Human Physiology

Lesson 45 : Special Sensory Organs (Nose, Tongue & Skin)

Taste Buds

Taste buds present in the oral cavity and function as to give the taste of the ingested food. In human there are four primary sensations of taste, sour, salty, sweet and bitter. The perception of taste to food varies with individual and to its own ecological needs. The taste bud is consisting of modified epithelial cells called taste cells. Each taste cell has a minute taste pore at the centre and at the tip a number of taste hairs that are projected into the oral cavity which function as receptor surface for the taste. These hairs detect the substance that comes in contact and change the potential of taste cell membrane, where it generate an impulse in the taste nerve fibers that convey to the brain (pons and medulla).

Skin

Skin is the largest single organ in the body. It covers the entire surface of the body. It functions to protect the internal environment of the body from the external environment.

Parts of the skin and functions
The human skin composed of two main layers:

1. The external stratified epithelial portion called epidermis
2. The deeper layer called dermis or corium

There is a loose connective tissue layer below the dermis called hypodermis.

Epidermis varies in thickness depending on its location. It is thickest on friction areas of the skin, e.g. palms of the hands, soles of the feet, and thinnest on the lips and eyelids. The epidermis has a series of projections called dermal papillae and is found in soles and palms that are inherited and unique to each individual e.g. fingerprints, footprints. The epidermis is divided into four layers or strata, namely, germinativum, granulosum, lucidum and corneum layers, through these layers the renewal of cells take place constantly by mitotic cell division. Skin appendages derive from epidermis, namely, glands, hair and nails.
Glands are exocrine whose secretory units are located in the dermis and are connected to epidermis through excretory ducts e.g. sweat gland (eccrine and apocrine sweat glands), ceruminous glands, mammary glands and sebaceous glands.
Hair follicle which produces and supports the hair, distributed over the surface of the body. It gives a great protection to thermal and radiation injury, act as efficient filter and insulator.
Nails are protective keratinized appendages.
The dermis, also called the corium or cutis is a sheet of fibrous connective tissue of the skin that supports and maintains the overlying epidermis. It consists of two layers, namely, superficial papillary through which oxygen and nutrients are pass to epidermis by diffusion. The other layer was deep reticular layer and is elastic in nature.
Hypodermis is a sheet of adipose connective tissues lying between dermis and organs. The hypodermal fat serves as fat reservoir, an insulator, and a temperature-regulating device.

Summary

Nervous system is structurally and functionally most complex system of body. Basic cell of nervous system is neuron which acts by way of generating electrical potentials (called nerve impulse) that propagates and transmitted along nerve fibers, crosses the synapse to reach another neuron in the chain and so on. These electrical signals, ultimately through specific neurotransmitter chemicals, regulates the functions of specific organs. The nerve impulse performs both excitatory and inhibitory functions. One particular function in an organ can be suppressed or stimulated by a separate nerve connected to separate inhibitory or excitatory nucleus in brain or spinal cord. Nerves carry information in both directions by separate nerves. Those carrying information away from CNS are motor nerves and those carrying towards CNS are sensory nerves. Special peripheral receptors help in recognizing particular stimulus (external conditions) and transmit them to CNS for their recognition and initiating suitable action. Special sensory organs are designed to perceive particular stimuli such as eyes for photoreception, ear for sound vibration perception, olfactory epithelium for smell and taste buds for sensation etc. Overall nervous system is involved in regulating all body functions and maintains suitable physiological conditions necessary for survival of human body.