Neurons are the structural core of our brain. Incredibly complex connections among them make all our thought, movement or emotion possible. Moreover, not all of them are equal.
It’s not surprising. Our nervous system is so complicated that it would be impossible to have just one type of neurons. They are extremely specialized cells and they have morphology and abilities based on their functions.
The multipolar cells
Multipolar neurons represent the majority of the nerve cells. They have many dendrites and one axon, as we saw in a previous article. Motoneurons and pyramidal neurons are examples of multipolar cells.
Purkinje’s cells, placed into the cerebellum, are very particular multipolar neurons. In facts, their axon goes into the white matter while one or two big dendrites go towards the cerebellum cortex. From them, an incredible arborization takes place and each Purkinje cell is able to receive information from thousands of other cells.
The cerebral cortex neurons
Into the cerebral cortex, we can identify two large families of neurons: pyramidal and non-pyramidal ones.
The first family represents 3/4 of all cortical neurons. This kind of cell has a triangular body, an apical dendrite of variable length which goes towards surface layers of the cortex, and different basal dendrites which run horizontally. When we make an EEG recording, we are analyzing the activity of the most superficial pyramidal neurons. In other words, through specific electrodes, we can record potential variations in the membrane of these cells.
Pyramidal neurons use Glutamate as a neurotransmitter (a molecule used in the synapsis making the communication between two neurons possible). This molecule is exclusively able to excite the postsynaptic neuron.
On the basis of the type of neurotransmitter, synapsis can be excitatory or inhibitory. In the first case, the input will be a stimulus for the second neuron to transmit the electrical potential through its axon. In the second one, it will be the opposite.
Furthermore, among pyramidal neurons, we find Betz giant cells. They are based in the motor cortex and form the nerve fibers which bring information on movements that are needed.
Non-pyramidal neurons are divided into two groups: spiny neurons and aspiny ones.
Spiny cells are interneurons and their axon ends near to their body. Many scientists believe that these cells could be modified pyramidal neurons.
On the other hand, aspiny neurons are a heterogeneous cells group. Their axons don’t exit from the gray matter and they use GABA (Gamma-aminobutyric acid) as a neurotransmitter. For this reason, they are inhibitory interneurons.