Dendrite of a neuron (dendra - branch) - a process of the body of a neuron, through which it receives a signal from other cells. The dendrite receives a signal from the axon of another neuron or a receptor protein that reacts to the environment.
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 the neuron makes.
Synaptic cleft
The signal from other cells comes to the body of the neuron through one of its dendrites. A dendrite in the human nervous system usually receives a chemical signal (a neurotransmitter) from an axon. The junction of a dendrite and an axon is called a synapse.
Synapses allow precise messages to be transmitted 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 arereceptors that accept the neurotransmitter. Receptors are specialized proteins that capture a neurotransmitter molecule and, depending on their type, trigger further reactions in the cell.
Dendrite spines
Small outgrowths are formed on the dendrites - spines. The latter can take many forms, but the most persistent is the form of the fungus.
The number of dendritic spines ranges from 20 to 50 per 10 microns of dendrite length. Spines are very variable in shape and volume.
There are 86 billion neurons in the brain. Axons, dendrites and neuron bodies form huge neural networks.
Dendrites are responsible for learning and memory, and also control the balance in the system. When there is a local increase in 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
Dendrite spines are responsible for learning and memory formation. Thanks to the spines and their plasticity, the neuron can easily connect to certain neighbors 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 memory of the past. In 2009, Nature published a paper investigating how learning experiences affect synaptic connections in mice.
The work shows that a large number of newspines formed from a new experience disappeared over time, if the experience was not repeated periodically. But those that remained, most likely, were responsible for the acquired skills.
At the same time, if the training was repeated for a long time, the spines were removed, apparently, the removed ones were responsible for the wrong actions. Learning and daily sensory experience leave permanent marks in the form of a small group of spines formed at different stages of learning.
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 (Z. G. Yang) showed that after training and sleep, after 24 hours, new dendritic spines appear in mice, and some of the existing ones disappear. The authors note that the rate of new spine formation in mice trained in the new behavior was significantly higher within 6 hours of training compared to untrained mice.
In addition, the authors showed that spinules form much more slowly when mice are deprived of sleep. And neither a new skill training nor a late sleep can fix the situation.
Dendrite as an independent unit
What are dendrites, they still find out. The thing is, it's hard to learn.behavior and functions of dendrites on living objects.
If the size of a neuron is about ten microns, then the length of a dendrite can be up to a thousand. Usually, dendrites are understood as not very active participants in the process.
In 2017, Science published a study that revisits the classic view of dendrites. It turned out that dendrites generate signals several times more often than the body of a neuron does, which leads to the assumption that information is encoded at the level of dendrites as well.
It was previously found that if during an experience the bodies of neurons were activated, and the dendrites were silent, then long-term memory was not formed regarding this experience. It was suggested that the activity of neurons is connected to a greater extent with real time, with actual experiences, and dendrites - with what will remain in memory.
What are dendrites given the new data? These are amazing constructs that make up 90% of the nervous tissue and perhaps 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 plasticity of dendrites is affected by an enriched environment.
3. Long-term learning is associated with the retention of spines associated with acquired skills.
4. Sleep allows you to remember the experience better.
5. Alcohol has a negative effect on the growth of dendrites.
6. With age, the number of dendritic branches becomesless.
Dendrites are amazing brain constructs. Each type of cell has its own "kind" of dendrites, and 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.
