Human Skeleton: Structure and Function

• The lecture discusses the structure of the skeleton
• By the end of the lecture, students should be able to describe the functions of the skeletal system.
• Students should also be able to describe the gross structure of bones, explain how they reflect their functions and the different classes of bone in the human skeleton and how their shape relates to function
• Students should also be able to identify the major bones of the skeleton, and understand why/how some are sexually dimorphic

Functions of the Skeleton

• Provides support and protection
• It allows movement due to bones acting as levers
• Bones store minerals and facilitate red blood cell formation in marrow

Structure of Bones

• There are two types of bone tissues which are the same material, but different structures
• Compact bone is strong and transmits force in one direction
• Cancellous (trabecular) bone is light and spongy, shock-absorbing, and resists and channels forces from multiple directions

Bone Classes

• Bones can be categorized into long, short, flat, and irregular bones

Long Bones

• Longer than they are wide
• They are composed of wider epiphyses and a longer, narrower diaphysis
• Act as levers for movement
• Have thicker compact bone in the diaphysis
• Mostly limb bones

Short Bones

• Close to equal width and length
• Mostly cancellous bone
• Weight-bearing from multiple directions
• Examples are carpals and tarsals

Flat Bones

• Provide function usually for muscle attachment like the scapula
• Provide protection like the skull or sternum
• Thin plates of compact bone with some cancellous bone

Irregular Bones

• Bones that don't fit into any other category
• Probably an irregular bone!
• Come in various shapes and functions
• They aren't long, round/square-shaped, cancellous, or flat
• Often have foramina (holes)

Divisions of the Skeleton

• The skeleton is divided into the axial and appendicular skeleton

Axial Skeleton

• Includes bones of the core such as the skull, sternum, ribs, vertebral column, sacrum, and coccyx
• Protects vital organs

The Skull

• The skull includes the cranium which encloses the brain and provides muscle attachments
• Facial bones protect and support sensory organs
• The skull joins at sutures
• These are immovable

The Vertebral Column

• Keeps the trunk upright, allowing lots of muscle/ligament attachments
• Supports the head
• Divisions include cervical (7), thoracic (12), lumbar (5), and sacrum and coccyx

The Rib Cage

• Also known as the thoracic cage
• Includes ribs and the sternum

Appendicular Skeleton

• Includes bones of the limbs and is most important for movement

Limbs

• Include the arm, forearm, thigh, and leg

Limb Structure

• Features a single proximal long bone
• Common bones are the humerus and femur
• Distal long bones are the ulna and radius or tibia and fibula
• The ulna and radius are more mobile
• Also includes the hands and feet

Skeleton Shapes

• Form is related to function
• Humans walk on two limbs (bipedalism), compared to other apes (quadrapedalism)
• Human lower limbs need stability and movement

Mobility vs Stability

• Hands are free and not involved in locomotion
• Hands lack stability
• They are adapted for manipulation of the environment for precision
• The humerus is shorter and lighter, with a deeper articulation for the proximal femur than the proximal humerus, favoring stability over movement
• Mobile forearms and wrists allow pronation and supination of the radius and ulna. The distal articulation shape also supports wrist mobility
• Legs prioritize stability
• There is no pronation/supination
• The ankle joint is stable
• The tibia is robust and can withstand weight-bearing

Hand and Feet Bones

• Hands feature 8 carpals, 5 metacarpals, and 14 phalanges (only 2 in the thumb)
• The foot features 7 tarsals, 5 metatarsals, and 14 phalanges

Limb Attatchment

• Limbs attach to the axial skeleton through pectoral and pelvic girdles

Pectoral Girdle

• Includes the clavicle and scapula
• The clavicle stabilizes, and the scapula allows free movement and provides muscle attachments

Pelvic Girdle

• Includes two hip bones, and the sacrum (axial), forming the pelvis.
• Is weight bearing

Female vs Male Pelvis

• Biological females have different pelvic anatomies to biological males
• Biological females have more circular pelvic cavities
• Females have more open pelvic outlets to create space for child birth
• Features a different shape from male pelvic cavity
• Features a larger subpubic angle