|There are three types
of muscle tissue:
Each of more than 600 muscles
is served by nerves which link the muscle to the brain
skeletal (or voluntary/striated)
muscle, the most abundant tissue in the human body, producing movement.
Each skeletal-muscle fiber is roughly cylindrical, contains many nuclei,
and is crossed by alternating light and dark bands called striations.
Fibers bind together, via connective
tissue, into bundles; and these bundles, in turn, bind together to
form muscles. Thus, skeletal muscles are composite structures composed
of many muscle fibers, nerves, blood vessels, and connective tissue. Skeletal
muscles are controlled by the somatic
nervous system (SNS).
smooth (or visceral)
muscle, forming the muscle layers in the walls of the digestive tract,
bladder, various ducts, arteries and veins, and other internal organs.
Smooth- muscle cells are elongated and thin, not striated, have only one
nucleus, and interlace to form sheets rather than bundles of muscles. Smooth
muscle is controlled by the autonomic
nervous system (ANS).
cardiac (or heart)
muscle, a cross between the smooth and striated muscles, comprising the
heart tissue. Like smooth muscle, it is innervated by the autonomic
nervous system (ANS).
The musculoskeletal system
consists of the skeletal system -- bones and
(union of two or more bones) -- and the skeletal muscle
system (voluntary or striated muscles).
These two systems work together to provide basic functions that are essential
to life, including:
Protection: protects the brain
and internal organs
Support: maintains upright posture
Blood cell formation: hematopoiesis
Storage: stores fat and minerals.
Leverage: A lever is a simple
machine that magnifies speed of movement or force. The levers are mainly
the long bones of the body and the axes are the joints where the bones
Each of these contains various
combinations of 4 connective
tissue building blocks:
There are 5 basic tissues
comprising the musculoskeletal system:
(attaching bone to bone)
gel-like subtance lining the joints and intervertebral discs),
tendons (attaching muscle
Schematic representation of the typical arrangement of musculoskeletal
How We Move
fibroblasts - the "mother"
cell, producing the other 3 connective tissue components.
- the principal protein manufactured by the fibroblast. Organized into
various configurations, these long, thin fibers intertwine to form very
strong fibers which do NOT stretch.
elastic fibers - highly
elastic fibers, unlike collagen, particularly abundant in the walls of
- the "ground substance," or "matrix," in which fibroblasts, collagen,
and elastic fibers reside.
Skeletal muscles, attached
to bone by tendons, produce movement by bending the skeleton at movable
joints. The connecting tendon closest to the body or head is called the
attachment: this is termed the origin of the muscle. The other end,
the distal attachment, is called the insertion. During contraction,
the origin remains stationary and the insertion moves.
producing the bending is always exerted as a pull by contraction,
thus making the muscle shorter: Muscles cannot actively push. Reversing
the direction in which a joint bends is produced by contracting a different
set of muscles. For example, when one group of muscles contracts, an antagonistic
group stretches, exerting an opposing pull, ready to reverse the direction
The contracting unit is the
fiber. Muscle fibers consist of two main protein strands - actin
and myosin. Where the strands overlap, the fiber appears dark. Where
they do not overlap, the fiber appears light. These alternating bands of
light and dark give skeletal muscle its characterisitc striated appearance.
The trigger which starts contraction comes from the motor
nerve attached to each muscle fiber at the motor end plate.
is released at the motor end plate when the electrical impulse reaches
the muscle fiber. As it binds to receptors on the surface of the muscle
cells, it causes the electrical impulse to be transmitted in both directions
along the fiber, activating the actin and myosin strands. The strands slide
past each other to flex, or to shorten, the fiber, thus producing contraction.
Muscles by Name
on the body regions and front/back views to see greater detail
from: The InnerBody: Anatomy Tutorials - Muscle
Muscles by Function
Each muscle has its own
special name. Muscles, however, are also described by their function. Muscles
that bend a limb are flexors; those which straighten a limb are
(e.g. elbow flexors and elbow extensors.) Muscles which move a limb to
the side, away from the body, are abductors; those which move a
limb sideways toward the body are adductors (e.g. hip abductors
and hip adductors.) Other functional groups are elevators, depressors,
rotators, doriflexors, planar flexors, and palmar flexors.
and Functions Available at Different Levels of Spinal Cord Injury
Good head balance
Reaches for object
Transfers objects from hand
Sitting at 6 months
Pulls to standing at 9-10 months
Takes first steps
Opens a small box
Marks with a pencil
Seats self in small chair
Feeds self with spoon
Places square and circle in
Builds a 3 block tower
Turns pages of a book
Scribbles with pencil
Makes tower of 7 blocks
Completes 3 piece formboard
Walks and runs fairly well
Toilet training, with assistance
Imitates drawings of circle
Builds 10 block tower
Imitates building of 4 block
Imitates 3 block bridge
Achieving toilet independence
Stands on one foot momentarily
Stands heel to toe 15 sec.,
Performs finger to nose well,
Hops in place on both feet 7/5
Balances on tiptoe for 10 sec.
Hops 15 feet on one foot
Parts lips and clenches teeth,
Balances on one foot for 10
Hits target (10 sq. in.) with
ball from 5 feet
Jumps over rope 8 inches high
Balances on tiptoes 10 sec.,
bending at hips
Walks straight line, heel to
toe for 6 feet
Maintains crouched position
on tiptoes for 10 sec., arms extended and eyes closed
Touches fingertips of one hand
successively with thumb starting with little finger and repeating in reverse
To Learn More
Joel DeLisa and Walter C. Stolov,
"Significant Body Systems," in: Handbook of Severe Disability, edited
by Walter C. Stolov and Michael R. Clowers. US Department of Education,
Rehabilitation Services Administration, 1981, pages 41-45.
Catherine Parker Anthony and
Gary A. Thibodeau, Textbook of Anatomy & Physiology. St. Louis:
Mosby, 1983, pages 498-548.
Mariana Newton, Professor emeritus,
UNCG Department of Communication Science
Muscles Tutorial by Dr. J. Crimando, GateWay Community College, Phoenix,