Chemical Senses

Chemical Senses (Smell and Taste)

Sense of Smell Olfaction (also known olfactics or smell) refers to the sense of smell. This sense is meditated by specialized sensory cells of the nasal cavity of vertebrates, and sensory cells of the antennae of invertebrates. For air breathing animals, the olfactory system detects volatile or, in the case of accessory olfactory system, fluid-phrase chemicals. For water-dwelling organism, e.g., fish or crustaceans, the chemicals are present in the surrounding aqueous medium. Olfactory, along with taste, is a form of chemoreception. The chemicals themselves which activate the olfactory system, generally at very low concentrations, are called odors. Olfactory system or nerve is the first cranial nerve which conveys smell sensations from nose to brain; nerve endings are specialize in detecting stimuli. Nerve fibers pass from the receptors through tiny holes in the root of nasal cavity and comes together to form a bulb.

Sense of Taste Gustatory sensation is the sensation that results when taste buds in the tongue and throat convey information about the chemical composition of a soluble stimulus. The inability is called ageusia.

Body Senses Sense of Touch It is a sense by which size, shape, surface, texture, temperature can be ascertained by physically contact. Signals from touch receptors via sensory nerves to spinal cord then to thalamus and on to the sensory cortex. The largest part in our body is our skin. It weights from six to ten pounds. It is made of two layers; the epidermis or the top layer, and the dermis or the bottom layer. The top part of epidermis is a layer of dead skin cells. These flake off and are replaced all the time. The skin contains hair follicles, nerve endings, sweat glands, and blood vessels. The skin is the main organ of the sense of touch. The skin is the outer covering of living tissue of an animal (or plant). It is the largest organ of the integumentary system made up of multiple layers of epithelial tissues, and guards the underlying muscle, bones, ligaments, and internal organs.

Sense of pain It is localized sensation ranging for mild to severe and excruciating experience stimulation of these receptors leads to transmission of pain messages to brain.

Kinesthetic Sense Kinesthesis refers to sensory input that occurs within the body. Postural and movement information are communicated via sensory systems by tension and compression of muscles in the body. Even when the body remains stationary, the kinesthetic sense can monitor its position. Humans possess three specialized types of neurons responsive to touch and stretching that help keep track of body movement and position. The first class, called Pacinian corpuscles, lies in the deep subcutaneous fatty tissue and response to pressure. The second class of neurons surrounds the internal organs, and the third class is associated with muscle, tendons, and joints. The neurons work in concert with one another and with cortical neurons as the body moves.

Sense of Balance and Acceleration The vestibular system, which is a contributor to our balance system and our sense of spatial orientation, is the sensory system that provides the dominant input about movement and equilibrioception. Together with the cochlea, a part of the auditory system, it constitutes the labyrinth of the inner ear, situated in the vestibulum in the inner ear. As our movements consist of rotations and translations, the vestibular system comprises two components: the semicircular canal system, which indicate rotational movements; and the otoliths , which indicate linear translations. The vestibular system sends signals primarily to the neural structures that control our eye movements, and to the muscles that keeps us upright. The projections to the former provide the anatomical basis of the vestibule-ocular reflex, which is required for clear vision; and the projections to the muscles that control our posture are necessary to keep us upright.

Sense of Temperature Thermoception is the sense of heat and the absence of heat (cold) by the skin and including internal skin passages. The thermoceptors in the skin are quit different from the homeostatic thermoceptors in the brain (hypothalamus) which provide feedback on internal body temperature.