What is Neuron ?

Synaptic Terminal or the Axon Terminal is the place where Synapses are present. These Synapses are highly specialized structures designed for releasing neurotransmitters (they are chemicals) so that communication with target Neurons can take place.

Our memory, basic reflexes, abstract thoughts, emotions – all come because of the Neural network in our body. These Neurons are very special and they require more glucose and oxygen than rest of the cells in our body.

A Neuron can have a diameter of anywhere between 4 microns and 100 microns (both included). The largest axon in human body is 1 meter long and the largest axon in a giraffe is 15 feet long.

Synaptic Terminals actually connect with Dendrites of other Neurons or with the Soma of other Neurons or with Effector Cells found in glands or muscles.

Note that Dendrites and Axon are called ‘Processes’. In case of a Multipolar Neuron, there are several process that include one Axon and several Dendrites.

A Neuron can have a diameter of anywhere between 4 microns and 100 microns (both included). The largest axon in human body is 1 meter long and the largest axon in a giraffe is 15 feet long.

In case of Bipolar Neurons, we have two Processes – one Dendrite and one Axon.

Each and every Neuron in our brain has anywhere between 1,000 and 10,000 connections with other Neurons in brain, taking the total number of neural connections in brain to 100 trillion.

In case of Unipolar Neurons, we have just one ‘Process’ that can branch out. This ‘Process’ can actually work as a Dendrite or it can work as an Axon.

There are some Unipolar Neurons that actually started out as Bipolar Neurons during the developmental stage. Such Unipolar Neurons are usually called as Pseudounipolar Neurons.

Sensory Neurons are those Neurons that will pick up information from sensory receptors on body, for example – Ears, Tongue, Eyes, Skin, Nose etc. The information picked up by these Neurons will send the information towards the Central Nervous System.

There are approximately 100 billion Neurons in our brain. That’s just 10% of all the brain cells we have. That’s more than the number of stars in our Milky Way. There are around 13.5 million Neurons in our spinal cord.

Motor Neurons are those Neurons that will take the information processed in the Central Nervous System and send it away to glands or muscles.

When the Neurotransmitters lock on to the receptor sites on next Neuron, a pathway is opened for ions, disturbing the membrane potential of the next Neuron and the whole process of Action Potential propagation starts all over again in the recipient Neuron. This is how electrical and chemical signals are transmitted by the Neurons

Sensory Neurons are also known as AFFERENT Neurons and Motor Neurons are also known as EFFERENT Neurons.

The chemicals that are released in the Synaptic Gap are called Neurotransmitters. These Neurotransmitters sail across the gap and will attach with receptor sites present on the next Neuron.

Finally, we have the Interneurons that connect the Sensory Neurons and the Motor Neurons for facilitating transmission of information or signals. These Interneurons are located entirely inside the Central Nervous System.

At the Synaptic Terminal, an Action Potential will caused Vesicles to be released in a small gap called Synaptic Gap. Vesicles are small bubbles of chemicals. Synaptic Gap is the gap that lies between an Axon ending of one Neuron and Dendrite of another Neuron or Effector.

Neurons have one sole purpose – communication. This takes place in four different steps. These steps are mentioned below.

There are 4 major types of tissues in our body. One of them is the Nervous Tissue. The Nervous Tissue makes up the nerves, the spinal cord and the brain.

Neurons will pick signals. These signals may originate from a source that is external (such us a touching a hot coal where the hot coal is the external source) or can originate from another Neuron (for example a Neuron in our brain can receive signals from hundreds and thousands of other Neurons that are interconnected with Interneurons forming what is known as the neural network).

The electrical activity because of the stimulus suddenly changes the balance of ions, disturbing the membrane potential for a brief period of time, generating electrical signals that propagate from the Soma to Axon and finally to Synaptic Terminals. These electrical signals are called ‘Action Potentials’.

The Nervous Tissue is made mainly of two types of cells – the Neurons (nerve cells) and the Neuroglia or the Glial Cells. Glial Cells are integral part of the Nervous Tissue because they are support cells and are very necessary. However, we will keep Glial Cells for another article.

When a Neuron is stimulated by any stimulus, an electrical activity takes place. It is known that the cell membrane of each and every living cell has a lining of electrically charged atoms called ions. These ions sit both inside and outside of the cell membrane. They stay in a balanced form and create what is known as membrane potential.

Once a Neuron picks up a signal, it will process or integrate the signal and decide whether or not to pass on the signal as output. This processing usually takes place in CNS. This integration is pretty interesting and takes place both in time and space. What does that mean? It means that processing will take place right at the point in time when the input is taking place and in case of multiple inputs, processing also takes place during the time between two inputs. This is called integration in time.