Download Chapter 9 Joints - Dr. Jerry Cronin

Organization of Muscle Tissue
• An aponeurosis is Epicranial aponeurosis
essentially a thick Frontal belly of the
occipitofrontalis m.
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
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
The Skeletal Muscle Fiber
• Muscle contraction occurs in the 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
Muscle Proteins
• In the thin filaments actin proteins are strung
together like a bead of pearls
• In the thick filaments myosin proteins look like
golf clubs bound together
Muscle Proteins
In this first graphic, the myosin binding sites on the actin
proteins are readily visible.
The regulatory proteins troponin and tropomyosin have
been added to the bottom graphic: The myosin binding
sites have been
covered
Muscle Proteins
In this graphic the troponin-tropomyosin complex has
slid down into the “gutters” of the actin molecule
unblocking the myosin binding site
Myosin binding site exposed
The troponin-tropomyosin complex can slide back and
forth depending on the presence of Ca2+
Muscle Proteins
• Ca2+ binds to troponin which changes the shape of the
troponin-tropomyosin complex and uncovers the
myosin binding sites on actin
Muscle Proteins
• Besides contractile and regulatory proteins, muscle
contains about a dozen structural proteins which
contribute to the alignment, stability, elasticity, and
extensibility of myofibrils
• Titan is the third most plentiful protein in muscle,
after actin and myosin - it extends from the Z disc and
accounts for much of the elasticity of myofibrils
• Dystrophin is discussed later as it relates to the disease
of muscular dystrophy
The Sliding-Filament
Mechanism
• With exposure of the myosin binding sites on actin
(the thin filaments)—in the presence of Ca2+ and
ATP—the thick and thin filaments “slide” on one
another and the sarcomere is shortened