A sensory organ converts external environmental stimuli into usable information for the organism. The stimuli converted into electrical impulses reach the brain via the nerve fibers and are processed there into the actual perceptions. Diseases of the individual sensory organs often lead to the failure of one of the five senses.
What are the sensory organs?
The human organism has five sensory organs. These process external environmental stimuli, such as light, sound, temperature, pressure, movement and chemical stimuli. The five sense organs include the eyes, ears, nose, tongue and skin. The eye can receive light stimuli with wavelengths between 380nm to 780nm via its receptors. These light stimuli are converted into images in the brain. The ear, in turn, is responsible for receiving sound impulses. Frequencies between 16 hertz and 20,000 hertz are perceived. Both eyes and ears are purely sensory organs, as they are only responsible for the reception and transmission of environmental stimuli. The nose, tongue and skin perform other functions in addition to processing sensory stimuli. For example, the nose contains in the olfactory mucosa the receptors for chemical stimuli triggered by scents and odors. However, its most important function is to maintain respiration. The tongue also has important functions to perform for chewing and speaking in addition to receiving chemical stimuli through the taste buds. At the same time, the skin, as the largest protective organ of the body, transmits stimuli such as temperature, pressure, or movement to the brain for information processing. Some animals have other sensory organs for perceiving specific environmental stimuli, such as electric and magnetic fields.
Anatomy and structure
The individual sensory organs differ significantly in structure. There are stimuli that evoke the corresponding perceptions only through multilevel processing. These include the light and sound stimuli. Therefore, the structure of eyes and ears is very complex. They are pure sensory organs because they have to concentrate on the processing of environmental stimuli. Such a complex structure is not necessary for processing chemical and mechanical stimuli. Simple receptors on the surface of the corresponding organs are sufficient for the reception of these stimuli. Therefore, the nose, tongue and skin are mainly responsible for other bodily functions in addition to stimulus reception. The eye, however, has a more complex structure and has an outer, middle and inner eye skin. The inner eye skin, as the retina, has many light-sensing cells that receive the light stimuli. The outer eye skin contains the sclera, which is connected to the eye muscles. In the middle eye skin, there are many blood vessels that supply the eye. The eye is spherical, with its largest part, the vitreous body, filled with a gel-like transparent substance. Furthermore, the eye has a variable lens, which serves to focus the image. The ear also has a complex structure. As an important sensory organ for sound processing, it consists of the outer ear with the typical relief elements, the middle ear with eardrum and ossicles, and the inner ear with two separate organs for the sense of balance and the sense of hearing.
Function and tasks
All sensory organs receive their respective environmental stimuli through specific receptors. Receptors, also called sensors, are target molecules for specific stimuli. They are located in special cells that are responsible for receiving the stimuli. Special proteins act as receptors, fulfilling their functions either as membrane receptors in the cell membrane or as nuclear receptors in the cell nucleus. According to the lock-and-key principle, they can connect with smaller molecules to which they have a specific fit. This reaction results in an excitation of the receptor, which is transmitted as an electrical impulse. There are different types of receptors that respond to different stimuli. For example, process or baroreceptors respond to pressure. In the ear, certain baroreceptors are necessary for processing sound because sound is produced by pressure changes in the air. Chemoreceptors are influenced by certain signal molecules or the change in PH. They are the prerequisite for the sensations of smell and taste. Photoreceptors are stimulated by photons (light) and are responsible for the function of the eyes. Thermoreceptors are sensitive to temperature.The sensory organ skin uses baroreceptors for the sense of touch or thermoreceptors for the sensation of temperature.
Diseases
In connection with the sensory organs, there are various health disorders that can lead to the limitation or even loss of certain senses. One example is the weakening of vision or complete blindness in certain eye diseases. Sight is also limited by a change in vision, as in nearsightedness, farsightedness, cataracts or glaucoma. A special form of defective vision is genetically caused color blindness. Glaucoma is caused by an increase in pressure in the vitreous humor of the eye. It can lead to total blindness if not treated. However, blindness can also be the result of severe diabetes. Among the most important diseases of the ear are various infections of the ear. Well known is the middle ear infection, which is well treatable, but in individual cases can lead to hearing loss. Hearing loss or even deafness can have many causes. These include infections, tumors, hearing loss, trauma, genetic defects or degenerative changes in old age. The other sensory organs can also show signs of failure. For example, the absence of the sense of smell is called anosmia and the absence of the sense of taste is called ageusia.
Typical and common nasal disorders
- Stuffy nose
- Nasal polyps
- Sinusitis
