Neurophysiology

Registry of neuronal activity and its topography.

Neurophysiology is the branch of physiology that studies the functionality of the nervous system. This recording of bioelectrical activity demonstrated that the nervous system is essentially dynamic.
The Etymology taken from the Greek νεῦρον neuron which means nerve and φύσις physis as nature and -λογία -logy as knowledge, would literally be: «knowledge of the nature of the nerve.

Every action or behavior is the result of functional modifications of said system. Neurophysiology demonstrates how this complicated system works and how it produces the variety of behavior patterns that organisms display. There have been interesting advances in research, especially in biochemical and electrical aspects.

History

In 1792 Luigi Galvani demonstrated that electricity could initiate muscle contractions. He performed his experiments on an electrostatic machine attached to frog limbs. It can be considered as the beginning of the study of the electrical excitability of muscles and the excitability of neurons.
In 1849 Emil du Bois-Reymond discovered that it was also possible to record electrical activity during the activity of muscle contraction.
In 1890, Étienne-Jules Marey recorded neuromuscular activity graphically, thus introducing the term electromyography.
In 1928 the physiologist Edgar Douglas Adrian demonstrated the presence of electricity within nerve cells. Adrian incorporated the method and language of basic-experimental neurophysiology into clinical practice. He received the Nobel Prize for his work on nerve cells (neurons). The set that forms an alpha motor neuron and the FMs innervated by it is known as a motor unit (MU) and constitutes the anatomical and functional unit of the muscle.

Basic principles

Elementary neurophysiology tries to study the behavior of neurons or groups of neurons (networks).
A single neuron cannot do much on its own. The function of the nervous system depends on groups of neurons that work together. Individual neurons connect to others to stimulate or inhibit their activity and form circuits that can process incoming information and produce a response.

Neurona
Dendrita Soma Axon Nucleus Node of Ranvier Axon terminal Schwann Cell Honeyin Vain
Structure of a classic neuron.

The main facts established by elementary neurophysiology are:

• A large brain of neurons.

The number of neurons in a human brain has been estimated to be more than 1.6 × 10¹⁰ neurons.

• Neurons consist of: a cellular body, a tree dendritic structure and an axon.

Neurons are cells that have numerous dendrites and one axon. The dendrites form an immense arboreal structure that can extend over wide areas of a brain, the axons can reach more than a meter in length.

• Neurons generate electric potentials.

Electrical potentials, which can either be sub-threshold such as EPSP (Excitatory Post - Synaptic Potential) and IPSP (Inhibitory Post - Synaptic Potential) or can be supra-threshold such as action potentials (PA), are electrophysiological phenomena caused because cell membranes have active properties that make them excitable or sensitive to electrical potentials from other neurons. The summation of electrical inputs converges along the length of the neuron and generates the potential at the beginning of the axon, which will propagate along its length to the axon terminal.

• Electrical potentials are the basic mechanisms for neuron communication.

Electrical activity of pyramidal neuron of the Hipocampus.

Action potentials are electrical signals that one neuron sends to another and represent a certain type of information. Each neuron receives many signals from other neurons (convergent potential) and in turn sends signals to many others (emergence potential).

• Neurons are functionally polarized.

That is, neurons receive electrical signals through their dendrites, process and superimpose those signals in the soma, and send a response to other neurons through their axon.

• The union between the axon of a neuron and the dendrites of another neuron is called sinapsis.

File:Dendritic voltage-gated ion channels.png

Dancers

Synapses can be electrical and/or chemical. An electrochemical synapse is made up of a presynaptic transmitter and a postsynaptic receptor, separated by an intersynaptic cleft. When an impulse reaches the end of an axon, a chain of physiological reactions is triggered at the axon terminal, leading to the release of chemicals (neurotransmitters) into the intersynaptic gap. These diffuse passively throughout the synaptic gap, producing changes in the potential of the postsynaptic membrane.

• The Dale Principle, it states that a neuron is either exciting or inhibitive.
  

It is excitatory if the potential of the postsynaptic membrane is increased, a fact known as "depolarization". When a neuron depolarizes, it facilitates the generation of an action potential in the postsynaptic neuron.
If, on the contrary, the potential decreases, the neuron is inhibitory. The hyperpolarization that an inhibitory neuron can suffer prevents the generation of action potential. However, we will find neurons that release certain types of neurotransmitters (eg, cholinergic neurons of the basal forebrain or dopaminergic neurons of the Prefrontal cortex) that will have diverse and different effects depending on the physiological conditions and the cells that receive said stimulus.

The facts established by elementary neurophysiology can be used by the mathematical theory of neural networks to build mathematical models that allow the identification of neurophysiological phenomena such as memory and learning.