Skin, Connective Tissue, Cutaneous Nerves & Nervous System Development

Vocabulary practice flashcards covering skin anatomy, subcutaneous injection routes, connective tissue, fascia, cutaneous receptors, dermatomes, and early embryonic development of the nervous system.

Epidermis

A keratinized stratified squamous epithelial tissue that forms the outer barrier of the skin and is completely avascular, receiving nutrients by diffusion from capillaries in the underlying dermis.

Layers of Epidermis (Deep to Superficial)

Stratum basale, stratum spinosum, stratum granulosum, stratum lucidum (thick skin only), and stratum corneum.

Thick Skin vs Thin Skin

Thick skin ($\sim 0.48\,\text{mm}$, 6 times thicker than thin skin) is located on palms and soles, contains stratum lucidum and numerous sweat glands, and lacks hair follicles; thin skin ($\sim 0.08\,\text{mm}$) covers most of the body and generally contains hair follicles.

Papillary Layer of Dermis

The superficial 20% layer of the dermis composed of loose (areolar) connective tissue, dermal papillae, capillaries, and sensory receptors that feed the epidermis.

Reticular Layer of Dermis

The deeper 80% layer of the dermis composed of dense irregular connective tissue with collagen and elastic fibers that provide strength and flexibility.

Hypodermis

Subcutaneous connective and adipose tissue beneath the dermis that anchors, insulates, cushions, and provides pathways for larger blood vessels and nerves (not technically part of the skin).

Injection Route Angles

Intramuscular (IM) at 90°, Subcutaneous (SC) at 45°, Intravenous (IV) at 25°, and Intradermal (ID) at 10° - 15°.

First-Pass Metabolism Bypass

Injection routes (IV, IM, SC, ID) bypass gastrointestinal absorption and hepatic first-pass metabolism, but they do not bypass systemic exposure to the liver or kidneys.

Connective Tissue Composition

Body tissue consisting of cells embedded within an extracellular matrix composed of ground substance, collagen fibers, elastic fibers, and reticular fibers.

Superficial Fascia

A connective tissue network located deep to the skin that contains variable amounts of loose connective tissue and adipose tissue.

Deep Fascia

Dense connective tissue that surrounds, invests, and separates muscles and muscle groups into fascial compartments.

Free Nerve Endings

Cutaneous sensory receptors widely distributed in the epidermis and dermis that detect pain, temperature, itch, and crude touch.

Merkel Discs

Mechanoreceptors in the stratum basale (especially abundant in fingertips) specialized for fine/discriminative touch and sustained pressure.

Meissner Corpuscles

Mechanoreceptors located in dermal papillae (abundant in glabrous skin) specialized for light touch and low-frequency vibration.

Pacinian Corpuscles

Specialized mechanoreceptors located in the deep dermis and subcutaneous tissue that detect deep pressure and high-frequency vibration.

Ruffini Endings

Cutaneous sensory receptors located in the deep dermis that detect skin stretch and sustained pressure.

Glabrous Skin

Hairless, highly sensory skin specialized for tactile discrimination.

Eccrine Glands vs Sebaceous Glands

Eccrine sweat glands use merocrine secretion onto the skin surface for thermoregulation, while sebaceous glands use holocrine secretion of sebum into hair follicles for lubrication and skin/hair protection.

Dermatome

A region of skin supplied primarily by sensory fibers from one single spinal nerve root.

Peripheral Nerve Territory

A region of skin supplied by a specific named peripheral nerve.

Gastrulation

The embryological process reorganizing the bilaminar disc (epiblast and hypoblast) into a trilaminar disc composed of ectoderm, mesoderm, and endoderm.

Neurulation

The process during the third week of embryonic development where the notochord signals overlying ectoderm to form the neural plate, neural groove, and closed neural tube.

Neural Tube Derivatives

Ectodermal derivatives that form the Central Nervous System (brain and spinal cord), ventricular system, and central canal.

Neural Crest Derivatives

Cells originating from the neural folds that form Peripheral Nervous System structures (dorsal root ganglia, autonomic ganglia, Schwann cells, satellite cells), melanocytes, adrenal medulla, and parts of the craniofacial skeleton.

Alar Plate

The dorsal/posterior region of the developing neural tube that serves a sensory function and gives rise to the posterior (dorsal) gray horn of the spinal cord.

Basal Plate

The ventral/anterior region of the developing neural tube that serves a motor function and gives rise to the anterior (ventral) gray horn of the spinal cord.

Primary Brain Vesicles

The three early divisions of the neural tube formed by day 28: Prosencephalon (forebrain), Mesencephalon (midbrain), and Rhombencephalon (hindbrain).

C6 Nerve Root Involvement

Clinical presentation characterized by sensory deficits along the lateral forearm and thumb combined with motor weakness during wrist extension.