Histology - USMLE- Muscle Tissue

Myofilaments are the contractile protein within a muscle cell. The myofilaments are actin and myosin. The thin filaments are actin and the thick filaments are myosin. The muscle cell is a muscle fiber. The term "muscle cell" and "muscle fiber" are synonymous. A myofibril is a longitudinal bundle of myofilaments within a muscle cell. Myocardium is the muscular layer of the heart. Thus, the myocardium is composed of cardiac muscle.

The perimysium is the connective tissue sheath which surrounds muscle fascicles.

The periosteum is the connective tissue covering of a bone.

The perichondrium is the connective tissue which surrounds cartilage.

The perineurium is the covering of nerve fascicles.

The endosteum is the lining of the inner bone (the side which abuts the
medullary cavity).

Note from Sarah Bellham: The prefix "peri" means around, such as in the word
"perimeter". The prefix "endo" means within or inner, such as in "endosteum",
"endocrine", "endoscope".

Skeletal muscle fibers can be classified as red fibers, white fibers or intermediate fibers. Red fibers are smaller in diameter; white fibers are larger in diameter. Red fibers have more mitochondria than white fibers. Red fibers make up slow-twitch muscle; white fibers make up fast-twitch muscle. Red fibers are more resistant to fatigue than are white fibers. Red fibers have more myoglobin (oxygen binding pigment) than white fibers. White fibers store glycogen and use anaerobic metabolism.

Red fiber and slow twitch muscle is for endurance.

White fiber and fast twitch muscle is for a burst of power.

A single motor neuron and the aggregation of muscle fibers innervated by that single neuron is called the motor unit. A motor neuron is a neuron which innervates a muscle cell. The point of contact where a neuron contacts a muscle is the motor end plate. A neuromuscular spindle is a receptor which is sensitive to stretching of the muscle. A neurotransmitter is the chemical released by a nerve at a synapse.

The outer connective tissue covering of a muscle is the epimysium. Within the muscle, there are subdivisions called fascicles. The perimysium surrounds these muscle fascicles. The endomysium is the covering around an individual muscle fiber. The sarcolemma is the plasma membrane of a muscle cell. The sarcoplasm is the cytoplasm of a muscle cell.

The A band is the darker staining band. The I band is the light band. The I band is made of thin filaments. The Z line runs through the I band. The H band bisects the A band. The M line runs through the H band.

A sarcomere is the segment that runs from Z line to Z line.

Skeletal muscle is multinucleated. The nuclei are seen on the periphery. Occasionally, cardiac muscle is bi-nucleated.

There are two chief categories of muscle: striated and non striated muscle (smooth muscle).

Striated muscle can be sub-categorized into cardiac muscle and skeletal muscle. The tongue, biceps muscle, and upper esophagus are made of striated muscle. The heart is composed of cardiac muscle.

Non striated muscle is also called smooth muscle. Smooth muscle is involuntary muscle. It is found in viscera and blood vessels.

Myofilaments are the contractile protein within a muscle cell. The myofilaments are actin and myosin. The thin filaments are actin and the thick filaments are myosin. The muscle cell is a muscle fiber. The term "muscle cell" and "muscle fiber" are synonymous. A myofibril is a longitudinal bundle of myofilaments within a muscle cell. Myocardium is the muscular layer of the heart. Thus, the myocardium is composed of cardiac muscle.

The outer connective tissue covering of a muscle is the epimysium. Within the muscle, there are subdivisions called fascicles. The perimysium surrounds these muscle fascicles. The endomysium is the covering around an individual muscle fiber. The sarcolemma is the plasma membrane of a muscle cell. The sarcoplasm is the cytoplasm of a muscle cell.

Red fibers are more resistant to fatigue compared to white fibers and intermediate fibers. This is because red fibers are slow-twitch muscle fibers that are designed for endurance activities. They have a high capacity for aerobic metabolism, which means they can generate energy for longer periods of time without fatiguing. In contrast, white fibers are fast-twitch muscle fibers that are designed for quick and powerful movements but fatigue more easily. Intermediate fibers have characteristics that fall between red and white fibers, so they are also less resistant to fatigue than red fibers.

Smooth muscle is composed of spindle shaped cells.

White fibers are the muscle fibers that are responsible for high-intensity, short-duration activities such as sprinting or weightlifting. These fibers primarily rely on anaerobic metabolism, which produces energy quickly but leads to the accumulation of lactic acid and fatigue. In contrast, red fibers are slow-twitch fibers that are more resistant to fatigue due to their reliance on aerobic metabolism. Intermediate fibers have characteristics of both red and white fibers. Therefore, white fibers fatigue more readily than red or intermediate fibers.

Myofilaments are the contractile protein within a muscle cell. The myofilaments are actin and myosin. The thin filaments are actin and the thick filaments are myosin. The muscle cell is a muscle fiber. The term "muscle cell" and "muscle fiber" are synonymous. A myofibril is a longitudinal bundle of myofilaments within a muscle cell. Myocardium is the muscular layer of the heart. Thus, the myocardium is composed of cardiac muscle.

Both skeletal muscle and cardiac muscle have visible striations. Collectively, skeletal muscle and cardiac muscle are classified as "striated muscle".

The A band is the darker staining band. The I band is the light band. The I band is made of thin filaments. The Z line runs through the I band. The H band bisects the A band. The M line runs through the H band.

A sarcomere is the segment that runs from Z line to Z line.

Lance Armstrong, being a seven-time winner of the Tour de France, is known for his exceptional endurance and stamina. Red muscle fibers, also known as slow-twitch fibers, are responsible for long-duration, low-intensity activities like cycling. These fibers are rich in mitochondria, which provide energy aerobically, and have a high capillary density, allowing for efficient oxygen delivery. Therefore, it is likely that red fibers predominate in Lance Armstrong's legs, enabling him to sustain the physical demands of the Tour de France.

All of the above is the correct answer because skeletal muscle contains different types of muscle fibers. Red fibers, also known as slow-twitch fibers, are rich in mitochondria and have a high capacity for aerobic metabolism. White fibers, or fast-twitch fibers, have a lower capacity for aerobic metabolism and fatigue more easily. Intermediate fibers have characteristics between red and white fibers. Therefore, all three types of muscle fibers (red, white, and intermediate) are present in skeletal muscle.

Skeletal muscle fibers can be classified as red fibers, white fibers or intermediate fibers. Red fibers are smaller in diameter; white fibers are larger in diameter. Red fibers have more mitochondria than white fibers. Red fibers make up slow-twitch muscle; white fibers make up fast-twitch muscle. Red fibers are more resistant to fatigue than are white fibers. Red fibers have more myoglobin (oxygen binding pigment) than white fibers. White fibers store glycogen and use anaerobic metabolism.

Red fiber and slow twitch muscle is for endurance.

White fiber and fast twitch muscle is for a burst of power.

The fundamental property of muscle tissue is that it is specialized for contraction.

Red fibers are smaller in diameter compared to white fibers and intermediate fibers.

White fibers are likely to predominate in Charles Atlas, the world's most famous power weight lifter. White fibers, also known as fast-twitch fibers, are responsible for generating quick and powerful contractions. These fibers are well-suited for activities that require bursts of strength and power, such as weightlifting. In contrast, red fibers (slow-twitch fibers) are more suited for endurance activities. Intermediate fibers possess characteristics of both red and white fibers. Since Charles Atlas is a power weight lifter, it is reasonable to assume that his muscles are predominantly composed of white fibers.

flattened cells with smaller nuclei and with centrioles
= proliferation ® regeneration

On a cross section of a muscle, each thick filament is surrounded by 6 thin filaments.

The A band is the darker staining band. The I band is the light band. The I band is made of thin filaments. The Z line runs through the I band. The H band bisects the A band. The M line runs through the H band.

A sarcomere is the segment that runs from Z line to Z line.