Chapter 6
The Muscular
System
Lecture Presentation by
Patty Bostwick-Taylor
Florence-Darlington Technical College
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The Muscular System
▪ Muscles are responsible for all types of body
movement
▪ Three basic muscle types are found in the body
1. Skeletal muscle
2. Cardiac muscle
3. Smooth muscle
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Muscle Types
▪ Skeletal and smooth muscle cells are elongated
(muscle cell = muscle fiber)
▪ Contraction and shortening of muscles are due to
the movement of microfilaments
▪ All muscles share some terminology
▪ Prefixes myo- and mys- refer to ―muscle‖
▪ Prefix sarco- refers to ―flesh‖
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Table 6.1 Comparison of Skeletal, Cardiac, and Smooth Muscles
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Table 6.1 Comparison of Skeletal, Cardiac, and Smooth Muscles (1 of 2)
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Table 6.1 Comparison of Skeletal, Cardiac, and Smooth Muscles (2 of 2)
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Muscle Types
▪ Skeletal muscle
▪ Most skeletal muscle fibers are attached by tendons to
bones
▪ Skeletal muscle cells are large, cigar-shaped, and
multinucleate
▪ Also known as striated muscle because of its obvious
stripes
▪ Also known as voluntary muscle because it is the only
muscle tissue subject to conscious control
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Muscle Types
▪ Skeletal muscle cells
are surrounded and
bundled by connective
tissue
▪ Endomysium—
encloses a single
muscle fiber
▪ Perimysium—wraps
around a fascicle
(bundle) of muscle fibers
▪ Epimysium—covers the
entire skeletal muscle
▪ Fascia—on the outside
of the epimysium
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Muscle Types
▪ The epimysium of skeletal muscle blends into a
connective tissue attachment
▪ Tendons—cordlike structures
▪ Mostly collagen fibers
▪ Often cross a joint because of their toughness and
small size
▪ Aponeuroses—sheetlike structures
▪ Attach muscles indirectly to bones, cartilages, or
connective tissue coverings
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Muscle Types
▪ Smooth muscle
▪ No striations
▪ Involuntary—no
conscious control
▪ Found mainly in the walls
of hollow visceral organs
(such as stomach,
urinary bladder,
respiratory passages)
▪ Spindle-shaped fibers
that are uninucleate
▪ Contractions are slow
and sustained
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Muscle Types
▪ Cardiac muscle
▪ Striations
▪ Involuntary
▪ Found only in the walls of
the heart
▪ Uninucleate
▪ Branching cells joined by
gap junctions called
intercalated discs
▪ Contracts at a steady rate
set by pacemaker
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Muscle Functions
▪ Whereas all muscle types produce movement,
skeletal muscle has three other important roles:
▪ Maintain posture and body position
▪ Stabilize joints
▪ Generate heat
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Microscopic Anatomy of Skeletal Muscle
▪ Sarcolemma—specialized plasma membrane
▪ Myofibrils—long organelles inside muscle cell
▪ Light (I) bands and dark (A) bands give the muscle its
striated (banded) appearance
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Microscopic Anatomy of Skeletal Muscle
▪ Banding pattern of myofibrils
▪ I band = light band
▪ Contains only thin filaments
▪ Z disc is a midline interruption
▪ A band = dark band
▪ Contains the entire length of the thick filaments
▪ H zone is a lighter central area
▪ M line is in center of H zone
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Microscopic Anatomy of Skeletal Muscle
▪ Sarcomere—contractile unit of a muscle fiber
▪ Structural and functional unit of skeletal muscle
▪ Organization of the sarcomere
▪ Myofilaments produce banding (striped) pattern
▪ Thick filaments = myosin filaments
▪ Thin filaments = actin filaments
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Microscopic Anatomy of Skeletal Muscle
▪ Thick filaments = myosin filaments
▪ Composed of the protein myosin
▪ Contain ATPase enzymes to split ATP to release
energy for muscle contractions
▪ Possess projections known as myosin heads
▪ Myosin heads are known as cross bridges when they
link thick and thin filaments during contraction
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Microscopic Anatomy of Skeletal Muscle
▪ Thin filaments = actin filaments
▪ Composed of the contractile protein actin
▪ Actin is anchored to the Z disc
▪ At rest, within the A band there is a zone that
lacks actin filaments called the H zone
▪ During contraction, H zones disappear as actin
and myosin filaments overlap
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Figure 6.3c Anatomy of a skeletal muscle fiber (cell).
Sarcomere
Thin (actin)
myofilament
Z disc
Thick (myosin)
myofilament
(c) Sarcomere (segment of a myofibril)
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M line
Z disc
Microscopic Anatomy of Skeletal Muscle
▪ Sarcoplasmic reticulum (SR)
▪ Specialized smooth endoplasmic reticulum
▪ Surrounds the myofibril
▪ Stores and releases calcium
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Stimulation and Contraction of Single Skeletal
Muscle Cells
▪ Special functional properties of skeletal muscles
▪ Irritability (also called responsiveness)—ability to
receive and respond to a stimulus
▪ Contractility—ability to forcibly shorten when an
adequate stimulus is received
▪ Extensibility—ability of muscle cells to be stretched
▪ Elasticity—ability to recoil and resume resting length
after stretching
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The Nerve Stimulus and Action Potential
▪ Skeletal muscles must be stimulated by a motor
neuron (nerve cell) to contract
▪ Motor unit—one motor neuron and all the skeletal
muscle cells stimulated by that neuron
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Figure 6.4a Motor units.
Axon terminals at
neuromuscular junctions
Spinal cord
Motor Motor
unit 1 unit 2
Nerve
Motor
neuron
cell bodies
Muscle
(a)
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Axon of
motor
neuron
Muscle fibers
Figure 6.4b Motor units.
Axon terminals at
neuromuscular junctions
Muscle
fibers
Branching
axon to
motor unit
(b)
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The Nerve Stimulus and Action Potential
▪ Neuromuscular junction
▪ Association site of axon terminal of the motor neuron
and sarcolemma of a muscle
▪ Neurotransmitter
▪ Chemical released by nerve upon arrival of nerve
impulse in the axon terminal
▪ Acetylcholine (ACh) is the neurotransmitter that
stimulates skeletal muscle
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The Nerve Stimulus and Action Potential
▪ Synaptic cleft
▪ Gap between nerve and muscle filled with interstitial
fluid
▪ Although very close, the nerve and muscle do not
make contact
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The Nerve Stimulus and Action Potential
▪ When a nerve impulse reaches the axon terminal
of the motor neuron,
Step 1: Calcium channels open, and calcium ions enter
the axon terminal
Step 2: Calcium ion entry causes some synaptic
vesicles to release acetylcholine (ACh)
Step 3: ACh diffuses across the synaptic cleft and
attaches to receptors on the sarcolemma of the muscle
cell
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The Nerve Stimulus and Action Potential
Step 4: If enough ACh is released, the sarcolemma
becomes temporarily more permeable to sodium ions
(Na+)
▪ Potassium ions (K+) diffuse out of the cell
▪ More sodium ions enter than potassium ions leave
▪ Establishes an imbalance in which interior has more
positive ions (depolarization), thereby opening more
Na+ channels
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The Nerve Stimulus and Action Potential
Step 5: Depolarization opens more sodium channels
that allow sodium ions to enter the cell
▪ An action potential is created
▪ Once begun, the action potential is unstoppable
▪ Conducts the electrical impulse from one end of the cell
to the other
Step 6: Acetylcholinesterase (AChE) breaks down
acetylcholine into acetic acid and choline
▪ AChE ends muscle contraction
▪ A single nerve impulse produces only one contraction
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The Nerve Stimulus and Action Potential
▪ Cell returns to its resting state when:
1. Potassium ions (K+) diffuse out of the cell
2. Sodium-potassium pump moves sodium and
potassium ions back to their original positions
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Figure 6.5 Events at the neuromuscular junction.
Slide 2
Nerve
impulse
Nucleus
Myelinated axon
of motor neuron
Axon terminal of
neuromuscular
junction
Sarcolemma of
the muscle fiber
Synaptic vesicle containing ACh
1 Nerve impulse reaches axon
terminal of motor neuron.
Axon terminal of motor neuron
Mitochondrion
Ca2+
Ca2+
Synaptic
cleft
ACh
ACh
receptor
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Sarcolemma
Fusing synaptic
vesicle
Sarcoplasm
of muscle fiber
Folds of
sarcolemma
Figure 6.5 Events at the neuromuscular junction.
Slide 3
Synaptic vesicle containing ACh
1 Nerve impulse reaches axon
terminal of motor neuron.
Axon terminal of motor neuron
Mitochondrion
2 Calcium (Ca2+) channels
open, and Ca2+ enters the
axon terminal.
Ca2+
Ca2+
Synaptic
cleft
ACh
ACh
receptor
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Sarcolemma
Fusing synaptic
vesicle
Sarcoplasm
of muscle fiber
Folds of
sarcolemma
Figure 6.5 Events at the neuromuscular junction.
Slide 4
Synaptic vesicle containing ACh
1 Nerve impulse reaches axon
terminal of motor neuron.
Axon terminal of motor neuron
Mitochondrion
2 Calcium (Ca2+) channels
open, and Ca2+ enters the
axon terminal.
3 Ca2+ entry causes some
synaptic vesicles to release their
contents (the neurotransmitter
acetylcholine) by exocytosis.
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Ca2+
Ca2+
Synaptic
cleft
ACh
ACh
receptor
Sarcolemma
Fusing synaptic
vesicle
Sarcoplasm
of muscle fiber
Folds of
sarcolemma
Figure 6.5 Events at the neuromuscular junction.
Slide 5
Synaptic vesicle containing ACh
1 Nerve impulse reaches axon
terminal of motor neuron.
Axon terminal of motor neuron
Mitochondrion
2 Calcium (Ca2+) channels
open, and Ca2+ enters the
axon terminal.
Synaptic
cleft
3 Ca2+ entry causes some
synaptic vesicles to release their
contents (the neurotransmitter
acetylcholine) by exocytosis.
4 Acetylcholine diffuses across
the synaptic cleft and binds to
receptors in the sarcolemma.
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Ca2+
Ca2+
ACh
ACh
receptor
Sarcolemma
Fusing synaptic
vesicle
Sarcoplasm
of muscle fiber
Folds of
sarcolemma
Figure 6.5 Events at the neuromuscular junction.
5 ACh binds and opens channels
that allow simultaneous passage
of Na+ into the muscle fiber and
K+ out of the muscle fiber. More
Na+ ions enter than K+ ions leave,
producing a local change in the
electrical conditions of the
membrane (depolarization). This
eventually leads to an action
potential.
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Slide 6
Na+ K+
Ion channel in
sarcolemma opens;
ions pass.
Figure 6.5 Events at the neuromuscular junction.
Slide 7
ACh
Degraded ACh
Na+
6 The enzyme acetylcholinesterase
breaks down ACh in the synaptic
cleft, ending the process.
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Acetylcholinesterase
K+
Ion channel closes;
ions cannot pass.
Figure 6.5 Events at the neuromuscular junction.
Slide 8
Nerve
impulse
Nucleus
Myelinated axon
of motor neuron
Axon terminal of
neuromuscular
junction
Sarcolemma of
the muscle fiber
Synaptic vesicle containing ACh
1 Nerve impulse reaches axon
terminal of motor neuron.
2 Calcium (Ca2+) channels
open, and Ca2+ enters the
axon terminal.
3 Ca2+ entry causes some
synaptic vesicles to release their
contents (the neurotransmitter
acetylcholine) by exocytosis.
Axon terminal of motor neuron
Mitochondrion
Ca2+
Ca2+
Synaptic
cleft
ACh
ACh
receptor
Sarcolemma
Fusing synaptic
vesicle
Sarcoplasm
of muscle fiber
Folds of
sarcolemma
4 Acetylcholine diffuses across
the synaptic cleft and binds to
receptors in the sarcolemma.
5 ACh binds and opens channels
that allow simultaneous passage
of Na+ into the muscle fiber and
K+ out of the muscle fiber. More
Na+ ions enter than K+ ions leave,
producing a local change in the
electrical conditions of the
membrane (depolarization). This
eventually leads to an action
potential.
6 The enzyme acetylcholinesterase
breaks down ACh in the synaptic
cleft, ending the process.
Na+ K+
ACh
Degraded ACh
Na+
Acetylcholinesterase
K+
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Ion channel in
sarcolemma opens;
ions pass.
Ion channel closes;
ions cannot pass.
Figure 6.6 Comparing the action potential to a flame consuming a dry twig.
Small twig
Match
flame
1 Flame ignites
the twig.
2 Flame spreads
rapidly along the twig.
(a)
Neuromuscular junction
Nerve
fiber
Striations
Muscle fiber
(cell)
1 Na+ diffuses
into the cell. 2 Action potential spreads
(b)
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rapidly along the sarcolemma.
A&P Flix : Events at the Neuromuscular
Junction
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Mechanism of Muscle Contraction: The
Sliding Filament Theory
▪ What causes filaments to slide?
▪ Calcium ions (Ca2+) bind regulatory proteins on thin
filaments and expose myosin-binding sites, allowing
the myosin heads on the thick filaments to attach
▪ Each cross bridge pivots, causing the thin filaments to
slide toward the center of the sarcomere
▪ Contraction occurs, and the cell shortens
▪ During a contraction, a cross bridge attaches and
detaches several times
▪ ATP provides the energy for the sliding process, which
continues as long as calcium ions are present
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Figure 6.7 Diagrammatic views of a sarcomere.
Actin
Myosin
Z
H
Z
I
A
I
(a) Relaxed sarcomere
Z
Z
I
A
(b) Fully contracted sarcomere
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I
Figure 6.8a Schematic representation of contraction mechanism: the sliding filament theory.
Regulatory proteins
Myosin myofilament
(a)
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Actin myofilament
In a relaxed muscle fiber, the regulatory proteins
forming part of the actin myofilaments prevent
myosin binding (see a). When an action potential
(AP) sweeps along its sarcolemma and a muscle
fiber is excited, calcium ions (Ca2+) are released
from intracellular storage areas (the sacs of the
sarcoplasmic reticulum).
Figure 6.8b Schematic representation of contraction mechanism: the sliding filament theory.
Myosin-binding site
Ca2+
Upper part of thick filament only
(b)
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The flood of calcium acts as the final trigger for
contraction, because as calcium binds to the
regulatory proteins on the actin filaments, the
proteins undergo a change in both their shape and
their position on the thin filaments. This action
exposes myosin-binding sites on the actin, to which
the myosin heads can attach (see b), and the myosin
heads immediately begin seeking out binding sites.
Figure 6.8c Schematic representation of contraction mechanism: the sliding filament theory.
(c)
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The free myosin heads are “cocked,” much like an
oar ready to be pulled on for rowing. Myosin
attachment to actin causes the myosin heads to snap
(pivot) toward the center of the sarcomere in a rowing
motion. When this happens, the thin filaments are
slightly pulled toward the center of the sarcomere
(see c). ATP provides the energy needed to release
and recock each myosin head so that it is ready to
attach to a binding site farther along the thin filament.
A&P Flix
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: The Cross Bridge Cycle
Contraction of a Skeletal Muscle as a Whole
▪ Graded responses
▪ Muscle fiber contraction is ―all-or-none,‖ meaning it will
contract to its fullest when stimulated adequately
▪ Within a whole skeletal muscle, not all fibers may be
stimulated during the same interval
▪ Different combinations of muscle fiber contractions
may give differing responses
▪ Graded responses—different degrees of skeletal
muscle shortening
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Contraction of a Skeletal Muscle as a Whole
▪ Graded responses can be produced in two ways
▪ By changing the frequency of muscle stimulation
▪ By changing the number of muscle cells being
stimulated at one time
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Contraction of a Skeletal Muscle as a Whole
▪ Muscle response to increasingly rapid stimulation
▪ Muscle twitch
Tension (g)
▪ Single, brief, jerky contraction
▪ Not a normal muscle function
(Stimuli)
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(a) Twitch
Contraction of a Skeletal Muscle as a Whole
▪ Muscle response to increasingly rapid stimulation
(continued)
▪ In most types of muscle activity, nerve impulses are
delivered at a rapid rate
▪ As a result, contractions are ―summed‖ (added)
together, and one contraction is immediately followed
by another
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Contraction of a Skeletal Muscle as a Whole
▪ Muscle response to increasingly rapid stimulation
(continued)
▪ When stimulations become more frequent, muscle
contractions get stronger and smoother
▪ The muscle now exhibits unfused (incomplete) tetanus
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Contraction of a Skeletal Muscle as a Whole
▪ Muscle response to increasingly rapid stimulation
(continued)
▪ Fused (complete) tetanus is achieved when the
muscle is stimulated so rapidly that no evidence of
relaxation is seen
▪ Contractions are smooth and sustained
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Contraction of a Skeletal Muscle as a Whole
▪ Muscle response to stronger stimuli
▪ Muscle force depends upon the number of fibers
stimulated
▪ Contraction of more fibers results in greater muscle
tension
▪ When all motor units are active and stimulated, the
muscle contraction is as strong as it can get
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Providing Energy for Muscle Contraction
▪ ATP
▪ Only energy source that can be used to directly power
muscle contraction
▪ Stored in muscle fibers in small amounts that are
quickly used up
▪ After this initial time, other pathways must be utilized
to produce ATP
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Providing Energy for Muscle Contraction
▪ Three pathways to regenerate ATP
1. Direct phosphorylation of ADP by creatine phosphate
2. Aerobic pathway
3. Anaerobic glycolysis and lactic acid formation
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Providing Energy for Muscle Contraction
▪ Direct phosphorylation of ADP by creatine
phosphate (CP)—fastest
▪ Muscle cells store CP, a high-energy molecule
▪ After ATP is depleted, ADP remains
▪ CP transfers a phosphate group to ADP to regenerate
ATP
▪ CP supplies are exhausted in less than 15 seconds
▪ 1 ATP is produced per CP molecule
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Figure 6.10a Methods of regenerating ATP during muscle activity.
(a) Direct phosphorylation
Coupled reaction of creatine
phosphate (CP) and ADP
Energy source: CP
Creatine
ADP
Creatine
ATP
Oxygen use: None
Products: 1 ATP per CP,
creatine
Duration of energy provision:
15 seconds
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Providing Energy for Muscle Contraction
▪ Aerobic respiration
▪ Supplies ATP at rest and during light/moderate
exercise
▪ A series of metabolic pathways, called oxidative
phosphorylation, use oxygen and occur in the
mitochondria
▪ Glucose is broken down to carbon dioxide and water,
releasing energy (about 32 ATP)
▪ This is a slower reaction that requires continuous
delivery of oxygen and nutrients
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Figure 6.10b Methods of regenerating ATP during muscle activity.
(b) Aerobic pathway
Aerobic cellular respiration
Energy source: glucose; pyruvic
acid; free fatty acids from adipose
tissue; amino acids from protein
catabolism
Glucose (from
glycogen breakdown or
delivered from blood)
Fatty
acids
Amino
acids
CO2
Pyruvic acid
Aerobic respiration
in mitochondria
O2
32 ATP
H2O
net gain
per
glucose
Oxygen use: Required
Products: 32 ATP per glucose,
CO2, H2O
Duration of energy provision:
Hours
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Providing Energy for Muscle Contraction
▪ Anaerobic glycolysis and lactic acid formation
▪ Reaction that breaks down glucose without oxygen
▪ Glucose is broken down to pyruvic acid to produce
about 2 ATP
▪ Pyruvic acid is converted to lactic acid, which causes
muscle soreness
▪ This reaction is not as efficient, but it is fast
▪ Huge amounts of glucose are needed
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Figure 6.10c Methods of regenerating ATP during muscle activity.
(c) Anaerobic pathway
Glycolysis and lactic acid
formation
Energy source: glucose
Glucose (from
glycogen breakdown or
delivered from blood)
Glycolysis
in cytosol
2
ATP
net gain
Released
to blood
Pyruvic acid
Lactic acid
Oxygen use: None
Products: 2 ATP per glucose,
lactic acid
Duration of energy provision:
40 seconds, or slightly more
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Muscle Fatigue and Oxygen Deficit
▪ If muscle activity is strenuous and prolonged,
muscle fatigue occurs
▪ Suspected factors that contribute to muscle
fatigue include:
▪ Ion imbalances (Ca2+, K+)
▪ Oxygen deficit and lactic acid accumulation
▪ Decrease in energy (ATP) supply
▪ After exercise, the oxygen deficit is repaid by
rapid, deep breathing
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Types of Muscle Contractions
▪ Isotonic contractions
▪ Myofilaments are able to slide past each other during
contractions
▪ The muscle shortens, and movement occurs
▪ Example: bending the knee; lifting weights, smiling
▪ Isometric contractions
▪ Muscle filaments are trying to slide, but the muscle is
pitted against an immovable object
▪ Tension increases, but muscles do not shorten
▪ Example: pushing your palms together in front of you
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Muscle Tone
▪ Muscle tone
▪ State of continuous partial contractions
▪ Result of different motor units being stimulated in a
systematic way
▪ Muscle remains firm, healthy, and constantly ready for
action
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Effect of Exercise on Muscles
▪ Exercise increases muscle size, strength, and
endurance
▪ Aerobic (endurance) exercise (biking, jogging) results
in stronger, more flexible muscles with greater
resistance to fatigue
▪ Makes body metabolism more efficient
▪ Improves digestion, coordination
▪ Resistance (isometric) exercise (weight lifting)
increases muscle size and strength
▪ Individual muscle fibers enlarge
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Figure 6.12 Muscle attachments (origin and insertion).
Origin: attachment to an
immovable or less movable
bone
Insertion: attachment to a
movable bone
Types of Body Movements
▪ Flexion
▪ Decreases the angle of the joint
▪ Brings two bones closer together
▪ Typical of bending hinge joints (e.g., knee and elbow)
or ball-and-socket joints (e.g., the hip)
▪ Extension
▪ Opposite of flexion
▪ Increases angle between two bones
▪ Typical of straightening the elbow or knee
▪ Extension beyond 180º is hyperextension
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Figure 6.13a Body movements.
Flexion
Hyperextension
Extension
Flexion
Extension
(a) Flexion, extension, and hyperextension of the shoulder and knee
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Figure 6.13b B
vnementEsx.tension
Hyo
pd
ery
extm
eno
sio
Flexion
(b) Flexion, extension, and hyperextension
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Types of Body Movements
▪ Rotation
▪ Movement of a bone
around its longitudinal axis
▪ Common in ball-and-socket
joints
▪ Example: moving the atlas
around the dens of axis
(i.e., shaking your head
―no‖)
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Types of Body Movements
▪ Abduction
▪ Movement of a limb away
from the midline
▪ Adduction
▪ Opposite of abduction
▪ Movement of a limb toward
the midline
▪ Circumduction
▪ Combination of flexion,
extension, abduction, and
adduction
▪ Common in ball-and-socket
joints
▪ Proximal end of bone is
stationary, and distal end
moves in a circle
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Special Movements
▪ Dorsiflexion
▪ Lifting the foot so
that the superior
surface approaches
the shin (toward the
dorsum)
▪ Plantar flexion
▪ Pointing the toes
away from the head
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Special Movements
▪ Inversion
▪ Turning sole of
foot medially
▪ Eversion
▪ Turning sole of
foot laterally
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Special Movements
▪ Supination
▪ Forearm rotates
laterally so palm faces
anteriorly
▪ Radius and ulna are
parallel
▪ Pronation
▪ Forearm rotates
medially so palm faces
posteriorly
▪ Radius and ulna cross
each other like an X
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Special Movements
▪ Opposition
▪ Moving the thumb to
touch the tips of other
fingers on the same
hand
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Interactions of Skeletal Muscles in the Body
▪ Muscles can only pull as they contract—not push
▪ In general, groups of muscles that produce
opposite actions lie on opposite sides of a joint
▪ Prime mover—muscle with the major
responsibility for a certain movement
▪ Antagonist—muscle that opposes or reverses a
prime mover
▪ Synergist—muscle that aids a prime mover in a
movement or reduces undesirable movements
▪ Fixator—specialized synergists that hold a bone
still or stabilize the origin of a prime mover
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Figure 6.14a Muscle action.
(a) A muscle that crosses on the anterior side of a joint produces flexion*
Example:
Pectoralis
major
(anterior view)
* These generalities do not apply to the knee and ankle because the lower limb is rotated during development.
The muscles that cross these joints posteriorly produce flexion, and those that cross anteriorly produce extension.
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Figure 6.14b Muscle action.
(b) A muscle that crosses on the posterior side of a joint produces extension*
Example: Latissimus
dorsi (posterior view)
The latissimus dorsi
is the antagonist of
the pectoralis major.
* These generalities do not apply to the knee and ankle because the lower limb is rotated during development.
The muscles that cross these joints posteriorly produce flexion, and those that cross anteriorly produce extension.
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Figure 6.14c Muscle action.
(c) A muscle that crosses on the lateral side of a joint produces abduction
Example: Deltoid
middle fibers
(anterolateral
view)
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Figure 6.14d Muscle action.
(d) A muscle that crosses on the medial side of a joint produces adduction
Example:
Teres major
(posterolateral view)
The teres major
is the antagonist
of the deltoid.
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Naming Skeletal Muscles
1 – Location of the muscle
2 – Shape of the muscle
3 – Size of the muscle
4 – Direction/Orientation of the muscle
fibers/cells
5 – Number of Origins
6 – Location of the Attachments
7 – Action of the muscle
Muscles Named by Location
Location:
⚫ frontalis – frontal bone
⚫ lateralis – lateral or on the side
⚫ tibialis anterior – front of tibia
⚫ fibularis longus – near fibula
⚫ supra – above
⚫ infra – below
⚫ sub - underneath
Muscles Named by Shape
Shape:
⚫ deltoid – triangle
⚫ Latissimus – wide
⚫ teres - round
⚫ trapezius – trapezoid
⚫ serratus –saw-toothe
⚫ orbicularis – circular
Muscles Named by Size
Size:
⚫ maximus – largest
⚫ minimis – smallest
⚫ vastus - huge
⚫ longus – longest
⚫ brevis – short
⚫ major – large
⚫ minor – small
Example: Pectoralis Major
Muscles Named by Direction of Fibers
Direction/Orientation:
⚫ rectus (straight) - parallel
to the muscle’s long axis
ex: rectus abdominis
⚫ transversus (transverse) –
at right angles to the
muscle’s long axis
⚫ oblique –
diagonal
Muscles Named for Number of Origins
Number of Origins:
⚫ biceps – two origins
ex: biceps brachii
⚫ triceps –
three origins
ex: triceps brachii
⚫ quadriceps – four origins
Muscles Named for
Origin and Insertion Points
Origin and Insertion:
sterno = sternum
cleiodo = clavicle
mastoid = location on
the temporal bone
sternocleiodomastoid muscle
Muscles Named for Action
Action:
⚫ flexor carpi radialis –
flexes wrist
⚫ abductor magnus –
abducts the thigh
⚫ extensor digitorum –
extends the fingers
⚫ levator – lifts a structure
Figure 6.15 Relationship of fascicle
arrangement to muscle structure.
(a)
(b)
(a) Circular
(orbicularis oris)
(b) Convergent
(pectoralis major)
(e)
(c)
(e) Multipennate
(deltoid)
(d)
(f)
(g)
(c) Fusiform
(biceps brachii)
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(d) Parallel
(sartorius)
(f) Bipennate
(rectus
femoris)
(g) Unipennate
(extensor digitorum longus)
Figure 6.16a Superficial muscles of the head and neck.
Figure 6.16b Superficial muscles of the head and neck.
Frontalis
Cranial
aponeurosis
Temporalis
Orbicularis
oculi
Occipitalis
Zygomaticus
Buccinator
Orbicularis
oris
Masseter
Sternocleidomastoid
Trapezius
Platysma
Posterior muscles of the neck.
Figure 6.17a
Muscles of the
anterior trunk,
shoulder, and
arm.
Clavicle
Deltoid
Sternum
Pectoralis
major
Biceps
brachii
Brachialis
Brachioradialis
Figure 6.19 The fleshy deltoid muscle is a favored
site for administering intramuscular injections.
Deltoid
muscle
Humerus
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Figure 6.17b Muscles of the anterior trunk, shoulder,
and arm.
Serratus
anterior
Pectoralis
major
Rectus
abdominis
Transversus
abdominis
Internal
oblique
External
oblique
Aponeurosis
Figure 6.18a
Muscles of
the posterior
neck, trunk,
and arm.
Occipital bone
Sternocleidomastoid
Trapezius
Spine of scapula
Deltoid (cut)
Deltoid
Triceps
brachii
Latissimus
dorsi
(a)
Humerus
Olecranon
process of
ulna (deep
to tendon)
Figure
6.18a
Muscles of
the
posterior
neck, trunk,
and arm.
Occipital bone
Sternocleidomastoid
Trapezius
Spine of scapula
Deltoid (cut)
Deltoid
Triceps
brachii
Latissimus
dorsi
Humerus
Olecranon
process of
ulna (deep
to tendon)
Figure 6.20c Pelvic,
hip, and thigh
muscles of the right
side of the body.
12th
thoracic vertebra
12th rib
Iliac crest
Iliopsoas
Psoas major
Iliacus
5th
lumbar vertebra
Anterior superior
iliac spine
Tensor Fasciae Latae
Quadriceps*
Sartorius
Adductor
group
Rectus femoris
Vastus lateralis
Vastus medialis
Patella
Patellar
ligament
(c)
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Figure 6.20d Pelvic, hip,
and thigh muscles of the
right side of the body.
Inguinal
ligament
Adductor
muscles
Sartorius
Vastus
lateralis
(d)
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Figure 6.21a Superficial muscles of the right
leg.
Fibularis longus
Tibia
Fibularis brevis
Soleus
Tibialis anterior
Extensor digitorum
longus
Fibularis tertius
(a)
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Figure 6.20 Pelvic, hip, and thigh muscles of
the right side of the body.
Posterior superior
iliac spine
Iliac crest
Gluteus medius
Safe area in
gluteus medius
Gluteus maximus
Gluteus maximus
Adductor
magnus
Sciatic nerve
Iliotibial tract
Biceps femoris
Semitendinosus
Semimembranosus
Gastrocnemius
(a)
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(b)
Hamstring group
Muscles of the Lower Leg
Superficial
Muscles:
Anterior
Superficial
Muscles:
Posterior
Figure 6.22
Major superficial
muscles of the
anterior surface of the
body.
Facial
Facial
• Temporalis
• Masseter
Shoulder
• Trapezius
• Frontalis
• Orbicularis oculi
• Zygomaticus
• Orbicularis oris
Neck
• Platysma
• Sternocleidomastoid
Thorax
• Deltoid
• Pectoralis minor
Arm
• Pectoralis major
• Serratus anterior
• Triceps brachii
• Biceps brachii
• Brachialis
• Intercostals
Abdomen
• Rectus abdominis
Forearm
• Brachioradialis
• Flexor carpi radialis
• External oblique
• Internal oblique
• Transversus abdominis
Pelvis/thigh
• Iliopsoas
Thigh
• Sartorius
• Adductor muscles
Thigh (Quadriceps)
• Rectus femoris
• Vastus lateralis
• Vastus medialis
• Vastus intermedius (not shown,
deep to rectus femoris)
Leg
• Fibularis longus
• Extensor digitorum longus
• Tibialis anterior
Leg
• Gastrocnemius
• Soleus
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Major superficial
muscles of the
posterior surface of
the body.
Neck
• Occipitalis
• Sternocleidomastoid
• Trapezius
Shoulder/Back
• Deltoid
Arm
• Triceps brachii
• Brachialis
• Latissimus dorsi
Forearm
• Brachioradialis
• Extensor carpi radialis
longus
• Flexor carpi ulnaris
Hip
• Gluteus medius
• Extensor carpi ulnaris
• Extensor digitorum
• Gluteus maximus
Iliotibial tract
Thigh
• Adductor muscle
• Hamstrings:
Biceps femoris
Semitendinosus
Semimembranosus
Leg
• Gastrocnemius
• Soleus
• Fibularis longus
Calcaneal
(Achilles)
tendon
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Table 6.3 Superficial Anterior Muscles of the
Body (See Figure 6.22) (2 of 3)
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Table 6.3 Superficial Anterior Muscles of the
Body (See Figure 6.22) (1 of 3)
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Table 6.3 Superficial Anterior Muscles of the
Body (See Figure 6.22) (3 of 3)
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Table 6.4 Superficial Posterior Muscles of the
Body (Some Forearm Muscles Also Shown) (See
Figure 6.23) (1 of 3)
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Table 6.3 Superficial Anterior Muscles of the
Body (See Figure 6.22) (2 of 3)
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Table 6.4 Superficial Posterior Muscles of the
Body (Some Forearm Muscles Also Shown) (See
Figure 6.23) (2 of 3)
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Table 6.4 Superficial Posterior Muscles of the
Body (Some Forearm Muscles Also Shown) (See
Figure 6.23) (3 of 3)
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Developmental Aspects of the Muscular
System
▪ Increasing muscular control reflects the
maturation of the nervous system
▪ Muscle control is achieved in a superior/inferior
and proximal/distal direction
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Developmental Aspects of the Muscular
System
▪ To remain healthy, muscles must be exercised
regularly
▪ Without exercise, muscles atrophy
▪ With extremely vigorous exercise, muscles
hypertrophy
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Developmental Aspects of the Muscular
System
▪ As we age, muscle mass decreases, and
muscles become more sinewy
▪ Exercise helps retain muscle mass and strength
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