Touch

• The skin is the receptor organ for tactile (touch), heat and pain sensations.

• There are 3 layers

The Epidermis• Is the waterproof outer skin layer

• made of dead cells, varying in thickness depending where they are found

• Are continuously replaced by cells from underneath

• At the bottom of the epidermal layer is a layer of basal cells

• Among these basal cells are melanocytes containing melanin *

• Melanin is the brown pigment that protects us from the sun’s harmful radiation

• The more sun exposure the more melanin is produced, “tanning”

• Over exposure to these harmful rays can cause mutations in the melanocytes causing melanoma (a deadly form of skin cancer) or basal cell carcinoma

• The epidermis is the main line of defence against the invasion by bacteria and other environmental dangers. *

Epidermis (2 parts)

• Dead layer• Living layer – new cells push old cells to the

surface. This helps with the healing process

The Dermis

• Constitutes the second layer of the skin

Dermis

• Sensory receptors• Blood vessels• Sebaceous glands – secrete oil that makes the

skin waterproof• Sweat glands • Hair• (Muscles)

The Subcutaneous Tissue or hypodermis

• Found under the dermis • Made of adipose tissue (fat)• Not uniformly spread in the body• Thicker in the hip• than in the eyelids *

How we “feel”• In the dermis there are sensors that detect

light pressure, touch, temperature, and pain and change it into a nerve impulse.

• The information is sent to the brain through the spinal chord

• The touch receptors are not spread out evenly over the body

• There are more touch receptors in the fingers and face, especially the lips, than in any of the other areas or the body

• If the human body were drawn proportionally according to the number of touch receptors we would look like this *

The Non Tactile function of the skin

Besides being a tactile receptor organ the skin has other functions:

1) First line of defence against bacteria

2) Protect the body against ultraviolet radiation

3) Thermal regulation of the body

4) Excretion of certain substances

5) Production of vitamin D *

Thermal regulation

• When the body temp reaches a certain level the blood vessels under the skin dilate (open up) allowing more blood to flow and give off body heat.

• Sweat glands produce sweat that evaporates from the skin producing a cooling effect.

• When the body temp drops below a certain level the blood vessels under the skin constrict slowing down the blood flow and conserving the body heat. *

Excretion of certain substances (see excretion notes)

• The sweat glands are involved with maintaining the mineral balance in the blood by excreting sweat, which contains urea, water and minerals. (similar to dilute urine)

Production of vitamin D• The skin contains cholesterol which when exposed

to the sun’s radiation is converted to Vitamin D.• *

• Vitamin D is needed for the absorption of calcium and phosphorus essential for proper bone development

• in the winter when we are not exposed to the sun’s radiation, it is important to drink milk enriched with Vitamin D or take cod liver oil which is also rich in vitamin D. *

The Nose (smell)

• Besides filtering, warming and humidifying air the nose’s other job is as an olfactory (smell) organ.

• The top of the nose is formed by 2 bones – nasal bones

• The end of the nose is made of cartilage *

• The olfactory membrane (smell area) is located in the top of the nasal cavity

• this area has specialized nerve cells that detect odours called the olfactory bulb.

• The nose can detect about 10,000 different odours

• The information is sent

to the olfactory area of the

brain by the olfactory nerve

For a substance to be perceived by the nose 4 conditions must be met:

1. It must be odoriferous, of a chemical nature that stimulates the smell receptor cells

2. It must be volatile (gaseous), transported by the air

3. It must be in a sufficient concentration to stimulate receptor cells

4. It must come into contact with the receptor cells(not blocked by mucus)

The Tongue (taste)

• The tongue is the organ that has receptors (taste buds) to capture flavour molecules

• The information is sent to the brain through the gustatory nerve

Tongue

• Taste only gives 10% of the information• Smell gives 90% of the experience of taste

Flavour detection• The tongue can only detect flavourful

molecules of the following 4 basic flavours:• Bitter• Sour• Salty• Sweet

For a substance to be tasted, 4 conditions must be met:

1. It must have a taste

2. It must be able to dissolve in saliva

3. It must be in a sufficient concentration to stimulate receptor cells

4. It must come into contact with the taste receptor cells

Senses ReviewSense (type of stimulus)

Receiver (organ)

Transformer Conductor Analyzer

Sight Eye Retina Optic Nerve BrainSound Ear Cochlea Auditory

NerveBrain

Taste Tongue Taste buds Gustatory Nerve

Brain

Touch Skin Dermis Spinal Chord BrainSmell Nose Olfactory

MembraneOlfactory

NerveBrain