Histology - 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".

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.

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.

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

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.

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.

Smooth muscle is composed of spindle shaped cells.

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

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 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.

Troponin is a muscle component that can bind or sequester calcium ions. It is a protein complex found on the regulatory protein tropomyosin, which is located on the thin filament of muscle cells. When calcium ions bind to troponin, it causes a conformational change in the troponin-tropomyosin complex, allowing the myosin heads to bind to the active sites on actin and initiate muscle contraction. Therefore, troponin plays a crucial role in regulating muscle contraction by controlling the availability of active sites on actin for myosin binding.

Skeletal muscle possesses triads. Triads are structural arrangements in skeletal muscle fibers that consist of a T tubule and two adjacent terminal cisternae of the sarcoplasmic reticulum. These triads play a crucial role in the excitation-contraction coupling process, allowing for the transmission of electrical signals deep into the muscle fiber and the release of calcium ions from the sarcoplasmic reticulum, which is essential for muscle contraction.