Appendicular Skeleton Overview

THE APPENDICULAR SKELETON NOTES

Introduction

  • These notes are based on a lecture by Dr. Kori Filipek about the appendicular skeleton.

Review of the Axial Skeleton

  • Components: The axial skeleton consists of the following elements:

    • Skull: 22 bones

    • Ossicles: 6 bones (the small bones in the ear)

    • Hyoid: 1 bone (supports the tongue)

    • Vertebrae: 24 bones (in the spine)

    • Sacrum: 1 bone (a fusion of five vertebrae)

    • Coccyx: 1 bone (the tailbone)

    • Sternum: 1 bone (breastbone)

    • Ribs: 24 bones (12 pairs)

  • Characteristics: The axial skeleton has many complex features critical for protecting internal organs and providing structural support.

  • Teeth: Humans have 20 deciduous (baby) teeth and between 28-32 permanent teeth, depending on the presence of wisdom teeth.

Aims of the Week

  • Focus on the appendicular skeleton.

  • Engage in questions during breaks to enhance understanding.

Definition of the Appendicular Skeleton

  • The term 'appendicular' comes from "appendage," which refers to limb structures.

  • Components Include:

    • Limbs: Upper and lower limbs.

    • Shoulder Girdle: Connects the arm to the trunk.

    • Pelvic Girdle: Connects the legs to the trunk.

  • Notable Feature: Unlike the axial skeleton, all elements of the appendicular skeleton are paired, which implies there are two of each (one for the right and one for the left side).

Bones of the Upper Limb

  • Upper limb Composition:

    • Humerus: the bone of the upper arm.

    • Radius and Ulna: two bones of the forearm.

    • Carpals: 8 wrist bones (trapezium, trapezoid, capitate, hamate, lunate, scaphoid, triquetral, pisiform).

    • Metacarpals: 5 bones in the palm.

    • Phalanges: 14 finger bones (proximal, middle, and distal phalanges).

Bones of the Lower Limb

  • Lower Limb Composition:

    • Femur: the thigh bone.

    • Tibia and Fibula: bones of the lower leg.

    • Tarsals: 7 ankle bones (calcaneus, talus, navicular, cuboid, medial cuneiform, intermediate cuneiform, lateral cuneiform).

    • Metatarsals: 5 bones in the foot.

    • Phalanges: 14 toe bones (proximal, middle, and distal phalanges).

Shoulder Girdle: Structure and Composition

  • Composition of the Shoulder Girdle:

    • Clavicle (collarbones): connects the upper limb to the body.

    • Scapula (shoulder blades): supports the arm and connects with the humerus.

  • Clavicle Description:

    • The flat end is known as the acromial end (lateral) and the round end as the sternal end (medial).

    • Development completes between the ages of 25 and 30.

Scapula (Shoulder Blade) Anatomy

  • Structure of the Scapula:

    • Key Features:

    • Acromion: the highest point of the scapula that also forms an articulation with the clavicle.

    • Coracoid Process: supports the cup-shaped glenoid cavity.

    • Glenoid Cavity: the socket for the humeral head.

    • Subscapular Fossa: a depression on the anterior side.

    • Borders & Angles:

    • Superior border, medial border, lateral border.

    • Inferior angle and superior angle.

  • Ossification Centers: There are at least 7 ossification centers that include the body, coracoid, acromion, and various borders and angles of the scapula.

  • Development Timeline: Significant development occurs by age 1 and continues until age 6.

Humerus (Upper Arm Bone)

  • Humerus Overview:

    • Characteristics include the humeral head, anatomical neck, greater and lesser tuberosities, and various grooves for muscle attachment.

    • The humerus can be viewed from anterior and posterior aspects, detailing its structure:

    • The Anatomical Neck separates the head from the shaft.

    • Greater Tuberosity and Lesser Tuberosity are sites for muscle attachment.

    • The Deltoid Tuberosity is where the deltoid muscle attaches.

    • The Surgical Neck is a common site for fractures.

    • Features of the distal end include the trochlea and capitulum, which form joints with the forearm bones.

Radius and Ulna (Forearm Bones)

  • Radius:

    • Anatomy includes:

    • Neck, Head, Radial Tuberosity, Styloid Process.

    • The radius is considered the lateral bone of the forearm when in anatomical position.

  • Ulna:

    • Key features include the Coronoid Process, the Trochlear Notch, and the Olecranon.

    • The ulna is the medial bone of the forearm, forming the inner structure of the elbow joint.

  • Articulations: Both bones include various articulating surfaces conducive to joint movement.

Lower Limb Structure

  • Pelvic Girdle: Composed of the os coxae and sacrum, which provide support to the lower limbs.

  • Os Coxae Composition:

    • Comprised of three fused bones:

    • Ilium

    • Ischium

    • Pubis

  • Connection with Axial Skeleton: The os coxae forms the acetabulum (hip socket) and fuses during puberty.

  • Femur: The longest bone in the body, with key characteristics including the head, neck, trochanters, and major articulation points at the knee.

  • Tibia and Fibula: The tibia is the larger bone that supports weight, while the fibula provides lateral support.

Tarsal Bones and Foot Structure

  • Tarsals: Eight bones in the ankle, including the calcaneus and talus, arranged according to their position.

  • Metatarsals: Comprising five bones forming the arch of the foot.

  • Phalanges: Comprised of proximal, middle, and distal phalanges in the toes, mirroring finger structure but adapted for weight distribution.

Joint Classification

  • Amphiarthrosis (Cartilaginous): e.g., the pubic symphysis allows some movement.

  • Diarthrosis (Synovial): Joints that allow free movement such as in the shoulder, knee, hip, and sacroiliac joints.

Development Overview

  • The timing of ossification centers varies between bones in both the upper and lower limbs.

  • Key Milestones: For many structures, significant ossification occurs by age 1, with completion around age 6.