Receptor transformation process
In the receptor transformation process , signals from the environment in humans and animals are converted into neural signals and passed on for central nervous information processing and selective storage (as a signal transduction process ).
The receptor potential can be viewed as a continuous voltage-time function with an amplitude proportional to the stimulus . The signal-transmitting properties can be described by the amplitude and phase frequency response (see also coding of the stimulus ). The analog-coded amplitude-modulated receptor potential is recoded into an analog sequence of action potentials with an amplitude of the voltage of 0.1 volts and a duration of 0.5 to 1 millisecond .
The action potentials are transmitted to the axons of the receptor or downstream nerve cell (neuron) with an upper limit frequency of 300 to 1000 Hz to the following neurons of the central switching points. The coding forms of the transmitted excitation are the pulse interval and the pulse frequency coding. In the case of the latter, time averaging takes place through integration with a specific time constant. In the experimental representation of the response function, not only is averaged over a certain period of time, but average values of the instantaneous responses to repeated stimulation are also determined. This averaging corresponds to the temporal and spatial integration of signals, ie the convergence of numerous axon endings on a nerve cell.
In the axon endings, the incoming action potentials release a transmitter substance that changes the conductance for sodium ions ( ) and potassium ions ( ) in exciting synapses or chloride ( ) or potassium ions in inhibitory synapses on the downstream neurons . This results in either a local depolarizing excitatory postsynaptic potential (EPSP) or a hyperpolarizing inhibitory postsynaptic potential (IPSP).
Due to the morphofunctional release of the pathogen and postsynaptic excitation, the synapse has a "rectifying effect " that guarantees the directed (reaction-free) flow of information typical for the control circuit . The EPSP and IPSP triggered at the various synapses of a neuron add up spatially and temporally (called: facilitating; see attention as perception ). If the depolarization of the membrane potential reaches a critical threshold value, action potentials are generated again at the output of the neuron (at the initial segment, axon hillock ), which are transmitted on the axon and its branches to downstream neurons.
The pulse frequency is in turn proportional to the size and duration of the local excitation summed up from EPSP and IPSP. Decoding, integration and coding operations are repeated at all switching levels. The formal transfer properties such as addition and multiplication enable different types of operations in connection with the variety of interconnections. While intensity and temporal receptor adaptation changes are represented (ie through adaptation), this coding form does not apply to the sensory quality (see perception of sensory qualities ).
The quality of the transmitted message is determined for each nerve path by its receptive output and its central address. In contrast to the frequency and time code, we speak of a topographical or spatial coding. In addition to the perception of quality, the localizability of information sources is based on innate neural circuit diagrams (such as receptive fields, peripheral-central corresponding projection).
There is an extensive correspondence between the subjective and central nervous results of information processing, so that a largely reliable image of the objective environment can also be assumed for memory. The functional relationship is also described by the basic psychophysical law ( Weber-Fechner law ) and in a general form by the Stevens power function .