Anatomy Introduction Overview

Osteology: 206 bones in the human skeleton: 80 in the axial skeleton and 126 in the appendicular skeleton

• Ossification

  • Intramembranous (direct laying down of bone without a cartilage model [skull]) or enchondral (with a cartilage

    precursor [most bones])

  • Enchondral growth begins in the diaphyses of long bones at primary ossification centers, most of which are present at birth.

    • Secondary ossification centers usually develop at proximal or distal ends of bones and are important for growth.

    • Frequently the site of pediatric physeal fractures

Arthrology: joints are commonly classified into three types on the basis of their freedom of movement.

• Synarthroses: joining of two bony elements with no motion during maturity (e.g., skull sutures)

• Amphiarthroses: have hyaline cartilage and intervening discs with limited motion (e.g., symphysis pubis)

• Diarthroses: characterized by hyaline cartilage, synovial membranes, capsules, and ligaments

Myology: classification based on the arrangement of muscle fibers

• Parallel (e.g., rhomboids)

• Fusiform (e.g., biceps brachii)

• Oblique (with tendinous interdigitation): further classified as pennate, bipennate, multipennate

• Triangular (e.g., pectoralis minor)

• Spiral (e.g., latissimus dorsi)

Nerves

Peripheral nerves

• Originate from the ventral rami of spinal nerves and are distributed via several plexuses (cervical, brachial, lumbosacral)

• The mnemonic “SAME” can be used to help understand the function of nerves: sensory = afferent; motor = efferent.

• Efferent (motor) fibers carry impulses from the central nervous system (CNS) to muscles.

• Afferent (sensory) fibers carry information toward the CNS.

Autonomic nerves

• Control visceral structures

• Consist of parasympathetic (craniosacral) and sympathetic (thoracolumbar) divisions

  • Preganglionic neurons of parasympathetic nerves

    • Arise in the nuclei of cranial nerves III, VII, IX, and X and in the S2, S3, and S4 segments of the spinal cord

    • Synapse in peripheral ganglia

  • Preganglionic neurons in the sympathetic system

  • Located in the spinal cord (T1–L3)

  • Synapse in chain ganglia adjacent to spine and collateral ganglia along major abdominal blood vessels

Vessels: arteries, veins, and lymphatic vessels