Anatomy of Back and Trunk Muscles

Nervous System Innervation

• Intrinsic back muscles are primarily innervated by posterior primary rami (PPRs); few have specific names.
• Trunk muscles like pectoralis major and latissimus dorsi are innervated by the brachial plexus; trapezius receives innervation from cranial nerve XI.
• Peripheral nerves arise from nerve plexuses and typically receive inputs from multiple anterior primary rami (APRs).
• Example: The femoral nerve serves the anterior thigh, receiving contributions from L2-L4 APRs, which also supply other nerves like the obturator.
• Most peripheral nerves carry both sensory and motor fibers; these fibers can separate as they approach targets.
• Dermatomes represent skin areas innervated by single spinal nerve roots, while sensory distributions differ among individual peripheral nerves.
• Myotomes refer to muscle groups innervated by specific spinal nerves, and understanding these is crucial for physical therapy (PT).

Nerve Plexuses

• Plexuses are networks formed from APRs of spinal nerve roots in specific regions.
• The brachial plexus derives inputs from C5-T1, producing five primary terminal branches and numerous smaller branches.

Relevance to Physical Therapy

• Injuries can affect spinal and peripheral nerves, requiring PTs to differentiate injuries based on the location of damage.
• A thorough understanding of spinal and peripheral nerve organization and function is essential for effective assessment and intervention in PT.

Sensory Innervation

• Sensory information travels along fibers from peripheral receptors (skin, muscles, joints) entering the spinal cord via the dorsal root.
• Cell bodies for peripheral sensory nerves are located in specific ganglia.
• Review of dermatomal distributions is important for ongoing applications in the PT field.

Motor Innervation

• Skeletal muscle receives motor signals from anterior horn cells via ventral roots through to spinal and peripheral nerves.
• Knowledge of myotomes is essential for identifying which muscles are innervated by specific spinal nerve roots.

Spinal Nerves vs Named Peripheral Nerves

• Peripheral nerves consist of spinal nerve components; trunk nerves often simply continue from spinal APRs.
• Named peripheral nerves from the lumbar plexus (e.g., iliohypogastric, ilioinguinal) also innervate abdominal muscles and skin.

Integumentary System Overview

• Comprises skin, hair, nails, sweat and sebaceous glands, subcutaneous fat, deep fascia, and mucous membranes.
• Skin types include thin hairy skin (most of the body) and thick hairless (glabrous) skin (palms, soles of feet).

Functions of the Integumentary System

• Protection against abrasions, chemicals, UV rays, and fluid loss; immune defense through cell turnover and barrier to microorganisms.
• Thermoregulation via sweat and blood flow; insulation through subcutaneous fat; sensory communication; vitamin D synthesis; and excretion via sweat.

Layers of the Skin

• Epidermis composed of stratified squamous keratinized epithelium for protection.
• Dermis mainly consists of dense irregular connective tissue.
• Hypodermis features loose connective tissue, often adipose, mediating skin mobility, acting as a shock absorber and thermal insulator.

Skeletal System Overview

• Axial skeleton includes cranium, vertebral column, ribs, and sternum; vertebral composition includes cervical, thoracic, lumbar, sacral, and coccygeal categories.
• Appendicular skeleton encompasses limbs and girdles.
• Bone functions include protection, support, movement, blood cell formation, and salt storage.

Types of Bone and Cartilage

• Types of cartilage include strong, load-bearing fibrocartilage and elastic cartilage, which provides flexibility.
• Most cartilage is avascular and relies on diffusion for nutrition; perichondrium provides vascular and lymphatic supply.

Arthrology and Joint Classification

• Joints classified as fixed (e.g., sutures) and movable (e.g., synovial joints like hinge, pivot).
• Movable joints can be further categorized into uniaxial, biaxial, and triaxial, affecting the movements allowed (gliding, angular, rolling).

Muscular System Overview

• Muscle types include skeletal (voluntary), smooth (involuntary, non-striated), and cardiac (involuntary, striated).
• Function classification for skeletal muscle encompasses movement, heat production, postural control, and protection.
• Motor units consist of a motor neuron and its innervated muscle fibers, with architecture varying across muscle types (e.g., pennate, fusiform).

Explore the intricate anatomy of muscles that contribute to the movement of the back and upper extremities. This quiz delves into the innervation of intrinsic back muscles and connection to cranial nerves. Test your knowledge of key muscle groups and their innervation pathways.