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Chapter 10 Muscular Tissue Lecture slides prepared by Curtis DeFriez, Weber State University

Functions of Muscular Tissue Like nervous tissue, muscles are excitable or "irritable” they have the ability to respond to a stimulus Unlike nerves, however, muscles are also: Contractible (they can shorten in length) Extensible (they can extend or stretch) Elastic (they can return to their original shape)

Functions of Muscular Tissue Muscle makes up a large percentage of the body’s weight Their main functions are to: Create motion – muscles work with nerves, bones, and joints to produce body movements Stabilize body positions and maintain posture Store substances within the body using sphincters Move substances by peristaltic contractions Generate heat through thermogenesis

Three Types of Muscular Tissue Location Function Appearance Control Skeletal skeleton movement, heat, posture striated, multi-nucleated (eccentric), fibers parallel voluntary Cardiac heart pump blood continuously striated, one central nucleus involuntary Visceral (smooth muscle) G.I. tract, uterus, eye, blood vessels Peristalsis, blood pressure, pupil size, erects hairs no striations, one central nucleus

Three Types of Muscular Tissue (a) Skeletal muscle (b) Cardiac muscle (c) Visceral smooth muscle

Skeletal Muscle Location Function Appearance Control Skeletal skeleton movement, heat, posture striated, multi-nucleated (eccentric), fibers parallel voluntary Cardiac heart pump blood continuously striated, one central nucleus involuntary Visceral (smooth muscle) G.I. tract, uterus, eye, blood vessels Peristalsis, blood pressure, pupil size, erects hairs no striations, one central nucleus

Skeletal Muscle All muscle start as these spindly shaped cells from myoblasts – skeletal muscle cells fuse to form large fibers… Satellite cells are small mononuclear progenitor cells with virtually no cytoplasm found in mature muscle. They are found sandwiched between the basement membrane and sarcolemma (cell membrane) of individual muscle fibres, and can be difficult to distinguish from the sub-sarcolemmal nuclei of the fibres. Satellite cells are able to differentiate and fuse to augment existing muscle fibres and to form new fibres. These cells represent the oldest known adult stem cell niche, and are involved in the normal growth of muscle, as well as regeneration following injury or disease.

A single skeletal muscle fiber Skeletal muscle fibers are very long “cells” - next to neurons (which can be over a meter long), perhaps the longest in the body The Sartorious muscle contains single fibers that are at least 30 cm long It’s difficult to find the sartorius muscle in some people (cadavers) A single skeletal muscle fiber

Skeletal Muscle The terminal processes of a motor neuron in close proximity to the sarcolemma of a skeletal muscle fiber Motor neuron Sarcolemma

Organization of Muscle Tissue The epimysium, perimysium, and endomysium all are continuous with the connective tissues that form tendons and ligaments (attach skeletal muscle to bone) and muscle fascia (connect muscles to other muscles to form groups of muscles)

Organization of Muscle Tissue Epimysium Perimysium These next few graphics show connective tissue elements associated with skeletal muscle: Starting with whole muscles and working our way down to fascicles and individual muscle cells (fibers). Organization of a single muscle belly

Organization of Muscle Tissue Organization of a fasciculus

Organization of Muscle Tissue Organization of a muscle fiber

Organization of Muscle Tissue A muscle, a fasciculus, and a fiber all visualized

Organization of Muscle Tissue In groups of muscles the epimysium continues to become thicker, forming fascia which covers many muscles This graphic shows the fascia lata enveloping the entire group of quadriceps and hamstring muscles in the thing

Organization of Muscle Tissue Many large muscle groups are encased in both a superficial and a deep fascia Real Anatomy, John Wiley and Sons

Organization of Muscle Tissue An aponeurosis is essentially a thick fascia that connects two muscle bellies. This epicranial aponeurosis connects the muscle bellies of the occipitalis and the frontalis to form “one” muscle: The occipitofrontalis Epicranial aponeurosis Frontal belly of the occipitofrontalis m. An aponeurosis is essentially a thick fascia that connects two muscle bellies. This epicranial aponeurosis connects the muscle bellies of the occipitalis and the frontalis to form “one” muscle: The occipitofrontalis

Organization of Muscle Tissue Veins, arteries, and nerves are located in the deep fascia between muscles of the thigh.

The Skeletal Muscle Fiber Beneath the connective tissue endomysium is found the plasma membrane (called the sarcolemma) of an individual skeletal muscle fiber The cytoplasm (sarcoplasm) of skeletal muscle fibers is chocked full of contractile proteins arranged in myofibrils

The Skeletal Muscle Fiber You should learn the names of the internal structures of the muscle fiber Sarcolemma Sarcoplasm Myofibril T-tubules Triad (with terminal cisterns Sarcoplasmic reticulum Sarcomere

The Skeletal Muscle Fiber Increasing the level of magnification, the myofibrils are seen to be composed of filaments Thick filaments Thing filaments Sarcomeres are multi-protein complexes composed of three different filament systems. The thick filament system is composed of myosin protein which is connected from the M-line to the Z-disc by titin. It also contains myosin-binding protein C which binds at one end to the thick filament and the other to actin. The thin filaments are assembled by actin monomers bound to nebulin, which also involves tropomyosin (a dimer which coils itself around the F-actin core of the thin filament) and troponin. Nebulin and titin give stability and structure to the sarcomere.

The Skeletal Muscle Fiber The basic functional unit of skeletal muscle fibers is the sarcomere: An arrangement of thick and thin filaments sandwiched between two Z discs A scanning electron micrograph of a sarcomere Z-line (from the German "Zwischenscheibe“). Each myofibril is made up of thin filament proteins and thick filament proteins, arranged (configured) in sarcomeres.

The Skeletal Muscle Fiber Muscle contraction occurs in the sarcomeres Each myofibril is made up of thin filament proteins, and thick filament proteins, arranged (configured) in sarcomeres The “Z line” is really a Z disc when considered in 3 dimensions. A sarcomere extends from Z disc to Z disc.

Muscle Proteins Myofibrils are built from three groups of proteins Contractile proteins generate force during contraction Regulatory proteins help switch the contraction process on and off Structural proteins keep the thick and thin filaments in proper alignment and link the myofibrils to the sarcolemma and extracellular matrix

Muscle Proteins The thin filaments are comprised mostly of the structural protein actin, and the thick filaments are comprised mostly of the structural protein myosin However, in both types of filaments, there are also other structural and regulatory proteins