A&p – Chapter 7 – The Muscular System

Thick and thin myofilaments are formed by proteins called myosin and actin. These proteins are responsible for the contraction of muscles. Myosin is a thick filament, while actin is a thin filament. During muscle contraction, myosin and actin interact with each other, causing the filaments to slide past each other and shorten the muscle. This interaction is regulated by the presence of calcium ions. Oxygen is not involved in the formation of myofilaments.

Hypothermia is the correct answer because it refers to any decrease below normal body temperature. This condition occurs when the body loses heat faster than it can produce, causing the body temperature to drop below 95 degrees Fahrenheit (35 degrees Celsius). Hypothermia can be caused by exposure to cold temperatures, prolonged immersion in cold water, or certain medical conditions. Symptoms of hypothermia include shivering, confusion, drowsiness, and loss of coordination. If left untreated, severe hypothermia can be life-threatening.

Tendons are fibrous connective tissues that anchor muscles firmly to bones. They are strong and flexible, allowing for the transmission of forces generated by muscle contractions to the bones, enabling movement and stability. Tendons are composed of collagen fibers, which provide strength and resistance to tension. Without tendons, muscles would not be able to effectively exert force on bones, resulting in impaired movement and functionality.

Hyperthermia refers to an increase in body temperature that is above normal. This can be caused by various factors such as heat stroke, prolonged exposure to high temperatures, or certain medical conditions. Hyperthermia can be dangerous and may lead to symptoms such as dizziness, rapid heartbeat, and even organ damage if not promptly treated.

Skeletal muscles are the correct answer because they attach to two bones that have a movable joint between them. These muscles are responsible for movement and provide support to the skeletal system. They work in pairs, with one muscle contracting while the other relaxes to allow for movement at the joint. This arrangement allows for the coordination and control of movement in the body.

The masseter muscle is responsible for closing the jaw. It is one of the main muscles involved in chewing and biting. When the masseter muscle contracts, it causes the jaw to close, allowing for the grinding and breaking down of food. The frontal and sternocleidomastoid muscles are not directly involved in closing the jaw, making the masseter the correct answer.

Muscle cells are often referred to as muscle fibers because they have a long and slender shape, similar to that of a thread or fiber. This term is commonly used to describe the individual units that make up skeletal muscles. These muscle fibers are responsible for contracting and generating force, allowing the muscles to perform their functions. Therefore, the correct answer is "fiber."

The given statement states that muscular movement occurs when chemical energy from nutrient molecules is transferred to protein filaments in each muscle fiber and then converted to mechanical energy that attempts to contract the muscle. This statement is true as it accurately describes the process of muscle contraction, where the chemical energy from nutrients is used to power the movement of protein filaments, resulting in muscle contraction.

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Smooth muscle tissue has a smooth appearance when viewed under the microscope. This is because smooth muscle cells are spindle-shaped and lack striations, giving them a uniform and sleek appearance. In contrast, skeletal muscle tissue has a striated appearance due to the arrangement of actin and myosin filaments, while cardiac muscle tissue also has striations but with an intercalated disc structure. Therefore, the correct answer is smooth muscle tissue.

The frontal muscle is responsible for raising the eyebrows. It is located in the forehead area and is involved in various facial expressions, including surprise or concern. When this muscle contracts, it pulls the eyebrows upward, causing them to raise. The masseter muscle is located in the jaw and is responsible for chewing, while the trapezius muscle is located in the upper back and is involved in shoulder movements and posture.

When muscles contract simultaneously, the other muscles that relax are called antagonist muscles. These muscles work in opposition to the prime mover muscles, which are responsible for the main movement. The antagonist muscles help to control and stabilize the movement by relaxing and allowing the prime mover muscles to contract effectively. Synergists, on the other hand, are muscles that assist the prime mover muscles in producing a specific movement.

A twitch refers to a quick and jerky response to a stimulus. This is a brief contraction of a muscle fiber that occurs in response to a single nerve impulse. It is characterized by a rapid and short-lived contraction and relaxation of the muscle. This type of muscle contraction is different from tetanic contraction, isotonic contraction, and isometric contraction, which involve sustained or constant muscle contractions.

Neurotransmitters are chemicals released by the motor neuron in response to a nervous impulse. They play a crucial role in transmitting signals between nerve cells and are responsible for the communication and coordination of various functions in the body. Neurotransmitters are released into the synapse, the gap between two nerve cells, and bind to receptors on the receiving cell, transmitting the signal and initiating a response.

Abduction refers to the movement of a body part away from the midline of the body. This means that the body part is being moved further away from the center of the body. In contrast, adduction refers to the movement of a body part towards the midline of the body. Flexion refers to the bending of a joint, while pronation refers to the rotation of the forearm so that the palm faces downwards. Therefore, the correct answer in this case is abduction, as it best describes the movement of a body part away from the midline.

Flexion is the correct answer because it is a movement that decreases the angle between two bones at their joint. This movement is commonly seen in joints like the elbow or knee, where the angle between the bones decreases as the joint bends. Flexion allows for movements like bringing the forearm closer to the upper arm or bending the leg at the knee.

Thick myofilaments are made from a protein called myosin. Myosin is a motor protein that plays a crucial role in muscle contraction. It interacts with thin filaments made of actin to generate the force required for muscle contraction. This interaction between myosin and actin allows for the sliding of the filaments, leading to muscle contraction and movement. Therefore, myosin is the correct answer as it is the protein responsible for the formation of thick myofilaments in muscle cells.

The prime mover is the muscle that is primarily responsible for producing a particular movement. It is the main muscle that contracts and generates the force needed to perform the desired action. Synergists are muscles that assist the prime mover in performing the movement, while antagonist muscles oppose or reverse the action of the prime mover. The prime mover is the key muscle that initiates and carries out the movement.

A single motor neuron, along with the muscle fibers it innervates, is referred to as a motor unit. This term describes the functional unit of the neuromuscular system, where the motor neuron transmits signals to multiple muscle fibers, causing them to contract simultaneously. The motor unit plays a crucial role in coordinating and controlling muscle movements in the body.

The correct answer is "Insertion." In the context of muscle anatomy, the term "insertion" refers to the attachment point of a muscle to the bone that moves when the muscle contracts. The insertion is typically located distally from the origin, and it is the site where the muscle exerts its force to produce movement.

Thin myofilaments are made from a protein called actin. Actin is a globular protein that forms long chains and is an essential component of muscle contraction. It is responsible for the sliding movement of the thin filaments past the thick filaments during muscle contraction. Actin filaments are thin and flexible, allowing them to interact with myosin filaments and generate the force required for muscle contraction. Myosin, on the other hand, is a thick myofilament that interacts with actin during muscle contraction but is not the correct answer in this case.

The formation of more ATP results in a rapid consumption of oxygen and nutrients. ATP is the primary source of energy for cellular processes, and when more ATP is being produced, it indicates that the cells are in an active state and require more oxygen and nutrients to sustain the increased energy demand.

The neuromuscular junction is the point of connection between a nerve and a muscle. It is where the nerve endings release neurotransmitters that stimulate the muscle fibers, causing them to contract. This allows for the transmission of signals from the nervous system to the muscles, enabling movement and coordination.

Exercise can lead to an increase in muscle size, which is known as hypertrophy. This occurs when the muscles are subjected to repetitive and intense physical activity, causing the muscle fibers to adapt and grow in size. This increase in muscle size is a result of an increase in the number of myofibrils within the muscle fibers, as well as an increase in the size of individual muscle fibers. Hypertrophy is a common goal for individuals who engage in strength training or bodybuilding, as it can improve muscle strength and overall physical performance.

Rotation refers to the movement of a body part around its longitudinal axis. This means that the body part is turning or twisting in a circular motion, without changing its position. For example, when we turn our head from side to side, we are performing a rotation around the longitudinal axis of our neck. Therefore, rotation is the correct answer for the given question.

Muscle fibers usually get shorter in order to create movement. When a muscle contracts, the actin and myosin filaments within the muscle fibers slide past each other, causing the muscle to shorten. This contraction generates the force needed to move the bones and joints, resulting in movement.

The correct answer is "sheaths, sheath". The word "tendon" is a noun referring to a tough band of fibrous connective tissue that connects muscle to bone. In this context, the word "enclose" suggests that there is a need for a plural form of the noun "sheath" to indicate that multiple tendons are being enclosed. Therefore, the correct answer is "sheaths". However, it is worth noting that "sheath" is also a valid singular form of the noun, so the combination of "sheaths, sheath" covers both possibilities.

Synergists are the other muscles that assist in producing movement. They work together with the prime mover muscle to create a coordinated and efficient movement. While the prime mover is primarily responsible for the movement, synergists help to stabilize the joint and provide additional force or control. Antagonist muscles, on the other hand, work in opposition to the prime mover and help to control the speed and precision of the movement.

Muscle hypertrophy refers to the increase in muscle size. This can be achieved through strength training, which involves resistance exercises that target specific muscle groups. Strength training causes micro-tears in muscle fibers, which then repair and grow larger and stronger during the recovery process. On the other hand, aerobic training primarily focuses on cardiovascular fitness and endurance, rather than muscle growth. Therefore, strength training is the more effective method for enhancing muscle hypertrophy.

Tendons are made of dense, fibrous connective tissues and are shaped like heavy cords. They are responsible for connecting muscles to bones and transmitting the force generated by the muscles to the bones, allowing movement.

When muscle fibers are stimulated repeatedly without enough rest, they become fatigued. This means that they are unable to contract with the same force and strength as before. Fatigue occurs due to the depletion of energy stores, build-up of waste products like lactic acid, and the inability of the muscle fibers to effectively transmit electrical signals. As a result, the muscle contraction becomes weaker, leading to a decrease in strength.

The correct answer is "Skeletal." This is because the organ described in the question is composed mainly of striated muscle fibers and connective tissue, which is a characteristic of skeletal muscle. Skeletal muscles are responsible for voluntary movements and are attached to bones by tendons. They are under conscious control and play a vital role in locomotion and body movement.

An eccentric contraction refers to a type of isotonic contraction where a muscle produces tension as it lengthens. In this type of contraction, the insertion point of the muscle moves away from its origin. This is different from a concentric contraction, where the muscle shortens as it produces tension. The information provided on page 162 supports the answer of eccentric contraction.

Skeletal muscle is referred to as striated because it has a striped appearance due to the arrangement of its contractile proteins. It is also referred to as voluntary muscle because it is under conscious control, meaning we can choose to contract or relax these muscles as needed.

The sarcomere is the smallest functional unit of muscle. It is a highly organized structure within the muscle fiber that is responsible for muscle contraction. It is composed of actin and myosin filaments, which slide past each other during muscle contraction. The sarcomere is bounded by Z-discs, which anchor the actin filaments, and the H-zone, which contains only myosin filaments. The interaction between actin and myosin within the sarcomere is what allows muscles to generate force and produce movement.

Muscle fibers are stimulated by a nerve fiber called a motor neuron. Motor neurons are responsible for transmitting signals from the central nervous system to the muscles, causing them to contract. These neurons release neurotransmitters, such as acetylcholine, at the neuromuscular junction, which then bind to receptors on the muscle fibers, initiating muscle contraction. This process allows for voluntary movement and control of muscles in the body.

In a concentric contraction, the muscle shortens as it generates force, causing the insertion end to move towards the point of origin. This type of contraction is commonly seen in activities such as lifting weights or doing bicep curls, where the muscle contracts to overcome resistance and move a load.

An isometric contraction refers to a type of muscle contraction where there is an increase in tension within the muscle, but no change in its length or movement. This means that the muscle remains static while exerting force against an immovable object or resisting an external force. In this case, the contraction increases the tension within the muscle, but does not cause any movement.

When impulses to certain skeletal muscles are shut off, it leads to paralysis. Paralysis is the loss of muscle function in part of the body, resulting in the inability to move or control the affected muscles. This can occur due to various reasons such as nerve damage, spinal cord injury, or certain medical conditions.

A tetanic contraction refers to a sustained and steady muscle contraction that occurs when a muscle is stimulated rapidly and at a high frequency. This type of contraction results in a continuous and smooth movement, unlike a twitch which is a brief and jerky contraction. Isotonic contraction refers to a muscle contraction where the muscle changes length and moves a load, while isometric contraction refers to a muscle contraction where the muscle does not change length but generates tension. Therefore, the correct answer is tetanic contraction.

Cardiac fibers have unique dark bands called intercalated disks where the plasma membranes of adjacent fibers come in contact with each other. These intercalated disks play a crucial role in the coordinated contraction of cardiac muscle cells, allowing for efficient pumping of blood. This feature is specific to cardiac muscle and is not present in skeletal or smooth muscle fibers.

The minimal level of stimulation required to cause a fiber to contract is called the threshold stimulus. This is the point at which the fiber becomes excitable and initiates a response. It is the minimum amount of stimulation needed to activate the muscle fiber and trigger a contraction.

Muscle fibers are said to respond "all or none." This means that when a muscle fiber is stimulated by a nerve impulse, it will contract fully or not at all. There is no partial contraction. This principle is important for muscle function and coordination, as it allows for precise control of movement. If all muscle fibers within a muscle are stimulated, the entire muscle contracts. If only some fibers are stimulated, only those fibers will contract while the rest remain relaxed.

Isotonic contraction is the correct answer because it refers to a type of muscle contraction where the muscle changes length and produces movement of a joint. During isotonic contractions, the tension in the muscle remains constant while the muscle shortens or lengthens, resulting in movement. This is in contrast to isometric contractions, where the muscle does not change length and no movement occurs. The information provided on page 162 further supports this explanation.

Aerobic training causes an increase in the number of mitochondria in muscle fibers. Mitochondria are the powerhouses of the cell and are responsible for producing ATP, which is a rapid energy source. Therefore, with more mitochondria, muscle fibers are able to produce more ATP, allowing for increased energy production during aerobic exercise.

Continuous, low-strength muscle contractions are known as tonic contractions. These contractions help maintain body posture by providing a constant level of muscle tension without causing any movement. Tonic contractions are important for activities such as standing or sitting upright, as they help stabilize the body and prevent it from collapsing.

During prolonged exercise, the body may not be able to supply enough oxygen to the muscles, resulting in the production of lactic acid. This lactic acid buildup leads to an oxygen debt, which refers to the increased metabolism required by the cell to remove the excess lactic acid. The body needs to break down this lactic acid and convert it back into glucose, which requires additional oxygen. Therefore, the term "oxygen debt" accurately describes the process of increased metabolism needed to eliminate lactic acid after prolonged exercise.

Muscle fibers undergo contraction, which refers to the shortening and tightening of the muscle fibers. This contraction generates heat, which is essential for maintaining the body temperature. Therefore, the contraction of muscle fibers is responsible for producing most of the heat required to regulate body temperature.

Smooth muscle is referred to as involuntary because it is not under conscious control. It is controlled by the autonomic nervous system. Smooth muscle is also referred to as visceral because it is found in the walls of internal organs such as the stomach, intestines, and blood vessels. It is not referred to as skeletal, voluntary, or striated as these terms are used to describe skeletal muscle, which is under conscious control, found in the skeletal system, and has a striped appearance.

The skeletal muscles have multiple functions, including movement, heat production, and maintaining posture. Skeletal muscles are responsible for generating movement by contracting and relaxing, allowing us to perform various actions such as walking, running, and lifting objects. They also play a role in heat production, as muscle contractions generate heat, which helps to maintain our body temperature. Additionally, skeletal muscles help to maintain posture by providing support and stability to our skeletal system, allowing us to stand and sit upright.