Eyebrow structure Flashcards
Eyebrows are located between the ____ and _____.
Superior orbital rim/margin (most superior part of the bony orbit) and superior nuchal line (fossa)
How many layers does the skin of the eyebrow have?
5: S- skin C- connective tissue (dense) A- Muscle instead of aponeurosis L- loose connective tissue P- periosteum
(Skin, dense connective tissue, muscle, loose connective tissue and the periosteum)
Function of the skin
Barrier to the outside environment. Prevents microbes from causing infections in underlying tissue.
What is the skin composed of
Epidermis, dermis, and hypodermis.
Characteristics of the epidermis (superficial layer of the skin)
Composed of keratinocytes (90%). There are 4 stages of keratinocytes in progressive stages of differentiation.
Keratinocytes
An epithelial cell found in the epidermis that produces keratin, a fibrous protein that provides structure and water resistant properties.
There are 4 layers of keratinocytes within the epithelium that are in progressive stages of differentiation.
4 stages of keratinocyte differentiation from bottom to top
Stratum basale (inner)- only these cells can undergo mitosis and then migrate through the other layers.
Stratum spinosum- Cells start degrading/losing organelles
Stratum granulosum- cells lose nucleus and become flattened
Stratum corneum (outer)- dead, flattened cells filled with keratin. Cells are shed every few weeks in a process known as desquamation.
Desquamation
Dead, flattened epithelial cells shedding off the stratum corneum and being replaced by cells below.
4 layers of the epidermis
Stratum basale (big) Stratum spinosum (spiders) Stratum granulosum (get) Stratum corneum (crushed)
4 Cell types in the epithelium
90% keratinocytes
10% melanocytes, langerhans, and merkel cells
Melanocytes
Found in the epidermal layer- usually depicted in a brown color. They produce melanin that filters UV light
Langerhans cells
Type of white blood cell found in the epidermis. Play a role in the immune system.
Where does the epidermis get it’s blood supply
From the dermis. The epidermis is avascular.
What connects the epidermis to the dermis?
The basement membrane connects epithelial cells to the underlying dermis.
Role of the basement membrane
Connects the epithelial cells of the epidermis to the dermis. Also seres as a partial barrier- allowing only water and small molecules to pass into the dermis.
What is the dermis composed of
Composted of connective tissue (fibroblasts, collagen fibers, elastic fibers, adhesive proteins, and ground substance), white blood cells, and adnexal structures (additional/attached/within an organ)
Fibroblasts
The main cells found in the dermis, dense connective tissue, loose connective tissue, and periosteum that produce collagen and elastin
Collagen- protein that provides structure and tensile strength.
Elastin- protein that provides elasticity and enables movement.
What cell type produces collagen and elastin?
Fibroblasts of the dermis
Ground substance
Transparent gel composed of water, glycosaminoglycans (GAGs) and proteoglycans (GAG + protein). All other connective tissues are embedded in it, such as fibroblasts, collagen fibers, elastic fibers, proteins…)
Adnexal structures include
Hair follicles, hair, sebaceous glands, and sweat glands
Fun fact about eyebrow growth in the womb
They are the first body hairs produced
Three layers of the skin
Epidermis, dermis, and hypodermis
Deepest layer of the skin
Hypodermis
What is the hypodermic composed of
Adipose and loose connective tissue
Another name for the hypodermis
Subcutanous
Dense connective tissue
1 layer below the epidermis and composed of fibroblasts, collagenous fibers, elastic fibers, ground substance and adhesive proteins.
Contains arteries, veins, and nerves supplying the eyebrows.
What does dense connective tissue connect
Connects the skin (epidermis, dermis, and hypodermis) to the underlying muscle. Arteries, veins, and nerves travel through this layer to reach the hypodermis and dermis.
Which four muscles influence eyebrow contour and position
Frontalis, corrugator, procesrus, and orbicularis oculi
Frontalis muscle is located where, gives a look of what and is innervated by which nerve
Vertical fibers originate high on the scalp and insert near the supraorbital margin. Elevates the brows and gives a look of surprise.
Innervated by the CN VII (facial nerve)
Corrugator muscle is located where, gives a look of what and is innervated by which nerve
Oblique fibers originate from the supracilary arch and insert into the medial forehead.
It depresses the medial brows and forms vertical wrinkles in the glabella.
Look of trouble or concentration.
Innervated by the CN VII (facial nerve)
Procerus muscle is located where, gives a look of what and is innervated by which nerve
Vertical fibers originate from the nasal bone and insert into the medial forehead.
Depresses the medial brows forming horizontal wrinkles across the bridge of the nose.
Look of penance or aggression.
Innervated by CN VII (facial nerve)
Orbicularis oculi muscle is located where, gives a look of what and is innervated by which nerve
Oblique fibres originate from the medial orbital rim (maximally and lacrimal bones) to encircle the eye and insert into the lateral palpebral ligament.
Depresses the brows and protracts (closes) the eyelids.
Innervated by the CN II (facial nerve)
What is loose connective tissue composed of
Composed of fibroblasts, collagenous fibers, elastic fibers, ground substance and adhesive proteins.
What is the role of lose connective tissues
Connects the top three layers, which are highly bound to each other, to the underlying periosteum.
Why is the loose connective tissue of the skin considered the danger zone
Pus and blood can spread easily in this layer and infections can pass into the cranial cavity through veins.
Periosteum
Covers bone
What is periosteum composed of
Dense, irregular connective tissue (fibroblasts, collagenous fibers, ground substance, osteogenic cells and osteoblasts.)
Osteogenic cells
Stem cells that divide and differentiate into ostebclasts, which form the bone matrix.
Function of the eyebrow
Shields liquids from dipping into the eye. Shields from bright lights above and plays a role in aging. Crucial to facial expressions.
How does the eyebrow play a role in aging.
Muscle atrophy-eyebrow and eyelids can droop. and wrinkles will form.
The lateral palpebral ligament is located where
Between the lateral check ligament and the orbital septum/palpebral fascia
