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:
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.
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.
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.
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.
Efferent nerves: These transmit signals from our CNS to their respective motor neurons which then pass on any message to muscles or tissue.
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.
FAQs on Neurons and Nerves
1. What is the main difference between a neuron and a nerve?
A neuron is a single, individual nerve cell, which is the basic structural and functional unit of the nervous system. A nerve, on the other hand, is a cable-like bundle of axons from many different neurons, wrapped together in a protective sheath. Essentially, a neuron is a single cell, while a nerve is a collection of parts from many of those cells.
2. What are the main parts of a neuron and what are their functions?
A typical neuron consists of three primary parts, each with a specific role in transmitting nerve impulses:
- Cell Body (Soma): This is the core of the neuron, containing the nucleus. It manages the cell's metabolic activities and integrates incoming signals.
- Dendrites: These are short, branch-like extensions that act as the neuron's receivers. They pick up signals from other neurons and transmit them towards the cell body.
- Axon: This is a long, slender projection that carries nerve impulses away from the cell body to other neurons, muscles, or glands, acting as the transmitter.
3. What are the primary types of neurons based on their function?
Based on their role in the nervous system, neurons are classified into three main types:
- Sensory Neurons: These neurons carry signals from sensory organs (like skin, eyes, or ears) to the central nervous system (brain and spinal cord).
- Motor Neurons: These carry commands from the central nervous system to effector organs, such as muscles and glands, to produce a response.
- Interneurons: Found entirely within the central nervous system, these neurons act as connectors, processing information and relaying signals between sensory and motor neurons.
4. How do neurons communicate signals to each other?
Neurons communicate at a specialized junction called a synapse. When an electrical impulse travels down the axon of one neuron, it triggers the release of chemical messengers called neurotransmitters into the synaptic gap. These chemicals then travel across the gap and bind to receptors on the dendrites of the next neuron, initiating a new electrical signal in that cell.
5. What is a reflex arc and why is it so fast?
A reflex arc is the neural pathway that controls an involuntary reflex action, like pulling your hand away from a hot object. It is exceptionally fast because the signal pathway is very short and direct. A sensory neuron sends a signal directly to the spinal cord, which immediately activates a motor neuron to cause a reaction. This process bypasses the brain, which is only notified after the action is complete, saving crucial time.
6. Does the brain contain nerves or neurons?
The brain is composed almost entirely of neurons—billions of them—along with supporting glial cells. These neurons form the intricate circuits for thought and processing. While nerves connect the brain to the body (like cranial nerves), the large bundles of axons that connect different regions within the brain itself are typically called tracts, not nerves.
7. Why can signals in a synapse only travel in one direction?
The one-way flow of information at a synapse is a result of its specialised structure. Neurotransmitters are released only from the axon terminal of the sending neuron (pre-synaptic neuron). The receptors that detect these chemicals are located only on the dendrites or cell body of the receiving neuron (post-synaptic neuron). This specific arrangement ensures that signals can only pass from the sender to the receiver, preventing them from flowing backward.
8. Can neurons in the human body be regenerated after damage?
A neuron's ability to regenerate largely depends on its location. In the Peripheral Nervous System (PNS), which includes nerves outside the brain and spinal cord, damaged axons can sometimes regenerate if the cell body is unharmed. However, in the Central Nervous System (CNS)—the brain and spinal cord—the capacity for regeneration is extremely limited. This is why injuries to the CNS often lead to permanent functional loss.
