What is the part of the neuron where messages are sent across to another called?

Neurons (also called neurones or nerve cells) are the fundamental units of the brain and nervous system, the cells responsible for receiving sensory input from the external world, for sending motor commands to our muscles, and for transforming and relaying the electrical signals at every step in between. More than that, their interactions define who we are as people. Having said that, our roughly 100 billion neurons do interact closely with other cell types, broadly classified as glia (these may actually outnumber neurons, although it’s not really known).

The creation of new neurons in the brain is called neurogenesis, and this can happen even in adults.

What does a neuron look like?

A useful analogy is to think of a neuron as a tree. A neuron has three main parts: dendrites, an axon, and a cell body or soma (see image below), which can be represented as the branches, roots and trunk of a tree, respectively. A dendrite (tree branch) is where a neuron receives input from other cells. Dendrites branch as they move towards their tips, just like tree branches do, and they even have leaf-like structures on them called spines.

The axon (tree roots) is the output structure of the neuron; when a neuron wants to talk to another neuron, it sends an electrical message called an action potential throughout the entire axon. The soma (tree trunk) is where the nucleus lies, where the neuron’s DNA is housed, and where proteins are made to be transported throughout the axon and dendrites. 

What is the part of the neuron where messages are sent across to another called?
The tree-like structure of a neuron. Dendritic spines are small structures that receive inputs from the axons of other neurons. Bottom-right image: a segment of dendrite from which spines branch off, like leaves off a tree branch. Note the very small size (~0.001mm). (Image: Alan Woodruff ; De Roo et al / CC BY-SA 3.0 via Commons)

There are different types of neurons, both in the brain and the spinal cord. They are generally divided according to where they orginate, where they project to and which neurotransmitters they use.

Concepts and definitions

Axon – The long, thin structure in which action potentials are generated; the transmitting part of the neuron. After initiation, action potentials travel down axons to cause release of neurotransmitter.

Dendrite – The receiving part of the neuron. Dendrites receive synaptic inputs from axons, with the sum total of dendritic inputs determining whether the neuron will fire an action potential.

Spine – The small protrusions found on dendrites that are, for many synapses, the postsynaptic contact site.

Action potential – Brief electrical event typically generated in the axon that signals the neuron as 'active'. An action potential travels the length of the axon and causes release of neurotransmitter into the synapse. The action potential and consequent transmitter release allow the neuron to communicate with other neurons.

Author: Dr Alan Woodruff

Key facts: action potential and synapses

  • Neurons communicate with each other via electrical events called ‘action potentials’ and chemical neurotransmitters.
  • At the junction between two neurons (synapse), an action potential causes neuron A to release a chemical neurotransmitter.
  • The neurotransmitter can either help (excite) or hinder (inhibit) neuron B from firing its own action potential.
  • In an intact brain, the balance of hundreds of excitatory and inhibitory inputs to a neuron determines whether an action potential will result.

Neurons are essentially electrical devices. There are many channels sitting in the cell membrane (the boundary between a cell’s inside and outside) that allow positive or negative ions to flow into and out of the cell.

Normally, the inside of the cell is more negative than the outside; neuroscientists say that the inside is around -70 mV with respect to the outside, or that the cell’s resting membrane potential is -70 mV.

This membrane potential isn’t static. It’s constantly going up and down, depending mostly on the inputs coming from the axons of other neurons. Some inputs make the neuron’s membrane potential become more positive (or less negative, e.g. from -70 mV to -65 mV), and others do the opposite.

These are respectively termed excitatory and inhibitory inputs, as they promote or inhibit the generation of action potentials (the reason some inputs are excitatory and others inhibitory is that different types of neuron release different neurotransmitters; the neurotransmitter used by a neuron determines its effect).

Action potentials are the fundamental units of communication between neurons and occur when the sum total of all of the excitatory and inhibitory inputs makes the neuron’s membrane potential reach around -50 mV (see diagram), a value called the action potential threshold.

Neuroscientists often refer to action potentials as ‘spikes’, or say a neuron has ‘fired a spike’ or ‘spiked’. The term is a reference to the shape of an action potential as recorded using sensitive electrical equipment.

What is the part of the neuron where messages are sent across to another called?

A neuron spikes when a combination of all the excitation and inhibition it receives makes it reach threshold. On the right is an example from an actual neuron in the mouse's cortex. (Image: Alan Woodruff / QBI)

Synapses: how neurons communicate with each other

Neurons talk to each other across synapses. When an action potential reaches the presynaptic terminal, it causes neurotransmitter to be released from the neuron into the synaptic cleft, a 20–40nm gap between the presynaptic axon terminal and the postsynaptic dendrite (often a spine).

After travelling across the synaptic cleft, the transmitter will attach to neurotransmitter receptors on the postsynaptic side, and depending on the neurotransmitter released (which is dependent on the type of neuron releasing it), particular positive (e.g. Na+, K+, Ca+) or negative ions (e.g. Cl-) will travel through channels that span the membrane.

Synapses can be thought of as converting an electrical signal (the action potential) into a chemical signal in the form of neurotransmitter release, and then, upon binding of the transmitter to the postsynaptic receptor, switching the signal back again into an electrical form, as charged ions flow into or out of the postsynaptic neuron.

What is the part of the neuron where messages are sent across to another called?

An action potential, or spike, causes neurotransmitters to be released across the synaptic cleft, causing an electrical signal in the postsynaptic neuron. (Image: By Thomas Splettstoesser / CC BY-SA 4.0)

Video: Action potentials in neurons

Concepts and definitions

Axon– The long, thin structure in which action potentials are generated; the transmitting part of the neuron. After initiation, action potentials travel down axons to cause release of neurotransmitter.

Dendrite – The receiving part of the neuron. Dendrites receive synaptic inputs from axons, with the sum total of dendritic inputs determining whether the neuron will fire an action potential.

Spine – The small protrusions found on dendrites that are, for many synapses, the postsynaptic contact site.

Membrane potential – The electrical potential across the neuron's cell membrane, which arises due to different distributions of positively and negatively charged ions within and outside of the cell. The value inside of the cell is always stated relative to the outside: -70 mV means the inside is 70 mV more negative than the outside (which is given a value of 0 mV).

Action potential – Brief (~1 ms) electrical event typically generated in the axon that signals the neuron as 'active'. An action potential travels the length of the axon and causes release of neurotransmitter into the synapse. The action potential and consequent transmitter release allow the neuron to communicate with other neurons.

Neurotransmitter – A chemical released from a neuron following an action potential. The neurotransmitter travels across the synapse to excite or inhibit the target neuron. Different types of neurons use different neurotransmitters and therefore have different effects on their targets. 

Synapse – The junction between the axon of one neuron and the dendrite of another, through which the two neurons communicate.

QBI research

QBI Laboratories working on neurons and neuronal communication: Professor Stephen Williams, Professor Pankaj Sah

QBI Laboratories working on synapses: Dr Victor Anggono, Professor Joseph Lynch, Professor Frederic Meunier

What is the place called where neurons communicate with another cell?

Communication between neurons occurs at tiny gaps called synapses, where specialized parts of the two cells (i.e., the presynaptic and postsynaptic neurons) come within nanometers of one another to allow for chemical transmission.

Which part of the neuron sends signals?

Axon – The long, thin structure in which action potentials are generated; the transmitting part of the neuron. After initiation, action potentials travel down axons to cause release of neurotransmitter.

What is the message that travels through a neuron called?

A neuron is a specialized cell for receiving messages from one part of the body and conducting them to the other parts. Messages along the neuron travel in the form of a wave of chemical disturbance. This chemical disturbance is called an impulse.