Neurons and Nerves

Both our Central Nervous System (CNS) and the Peripheral Nervous System (PNS) rely on neurons to relay information across our body. While nerves and neurons may seem similar or even synonymous, they are not. 

A neuron is a specialised nerve cell which acts as the building blocks of our nervous system. It is specialised because it has the power to transmit and receive sensory data. The difference between nerves and neurons is that the latter are subparts of a nerve. 

To understand the functions of our nervous system, read on to know more on nerve cell parts.

About Neurons

Unlike other cells, neurons stop reproducing after birth. That means we only have a limited number of neurons. This aspect separates it from other cells.

A neuron has a slightly elongated shape and has three major parts.

• Nerve cell body: This is the first part of a neuron nerve cell. It is slightly round in shape and features all usual eukaryotic components including a nucleus, cell organelles and the usual membranes. 

• Dendrites: The second part of a neuron cell structure is its dendrites. It receives and transmits signals. These signals can be excitatory or inhibitive. If a signal is excitatory, that neuron will ‘fire’ by generating a small surge of electricity. Inhibitory responses mean the neuron does not fire. 

• Axon: This part plays the most crucial role in working of neuron. An axon is a long fibre which ends in synaptic terminals. Each terminal is dotted with receptive organs called synaptic knobs. Finally, a myelin sheath, usually made of fat, covers these axons. 

Did you know? Axons can be surprisingly long. The longest ones, called the ‘sciatic nerve’ travels all the way from the spine to your big toe!

Different Types of Neurons in the Nervous System

There are three major types of neurons. These are:

1. Sensory neurons: When studying on nerves and neurons, you must not forget that sensory neurons are by far the most important ones. It collects information from around the body and transmits it to our CNS.

2. Interneurons: Once a sensory unit has caught hold of information, it is passed on to an interneuron. These are also called connector neurons. These decide what response is needed for a specific stimulus.

3. Motor neurons: These are the messengers; they collect a response and pass them along to other cells which then take appropriate measures.

Task for you: You can write a short note on neurons, especially on motor neurons. As you know, the late Professor Stephen Hawking suffered from Motor Neurone disease. It is a degenerative disorder called Amyotrophic Lateral Sclerosis (or ALS). Another name for it is Lou Gehrig's disease.

About Nerves

A nerve is a bundle of axons which stays encased in epineurium. This is a connective tissue. All nerves carry ‘action impulses’ to different parts of the body based on stimuli. As you know by now, an axon is a part of a neuron. Therefore, if you are asked to write a nerve cell short note, it means you are writing on neurons.

There are 3 broad types of nerves. 

1. Afferent nerves: This type carries messages received from sensory neurons or nerve cells to our CNS. These are the most common nerves in our body. A good example would be the mechanoreceptor nerves found in our skin. 

2. Efferent nerves: These transmit signals from our CNS to their respective motor neurons which then pass on any message to muscles or tissue.

3. Mixed nerves: These are capable of receiving and transmitting signals. When studying nerves and neurons, remember that most of the cranial nerves are mixed ones. 

For advanced students: Find out more about all 13 cranial nerves. What do they  do? Why is there a dispute over whether there are 12, and not 13, nerves? 

You will find more information on our nervous system, including the parasympathetic and sympathetic ones on Vedantu. Download the Vedantu app today to browse through our other resources.