Section 1 Flashcards
Describe the distinctive features of the sarcomere as seen under a light microscope
Describe the functions of the skeletal muscle contractile proteins
What are the three types of muscle?
Skeletal, smooth and cardiac
Skeletal muscle is _______ and under _______ control.
Skeletal muscle is STRIATED and under VOLUNTARY control.
Is skeletal muscle under involuntary or voluntary control?
Voluntary
Which neurotransmitter innervates the muscle at the neuromuscular junction?
Acetylcholine (Ach)
A whole skeletal muscle is made up of individual _________________, each of which runs the entire length of the muscle.
A whole skeletal muscle is made up of individual muscle fibres, each of which runs the entire length of the muscle.
Describe muscle fibers
- run parallel to each other
- surrounded by connective tissues
- a muscle fiber is a single muscle cell
- multinucleated and have very large number of mitochondria
What are myofibrils?
Discrete, contractile elements that are divided up along the length of a muscle fiber
Describe how a myofibril would look when viewed from the side using a light microscope?
It would display a pattern of light and dark bands that give the muscle fiber a striated pattern
Describe what a cross section of myofibril would look like.
A highly organized cytoskeletal pattern of thick and thin filaments (thick myosin and thin actin)
What are A bands?
- aka dArk bands
- made up of stacked thick and thin filaments that are aligned parallel to each other
- the middle of the A bind is slightly lighter since the thin filaments do not reach this far from the ends
- the lighter portion is also called the H zone
What are the I bands?
- aka lIght bands
- made up of the part of the thin filaments that do not extend into the A band
- in the middle of the I band is a vertical line called the Z line
What is the H zone?
- the slightly lighter portion of the A band
- contains proteins that hold the thick filaments, myosion, together in a stack
- Myosin is composed of 2 heavy chains and 2 light chains and the H zone contains the HEAVY CHAINS
- these proteins are seen as the M line running down the middle of the H zone
What is the M line?
- the proteins that hold the thick filaments together in a stack are seen as the M line
- runs down the middle of the H zone
What is the Z-line
- the middle of the I band
- distance from one z-line to the next is a sarcomere
What is the distance from one Z-line to the next called?
A sarcomere
this is what we consider to be the functional unit of skeletal muscle
How do muscles extend the length of the muscle fiber when they’re growing?
My adding new sarcomeres onto the ends
What does the area in the A band where the thick and thin filaments overlap contain?
Cross-bridges that extend from the thick filaments and form when thin filaments bind
(mobile myosin heads bind to actin molecules in muscles)
Describe the thick filament
- composed of myosin
- each myosin molecule is a dimer of two subunits
- each subunit looks like a golf club (has a long shaft with a globular head)
When the dimers come together, the “shaft” or tail portions wrap around each other. Within a thick
filament, two dimers come together in a tail-to-tail formation and then these stack up with other myosin molecules. The heads stick out and contain two important sites, an actin binding site, and a
myosin ATPase site.
What is myosin?
(a motor protein that uses ATP to move along actin filaments)
Describe the thin filament.
The thin filament is made up of the proteins actin, tropomyosin and troponin. The main structural component is two actin filaments
What are actin filaments?
Actin filaments are made up of individual spherical actin molecules that come together to form a
double helix structure
What is tropomyosin?
a thin, double helix protein that lies end to end along the actin helix structure.
It is a regulatory protein that covers the active binding sites, preventing the interaction of actin and myosin
What is troponin?
is a regulatory protein complex made of three polypeptides. One binds to tropomyosin, one bind to actin, one binds to Ca2+
