Bones of the Upper Limb and Shoulder

Scapula Anatomy

The scapula, or shoulder blade, is a flat, triangular bone that forms the posterior part of the shoulder girdle. It provides attachment points for muscles and articulates with the humerus and clavicle.

• Key Landmarks:

  • Spine: Prominent ridge on the posterior surface.

  • Acromion: Lateral extension of the spine; articulates with the clavicle.

  • Coracoid process: Anterior projection for muscle attachment.

  • Glenoid cavity: Shallow socket for the head of the humerus.

  • Suprascapular notch: Passage for the suprascapular nerve.

  • Borders: Superior, medial (vertebral), and lateral (axillary).

  • Angles: Superior, inferior, and lateral.

  • Fossae: Subscapular (anterior), supraspinous and infraspinous (posterior).

• Clinical Application: Fractures of the scapula are rare but may occur with high-energy trauma.

Bones of the Hand

The human hand consists of phalanges (finger bones), metacarpals (palm bones), and carpals (wrist bones). Proper identification of these bones is essential for understanding hand anatomy and function.

• Phalanges: Each finger has three phalanges (proximal, middle, distal), except the thumb, which has two.

• Metacarpals: Five metacarpal bones form the palm, numbered I-V from thumb to little finger.

• Carpals: Eight carpal bones form the wrist.

• Key Landmarks:

  • Ulnar styloid process: Bony prominence on the distal ulna.

  • Pisiform: Small, pea-shaped carpal bone.

• Example: In the labeled diagram, A = Distal phalanx V, B = Proximal phalanx V, C = Metacarpal V, D = Distal phalanx I, E = Metacarpal I.

Bones of the Pelvic Girdle

Coxal Bone Anatomy

The coxal bone (hip bone) is a large, irregular bone forming the pelvis. It consists of three fused parts: ilium, ischium, and pubis.

• Views:

  • Medial view: Shows the inner surface, including the sacroiliac joint area.

  • Lateral view: Shows the acetabulum, where the femur articulates.

• Key Markings:

  • Acetabulum: Socket for the femoral head.

  • Sacrum: Articulates with the medial aspect of the coxal bone.

• Example: The medial view of the right coxal bone shows the articulation with the sacrum.

Joints and Their Classification

Types of Joints

Joints, or articulations, are connections between bones that allow for varying degrees of movement. They are classified based on structure and function.

• Synchondrosis: A cartilaginous joint where bones are joined by hyaline cartilage; typically immovable (e.g., epiphyseal plate in children).

• Synovial Joint: Freely movable joint characterized by a synovial cavity, articular cartilage, and a joint capsule.

• Degree of Movement:

  • Synarthrosis: Immovable joint.

  • Amphiarthrosis: Slightly movable joint.

  • Diarthrosis: Freely movable joint (all synovial joints).

Structure of a Synovial Joint

Synovial joints are the most common and movable type of joint in the body. They have a complex structure that allows for a wide range of motion.

• Articular cartilage: Hyaline cartilage covering bone surfaces within the joint.

• Synovial membrane: Produces synovial fluid for lubrication.

• Fibrous layer: Outer layer of the joint capsule providing strength.

• Ligaments: Bands of connective tissue stabilizing the joint.

• Example: The knee joint includes articular cartilage, synovial membrane, fibrous capsule, and stabilizing ligaments.

Knee Joint Anatomy

The knee joint is a complex synovial joint involving several important structures for stability and movement.

• Key Structures:

  • FCL (Fibular Collateral Ligament): Stabilizes the lateral aspect.

  • ACL (Anterior Cruciate Ligament): Prevents anterior displacement of the tibia.

  • PCL (Posterior Cruciate Ligament): Prevents posterior displacement of the tibia.

  • Menisci: Medial and lateral fibrocartilaginous pads that cushion and stabilize the joint.

Muscle Tissue Structure

Connective Tissue Layers of Muscle

Skeletal muscle is organized into bundles surrounded by connective tissue layers, each with a specific function.

• Endomysium: Thin connective tissue surrounding individual muscle fibers.

• Perimysium: Connective tissue surrounding bundles of muscle fibers called fascicles.

• Epimysium: Dense connective tissue surrounding the entire muscle.

• Which layer holds a muscle fascicle? The perimysium surrounds and holds muscle fascicles.

Sarcomere Structure

The sarcomere is the basic contractile unit of muscle fiber, composed of organized thick and thin filaments.

• Key Components:

  • A band: Dark region containing thick filaments (myosin).

  • I band: Light region containing thin filaments (actin).

  • H zone: Central region of the A band with only thick filaments.

  • M line: Center of the sarcomere, anchoring thick filaments.

  • Z disc: Boundary of the sarcomere, anchoring thin filaments.

  • Thin filament: Composed mainly of actin.

  • Thick filament: Composed mainly of myosin.

• Which part does not change length during contraction? The A band remains the same length during muscle contraction.

Nervous Tissue: Myelination

Myelinated vs. Unmyelinated Axons

Axons in the nervous system may be myelinated or unmyelinated, affecting the speed and efficiency of nerve impulse transmission.

• Myelin Sheath: An insulating layer of protein and fatty substances that surrounds axons, produced by Schwann cells in the peripheral nervous system (PNS) and oligodendrocytes in the central nervous system (CNS).

• Function: Increases the speed of electrical impulse conduction via saltatory conduction.

• Symptoms of Myelin Loss: May include vision loss, numbness, weakness, paralysis, and loss of bladder/bowel control (e.g., multiple sclerosis).

• Unmyelinated Axons: Conduct impulses more slowly because the action potential must propagate along the entire membrane.

• Why is White Matter White? White matter appears white due to the high concentration of myelinated fibers.

Summary Table: Muscle Connective Tissue Layers

Summary Table: Types of Joints

Key Formula: Muscle Contraction

The sliding filament theory describes muscle contraction as the sliding of actin (thin) filaments past myosin (thick) filaments, shortening the sarcomere:

Additional info: Academic context and terminology have been expanded for clarity and completeness.