The Skeletal System
Two Parts:
- axial skeleton
3 Parts – skull, thorax, (pelvis), & vertebral column
- appendicular skeleton
4 Parts–left and right, upper and lower extremities
Classification of Bones
Wolff’s Law:
The shape of a bone to some extent determines its function,
& conversely, the function may alter its shape over a period
of time.
- Long bones in the extremities
- lower extremities – larger and stronger – weight bearing
- upper extremities – smaller and lighter – reaching, grasping, throwing
- Short bones in hands and feet – elasticity, flexibility, shock absorption
Directional Definitions
For long bones (in anatomical position):
- proximal ends – closer to the trunk
- distal ends – farther from trunk
- lateral side – side away from the midline
- medial side – side closest to the midline
For axial skeleton:
- superior border of the bone – border closest to the head
- inferior border of the bone – border closest to the feet
Features
Condyle – A rounded process of a bone – articulates with another bone
Facet – A small fairly flat smooth surface – generally an articular surface
Fossa - A shallow, dish shaped section - providing space for an articulation
or serving as a muscle attachment
Tuberosity – A raised section of the bone to which a muscle or tendon
attaches, usually created by stress/pull on the bone during
growth
insertion of muscle or tendon into the bone (also separated fron
the cortex by an apophyseal plate)
Articulations
Classification according to amount of movement:
synarthrodial articulation – immovable –do not display movement in
response to force – inability to absorb shock
amphiarthrodial articulation – slightly moveable – have fibrocartilaginous
disc – eg. Vertebrae
diarthrodial articulation – freely moveable joint, most common type, has:
ligaments – connective tissue connecting the two bones
tendons – connective tissue attaching muscle to bone
mobility of articulations – ability to move before being restricted by
surrounding structures
ROM – range of motion – total amount of movement (in degrees)
through which the articulations segments may pass.
Articular Movement
Flexion - reducing the angle of the articulation
e.g. from full extension (180°) to 90° or less
Extension - increasing the angle of the articulation
e.g. from 90° to 180°
Muscles
Muscle-Tendon Attachment (to the Skeletal System)
Proximal Attachment of a Muscle – attached to periosteum
- attached to the more stable or stationary bone
Distal Attachment of the muscle - usually tendinous attachment
- attached to the more moveable bone
Muscles and Types of Articulations
uniarticulate - one joint muscle - spans a single articulation
biarticulate - spans 2 articulations - pulls two articulations together when
stimulated and moves both
- considered more efficient since it produces motion in more
than one
multiarticulate - Spans several - tends to produce motion in all of these
Muscular Functions
Concentric Tension - muscle acts to move a body segment – i.e. muscle
contracts and rotates the segment which it spans
- acts with the motion and muscle shortens
(Shortening Tension)
Eccentric Tension - acts to resist the movement of a body segment
– acts opposite to the motion still pulling even while
muscle lengthens
(Lengthening Tension)
Isometric Tension - muscle acts to stabilize (a joint or) body part
- muscular tension but no motion
(Static Tension)
eg. muscle holding against external force,
antagonist muscle immobilizing the second joint
for a biarticulate agonistic muscle