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Applied Industrial Ergonomics (IE 665)
Anatomy, Physiology and Biomechnics
Arijit Sengupta, Ph.D.
New Jersey Institute of Technology
The material provided in this lecture note is based on information
provided in
U.S. National Cancer Institute's Surveillance, Epidemiology and
End Results (SEER) Program
(http://training.seer.cancer.gov/module_anatomy/anatomy_ph
ysiology_home.html)
A. K. Sengupta, Ph.D
9/8/2004
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• Directional terms and anatomical planes
• The skeletal System –
i. function
ii. bone tissue
iii. important skeletal subsystems, and
iv. articulation
• The muscular system
i. Function
ii. Muscle types
iii. Structure of skeletal muscle
iv. Important muscle groups
• The nervous system
i. Function
ii. Nerve tissues
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Directional terms describe the positions of human structures
relative to other structures or locations in the body.
Proximal
toward or nearest the trunk or the point of origin of a part (example, the
proximal end of the femur joins with the pelvic bone).
Distal
away from or farthest from the trunk or the point or origin of a part
(example, the hand is located at the distal end of the forearm).
Anterior or ventral
front (example, the kneecap is located on the anterior side of the leg).
Posterior or dorsal
back (example, the shoulder blades are located on the posterior side of the
body).
Medial
toward the midline of the body (example, the middle toe is located at the
medial side of the foot).
Lateral
away from the midline of the body (example, the little toe is located at the
lateral side of the foot).
Superior or cranial
toward the head end of the body; upper (example, the hand is part of the
superior extremity).
Inferior or caudal
away from the head; lower (example, the foot is part of the inferior
extremity).
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Medical professionals often refer to sections of the body in terms of
anatomical planes. These planes are imaginary lines - vertical or
horizontal - drawn through an upright body. The terms are used to describe
a specific body part.
Coronal Plane (Frontal Plane)
A vertical plane running from side to
side; divides the body or any of its parts
into anterior and posterior portions.
Sagittal Plane (Lateral Plane)
A vertical plane running from front to
back; divides the body or any of its parts
into right and left sides.
Axial Plane (Transverse Plane)
A horizontal plane; divides the body or
any of its parts into upper and lower
parts.
Median plane
Sagittal plane through the midline of the
body; divides the body or any of its parts
into right and left halves
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Functions of Skeletal System
Humans are vertebrates, animals having a vertabral column or backbone.
They rely on a sturdy internal frame that is centered on a prominent
spine. The human skeletal system consists of bones, cartilage, ligaments
and tendons and accounts for about 20 percent of the body weight.
The living bones in our bodies use oxygen and give off waste products in
metabolism. They contain active tissues that consume nutrients, require a
blood supply and change shape or remodel in response to variations in
mechanical stress.
Bones provide a rigid frame work, known as the skeleton that supports the
body against the pull of gravity. The large bones of the lower limbs
support the trunk when standing.
The skeleton also protects the soft body parts. The fused bones of the
cranium surround the brain to make it less vulnerable to injury. Vertebrae
surround and protect the spinal cord and bones of the rib cage help protect
the heart and lungs of the thorax.
Bones work together with muscles as simple mechanical lever
systems to produce body movement.
Bones contain more calcium than any other organ. The intercellular matrix
of bone contains large amounts of calcium salts, the most important being
calcium phosphate. When blood calcium levels decrease below normal,
calcium is released from the bones so that there will be an adequate supply
for metabolic needs. When blood calcium levels are increased, the excess
calcium is stored in the bone matrix. The dynamic process of releasing and
storing calcium goes on almost continuously.
Hematopoiesis, the formation of blood cells, mostly takes place in the
red marrow of the bones. In infants, red marrow is found in the bone
cavities. With age, it is largely replaced by yellow marrow for fat storage. In
adults, red marrow is limited to the spongy bone in the skull, ribs, sternum,
clavicles, vertebrae and pelvis. Red marrow functions in the formation of red
blood cells, white blood cells and blood platelets.
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There are two types of bone tissue: compact and spongy. The names
imply that the two types of differ in density, or how tightly the tissue is
packed together. There are three types of cells that contribute to bone
homeostasis. Osteoblasts are bone-forming cell, osteoclasts resorb or
break down bone, and osteocytes are mature bone cells. An equilibrium
between osteoblasts and osteoclasts maintains bone tissue.
Compact bone
consists of closely
packed osteons or
haversian systems. The
osteon consists of a
central canal called the
osteonic (haversian)
canal, which is
surrounded by
concentric rings
(lamellae) of matrix.
Between the rings of
matrix, the bone cells
(osteocytes) are
located in spaces called lacunae. Small channels (canaliculi) radiate from the
lacunae to the osteonic (haversian) canal to provide passageways through
the hard matrix. In compact bone, the haversian systems are packed tightly
together to form what appears to be a solid mass.
Spongy (cancellous) bone is lighter and less dense than compact bone.
Spongy bone consists of plates (trabeculae) and bars of bone adjacent to
small, irregular cavities that contain red bone marrow. It may appear that
the trabeculae are arranged in a haphazard manner, but they are organized
to provide maximum strength similar to braces that are used to support a
building. The trabeculae of spongy bone follow the lines of stress and can
realign if the direction of stress changes.
The adult human skeleton usually consists of 206 named bones. These
bones can be grouped in two divisions: axial skeleton and appendicular
skeleton.
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Vetebral Column
•
•
•
•
•
Cervical vertebrae (7)
Thoracic vertebrae (12)
Lumbar vertebrae (5)
Sacrum (1)
Coccyx (1)
Pectoral girdles
•
Clavicle (2)
• Scapula (2)
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Upper Extremity
•
•
•
•
•
•
Humerus (2)
Radius (2)
Ulna (2)
Carpals (16)
Metacarpals (10)
Phalanges (28)
Pelvic Girdle
Coxal, innominate, or hip bones
(2)
Lower Extremity
•
•
•
•
•
•
•
Femur (2)
Tibia (2)
Fibula (2)
Patella (2)
Tarsals (14)
Metatarsals (10)
Phalanges (28)
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An articulation, or joint, is where two bones come together. In terms
of the amount of movement they allow, there are three types of joints:
immovable (Synarthroses), slightly movable (amphiarthroses) and freely
movable (diarthroses).
The sutures in the skull are examples of immovable joints.
The ribs connected to the sternum by costal cartilages are slightly movable
joints connected by hyaline cartilage. The joints between the vertebrae and
the intervertebral disks are also of this type.
Most joints in the adult body are
freely movable joints. The singular
form is diarthrosis. In this type of
joint, the ends of the opposing
bones are covered with hyaline
cartilage, the articular cartilage,
and they are separated by a space
called
the
joint
cavity.
The
components of the joints are
enclosed in a dense fibrous joint
capsule. The outer layer of the
capsule consists of the ligaments
that hold the bones together. The
inner
layer
is
the
synovial
membrane that secretes synovial
fluid into the joint cavity for
lubrication. Because all of these
joints have a synovial membrane,
they are sometimes called synovial
joints.
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Muscular System:
Functions
The muscular system is composed of specialized
cells called muscle fibers. Their predominant
function is contractibility. Muscles, where attached
to bones or internal organs and blood vessels, are
responsible for movement. Nearly all movement in the body is the result of
muscle contraction. Exceptions to this are the action of cilia, the
flagellum on sperm cells, and amoeboid movement of some white
blood cells.
The integrated action of joints, bones, and skeletal muscles produces
obvious movements such as walking and running. Skeletal muscles also
produce more subtle movements that result in various facial expressions,
eye movements, and respiration.
In addition to movement, muscle contraction also
fulfills some other important functions in the body,
such as posture, joint stability, and heat
production. Posture, such as sitting and standing, is
maintained as a result of muscle contraction. The
skeletal muscles are continually making fine
adjustments that hold the body in stationary positions.
The tendons of many muscles extend over joints and
in this way contribute to joint stability. This is
particularly evident in the knee and shoulder joints,
where muscle tendons are a major factor in stabilizing
the joint. Heat production, to maintain body temperature, is an important
by-product of muscle metabolism. Nearly 85 percent of the heat
produced in the body is the result of muscle contraction.
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Muscles Types:
In the body, there are three types of muscle: skeletal (striated), smooth,
and cardiac.
Skeletal Muscle
Skeletal muscle, attached to bones, is responsible for skeletal movements.
The peripheral portion of the central nervous system (CNS) controls the
skeletal muscles. Thus, these muscles are under conscious, or voluntary,
control. The basic unit is the muscle fiber with many nuclei. These muscle
fibers are striated (having transverse streaks) and each acts independently
of neighboring muscle fibers.
Smooth Muscle
Smooth muscle, found in the walls of the hollow internal organs such as
blood vessels, the gastrointestinal tract, bladder, and uterus, is under
control of the autonomic nervous system. Smooth muscle cannot be
controlled consciously and thus acts involuntarily. The non-striated (smooth)
muscle cell has one central nucleus. Smooth muscle contracts slowly and
rhythmically.
Cardiac Muscle
Cardiac muscle, found in the walls of the heart, is also under control of the
autonomic nervous system. The cardiac muscle cell has one central nucleus,
like smooth muscle, but it also is striated, like skeletal muscle. The cardiac
muscle cell is rectangular in shape. The contraction of cardiac muscle is
involuntary, strong, and rhythmical.
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Each muscle consists of skeletal muscle tissue, connective tissue, nerve
tissue, and blood or vascular tissue. Skeletal muscles vary considerably in
size, shape, and arrangement of fibers. They range from extremely tiny
strands such as the stapedium muscle of the middle ear to large masses
such as the muscles of the thigh.
Each skeletal muscle fiber is a single cylindrical muscle cell. An individual
skeletal muscle may be made up of hundreds, or even thousands, of muscle
fibers bundled together and wrapped in a connective tissue covering. Each
muscle is surrounded by a connective tissue sheath called the epimysium.
Fascia, connective tissue outside the epimysium, surrounds and separates
the muscles. Portions of the epimysium project inward to divide the muscle
into compartments. Each compartment contains a bundle of muscle fibers.
Each bundle of muscle fiber is called a fasciculus and is surrounded by a
layer of connective tissue called the perimysium. Within the fasciculus, each
individual muscle cell, called a muscle fiber, is surrounded by connective
tissue called the endomysium.
Skeletal muscle cells (fibers), like other body cells, are soft and fragile. The
connective tissue covering furnish support and protection for the delicate
cells and allow them to withstand the forces of contraction. The coverings
also provide pathways for the passage of blood vessels and nerves.
Commonly, the epimysium, perimysium, and endomysium extend beyond
the fleshy part of the muscle to form a thick ropelike tendon or a broad, flat
sheet-like aponeurosis. The tendon and aponeurosis form indirect
attachments from muscles to the bones or to the connective tissue of other
muscles. Typically a muscle spans a joint and is attached to bones by
tendons at both ends. One of the bones remains relatively fixed or stable
while the other end moves as a result of muscle contraction.
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Skeletal muscles have an abundant supply of blood vessels and nerves. This
is directly related to the primary function of skeletal muscle, contraction.
Before a skeletal muscle fiber can contract, it has to receive an impulse from
a nerve cell. Generally, an artery and at least one vein accompany each
nerve that penetrates the epimysium of a skeletal muscle. Branches of the
nerve and blood vessels follow the connective tissue components of the
muscle of a nerve cell and with one or more minute blood vessels called
capillaries.
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Muscles of trunk
These include those that move the vertebral column, the muscles that form
the thoracic and abdominal walls, and those that cover the pelvic outlet.
The erector spinae group of muscles on each side of the vertebral column
is a large muscle mass that extends from the sacrum to the skull. These
muscles are primarily responsible for extending the vertebral column to
maintain erect posture. The deep back muscles occupy the space between
the spinous and transverse processes of adjacent vertebrae.
The muscles of the thoracic wall are involved primarily in the process of
breathing. The intercostal muscles are located in spaces between the ribs.
They contract during forced expiration. External intercostal muscles contract
to elevate the ribs during the inspiration phase of breathing. The diaphragm
is a dome-shaped muscle that forms a partition between the thorax and the
abdomen. It has three openings in it for structures that have to pass from
the thorax to the abdomen.
The abdomen, unlike the thorax and pelvis, has no bony reinforcements or
protection. The wall consists entirely of four muscle pairs, arranged in
layers, and the fascia that envelops them.
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The muscles of the upper extremity include those that attach the scapula to
the thorax and generally move the scapula, those that attach the humerus
to the scapula and generally move the arm, and those that are located in the
arm or forearm that move the forearm, wrist, and hand. The illustration
below shows some of the muscles of the upper extremity.
Muscles that move the shoulder and arm include the trapezius and serratus
anterior. The pectoralis major, latissimus dorsi, deltoid, and rotator cuff
muscles connect to the humerus and move the arm.
The muscles that move the forearm are located along the humerus, which
include the triceps brachii, biceps brachii, brachialis, and brachioradialis. The
20 or more muscles that cause most wrist, hand, and finger movements are
located along the forearm.
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The nervous system is the major controlling, regulatory, and
communicating system in the body. It is the center of all mental activity
including thought, learning, and memory.
Together with the endocrine system (producing
hormones), the nervous system is responsible for
regulating and maintaining homeostasis.
Through its receptors, the nervous system keeps
us in touch with our environment, both external
and internal.
The nervous system is composed of organs, principally the brain, spinal
cord, nerves, and ganglia (a mass of nerve tissue containing nerve cells
external to the brain or spinal cord). These, in turn, consist of various
tissues, including nerve, blood, and connective tissue.
The various activities of the nervous system can be grouped together as
three general, overlapping functions: Sensory,
Integrative, and Motor.
Millions of sensory receptors detect changes, called
stimuli, which occur inside and outside the body. They
monitor such things as temperature, light, and sound
from the external environment. Inside the body, the
internal environment, receptors detect variations in
pressure, pH, carbon dioxide concentration, and the levels of various
electrolytes. All of this gathered information is called sensory input.
Sensory input is converted into electrical signals called nerve impulses that
are transmitted to the brain. There the signals are brought together to
create sensations, to produce thoughts, or to add to memory; Decisions are
made each moment based on the sensory input. This is integration.
Based on the sensory input and integration, the nervous system responds by
sending signals to muscles, causing them to contract, or to glands, causing
them to produce secretions.
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Nerve Tissue
Although the nervous system is very complex, there are only two main types
of cells in nerve tissue. The actual nerve cell is the neuron. It is the
"conducting" cell that transmits impulses and the structural unit of the
nervous system. The other type of cell is neuroglia, or glial, cell. The word
"neuroglia" means "nerve glue." These cells are nonconductive and provide a
support system for the neurons. They are a special type of "connective
tissue" for the nervous system.
Neurons, or nerve cells, carry out the functions of the nervous system by
conducting nerve impulses. They are highly specialized and amitotic. This
means that if a neuron is destroyed, it cannot be replaced because neurons
do not go through mitosis. The image below illustrates the structure of a
typical neuron.
Each neuron has three basic parts: cell body (soma), one or more dendrites,
and a single axon.
In many ways, the cell body is similar to other types of cells. It has a
nucleus with at least one nucleolus and contains many of the typical
cytoplasmic organelles. It lacks centrioles, however. Because centrioles
function in cell division, the fact that neurons lack these organelles is
consistent with the amitotic nature of the cell.
Dendrites and axons are cytoplasmic extensions, or processes, that
project from the cell body. They are sometimes referred to as fibers.
Dendrites are usually, but not always, short and branching, which increases
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their surface area to receive signals from other neurons. The number of
dendrites on a neuron varies. They are called afferent processes because
they transmit impulses to the neuron cell body. There is only one axon
that projects from each cell body. It is usually elongated and because it
carries impulses away from the cell body, it is called an efferent process.
An axon may have infrequent branches called axon collaterals. Axons and
axon collaterals terminate in many short branches or telodendria. The distal
ends of the telodendria are slightly enlarged to form synaptic bulbs. Many
axons are surrounded by a segmented, white, fatty substance called myelin
or the myelin sheath. Myelinated fibers make up the white matter in the
CNS, while cell bodies and unmyelinated fibers make the gray matter. The
unmyelinated regions between the myelin segments are called the nodes of
Ranvier.
In the peripheral nervous system, the myelin is produced by Schwann cells.
The cytoplasm, nucleus, and outer cell membrane of the Schwann cell form
a tight covering around the myelin and around the axon itself at the nodes
of Ranvier. This covering is the neurilemma, which plays an important role in
the regeneration of nerve fibers. In the CNS, oligodendrocytes produce
myelin, but there is no neurilemma, which is why fibers within the CNS do
not regenerate.
Functionally, neurons are classified as afferent, efferent, or interneurons
(association neurons) according to the direction in which they
transmit impulses relative to the central nervous system. Afferent, or
sensory, neurons carry impulses from peripheral sense receptors to the CNS.
They usually have long dendrites and relatively short axons. Efferent, or
motor, neurons transmit impulses from the CNS to effector organs such as
muscles and glands. Efferent neurons usually have short dendrites and long
axons. Interneurons, or association neurons, are located entirely within the
CNS in which they form the connecting link between the afferent and
efferent neurons. They have short dendrites and may have
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