The Skeletal System

Skeletal Categories and Functions

​​The skeletal system of the human body consists of 206 bones. These bones can be divided into two categories:

  • Axial Skeleton: Eighty bones that form the head, neck, and trunk.
  • Appendicular Skeleton: One hundred twenty-six bones that comprise the extremities.

The skeletal system provides five major functions for the body:

  • Protection for many vital organs, including the heart, brain, and spinal cord.
  • Support that enables the body to sustain its form and its erect posture.
  • The structure consists of levers that have muscles attached to them to create movement.
  • Production of red blood cells, certain types of white blood cells, and blood platelets (which all occurs in the red marrow of the bones).
  • Storage area for calcium, phosphorus, potassium, sodium, and certain other minerals.

Standard Anatomical Position

Standard Anatomical Position is a term used as a reference to describe the following three positions:

  • Body standing erect
  • Feet facing forward
  • Palms facing forward

Axial Skeleton

Eighty bones make up the head, neck, and trunk:

  • Cranium 8 bones
  • Face 14 bones
  • Hyoid Bone 1 bone (located in the neck)
  • Ears 6 bones (auditory ossicles)
  • Vertebral Column 26 movable bones
  • Sternum 1 bone
  • Ribs 24 bones

Appendicular Skeleton

One hundred twenty-six bones make up the legs and arms:

  • Phalanges (upper) 28 bones
  • Phalanges (lower) 28 bones
  • Metatarsals 10 bones
  • Tarsals 14 bones
  • Patella 2 bones
  • Tibia 2 bones
  • Fibula 2 bones
  • Femur 2 bones
  • Hip and Pelvis 2 bones
  • Clavicle 2 bones
  • Scapula 2 bones
  • Metacarpals 10 bones
  • Carpals 16 bones
  • Radius 2 bones
  • Ulna 2 bones
  • Humerus 2 bones

Bones of the Skull

Twenty-eight bones make up the cranium, face, and ears.

Cranium

Eight bones form the cranium, which surrounds the brain:

  • One frontal bone
  • Two temporal bones
  • Two parietal bones
  • One occipital bone
  • One ethmoid bone
  • One sphenoid bone

Face

Fourteen bones for the cheek, jaw, and nasal cavity:

  • Two maxilla bones
  • Two palatine bones
  • Two zygomatic bones
  • Two lacrimal bones
  • Two nasal bones
  • One vomer bone
  • Two inferior nasal concha bones
  • One mandible (jaw bone)

Ears

Each is made up of three bones:

  • One malleus (hammer) per ear
  • One incus (anvil) per ear
  • One stapes (stirrup) per ear

Technically, the ear bones are not considered part of either the axial skeleton or the appendicular skeleton. However, they are sometimes associated with the axial skeleton. The fact is, they are just part of the ear.

Bones of the Vertebral Column

Vertebral Column protects the spinal cord from injury. It encloses the spinal cord and the fluid surrounding it. Comprised of twenty-six bones, as follows:

  • Seven cervical vertebrae in the neck
  • Twelve thoracic vertebrae at the back wall of the chest
  • Five lumbar vertebrae at the inward curve of the small of the lower back
  • One sacrum comprised of five fused vertebrae between the hip bones
  • One coccyx is comprised of four fused vertebrae at the lower tip of the vertebral column

Joints

Joints are the points of contact or connection between bones, and between bones and cartilage. Also called articulations.

Ligaments

The dense fibrous strands of connective tissue that link bones to bones and maintain the stability and integrity of all joints.

Joint Cavity

The space between the connected bones.

Synovial Fluid

The viscous, thick, lubricating fluid is located within the joints of the body. Synovial fluid also provides nutrition to the cartilage within the joint.

Sometimes when overuse or an acute injury occurs to a joint, the synovial membrane will produce an excess of synovial fluid. This, in turn, produces swelling and increases pain at the joint, particularly when movement occurs.

Bursa

Bursa is a small fluid-filled sac that is located around a joint that reduces friction between bones and ligaments by secreting a lubricating fluid.

Three Primary Joints Types

Major characteristics that define the three primary joint types are:

  • The existence or nonexistence of a joint cavity.
  • The type of connective tissue that holds a joint together.
  • Types of motion the joint is capable of.

Fibrous Joints (Syndesmosis)

Fibrous Joints do not have a joint cavity but are held together by ligaments. Little or no motion occurs at these joints. Locations of this joint are in the skull and between the radius and ulna.

Cartilaginous Joints (Synchondroses)

Cartilaginous Joints do not have a joint cavity, and cartilage unites the bones. Little or no motion occurs at these joints. Locations of these joints are in the spinal cord and the connection between the ribs and the sternum.

Synovial Joints (Diarthroses)

Synovial Joints have a joint cavity and are surrounded by fibrous connective tissue. Synovial is the largest functional category of joints and many different types of motions occur at their various locations throughout the body, including the knee, shoulder, elbow, and ankle.

Anatomical Planes

There are three primary planes:

Sagittal Plane (Lateral Plane)

An imaginary vertical line that divides the body or a body part into right and left sections.

Frontal Plane (Coronal Plane)

An imaginary vertical line that divides the body or a body part into anterior (front) and posterior (back) sections. The sagittal plane and the frontal plane bisect each other at right angles.

Transverse Plane (Axial Plane)

An imaginary horizontal line that divides the body or a body part into superior (upper) and inferior (lower) sections.

Synovial Joint Motions

Flexion creates motion on a Sagittal Plane

Action brings two connected body parts closer together, like bending an elbow during the positive phase of a biceps curl. It is the opposite of extension.

Extension creates motion on a Sagittal Plane

The action moves two connected body parts toward a straight line, like straightening the elbow during the negative phase of a biceps curl. It is the opposite of flexion.

Adduction creates motion on a Frontal Plane

The action moves a body part toward the midline of the body. Abduction creates motion on a Frontal Plane Action moves a body part away from the midline of the body.

Horizontal Flexion creates motion on a Transverse Plane

Action as an example, if an arm starts off in a ninety-degree abducted position, the humerus is then flexed in toward the midline of the body.

Horizontal Extension creates motion on a Transverse Plane

Action as an example, if an arm starts off in the adducted position, the humerus is extended away from the midline of the body out toward a ninety-degree abducted position.

Elevation creates motion on a Frontal Plane

Action the scapula moves upward and away from the rib cage. Muscles involved are the upper trapezius, rhomboids, and levator scapulae. Elevation applies only to motions where the shoulder is raised, whether by exercising or any other reason.

Depression creates motion on a Frontal Plane

Action the scapula moves downward and toward the ribcage. The muscles involved are the lower trapezius, and the lower serratus anterior. Depression applies only to motions where the shoulder is lowered, whether by exercising or any other reason.

Rotary Motion creates motion on a Transverse Plane

Action moving a body part around a nonmoving point. For example, turning your head right or left while keeping your trunk still.

Rotation creates motion on a Transverse Plane

Action the inward (medial) or outward (lateral) turning of a body part around a bone that is fixed in a vertical position. For example, turning your upper body to the right or to the left while your feet remain stationary on the floor.

Inversion creates motion on a Transverse Plane

Action is the inward movement of the sole of the foot so that the sole faces toward the opposite foot. An anatomical term that only applies to the feet.

Eversion creates motion on a Transverse Plane

Action is the outward movement of the sole of the foot so that the sole faces away from the opposite foot. An anatomical term that only applies to the feet.

Plantar Flexion creates motion on a Sagittal Plane

Action is an ankle joint motion that moves the toes to a pointing downward position. An anatomical term that only applies to the feet.

Dorsiflexion creates motion on a Sagittal Plane

Action is an ankle joint motion that moves the toes to a pointing upward position. An anatomical term that only applies to the feet.

Pronation creates motion on a Transverse Plane

Action when the forearm is positioned with the palm facing downward or backwards. An anatomical term that only applies to the wrist.

Supination creates motion on a Transverse Plane

Action when the forearm is positioned with the palm facing upward or forward. An anatomical term that only applies to the wrist.

Circumduction creates motion on a Multiplanar Plane

Action is a circular motion similar to rotation; particularly applicable to the shoulder and hip joints. This circular movement requires flexion, abduction, extension, and adduction all in sequential combination.

Opposition creates motion on a Multiplanar Plane

Action is the unique movement of the thumb. Opposition allows the hand to perform such actions as grabbing, squeezing, or holding an object.

Skeletal System Injuries and Conditions

Arthritis

Arthritis is the inflammation of one or more joints. Symptoms include:

  • Joint pain (arthralgia)
  • Swelling
  • Stiffness
  • Redness in and around the affected area
  • Grating or grinding sound in a joint (crepitus)

Some of the more common forms of arthritis are as follows:

Rheumatoid Arthritis

An autoimmune disease (wherein the body’s own immune system attacks the body’s own tissues) that results in inflammation, pain, stiffness, swelling, and redness in the diseased joint.

In severe cases the fingers, wrists, and/or toes become deformed.

Osteoarthritis

Characterized mainly by the degeneration of the cartilage that lines and protects the joints of the body and outgrowths of new bone called osteophytes, particularly along the perimeter of the affected joint surface.

These conditions result in inflammation, pain, stiffness, swelling, and redness in the diseased joint.

Ankylosing Spondylitis

A type of arthritis that causes inflammation to the joints and ligaments to the spine. This causes pain and stiffness usually beginning in the lower back or buttocks area.

Progression of this condition may also affect the upper spine, chest and neck. Eventually, vertebrae may connect to each other (fuse), resulting in a rigid and inflexible spine. As this disease progresses further, knee, hip and shoulder joints may also become affected.

Ankylosing spondylitis is a systemic disease, and that means it may affect any number of organs and tissues, or affect the entire body.

Seronegative Arthritis

May be related to certain skin disorders, such as psoriasis, and certain inflammatory intestinal disorders, such as Crohn’s disease.

Still’s Disease

A type of arthritis that affects children, usually under the age of four.

Infective Arthritis

Inflammation of a joint as a result of an infected wound that is close to the joint or from an infection in the bloodstream.

Infective arthritis can cause a dangerous condition where there is the presence of bacteria or their toxins in the blood or tissues (sepsis), as well as be pus producing (pyogenic).

Gout

Caused by an accumulation of uric acid in the joints. The uric acid build-up occurs in the form of crystals that creates joint inflammation.

Posture Abnormalities

There are three classic abnormalities in posture:

Lordosis

An increase in the normal forward curvature of the lumbar spine. The result is often a posture with a protruding abdomen and buttocks, rounded shoulders, and forward head.

Kyphosis

An increase in the normal backward curvature of the thoracic spine. The result is often a posture with rounded shoulders, a sunken chest, and a forward-downward head position.

This abnormal head position is compensated for by an exaggerated tilt of the neck toward the rear of the body, referred to as hyperextension of the neck.

Scoliosis

An abnormal curvature of the spine, commonly in the thoracic area. There are usually two abnormal curves, one to the right of the spine and the other to the left of the spine, or vice versa. These opposing curves tend to compensate for each other.

Cortisone for Pain Relief

Cortisone is a popular steroid medication that is commonly injected into muscles, joints, and connective tissue to relieve pain by reducing inflammation. Too many cortisone injections may cause tissue damage, and occasionally, cause tendon rupture.

Physical therapy is believed to be more effective than the use of cortisone for rehabilitating an injury. However, it is not always possible as the first step because the pain is too strong.

Therefore, the temporary relief of cortisone can enable a patient to facilitate treatment by reducing or eliminating inflammation and pain, and rehabilitate an injury faster.

The benefit of a cortisone injection should be weighed carefully against the risks before being used.

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