Muscle General Flashcards
Common properties of all three types of muscle
Excitability
Elasticity
Extensibility
Contractility
Differences among the three muscle types
Organization of actin and myosin - cardiac and skeletal have striations
Skeletal muscle fibres are multinucleated structures
Cardiac muscle fibres have 1-2 nuclei and are physically and electrically connected to each other so that the entire heart contracts as one unit (called a syncytium).
Smooth muscle has 1 nucleus
Skeletal muscle functions
Cause movement
Stop movement: eg. resisting gravity to maintain posture, prevent excess movement of the bones and joints
Control the movement of various substances: sphincters
Protect internal organs by acting as an external barrier to external trauma and by supporting the weight of the organs
Generating heat. -eg. shivering
What tissues does the skeletal muscle fibre consist of?
Skeletal muscle fibers
Blood vessels
Nerve fibers
connective tissue
What or the three layers of skeletal muscle connective tissue?
Epimysium
Perimysium
Endomysium
What is the epimysium?
A sheath of dense, irregular connective tissue each muscle is wrapped in:
allows a muscle to contract and move powerfully while maintaining its structural integrity
separates muscle from other tissues and organs in the area
What is the perimysium?
a middle layer of connective tissue that organizes muscle fibers into individual bundles, each called a fascicle.
What is the endomysium?
Inside each fascicle, each muscle fiber is encased in a thin connective tissue layer of collagen and reticular fibers.
Contains the extracellular fluid and nutrients to support the muscle fiber.
These nutrients are supplied via blood to the muscle tissue.
How do muscle fibres form?
During early development, embryonic myoblasts, each with its own nucleus, fuse with up to hundreds of other myoblasts forming the multinucleated skeletal muscle fibers.
Why do myofibers need many nuclei?
Multiple nuclei mean multiple copies of genes: allow production of the large amounts of proteins and enzymes needed for muscle contraction.
List the most important molecules in muscle.
Myosin Actin Tropomyosin Troponin Titin Nebulin
Describe myosin structure
large complex: 2 identical heavy chains and 2 pairs of light chains.
Myosin heavy chains are thin, rodlike motor proteins twisted together as myosin tails
Globular projections containing the four myosin light chains form a head at one end of each heavy chain.
What are the functions of the myosin head?
Bind to actin (crossbridges)
Bind to ATP, catalyzing energy release (actomyosin ATPase activity).
What are the two types of actin?
G-actin (globular): present as either a free monomer
F-actin(filamentous): linear polymer microfilament
Describe the structure of F-actin
thin, helical filaments (double stranded pearl structure)
Each G-actin monomer contains a binding site for myosin
Filaments anchored perpendicularly on the Z disc by the actin-binding protein α-actinin and exhibit opposite polarity on each side of this disc
