A dendrite of a neuron (dendra is a branch) is a process of the body of a neuron through which a signal from other cells comes to it. A dendrite receives a signal from the axon of another neuron or receptor protein that responds to the medium.
Answering the question of what dendrites are, we can say that traditionally dendrites are considered as antennas of a neuron. The exchange of information occurs in one direction: from the axon to the dendrite. The more dendrites a neuron has, the more information channels, the more complex decisions a neuron makes.
Synaptic cleft
The signal from other cells enters the body of the neuron through one of its dendrites. Dendrite in the human nervous system usually receives a chemical signal (neurotransmitter) from the axon. The junction of the dendrite and axon is called the synapse.
Synapses allow the transmission of accurate messages from neuron to neuron. Thanks to synapses, there is neuroplasticity and the ability to fine-tune the functions and behavior of the body.
On the dendrite are receptors that take a neurotransmitter. Receptors are specialized proteins that capture a neurotransmitter molecule and, depending on their type, trigger further reactions in the cell.
Dendritic spines
Small growths - spines are formed on the dendrites. The latter can take many forms, but the most stable is the form of the fungus.
The number of dendritic spines ranges from 20 to 50 per 10 microns of the length of the dendrite. Spines are very variable in shape and volume.
There are 86 billion neurons in the brain. Axons, dendrites, and bodies of neurons form huge neural networks.
Dendrites are responsible for learning and memory, and also control the balance in the system. When there is a local strengthening of the connections between certain neurons, it is in the dendrites that the production of a protein that regulates the decrease in the activity of other synapses increases.
Training and spikes
Dendritic spines are responsible for learning and memory formation. Due to the spines and their plasticity, the neuron can easily connect to one or another neighbor and quickly disconnect from them, controlling the possibility of receiving a signal.
It would be logical to assume that if synaptic connections are responsible for memories, then their plasticity is a problem for preserving the memory of the past. In 2009, Nature published a publication in which the authors examined how learning experiences affect the synaptic connections of mice.
The work showed that a large number of new spikes formed from a new experiment disappeared over time if the experiment was not repeated periodically. But those that were preserved were most likely responsible for the acquired skills.
Moreover, if the training was repeated for a long time, the spines were removed, apparently, the removed ones were responsible for incorrect actions. Training and daily sensory experience leave constant litters in the form of a small group of spines formed at different stages of training.
What are dendrites, if not a huge library of memories? But the main problem of dendritic spines is that they are very sensitive to any mechanical and chemical influences. Therefore, brain injuries, even if localized in one place, usually affect the entire neural network.
Sleep and Learning
A 2014 study (ZG Yang) showed how, after training and sleep, 24 hours later, new dendritic spines appear in mice, and some of the existing ones disappear. The authors note that the rate of formation of new spines in mice trained in new behavior was significantly higher within 6 hours after training compared to untrained mice.
In addition, the authors showed that spines during deprivation of sleep mice form much more slowly. And neither a new skill training, nor a late dream can correct the situation.
Dendrite as an independent unit
What are dendrites, they are still figuring out. The fact is that it is difficult to study the behavior and functions of dendrites on living objects.
If the size of the neuron is about ten microns, then the length of the dendrite can reach up to a thousand. Usually, dendrites are understood as not very active participants in the process.
In 2017, a study was published in the journal Science, which allows you to revise the classic look at dendrites. It turned out that dendrites generate signals several times more often than the body of a neuron does, which suggests an encoding of information at the level of dendrites.
It was previously discovered that if during the experience of an experiment the bodies of neurons were activated and the dendrites were silent, then a long-term memory was not formed relative to this experiment. It has been suggested that the activity of neurons is associated more with real time, with actual experiences, and dendrites with what remains of this in memory.
What are dendrites, given the new data? These are amazing constructions that make up 90% of the nervous tissue and, possibly, take on most of the work of preserving and transforming the experience.
Sum of facts
1. The dendritic branch is variable, especially in the young brain.
2. The enriched environment influences the plasticity of dendrites.
3. Long-term training is associated with the preservation of spines associated with acquired skills.
4. Sleep allows you to better remember the experience.
5. Alcohol has a negative effect on the growth of dendrites.
6. With age, the number of branches of dendrites becomes less.
Dendrites are amazing brain structures. Each type of cell has its own “look” of dendrites, besides, dendrites are extremely plastic and can change in a few minutes. Apparently, dendrites perform complex information processing, take on tasks related to long-term memory and learning.