Hear, see, taste, smell and feel
When you talk about senses, you probably think of the five classics: hearing, seeing, tasting, smelling and feeling. Not all scientists agree on the definition of our senses. It also seems more complicated than just the classic five.
The dictionary describes a sense organ as an organ capable of receiving external stimuli or the ability to receive external stimuli. So ear, eye, nose, tongue and skin or hearing, sight, smell, taste and feeling.
In practice, however, senses are involved in perception, but not the same. What you see is a conscious interpretation of light and before you actually hear sound vibrations, all kinds of processes have preceded it. The sensation thus takes place in the brain, after receptors have converted physical phenomena (light, vibration, molecules, etc.) into neural signals.
The senses
The first four of the classical senses, sight, hearing, smell, and taste are the special senses. Feeling is subdivided into three separate senses, which are mainly located in the skin. The so-called somatic senses: touch, thermoception (heat and cold) and nociception (pain).
In addition to the senses for conscious perception, a sense of balance and proprioception (muscle tension and stretch in tendons) are also distinguished. These senses mainly maintain body posture and ensure that you are aware of the presence of your body or a certain body part.
eyesight
You are probably familiar with the receptors in the eyes, the so-called rods and cones. These photoreceptors ensure that you can perceive light and color respectively and are located in the retina. The receptors convert light into impulses that are then conducted via the optic nerve to the visual cortex in the brain. The brain processes and interprets the information. So the actual seeing actually happens there.
hearing
The hearing responds to sound waves. These are routed through the outer ear and middle ear to the inner ear. The inner ear consists of the cochlea and the labyrinth. Attached to this is the auditory and balance nerve. The cochlea is filled with liquid and has a special membrane with small cilia. Movement of these cilia – as a result of amplified sound waves – provides a signal to the brain.
Sense of smell
There are many different olfactory receptors in the nose. These receptors are highly sensitive and selective. As a result, you are able to smell so many different substances. Each receptor is stimulated by a specific type of molecule. These impulses then travel through the olfactory nerve, the olfactory nerve, to the cerebral cortex, where actual smelling takes place.
sense of taste
The sense cells for taste are located in the taste buds on the tongue and in the back of the oral cavity. Unlike the olfactory epithelium, the taste bud is not as sensitive at all. You can only distinguish five tastes: sweet, sour, salty, bitter and umami. That is why smell also plays an important role in tasting. Three facial nerves ensure that taste gets to the brain. The information is then processed in the taste center.
sense of touch
The sensory cells of the sense of touch are also called mechanoreceptors. They respond to various impulses such as light touch, sustained touch, vibrations and pressure. You can find the receptors for the sense of touch in the skin, mucous membranes, throat and tongue. The distribution over the body is not even: your fingers, feet, lips and tongue, for example, have a lot of them. The back is a lot less sensitive, so there are fewer tactile cells there.
Thermoception
This sense allows you to feel cold and heat, thanks to the so-called thermoreceptors that occur in two places in your body. First of all spread over the body and especially in the skin: these are stimulated by the temperature of an object. In addition, you will also find thermoreceptors in the brain itself to monitor fluctuations in body temperature. In order to keep the body temperature ‘normal’, the brain controls both warming (teeth chattering, goosebumps) and cooling (widening skin pores, sweating) body processes.
nociception
Pain stimuli are not pleasant and for a reason. Pain must ensure that you avoid situations (now and in the future) that can lead to tissue damage. Nocireceptors (in the skin, joints and internal organs) are the sensory cells that are stimulated by pain. On the outside of the body a distinction is made between stabbing and dull pain, on the inside pain is dull or indefinable. As with the other senses, the actual sensation of pain takes place in the brain.
sense of balance
The sense of balance does not actually measure your balance, but looks at rotation and acceleration. Your eyes and impulses from the musculoskeletal system (vision and proprioception) play an important role in maintaining your balance.
The vestibular system is located in the inner ear, behind the petrous bone. It roughly consists of two parts: the three semicircular canals and two otolith organs (utricle and saccule). The sensory cells are located in both parts. Information from the vestibular system travels to the brain via the auditory vestibular nerve.
proprioception
Thanks to this last sense you can perceive the position of your body(s). The receptors are located in various places in the musculoskeletal system, including the muscles, tendons and joint capsules and ligaments. In the muscles themselves, the muscle spindles are the sensory cells, in the other tissues you will find other types. Changes in the position of the joints, muscle tension or muscle length cause stimuli. Some of the impulses are already processed in the spinal cord and directly fed back to the involved muscles. These are reflexes. The rest of the processing and perception takes place in the brain.
