dendrit

definition

Dendrites are the cytoplasmic processes of a nerve cell, which are usually branch-like from the nerve cell body (Soma) and branch out more and more finely, dividing into two. They serve to receive electrical stimuli from upstream nerve cells via synapses and to pass them on to the soma. The dendrites also help nourish the nerve cells.

A nerve cell has an average of 1 to 12 dendrites. Most dendrites have a smooth surface (smooth dendrites). However, there are also nerve cells whose dendrites have so-called spinous processes or spines (spiny dendrites). These spinous processes enable the formation of a special type of synpase, since the processes allow the plasma composition of a small area to be coordinated very precisely.

Illustration of a nerve cell

Nerve cell -
Neuron

1. Dendrites
2. Synapse
   (axodendritic)
3. Nucleus -
   Nucleolus
4. Cell bodies -
   Nucleus
5. Axon mounds
6. Myelin sheath
7. Ranvier lace-up
8. Swan cells
9. Axon terminals
10. Synapse
    (axoaxonal)
    A - multipolar neuron
    B - pseudounipolar neuron
    C - bipolar neuron
    a - Soma
    b - axon
    c - synapses

You can find an overview of all Dr-Gumpert images at: medical illustrations

Structure of dendrites

Research continues into the exact structure and growth of dendrites. Dendrite growth usually begins at the end of the embryonic phase after axon growth and continues into early childhood. It is assumed that newly emerging dendrites, similar to newly sprouting axons, form a structure with which they orient themselves and find their way to the next target cell. This structure is called Growth cone and follows a chemically determined path to a target cell. This growth cone is mobile and searches the environment for suitable signals. If there is an attraction, the dendrite grows longer. If rejection occurs, their growth period is shortened or it comes to a standstill. There are different for the growth of the dendrites Enzymes very important. If one of these enzymes is missing, growth can stop and nerve cell activity can be restricted.

You can find more on the topic here: Enzymes

Whether, how fast and in which direction a dendrite grows is presumably regulated by chemical and physical processes and reactions in the body. These signals also initiate pauses in growth. The principle of growth can be found in development, as well as after damage, for example.

The term dendrite is derived from the ancient Greek dendron or dendrites, which means "tree" or "belonging to the tree". Accordingly, the dendrites sprout "tree-like" branching out of the nerve cell bodies.They usually have a total length of over 100 kilometers. Compared to the axons, they are much shorter with a length of about a few hundred micrometers. In contrast to the axon, the diameter of the dendrite changes. It tapers towards the tip of the dendrite. The dendritic stem contains a cell organelle for protein production, which is also known as a rough endoplasmic reticulum. These protein factories are located in the nerve cells Nissl clods called. The so-called is located in the dendrite tips Golgi apparat, in which substances are "addressed" and forwarded, similar to a post office. Most, but not all, of the dendrites have Mitochondriaknown as the "powerhouse of the cell". In the case of very thin dendrites, these are absent.

You can find out more about the topic here Mitochondria

Furthermore, there are in the dendrite tips Microtubules, Structures that have a transport function. The microtubules also ensure that the growth cones are “pushed” during the growth phase. Some authors see nerve cell bodies and dendrites as one unit. The dendrite pattern and number of dendrites mainly determine the diversity and functions of the nerve cell. Multipolar nerve cells characteristically have several dendrites. They are most common in the body, for example in the motor neurons in the spinal cord.

You can read more about the subject here Motor neurons Experienced

Bipolar nerve cells only have one dendrite. Its structure is similar to that of an axon, except that it is no special link endpoint, a so-called synaptic end bulb, owns. These nerve cells are found in the retina of the eye and in the ear. Unipolar nerve cells are very rare and have no dendrites. It is found in the first neuron in the retina.

Read more about the topic here Retina of the eye

As a rule, the dendrites do not have a coating, the so-called myelin sheaths. The pseudounipolar nerve cells are an exception. These are located in the spinal and cranial nerves.

Here you can find out more about the Nervous system structure

Thorny processes

Dendrites that do not have a thorn process are called "smooth" dendrites. They pick up the nerve impulses directly. While the dendrites have the thorns, the nerve impulses can receive both via the thorns and the dendritic stem. The thorns emerge from the dendrites like small mushroom heads. You can zoom in or out depending on your activity. If you enlarge the surface of the dendrites, you create more space for connections. They often contain a kind of calcium store, the function of which is still being researched.

Here you can read more about calcium Experienced

With the dendrite trunk and the thorns, they absorb the information. Usually these are stimulating impulses. In addition, they can “temporarily store” information and thus protect it from overstimulation. It is also believed that with increased activity, a species Competition between the connection points comes. The “stronger” connection point receives more proteins and can develop further, while the “weaker” connection points decrease due to a lack of protein. This means that there is a growth in specific connection points associated with a decrease in other points. This could explain how specific skills improve while other skills and abilities of the person concerned become more difficult.

Axonal transport

The axon is a long tube-like nerve cell extension that differs from the dendrites in some aspects. The axon is used to transport substances from the nerve cell body to another cell. For example, certain messenger substances that are packaged in so-called vesicles, as well as nutrients, reach another point of attachment. On the other hand, substances can also be transported to the nerve cell. In this way, not only substances that are good for the cell can get inside, but also Pathogens. Since the transport mechanisms are complex and slow, the cell restores the messenger substances released and repackages them in vesicles. The transport can take place with or without the so-called microtubules. The transport of enzymes and large cell framework proteins takes place without microtubules. The excitatory or inhibitory information also reaches the nerve cell through the axon. The information is only passed on in one direction, that of the target organ. However, the information can propagate in both directions in the dendrite and in the nerve cell body.

Read more about the topic here: Axon

Abandonment of dendrites

The main task of the dendrites lies in this Receive information. They act like antennas, pick up information and pass it on. The information can flow in both directions within the dendrites, both to the Cell body there, as well as back to the so-called Dendrite tip. This happens when the Axon a Action potential forms, which then not only along the axon path guided by the nerve cell body, but also declining is spread in the sense of a feedback on the dendrites. This forwarding takes place actively, i.e. the dendrites are able to change and process the signals. They do this with the help of Proteins. Especially near the point of attachment, the dendrites have many structures that enable them to form proteins and to modify them. In order to fulfill their tasks, the dendrites always need new proteins, which are transported from the cell body into the dendrites. Furthermore, messenger molecules, so-called mRNA promoted into the dendrites. These messenger molecules contain the blueprint for proteins. This enables proteins to be produced in the dendrite.

Read more about the topic here DNA

This plays an important role in the malleability of nerve cells, the so-called Neuroplasticitywhich is of great importance to Learning processes is. The connection points of the dendrites can be different. An exchange between axon and dendrite is common. However, an exchange between different dendrites is also possible. There is another, rarer exchange possibility between the axon and the thorny processes of the dendrites that has not been further explored.

Read more about the topic here Axon

Depending on the type and task of the nerve cells, different dendrite patterns can be microscopically displayed. However, their structure and function are very similar. The so-called Pseudounipolar However, nerve cells are an exception. Like some axons, they are surrounded by a mantle, the so-called Medullary sheaths. As a result, they show similarities to axons.

The dendrite absorbs information from the body and forwards it to the brain. Due to its sheathing, this dendrite can transmit information over long distances. Hence one speaks of a dendritic axon or an axon with a dendritic character. Furthermore, the thorns of the dendrites can front the nerve cells Overstimulation protect, as they can store information temporarily. They do this when too much information is being processed at once in the cell body. These adjust a suitable time to "deliver" information. Another task of the dendrites is that nutrition of the nerve cells, whereby they are the Glial cells support. In addition, the dendritic branches contribute to a Surface enlargement the nerve cell. This enables you to increase the number of links to other cells.

Read more about the topic here Nerve cell