Muscles and Muscle Tissue
Smooth and cardiac cells develop from single myoblasts and
display gap junctions.
For the most part, specialized skeletal and cardiac muscle cells
lose their ability to divide but retain the ability to hypertrophy.
Smooth muscle regenerates well and undergoes hyperplasia.
Skeletal muscle development reﬂects maturation of the nervous
system and occurs in head-to-toe and proximal-to-distal
directions. Natural neuromuscular control reaches its peak in
Women’s muscles account for about 36% of their total body
weight and men’s for about 42%, a diﬀerence due chieﬂy to the
eﬀects of male hormones on skeletal muscle growth.
Skeletal muscle is richly vascularized and quite resistant to infection,
but in old age, skeletal muscles become ﬁbrous, decline in strength,
and atrophy. Regular exercise can oﬀset some of these changes.
Special features of smooth muscle contraction include the stress-
relaxation response, the ability to generate large amounts of force
when extensively stretched, and hyperplasia under certain conditions.
Types of Smooth Muscle
Unitary smooth muscle has electrically coupled ﬁbers that
contract synchronously and o±en spontaneously.
Multi unit smooth muscle has independent, well-innervated
ﬁbers that lack gap junctions and pacemaker cells. Stimulation
occurs via autonomic nerves (or hormones). Multi unit muscle
contractions are rarely synchronous.
Developmental Aspects of Muscles
(pp. 312–313, 315)
Muscle tissue develops from embryonic mesoderm cells called
myoblasts. Several myoblasts fuse to form a skeletal muscle ﬁber.
(Some questions have more than one correct answer. Select the best
answer or answers from the choices given.)
Te connective tissue covering that encloses the sarcolemma
of an individual muscle ﬁber is called the
A fascicle is a
bundle of muscle ﬁbers enclosed by
a connective tissue sheath,
bundle of myoﬁbrils,
Tick and thin myoﬁlaments have diﬀerent compositions. For
each descriptive phrase, indicate whether the ﬁlament is
attaches to the Z disc
does not lie in the I band
Te function of the ² tubules in muscle contraction is to
and store glycogen,
into the cell interior and then
pick it up again,
transmit the action potential deep into the
Te sites where the motor nerve impulse is transmitted from the
nerve endings to the skeletal muscle cell membranes are the
Contraction elicited by a single brief stimulus is called
multiple motor unit summation,
A smooth, sustained contraction resulting from very rapid
stimulation of the muscle, in which no evidence of relaxation
is seen, is called
motor unit summation,
Characteristics of isometric contractions include all but
increased muscle tension throughout the contraction phase,
absence of shortening,
used in resistance training.
During muscle contraction, A²P is provided by
reaction of creatine phosphate with ADP,
of glucose, and
Which provides A²P fastest?
Which does (do) not require that oxygen be available?
Which provides the highest yield of A²P per glucose
Which results in the formation of lactic acid?
Which has carbon dioxide and water products?
Which is most important in endurance sports?
Te neurotransmitter released by somatic motor neurons is
Te ions that enter the skeletal muscle cell during the generation
of an action potential are
Myoglobin has a special function in muscle tissue. It
is a contractile protein,
holds a reserve
supply of oxygen in the muscle.
Aerobic exercise results in all of the following except
cardiovascular system eﬃciency,
more mitochondria in the
increased size and strength of existing muscle
increased neuromuscular system coordination.
Te smooth muscle type found in the walls of digestive and
urinary system organs and that exhibits gap junctions and
pacemaker cells is
Short Answer Essay Questions
Name and describe the four special functional abilities of muscle
that are the basis for muscle response.
Distinguish between (a) direct and indirect muscle attachments
and (b) a tendon and an aponeurosis.
(a) Describe the structure of a sarcomere and indicate the
relationship of the sarcomere to myoﬁlaments. (b) Explain the
sliding ﬁlament model of contraction using appropriately labeled
diagrams of a relaxed and a contracted sarcomere.
What is the importance of acetylcholinesterase in muscle cell
Explain how a slight (but smooth) contraction diﬀers from a
vigorous contraction of the same muscle. Use the concepts of
multiple motor unit summation.
Explain what is meant by the term excitation-contraction coupling.
Deﬁne and draw a motor unit.
Describe the three distinct types of skeletal muscle ﬁbers.
²rue or false: Most muscles contain a predominance of one skeletal
muscle ﬁber type. Explain the reasoning behind your choice.
Describe some cause(s) of muscle fatigue and deﬁne this term