Muscle Types and Skeletal Muscle Functions

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Questions and Answers

What is the primary role of troponin and tropomyosin in skeletal muscle contraction?

To generate ATP

To transmit nerve signals to the muscle

To store calcium ions

To modulate the interaction between actin and myosin (correct)

Which type of muscle is described as striated and involuntary?

Cardiac muscle (correct)

Connective muscle

Smooth muscle

Skeletal muscle

What happens during the cross-bridge cycle in skeletal muscle?

Calcium ions are released into the blood stream

The muscle lengthens and prepares for relaxation

ATP is produced to fuel muscle contractions

Myosin heads bind to actin filaments creating a power stroke (correct)

Which structure is responsible for the storage and release of calcium ions in skeletal muscle?

Sarcoplasmic reticulum Signup and view all the answers

What process describes the steps involved in converting an electrical signal from a nerve into a contraction of skeletal muscle?

Excitation-contraction coupling Signup and view all the answers

Which neurotransmitter is primarily involved in the neuromuscular junction for skeletal muscles?

Acetylcholine Signup and view all the answers

What role does the Ca2+-ATPase pump serve in skeletal muscle function?

It accumulates calcium ions in the sarcoplasmic reticulum Signup and view all the answers

Which structure in skeletal muscle allows for the transmission of the electrical signal deep into the muscle fibers?

Transverse tubules Signup and view all the answers

What is the primary function of the skeletal muscles in terms of body movement?

Producing body movements like walking and running Signup and view all the answers

What property of muscles allows them to stretch without damage?

Extensibility Signup and view all the answers

What is thermogenesis in muscle function?

The process of muscle contraction generating heat Signup and view all the answers

What role does acetylcholine play in skeletal muscle control?

It signals the muscle to contract at the neuromuscular junction Signup and view all the answers

Which of the following statements about the somatic nervous system is correct?

It sends commands to activate skeletal muscles Signup and view all the answers

Which property of muscles allows them to return to their original length after being contracted?

Elasticity Signup and view all the answers

Skeletal muscle contractions stabilize joints and maintain body positions. What is the role of postural muscles?

They contract continuously when awake to hold body positions Signup and view all the answers

What happens at the neuromuscular junction when an action potential arrives?

Acetylcholine is released to stimulate muscle contraction Signup and view all the answers

What is the primary protein of the thin filament in skeletal muscles?

Actin Signup and view all the answers

Which protein serves as a calcium sensor that triggers muscle contraction?

Troponin Signup and view all the answers

What is the role of tropomyosin in skeletal muscle fibers?

Blocking myosin binding sites during relaxation Signup and view all the answers

Which of the following describes the structure known as a sarcomere?

A contractile assembly of proteins in a muscle cell Signup and view all the answers

What is the primary role of structural proteins in skeletal muscles?

To contribute to alignment, stability, extensibility, and elasticity Signup and view all the answers

Which protein acts as a spring-like connector of the thick filament to the Z-disc?

Titin Signup and view all the answers

What are transverse tubules in striated muscle?

Extensions of the plasma membrane Signup and view all the answers

What type of muscle protein is myosin classified as?

Contractile Signup and view all the answers

Which protein is involved in connecting the Z-disc to the membrane cytoskeleton?

Dystrophin Signup and view all the answers

What is the primary structural protein of the Z-disc?

Alpha-actinin Signup and view all the answers

What initiates the attachment of myosin to actin during muscle contraction?

Hydrolysis of ATP Signup and view all the answers

What structural change in myosin occurs during ATP hydrolysis?

From weak to strong affinity for actin Signup and view all the answers

What is the role of the phosphate group that is released during the power stroke?

It allows the myosin head to pivot and generate force. Signup and view all the answers

During the detachment phase of the crossbridge cycle, what must occur for myosin to release actin?

Myosin binds to another ATP Signup and view all the answers

In the absence of calcium ions, what occurs that prevents muscle contraction?

Tropomyosin blocks myosin binding sites. Signup and view all the answers

What causes the myosin heads to change from a 'perpendicular' position to a 'pivoting' position?

The release of ADP and Pi Signup and view all the answers

Which phase of the contraction cycle involves the actual generating of force?

Power stroke Signup and view all the answers

What happens to the myofibrils as a result of sarcomere shortening?

They shorten, leading to whole muscle contraction. Signup and view all the answers

What is the primary function of tropomyosin in the process of excitation-contraction coupling?

It prevents myosin from binding to actin in the absence of calcium. Signup and view all the answers

Which of the following correctly describes the role of calcium ions during muscle contraction?

They bind to troponin, causing tropomyosin to shift and expose binding sites on actin. Signup and view all the answers

What is the role of the sarcoplasmic reticulum in skeletal muscle contraction?

It stores and releases calcium ions necessary for muscle contraction. Signup and view all the answers

What sequence describes the steps involved in neuromuscular transmission at the neuromuscular junction?

Calcium influx, acetylcholine release, action potential generation. Signup and view all the answers

What is a key function of the transverse tubules in skeletal muscles?

They conduct action potentials deep into the muscle fiber. Signup and view all the answers

Which of the following best describes the term 'cross-bridge cycle'?

The repetitive formation and breaking of bonds between actin and myosin during muscle contraction. Signup and view all the answers

What are the three primary roles of ATP in skeletal muscle contraction and relaxation?

Providing energy for muscle contraction, facilitating calcium ion reuptake, and powering the sodium-potassium pump. Signup and view all the answers

What is the importance of the neuromuscular junction in muscle function?

It allows for communication between motor neurons and muscle cells to initiate contraction. Signup and view all the answers

What is the role of the motor end plate in the neuromuscular junction?

It is the specialized region of the muscle membrane that receives neurotransmitter signals. Signup and view all the answers

During muscle contraction, what happens to the A-band in the sarcomere?

It remains the same width. Signup and view all the answers

What initiates the end plate potential at the muscle membrane?

Binding of acetylcholine to nicotinic receptors. Signup and view all the answers

What role does acetylcholinesterase play at the neuromuscular junction?

It breaks down acetylcholine in the synaptic cleft. Signup and view all the answers

Which structure is crucial for the propagation of the action potential in muscle fibers?

T-tubules. Signup and view all the answers

What is the primary function of the dihydropyridine receptor (DHP) in muscle fibers?

To act as a voltage sensor responding to action potentials. Signup and view all the answers

Which component of the sarcomere appears to narrow during contraction?

I-band. Signup and view all the answers

What happens when the end plate potential exceeds the threshold at the motor end plate?

An action potential is generated in the muscle fiber. Signup and view all the answers

What structural change occurs in the sarcomere during contraction?

The Z-discs come closer together. Signup and view all the answers

Which receptor is primarily responsible for calcium release from the sarcoplasmic reticulum during muscle contraction?

Ryanodine receptor. Signup and view all the answers

Which of the following accurately describes the sliding filament mechanism?

Thick filaments pull on the thin filaments, resulting in shortening of the sarcomere. Signup and view all the answers

What is the significance of the triad structure in muscle fibers?

It connects the T-tubule to the sarcoplasmic reticulum for efficient calcium release. Signup and view all the answers

Which condition leads to muscle contraction at the molecular level?

Elevated calcium ion concentrations in the cytoplasm. Signup and view all the answers

What is the role of the sarcoplasmic reticulum calcium-ATPase during muscle relaxation?

To pump calcium ions back into the sarcoplasmic reticulum. Signup and view all the answers

What is the primary function of Creatine Kinase in skeletal muscle?

It regenerates ATP by transferring phosphate from Creatine-phosphate to ADP. Signup and view all the answers

How many ATP molecules are produced from one glucose molecule in the glycolysis process?

2 ATP Signup and view all the answers

Which process relies on the presence of oxygen and occurs in mitochondria to produce ATP?

Oxidative phosphorylation Signup and view all the answers

What limits the duration of ATP production via Creatine Kinase during muscle contraction?

The quantity of Creatine Phosphate stored in the cell Signup and view all the answers

What happens to Creatine Phosphate during periods of rest in muscle cells?

It accumulates and helps regenerate ATP from ADP. Signup and view all the answers

Which muscle fiber type has the highest likelihood of rapid fatigue?

Fast glycolytic Signup and view all the answers

What contributes most significantly to the generation of greater tension in muscles?

The number of active motor units Signup and view all the answers

Which factor is NOT considered a mechanism of fatigue in skeletal muscles?

Excess ATP production Signup and view all the answers

Which characteristic is true for fast oxidative muscle fibers?

They are moderately likely to fatigue. Signup and view all the answers

What does the term 'motor unit' refer to in muscle physiology?

A motor neuron and its associated muscle fibers Signup and view all the answers

Which type of motor unit generates the most tension quickly?

Fast-glycolytic fibers Signup and view all the answers

How does the size of a motor unit relate to the force it can generate?

Larger motor units generate more tension Signup and view all the answers

What characterizes slow-oxidative motor units?

Small diameter muscle fibers Signup and view all the answers

Which motor unit type would most likely be recruited first during low-intensity activities?

Slow-oxidative fibers Signup and view all the answers

What is the relationship between the number of fibers in a motor unit and the tension it generates?

More fibers lead to more tension generation Signup and view all the answers

What is the primary function of glycolysis in muscle metabolism?

Converts glucose to ATP in the absence of O2 Signup and view all the answers

How many ATP molecules are produced by glycolysis from one molecule of glucose?

2 ATP Signup and view all the answers

What is required for oxidative phosphorylation to occur?

Mitochondria and oxygen Signup and view all the answers

Which metabolic pathway can produce ATP during high intensity exercise?

Glycolysis Signup and view all the answers

What is the total ATP yield from one glucose molecule during oxidative phosphorylation?

36 ATP Signup and view all the answers

Under which condition does glycolysis primarily occur in muscle cells?

Insufficient oxygen supply Signup and view all the answers

What byproducts are produced from glycolysis when oxygen is insufficient?

Lactic acid and pyruvic acid Signup and view all the answers

In which metabolic pathway is fatty acid converted to ATP?

Aerobic respiration Signup and view all the answers

What is the primary function of creatine kinase (CK) during muscle activity?

To transfer a phosphate from creatine phosphate to ADP Signup and view all the answers

What is the main energy source for muscle activity during high-intensity exercise?

Glucose through glycolysis Signup and view all the answers

What is a characteristic of oxidative phosphorylation in ATP production?

It occurs in the mitochondria and requires oxygen Signup and view all the answers

During what condition does glycolysis predominantly supply ATP to muscle cells?

High-intensity, anaerobic exercise Signup and view all the answers

Which of the following statements correctly describes creatine phosphate (CP) in muscle cells?

It is a short-term storehouse of energy rich phosphate Signup and view all the answers

Which of these describes a key difference between glycolysis and oxidative phosphorylation?

Glycolysis generates ATP without oxygen, oxidative phosphorylation requires oxygen Signup and view all the answers

Which source of fuel transitions to become predominant during extended periods of muscle activity?

Fatty acids Signup and view all the answers

What limits the effectiveness of ATP production using creatine kinase during muscle contraction?

The amount of creatine phosphate stored in muscle Signup and view all the answers

What type of neurons have cell bodies located in the brain stem and spinal cord, serving as the final common pathway to skeletal muscles?

Lower motor neurons Signup and view all the answers

Which part of the neural circuitry is responsible for integrating sensory feedback to influence motor programs?

Association cortex Signup and view all the answers

What is the role of local circuit neurons in the neural control of movement?

To provide input from sensory neurons and interneurons Signup and view all the answers

What component considered part of the middle level of control assists in coordinating movements based on sensory feedback?

Cerebellum Signup and view all the answers

Which term best describes the role of lower motor neurons in the context of muscle output?

Final common pathway Signup and view all the answers

Which structure directly influences the coordination of voluntary movements by processing intended actions and sensory feedback?

Cerebellum Signup and view all the answers

What broadly defines the process that regulates the activity of lower motor neurons?

Neural circuits Signup and view all the answers

Which type of neurons serve at the lowest level of motor control receiving inputs from sensory neurons and local interneurons?

Local circuit neurons Signup and view all the answers

What is a key distinction between the motor neuron pathways of the autonomic and somatic nervous systems?

Somatic pathways consist of a single motor neuron. Signup and view all the answers

Which effectors are primarily controlled by the autonomic nervous system?

Smooth muscle and cardiac muscle Signup and view all the answers

Which neurotransmitter is released by all somatic motor neurons?

Acetylcholine Signup and view all the answers

Which proprioceptors are involved in muscle tension and provide a feedback mechanism?

Golgi tendon organs Signup and view all the answers

What initiates the knee jerk reflex when striking the patellar tendon?

Activation of the somatic motor neuron Signup and view all the answers

Which regions of the brain are identified as primarily involved in the middle level of motor control?

Motor cortex and basal ganglia Signup and view all the answers

Which of the following best describes the function of higher centers in motor control?

Integrating sensory input and planning motor responses Signup and view all the answers

How does smooth muscle activation differ from skeletal muscle activation?

Skeletal muscle predominantly uses calcium released from the sarcoplasmic reticulum. Signup and view all the answers

What is the primary role of the muscle spindle in skeletal muscle?

To detect changes in muscle length Signup and view all the answers

Which motor neurons innervate the contractile ends of muscle spindles?

Gamma motor neurons Signup and view all the answers

How does the Golgi Tendon Organ function in response to muscle contraction?

It relaxes the muscle fibers undergoing tension. Signup and view all the answers

What type of reflex arc describes the knee jerk reflex?

Monosynaptic reflex Signup and view all the answers

What happens to the opposing muscle during the knee jerk reflex?

It experiences reciprocal inhibition. Signup and view all the answers

What type of sensory endings are found within the Golgi Tendon Organs?

Sensory nerve endings intertwining with collagen fibers Signup and view all the answers

What type of reflex arc allows sensory input to enter the spinal cord on the same side from which motor output leaves?

Ipsilateral reflex Signup and view all the answers

What aspect of muscle spindle function is involved in controlling muscle length?

The recruitment of gamma motor neurons Signup and view all the answers

What are the components of a reflex arc according to Wu’s Rule?

Stimulus, Receptor, Afferent Pathway, Integrating Center, Efferent Pathway, Effector, Response Signup and view all the answers

What role do muscle spindles serve in the context of skeletal muscle reflexes?

They respond to changes in muscle length. Signup and view all the answers

In the local level of motor control, what is the primary function of the interneuron?

To relay sensory information. Signup and view all the answers

Which of the following statements explains the importance of feedback from peripheral sensors?

They ensure a faster response to environmental changes. Signup and view all the answers

What results from the activity of the basal nuclei and cerebellum on upper motor neurons?

Modulation of upper motor neuron activity. Signup and view all the answers

What type of sensory receptors provide input for reflex actions related to excessive muscle tension?

Tendon organs. Signup and view all the answers

Which element of a reflex arc acts as the integrating center?

Interneuron. Signup and view all the answers

What is the main function of peripheral receptors in motor control?

To provide sensory information to central motor control centers. Signup and view all the answers

What is the primary function of the Golgi tendon organ reflex?

Causes muscle relaxation in response to excessive tension Signup and view all the answers

Which part of the reflex arc is responsible for processing sensory information?

Integrating center Signup and view all the answers

What type of reflex arc is associated with muscle spindle function?

Monosynaptic Signup and view all the answers

In response to excessive tension, what role do inhibitory action potentials play in the Golgi tendon organ reflex?

They promote muscle relaxation Signup and view all the answers

Which component of the Golgi tendon organ reflex is activated during excessive tension in the tendon?

Inhibitory interneurons Signup and view all the answers

What type of arc is characteristic of muscle spindle reflex elements?

Monosynaptic reflex arc Signup and view all the answers

What is the role of the integrating center in the muscle spindle reflex?

To modify and process incoming sensory signals Signup and view all the answers

What occurs at the spinal cord level during the Golgi tendon organ reflex?

Inhibition of antagonist muscle contraction Signup and view all the answers

What is the primary function of the basal nuclei in relation to movement control?

Suppressing unwanted movements and initiating movement Signup and view all the answers

Where are the cell bodies of alpha-motor neurons primarily located?

In the brain stem and spinal cord Signup and view all the answers

Which sequence correctly represents the pathway involved in the initiation of movement from the cerebral cortex?

Cerebral Cortex → Basal Nuclei → Thalamus → Motor Cortex Signup and view all the answers

What type of neurons provide the output to skeletal muscles?

Alpha-motor neurons Signup and view all the answers

What role do the basal nuclei play in the control of movement?

Controlling the suppression of unwanted movements Signup and view all the answers

What accounts for the large representation of the face in the motor homunculus?

The face is emotionally expressive. Signup and view all the answers

Which structure integrates sensory feedback in the control of lower motor neurons?

Local circuit neurons Signup and view all the answers

Which component represents the highest level of control for motor functions?

Upper motor neurons from the cerebral cortex Signup and view all the answers

What is the primary function of the basal nuclei in motor control?

Coordinating voluntary movement execution Signup and view all the answers

Which type of neurons provide the final output to the muscles for movement?

Lower motor neurons Signup and view all the answers

In the hierarchy of motor control, which structure is involved in refining motor output based on sensory feedback?

Cerebellum Signup and view all the answers

Which level of motor control is primarily associated with generating local reflexes?

Lowest level of control Signup and view all the answers

What is the role of upper motor neurons in motor control?

They transmit commands to lower motor neurons. Signup and view all the answers

What is a key characteristic of smooth muscle cell structure?

They are spindle-shaped with one centrally located nucleus. Signup and view all the answers

Which organ is responsible for regulating blood pressure through smooth muscle contraction?

Arteries Signup and view all the answers

How does calcium influence smooth muscle contraction compared to skeletal muscle?

Cytosolic calcium concentration in smooth muscle can change in a graded manner. Signup and view all the answers

What structure is absent in smooth muscle that is typically present in skeletal muscle?

Myofibrils Signup and view all the answers

What role do dense bodies perform in smooth muscle cells?

They connect thin filaments to the cell membrane. Signup and view all the answers

In which part of smooth muscle contraction is the sarcoplasmic reticulum's contribution less significant compared to that in skeletal muscle?

Calcium release Signup and view all the answers

Which component interacts with calcium in smooth muscle contraction that is not present in skeletal muscle?

Calmodulin Signup and view all the answers

What mechanism allows smooth muscle to maintain contraction over extended periods without fatigue?

Gradual changes in calcium concentration Signup and view all the answers

What distinguishes single-unit smooth muscles from multi-unit smooth muscles?

Single-unit smooth muscles are connected by gap junctions. Signup and view all the answers

What is the role of calmodulin in smooth muscle contraction?

It phosphorylates myosin light-chain kinase. Signup and view all the answers

Which statement accurately describes the nature of pacemaker cells in smooth muscle?

They have leaky ion channels leading to an unstable resting membrane potential. Signup and view all the answers

What is a key feature of slow waves in autorhythmic cells?

They create undulating changes in the membrane potential. Signup and view all the answers

What initiates contraction in both single-unit and multi-unit smooth muscles?

The binding of neurotransmitters to receptors on muscle cells. Signup and view all the answers

What happens to calcium channels during the repolarizing phase of pacemaker potential?

Calcium channels close while potassium channels open. Signup and view all the answers

What is the primary cellular mechanism by which smooth muscle contracts?

Phosphorylation of myosin by myosin light-chain kinase. Signup and view all the answers

Why is entering of Ca2+ significant for pacemaker potential?

It decreases K+ movement out of the cell. Signup and view all the answers

How does the excitation of one single-unit smooth muscle cell affect the others?

They contract synchronously due to gap junctions. Signup and view all the answers

What is the role of desmosomes in smooth muscle cells?

They maintain structural integrity during tension development. Signup and view all the answers

Which of the following best describes how myosin crossbridges function after phosphorylation?

They bind effectively to actin filaments. Signup and view all the answers

What is characteristic of multi-unit smooth muscle activation?

It is activated individually upon receiving signals. Signup and view all the answers

Which best describes the changes in membrane potential during the depolarizing phase of a pacemaker cell's action potential?

The potential increases as Ca2+ influx occurs. Signup and view all the answers

What differentiates the autonomic control of smooth muscle from that of skeletal muscle?

Smooth muscle does not have individual neuromuscular junctions. Signup and view all the answers

What must occur for a stimulus to successfully reach threshold in smooth muscle?

The slow wave potential must be at the crest of a cycle. Signup and view all the answers

What primarily causes fluctuations in the slow wave potential of smooth muscle?

Fluctuations in Na+ movement out of the cell. Signup and view all the answers

What triggers the opening of L-type voltage-gated Ca2+ channels in smooth muscle contraction?

Action potential generation. Signup and view all the answers

Which of the following pathways allows for calcium concentration changes that can initiate smooth muscle contractions?

Receptor-activated channels and IP3-gated channels. Signup and view all the answers

During cardiac muscle contraction, what initiates the increased calcium concentration in the sarcoplasm?

Calcium-induced calcium release (CICR). Signup and view all the answers

What is indicated by a subthreshold depolarization in smooth muscle physiology?

It can lead to smooth muscle contraction without an action potential. Signup and view all the answers

What is the role of L-type voltage-gated calcium channels in the excitation-contraction coupling of smooth muscles?

They facilitate calcium influx during depolarization. Signup and view all the answers

In smooth muscle, what is a potential outcome when there is no change in membrane potential?

Immediate contraction. Signup and view all the answers

Which of the following components is critical for the calcium-induced calcium release mechanism in cardiac muscle?

Dihydropyridine receptors. Signup and view all the answers

Which factor does NOT contribute to the excitation-contraction coupling mechanism in smooth muscle cells?

Direct action potential correlation with contraction. Signup and view all the answers

What phenomenon allows for muscle contraction without direct changes in membrane potential?

Calcium release from the sarcoplasmic reticulum. Signup and view all the answers

Which statement most accurately describes the role of IP3 in calcium regulation within smooth muscle?

It promotes calcium release from the sarcoplasmic reticulum. Signup and view all the answers

How do receptor-activated channels contribute to smooth muscle contraction?

By facilitating calcium ion influx. Signup and view all the answers

What physiological event is initiated by the rise in intracellular calcium in cardiac muscle?

Initiation of muscle contraction. Signup and view all the answers

Which statement about the lateral corticospinal tract is correct?

It is responsible for precise and agile movements of the hands and feet. Signup and view all the answers

What is the primary function of the vestibular nuclei in the context of upper motor neurons?

They assist with posture and balance. Signup and view all the answers

Which of the following structures is primarily involved in controlling precise voluntary movements of the upper limbs?

Red nucleus Signup and view all the answers

In the context of upper motor neurons, which statement about the corticobulbar pathways is accurate?

They control voluntary movements in the head. Signup and view all the answers

Which tract is responsible for regulating posture and muscle tone during ongoing movements?

Medial reticulospinal tract Signup and view all the answers

Which of the following correctly describes the representation of body parts in the primary motor cortex homunculus?

Regions with larger representations are associated with more precise control. Signup and view all the answers

What is the primary structural characteristic of smooth muscle cells?

Spindle-shaped with one centrally located nucleus Signup and view all the answers

Which statement about the upper motor neurons and their lateral and ventral corticospinal tracts is true?

The ventral tract controls more proximal parts of the limbs. Signup and view all the answers

How does calcium concentration affect smooth muscle contraction?

Tension generated is dependent on the cytosolic calcium concentration Signup and view all the answers

Which structure allows for the attachment of thin filaments in smooth muscle?

Dense bodies Signup and view all the answers

Which structure aids in saccadic eye movements and responses to unexpected stimuli?

Superior colliculus Signup and view all the answers

What is the role of the red nucleus in the motor pathways?

It controls precise movements of the upper limbs. Signup and view all the answers

What role does the sarcoplasmic reticulum (SR) play in smooth muscle contraction?

It provides a small percentage of the calcium required for contraction Signup and view all the answers

Which of the following organs does smooth muscle NOT line?

Skeletal muscle Signup and view all the answers

How is the contraction in smooth muscle primarily initiated?

By graded increases in cytosolic calcium concentration Signup and view all the answers

What connects smooth muscle cells to each other at their cell membrane?

Desmosomes Signup and view all the answers

Which feature is NOT characteristic of smooth muscle contraction compared to skeletal muscle contraction?

Dependence on troponin for calcium binding Signup and view all the answers

What is one primary function of the basal nuclei in the central nervous system?

Initiating and terminating emotional behaviors Signup and view all the answers

Which disorder is primarily associated with dysfunction in the basal nuclei?

Parkinson's Disease Signup and view all the answers

What type of neuron provides inputs to lower motor neurons from the association cortex?

Upper motor neurons Signup and view all the answers

Which of the following structures is crucial for the integration of sensory feedback in motor control?

Cerebellum Signup and view all the answers

What mechanism is primarily responsible for local reflexes in motor control?

Local circuit neurons Signup and view all the answers

What role does the reticulospinal tract play in the nervous system?

Regulation of muscle tone Signup and view all the answers

Which of the following processes is NOT regulated by the thalamus?

Hormonal regulation Signup and view all the answers

What is a key effect of disruptions in the basal nuclei?

Motor control disorders Signup and view all the answers

What distinguishes single-unit smooth muscle from multi-unit smooth muscle?

Single-unit smooth muscles allow for coordinated contraction. Signup and view all the answers

Which channel type is primarily involved in the depolarizing phase of the pacemaker potential?

L-type voltage-gated Ca2+ channels. Signup and view all the answers

During contraction of smooth muscle, which enzyme plays a crucial role in activating myosin?

Myosin light-chain kinase. Signup and view all the answers

What triggers the opening of voltage-gated K+ channels during repolarization in pacemaker cells?

Closure of voltage-gated Ca2+ channels. Signup and view all the answers

Which physiological feature of autorhythmic cells allows for the generation of a rhythm in contraction?

Leaky ion channels causing unsteady potentials. Signup and view all the answers

How do the physical interconnections by desmosomes affect smooth muscle function?

They enhance the overall tension development in muscle tissue. Signup and view all the answers

Which ion movement is primarily responsible for the pacemaker potential in autorhythmic cells?

Increased Ca2+ influx. Signup and view all the answers

What is a consequence of the coordinated contraction of single-unit smooth muscle?

Entire muscle layers contract simultaneously. Signup and view all the answers

Which of the following best describes the action of myosin light-chain kinase?

It uses ATP to phosphorylate myosin, enabling contraction. Signup and view all the answers

In multi-unit smooth muscle, how do individual muscle fibers respond to stimulation?

They activate only upon receiving direct neural stimulation. Signup and view all the answers

What is the primary role of gap junctions in single-unit smooth muscles?

They synchronize contractions among interconnected muscle cells. Signup and view all the answers

What primarily governs the contraction mechanism in smooth muscle compared to skeletal muscle?

The phosphorylation of myosin light chains. Signup and view all the answers

Which characteristic best describes slow wave potentials in smooth muscle?

They are unstable and undulating membrane potentials. Signup and view all the answers

What is involved in the repolarization phase of the action potential in pacemaker cells?

Opening of voltage-gated K+ channels. Signup and view all the answers

What is the role of activated Myosin Light Chain Kinase (MLCK) in smooth muscle contraction?

It phosphorylates the myosin regulatory light chain. Signup and view all the answers

Which event initiates the phosphorylation of the myosin regulatory light chain?

Activation of calmodulin by calcium ions. Signup and view all the answers

What is the primary signal for muscle contraction in smooth muscle fibers?

Increase in calcium ion concentration. Signup and view all the answers

How do contractions in smooth muscle compare to skeletal muscle?

They are slower and last longer. Signup and view all the answers

What occurs during relaxation of smooth muscle after contraction?

Dephosphorylation of myosin by MLCP. Signup and view all the answers

Which component is involved in the binding of myosin to actin during the contraction process?

Myosin heads. Signup and view all the answers

What role does the Ca2+-calmodulin complex play in the activation of MLCK?

It binds to and activates MLCK. Signup and view all the answers

What is the primary effect of calcium-induced changes in thick filaments during smooth muscle contraction?

Enhanced binding of myosin to actin. Signup and view all the answers

Study Notes

Muscle Types

Three types of muscle: skeletal, cardiac, and smooth
Skeletal muscle: striated, voluntary, attached to bone
Cardiac muscle: striated, involuntary, found in the heart
Smooth muscle: not striated, involuntary, found in hollow organs

Skeletal Muscle Functions

Produce body movements
Stabilize body positions
Generate heat (thermogenesis)

Skeletal Muscle Properties

Electrical excitability: Ability to respond to stimuli by producing action potentials
Contractility: Ability to contract forcefully when stimulated
Extensibility: Ability to stretch without being damaged
Elasticity: Ability to return to original length and shape after contraction or extension

Skeletal Muscle Control: The Somatic Nervous System

Division of the peripheral nervous system controlling skeletal muscles
Motor neuron cell bodies reside in the spinal cord's gray matter
Axons leave the spinal cord via the ventral root and travel to the target muscle without intermediary synapses
Neuron terminates as the presynaptic terminal of the neuromuscular junction, releasing acetylcholine upon action potential arrival

Skeletal Muscle Organization

Whole muscle: bundle of muscle fascicles
Muscle fascicle: bundle of muscle fibers (cells)
Muscle fiber (cell): contains myofibrils and sarcomeres
Myofibril: contractile assembly of proteins within muscle cells
Sarcomere: contractile subunits making up each myofibril

Sarcomere Components

Sarcoplasmic reticulum: intracellular calcium ion storehouse
Transverse tubules: extensions of the plasma membrane forming a network within striated muscle
Thin filaments: Primarily composed of actin
Thick filaments: Primarily composed of myosin

Sarcomeric Proteins

Contractile proteins:
- Actin: primary protein of thin filament
- Myosin: primary protein of thick filament, acts as ATP-driven molecular motor for muscle contraction
Regulatory proteins:
- Tropomyosin: blocks myosin binding sites on thin filament during relaxation, moves out of the way upon muscle contraction
- Troponin: three-subunit complex on the thin filament that senses calcium and triggers muscle contraction
Structural proteins:
- Titin: spring-like connector of thick filament to the Z-disc
- Alpha-actinin: primary structural protein of the Z-disc
- Myomesin: primary structural protein of the M-line
- Dystrophin: connects the Z-disc to the membrane cytoskeleton
- Nebulin: template for actin filament length

Skeletal Muscle Anatomy

Muscle fascicles are groups of muscle cells bundled together
Single muscle cells are also called muscle fibers
Myofibrils are bundles of protein filaments responsible for muscle contraction
Sarcomeres are the basic contractile unit of muscle fiber
Sarcomere is made of thick filament called myosin and thin filament called actin
Striated appearance of muscle comes from arrangement of myosin and actin filaments
Skeletal muscle is made of many individual muscle fibers bundled together
Different stages of myofilament overlap contributes to muscle contraction

Neuromuscular Junction

The Neuromuscular Junction (NMJ) is the synapse between a somatic motor neuron and a skeletal muscle fiber
Pre-synaptic terminal is the neuronal axon terminal
Motor end plate is a specialized region of the skeletal muscle membrane
End Plate Potential (EPP) is a depolarization generated at the muscle membrane due to binding of Acetylcholine (ACh)

Neuromuscular Transmission

Nerve action potential arrives at the pre-synaptic terminal
Ca2+ enters the pre-synaptic terminal through voltage-gated Ca2+ channels
ACh is released from synaptic vesicles into the synaptic cleft
ACh binds to nicotinic receptors on the motor end plate, leading to EPP
EPP spreads to adjacent membrane, reaching the threshold for voltage-gated Na+ channels
Muscle action potential is generated and propagates along the muscle fiber
Acetylcholinesterase (AChE) breaks down ACh in the synaptic cleft
ACh removal stops the signal and allows the muscle fiber to relax

Excitation-Contraction Coupling

Action potential travels along the sarcolemma and down the transverse tubules (T-tubules)
Dihydropyridine receptors (DHP) in T-tubules are voltage-sensitive and change conformation with the action potential
DHP receptors are physically linked to ryanodine receptors (RyR) on the sarcoplasmic reticulum (SR)
RyR open, releasing Ca2+ from the SR into the cytoplasm
Ca2+ binds to troponin on the thin filament, exposing the myosin binding sites on actin

Sliding Filament Mechanism

Myosin heads bind to actin and pull on the thin filaments
Thin filaments slide inward towards the center of the sarcomere
A-band width remains the same, I-band narrows
Sarcomere shortens, myofibrils shorten, and the whole muscle shortens
Z discs move closer together as the sarcomere shortens

Cross-Bridge Cycle

ATP hydrolysis “energizes” the myosin head, changing its conformation
Myosin head binds to exposed actin site, forming a crossbridge
Power stroke: myosin head pivots, pulling the thin filament towards the center, generating force
ADP detaches from myosin head
ATP binds to myosin head, causing it to detach from actin

Muscle Relaxation

Ca2+- ATPase pumps Ca2+ back from cytoplasm into the SR
Troponin returns to its original conformation, blocking myosin binding sites
Myosin cannot bind to actin, the muscle relaxes

Roles of ATP in Muscle Contraction and Relaxation

ATP hydrolysis provides energy for the myosin head to change conformation and bind to actin
ATP binding to myosin head causes detachment from actin
ATP is used by Ca2+-ATPase to pump Ca2+ back into the SR, allowing for muscle relaxation

ATP Production in Skeletal Muscle

Creatine Kinase (CK) provides ATP for the first few seconds of muscle contraction.
- CK is a one-step reaction that transfers phosphate from creatine phosphate (CP) to ADP to regenerate ATP.
- CP is a store of high-energy phosphate accumulated during rest in muscle cells.
- CK is reversible and can regenerate CP from ATP during rest.

Glycolysis

Glycolysis occurs in the sarcoplasm of muscle fibers and is a multi-step anaerobic process.
Breaks down glucose into pyruvate, producing 2 ATP molecules per glucose molecule.
Glycolysis allows for ATP production in the absence of oxygen.
Glucose is sourced from the blood or the breakdown of muscle glycogen.
Powers short-duration, high-intensity muscle activity.

Oxidative Phosphorylation

Occurs in the mitochondria of muscle fibers and utilizes oxygen.
This is a multi-step, aerobic process that produces 36 ATP molecules per glucose molecule.
Can also utilize fatty acids and amino acids as fuel sources.
Provides ATP for extended periods of muscle activity.

Muscle Fiber Types

Muscle fibers are categorized based on metabolic properties and contraction speed.
Slow oxidative fibers are fatigue-resistant, have a slow myosin ATPase, generate the least tension, and are most active in endurance activities.
Fast oxidative fibers have moderate fatigue resistance, a faster myosin ATPase, generate moderate tension, and are involved in activities for moderately sustained activity.
Fast glycolytic fibers are the most fatigable, have the fastest myosin ATPase, generate the greatest tension, and are primarily used for short, intense bursts of activity.

Motor Units

A motor unit consists of a motor neuron and the muscle fibers it innervates.
More motor units are recruited to produce a greater force of contraction.
Smaller motor units with slow oxidative fibers are recruited first.

Recruitment

Recruitment involves activating motor units in a specific order based on the demand for force.
Small, slow-oxidative motor units are activated first, followed by larger, fast-oxidative motor units.
When maximum force is required, fast glycolytic motor units are recruited to provide the most power.

Fatigue

Muscle fatigue is a complex process and is not fully understood.
The mechanisms of muscle fatigue do not occur due to a lack of ATP or the accumulation of lactic acid.
Potential contributors to fatigue could include:
- High extracellular potassium concentrations.
- Build-up of ADP, inhibiting crossbridge cycling.
- Disruption of calcium regulation.

Factors Affecting Muscle Tension

The amount of tension a whole muscle can produce is influenced by:
- The number of active motor units.
- The number of muscle fibers in each motor unit.
- The fiber types of the activated motor units.

Comparing the Somatic and Autonomic Nervous Systems

The somatic nervous system (SNS) controls voluntary movement, while the autonomic nervous system (ANS) controls involuntary functions.
The SNS has a single neuron pathway, while the ANS typically uses a two-neuron pathway with a preganglionic neuron and a postganglionic neuron.
Both systems use acetylcholine (ACh) as a neurotransmitter, but the ANS also uses norepinephrine (NE).

Muscle Spindles and Golgi Tendon Organs

Muscle spindles are sensory receptors within muscles, consisting of intrafusal muscle fibers surrounded by sensory afferents.
Muscle spindles detect changes in muscle length, triggering adjustments for maintaining muscle length.
Golgi tendon organs are located within tendons, acting as sensory receptors for detecting muscle tension.
They are activated by tension, protecting muscles and tendons from damage due to excessive force.

The Knee-Jerk Reflex

This reflex is an example of a muscle spindle stretch reflex.
Tapping the patellar tendon stretches the quadriceps muscle, activating the muscle spindle.
This triggers a monosynaptic reflex arc, causing the quadriceps to contract and extend the lower leg.
The opposing muscle (hamstring) is inhibited through a polysynaptic reflex arc, ensuring coordinated movement.

The Withdrawal Reflex

This reflex occurs in response to pain, initiated by nociceptors.
It is a polysynaptic reflex arc that involves sensory neurons, interneurons, motor neurons, and effector muscles.
The withdrawal reflex causes the affected limb to move away from the painful stimulus, providing protection.

Levels of Motor Control

Local Level: This level involves local circuit neurons, sensory neurons, and lower motor neurons.
Middle Level: This level comprises the basal nuclei, cerebellum, motor centers in the brainstem, and the thalamus. It coordinates and refines movements based on intention, sensory feedback, and other factors.
Higher Level: This level encompasses areas of the cerebral cortex and association cortex, responsible for planning, decision-making, and sequencing movements.

Activation and Relaxation of Smooth Muscle

Unlike skeletal muscles, smooth muscle activation involves various calcium sources:
- Calcium release from the sarcoplasmic reticulum.
- Calcium influx from the extracellular space.
The process is slower than skeletal muscle contraction and does not require a specific arrangement of actin and myosin.

Wu's Rule

A reflex arc consists of 7 elements:
- Stimulus
- Receptor/Sensor
- Afferent Signaling Pathway
- Integrating Center
- Efferent Signaling Pathway
- Effector
- Response

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Description

Explore the three types of muscles: skeletal, cardiac, and smooth, with a focus on skeletal muscle functions and properties. This quiz will test your knowledge on the role of the somatic nervous system in controlling skeletal muscles.