Epidermis (ep-uh-DER-mis): The outermost layer of the skin, composed of keratinized stratified squamous epithelium; it is avascular and provides the primary protective barrier against the environment. Contains: stratum basale (basal layer), stratum spinosum (spiny layer), stratum granulosum (granular layer), stratum lucidum (translucent layer – primarily in thick skin), and stratum corneum (corny layer).
Dermis (DER-mis): The layer of connective tissue located deep to the epidermis; it provides structural support, houses blood vessels, nerves, hair follicles, and glands, and is divided into the papillary (loose) and reticular (dense irregular) layers.
Sudoriferous gland (Sweat gland) (soo-duh-RIF-uh-rus gland): Exocrine glands located deep in the dermis or hypodermis; their function is to produce and secrete watery sweat for thermoregulation or in response to anxiety/stress (fight or flight response).
Sebaceous gland (sih-BAY-shus gland): Simple, branched alveolar exocrine glands that typically empty their oily secretion (sebum) into a hair follicle; they use a holocrine mechanism of secretion to lubricate the skin and hair.
Hair follicle receptor (Root hair plexus) (hair FOL-ih-kul ri-SEP-ter): A fine, web-like network of sensory free nerve endings that wraps around the base of a hair follicle; it detects movement of the hair shaft.
Free nerve ending (free nerv EN-ding): The simplest and most common type of sensory receptor in the skin; it is an unencapsulated receptor composed of unmyelinated terminal branches of sensory neurons that penetrate the epidermis and detect pain, temperature, and crude touch.
Type I cutaneous mechanoreceptor (Merkel cell) (type wun kyoo-TAY-nee-us mek-uh-noh-ri-SEP-ter/Mur-kull sell): A sensory complex consisting of a tactile epithelial cell (Merkel cell) in the epidermis associated with a single large, myelinated sensory axon terminal; it is an unencapsulated receptor that detects sustained pressure and deep touch.
Tactile corpuscle (Meissner's corpuscle) (TAK-til KOR-pus-ul/MYZ-nerz KOR-pus-ul): An encapsulated oval receptor found primarily in the dermal papillae of the dermis (especially in sensitive, hairless skin like the fingertips); it is responsible for detecting light touch and low-frequency vibration.
Type II cutaneous mechanoreceptor (Ruffini corpuscle) (type too kyoo-TAY-nee-us mek-uh-noh-ri-SEP-ter/roo-FEE-nee KOR-pus-ul) A large, elongated encapsulated receptor located deep in the dermis and hypodermis; it is specialized to detect sustained pressure, continuous deformation, and skin stretch.
Lamellar corpuscle (Pacinian corpuscle) (LAM-uh-ler KOR-pus-ul/puh-SIN-ee-un KOR-pus-ul): A very large, onion-shaped encapsulated receptor found deep in the dermis and hypodermis; it is specialized to detect high-frequency vibration and deep pressure.
Encapsulated receptors (en-KAP-suh-lay-ted ri-SEP-ters): Sensory nerve endings in the skin (e.g., tactile corpuscles, lamellar corpuscles) where the axon terminal is enclosed by a capsule of connective tissue and/or Schwann cells; the capsule enhances the sensitivity to specific mechanical stimuli.
Unencapsulated receptors (un-en-KAP-suh-lay-ted ri-SEP-ters): Sensory nerve endings in the skin (e.g., free nerve endings, Type I cutaneous mechanoreceptors) that lack a surrounding connective tissue capsule; they are typically bare nerve endings.