Lecture 7
Muscular System
Muscle Types and Functions
 Types of Muscle
o ________________ muscle – voluntary striated muscle that is usually
attached to one or more bones
 Long, thin, cylindrical fibers
 Packed with ______________ microfilaments that overlap each
other producing light and dark bands (striations)
 More than one _________________ per cell
o Cardiac muscle – heart muscle, involuntarily controlled
 ____________________, but involuntary
 One nucleus per cell
o __________________ muscle – involuntarily controlled
 No striations
 One nucleus per cell
 Functions of Muscle
o ___________________ – Allow body to move from place to place and
movement of individual body parts
 Also moves body contents in course of respiration, circulation,
digestion, urination, and childbirth
o Stability – Muscles maintain posture for resisting the pull of
________________
o Communication – Muscles are used for facial expression, _____________
language, writing and speech
o Control of body openings and passages – Sphincter muscles around
eyelids, pupils, and ______________ control admission of light, food, and
drink into the body; other sphincter muscles control movements out of the
body
o _____________ production- The skeletal muscles produce 85% of body
heat
 Properties of Muscle
o Excitability – When stimulated, muscle cells respond with
___________________ changes across the plasma membrane
o Conductivity – When the muscle is stimulated, electrical excitation is
conducted throughout the entire plasma membrane
o Contractility- Muscle fibers shorten ____________________ when
stimulated, which allows them to create movement
o Extensibility – Muscle cells can be stretched as much as ____________
times their contracted length.
o Elasticity – If a muscle is stretched, and then the tension is released, it can
___________________ to its original resting length
General Anatomy of Muscles
 Connective Tissues and Fascicles
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o Endomysium – a thin sleeve of connective tissue that surrounds each
muscle _________________ (muscle cell)
o Fascicles – bundles of muscle fibers, visible to the naked eye as parallel
strands
o Perimysium – connective tissue that surrounds ____________________
o Epimysium – a fibrous sheath that surrounds and entire skeletal muscle
o Fascia – connective tissue that separates muscles from one another (deep
fascia) or that separates muscles from the overlying _______________
Fascicles and Muscle Shapes
o Fusiform muscles – muscles that are thick in the middle and tapered at
each end
 Moderately strong contractions
o Parallel muscles – muscles that are of uniform width and that have parallel
fascicles
 Span _______________ distances, weaker than fusiform
o Convergent muscles – muscles that are fan shaped, with fibers meeting at
a single point
 Relatively strong because of the relatively ______________
insertion
o Pennate muscles- feather shaped, with fascicles inserting obliquely on a
tendon that runs the length of the muscle (fibers meet at a
______________, rather than a single point)
 Strong muscles such as rectus femoris
o ________________________ muscles (Circular muscles) – form rings
around body openings
Muscle Attachments
o _________________ – relatively stationary (and proximal) point of
muscle attachment
o Insertion – more mobile (and distal) point of muscle attachment
o Belly – middle region between the origin and the insertion
Functional Groups of Muscles
o Prime mover (agonist) – muscle that produces most of the
______________ during a particular contraction
 Example: biceps brachii for flexion of the elbow
o __________________ – Muscle that aids the prime mover to produce
more power than a single muscle could
 Example: brachialis muscle assists the biceps brachii
o Antagonist – Muscle that _________________ the prime mover
 It relaxes to give the prime mover almost complete control over an
action
 It may maintain some tension on a joint, limiting the speed or
range of the prime mover, preventing excessive movement and
joint injury
 Example: triceps brachii opposes the biceps brachii
o ___________________ – Muscle that prevents a bone from moving
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Example: The fixator muscles of the scapula hold the scapula
firmly in place during flexion of the elbow
Intrinsic and Extrinsic Muscles
o Intrinsic muscles are entirely contained within a particular region, having
both its origin and _______________________ there
o Extrinsic muscles act on a particular region, but has its origin elsewhere
 Some movements of the fingers are produced by extrinsic muscles
in the _____________________
Muscles, Bones, and Levers
o ______________- any elongated, rigid object that rotates around a fixed
point
o Fulcrum – fixed point around which a lever rotates
o Effort- _________________ applied against inertia; something done
through exertion
o Resistance- force that tends to oppose motion
o Effort arm- part from the fulcrum to the point of __________________
o Resistance arm- part from the _________________ to the point of
resistance
o Functions of a lever?
 Exert more __________________ against a resisting object than
the force applied to the lever
 OR move the resisting object farther or _________________ than
the effort arm is moved
 There is a trade-off between force and speed or distance
o Mechanical advantage-Ratio of its output force to its input force
o Lever classes
 First-class lever – _____________________ is between the effort
and the resistance
 Second-class lever – _____________________ is between the
effort and the fulcrum
 Third-class lever – ____________________ is between the
fulcrum and the resistance
Microscopic Anatomy
 Ultrastructure of Muscle Fibers
o Sarcolemma – plasma membrane of a muscle cell
o Transverse tubules – tunnel-like infoldings of the sarcolemma that
penetrate through the cell membrane and carry an electrical current from
the surface of the cell to the interior when the cell is stimulated
o ____________________________- cytoplasm of a muscle cell
o Myofibrils – long protein bundles about 1 micrometer in diameter
o Glycogen – provides stored __________________ for the muscle during
exercise
o Myoglobin – binds oxygen until it is needed for muscular activity
o Sarcoplasmic reticulum – reservoir for ___________________ ions which
are needed to activate the muscle contraction process
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o Myofilaments – parallel protein microfilaments that make up myofibrils
 2 main kinds
 Myosin myofilaments – thick – about ____ nm in diameter
 Actin myofilaments – thin – about 7 nm in diameter
o Striations and Sarcomeres
 Actin myofilaments run ___________________ to each other and
are anchored at one end to a Z line (or Z disc)
 Mysosin myofilaments run parallel to each other and fit
___________________ actin myofilaments
 A sarcomere is the term for the segment that spans from one Z line
to the next Z line
 Because the sarcomere contains areas where there are only thin
filaments, areas where there are only thick filaments, and areas
with overlapping thick and thin filaments, there are ____________
areas and light areas
 I bands are light (lIght) and contain only _____________
filaments
 A bands are dark (dArk) and contain thick filaments
(overlapping with thin filaments at the ends)
 H bands are found in the middle of the _____ band
o They are found where actin and myosin filaments
do no overlap (containing only thick filaments)
 Shortening
 The sarcomere shortens during muscle contraction, but the
______________________ do not
o As the Z lines get closer together, actin and myosin
filaments overlap more and more.
o Because I bands are the areas consisting of areas where
thin filaments are not overlapped by thick filaments, the I
bands ___________________ during muscle contraction
o Because the H bands are the areas consisting of areas
where thick filaments are not overlapped by thin
filaments, the H bands _____________________ during
muscle contraction
o Because the A bands extend from one end of the thick
filaments to the other end (overlapping with thin, or not),
and because the filaments themselves do not shorten, A
bands remain the same length
The Nerve-Muscle Relationship
o Skeletal muscles only contract when stimulated by neurons
o Motor neurons are nerve cells that lead from the central nervous system to
muscles (or glands)
 Each motor nerve fiber branches about 200 times at its distal end,
leading to different muscle fibers
 Each muscle fiber is innervated by only ______________ motor
neuron
o Synapse – a __________________ at the end of an axon where it
stimulates another cell
o Neuromuscular junction – a synapse between a nerve fiber and a muscle
cell
o Synaptic ________________ – The swollen tip at the distal end of an
axon; the site of synaptic vesicles and neurotransmitter release
o Synaptic vesicles – A spheroid organelle in a ___________________
knob; contains neurotransmitter
o Neurotransmitter – A chemical released at the distal end of an axon that
stimulates an adjacent cell
o Motor ________ plate – A depression in a muscle fiber where it has
synaptic contact with a nerve fiber and has a high density of
neurotransmitter receptors
o Synaptic cleft – a narrow ______________ between the synaptic knob of
an axon and the adjacent cell
 A neurotransmitter has to diffuse across this space
 Motor Unit – a motor neuron and all the skeletal ________________ innervated
by it
o Small motor units – where fine control is needed
 Very few muscle fibers per nerve fiber
 Provide fine degree of control needed for subtle movements
 Small neurons that are _________________ stimulated
o Large motor units
 Many muscle fibers per nerve fiber
 Much stronger, but lacking _____________ control
 Large neurons that are harder to stimulate
Functional Perspectives
 Muscle Growth and Atrophy
o Growth - Exercise stimulates muscle fibers to produce more protein
myofilaments
 Myofibrils, as a result, grow ___________________
 At a certain point, a large myofibril splits longitudinally, so a wellconditioned muscle cell has more ____________________
 Some scientists think that entire muscle cells may split, leading to
increased numbers of muscle ________________ (not just
myofibrils)
o Atrophy – muscle shrinks if it is not used
 Disuse atrophy – typically seen when a limb is kept in a cast for
weeks
 Denervation atrophy – seen in cases where the spinal cord or
______________ connections to a muscle are damaged
 Senescence atrophy – occurs due to aging, regardless of exercise
 Physiological Classes of Muscle Fibers
o Slow-twitch
 Well adapted to ______________ respiration
 Fibers do not generate lactic acid or fatigue easily
o Fast-twitch
 Rich in enzymes for ______________________ fermentation
 Fibers do produce lactic acid and fatigue more easily
 Well adapted for quick responses but not for endurance
Cardiac and Smooth Muscle
 Cardiac Muscle
o Makes up most of the ___________________
o Striated like skeletal muscle
o Short, stumpy, slightly branched cells
o Have intercalated discs where the cells meet
o Each cell has one centrally-placed nucleus
 Smooth Muscle
o Found in blood vessels, _____________ passages, the iris of the eye, and
digestive, respiratory, urinary and reproductive tracts
o Fusiform in shape
o Each cell has a single nucleus