What is the largest organ in the human body?

The brain

The liver

The skin

The Skin as a Receptor for

Stimuli

Three basic layers of skin

Sub-cutaneous

Layers of the skin• Epidermis (2 parts):

1) dead layer (outermost)

• Cells we see on the surface of the skin

2) living layer (under the dead layer):

• cells are continually multiplying

(process that is very important in the healing of

wounds)

• Contains melanin = brown pigment responsible

for the differences in skin colour

Albinism• Albinos don’t produce melanin and

therefore have white or pinkish skin (due to the presence of blood)

• African people have a high concentration of melanin in their skin

Layers of the skin

The Dermis contains:

– Nerve endings

– Blood vessels

• These supply the skin with oxygen and nutrients

• Help regulate body temperature

– Roots of the hair

• At the base of the hair follicle are muscle fibers

known as erector pili muscles

• These muscles cause the hair to stand up when

the body shivers from cold

Dermis (continuation):– Sebaceous glands (secrete sebum)

• Sebum is an oily substance whose main purpose is to

make the skin and hair waterproof and to protect them

from drying out

– Sweat glands (eliminates wastes- excretory system, lowers

body temp)

Subcutaneous layer contains:– Fat cells (lipids)

• Energy storage

• Insulates the body against variations in air temperature

Non-sensory functions of the skin(ie. What does the skin do, other than allow you to feel

things?)

1. Protection from burns, infections, the sun, insects, etc.

2. Excretion of sweat and nitrogenous wastes

3. Vitamin D production

• Vitamin D is a fat-soluble vitamin that is used by the body in the absorption of calcium.

• Sun’s UV rays convert fatty deposits of subcutaneous layer into Vit. D

• It is recommended people get 10 to 15 minutes of sunshine 3 times a week

The main sensations perceived by the receptors (nerve endings) in the skin

1. Tactile sensations (touch/pressure)

2. Painful sensations

3. Thermal sensations (hot & cold)

The structures responsible for the sensations perceived by the skin:

• Specialized nerve endings

– Also known as “dendrites”

• Most are covered by a protective oval capsule = called corpuscles

1010

• Different sensations you feel are due to different types of nerve endings (receptors) (receptors)

(each type of receptor responds to only one type of stimulus- these are distributed unevenly over the entire surface of the body)

• Tactile sensations: received by touch & pressure receptors (these nerve endings are protected by corpuscles)

• Thermal sensations: received by heat & cold receptors (these nerve endings are also protected by corpuscles)

• Painful sensations: received by pain receptors (these nerve endings are not protected by corpuscles)

Skin as a receptor for stimuli

1212

How are sensations (touch, temperature, pain) transmitted to the brain?

1. Receptors (tactile corpuscles) are excited

(electrical impulse) by a stimulus (temp, pain,

touch).

2. The nerve impulse then travels to the brain via

the sensory nerve in the spinal cord

3. Only when the brain receives the nerve impulse,

the sensation perceived

The sense of touch involves:

• Receiver = the skin

– Receives sense of touch (light, soft, hot, cold, painful)

• Transformer =Nerve endings of the skin

– Transforms touch into a nerve impulse (action potential)

• Conductor = – Sensory nerves of the spinal cord

– Conduct the nerve impulses

• Analyzer = – the brain (centre for sensory information)

– Analyses the incoming nerve impulses

Levels of burns (fire, sun, etc.)• The depth of a burn determines its severity.

– First degree burns damage the outer layer of skin

(epidermis) and cause pain, redness and swelling

(erythema)

– Second degree burns damage the epidermis and the

inner layer, the dermis, causing erythema and

blistering.

– Damage from third degree burns extend into the

hypodermis (sub-cutaneous), causing destruction of

the full thickness of skin with its nerve supply

(numbness). Third degree burns leave scars and may

cause loss of function and/or sensation.

1616

Skin diagram to labelWord bank: dermis, melanocyte (cell which produces malanin), subcutaneous tissue, sweat gland, blood vessels, erector pili muscle, sebaceous gland, epidermis, Pacinian corpuscle, hair follicle

19

Take home• There are 3 layers of skin

– Dermis• dead layer• living layers

– Epidermis• blood vessels• nerve endings• hair roots• sebaceous glands• sweat glands

– sub-cutaneous• fat cells

19

20

• The non-sensory functions of the skin are:– Protection– Sweat (homeostasis)– Production of vitamin D

20

21

• Different nerve endings produce different types of sensations:– Thermal– Painful– Tactile

21

22

• Receiver = skin• Transformer = nerve endings of the skin• Conductor = nerves of the central nervous

system• Analyzer = brain

22