP) at the neuromuscular junction?
Release of acetylcholine
What is the role of myosin heads during muscle contraction?
Latching onto myosin-binding sites on actin
What type of ion channels underpin all action potentials?
Voltage-gated ion channels
What happens to the I bands during muscle cell shortening?
They shorten
What is the role of the synaptic cleft at the neuromuscular junction?
Filled with a gel-like extracellular substance rich in glycoproteins and collagen fibers
What triggers muscle fiber excitation at the neuromuscular junction?
End plate potential (EPP)
What type of neurons connect with skeletal muscle fibers?
Somatic motor neurons
What is the primary factor causing the sliding and shortening of muscle cells?
Myosin heads latching onto myosin-binding sites on actin
Study Notes
Muscle Contraction and Neuromuscular Junction: Key Points
- Muscle contraction is initiated by the nervous system stimulating muscle fibers, causing myosin heads to latch onto myosin-binding sites on actin in the thin filaments, leading to sliding and shortening of muscle cells.
- During muscle cell shortening, the I bands shorten, the distance between Z discs decreases, H zones disappear, and A bands move closer together.
- Skeletal muscle contractions are voluntary and are initiated by motor neurons in the spinal cord, which connect with skeletal muscles and use acetylcholine as a neurotransmitter to signal muscle contraction.
- Both neurons and muscles are excitable cells, responding to external stimuli by changing their resting membrane potential, with action potentials (AP) being the electrical signals that spread within a cell.
- Voltage-gated ion channels open or close in response to changes in membrane potential, underpinning all action potentials, with chemically gated ion channels causing a small local depolarization that triggers the voltage-gated ion channels.
- Motor neurons connecting with skeletal muscle fibers are somatic motor neurons, residing in the spinal cord and innervating multiple muscle fibers via axon terminals that form neuromuscular junctions with muscle cells.
- The neuromuscular junction consists of the axon terminals, junctional folds of muscle cells, and the synaptic cleft filled with a gel-like extracellular substance rich in glycoproteins and collagen fibers.
- Events at the neuromuscular junction involve the release of acetylcholine by the motor neuron, stimulating the skeletal muscle fiber and causing a local depolarization called an end plate potential (EPP).
- Muscle fiber excitation is triggered by the EPP, leading to an action potential that travels across the entire sarcolemma, and subsequently, excitation-contraction coupling occurs, where the action potential causes the release of Ca2+ from the terminal cisterns of the SR.
- The released Ca2+ binds to troponin, exposing the myosin-binding sites on actin, allowing myosin heads to bind to actin and initiating muscle contraction.
- The cross bridge cycle is a series of events that occur during muscle contraction, involving the formation and breaking of cross bridge attachments between myosin and actin.
- The process of muscle contraction and the neuromuscular junction is a complex interplay of cellular and molecular events that ultimately lead to the shortening of muscle cells and the generation of tension.
Test your knowledge of muscle contraction and the neuromuscular junction with this quiz. Explore key points such as the role of motor neurons, the events at the neuromuscular junction, excitation-contraction coupling, and the cross bridge cycle. Dive into the intricate process of muscle cell shortening and tension generation.
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