They are one of the largest types of neurons, and are found in the heart and cerebellum.
It is estimated that, at the time of our birth, we have approximately 80 million neurons or brain cells. Thanks to their activity, our nervous system is able to function at full power.
One of the types of neurons that inhabit our brain are neurons or Purkinje cells. Throughout this article we will explain what these neurons consist of, how they work and what they are for, as well as the pathologies associated with them.
What are Purkinje neurons?
Purkinje cells or neurons are named after the Czech anatomist, physiologist and botanist Jan Evangelista Purkyne, who discoverer of these elements. These large cells are found in all invertebrate animals, are a type of GABAergic neuron, and constitute the functional units of the cerebellum.
After its discovery, many researchers have tried to decipher the enigmas of this neuron. The well-known scientists Camillo Golgi and Santiago Ramón y Cajal, dedicated years of their lives to study these cells. Thanks to these investigations, we currently have practically absolute knowledge about the anatomy and structure of Purkinje neurons, as well as the details and specific functions of these.
Although they are mainly found in the cerebellar cortex, forming the Purkinje layer between the molecular layer and the granular layer, they can also be found in the myocardium, that is, in the muscular part of the heart.
Purkinje cell connections
Only in the cerebellum there are approximately 30 million neurons of this type, each one of them being united to around a million nerve endings of other different types of cells. These cells to which Purkinje neurons are attached are classified into two types:
They come from the brain stem and spinal cord. As they are closer to the Purkinje neurons they branch out into fibers that are located in parallel.
They rise from the medulla oblongata and the brainstem. However, these types of climbing cells only bind to a single Purkinje neuron.
What is the structure of these nerve cells?
As discussed above, Purkinje neurons are one of the largest cells found in our brain. Its dendritic axis is extremely complex and is distinguished by having a large number of entangled dendritic spines.
These cells are placed opposite each other, as if they were dominoes, forming layers between which the parallel fibers that come from the deeper layers pass.
Across synapses, parallel fibers transmit excitatory impulses of weak potential to the dendritic spines of Purkinje neurons. However, the impulses of those ascending fibers that come from the inferior olivary nucleus of the medulla emit excitatory impulses of great intensity. Furthermore, these parallel fibers circulate at right angles through the dendritic axis of the Purkinje cell. These fibers, which can number in the hundreds of thousands, form synapses with a single neuron of this type.
Finally, Purkinje neurons transmit inhibitory fiber projections to the deep cerebellar nuclei, constituting the only escape route from the cerebellar cortex with effects on motor coordination.
What functions do they have?
Purkinje neurons exert their effects through the use of electrophysiological activity. This type of activity can occur in two different ways, depending on whether the spikes of the neuron are simple or complex.
1. Activity in simple spikes
The electrophysiological activity rate of simple spikes ranges from 17 to 150 Hz. This activity can appear spontaneously or at times when Purkinje neurons are activated by parallel fibers.
2. Activity in complex spikes
In the case of complex spikes, the intensity slows down considerably, oscillating between 1 and 3 hz of power.
Complex spikes are distinguished by having a long, high-amplitude initial spike, which follows a high-frequency shot but with a smaller amplitude. These bursts of electrical activity originate from the activation of the climbing fibers, named above.
What is known about them through research
Sodium and calcium play a fundamental role in the electrophysiological activity of Purkinje neurons and, therefore, in the correct function of the cerebellum. Furthermore, in recent years it has been revealed that the stimulation of the climbing fibers triggers an alteration in the activity of the cell, going from a state of rest to an active one and vice versa) as if it were a kind of button or push button.
However, the results of these investigations have been widely debated. The reason is that the data obtained in other studies point to the idea that these alterations in activity only occur when the person or animal is anesthetized; Whereas if they are awake, the Purkinje neurons always function in a full state of activity.
Finally, the results obtained from recent research suggest that Purkinje neurons have the capacity to discharge endocannabinoid substances that can reduce the potential of synapses, both excitatory and inhibitory.
Associated pathologies and diseases
Since Purkinje neurons are found in both animals and humans, there are a wide variety of factors that can cause specific and species-specific abnormalities.
In the case of people, there are a large number of causes that can cause the deterioration or injury of the Purkinje neurons. Genetic alterations, autoimmune or neurodegenerative diseases and toxic elements present in certain substances such as lithium, can cause serious damage to this type of cells.
Furthermore, in Alzheimer’s disease, a decrease in the dendritic branches of these neurons has been described.
On the other hand, in the animal world there is a strange condition that causes atrophy and malfunction of these neurons long after birth. This disease known as cerebellar abiotrophy is distinguished by presenting a large number of symptoms, among which are:
- Lack of reflexes.
- Lack of ability to perceive space and distances.
In the case of cerebellar hypoplasia, the Purkinje neurons have not finished developing or die while the child is still in the mother’s womb.