9. Muscles and Muscle Tissue

Muscle Contraction

Neuromuscular Junction

The Mechanism of Muscle Contraction: Sarcomeres, Action Potential, and the Neuromuscular Junction

 ATP, CP, glucose, and oxygen all decrease during muscle contraction. 

 Which of the following substances increases in quantity during repetitive muscle contraction during oxygen deficit? 

 The bonding of globular actin and troponin is not responsible for the formation of cross bridges between the thick and thin filaments. 

 The bonding of troponin and tropomyosin is not responsible for the formation of cross bridges between the thick and thin filaments. 

 The bonding of the heads and tails of myosin filaments is not responsible for the formation of cross bridges between the thick and thin filaments. 

 Myofilament cross bridges form when which two structures bond? 

 An action potential is the result of a predictable sequence of electrical changes that occurs along the length of the sarcolemma. 

 The sequence of electrical changes that occurs along the sarcolemma when a muscle fiber is stimulated is known as the __________. 

 the release of acetylcholine from the motor neuron 

The first step toward generating a skeletal muscle fiber contraction is nervous stimulation of the muscle fiber. When an action potential arrives at the neuromuscular junction, acetylcholine (ACh) is released. ACh then binds to receptors on the sarcolemma of the muscle fiber. This binding event leads to depolarization of the sarcolemma. As depolarization occurs, a muscle action potential is propagated along the sarcolemma and down the T tubules. The sarcoplasmic reticulum then releases Ca2+ ions into the intracellular environment, and the Ca2+ ions bind to troponin in order to facilitate the formation of actin-myosin cross bridges.

a rise in intracellular Ca2+ levels in the muscle fiber

 the formation of actin-myosin cross bridges 

 When an action potential arrives at the neuromuscular junction, the most immediate result is __________. 

 In the sliding filament model, during contraction, actin and myosin filaments overlap to a greater degree, shortening the muscle fiber. 

 In the sliding filament model of muscle contraction, the myofilaments slide over each other, resulting in the overlapping of actin and __________. 

Contraction Coupling

 Skeletal muscle can exert tremendous power. 

 It can perform both anaerobic and aerobic metabolism. 

 Skeletal muscle can perform both anaerobic and aerobic metabolism. 

 It can contract for long periods of time without tiring.  

 Which of the following is NOT a characteristic of skeletal muscle contraction? 

 A motor unit is a nerve-muscle functional unit, with a motor neuron supplying all the muscle fibers within the motor unit. 

 A motor neuron along with all the muscle fibers it supplies is called a(n) __________. 

The response of a motor unit to a single action potential of its motor neuron is called a muscle twitch. Muscle twitches are single jerking contractions. However, skeletal muscles normally respond to stimulation in a controlled and smooth manner. The variation needed in skeletal muscle contraction in order to have controlled movement is called a graded muscle response. The term wave summation describes how a muscle response changes with respect to changes in stimulus frequency. The term multiple motor unit summation describes how a muscle response changes with respect to changes in stimulus strength.

 Properly controlled skeletal muscle contractions produced by changing the frequency of stimulation and the strength of stimulation are referred to as __________. 

 Isometric contraction is only seen in skeletal muscle. 

 The ability to automatically contract is a property of smooth and cardiac muscle but not a pattern of contraction. 

 Isotonic contraction is only seen in skeletal muscle. 

 The alternating contraction and relaxation of opposing layers of smooth muscle is referred to as __________. 

Ca2+ combines with troponin, causing troponin to change shape, which removes the blocking action of tropomyosin, allowing cross bridges to form.

 What is the ion released from the terminal cisternae that combines with troponin and removes the blocking action of tropomyosin, resulting in the formation of cross bridges? 

Muscle Contraction - Cross Bridge Cycle

Muscle Twitch

The Mechanism of Muscle Contraction

 Under aerobic conditions, muscle cells can carry out aerobic respiration, which is the most efficient metabolic pathway for ATP production. Under anaerobic conditions (oxygen deficient conditions), most of the pyruvic acid produced in glycolysis will be converted to lactic acid to ensure that the muscle cell maintains a supply of ATP. While lactic acid can subsequently be used by some cells to make ATP, the process is not efficient; ATP yields per glucose molecule are extremely low in anaerobic glycolysis. 

 The most efficient means of producing ATP for muscle contraction is __________. 

 Muscles that maintain upright posture are contracting isometrically. 

 The type of muscle contraction in which the muscle fibers produce increased tension although the muscle neither shortens nor lengthens is called __________. 

 Acetylcholine is released from the axon terminus. 

 Transmission of the action potential along the T tubules of the triads causes the voltage-sensitive tubule proteins of the sarcoplasmic reticulum to change shape, releasing calcium into the cytosol. 

 The sarcoplasmic reticulum releases calcium. 

 During the phase of excitation-contraction coupling of skeletal muscle, what occurs immediately after the action potential spreads down the T tubule? 

 The muscle would exhibit isotonic contraction. 

 ATP is needed to break actin-myosin cross bridges. If these bridges are not broken, the muscle remains in a contracted state. 

 The muscle would exhibit isometric contraction. 

 The muscle would relax and lengthen because of an inability to sustain actin-myosin cross bridges. 

 The muscle would remain in a contracted state because of an inability to break actin-myosin cross bridges. 

 What would occur if a contracting muscle became totally depleted of ATP? 

The Muscular System

 Elastic filaments maintain the organization of the A band and provide for elastic recoil when muscle contraction ends. 

 Which of the following allows recoil of the muscle fiber when contraction ends? 

 After acetylcholine binds to its receptor, its effects are quickly stopped when it is enzymatically broken down by acetylcholinesterase. 

 helps acetylcholine bind to its receptor 

 Smooth muscle depends on the calcium-calmodulin system to regulate contraction, while skeletal muscle relies on the calcium-troponin system to regulate contraction. 

 Unlike skeletal muscle, smooth muscle does not depend on ATP to fuel contractions. 

 Skeletal muscle and smooth muscle both employ a sliding filament mechanism for contraction, they both depend upon a rise in intracellular calcium to trigger contraction, and they both depend on ATP to fuel contraction. Unlike skeletal muscle, smooth muscle depends on the calcium-calmodulin system to regulate contraction. Skeletal muscle utilizes a calcium-troponin regulation mechanism. 

 Unlike skeletal muscle, contraction in smooth muscle does not involve a sliding filament mechanism. 

 The final signal for contraction in smooth muscle is a rise in extracellular calcium, while the final signal for contraction in skeletal muscle is a rise in intracellular calcium. 

 During contraction, the distance between Z discs of a sarcomere decreases. 

 The sliding filament model of contraction states that during contraction, thin filaments slide past thick filaments so that actin and myosin filaments overlap to a greater degree than in a relaxed muscle fiber. When the muscle relaxes, the thick and thin filaments overlap only at the ends of the A band. The sliding of the filaments is accomplished by the formation of actinâ€“myosin cross bridges. As the sliding occurs, Z discs of the sarcomere are brought closer together. 

 During contraction, thin filaments slide past thick filaments so that actin and myosin filaments do not overlap. 

 During contraction, actin-myosin cross bridges form. 

 During contraction, thin filaments slide past thick filaments so that actin and myosin filaments overlap. 

 Which of the following statements is FALSE? 

Tetanus Skeletal Muscle 

 an increase in intracellular calcium ion levels 

 an increase in extracellular calcium ion levels 

A short-lived rise in intracellular calcium ion levels (Ca2+) is the final trigger for contraction of skeletal muscle.

 a decrease in intracellular calcium ion levels 

 a decrease in extracellular calcium ion levels 

 The final "go" signal for skeletal muscle contraction is __________. 

Skeletal Muscle Length-Tension Relationship

Muscle Contraction - Cross Bridge Cycle, Animation.

 The axon of each motor neuron divides as it enters the muscle, and each of these axonal endings forms a branching neuromuscular junction with a single muscle fiber. As a rule, each muscle fiber has only one neuromuscular junction. 

 Each skeletal muscle fiber is controlled by a neuron at a single __________. 

The axonal terminus and the muscle fiber do not actually touch and remain separated by a space called the synaptic cleft, which is filled with a gel-like substance rich in glycoprotein.

 The space between the axon terminus of the neuron and the sarcolemma of the muscle fiber is the __________. 

 Excitability is the ability to receive and respond to a stimulus. 

 Irritability is the ability to receive and respond to a stimulus. 

 Responsiveness is the ability to receive and respond to a stimulus. 

 All of the following terms refer to the ability to receive and respond to a stimulus EXCEPT __________. 

 A sarcomere is the smallest contractile unit of a skeletal muscle fiber. 

 The functional unit of contraction in a skeletal muscle fiber is the __________. 

 Calmodulin causes smooth muscle contractions. 

 Which one of the following binds calcium ions in a smooth muscle, causing contraction? 

Sliding Filament

What is EPOC - Excess Post Exercise Oxygen Consumption Explained

 While muscles can respond to nerve impulses and conduct impulses once stimulated, they do not initiate them. Neurons are responsible for initiating nerve impulses. 

Muscle Fatigue

 Muscle tone is a state of partial, sustained contraction in a muscle that results from tetanic contraction of about 10% of the muscle fibers on a rotating basis. Tetanic contraction is sustained and forceful contraction that results from high-frequency stimulation from the nervous system. A muscle twitch is a brief, maximum contraction of a muscle in response to a stimulus. 

 Continued mild or partial contraction of a muscle that keeps it healthy and ready to respond is known as muscle __________. 

 The refractory period occurs during repolarization. 

 The refractory period in which the muscle will NOT contract if stimulated occurs during __________ of the muscle cell. 

Cross Bridge Cycle

 Calcium concentration in the sarcoplasm increases. 

 Increase of hemoglobin concentration in muscle fibers is not a process that occurs during muscle contraction. 

 The I bands shorten, and H zones disappear. 

 Which of the following does NOT occur during skeletal muscle contraction?   

Skeletal Muscle

Learn the toughest concepts covered in Anatomy & Physiology 1&2 with step-by-step video tutorials and practice problems by world-class tutors

