Section 8-11: The Pectoral (Shoulder) Girdle and Upper Limb

Pectoral Girdle Structure and Articulations

The pectoral girdle consists of the clavicle and scapula, providing attachment for the upper limb to the axial skeleton. Its articulations allow for a wide range of shoulder movements.

• Shoulder Joint: The shoulder (glenohumeral) joint is a ball-and-socket synovial joint between the head of the humerus and the glenoid cavity of the scapula.

• Sternoclavicular Joint: The only articulation between the pectoral girdle and the axial skeleton, formed by the clavicle and the manubrium of the sternum.

• Acromioclavicular Joint: Articulation between the acromion of the scapula and the clavicle.

• Scapula: The scapula articulates with the humerus at the glenoid cavity and with the clavicle at the acromion.

Example: The sternoclavicular joint allows the shoulder to move in multiple planes, contributing to the flexibility of the upper limb.

Key Landmarks and Movements

• Coracoid Process: A projection on the scapula serving as an attachment for muscles and ligaments.

• Acromion: The lateral extension of the scapular spine, articulates with the clavicle.

• Glenoid Cavity: The shallow socket on the scapula that receives the head of the humerus.

• Metaphysis: The region of a long bone between the diaphysis and epiphysis; in the humerus, the surgical neck corresponds to the metaphysis.

• Surgical Neck: Common site for fractures in the humerus.

• Radial Tuberosity: Attachment site for the biceps brachii muscle.

• Olecranon Fossa: A depression on the posterior humerus that receives the olecranon of the ulna during elbow extension.

• Styloid Process: A pointed projection at the distal end of the radius and ulna.

• Pollex: The anatomical term for the thumb.

Additional info: The radius is positioned laterally (thumb side) in anatomical position, while the ulna is medial (little finger side).

Section 8-12: The Pelvic Girdle and Lower Limb

Pelvic Girdle Structure and Articulations

The pelvic girdle consists of two hip bones (os coxae), which articulate with the sacrum and femur, supporting the weight of the upper body and enabling locomotion.

• Pubic Symphysis: A cartilaginous joint uniting the left and right pubic bones.

• Acetabulum: The deep socket in the hip bone that receives the head of the femur, forming the hip joint.

• Sacroiliac Joint: The articulation between the sacrum and the ilium of the hip bone.

• Obturator Foramen: A large opening created by the ischium and pubis, allowing passage of nerves and blood vessels.

• Pelvic Outlet: The lower opening of the pelvis, important in childbirth.

Example: The acetabulum is a much deeper socket than the glenoid cavity, providing greater stability for weight-bearing activities.

Key Landmarks and Functions

• Sacrum and Coccyx: Complete the posterior aspect of the pelvic girdle.

• Ischial Tuberosity: The part of the pelvis that bears weight when sitting.

• Pubic Tubercle: A prominent forward-projecting point on the pubic bone.

• Pelvic Inlet and Outlet: Boundaries important for obstetrics.

Section 8-14: Bones of the Lower Limbs Adapted for Movement and Support

Lower Limb Bones and Their Functions

The bones of the lower limb are specialized for support, movement, and weight-bearing. They include the femur, patella, tibia, fibula, tarsals, metatarsals, and phalanges.

• Femur: The longest and strongest bone in the body; articulates proximally with the acetabulum and distally with the tibia.

• Patella: A sesamoid bone embedded in the quadriceps tendon; protects the knee joint and improves leverage.

• Tibia: The main weight-bearing bone of the lower leg; forms the medial malleolus at the ankle.

• Fibula: The lateral bone of the lower leg; forms the lateral malleolus at the ankle.

• Tarsals: Seven bones forming the ankle; includes the talus and calcaneus (heel bone).

• Metatarsals: Five bones forming the arch of the foot.

• Phalanges: Fourteen bones forming the toes.

Example: The patella increases the efficiency of the quadriceps muscle by acting as a fulcrum.

Key Landmarks and Movements

• Medial and Lateral Malleolus: Bony prominences on the tibia and fibula, respectively, forming the ankle.

• Calcaneus: The heel bone; largest tarsal bone.

• Talus: Articulates with the tibia and fibula to form the ankle joint.

• Arches of the Foot: Provide support and flexibility; include the longitudinal and transverse arches.

Section 8-15: Differences in Sex and Age in Human Skeleton

Sexual Dimorphism in the Human Skeleton

Sexual differences in the human skeleton are most evident in the pelvis, which adapts for childbirth in females. Other differences include general appearance, bone size, and pelvic angle.

Additional info: The female pelvis is adapted for childbirth, with a wider pelvic inlet and outlet, and a greater pubic angle.

Key Terms and Definitions

• Pollex: The anatomical term for the thumb.

• Hallux: The anatomical term for the big toe.

• Metaphysis: The region between the diaphysis and epiphysis of a long bone.

• Styloid Process: A pointed projection at the distal end of the radius and ulna.

• Acetabulum: The socket in the hip bone for the femur.

• Obturator Foramen: Large opening in the hip bone for nerves and vessels.

Formulas and Equations

• Bone Strength:

• Leverage (Mechanical Advantage):