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Muscle
Structure
and Function
Chapter 8
Day 3
Review Questions:
What chemical exposes the binding site for actin and myosin?
•Calcium
What is the source of energy for a contraction?
•ATP
What is the name of the step in which the actin filament is
actively contracted?
•Powerstroke
What chemical must be present in order for the actin and
myosin filaments to separate?
•ATP
Think it over
•The boat (myosin) does not move far in one cycle, a
muscle contraction requires many cycles
▫ If a muscle is contracted what happens if a new
molecule of ATP is not available?
▫ Muscle stays contracted – cramps!
•Why does rigor mortis occur? (Hint: What chemical
is no longer available to the body?)
▫ ATP is not available to control calcium release so
contractions are continuous 6-8 hours after death.
▫ Body relaxes 16-24 hours as enzymes break down
contractile structures.
Muscle Fiber Contraction Speed
• Muscle fibers differ in:
▫ Contraction speed
 Slow twitch
 Fast twitch
▫ Production of ATP
 Oxidatively – presence of oxygen
 Glycolyitically – in absence of oxygen
• The speed of contraction and aerobic
capacities of the fibers reflect the
specialized functions of the muscle
Muscle Fibers
Slow-Twitch Muscle Fibers
• Nickname: red fibers
• Contain red, oxygen-storing
pigment myoglobin
▫ Well supplied with oxygencarrying blood
• Contain a ton of mitochondria
▫ Enables the aerobic cycle of
cellular respiration to occur
• Fibers have a high respiratory
capacity
▫ Generate ATP fast enough to deal
with the ATP breakdown
• Can contract for a long period of
time without fatiguing
• Found in muscles of the back
Fast-Twitch Muscle Fibers
• Nickname: white fibers
• Have few myoglobin
▫ Poor blood supply
• Few mitochondria
• Extensive sarcoplasmic reticulum,
store Calcium
▫ ATPase (enzyme that
transports various ions) is
faster
• Contract rapidly
▫ Fatigue as lactic acid builds
▫ ATP depletes quicker, causes
fatigue as well
• Found in muscles of the hands,
feet, eyes
Uh oh, there’s a third fiber…
• Fast-twitch fatigue-resistant
▫ Nickname: intermediate fibers
▫ Have the fast-twitch speed like the white fibers
▫ Also have the substantial oxidative capacity of red
fibers
• Some muscles have only one fiber type or another,
majority of muscles include a combination of fiber
types
Head and Neck Muscles
There are 4 basic functions
of head and neck muscles:
o swallowing and
chewing (mastication)
o making facial
expressions
o moving your neck
o supporting your head
Muscles of the Head and Neck
Posterior neck muscles
The muscles in the neck help to support the head. How much do you
think an average adult head weighs?
(over 11 pounds)
Limb muscles
Muscles of the
limb function in:
• movement
• grasping
• balance
Color Key
•Purple: Muscles that move the
arm
•Orange: Muscles that move the
forearm
•Brown: Muscles that move the
hand
Anterior
superficial
muscles of
the shoulder
and arm
Posterior
superficial
muscles of
the arm
14
Extensor digiti
minimi
Find the muscles on your body.