Chapter 10: Components of Skeletal Muscle

What other names can the Deep Fascia be called ?

Visceral or muscular fascia

What is Epimysium ?

A layer of dense irregular connective tissue that surrounds the whole skeletal muscle.

What are myofilament ?

Contractile proteins that are bundled within myofibrils. A myofilament is not as long as a myofibril; rather it takes many successive units of myofilaments to extend the entire length of the myofibril. Myofibril bundles contain two types of myofilaments: thick filaments and thin filaments.

What is Perimysium ?

Surrounds the fascicles. The dense irregular connective tissue sheath of the perimysium contains extensive arrays of blood vessels and nerves that branch to supply muscle fibers within each individual fascicle

What is a sarcoplasmic reticulum ?

An internal membrane complex similar to the smooth endoplasmic reticulum of other cells. Segments of the sarcoplasmic reticulum fit around the myofibril like a sleeve membrane netting.

What is the terminal cisternae ?

Blind sacs that found in the ends of individual sections of the sarcoplasmic reticulum. They are like the hem of a sleeve; they serve as the reservoirs for calcium ions, and are immediately adjacent to each T- tubule. Together, 2 terminal cisternae and a centrally located T- tubule form a structure called a triad that functions during muscle contraction.

What are T-Tubules ?

Deep invaginations of the sarcolemma that extend into the skeletal muscle fiber as a network of narrow membranous tubules to the sarcoplasmic reticulum, which is the endoplasmic reticulum of the muscle. Located within the membrane of both the sarcolemma and the T-tubules are voltage gated channels. These channels include both the volatage gated Na+ channels and voltage gated K+ channels, which participate in conducting an electrical signal in other words action potential

What are the three layers of connective tissue in muscles?

Epimysium, perimysium, and endomysium.

What is a myoblasts ?

Groups of embryonic cells that fuse to form single skeletal muscle fibers during development. During this fusion process, each myoblast nucleus contributes to the eventual total number of nuclei in the fiber. Consequently, skeletal muscle fibers are multinucleated.

What is a muscle fiber ?

It contracts when stimulated and are composed predominately of myofibrils, which extend the length of a muscle fiber myofibril is composed of bundles of myofilaments (protein filaments) and is enclosed within segments of the sarcoplasmic reticulum. The sarcoplasmic reticulum is a reservoir for calcium ions. The sarcolemma is physically connected to the sarcoplasmic reticulum by invaginations of the sarcolemma called T-tubules, both contain voltage gated Na+ channels, voltage gated K+ channels. The sarcoplasmic reticulum membrane contains both Ca 2+ pumps and voltage gated Ca2+ channels.

What is Myofibril ?

Long cylindrical structures that compose approx. 80% of the volume of the skeletal muscle. A skeletal muscle fiber contains hundreds to thousands of myofibrils. Each myofibril extends the length of the entire skeletal muscle fiber (and is 1 to 2 micrometers in diameter). Note that each myofibril is composed of bundles of contractile proteins called myofilaments and is enclosed in portions of the sarcoplasmic reticulum.

What is the sarcolemma ?

The plasma membrane of a skeletal muscle fiber

What is Endomysium ?

The innermost connective tissue layer. It is a delicate, areolar connective tissue layer that surrounds and electrically insulates each muscle fiber. It contains reticular protein fibers to help bind together neighboring muscle fibers and to support capillaries near these fibers.

What are Thick filament ?

They are assembled from bundles of 200 to 500 myosin protein molecules. Each myosin protein consists of two strands; each strand has a globular head and an elongated tail. The head also has catalytic site where ATP attaches and is split into ADP and phosphate (it is because the head of myosin functions as an ATPase enzyme that myosin is often referred to more specifically as myosin ATPase). The tails of two strands of a myosin molecule are intertwined. The myosin molecules are oriented so that the long tails point toward the center of the thick filaments and the heads point toward the ends of thick filaments.

What are thin filaments ?

They are approx. half of the diameter of thick filaments (about 5 to 6 nanometers). Thin filaments are primarily composed of two strands of actin protein that are twisted around each other to form a helical shape. In each strand of actin, many (about 300 to 400) small, spherical molecules (G, or globular, actin) are connected to form a fibrous strand (F, or filamentous, actin). F- actin resembles two beaded necklaces that are twisted and intertwined together, with G- actin as the individual beads. Each globular G- actin molecule has a significant feature called a myosin binding site. The myosin head attaches to the myosin binding site of actin during muscle contraction

What do the three layers of connective tissue in muscle do?

They provide protection, sites for distribution of blood vessels and nerves, and a means of attachment to the skeleton or other structures within the body.

What is Deep Fascia ?

is an additional expansive sheet of dense irregular connective tissue that is external to the epimysium. It separates individual muscles, binds together muscles with similar functions contains nerves, blood vessels, and lymph vessels, and serves to fill spaces between muscles. It is a deep fascia since its in the internal or deep layer of the superficial fascia.

What is the superficial fascia composed of and function ?

it is composed of areolar connective tissue and adipose connective tissue that separates muscle from skin.

What is the somatic motor neuron ?

they extend from the brain and spinal cord to skeletal muscle fibers. Each motor neuron has a long extension called axon (nerve fiber) that branches extensively at its terminal end. The axon extends through all three connective tissues layers to almost contact with an individual muscle fiber. The junction between the axon and the muscle fiber is called a neuromuscular junction. Skeletal muscle is classified as voluntary muscle because the muscle fibers can be consciously controlled by the nervous system