Afferent (from Latin affere, "carry, feed") are those extensions of nerve cells called neurophysiologically through which signals flow to a certain area. This general marking according to the direction of the signal line can be used for different structures on different levels:
- At the cellular level in relation to the nerve cell body, the dendrites are referred to as afferent .
- At the regional level, referring to a certain brain region, the respective feeding pathways are also called afferents, in contrast to the outgoing efferents .
- At the systemic level in relation to the central nervous system (CNS), the incoming nerve fibers, through which signals are received, are collectively referred to as afferent nerve fibers or "afferents" and are divided into somatic and visceral.
Opposite these are efferents for the signal output. Afferent and efferent thighs are used as components of a reflex arc .
Afferents to the CNS
The totality of all in the periphery of the central nervous system occurring and in this direction the CNS signals from receptors or from sensory organs afferent nerve fibers is also afferents mentioned. As afferent neurons , the nerve cells involved are each part of an afferent system , whereby the afferents of the first (1st) afferent neurons of a neuron chain are also called primary afferents , and their nerve fibers are primarily afferent .
In German-speaking anatomy , a distinction is often made between afferents in more highly developed animals and humans
- sensitive - the surface sensitivity and the depth sensitivity for haptic perception
- and sensory - for olfactory , visual , auditory and gustatory sensory perceptions , even if this subdivision is often justified no other than that the latter are limited to narrowly defined body regions. In the case of vertebrates, the afferents are further subdivided by some authors, even if the boundaries here are not always plausible.
The somatic afferents (from Gr. Soma "body") convey information of the body and belong to the somatic nervous system . Here are general somatic afferent (ASA, Eng. , General somatic afferent , GSA) and special somatic afferent (SSA, Eng. Special somatic afferent ) distinguished. To the ASA, all paths of the haptic perception ( tactile sensation , temperature sensation , pain perception , proprioception ) to the SSA, the webs of the face , auditory and vestibular counted.
The visceral afferents (from lat. Viscera "entrails") are those of the vegetative nervous system and convey information from the internal organs to the central nervous system. Here, too, a distinction is sometimes made between general (AVA, GVA) and special (SVA). The AVA conduct pain sensations, chemical and mechanical stimuli from the organs to the brain, the SVA smell and taste perceptions .