6.3 Axial and Appendicular Skeleton

The axial and appendicular skeletons form the framework of our bodies. The axial skeleton, including the skull, spine, and rib cage, protects vital organs and provides support. The appendicular skeleton, comprising our limbs, enables movement and manipulation of our environment.

Together, these skeletal systems work in harmony to support our body's structure and function. The axial skeleton anchors the appendicular skeleton, allowing for a wide range of motions and activities essential for daily life, from walking to writing.

Axial Skeleton Bones

Skull Composition

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• The skull is composed of cranial and facial bones
• Cranial bones include the frontal, parietal, temporal, occipital, sphenoid, and ethmoid bones
• Facial bones include the maxilla, mandible, nasal bones, and zygomatic bones (cheekbones)
• The skull protects the brain and sensory organs (eyes, ears, nose) and provides attachment points for muscles of the head and neck

Vertebral Column Regions

• The vertebral column is divided into five regions: cervical, thoracic, lumbar, sacral, and coccygeal
  • There are 7 cervical vertebrae in the neck region
  • 12 thoracic vertebrae in the chest region
  • 5 lumbar vertebrae in the lower back region
  • 5 fused sacral vertebrae in the pelvis region
  • 3-5 fused coccygeal vertebrae in the tailbone region
• The vertebral column provides support for the head and trunk, protects the spinal cord, and allows for flexibility and movement of the spine

Rib Cage Composition

• The rib cage is composed of 12 pairs of ribs
  • The first 7 pairs are true ribs, which directly attach to the sternum
  • The next 3 pairs are false ribs, which indirectly attach to the sternum via cartilage
  • The last 2 pairs are floating ribs, which do not attach to the sternum
• The sternum is a flat bone that connects to the ribs anteriorly and is divided into the manubrium, body, and xiphoid process
• The rib cage protects vital organs (heart, lungs) and assists in breathing by providing attachment points for respiratory muscles

Functions of the Axial Skeleton

Protection and Support

• The skull protects the brain and sensory organs, while also supporting the structures of the face
• The vertebral column supports the head and trunk, protecting the spinal cord and providing flexibility
• The rib cage protects vital organs such as the heart and lungs, while also assisting in breathing

Muscle Attachment and Movement

• The axial skeleton provides attachment points for muscles of the head, neck, chest, and upper abdomen
• These muscle attachments allow for movements such as head rotation, trunk flexion and extension, and breathing
• The vertebral column's flexibility enables bending, twisting, and turning movements of the spine

Upper vs Lower Limb Bones

Upper Limb Bones

• The upper limb consists of the humerus, radius, ulna, carpals, metacarpals, and phalanges
  • The humerus is the bone of the upper arm
  • The radius and ulna are the bones of the forearm
  • The carpals, metacarpals, and phalanges make up the bones of the wrist and hand
• The shoulder joint connects the upper limb to the axial skeleton via the clavicle (collarbone) and scapula (shoulder blade)

Lower Limb Bones

• The lower limb consists of the femur, patella, tibia, fibula, tarsals, metatarsals, and phalanges
  • The femur is the bone of the thigh
  • The tibia and fibula are the bones of the lower leg
  • The patella is a sesamoid bone located within the quadriceps tendon
  • The tarsals, metatarsals, and phalanges make up the bones of the ankle and foot
• The hip joint connects the lower limb to the axial skeleton via the pelvis

Appendicular Skeleton Role in Movement and Support

Muscle Attachment and Leverage

• The appendicular skeleton provides attachment points for muscles, allowing for a wide range of movements in the upper and lower limbs
• The bones of the appendicular skeleton act as levers, which muscles can pull on to generate movement and force
• The structure and arrangement of muscle attachments on the bones determine the type and range of motion possible at each joint

Joint Stability and Mobility

• The joints between the bones of the appendicular skeleton, such as the shoulder, elbow, hip, and knee, facilitate movement and provide stability
• The shape and structure of the articulating surfaces of the bones at each joint determine the type and range of motion possible
• Ligaments, tendons, and muscles surrounding the joints help to stabilize and support the bones during movement

Weight-Bearing and Distribution

• The appendicular skeleton supports the weight of the body and distributes forces during weight-bearing activities (standing, walking, running)
• The bones of the lower limbs, particularly the femur, tibia, and fibula, are adapted to withstand the stresses of weight-bearing
• The structure and arrangement of the bones in the feet allow for weight distribution, balance, and propulsion during locomotion

Precision and Adaptability

• The structure and arrangement of the bones in the hands and feet allow for precise movements and adaptations to various tasks and environments
• The numerous bones and joints in the hands (carpals, metacarpals, phalanges) enable fine motor skills, grasping, and manipulation of objects
• The bones and joints of the feet (tarsals, metatarsals, phalanges) provide stability, flexibility, and adaptability to different surfaces and terrains