Transcript muscles2004

The Big Picture
Skeletal muscle is STRIATED and
VOLUNTARY
Attach to bones at tendons
Durable – not harmed by rough surface of
bone
Smaller than muscle – several can fit at a
joint
Built for contraction
Inside the cell
Each cell, many
myofibrils
The myofibril has
alternating
light/dark bands
A functional unit
runs from z-disc to
z-disc
sarcomere
Inside the cell
Each myofibril, 2
filaments
Actin (thin)
Myosin (Thick
Also has “heads”
I band stays put, A
band shrinks during
contraction
Other cellular features
Sarcoplasmic reticulum (SR)
Like a sleeve
Stores and releases Ca
Multi-nucleate
Stimulation
Nerve runs to muscle cell, carrying
signal
Neurotransmitter is acetlycholine (Ach)
Release of Ach opens protein channels
Allows Na+ to cross membrane
Creates action potential
Triggers Ca release from SR
Stimulation
Video
Contraction
At rest, binding sites are covered
Calcium opens them
Myosin heads attach to binding sites on
actin
Unique structure
Heads are “cocked”
Automatically “uncock” after attaching to
actin
Contraction
Myosin releases and “recocks” only with ATP
input
Then attaches to next site
This repeats until full contraction is reached
Actin and myosin slide past each other
Myosin heads resemble caterpillar walking
Contraction
Potential Problems
Not enough ATP?
Cramping?
Not enough calcium?
No binding sites
Cerebral palsy and Parkinson’s (brain),
multiple sclerosis (nerves), Muscular
dystrophy (muscles weakness), ALS
(nerves)
How do muscles get bigger?
Muscles cells don’t
divide….
So….
They get bigger!
More protein
filaments (myofibrils)
increase the size and
effectiveness of
muscles