Muscle - Lecture 1 Flashcards
3 types of muscle + Vol. or involuntary
1) Skeletal muscle : vol
2) Cardiac muscle : Invol
3) Smooth muscle : invol
Skeletal muscle what it does
Posture and locomotion/arms legs etc
Cardiac muscle responsible for
rhythmic contractions of the heart
Smooth muscle causes contraction in (4) etc
blood vessels, gut, bronchi and uterus
What does each end of muscle do
Attached to tendons which attach to bones on both sides of joint
2 muscles states
Contracted : shorter
Relaxed : longer
What defines muscle function
How they interact with the body and the skeletal frame
Tendon constitution
strong connective tissue
Skeletal muscle cells name and how they’re organized and max length
muscle fibers (cells) organized in bundles called fascicles. muscle fiber up to 1ft long
Vertical stripes seen on muscle microscope image what they represent
Light and dark regions on muscle fibers (cells) that are organized horizontally
Why we see regular stripes in ‘‘side’’ view of muscle fibers (light/dark regions)
Organized to work synchronously/are coordinated
muscle microscope image black spots and something particular
black spots = nuclei
muscle fibers are multinucleated cells
Name of muscle fibers precursor cells in development (in utero) and how many nuclei
myoblasts - 1 nucleus
How muscle fibers formed during development
fusion of myoblasts to form multinucleated cells
2 advantages of having multiple nuclei for the muscle fiber
- Huge lot of protein required can be constantly made (multiple nuclei = multiple copies of a gene)
- Less need for protein exportation within the cytoplasm of the long muscle fiber
What constitutes skeletal muscle fibers
myofibrils (cylindrical shape)
Components of muscle from large scale to small scale
Muscle/fascicles/muscle fiber(cells)/myofibrils
3 important regions found repetitively on a myofibril
Light I-band
Dark A-bands
Z line in the center of each I band / in the center of each light band
what is the contractile unit of the skeletal muscle and how do you delimitate it
Sarcomeres : Region between 2 Z lines. From Z line in the middle of a I-band (light), A-band (dark), Z-line in the middle of the next I-band (light)
What happens to sarcomere during contraction
gets smaller : Z-lines get closer
Special region in A-band/why + its middle line
Lighter region in A band is called H-ZONE .
Middle line of the H-zone is the M-line
Sarcomere structure summary
I-band (light) + Z-line in its middle, A band + H-zone w/ M-line in its middle, I band (light) + Z line in its middle
Where do thick filaments extend in the sarcomere
From one end to the other end of the A-band (dark)
Where do thin filaments extend in the sarcomere
Start at Z-line. Go in I-band (light) and part of the A-band (dark)
What would be the A-band and the H-zone
A-band : where thin and thick filaments overlap H-zone within it = only thick filaments
Anchor point in the sarcomere
Z-line
What are crossbridges
Structures found on thick filaments and that interact with thin filaments in the A-band. Are what allows myofibril to contract
Microscope cut in the A zone of a myofibril what do we see
Thin and thick filaments. Each thin has 3 thick around it. Each thick has 6 thin around it. (Myofibril constituted of lots of filaments)
Microscope cut in the I band of a myofibril what do we see
Thin filaments only
Microscope cut in the H-zone of a myofibril what do we see
Thick filaments only
What protein constitutes THIN filaments. Shape + interactions
Actin. 2 chains of globular actin interacting together form a helix
General function of actin in all cells
Part of cell skeleton
What protein makes up THICK filaments. Shape and organization
Myosin. Twisted protein with 2 head groupes at its end.
Myosin forms bundles with head groupes going in the same direction
M line (H-zone) seperates bundles of myosine with head groupes going in opposite directions
What is found around a bundle of myosin in the A-zone
Thin filaments that surround it
What happens to myosin during muscle contraction
Head groups repeatedly grab, pull and release the thin filaments.
3/4 steps of sliding filament model
1) Energized (ATP hydrolysis) myolin binds to actin in thin filaments.
2) Power stroke (pulls thin filaments towards M-line
3) Myosin unbinds and is reenergized
Something particular about all head groups functioning
Don’t work together but there’s always some head groups attached to the thin filaments so are never left free
What happens to length of myofibril upon contraction
Reduced (and Z-lines get closer together)
Relationship between maximal tension in a muscle fiber and its length : what it depends on
depends on degree of overlap of thick and thin filaments
Interesting point in the relationship between muscle fiber length and its maximal tension
There’s a point of optimal overlapping between thick and thin filaments where maximal tension in the muscle fiber reaches a maximum
What happens when thin and thick filaments overlap too much
Maximal tension in the muscle fiber is decreased because when thick filaments run into the Z-line, contraction is no more possible (some thick filaments will take off ?)
What happens when thin and thick filaments don’t overlap enough
Maximal tension in the muscle fiber is decreased because there is less interaction between thin and thick filaments
How are muscles designed in respect to thin and thick filaments overlapping
Are designed to work at an optimal range of overlapping in order to maximize tension.
