Eyebrow Structure Flashcards
Where are eyebrows located?
Between the superior orbital rim and superior unchallenged line
What are the 5 layers of the eyebrows?
Skin, dense CT, muscle, loose CT, periosteum
What is the purpose of the skin of the eyebrows?
Barrier to outside environment, preventing microbes from causing infections in underlying tissues
What are the layers of the skin?
Epidermis, dermis, and hypodermis
What is the epidermis?
Outer avascular layer, composed of many cells, attached to basement membrane
What cells make up the epidermis of the eyebrow?
Keratinocytes, melanocytes, langerhan, Merkel
What are keratinocytes?
Epithelial cell, 90% of the epidermis, produce fibrous protein keratin that provides structure and water resistant properties
What are the 4 layers of keratinocytes in progressive stages of differentiation?
Stratum basal (inner) spinous, granulosum, corneum
What is stratum basal?
Inner epithelial cell layer of keratinocytes, the only cells in the layer that undergo mitosis and then migrate through other layers
What is stratum granulosum?
The layer of the keratinocytes in the epidermis where cells lose their nucleus and become more flattened
What is stratum corneum?
The outer keratinocyte layer of the epidermis composed of dead, flattened cells filled with keratin, cells shed every few weeks (desquamation)
What are melanocytes?
Cells in the epidermis that produce melanin pigment that filters UV light
What are langerhans cells?
A WBC in the epidermis playing a role in the immune response
What is a merkel cell?l
Attached to nerve endings in the epidermis to form “light touch” receptors
What does the basement membrane attached to the epidermis do?
Connects epithelial cells to the underlying dermis, serves as a partial barrier allowing only water and small molecules to pass into the dermis
What is the dermis of the eyebrow skin?
Connective tissue, WBCs, and adrenal structures
What makes up connective tissue?
Fibroblasts, collagenous fibers, elastic fibers, adhesive proteins, ground substance
What are fibroblasts?
Cells that produce collagen and elastin
What is collagen?
Protein providing structure and tensile strength
What is elastin?
Protein providing elasticity and enabling movement
What is ground substance?
Transparent gel composed of water, glycosaminoglycans, and proteoglycans
What is the role of ground substance?
Connective tissue elements are embedded in it and substances travel through it
What are a decal structures of the dermis?
Hair follicles, hair, sebaceous glands, sweat glands
What is the first body hair produced during embryologic development?
Eyebrows
What is the hypodermis of the eyebrow composed of?
Adipose and loose connective tissue
What is dense connective tissue made of?
Fibroblasts, collagenous fibers, elastic fibers, adhesive proteins, ground substance
What does dense CT do?
Connects skin to underlying muscle and contains arteries, veins, and nerves supplying the eyebrows
What for muscles influence eyebrow contour and position?
Frontalis, Corrugator, Procerus, and orbicularis oculi
What innervates the four muscles of the eyebrow?
voluntary muscles, CN VII facial
What is the frontalis?
Vertical fibers originate high on scalp and insert near the Supra orbital margin
What does the frontalis do?
Elevates the brow “surprise”
What is the Corrugator?
Oblique fibers originate from the supraciliary arch and insert into the medial forehead
What does the corrugator do?
Depresses the medial brows forming vertical wrinkles in the glabella (look of trouble or concentration)
What is the procerus?
Vertical fibers originate from the nasal bone and insert into the medial forehead
What does the procerus do?
Depresses the medial brows forming a horizontal wrinkle across the bridge of the nose (look of menace or aggression)
What is the orbicularis oculi?
Oblique fibers originate from the medial orbital rim (maxillary and lacrimal bones) to encircle the eye and insert into the lateral palpebral ligament
What does the orbicularis oculi do?
Depresses the brows and protracts (closes) the eyelids
What is loose CT of the eyebrows composed of?
Fibroblasts, collagenous fibers, elastic fibers, adhesive proteins, ground substance
What is the purpose of the loose CT of the tissue?
Connects the top 3 layers (tightly bound to each other) to the underlying periosteum
Why is the loose CT of the eyebrow considered the danger zone?
Pus and blood can spread easily in this layer and infections can pass into the cranial cavity through veins
What area of the eyebrows is considered the danger zone?
Loose connective tissue
What is the periosteum of the eyebrow composed of?
Dense, irregular connective tissue (fibroblasts, collagenous fibers, ground substance), osteogenic cells and osteoblasts
What are osteogenic cells?
Stem cells that divide and differentiate into osteoblasts that form the bone matrix
What does the periosteum cover?
Bone
What are the 4 roles of the eyebrows?
Shields liquids from dripping into the eye, shields from bright light above, plays a role in aging, crucial to facial expressions
