The Muscular System
Functions of the Muscular System
• Movement
-what examples can you think of?
• Maintaining posture and body position
• Stabilizing joints
• Heat generation (generates 85% of the body’s
heat…especially skeletal muscle)
– How does this happen?
Structures of the Muscular System
• Muscle fibers
– Long, slender cells that make up the muscle
– Each muscle consists of a group of fibers that are
held together by a connective tissue and enclosed
in a fibrous sheath
• Fascia
– Sheet of connective tissue that covers, supports,
and separates muscles or groups of muscles
– Flexible tissue but not elastic. Crush injuries can
cause compartment syndrome
Structures of the Muscular System
• Tendons
– Narrow band of non-elastic, dense fibrous
connective tissue that attaches a muscle to a bone
***do not confuse with a ligament! Ligaments
connect bone to bone
Types of Muscle Tissue
• Smooth
– Located in the walls of internal organs like the
digestive tract and blood vessels, and ducts
– Move and control the flow of fluids through these
structures
– Unstriated
– Involuntary
Types of Muscle Tissue
• Skeletal
– Attached to the bones of the skeleton and make
movement possible
– Voluntary
– Striated (appear striped)
Types of Muscle Tissue
• Myocardial (Cardiac)
– Form the muscular walls of the heart
– Striated
– Involuntary
How do Muscle Move?
• Muscle innervation
– Muscles are supplied with motor nerves
– Motor nerves enable the brain to stimulate a
muscle to contract
– When the stimulus stops, the muscle relaxes
– If nerve impulse is interrupted due to injury or
disease, paralysis occurs
Muscle Innervation
Antagonistic Muscle Pairs
• Muscles are arranged into antagonistic pairs
– When one muscle contracts, it’s antagonist relaxes
Example: Biceps and Triceps work as a pair to make
arm movement possible
Contraction: The tightening of a muscle. As a muscle
contracts, it shortens and thickens causing the belly of
the muscle to enlarge
Relaxation: Occurs when a muscle returns to its
original form. As the muscle relaxes, it elongates,
thins and the belly is no longer enlarged
Contrasting Muscle Motion
Abduction: moves away from the
midline
Adduction: moves toward the midline
Flexion: decreases an angle as in
bending a joint
Extension: increases an angle, as in
straightening a joint
Elevation: raises a body part. Ex. Smiling
Depression: lowers a body part. Ex.
Frowning
Rotation: turns a bone on its own axis
Circumduction: the circular movement
at the far end of a limb
Supination: turns the palm of the hand
upward or forward
Pronation: turns the palm of the hand
downward or backward
Dorsiflexion: bends the foot upward at
the ankle
Plantar flexion: bends the foot
downward at the ankle
Hyperextension: extreme overextension of a limb or
body part beyond its normal limit
How Muscles are Named
• Muscles can be named for their insertion and
origin points
Origin: the less moveable attachment. The place
where the muscle begins
Insertion: the more moveable attachment. This is the
place where the muscle ends by attaching to a bone
or tendon.
Example: the sternocleidomastoid (SCM) muscle is
named for its two points of origin (sternum and
clavicle) and the one point of insertion (mastoid
process).
Example: the sternocleidomastoid (SCM) muscle is
named for its two points of origin (sternum and clavicle)
and the one point of insertion (mastoid process).
How Muscles are Named
• Some muscles can be named for their location
on the body or the organ they are near:
Example: pectoralis major
Pectoral means pertaining to the chest and the
Pectoralis major is the large, fan shaped muscle of
the chest.
How Muscles are Named
• Muscles may be named for their action
– Flexor carpi muscles flex the wrist
– Extensor carpi muscles extend the wrist
• Muscle may be named for fiber direction
– Oblique means slanted or at an angle
– Rectus means in strait alignment
– Transverse means in a crosswise fashion
– Sphincter is a ring-like muscle that constricts the
opening of a passageway.
Ex. Anal sphincter
How Muscles are Named
• Some muscles are named for the number of
divisions forming them.
– Biceps brachii is formed from 2 divisions
– Tricps brachii is formed from 3 divisions
• Muscles may be named for their size or shape
– Gluteus maximus is the larges of the gluteal
muscles
– The Deltoid muscle is shaped like an inverted
triangle or the Greek letter Delta
How Muscles are Named
• Some muscles are just named for strange
reasons…
– Example: the hamstring group is the group of
muscles located at the back of the upper leg and
these are the muscles by which a butcher hangs a
slaughtered pig!