Ch 8

Appendicular Skeleton Overview

  • Definition: The appendicular skeleton is comprised of bones that support the appendages (arms and legs) and includes the girdles (pectoral and pelvic) that attach these limbs to the trunk.

  • Main Components:

    • Pectoral girdle: Attaches upper limbs to the trunk.

    • Pelvic girdle: Attaches lower limbs to the trunk.

    • Upper and lower limbs: Their structure and function will be analyzed in detail.

Pectoral Girdle

  • Consists of two major bones:

    • Clavicle (collarbone)

    • Scapulae (shoulder blades)

  • Characteristics:

    • The pectoral girdle does not encircle the body entirely; it is open dorsally (in the back) where the spine is located.

    • The medial end of each clavicle articulates with the manubrium (the upper part of the sternum) and is located near the first rib.

    • Laterally, the ends of the clavicle articulate with the scapulae, which do not connect to each other or the axial skeleton directly, relying instead on muscular attachments.

    • Provides attachment points for muscles that move the upper limb, allowing for high mobility due to its light structure.

  • Comparison to Nonhuman Ancestors:

    • Analyzing differences in the pectoral girdle between humans and other species, such as chimpanzees and cats, can provide insights into evolutionary adaptations related to mobility and habitat.

Clavicle

  • Anatomy:

    • Extends horizontally across the superior thorax.

    • The medial (sternal) end articulates with the manubrium, and the lateral (acromial) end articulates with the scapula.

    • Acromial End: Concave anteriorly.

    • Sternal End: Convex anteriorly.

  • Functional Importance:

    • Serves as a strut to hold the shoulder away from the body, providing upper limb mobility.

    • Shape features resemble bows or arcs, which provide structural strength and resistance to breaking.

  • Includes features such as the trapezoid line and conoid tubercle, which serve as attachment points for ligaments.

Scapula

  • Location:

    • Lies on the dorsal surface of the rib cage, between ribs 2-7.

  • Structure:

    • Shape: Wing-like with three borders (superior, medial, lateral) and three angles (superior, inferior, lateral).

    • The glenoid cavity is vital for shoulder joint formation but is susceptible to injuries like rotator cuff problems due to its shallow design, favoring flexibility over stability.

  • Anatomy Description:

    • Has structures such as the acromion (part of the scapula articulating with the clavicle), coracoid process, and various fossae (supraspinous, infraspinous).

Upper Limb

  • Composed of 30 bones divided into:

    • Arm: Humerus (single bone between shoulder and elbow).

    • Forearm: Radius and ulna (two bones).

    • Hand: Comprises carpals, metacarpals, and phalanges.

  • Humerus:

    • Characteristics:

    • Longest and strongest bone of the upper limb, articulates with the scapula at the shoulder and the radius and ulna at the elbow.

    • Anatomical structures enabling muscle attachment and articulation, such as the greater and lesser tubercles.

    • Notable features include the deltoid tuberosity, anatomical neck, and surgical neck.

Forearm

  • Radius and Ulna: Interconnected by the interosseous membrane.

  • Anatomical Position:

    • In anatomical position, the radius is lateral; the ulna is medial, allowing for movements like pronation and supination.

  • Ulna: Forms the hinge joint at the elbow with the humerus, does not contribute directly to wrist movement but aids in stabilizing the joint.

    • Key landmarks: Olecranon (articulates with the humerus), trochlear notch, coronoid process, and styloid process.

  • Radius: Functions primarily in hand and wrist movements, articulates with carpal bones.

Hand Anatomy

  • Carpals: 8 bones forming the wrist, organized in two rows.

    • Proximal Row (lateral to medial): Scaphoid, Lunate, Triquetrum, Pisiform.

    • Distal Row (lateral to medial): Trapezium, Trapezoid, Capitate, Hamate.

    • Mnemonic for remembering: Sally Left The Party To Take Carmen Home.

  • Metacarpals: 5 bones forming the palm, numbered 1 (thumb) to 5 (pinky).

  • Phalanges: 14 in total, with each finger having a proximal, middle, and distal phalanx, except the thumb (which has only two: proximal and distal). Two sesamoid bones are also present in the thumb.

Pelvic Girdle

  • Functions:

    • Attaches lower limbs to spine, supports visceral organs, and connects to the axial skeleton through strong ligaments.

    • Offers less mobility than the pectoral girdle, but provides greater stability.

  • Consists of paired coxal bones and the sacrum.

  • Anatomical Features:

    • Coxal Bones: Composed of ilium, ischium, and pubis, articulating with each other anteriorly and with the sacrum posteriorly.

  • Acetabulum: Deep socket that receives the femoral head at the hip joint.

  • Differences in Male and Female Pelvis:

    • The female pelvis is generally wider and has a larger pelvic inlet to accommodate childbirth, whereas the male pelvis is narrower and more robust.

  • Pubic Symphysis: Joins the two pubis bones at the midline, containing fibrocartilage.

Lower Limb

  • Major Components:

    • Thigh: Femur (longest bone in the body), articulates with the acetabulum of the pelvis.

    • Leg: Tibia and fibula, with the tibia being the weight-bearing bone.

  • Femur: Notable features include the neck, greater and lesser trochanters, and medial and lateral condyles.

  • Tibia: Forms the knee joint (superior end) and articulates with the talus at the ankle (distal end). Key features include the medial malleolus and tibial tuberosity.

  • Fibula: Lateral bone of the leg, providing stability to the ankle but not involved in the knee joint.

Foot Anatomy

  • Composed of tarsals, metatarsals, and phalanges:

    • Tarsals: 7 bones including talus (articulates with the tibia) and calcaneus (heel bone).

    • Metatarsals: 5 long bones in the foot numbered 1 (big toe) to 5 (little toe).

    • Phalanges: 14 total with similar structure to hand phalanges, with each toe possessing proximal, middle, and distal phalanges except for the big toe.

  • Foot's structure allows it to support body weight and enable movement over uneven terrain, with arches providing stability during movement.

Development and Changes

  • At birth, the proportion of the head and trunk to lower limb length is different than in adults. Changes occur until the age of 10 when the lower limb to trunk ratio equalizes.

  • Throughout middle age, bones may lose mass, leading to conditions like osteoporosis.

  • Notable disorders include hip dysplasia and variations in leg length, potentially leading to other complications.

Conclusion

  • A comprehensive understanding of the appendicular skeleton involves examining each component's structure, function, and their interconnections, as well as the implications for human evolution and functionality in daily activities.