Skeletal System

Introduction The framework of bones and cartilage that

protects our organs and allows us to move is called the skeletal system.

The branch of medicine that deals with the preservation and restoration of the skeletal system, articulations (joints), and associated structures is called orthopaedics.

The skeletal system performs the following functions: Support Protection (for internal organs) Movement Mineral storage Storage of blood cell-producing cells Storage of energy

Types of BonesThere are five principal types of bones based on shape

1. Long bones (e.g. thighs, legs, toes, arms, forearms, and fingers)

greater length than width consist of a shaft and extremities (ends) slightly curved for strength consist mostly of compact bone (dense bone with

few spaces) but also contain considerable amounts of spongy bone (bone with large spaces)

2. Short bones (e.g. wrist, ankle bones)

Somewhat cube-shaped and nearly equal in length and width

Spongy except at the surface where there is a thin layer of compact bone

3. Flat bones (e.g. cranial bones, sternum, ribs, scapulas) Generally thin and composed of two more or

less parallel plates of compact bone enclosing a layer of spongy bone

Flat bones afford considerable protection and provide extensive areas for muscle attachment

4. Irregular bones (e.g. vertebrae, and certain facial bones)

Have complex shapes and cannot be grouped into any of the other three categories

They vary in the amount of spongy and compact bone

5. Sesamoid bones Are small bones in tendons where

considerable pressure develops, for instance, the wrist

Their number varies greatly from person to person

All people have at least two sesamoid bones: the patella (kneecap)

Divisions of the Skeletal System The adult human skeleton consists of 206 bones grouped as

the axial skeleton and the appendicular skeleton. The axial division consists of the bones of the skull, auditory

ossicles, hyoid bone, ribs, breastbone, and the backbone. The appendicular division consists of the bones of the upper

and lower extremities (limbs), plus the bones called girdles, which connect the extremities to the axial skeleton.

There are 80 bones in the axial division and 126 in the appendicular. Listed below are the divisions of the skeletal system.

Anatomical Position (AP)AP is the reference position used to describe the

location of anatomical parts and to describe and explain human movement.

The subject is: standing upright with feet flat on the floor arms at the side of the body facing the observer palms are facing forward (supinated)

Anatomical Position

Directional TermsNote: the midline is an imaginary vertical line

that divides the body into equal left and right sides

Superior: nearer the head e.g. the heart is superior to the liver

Inferior:farther away from the head e.g. the stomach is inferior to the lungs

Directional TermsAnterior (ventral): nearer to or in front of the

body e.g. the sternum is anterior to the heart

Posterior (dorsal): nearer to or at the back of the body

e.g. the esophagus is posterior to the trachea

Directional TermsMedial: closer to the midline of the body e.g. the ulna is on the medial side of the

forearm

Lateral: farther away from the midline of the body

e.g. the ear is lateral to the nose in all individuals

Directional TermsProximal: nearer to the attachment of an extremity

(limb) to the trunk; nearer to the point of origin e.g. the humerus is proximal to the radiusDistal: farther from the attachment of an extremity

(limb) to the trunk; farther away from the point of origin e.g. the phalanges are distal to the carpals (wrist

bones)

Directional TermsSuperficial: on or near the surface of the body e.g. the skin is the most superficial organ of

the body

Deep: farther away from the surface of the body e.g. the ribs are deep to the skin of the chest

Planes of Motion and Axes Biomechanics is the study of human

movements through the use of physics. As such, biomechanics has its own language and terminology. The language of biomechanics establishes a common reference system of standard terms. Planes and axes of motion are an important part of this language.

Planes of MotionA plane of motion can be defined as the two dimensional space cut by a

moving body or the plane along which movements occur. There are generally three planes used to describe segmental and body movements in physical activity. These are:

Sagittal plane a vertical plane that cuts the body into right and left sidesFrontal plane vertical plane that cuts the body into anterior (front) and posterior (back)

partsTransverse plane horizontal plane that cuts the body into superior and inferior parts

Anatomical Planes

Anatomical Axes

An axis is the point about which rotation of a body or of a body segment occurs. There are three axes of rotation. Each axis is associated with a plane of motion and the axis is perpendicular to that plane.

Horizontal axis (…think East and West) passes through the body from side to side perpendicular to the sagittal planeAntereoposterior axis (axis) passes through the body from front to back perpendicular to the frontal planeLongitudinal axis (…think North and South pole) passes through the body from top to bottom perpendicular to the transverse plane

Planes & MovementsMovements in the sagittal plane around a horizontal

axis (e.g. front roll, back roll, cycling, running)Flexion flexion at a joint results in a decrease of the angle

between the two segments that meet at that jointExtension extension at a joint results in an increase of the angle

between the two segments that meet at that joint if the movement occurs beyond the extended

position, the action is called hyperextension

Examples of flexion and extension shoulder flexion and extension elbow flexion and extension wrist flexion and extension fingers flexion and extension hip flexion and extension knee flexion and extension ankle dorsi flexion and plantar flexion tilt of pelvis under Dorsi flexion: bringing the toes toward the shin Plantar flexion: pointing the toes away from the shin

(toward the floor)

Planes & Movements Movements in the frontal plane around a antereoposterior axis (e.g. cartwheel, jumping jacks, galloping)Abduction occurs when a body part is moved away from the midline of

the body e.g. shoulder, hip, fingersAdduction occurs when a body part is moved toward the midline of the

body e.g. shoulder, hip, fingers remember “add to your midline” e.g. shoulder, hip, fingers

Movements & PlanesInversion Turning the sole of the foot inward at the ankle (so the sole of the foot

faces toward the midline)Eversion turning the sole of the foot outward at the ankle (so the sole of the foot

faces away from the midline)Elevation raising a part to a superior position e.g. raising your shoulders toward your ears; closing your jaw Depression lowering a part to an inferior position e.g. lowering your shoulders to normal or lower than normal position;

lowering your jaw to an open position

More…Protraction Sticking jaw out (pouting)Retraction Bringing jaw back to anatomical position Lateral bending bending of the spinal column in the frontal plane to

the left or right e.g. bending side to side at the waist

And More…Movements in the transverse plane around a longitudinal axis (e.g. twist, pirouette)Rotation the movement of a bone around its own axis; this is also known as a pivot e.g. the head, neck, and trunk can pivot around the longitudinal axisInternal (medial) rotation Rotation towards the midline E.g. turning forearn in towards bodyExternal (lateral) rotation Rotation away from midline E.g. turning forearm away from body

More…Pronation rotation of the forearm and hand to the palms down positionSupination rotation of the forearm and hand to the palms up position

(remember holding a cup of “soup”)Protraction Shoulder rounding (hunching shoulders)Retraction Bringing shoulders back to anatomical position, or squeezing

shoulder blades together at back

Special movementsCircumduction a combination of abduction, adduction, flexion and extension this action describes a circle e.g. moving the shoulder in a circle (swimming, windmill

throw in baseball); can also be done at the hip jointOpposition Bringing thumb towards fingersReposition Returning thumb back to anatomical position

Skeletal Surface Markings The surfaces of bones have various structural

features adapted to specific functions. These features are called surface markings. Long bones that bear a great deal of weight have large, rounded ends that can form sturdy joints, for example. Other bones have depressions that receive the rounded ends.

Depressions and Openings

Foramen an opening through which blood vessels, nerves, or ligaments pass

Example:

Meatus a tubelike passageway running within a bone

Example:

Paranasal sinus

an air-filled cavity within a bone connected to the nasal cavity

Fossa a depression in or on a bone Example:

Processes that form Joints

Condyle a large, rounded articular prominence

Example:

Head a rounded articular projection supported on the constricted portion (neck) of a bone

Example:

Facet a smooth, flat surface Example:

Processes to which tendons, ligaments and other connective tissues attach

Tuberosity a large, rounded, usually roughened process

Example:

Spinous process

a sharp, slender projection Example:

Trochanter a large, blunt projection found only on the femur

Example:

Crest a prominent border or ridge Example: