The Exteroception forms together with interoception the totality of human perception. Extroception is the perception of external stimuli by specialized sensory cells called extroceptors. The processing of the stimuli takes place in the central nervous system and can be disturbed in neurological diseases.
What is exteroception?
Human perception allows people to get an idea of themselves and their environment. The perception of internal stimuli and the perception of external stimuli make up the overall perceptual capacity of humans.
Internal stimuli are perceived from within the body and are therefore an important part of self-perception. External stimuli are all external environmental stimuli that allow people to perceive them externally.
Inner perception is interoception. The external perception is analogously called exteroception. It is made up of visual, auditory, gustatory, olfactory and vestibular perception. In addition, the sensitivity counts. Like internal perception, external perception also works with stimulus-specialized sensory cells called receptors.
The receptors of external perception are the extroceptors. They are responsible for the external stimulus absorption, the stimulus processing and the transmission of the stimulus information in physiologically processable form. The stimulus conduction takes place via afferent pathways and has the central nervous system as its goal, where the stimuli from the environment are combined with one another and enter the consciousness as a comprehensive image.
Function & task
The exteroceptors are the first place that external stimuli pass on their way into the human body. These receptors are each specialized for certain stimuli. Stimulus molecules bind to the designated locations and thus stimulate the receptor, which converts the stimulus into a physiological form of nerve excitation. For example, there are specialized extroceptors for measuring vibrations, touch, temperatures and many other external stimuli.
The opposite of the extroceptors are the interoceptors, which measure internal stimuli. Perceptual structures such as the deep sensitivity of the musculoskeletal system register both external and internal stimuli and can thus be referred to as interoceptors and exteroceptors at the same time.
The exteroceptors include receptors such as the Vater-Pacini corpuscles for the perception of vibrations or the Meissner corpuscles and Ruffini corpuscles for registering touch, pressure and pressure differences. The eye's photoreceptors are sensitive to light and the hair cells in the inner ear enable auditory perception.
The interconnection of all exteroceptors takes place via the first neuron to the second neuron. The cell bodies of exteroceptive nerve cells are located in the spinal ganglion. Their central processes cross the posterior cord tracts without switching or crossing and thus reach the nucleus gracilis or nucleus cuneatus. Only here is the information switched to the second neuron. The fibers emanating from there are called the fibrae arcuatae internae and extend towards the thalamus. In the Decussatio lemnisci medialis they are involved in an intersection. The fibers end in the nucleus ventralis posterior of the thalamus and the information from the exteroceptors is switched to the third neuron. This third neuron runs through the superior thalami or posterior crus of the internal capsule and from there reaches the primarily somatosensitive brain center in the postcentral gyrus. The Brodmann areas 3, 2 and 1 are located there. In addition to the storage, classification and interpretation of exteroceptive perceptions, an initial stimulus response may also take place in the brain.
Exteroception is described by some authors in epicritical sensitivity and protopathic perception divided. Epicritical sensitivity is defined as the perception of the finest touch, perception of vibrations and perception of pressure and is based on two-point discrimination. Information gathered in this way reaches the brain via the gracilis fasciculus and cuneatus fasciculus. The authors understand protopathic perception to be the perception of pain and temperature that is transmitted to the brain via the anterior lateral cord of the anterior and lateral spinothalamic tract.
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Exteroception can be irreversibly damaged by neurological diseases or traumatic lesions of the nerve structures involved and thus be permanently disturbed. Possible causative diseases in this context are, for example, central nervous diseases such as multiple sclerosis or peripheral nervous diseases such as polyneuropathy.
However, extroceptive disturbances of perception are not always preceded by actual nerve lesions. In some cases only the sensory integration of the external information is disturbed. This integration takes place in the brain and corresponds to the combination of several stimuli to form an overall stimulus image. The image of the surroundings is thus a product of the exact interaction of the individual senses. Disturbances in sensory integration prevent this interaction.
Sensory integration disorders are mostly related to a person's attention and correspond to a sensory under-sensitivity to certain external stimuli. The brain has to select sensory stimuli in order not to overload itself. The attention to external stimuli is accordingly limited and is not always adequately distributed.
For example, maintaining posture on the basis of external stimuli requires attention that other activities may lack at the same time. Sensory integration disorders with poor posture are often expressed, for example, in chronic restlessness. Insensitivities of the tactile and proprioceptive apparatus show up in inadequate movement planning and clumsiness. Hypersensitivities in this area are modulation disorders and do not allow the nervous system to filter sufficiently, which leads to tactile defense. This avoids unexpected contact and social fears can arise.
Most often, but not only, children are affected by integration disorders. Sometimes sensory-integrative disorders develop from neurological diseases such as a stroke. In such a case we are talking about an SI disturbance. A particular example of a disease with an integrative perception disorder is autism, which is often also characterized by an altered perception of pain.
