Download The Muscular System Muscles are classified into 4 functional groups

The Muscular System
Muscles are classified into 4 functional groups:
Prime movers (agonists)
Antagonists
Synergists
Fixators
1 muscle can be all four
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Interactions of Skeletal Muscles
Skeletal muscles work together or in opposition
Muscles only pull (never push)
As muscles shorten, the insertion generally moves
toward the origin
Whatever a muscle (or group of muscles) does,
another muscle (or group) “undoes”
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Muscle Classification: Functional Groups
Prime movers (agonists) – provide the major force for producing a
specific movement
Antagonists – oppose or reverse a particular movement
Regulate the motion of prime mover by contracting and
providing resistance
Agonists & antagonists are located on opposite sides of a joint across
which they act
Synergists – help prime movers by:
Adding extra force to a movement
Reduce undesirable or unnecessary movement as prime mover contracts
E.g. fingers and wrist: can make a fist without bending the wrist
Fixators – synergists that immobilize a bone or muscle’s origin (e.g.
scapula)
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Naming Skeletal Muscles
Location of muscle – indicate the bone or body
region associated with the muscle
Shape of muscle – e.g., the deltoid muscle (deltoid
= triangle; trapezius = trapezoid)
Relative size – e.g., maximus (largest), minimus
(smallest), longus (long)
Direction of fibers – e.g., rectus (fibers run
straight), transversus, and oblique (fibers run at
angles to an imaginary defined axis)
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Naming Skeletal Muscles
Number of origins – e.g., biceps (two origins), triceps
(three origins), quadriceps (four origins)
Location of attachments – named according to point of
origin or insertion
Origin is named first
Insertion is named second
E.g. sternocleidomastoid (sternum, clavicle, mastoid
process of the temporal bone)
Action – e.g., flexor or extensor, as in the names of
muscles that flex or extend, respectively
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Arrangement of Fascicles
Parallel – fascicles run parallel to the long axis of the
muscle (e.g., sartorius)
Fusiform – spindle-shaped muscles (e.g., biceps brachii)
Pennate – short fascicles that attach obliquely to a central
tendon running the length of the muscle (e.g., rectus
femoris)
Unipennate: insertion on one side
Bipennate: insertion on opposite sides
Mulipennate: many insertions into 1 tendon
E.g. deltoid muscle
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Arrangement of Fascicles
Convergent – fascicles converge from a broad
origin to a single tendon insertion
Triangular or fan shaped (e.g., pectoralis major
of the anterior thorax)
Circular – fascicles are arranged in concentric
rings
Surround external body openings (e.g.,
orbicularis oris, sphincter)
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Arrangement of Fascicles
Arrangement of fascicles determines muscles
range of motion and power
Muscles with parallel fascicle arrangement shorten
the most, but are not powerful
Power depends on the total number of muscle cells
in the muscle
E.g. bipennate and multipennate muscles
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Arrangement of Fascicles
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Figure 10.1
Bone-Muscle Relationships: Lever Systems
Lever – a rigid bar that moves on a fulcrum, or fixed point,
when a force is applied
Used to move a resistance (load)
Load – resistance moved by the effort
Effort – force applied to a lever
E.g. Joints = fulcrum
Bones = levers
Muscle contraction = force
Load = bone or tissue or objects
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Bone-Muscle Relationships: Lever Systems
Mechanical Advantage (Power lever)
Load is close to the fulcrum
Effort is applied far from the fulcrum
Thus, a small effort over a large distance can move a large load a
small distance
Mechanical Disadvantage (Speed lever)
Load is far from the fulcrum
Effort is applied near the fulcrum
Thus the force exerted must be greater than the load moved or
supported
These types of levers provide rapid contraction with a wide range of
motion
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Bone-Muscle Relationships: Lever Systems
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Figure 10.2a
Bone-Muscle Relationships: Lever Systems
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Figure 10.2b
Bone-Muscle Relationships: Lever Systems
In summary, small differences in the site of a
muscle’s insertion (relative to the fulcrum or joint)
can translate into large differences in the amount
of force a muscle can generate
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Lever Systems: Classes
All levers follow the same principle of:
Mechanical advantage: effort farther than load from the
fulcrum
Mechanical disadvantage: effort closer than load to fulcrum
First class – the fulcrum is between the load and the effort
Second class – the load is between the fulcrum and the
effort
Third class – the effort is applied between the fulcrum and
the load
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Lever Systems: First Class
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Figure 10.3a
Lever Systems: Second Class
Effort applied at one end, fulcrum at the other end, with the load
in between.
Second Class lever systems are rare in the body, but when they
occur they are always working at a mechanical advantage
e.g. muscle insertion is always farther from the fulcrum than the
load to be moved
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Figure 10.3b
Lever Systems: Third Class
Effort is applied between the load and the fulcrum
Third class levers operate at great speed and always at a
Mechanical disadvantage
e.g. forceps
e.g. most skeletal muscles
e.g. biceps
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Figure 10.3c
Lever Systems
In summary, differences in positioning of the
effort, load, and fulcrum modify muscle activity
with respect to:
1) speed of contraction
2) range of motion
3) the weight of the load that can be moved
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Lever Systems
Mechanical disadvantage levers (speed levers)
Force is lost (not strong)
Speed, range of motion is gained
Mechanical Advantage levers (power levers)
Force is gained (strong)
Speed, ranged of motion is lost…but stability is
gained
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Major Skeletal Muscles: Anterior View
Over 600 muscles in
the body
We will consider the
125 principal pairs
The 40 superficial
muscles here are
divided into 10
regional areas of the
body
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Figure 10.4b
Major Skeletal Muscles: Posterior View
The 27 superficial
muscles here are
divided into seven
regional areas of the
body
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Figure 10.5b
Muscles: Name, Action, and Innervation
Name and description of the muscle – be alert to
information given in the name
Origin and insertion – there is always a joint
between the origin and insertion
Action – best learned by acting out a muscle’s
movement on one’s own body
Nerve supply – name of major nerve that
innervates the muscle
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Muscles of the Scalp
Epicranius (occipitofrontalis) – bipartite muscle consisting of the:
Frontalis: w/ the aponeurosis fixed; raises the eyebrows, wrinkles
forehead skin
Occipitalis: fixes aponeurosis and pulls scalp posteriorly
Galea aponeurotica – cranial aponeurosis connecting above muscles
These two muscles have alternate actions of pulling the scalp forward and
backward
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Muscles of the Face
11 muscles are involved in lifting the eyebrows,
flaring the nostrils, opening and closing the eyes
and mouth, and smiling
All are innervated by cranial nerve VII (facial
nerve)
Usually insert in skin (rather than bone), and
adjacent muscles often fuse
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Muscles of the Face
Corrugator supercilii: draws eyebrows together & inferiorly
Orbicularis oculi: blinking
Zygomaticus: smile muscle
Risorius: draws corner of lips laterally
Levator labii superioris: raises upper lip
Depressor labii inferioris: pout muscle
Depressor anguli oris: draws corners of mouth downward and laterally
Orbicularis oris: kissing and whistling muscle
Mentalis: protrudes lower lip & wrinkles chin
Buccinator: compresses cheek
Platysma: helps depress mandible
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Muscles of the Scalp, Face, and Neck
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Figure 10.6
Muscles of Mastication
There are four pairs of muscles involved in mastication
(chewing and biting)
Prime movers – temporalis and masseter
Grinding movements – pterygoids and buccinators
All are innervated by cranial nerve V (trigeminal nerve)
Gravity can depress the jaw. When it can not, the digastric
and mylohyoid of the neck contract
Intrinsic tongue muscles are arranged in several planes to
change the shape of the tongue. But they do not move the
tongue
Extrinsic tongue muscles anchor and move the tongue.
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Muscles of Mastication
Masseter: prime mover of jaw closure
Temporalis: closes jaw, synergist of pterygoids
Medial pterygoid: elevates jaw, synergist of temporalis &
masseter muscles
Lateral pterygoid: pulls mandible aneriorly & helps move
mandible side to side
Buccinator: keeps food between teeth
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Muscles of Mastication
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Figure 10.7a
Muscles of Mastication
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Figure 10.7b
Extrinsic Tongue Muscles
Three major muscles that anchor and move the
tongue
All are innervated by cranial nerve XII
(hypoglossal nerve)
Genioglossus: protrudes tongue
Hyoglossus: depresses tongue and draws its sides
downward
Styloglossus: retracts tongue
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Extrinsic Tongue Muscles
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Figure 10.7c