Which neurotransmitter is released by somatic motor neurons?
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Acetylcholine.
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Which neurotransmitter is released by somatic motor neurons?
Acetylcholine.
What occurs in the contralateral leg during the crossed-extensor reflex?
It undergoes extension.
What changes in muscle fibers are possible with exercise?
Metabolic capacity, amount of mitochondria, number of capillaries, and size of muscle fibers.
What is the recruitment order of small motor units and why?
Small motor units are recruited first because they have the lowest threshold for firing.
What is the term for sustained contractions resulting from summation?
Tetanus.
What happens to the affected limb during the withdrawal reflex?
It undergoes flexion (withdrawal).
What type of muscle fibers are favored by high intensity, short duration exercise?
Type II
What are the characteristics of fatigued muscles?
Decreased tension, longer contraction time, slower relaxation, and incomplete relaxation.
What is the maximum isotonic contraction load this muscle can produce?
17 grams.
Why do sarcomeres shorten during isotonic concentric contractions?
Sarcomeres shorten to facilitate muscle shortening and generate force.
What cannot be changed in muscle fibers with exercise?
Myosin ATPase type and creation of new muscle fibers in adults.
What happens to the speed of contraction as the load increases?
The speed of contraction becomes slower.
Which part of the sarcomere does not change in size during muscle contraction?
The A-band does not change in size.
What does the American Academy of Pediatrics report state about the performance benefits of creatine monohydrate supplements?
The performance benefit is small and primarily seen in short-duration, maximum-intensity resistance training, with no general benefit in aerobic activities or 'on-field' athletic performance.
What is a motor unit composed of?
A motor unit is composed of an alpha motor neuron and all of the muscle fibers it innervates.
How does the size of a motor unit affect muscle force generation?
Activation of larger or more motor units generates a greater force of contraction.
How does ATP hydrolysis affect the myosin head?
Energy released from ATP hydrolysis by the myosin head provides energy for the conformational change that puts the myosin head in the high-energy form.
What type of receptors does acetylcholine bind to at the motor end plate?
Nicotinic receptors.
What is the result of acetylcholine binding to nicotinic receptors at the motor end plate?
Depolarization of the muscle fiber.
What happens as the frequency of action potentials increases in neuron W?
Larger motor units will be recruited, starting with Y and then Z.
What is the stimulus for the Golgi Tendon Organ (GTO) Reflex?
Tendon stretch.
What initiates the withdrawal and crossed-extensor reflex?
Activation of nociceptors.
What type of muscle fibers are favored by endurance exercise?
Type I
What are the safety concerns regarding the use of creatine monohydrate supplements in the pediatric population?
Short-term use at usual doses appears safe in normal adults, but has not been evaluated specifically in the pediatric population. There is potential concern with the impact on kidneys due to nephrotic metabolites, and it is specifically recommended against use for those with kidney dysfunction.
What activates the Ryanodine Ca2+ receptor/channel in the sarcoplasmic reticulum (SR)?
The activation of the Dihydropyridine (DHP) Receptor.
How does the frequency of stimuli affect tension production in muscle fibers?
The closer together the stimuli, the more fused the contractions will be, leading to greater tension production.
What happens when calcium binds to troponin?
It facilitates muscle contraction.
What happens to muscle tension if the muscle is not stretched enough or stretched too much?
Tension is reduced if the muscle is not stretched enough or if it is stretched too much.
What type of reflex is the Golgi Tendon Organ (GTO) Reflex?
It is a protective reflex.
What are the dynamic and static components of the muscle spindle reflex?
Dynamic component is immediate reflex action, and static component maintains muscle tone through constant contraction.
What characteristics does neuron Z have compared to other neurons?
Neuron Z has a larger neuron cell body and communicates with larger diameter muscle fibers, requiring more excitatory input to depolarize.
What are the two types of skeletal muscle fibers based on speed of tension production?
Slow-twitch and fast-twitch.
What is the effect of the Golgi Tendon Organ Reflex on skeletal muscle contraction?
Skeletal muscle contraction is decreased (relaxation).
What are the components of the Golgi Tendon Organ Reflex?
The reflex has dynamic and static components.
Why is it called the 'Series' Elastic Component?
Because it is in series (in line) with the skeletal muscle cell sarcomeres.
What happens to the force of contraction until the isometric contraction becomes an isotonic contraction?
The force of contraction increases.
What role do T-tubules play in muscle cells?
The sarcolemma of the muscle cell penetrates the cell’s interior in structures called Transverse Tubules (T-tubules).
Why is an IM contraction occurring in this scenario?
Because the muscle is not strong enough to move the load and shorten.
What events occur at the neuromuscular junction (NMJ)?
Events at the NMJ include the release of neurotransmitters that bind to nicotinic receptors, initiating a muscle fiber action potential.
What type of fibers are small motor units composed of?
Small motor units are composed of slow-twitch oxidative fibers.
What conformational change does myosin undergo in the sliding filament theory?
Myosin undergoes a conformational change that brings the thin filaments towards the center of the sarcomere.
What is the recruitment order of larger motor units and why?
Larger motor units are recruited last because they have the highest threshold for firing.
What is the stimulus for the muscle spindle reflex?
Stretch (change in muscle length).
What happens to the sensory fibers of the muscle spindle when the muscle stretches?
They are squeezed and their action potential frequency changes.
What happens during the power stroke in the sliding filament theory?
The myosin head pulls actin towards the center of the sarcomere, shortening the sarcomere.
Why does complete tetanus produce a force 3-5 times greater than a single twitch?
Because twitches are close enough together that calcium from the first twitch is still present in the sarcoplasm when the second twitch is activated, preventing complete relaxation between stimuli.
Which motor units are activated only at lower frequencies of action potentials?
Smaller motor units, such as X.
Do muscles have varying numbers of motor units?
Yes, muscles have varying numbers of motor units.
What occurs during muscle contraction at the molecular level?
Contraction occurs when the myosin head of the thick filament binds to actin on the thin filament.
What does the endomysium surround?
Individual muscle fibers.
What ensures that the muscle spindle maintains sensitivity to changes in muscle length?
The simultaneous activation of both alpha and gamma motor neurons.
What regulates Lower Motor Neuron (LMN) activity?
Excitatory and inhibitory interneurons in the spinal cord.
How do myosin tails contribute to the structure of thick filaments?
The myosin tails associate with one another to produce the filament.
Where are thick filaments located within the sarcomere?
Thick filaments are in the middle of the sarcomere, with myosin heads oriented in opposite directions at each end.
What type of sensory fiber is associated with the Golgi tendon organ?
The 1b fiber is associated with the Golgi tendon organ.
What reflex is associated with muscle receptors?
Stretch Reflex.
Where are thin filaments anchored in a sarcomere?
Thin filaments are anchored into the Z-lines.
What is the modified endoplasmic reticulum in muscle cells called?
Sarcoplasmic reticulum.
What does the I-band (light band) consist of?
Only thin filaments.
What changes occur in the sarcomere during muscle contraction?
The Zone of Overlap increases, the I-Band decreases, and the H-Zone decreases.
What types of muscle fibers are each motor unit within a muscle composed of?
Each motor unit within a muscle is composed of the same types of muscle fibers.
What occurs when a second stimulus is given before the contraction from the first twitch is completed?
The twitches fuse and produce more force collectively, a phenomenon called summation.
What do skeletal muscle cells require to contract?
Nerve stimulation.
How many motor neurons innervate each muscle fiber?
Each muscle fiber is innervated by only one motor neuron.
What is the result of the fusion of isometric contractions due to sustained or repetitive stimulation?
Tetanus.
What is the difference between incomplete tetanus and complete tetanus?
Incomplete tetanus has relaxation periods between contractions, while complete tetanus does not and results in force production 3-5 times greater than a single twitch.
What is the state of the muscle when cytosolic Ca2+ levels are high?
The muscle is activated.
What is the relationship between the length of a muscle and the tension it can develop?
Muscle tension is maximized at the optimal length where actin and myosin filaments have the best overlap.
What does the epimysium surround?
The whole muscle.
Provide an example of an isotonic concentric contraction.
Bicep curl when lifting the weight.
What do myofibrils contain and how are they arranged?
Myofibrils contain myofilaments (thick and thin) that are arranged into sarcomeres.
What is the functional unit of a myofibril and how is it defined?
The functional unit is the sarcomere, which runs from Z-line to Z-line.
What is the Series Elastic Component?
It does not actively generate force but transmits force passively to the ends of the muscle.
What are the characteristics of Fast Oxidative/Glycolytic (Type IIa) muscle fibers?
They are fast-twitch and can use both oxidative and glycolytic metabolism.
What is the Triad in muscle cells?
The Triad is a structure formed by T-tubules close to the lateral sacs (terminal cisternae) of the Sarcoplasmic Reticulum.
What enzyme activity does the myosin head contain and what is its function?
The myosin head contains an ATPase to break down ATP and release energy.
What factors determine the contribution of aerobic and anaerobic metabolism in muscle fibers?
The metabolic enzymes present in the cell and the intensity of the exercise.
What is the role of creatine kinase (CK) in muscle tissue?
CK levels in the blood are measured to determine if damage to muscle tissue has occurred.
What is the equivalent term for a muscle cell?
Muscle fiber.
Name other protein biomarkers used to detect muscle tissue damage.
TnT, TnI, Myoglobin, and Myosin Light Chain.
What creates the striated appearance in skeletal and cardiac muscle?
Alternating A-bands (dark) and I-bands (light).
What are some theories for muscle fatigue?
Change in membrane potential, decreased ACH, blockage of blood flow, central fatigue, increased metabolic byproducts, and depleted glycogen.
What is the role of ATP in the cross-bridge cycle?
ATP binding to the myosin head breaks the cross-bridge connection between actin and myosin.
What are the three types of muscle fibers mentioned in the text?
Type I, Type IIa, and Type IIb.
What event provides energy for the power stroke in the cross-bridge cycle?
The release of inorganic phosphate from the myosin head provides energy for the power stroke.
What is the definition of an Isometric Contraction?
An isometric contraction is when the muscle generates force without changing its length.
Can you provide an example of an isometric contraction?
Holding a plank position.
How many twitches can muscle cells perform with their initial ATP supply?
Muscle cells only have enough ATP for approximately 8 twitches.
Why is ATP important in muscle contraction?
ATP is necessary to break the cross-bridge between actin and myosin and to provide energy for conformational changes and the power stroke.
What role does the gamma motor neuron play in the muscle spindle reflex?
It stimulates intrafusal fiber contraction to maintain sensitivity to changes in muscle length.
Why is it necessary for intrafusal fibers to contract during muscle spindle activation?
To prevent the sensory fibers from becoming slack and losing the ability to sense further changes in muscle length.
What are the two types of skeletal muscle fibers based on metabolism?
Glycolytic and oxidative.
What are the characteristics of Slow Oxidative (Type I) muscle fibers?
They are slow-twitch and oxidative.
What type of neuron is an Alpha Motor Neuron?
Aα (Alpha Motor Neuron) is a lower motor neuron that releases ACh and causes contraction of the extrafusal fibers.
What is the function of a Gamma Motor Neuron?
Aγ (Gamma Motor Neuron) is an efferent neuron that causes contraction of intrafusal fibers.
What nervous system is required for skeletal muscle stimulation?
The Somatic Nervous System.
What protein covers the myosin binding sites on actin?
Tropomyosin.
What reflex is associated with skin receptors?
Withdrawal Reflex.
What can phosphocreatine donate to ADP to reform ATP?
A phosphate group.
What is the H-zone composed of?
Only thick filaments.
What is the latent period in muscle contraction?
The latent period is the time between the muscle AP (action potential) and the production of muscle tension.
What type of fibers are larger motor units composed of?
Larger motor units are composed of fast-twitch glycolytic fibers.
What is the function of the Dihydropyridine (DHP) Receptor during excitation-contraction coupling?
DHP functions as a voltage sensor.
Why is the optimal length of a muscle important for tension production?
At the optimal length, the greatest number of actin/myosin cross-bridges can form, resulting in maximal tension production.
What is the state of the muscle when cytosolic Ca2+ levels are low?
The muscle is relaxed.
What is the effect of muscle spindle activation?
Contraction.
What are the hierarchical structures of skeletal muscle from largest to smallest?
Whole Muscle, Muscle Fascicles, Muscle Cells (Fibers), Myofibrils, Myofilaments.
What is the definition of an Isotonic Contraction?
An isotonic contraction is when the muscle changes its length while generating force.
What happens when tendons stretch in response to contraction?
The GTO and afferent neurons send information to the spinal cord.
What variability exists within motor units?
Motor units vary in the number of muscle cells they communicate with, and in the diameter and strength of the muscle fibers in different motor units.
How is the recruitment of specific motor units determined?
The specific motor units recruited are based on the force needed.
What are muscle fibers filled with?
Myofibrils.
What surrounds each myofibril?
Each myofibril is surrounded by the Sarcoplasmic Reticulum (SR).
What are the characteristics of Fast Glycolytic (Type IIb) muscle fibers?
They are fast-twitch and glycolytic.
What type of control is skeletal muscle under?
Voluntary control.
What type of sensory fiber is associated with the Golgi Tendon?
1b fiber.
What is the role of troponin in muscle contraction?
Troponin is a Ca2+ binding protein that helps retain tropomyosin’s position on actin. For a contraction to occur, Ca2+ must bind to troponin, which allows tropomyosin to move and expose the myosin binding sites on actin.
What are the different isoforms of creatine kinase found in skeletal and cardiac muscle?
CK-MM is found in skeletal muscle, and CK-MB is found in cardiac muscle.
What is the function of sensory receptors in the muscle spindle?
Sensory receptors in the muscle spindle are mechano-sensitive receptors that monitor changes in muscle length.
What happens during the contraction phase of muscle activity?
During the contraction phase, the muscle generates tension due to the cross-bridge cycle.
What is a twitch in muscle physiology?
A twitch is the mechanical response of a muscle fiber to a single action potential.
When does the skeletal muscle action potential occur in relation to the mechanical response?
The skeletal muscle action potential occurs in the latent period of the mechanical response.
What are Golgi Tendon Organs (GTOs) sensitive to?
They are sensitive to changes in force.
Where are Golgi Tendon Organs located?
At the junction of tendons and muscle.
What is the optimal length of a muscle?
The optimal length is where there is the best degree of overlap between the thick and thin filaments.
What role does the arrival of an action potential (AP) play at the triad (T-tubule/SR)?
It activates the Dihydropyridine (DHP) Receptor.
What are the main structural components of a skeletal muscle?
Whole muscle, muscle fascicles, muscle cells (fibers), myofibrils, and myofilaments.
What does the stimulation of an inhibitory interneuron in the GTO Reflex lead to?
It decreases the activity of the alpha motor neuron.
What happens to the velocity, duration, and distance of shortening of isotonic contractions with heavier loads?
They decrease.
What happens to sarcomeres during muscle contraction?
Sarcomeres shorten because the thick filaments pull the thin filaments towards the center of the sarcomere.
What are the three regions of a myosin protein?
Myosin has a head region, a hinge region, and a tail.
What are the characteristics of skeletal muscle cells?
Skeletal muscle cells are multinucleate, long, striated, and under voluntary control.
What type of sensory fiber is associated with the muscle spindle?
The 1a fiber is associated with the muscle spindle.
What is the name of the neuron that stimulates skeletal muscles?
Alpha, Somatic, or Lower Motor Neuron (LMN).
What are the three proteins that make up the troponin complex?
Troponin C (binds Ca2+), Troponin I (binds Actin), Troponin T (binds Tropomyosin).
What is the muscle spindle reflex also known as?
The muscle spindle reflex is also known as the stretch reflex or myotactic reflex.
What does the A-band (dark band) consist of?
The entire length of thick filaments, including the zone of overlap.
What is the function of the M-line in a sarcomere?
The M-line links the central regions of thick filaments.
What is required for skeletal muscle relaxation?
Skeletal muscle relaxation requires the removal of calcium from the cytoplasm.
What happens to the alpha motor neuron when afferent information enters the spinal cord?
It is activated, stimulating muscle contraction and inhibiting the alpha motor neuron of antagonistic muscles.
What is the function of the perimysium?
Divides the muscle into compartments called fascicles.
Provide an example of an isotonic eccentric contraction.
Lowering the weight slowly during a bicep curl.
How does myosin contribute to muscle contraction?
Myosin undergoes a conformational change that brings the thin filaments towards the center of the sarcomere.
How many myosin proteins make up each thick filament?
Each thick filament is made from approximately 500 individual myosin proteins.
How is interneuron activity regulated?
By a variety of reflex pathways and descending motor pathways.
What are the types of motor neurons mentioned?
Alpha Motor Neuron (Aα) and Gamma Motor Neuron (Aγ).
What type of sensory fiber is associated with the Muscle Spindle?
1a fiber.
What is the role of the Alpha Motor Neuron in muscle contraction?
The Alpha Motor Neuron (Aα) is an efferent neuron that releases acetylcholine (ACh) and causes contraction of the extrafusal fibers.
What are extrafusal fibers?
Extrafusal fibers are skeletal muscle cells.
What reflex is associated with tendon receptors?
Golgi Tendon Reflex.
What are intrafusal fibers?
Intrafusal fibers are the muscle fibers within the muscle spindle.
What is the cytoplasm of a muscle fiber called?
Sarcoplasm.
What is the Z-line in a sarcomere?
The Z-line is where thin filaments are anchored.
What two types of metabolism produce ATP for muscle fibers?
Aerobic and Anaerobic metabolism.
What is the neuromuscular junction (NMJ)?
It is the synapse where each skeletal muscle cell acts independently and synapses with one nerve terminal.
What is the term for the cell membrane of a muscle fiber?
Sarcolemma.
How does the time frame for a twitch vary?
The time frame for a twitch varies based on the type of muscle fiber, such as fast-twitch versus slow-twitch fibers.
What occurs during the relaxation phase of muscle activity?
During the relaxation phase, muscle tension decreases due to a decrease in Ca2+ and the ending of the cross-bridge cycling.
