Skeletal System: Bone Structure and Function

• Objectives from this lecture include describing the functions of the skeletal system, describing the gross structure of bones and their functions, describing the different classes of bone in the human skeleton and how their shape relates to function, and identifying the major bones of the skeleton and why/how some are sexually dimorphic.
• The skeletal system functions in support, movement, protection of major organs, storage of minerals, and red blood cell formation in marrow.
• Bones act as levers for movement.

Structure of Bones

• There are two types of bone tissue from the same material, but with a different structure.
• Compact bone is strong and transmits force in one direction.
• Cancellous/trabecular bone is light, spongy, shock-absorbing, and resists/channels forces from multiple directions.

Bone Classes

• Long bones are longer than they are wide.
• Long bones are composed of wider epiphyses and a longer, narrower diaphysis
• Long bones act as levers for movement.
• Long bones have a thicker compact bone in the diaphysis and are mostly in the limbs.
• Short bones have close to equal width and length and are mostly cancellous bone.
• Short bones are weight-bearing from multiple directions.
• Carpals and tarsals are examples of short bones.
• Flat bones usually function for muscle attachment, such as the scapula.
• Flat bones also provide protection for structures like the skull and sternum.
• Flat bones are thin plates of compact bone with some cancellous bone as well.
• Irregular bones do not seem to fit into any other category.
• Irregular bones are not long, round, square, cancellous, or flat, and often have foramina or holes.
• Irregular bones have various shapes and functions.

Divisions of the Skeleton

• The axial skeleton has bones of the core, including the skull, sternum, ribs, vertebral column, sacrum and coccyx.
• The axial skeleton functions in the protection of vital organs.
• The appendicular skeleton has bones of the limbs and is important for movement.

Axial Skeleton: The Skull

• The cranium (vault) encloses the brain and provides muscle attachments.
• Facial bones protect and support sensory organs.
• Bones in the skull join at sutures (immovable).

Axial Skeleton: The Vertebral Column

• The vertebral column keeps the trunk upright
• The vertebral column has lots of muscle and ligament attachments and supports the head.
• Divisions of the vertebral column include cervical (7), thoracic (12), lumbar (5), and sacrum and coccyx.
• The axial rib cage is the thoracic cage made up of ribs and the sternum.
• The ribs and the sternum make up the axial rib cage (thoracic cage).

Appendicular Skeleton

• Appendicular skeleton includes the limbs
• Appendicular skeleton regions include the arm, forearm, thigh, and leg.
• The limb structure consists of a single proximal long bone(humerus, femur); two distal long bones (ulna and radius/tibia and fibula).
• The ulna and the radius are more mobile.
• The appendicular skeleton also includes the hands and feet.

Skeleton Shape

• The shape of the human skeleton relates to function, bipedalism, and stabilization and movement of the human lower limb.
• Hands are free and not involved in locomotion, which results in a lack of stability, but are adapted for manipulation of environment/precision.
• The Humerus is shorter and lighter than the Femur.
• The articulation for prox.femur is deeper than the than the prox. humerus

Forearm and Wrist Mobility

• Mobile forearms and wrists allow for pronation and supination of the radius and ulna.
• The shape of the distal articulation allows for wrist mobility.
• Legs have no pronation/supination, with an ankle joint.
• The tibia is very robust and weight-bearing.
• The hand consists of 8 carpals, 5 metacarpals, and 14 phalanges (only 2 in the thumb).
• The foot consists of 7 tarsals, 5 metatarsals, and 14 phalanges.

How Limbs Attach to the Axial Skeleton

• The pectoral (shoulder) girdle includes the clavicle and scapula.
• The pelvic girdle includes hip bones (2) and the sacrum (axial).
• The clavicle in the pectoral girdle is stabilizing.
• The scapula in the pectoral girdle is free-moving and has muscle attachments.
• The pelvic girdle includes two hip bones (os coxae) and the sacrum.
• The sacrum is part of the axial skeleton.
• Pelvic bones and sacrum form the pelvis.

Pelvis

• the Pelvis has lots of weight bearing.
• Biological females have a more circular pelvic cavity and a more open pelvic outlet than males.
• This is Maximising the space for childbirth.
• The shape of the pelvic cavity is different and the subpubic angle is bigger in biological females than in biological males.