Mechanoreceptor

Mechanoreceptors are sensory cells that convert mechanical forces into nerve excitation. They can be found in sensory organs as diverse as the ears , skin, or arteries . Accordingly, there is a great variety of mechanoreceptors that vary greatly in structure and function.

Examples of occurrence and function

• Inner ear / hair cell : sense of hearing
• Semicircular canals : sense of balance
• Skin : sense of vibration and touch
• Blood circulation : reception of blood pressure
• Lateral line organ : water currents
• Muscle : Reception of the muscle length

Classification

The main classification of mechanoreceptors is based on their origin. One part of the mechanoreceptors evolved from epithelium - the other from the ganglion cells .

Epithelial Mechanoreceptors

Epithelial mechanoreceptors originally arose from cells that were on the surface of the organism. However, this does not automatically mean that the receptors are still on the surface today. All epithelial mechanoreceptors are characterized by the fact that the conversion of an external stimulus into a physiological signal (transduction) takes place in cell appendages - the cilia . As a rule, mechanical deformation of the cilia leads to the opening or closing of ion channels and thus to inhibition or excitation of the respective receptor (example: hair cell in the mammalian ear). In addition to the sensory cells of the inner ear, most proprioceptors in vertebrates and invertebrates belong to this class, as well as flow-sensitive receptors in fish and amphibians or the vibration-sensitive sensory cells in insects . It is assumed that epithelial receptor cells emerged 2 to 3 times independently in the course of evolution and that all recent sensory cells of this type represent modifications of such archetypes.

Ganglionic Mechanoreceptors

Ganglionic mechanoreceptors are usually located in the tissue and have a widely ramified structure with up to 1000 terminals. The transduction always takes place in these endings. Each ending can be excited independently, but the individual excitations are then added up in the cell body at the latest . The combination of mechanical characteristics of the stimulus reception and these electrical summation properties allow a multitude of different sensory functions (example: mechanoreceptors of the skin ). The most important example of ganglionic mechanoreceptors are the sensory cells of the sense of touch in vertebrates: their cell body lies next to the spinal cord in the spinal ganglia, while their endings can grow into the most remote places under the skin. Ganglionic mechanoreceptors are also found in invertebrates , for example as tactile receptor cells in leeches .

swell

• Rüdiger Wehner, Walter Gehring: Zoology. 22nd edition. Georg Thieme Verlag, Heidelberg 1995, ISBN 3-13-367423-4 .
• Josef Dudel, Randolf Menzel, Robert F. Schmidt (Eds.): Neurosciences. 2nd Edition. Springer-Verlag, Berlin 2001, ISBN 3-540-41335-9 .