Anatomy of the
Muscular System
A Few Facts…
There are more than 600 skeletal muscles
in the body
They constitute 40-50% of our body weight
Along with the skeleton they determine the
form and contours of our body
Skeletal Muscle
Structure
Connective Tissue Components
Muscles cells (fibers) are covered by a
delicate connective tissue membrane
called the endomysium.
Groups of skeletal muscle fibers are called
fascicles, and bound together by a tougher
connective tissue envelope called the
perimysium.
The muscle as a whole is covered by a
course sheath called the epimysium.
Skeletal Muscle Structure
Tendon – bands or cords of fibrous
connective tissue that attach a muscle to a
bone or other structure
Aponeurosis – broad, flat sheet of
connective tissue
Fascia – surrounds the muscle organ and
outside the epimysium
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Superficial
Deep
Size, Shape, and Fiber
Arrangement
Skeletal muscles are organs
Vary widely in size and shape
Muscle fiber arrangement differs
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Parallel to the long axis of the muscle
Converge to a narrow attachment
Oblique and pennate (like a feather pen)
Bipennate (double-feathered)
Curved -- sphincter
Fiber Arrangement
A. Parallel
B. Convergent
C. Pennate
D. Bipennate
E. Sphincter
Attachment of Skeletal Muscle
Most muscles span at least one joint and
attach to both articulating bones
Origin – attachment of a muscle to the
bone, which does not move when
contraction occurs
Insertion – attachment of a muscle to the
bone that it moves when conctraction
occurs
Muscle Attachment
Muscle Actions
Most muscles act in groups and not alone—
some contract while others relax
Agonist (prime mover) – used to describe a
muscle or group of muscles that directly
performs a specific movement. Example:
biceps brachii is the prime mover in the flexion of
the forearm.
Antagonists – muscles that, when contracting,
directly oppose prime movers – they relax while
the prime mover is contracting
Synergists – muscles that contract at the same
time as the prime mover
Fixator muscles – generally function as joint
stabilizers
Most muscles function not only as prime movers
but also as antagonists, synergists, and fixators.
A prime mover in a particular movement , such
as flexion, may be an antagonist during
extension
Lever Systems
A lever is any rigid bar free to turn about a
fixed point called its fulcrum.
Bones serve as levers and joints serve as
fulcrums
First Class Lever
Second Class Lever
Third Class Lever
How Muscles are Named
Most are Latin in origin (some Greek)
Location (gluteus = buttock)
Function (adductor)
Shape (deltoid = triangular)
Muscle Naming Continued…
Direction of fibers (rectus = straight)
Number of heads of divisions (biceps = two
points of origin)
Points of attachment (sternocleidomastoid =
origin on the sternum and clavicle and inserts on
the mastoid process)
Size of muscle (maximus = largest)