Definition
Reflexes are uncontrollable, fast and always the same reaction to certain stimuli. Reflexes are mediated by our nervous system, consisting of nerve fibers that communicate with each other via so-called synapses. A reflex always involves a sensor/receptor on which the stimulus acts.
Also always involved is an effector, on which the reflex response takes place. Sensor and effector are connected by the nerve fibers of our nervous system. The spinal cord and the brain stem serve as a central switch point in which the signal-receiving nerve fibers are switched to the reaction-triggering nerve fibers. The presence or absence of a reflex and the intensity of the reflex response can allow important conclusions about diseases of the nervous system during a medical neurological examination.
Reflex Arc
The basis of all reflexes are the so-called reflex arcs. These are interconnections of different nerve tracts which always run across the spinal cord. In principle they are always structured as follows: A stimulus from outside is perceived by a sensor (e.g. muscle spindle).
This sensor transmits the information to the spinal cord. Here, a connection to another nerve fiber takes place. This in turn transmits the information to an effector (e.g.
muscle), which as the last station of the circulation then carries out the corresponding action in response to the stimulus (e.g. stretching the leg). These reflex arcs can be of varying complexity. The muscle reflexes, such as the patellar tendon reflex, are kept quite simple: the sensor and effector are located at the same place and are, so to speak, directly transmitted.
However, there are also situations in which other modulating nerve fibers are interposed which ensure that the incoming signals are amplified or inhibited. It is also possible that the sensor and effector are located at different points in the body. In this case, one speaks of so-called extraneous reflexes. What they all have in common, however, is that the information does not first reach the brain and therefore does not require an arbitrary decision about the action, but rather that this is “automatic” due to the direct connection in the spinal cord.