In addition to tasting, seeing, feeling, hearing and smelling, humans can orient themselves with the help of their depth sensitivity. This ability enables him to assume a certain position and perform movements. If it is disturbed, accidents and disabilities occur in daily life.
What the depth sensitivity?
Depth sensitivity is composed of position sense, movement sense and force sense. In addition, there is the sense of body position in space. Depth sensitivity (bathyesthesia) refers to the part of self-awareness that relates to the perception of stimuli within the body. These deeper body regions are muscles, tendons and joints. With the help of its ability to perceive, the body continuously informs the spinal cord and the brain about its position, posture, the position (e.g. of the limbs). The depth sensibility is composed of position sense, movement sense and strength sense. In addition, there is the sensation of the body’s position in space. The receptors necessary for receiving the stimuli (proprioceptors) are, for example, tendon spindles (Golgi apparatus) and muscle spindles in the skeletal muscles. In the connective tissue of the joint capsule, fibers register every change in speed and direction. The Golgi apparatus monitors muscle tone. Once the stimuli are perceived, they are transmitted to the spinal cord, where they are immediately responded to by triggering a specific reflex. Then a message is sent to the brain. The sensory impression is evaluated there and answered with a reaction. It consists, for example, in a change in body posture. A large part of the processes involved in proprioception takes place subconsciously. Our psyche reacts with this protective mechanism in order not to be overwhelmed with information. In the process, conscious and subconscious depth perceptions use different pathways to the brain. Proprioception works 24 hours a day without interruption, even during sleep.
Function and task
Through depth sensitivity, a person is able to assess what position his body is in (sitting, standing, etc.). He can accurately assess his posture during a particular movement or at rest. For example, he recognizes that his right foot is not exactly next to his left or that he is bending his upper body slightly forward. Humans can also assess their applied force and experienced resistance by means of certain stimuli. The three arcades in the organ of equilibrium of the ear convey an accurate picture of the three-dimensionality of space. In the atrial sacs, which are also located there, there are receptors that register the smallest changes in speed and transmit them to the organs of the periphery, where the corresponding actions are triggered. Noticing that the speed of rotation has changed, for example, enables the child riding the merry-go-round to accurately recognize its parents standing a little further away. The motor system is controlled by the sense of force and movement. There are conscious and unconscious actions that are performed with muscle power. Through certain receptors in the eye muscles, humans are able to recognize the extent of space and their bodies as a whole. If movements associated with muscle contractions then occur, the person feels positive emotions. The importance of depth perception for human beings can be seen, for example, in the unsteady gait of people who are under the influence of alcohol. They are no longer able to walk in a straight line and fall down because they misjudge the distance between the ground and their own feet. Alcohol interferes with the stimuli transmitted by the receptors from inside the body.
Diseases and ailments
Impaired depth sensitivity can lead to general hyposensitivity. The affected person can no longer control his movements and appropriately dose the associated exertion of force. Some patients refrain from movement altogether because their muscle tone is too low. Another disorder of depth perception is syringomyelia. In this very rare disease, a more or less large cavity filled with cerebrospinal fluid (syrinx) is located in the spinal cord at the level of the cervical spine. The cavity is filled with dead nerve cells that expand and press on the surrounding nerves, causing neurological deficits.The health disorder is congenital or acquired through an accident. The first symptoms usually appear in the second decade of life. The patient has severe neck, arm, shoulder and head pain and numbness in his limbs. Since he does not know where his arms and legs are, he can no longer control their movements. He has spastic or flaccid paralysis, impaired vision, hearing, speech or swallowing. The inability to make coordinated movements causes unsteady gait and falls. If the affected person also develops circulatory problems due to syrinx, his or her skin feels cold and sometimes shows a bluish discoloration. Depending on the extent of the condition, the doctor may treat his patient with physiotherapy and pain therapy. In severe cases, surgery is required. Usually, a permanent shunt is placed or foramen magnum decompression surgery is performed to remove cerebrospinal fluid and relieve pressure.
