Anatomy & Physiology Study Guide: Bones, Joints, Muscles, and Nervous Tissue

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 serves as an attachment site for several muscles and articulates with the humerus and clavicle.

• Key Landmarks:

  • Spine: A prominent ridge running across the posterior surface.

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

  • Coracoid process: A hook-like projection on the anterior surface.

  • Glenoid cavity: A shallow socket that articulates with the head of the humerus.

  • Suprascapular notch: Located at the superior border, passage for the suprascapular nerve.

  • Subscapular fossa: Broad concavity on the anterior surface.

  • Infraspinous fossa: Large area below the spine on the posterior surface.

  • Medial, lateral, and superior borders: Edges of the scapula.

  • Inferior and superior angles: Corners of the scapula.

• Example: The acromion is palpable at the top of the shoulder and is a common site for muscle attachment.

Bones of the Hand

The human hand consists of multiple bones organized into phalanges, metacarpals, and carpals. Proper identification of these bones is essential for understanding hand anatomy and function.

• Phalanges: The fingers contain proximal, middle, and distal phalanges. The thumb (pollex) has only proximal and distal phalanges.

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

• Carpals: Eight carpal bones form the wrist.

• Ulnar styloid process: A bony prominence on the distal end of the ulna, palpable on the medial side of the wrist.

• Pisiform: A small, pea-shaped carpal bone on the medial side of the wrist.

• Example: In anatomical diagrams, the right hand is identified by the position of the thumb (lateral in anatomical position) and the ulnar styloid process (medial).

Pelvic Bones

Coxal Bone Anatomy

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

• Medial View: Shows the inner surface facing the sacrum and pelvic cavity.

• Lateral View: Shows the outer surface, including the acetabulum (hip socket).

• Key Markings:

  • Acetabulum: Articulates with the head of the femur.

  • Sacrum: The bone that articulates with the medial aspect of the coxal bone.

• Example: The medial view of the right coxal bone displays the auricular surface for sacral articulation.

Joints and Joint Types

Classification 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 type of cartilaginous joint where bones are joined by hyaline cartilage. Typically immovable (synarthrosis).

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

• Example: The epiphyseal plate in growing bones is a synchondrosis; the knee and shoulder are synovial joints.

Synovial Joint Structure

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: Covers the ends of bones, reducing friction and absorbing shock.

• Synovial membrane: Lines the joint capsule and secretes synovial fluid for lubrication.

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

• Ligaments: Bands of connective tissue that reinforce the joint.

• Example: The shoulder joint (glenohumeral joint) is a synovial joint with a loose capsule for extensive mobility.

Knee Joint Anatomy

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

• Key Structures:

  • FCL (Fibular Collateral Ligament): Provides lateral stability.

  • 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.

• Example: Injury to the ACL is common in athletes and can lead to joint instability.

Muscle Structure

Connective Tissue Layers of Muscle

Skeletal muscle is organized into bundles surrounded by connective tissue layers that provide support and transmit force.

• Endomysium: Thin connective tissue surrounding individual muscle fibers.

• Perimysium: Connective tissue that groups muscle fibers into fascicles.

• Epimysium: Dense connective tissue that surrounds the entire muscle.

• Example: The perimysium holds muscle fascicles together, allowing coordinated contraction.

Sarcomere Structure and Function

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

• Key Components:

  • A band: Contains thick filaments; does not change length during contraction.

  • I band: Contains thin filaments; shortens during contraction.

  • H zone: Central region of the A band; shortens during contraction.

  • M line: Center of the sarcomere, where thick filaments are anchored.

  • Z disc: Defines the boundaries of each sarcomere; anchors thin filaments.

  • Thick filaments: Composed of myosin.

  • Thin filaments: Composed of actin, troponin, and tropomyosin.

• Example: During muscle contraction, the I band and H zone decrease in width, but the A band remains unchanged.

Component	Changes During Contraction?
A band	No
I band	Yes (shortens)
H zone	Yes (shortens)

Nervous Tissue

Myelinated vs. Unmyelinated Axons

Axons in the nervous system may be covered by a myelin sheath, which affects the speed and efficiency of nerve impulse transmission.

• Myelin Sheath: An insulating layer composed of protein and fatty substances, 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.

• Unmyelinated Axons: Lack a myelin sheath; impulses travel more slowly as the entire membrane must be depolarized.

• Example: Loss of myelin sheaths, as seen in multiple sclerosis, can result in symptoms such as vision loss, numbness, weakness, or paralysis.

Feature	Myelinated Axon	Unmyelinated Axon
Impulse Speed	Fast	Slow
Cell Type (CNS)	Oligodendrocyte	None
Cell Type (PNS)	Schwann cell	None

White Matter

White matter in the CNS appears white due to the high concentration of myelinated axons. Myelin's lipid-rich composition gives it a pale color.

• Function: Facilitates rapid transmission of nerve impulses between different regions of the brain and spinal cord.

• Example: The corpus callosum is a major white matter tract connecting the two cerebral hemispheres.

Additional info: Academic context and expanded explanations have been added to ensure completeness and clarity for exam preparation.