120 Chapter 6
- Nerve impulses first stimulate a skeletal muscle fiber at
.
a. T tubules c. neuromuscular junctions
b. sarcomeres d. actin binding sites - A motor unit is.
a. a single muscle fiber c. a muscle twitch
b. a single sarcomere d. a motor neuron and the
fibers it synapses with - Muscle fatigue.
a. occurs when ATP runs out
b. may be caused by oxygen debt
c. is a state in which a muscle can no longer contract
d. all of the above - Muscle tone is.
a. the same as muscle tension
b. a steady, low-level state of contraction
c. not present when a muscle is relaxed
d. all of the above - Match the M words with their defining feature.
muscle a. actin’s partner
muscle twitch b. delivers contraction signal
muscle tension c. a muscle cannot contract
myosin d. motor unit response
motor neuron e. force exerted by cross-
myofibrils bridges
muscle fatigue f. muscle cells bundled in
connective tissue
g. threadlike parts in a
muscle fiber
CritiCaL thinking
- You are training athletes for the 100-meter dash. They need
muscles specialized for speed and strength, not endurance.
What muscle characteristics would your training regimen
aim to develop? How would you alter it to train a long-
distance swimmer? - Jay thinks he has torn a muscle in his calf while doing
yardwork. His best friend tells him that the tear will likely
heal itself over time, and because his yard is still a mess he
decides to “work through the pain.” Do you think this plan
is OK? Explain why or why not.
3. Curare, a poison extracted from a South American shrub,
blocks the binding of ACh by muscle cells. What do you
suppose would happen to your muscles, including the ones
involved in breathing, if a toxic dose of curare entered your
bloodstream?
4. At the gym Sean gets on a stair-climbing machine and
“climbs” as fast as he can for fifteen minutes. At the end
of that time he is breathing hard and his quadriceps and
other leg muscles are aching. What is the physio logical
explanation for these symptoms?
5. In training for a marathon, Maria plans to secretly take a
performance-enhancing drug because she believes it will
help her place in the top five finishers and she desperately
wants to build a reputation as a world-class competitive
marathoner. What is your opinion on this plan?
It’s long been known that exercise
can “sharpen” thinking, and
evidence suggests that it may also
reduce symptoms of Alzheimer’s
disease, depression, and some
other neurological disorders. But
how does exercise produce these
benefits? Recently, researchers
discovered that during extended
exercise, skeletal muscles release
large amounts of a substance
called irisin into the bloodstream.
Working to pin down the exact
role of this “muscle hormone,” a
team at Harvard University’s Beth
Israel Hospital has discovered that
when irisin reaches the brain, it
triggers the release of a factor that is thought to play a key role
in boosting brain activity involved in thinking and reasoning.
The planned next step is to synthesize a form of irisin that may
one day be used to help treat brain disorders that skew normal
thinking processes.your Future
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