Eyebrows Flashcards
Where is the eyebrow located?
Between the superior orbital rim (margin) and superior nuchal line
What are the 4 layers of the eyebrow?
Skin
Connective tissue (dense)
Aponeurosis (muscle)
Loose connective tissue
Periosteum
What is the function of the skin in the eyebrow?
Barrier to the outside environment - prevent microbes from causing infections in underlying tissue
What are the 3 layers of skin in the eyebrow?
Epidermis: outermost layer
Dermis
Hypodermis: innermost layer
What cells make up the epidermis?
Keratinocytes
Melanocytes
Langerhan cells
Merkel cells
What are the characteristics and function of keratinocytes?
Epithelial cell; 90% of cells.
Produce fibrous protein - keratin.
Provide structure and water-resistant properties
What are the 4 layers of keratinocytes in progressive stages of differentiation?
- Stratum basale: undergo mitosis and migrate through the other layers
- Stratum spinosum
- Stratum granulosum: cells lose their nucleus and become more flattened (aka dying)
- Stratum corneum: dead, flattened cells filled w keratin
What is desquamation?
Cells are shed every few weeksW
What is the function of melanocytes?
Produce pigment (melanin) that filters UV light
What is the function of Langerhan cells?
WBC that plays a role in immune response
What is the function of Merkel cells?
Attach to nerve endings to form “light touch” receptors.
Ex. feeling a piece of hair on you
Is the epidermis vascular or avascular? If avascular, what does it rely on for nutrient supply?
Avascular; relies on dermis for blood supply
What is the epidermis attached to?
Basement membrane - connects epithelial cells to underlying surface
What type of barrier does the basement membrane have?
Partial barrier - allows only water and small molecules to pass into the dermis
What is the dermis composed of?
Connective tissue, WBCs, and adnexal structure
What are fibroblasts?
Cells that produce collagen and elastin?
What is the function of collagen?
Structure and tensile strength
What is the function of elastin?
Elasticity and enabling movement
What is ground substance?
Transparent gel composed of water, glycosaminoglycans, and proteoglycans
What is embedded in ground substance?
Connective tissue elements
What are the adnexal structures found in the dermis?
Hair follicles, hair, sebaceous glands, sweat glands
What is the hypodermis composed of?
Aka subcutaneous tissue.
Mainly composed of adipose and loose connective tissue, which allows the upper layers to move as one
What is dense connective tissue composed of?
Fibroblasts, collagenous fibers, elastic fibers, adhesive proteins, ground substance
What is the function of dense connective tissue?
Connect skin to underlying muscle
What are the 4 muscles that influence eyebrow contour and position?
- Frontalis
- Corrugator
- Procerus
- Orbicularis oculi
What nerve innervates all 4 muscles that influence eyebrow contour and position?
CN VII (facial nerve)
Where is the frontalis muscle located and what is its function?
Location: Vertical fibers originate high on the scalp and insert near supraorbital margin.
Function: elevates brow –> surprised look
Where is the corrugator muscle located and what is its function?
Location: oblique fibers originate from the supraciliary arch and insert into the medial forehead.
Function: depresses medial brows –> vertical wrinkles in glabella–> confused/concentrated look
Where is the procerus muscle located and what is its function?
Location: vertical fibers originate from nasal bone and insert into medial forehead.
Function: depresses medial brows –> horizontal wrinkles across bridge of nose –> aggressive/mad look
Where is the orbicularis oculi muscle located and what is its function?
Location: oblique fibers originate from medial orbital rim to encircle the eye and insert into lateral palperal ligament.
Function: depresses the brows & protracts eyelids
What is loose connective tissue composed of?
Fibroblasts
Collagenous fibers
Elastic fibers
Adhesive proteins
Ground substance
What is the function of loose connective tissue?
Connects top 3 layers (tightly bound to each other) to the underlying periosteum
What is the “danger zone?”
Loose CT - pus and blood spread easily and infections can pass into cranial cavity through veins.
Get very bad very quick
What is the function of the periosteum?
Point of connection; covers bone
What is the periosteum composed of?
Dense, irregular connective tissue.
Osteogenic cells.
Osteoblasts
What are osteogenic cells?
Stem cells that divide and differentiate into osteoblasts
What do osteoblasts form?
Bone matrix
What are the functions of eyebrows?
Shield liquids from dripping into the eye and from bright light above.
Facial expressions
