Dendrite | Introduction, Structure & Functions


Dendrite Definition:

What is a Dentrite: The word dendrite derived from the Greek word �Dendron�, which means the �tree� or the �branched such as e tree�. The dendrite is a short arm like protuberance from a neuron. Dendrites work as transmitters and receivers for chemical messages between the cells.

Dendrites used to receives from the nerve cell (neuron) and transfer it to another nerve cell (neuron). The process of transferring information from one nerve cell to another cell is done by using chemical signals and electric impulses, which are electrochemical signals. The information which is transferred from one neuron is often received at the dendrite by the chemical signals, it then transfers to the cell body (soma), and continues across the neuronal axon as an electric impulse. Then, it is finally successfully transferred to the next neuron at the synapse, which is the region or place where two nerve cells (neurons) exchange their information with the help of chemical signals. The ending point of one neuron at the synapse, and it is the beginning of the other dendrites. Dendrites are the branches from the cell body used to send and receive signals from one neuron to the other.

Dendrite Structure

dendrite structure

Dendrites Function:

The dendrite functions are to receive a signal from the one neuron, process these signals and then transfer to an informational signal to the cell body (soma) of the neuron.

There are main three functions performed by the dendrites; Receive information, process information, and transfer information.

  • Receive Information:

Receive information is the first function of dendrites. The dendrites are such as the branches of the tree because they are used to transfer information. The dendrites extend from the cell body or soma of the neuron and open it in the form of smaller projections. Synapses are lies at the end of these projections, the region where the transfer of takes place. In other words, the synapses are the sites or regions, where two neurons exchange their signals. The pre-synaptic or upstream neurons release neurotransmitters, which lies at the end neurons, known as �axonal terminal�. While the post-synaptic or downstream neurons detect the neurotransmitters usually in dendrites.

The pre-synaptic neuron releases neurotransmitters at the synapse. The neurotransmitters are the molecules that are detected by post-synaptic neurons. The post-synaptic neuron detects the neurotransmitters because of it has receptors of neurotransmitters to which these molecules bind. If the post-synaptic neuron has no particular neurotransmitter receptor, the neurotransmitter then will have not any effect. Some examples of neurotransmitters are norepinephrine, Glutamate, GABA, serotonin, and dopamine.

Some kinds of neurons have dendritic spines on the dendrites that are the small protrusions. These small protrusions project from the dendrites and the dendrite with neurotransmitter receptors increase the detection of the neurotransmitters.

  • Process Information:

After the receive information function is done, the next function is process information performed by the dendrites. After the binding of the neurotransmitter receptor in the post-synaptic neuron, a cascade of the signals begin, this enables the processing of the information at the synapse. This cascade of signals or signaling cascade depends on the neurotransmitter and the receptors of neurotransmitters. There are many other neurotransmitters including glutamate and inhibitory neurotransmitters such as GABA. The neurotransmitter receptors start a cascade of signal or signaling cascade which used to activate certain the ligand-gated ion channels. The ligand-gated ion channel enables the ions to enter in neurons, such as sodium, calcium, chloride, etc. or exist from the neurons, such as potassium.

In the inhibitory neurotransmitters, something similar occurs but binding of the result from the activation of ligand-gated Cl- channels, instead of activating ligand-gated Na+ channels. The Cl- channel flows into the post-synaptic neuron, while K+ will flow out from the cell. Although, the negative charge net influx (Cl-) leads to decrease potential in the cell membrane. Then the cell will be Hyperpolarized.

  • Transfer Information:

At the last, dendrites perform the function of transfer information. The summation of various EPSPs can surpass the threshold required for the post-synaptic neuron in order to start an action potential.

The physiological testing or normal membrane potential of the neuron is around -65mV. It means that the negative charge inside the neurons is with respect to the outside of the cell. This is because, some positive charge (K+) and also some negatively charged ions (A-) present inside the region of the cell, but the outside of the cell has many positive ions such as Na+ and Ca2+, and one negative charge ion such as Cl-. The result of the summation of all charges makes the outside of the cell much positive and the inside of the cell much negative.

The membrane potential of the postsynaptic neuron increases, when an EPSP takes place, for example from -65mV to -64mV which cause becomes the less negative charge. When the summation of various EPSPs makes the neuron membrane potential, it reaches a threshold value of around -55mV. Then, the action potential fired by the neuron which transfers the information to the some or cell body and the across the axon to the end of the post-synaptic neuron.

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Dendrites Malfunction:

The malfunctions in dendrites associated with a variety of nervous system disorders. Malfunctions of dendrites are varying in type and degree of severity. Its range is from abnormal morphology to the disturbance in dendritic branching. All of the malfunction of dendrites link with the disorders including autism, depression, schizophrenia, anxiety, Alzheimer�s and Down syndrome.