Skin, Smell, Taste

Our brain receives sensory nformation from the environment through 5 special sensations. They are

1. Touch
2. Smell
3. Taste
4. Hearing 
5. Vision

 Skin 

• Skin is the outermost covering of the body.
• The sensation of touch is subserved by the skin.
• It is the largest organ in the body.
• Skin contains glands, hair, nails and 2 layers, which are:
• Epidermis 
• Dermis

Epidermis

It is made of stratified squamous epithelium.

It has 5 layers

1. Stratum corneum
2. Stratum lucidum
3. Stratum granulosum
4. Stratum spinosum
5. Stratum germinatium

Stratum germinatium contains melanocytes which synthesise a pigment called melanin which is responsible for the colour of the skin.

Dermis

It is made of connective tissue.

Hairs

They arises from the hair follicles.

They are attached to erector pilae muscle.

During sympathetic stimulation like fear, excitement, exposure to cold etc. the hair stands erect.

Glands

Two types of glands are present in the skin

1. Sabeceous glands which secrete oily sebum
2. Sweat glands are of 2 types
1. Aporice sweat glands presnet in axilla, genital area and around nipple
2. Eccrine sweat glands which are responsible for heat regulatory mechanism.

 Functions of the skin 

1) Protective function

• Melanin pigment absorbs ultraviolet rays and prevents the tissue damage by ultraviolet radiation.
• Skin acts as a barrier to invasion of harmful agents like bacteria and toxic chemicals.

2) Sense perception

• The receptors present in the the skin helps in sensory perception.

3) Temperature regulation

• Skin helps in dissipiation of heat from the body by conduction, convection & radiation there by helping the regulation of temperature in the body.

4) Water balance

• Skin doesnot allow large amount of water to pass through it this helping the water balance of the body.

5) Elimination

• Substance such as urea is excreted in sweat though the skin.

 Smell 

• The sense of smell is called olfaction.
• The receptors for smell are olfactory receptors which are present in the roof of the nasal cavity.

Olfactory pathway

Olfactory receptors

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Through Cribriform plate

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Olfactory bulb

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Second order neurons project on to olfactory area in the sensory cortex

Olfactory pathway

Unique feature of olfaction

• Humans can differentiation 2000 to 4000 different smells
• Olfactory receptors are highly adaptable which is known as olfactory fatigue.
• Smell pathway do not relay in the thalamus unlike other sensations.

Application & Implication in Nursing

• Anosmia – loss of sense of smell
• Hyposmia – reduced ability to smell

 Taste 

The sensation of taste is known as Gustation.

The receptors for taste sensation are chemoreceptors present on the tongue, glottis, soft palate & pharynx.

The taste buds are embedded in papillae present on the the surface of tongue.

There are 4 types of papillae

1. Fungiform papillae
2. Filiform papillae
3. Circumvillate papillae
4. Foliate papillae

In humans there are about 10,000 taste buds which decline after age.

Taste buds

They are oval shaped cluster of cells containing gustatory receptors cells & sustenticular/supporting/basal cells.

Structure of Taste bud

Taste pathway

Taste pathway

Anterior 2/3rd from 7th cranial nerve and Posterior 1/3rd from 9th and 10th cranial nerve

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Medulla

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Post central gyrus (Sensory cortex)

Types of taste sensations

1. Sweet
2. Salt
3. Sour
4. Bitter
5. Umami

Types of taste sensations

Application & Implication in Nursing

• Flavour: it is a complex sensation consisting of taste, odour, roughness/smoothness, hotness/coldness, pungent/blandness.
• Aguesia: Complete loss of taste sensation
• Dysgeusia: Partial loss of taste sensation

Disorders of taste sensation are seen in salivary gland infections, sinusitis, poor dental hygiene.