OPT114 eyebrows

Where are eyebrows located?

Between the superior orbital rim (margin) and superior nuchal line

What are the 5 layers of of the eyebrow?

Skin, dense connective tissue, muscle, loose connective tissue, and periosteum (not a true layer)

What are the functions of the skin of eyebrow?

Barrier to the outside environment (prevents microbes from causing infections in underlying tissue)

What are the layers of the skin?

epidermis, dermis, hypodermis

Outermost layer of skin

epidermis

What cells compose the epidermis?

Keratinocytes, melanocytes, langerhans cells, merkel cells

What cell composes 90% of cells in epidermis?

Keratinocytes

What is the function of keratinocytes?

Produce the fibrous protein keratin that provides structure and water-resistant properties

What are keratinocytes layers based on stages of differentiation?

-stratum basale (inner) - only layer where cells undergo mitosis
-stratum spinosum (next layer)
-stratum granulosum (3rd layer) - cells lose their nucleus and become flattened
-stratum corneum (outer)- dead, flattened cells filled with keratin where cells shed every few weeks

What is desquamation?

Shedding off of dead skin cells

Cell within epidermis that produce melanin pigment

melanocytes

Why is melanin important for the epidermis layer?

Filter UV light to protect from DNA damage

What is the type of white blood cell found in epidermis?

Langerhans cells

Why are Langerhans cells important in the epidermis?

Play a role in immune response to protect against pathogens

What cells within the epidermis attach to nerve endings to form the "light touch" receptors?

Merkel cells

Why does the epidermis rely on the dermis for blood supply?

Epidermis is avascular

The epithelial cells are connected the the underlying dermis by:

basement membrane

Why is the basement membrane important?

Serves as a partial barrier allowing only water and small molecules to pass into the dermis

What is the dermis composed of?

Connective tissue (fibroblasts, collagenous fibers, elastic fibers, adhesive proteins, and ground substances), WBCs, adnexal structures

What do fibroblast produce?

collagen and elastin

Why is collagen important in the dermis?

Provides structure and tensile strength

Why is elastin important in the dermis?

provides elasticity which enables movement

What is ground substance?

a transparent gel composed of water, glycoaminoglycans, and proteoglycan

Why is ground substance important?

All other connective tissue of the dermis is imbedded in the ground substance and other substances travel through it

What are adnexal structures of the dermis?

Adnexal structures attach to an organ (skin) so that would include hair follicles, hair, sebaceous (oil) glands, and sweat glands

What is significant about eyebrow hairs in embryological development?

They are the first body hairs produced

Layer below the skin that is mainly composed of adipose and loose connective tissue

hypodermis

-Composed of fibroblasts, collagenous fibers, elastic fibers, ground substance, and adhesive proteins
-along with arteris, veins, and nerves

Describe dense connective tissue:

What is the function of dense connective tissue?

connect the skin to underlying muscle

What are the four muscles that influence eyebrow contour and position?

frontalis, corrugator, procerus, and orbicularis oculi

muscle with vertical fibers that originate high on the scalp and insert near the supraorbital margin

frontalis muscles

What does the frontalis muscle do?

Elevate the brows (look of surprise)

Muscle with oblique fibers that originate from the supraciliary arch and insert into the medial forehead

corrugator muscle

What does the corrugator muscle do?

Depresses the medial brows forming vertical wrinkles in the glabella (look of trouble or concentration)

Muscle with vertical fibers that originate from the nasal bone and insert into the medial forehead

Procerus muscle

What does the procerus muscle do?

Depresses the medial brows forming horizontal wrinkles across the bridge of the nose (look of menace or aggression)

Muscle with oblique fibers that originate from the medial orbital rim (maxillary and lacrimal bones) to encircle the eye and insert into the lateral palpebral ligament

Orbicularis oculi

What does the orbicularis oculi do?

-Depresses the brows
-protracts (closes) the eyelids

What nerve is innervated by all four muscles?

CN VII (facial nerve)

What is loose connective tissue composed of?

fibroblasts, collangenous fibers, elastic fibers, adhesive proteins, and ground substance

What is the function of the loose connective tissue?

Connect the top 3 layers (tightly bound to each other) to the underlying periosteum

Why is loose connective tissue called the danger zone?

Pus and blood can spread easily in this layer and infections can pass into the cranial cavity through veins

What is the periosteum composed of?

dense irregular connective tissue, osteogenic cells, and osteoblasts

What are osteoblasts?

cells from osteogenic cells that form bone matrix

What is the function of periosteum?

covers bone

What are the functions of the eyebrows?

-shield liquids from dripping into the eye
-shield bright light from above
-plays a role in aging
-crucial to facial expressions

What happens during muscle atrophy of eyebrows?

eyebrows (and eyelids) can droop and wrinkles form