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MUSCULAR
SYSTEM
SEELEY'S ESSENTIALS OF ANATOMY AND
PHYSIOLOGY, 9TH EDITION.
Created by: Johmel De Ocampo
Created by: Johmel De Ocampo
MUSCULAR SYSTEM
The muscular system is responsible for the movement of
the human body.
FUNCTIONS OF
MUSCULAR SYSTEM
1. Movement of the body. Contraction of
skeletal muscles is responsible for the
overall movements of the body, such as
walking, running, and manipulating
objects with the hands.
2. Maintenance of posture. Skeletal muscles
constantly maintain tone, which keeps us
sitting or standing erect.
3. Respiration. Muscles of the thorax carry
out the movements necessary for
respiration.
4. Production of body heat. When skeletal
muscles contract, heat is given off as a
by-product. This released heat is critical to
the maintenance of body temperature.
5. Communication. Skeletal muscles are
involved in all aspects of communication,
including speaking, writing, typing,
gesturing, and facial expressions.
6. Constriction of organs and vessels. The
contraction of smooth muscle within the
walls of internal organs and vessels causes
those structures to constrict. This
constriction can help propel and mix food
and water in the digestive tract, propel
secretions from organs, and regulate blood
flow through vessels.
7. Contraction of the heart. The contraction
of cardiac muscle causes the heart to beat,
propelling blood to all parts of the body
OVERVIEW OF
MUSCULAR SYSTEM
Created by: Johmel De Ocampo
MUSCULAR SYSTEM
STRUCTURE OF A MUSCLE
(a) Part of a muscle attached by a tendon to a bone. A muscle is composed of muscle fasciculi, each
surrounded by perimysium. The fasciculi are composed of bundles of individual muscle fibers (muscle
cells), each surrounded by endomysium. The entire muscle is surrounded by a connective tissue sheath
called epimysium, or muscular fascia. (b) Enlargement of one muscle fiber containing several
myofibrils. (c) A myofibril extended out the end of the muscle fiber, showing the banding patterns of
the sarcomeres. (d) A single sarcomere of a myofibril is composed mainly of actin myofilaments and
myosin myofilaments. The Z disks anchor the actin myofilaments, and the myosin myofilaments are
held in place by the M line. (e) Part of an actin myofilament is enlarged. (f) Part of a myosin
myofilament is enlarged.
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MUSCULAR SYSTEM
CHARACTERISTICS OF SKELETAL MUSCLE
SKELETAL MUSCLE
Skeletal muscle, with its associated connective tissue, constitutes
approximately 40% of body weight. Skeletal muscle is so named because
most of the muscles are attached to the skeletal system. It is also called
striated muscle because transverse bands, or striations, can be seen in the
muscle under the microscope.
FOUR MAJOR FUNCTIONAL
CHARACTERISTICS
CONTRACTILITY
is the ability of skeletal muscle to shorten with force. When skeletal
muscles contract, they cause the structures to which they are attached to
move. Skeletal muscles shorten forcefully during contraction, but they
lengthen passively. Either gravity or the contraction of an opposing
muscle produces a force that pulls on the shortened muscle, causing it to
lengthen.
EXCITABILITY
is the capacity of skeletal muscle to respond to a stimulus. Normally, the
stimulus is from nerves that we consciously control.
EXTENSIBILITY
means that skeletal muscles stretch. After a contraction, skeletal
muscles can be stretched to their normal resting length and beyond to a
limited degree
ELASTICITY
is the ability of skeletal muscles to recoil to their original resting length
after they have been stretched.
Created by: Johmel De Ocampo
MUSCULAR SYSTEM
STRUCTURE OF SKELETAL MUSCLE
(a) Organization of skeletal muscle
components. (b) Electron micrograph of
skeletal
muscle,
showing
several
sarcomeres in a muscle fiber. (c) Diagram
of two adjacent sarcomeres, depicting the
structures responsible for the banding
pattern.
THE SARCOMERE
The striated appearance of skeletal muscle fibers is due
to the arrangement of the myofilaments of actin and
myosin in sequential order from one end of the muscle
fiber to the other. Each packet of these microfilaments
and their regulatory proteins, troponin and tropomyosin
(along with other proteins) is called a sarcomere.
Created by: Johmel De Ocampo
MUSCULAR SYSTEM
EXCITABILITY OF MUSCLE FIBERS
ION CHANNELS AND THE ACTION POTENTIAL
Step 1 illustrates the status of Na+ and K+ channels in a
resting cell.
Steps 2 and 3 show how the channels open and close to
produce an action potential.
Next to each step, the charge difference across the
plasma membrane is illustrated.
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MUSCULAR SYSTEM
NERVE SUPPLY & MUSCLE FIBER STIMULATION
NEUROMUSCULAR JUNCTION
Another specialization of the skeletal muscle is the site where a motor neuron’s
terminal meets the muscle fiber—called the neuromuscular junction (NMJ). This is
where the muscle fiber first responds to signaling by the motor neuron. Every
skeletal muscle fiber in every skeletal muscle is innervated by a motor neuron at
the NMJ. Excitation signals from the neuron are the only way to functionally
activate the fiber to contract.
(a) In a neuromuscular junction, several branches of an axon junction with a single
muscle fiber.
(b) Photomicrograph of neuromuscular junctions.
Created by: Johmel De Ocampo
MUSCULAR SYSTEM
FUNCTION OF NEUROMUSCULAR JUNCTION
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MUSCULAR SYSTEM
SKELETAL MUSCLE CONTRACTION
(a) The active site on actin is
exposed as calcium binds to
troponin.
(b) The myosin head is attracted to
actin, and myosin binds actin at its
actin-binding site, forming the
cross-bridge.
(c) During the power stroke, the
phosphate
generated
in
the
previous contraction cycle is
released. This results in the myosin
head pivoting toward the center of
the sarcomere, after which the
attached ADP and phosphate group
are released.
(d) A new molecule of ATP attaches
to the myosin head, causing the
cross-bridge to detach.
(e) The myosin head hydrolyzes
ATP to ADP and phosphate, which
returns the myosin to the cocked
position.
Created by: Johmel De Ocampo
MUSCULAR SYSTEM
SUMMARY OF SKELETAL MUSCLE
CONTRACTION
MUSCLE METABOLISM
Some ATP is stored in a resting
muscle. As contraction starts, it
is used up in seconds. More ATP
is generated from creatine
phosphate for about 15 seconds.
Each glucose molecule produces two ATP
and two molecules of pyruvic acid, which
can be used in aerobic respiration or
converted to lactic acid. If oxygen is not
available, pyruvic acid is converted to
lactic acid, which may contribute to
muscle fatigue. This occurs during
strenuous exercise when high amounts of
energy are needed but oxygen cannot be
sufficiently delivered to muscle.
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MUSCULAR SYSTEM
Aerobic respiration is the breakdown
of glucose in the presence of oxygen
(O2) to produce carbon dioxide,
water, and ATP. Approximately 95
percent of the ATP required for
resting or moderately active muscles
is provided by aerobic respiration,
which takes place in mitochondria.
BREAKDOWN OF ATP
AND CROSS-BRIDGE
MOVEMENT DURING
MUSCLE
CONTRACTION
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MUSCULAR SYSTEM
PHASE OF A MUSCLE
TWITCH
MULTIPLE WAVE
SUMMATION
ENERGY REQUIREMENT FOR MUSCLE
CONTRACTION
Muscle fibers are very energy-demanding cells whether at rest or during any form of
exercise. This energy comes from either aerobic (with O2) or anaerobic (without O2) ATP
production
Generally, ATP is derived from four processes in skeletal muscle:
1. Aerobic production of ATP during most exercise and normal conditions
2. Anaerobic production of ATP during intensive short-term work
3. Conversion of a molecule called creatine (kr̄ ′ a-t̄n) phosphate to ATP
4. Conversion of two ADP to one ATP and one AMP (adenosine monophosphate) during
heavy exercise
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MUSCULAR SYSTEM
FATE OF ATP IN RESTING AND
EXCERCISING MUSCLE
Glycolysis is an anaerobic (non-oxygen-dependent) process that breaks down glucose (sugar) to
produce ATP.
Aerobic respiration is the breakdown of glucose or other nutrients in the presence of oxygen (O2)
to produce carbon dioxide, water, and ATP.
Muscle tension, force generated by the contraction of the muscle (or shortening of the
sarcomeres)
Isotonic contractions, where the tension in the muscle stays constant, a load is moved as the
length of the muscle changes (shortens).
A concentric contraction involves the muscle shortening to move a load.
An eccentric contraction occurs as the muscle tension diminishes and the muscle lengthens.
Isometric contractions involve sarcomere shortening and increasing muscle tension, but do not
move a load, as the force produced cannot overcome the resistance provided by the load.
You have 640 skeletal muscles in your body
Sartorius – the longest muscles, located in your upper thigh
Stapedius – the tinniest muscle, located in the middle ear
Muscles Are Actually PULLING Their Insertions toward their origins
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MUSCULAR SYSTEM
SKELETAL MUSCLE
PRIME MOVERS
Muscles that are primary concern with the movement (Agonist Muscles)
ANTAGONISTS
working in reverse of that particular movement, preventing the prime mover to over
extend
SYNERGISTS
Helps the prime movers lending a little extra oomph stabilizing joints against
dislocation
FIXATORS
if a synergist immobilize the muscles’ origin bone so that the prime mover can be more
effective.
MOTOR UNITS
a group of muscle fibers that all get their Signals from the same, single motor neuron
LARGE MOTOR UNIT
motor neurons may synapse with and innervate a thousand muscle fibers
SMALL MOTOR UNIT
A hand full of motor neuron connect to a single fine neuron that produce a specialized
movement/ function
TYPES OF MUSCLE FIBERS
SLOW OXIDATIVE
Slow oxidative (SO) fibers contract
relatively slowly and use aerobic
respiration (oxygen and glucose) to
produce ATP.
FAST OXIDATIVE
Fast oxidative (FO) fibers have fast
contractions and primarily use
aerobic respiration, but because
they may switch to anaerobic
respiration (glycolysis),can fatigue
more quickly than SO fibers.
FAST GLYCOLYTIC
Fast glycolytic (FG) fibers have fast
contractions and primarily use
anaerobic glycolysis. The FG fibers
fatigue more quickly than the
others.
Created by: Johmel De Ocampo
MUSCULAR SYSTEM
FATIGUE
Fatigue is a temporary state of reduced work capacity. Without fatigue, muscle fibers
would be worked to the point of structural damage to them and their supportive tissues.
Historically it was thought that buildup of lactic acid and the corresponding drop in pH
(acidosis) was the major cause of fatigue. However, it is now established that there are
multiple mechanisms underlying muscular fatigue.
These mechanisms include:
Acidosis and ATP depletion due to either an increased ATP consumption or a
decreased ATP production
Oxidative stress, which is characterized by the buildup of excess reactive oxygen
species (ROS; free radicals)
3. Local inflammatory reactions
TYPES OF MUSCLE CONTRACTIONS
ISOMETRIC
isometric (equal distance) contractions, the length of the muscle does not change, but
the amount of tension increases during the contraction process. Isometric
contractions are responsible for the constant length of the body’s postural muscles,
such as the muscles of the back.
ISOTONIC
isotonic (equal tension) contractions, the amount of tension produced by the muscle is
constant during contraction, but the length of the muscle decreases.
CONCENTRIC CONTRACTION
Concentric (kon-sen′ trik) contractions are isotonic contractions in which muscle
tension increases as the muscle shortens. Many common movements are produced
by concentric muscle contractions.
ECCENTRIC CONTRACTION
Eccentric (ek-sen′ trik) contractions are isotonic contractions in which tension is
maintained in a muscle, but the opposing resistance causes the muscle to lengthen.
Eccentric contractions are used when a person slowly lowers a heavy weight.
MUSCLE TONE
Muscle tone is the constant tension produced by body muscles over long periods of time.
Muscle tone is responsible for keeping the back and legs straight, the head in an upright
position, and the abdomen from bulging. Muscle tone depends on a small percentage of
all the motor units in a muscle being stimulated at any point in time, causing their
muscle fibers to contract tetanically and out of phase with one another.
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MUSCULAR SYSTEM
SMOOTH MUSCLE
Smooth muscle fibers are spindle-shaped (wide in the middle and tapered at both ends,
somewhat like a football) and have a single nucleus; Although they do not have
striations and sarcomeres, smooth muscle fibers do have actin and myosin contractile
proteins, and thick and thin filaments. These thin filaments are anchored by dense
bodies. A dense body is analogous to the Z-discs of skeletal and cardiac muscle fibers and
is fastened to the sarcolemma. Calcium ions are supplied by the SR in the fibers and by
sequestration from the extracellular fluid through membrane indentations called
calveoli.
Created by: Johmel De Ocampo
MUSCULAR SYSTEM
CARDIAC MUSCLE
Cardiac muscle tissue is only found in the heart. Highly coordinated contractions of
cardiac muscle pump blood into the vessels of the circulatory system. Similar to skeletal
muscle, cardiac muscle is striated and organized into sarcomeres, possessing the same
banding organization as skeletal muscle.
Contractions of the heart (heartbeats) are controlled by specialized cardiac muscle cells
called pacemaker cells that directly control heart rate. Although cardiac muscle cannot
be consciously controlled, the pacemaker cells respond to signals from the autonomic
nervous system (ANS) to speed up or slow down the heart rate. The pacemaker cells can
also respond to various hormones that modulate heart rate to control blood pressure.
This group of cells is self-excitable and able to depolarize to threshold and fire action
potentials on their own, a feature called autorhythmicity; they do this at set intervals
which determine heart rate. Because they are connected with gap junctions to
surrounding muscle fibers and the specialized fibers of the heart’s conduction system,
the pacemaker cells are able to transfer the depolarization to the other cardiac muscle
fibers in a manner that allows the heart to contract in a coordinated manner.
Created by: Johmel De Ocampo
MUSCULAR SYSTEM
MUSCLE TYPES
Interactions of Skeletal Muscles, Their
Fascicle Arrangement, and Their Lever
Systems
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MUSCULAR SYSTEM
SUPERFICIAL BODY MUSCULATURE
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MUSCULAR SYSTEM
SUPERFICIAL BODY MUSCULATURE
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MUSCULAR SYSTEM
FASCICLE ARRANGEMENT
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MUSCULAR SYSTEM
MUSCLES OF THE HEAD AND NECK
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MUSCULAR SYSTEM
FACIAL EXPRESSION
MASTICATION
TONGUE AND SWALLOWING MUSCLE
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MUSCULAR SYSTEM
DEEP NECK AND BACK MUSCLE
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MUSCULAR SYSTEM
MUSCLE OF THE THORAX
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MUSCULAR SYSTEM
MUSCLE OF THE ABDOMINAL WALL
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MUSCULAR SYSTEM
MUSCLE OF THE PELVIC FLOOR AND PERINEUM
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MUSCULAR SYSTEM
MUSCLE OF THE SHOULDER
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MUSCULAR SYSTEM
ARM MUSCLES
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MUSCULAR SYSTEM
MUSCLES OF THE FOREARM
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MUSCULAR SYSTEM
MUSCLES OF THE UPPER LIMB
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MUSCULAR SYSTEM
MUSCLES OF THE HIP AND THIGH
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MUSCULAR SYSTEM
MUSCLES OF THE LOWER LIMB
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MUSCULAR SYSTEM
MUSCLES OF THE LEG
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MUSCULAR SYSTEM
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MUSCULAR SYSTEM
DISEASES AND DISORDERS
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SUMMARY
FUNCTIONS OF THE MUSCULAR SYSTEM
The muscular system produces body movement, maintains posture, causes respiration,
produces body heat, performs movements involved in communication, constricts organs
and vessels, and pumps blood.
CHARACTERISTICS OF SKELETAL MUSCLE
Skeletal muscle has contractility, excitability, extensibility, and elasticity.
SKELETAL MUSCLE STRUCTURE
1. Muscle fibers are organized into fasciculi, and fasciculi are organized into muscles by
associated connective tissue.
2. Each skeletal muscle fiber is a single cell containing numerous myofibrils.
3. Myofibrils are composed of actin and myosin myofilaments.
4. Sarcomeres are joined end-to-end to form myofibrils.
EXCITABILITY OF MUSCLE FIBERS
1. Cell membranes have a negative charge on the inside relative to a positive charge
outside. This is called the resting membrane potential.
2. Action potentials are a brief reversal of the membrane charge. They are carried rapidly
along the cell membrane.
3. Sodium ions (Na+) move into cells during depolarization, and K+ moves out of cells during
repolarization.
NERVE SUPPLY AND MUSCLE FIBER STIMULATION
1. Motor neurons carry action potentials to skeletal muscles, where the neuron and muscle
fibers form neuromuscular junctions.
2. Neurons release acetylcholine, which binds to receptors on muscle cell membranes,
stimulates an action potential in the muscle cell, and causes the muscle to contract.
MUSCLE CONTRACTION
1. Action potentials are carried along T tubules to the sarcoplasmic reticulum, where they
cause the release of calcium ions.
2. Calcium ions, released from the sarcoplasmic reticulum, bind to the actin myofilaments,
exposing attachment sites.
STRUCTURAL AND FUNCTIONAL ORGANIZATION OF THE HUMAN BODY
1. The human body can be organized into six levels: chemical, cell, tissue, organ, organ
system, and organism.
2. The eleven organ systems are the integumentary, skeletal, muscular, lymphatic,
respiratory, digestive, nervous, endocrine, cardiovascular, urinary, and reproductive
systems.
3. Myosin forms cross-bridges with the exposed actin attachment sites.
4. The myosin molecules bend, causing the actin molecules to slide past; this is the sliding
filament model. The H and I bands shorten; the A bands do not.
Created by: Johmel De Ocampo
SUMMARY
5. This process requires ATP breakdown.
6. A muscle twitch is the contraction of a muscle fiber in response to a stimulus; it consists
of a lag phase, a contraction phase, and a relaxation phase.
7. Tetanus occurs when stimuli occur so rapidly that a muscle does not relax between
twitches.
ENERGY REQUIREMENT FOR MUSCLE CONTRACTION
1. Small contraction forces are generated when small numbers of motor units are recruited,
and greater contraction forces are generated when large numbers of motor units are
recruited.
2. Energy is produced by aerobic (with oxygen) and anaerobic (without oxygen) respiration.
3. After intense exercise, the rate of aerobic respiration remains elevated to repay the
oxygen deficit.
FATIGUE
Muscular fatigue occurs as ATP is depleted during muscle contraction. Physiological
contracture occurs in extreme fatigue when a muscle can neither contract nor relax
EFFECT OF FIBER TYPE ON ACTIVITY LEVEL
1. Muscles contract either isometrically (tension increases, but muscle length stays the
same) or isotonically (tension remains the same, but muscle length decreases).
2. Muscle tone consists of a small percentage of muscle fibers contracting tetanically and is
responsible for posture.
3. Muscles contain a combination of slow-twitch and fast-twitch fibers.
4. Slow-twitch fibers are better suited for aerobic respiration, and fast-twitch fibers are
adapted for anaerobic respiration.
5. Sprinters have more fast-twitch fibers, whereas distance runners have more slow-twitch
fibers.
SKELETAL MUSCLE ANATOMY
GENERAL PRINCIPLE
1. Most muscles have an origin on one bone, have an insertion onto another, and cross at
least one joint.
2. A muscle causing a specific movement is an agonist. A muscle causing the opposite
movement is an antagonist.
3. Muscles working together are synergists.
4. A prime mover is the muscle of a synergistic group that is primarily responsible for the
movement.
NOMENCLATURE
Muscles are named according to their location, origin and insertion, number of heads, or
function.
Created by: Johmel De Ocampo
SUMMARY
MUSCLES OF THE HEAD AND NECK
1. Muscles of facial expression are associated primarily with the mouth and eyes.
2. Four pairs of muscles are involved in mastication.
3. Tongue movements involve intrinsic and extrinsic muscles.
4. Swallowing involves the suprahyoid and infrahyoid muscles, plus muscles of the soft
palate, pharynx, and larynx.
5. Neck muscles move the head.
TRUNK MUSCLES
1. The erector spinae muscles hold the body erect.
2. Intercostal muscles and the diaphragm are involved in breathing.
3. Muscles of the abdominal wall flex and rotate the vertebral column, compress the
abdominal cavity, and hold in and protect the abdominal organs.
4. Muscles form the floor of the pelvis.
UPPER LIMB MUSCLES
1. The upper limb is attached to the body primarily by muscles.
2. Arm movements are accomplished by pectoral, rotator cuff, and deltoid muscles.
3. The elbow is flexed and extended by anterior and posterior arm muscles, respectively.
4. Supination and pronation of the forearm are accomplished by supinators and pronators
in the forearm.
5. Movements of the wrist and fingers are accomplished by most of the twenty forearm
muscles and nineteen intrinsic muscles in the hand.
LOWER LIMB MUSCLES
1. . Hip muscles flex and extend the hip and abduct the thigh.
2. Thigh muscles flex and extend the hip and adduct the thigh. They also flex and extend
the knee.
3. Muscles of the leg and foot are similar to those of the forearm and hand.
REFERENCE
Seeley's Essentials of Anatomy and Physiology, 9th Edition.
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