What Is a Neuron? – Definition, Structure, and Function

Overview

The neurological systems of the human body sense what is happening around and inside us! The nervous system determines how an individual should act, alters the status of inner organs (for example, heart rate), and allows individuals to engage and recall what is going on. It is accomplished through the use of a sophisticated network of neurons.

Curiously Enough It is believed that the brain contains approximately 86 billion neurons; a developing foetus must generate approximately 2,50,000 neurons per minute.

Each neuron is linked to the next 1,000 neurons, resulting in an immensely intricate communication network. Neurons are the primary building blocks of the central nervous system. Neurons, also known as nerve cells, constitute around 10% of the brain; the remainder comprises glial cells and astrocytes, which maintain and replenish the other neurons. Neurons are in charge of transporting messages all across the human body. They assist and coordinate all necessary operations using chemical and electrical impulses. This post defines neurons and describes how they function.

What is Neuron?

Neurons (also known as nerve cells) are the basic units of the brain and nervous system, involved in absorbing sensory information from the outside world, transmitting motor commands to the muscles, and converting and passing electrical signals at each step between these. The interaction of these neurons helps the individual to know each other. There are about 100 billion neurons that interact intimately with other cell types known as glia (which may exceed neurons, but this is unknown).

Neuron Structure

A neuron structure comprises three major components: dendrites, an axon, and a cell body or soma, which can be equated to the branches, roots, and trunk of a tree. Neuron structures may only be seen under a microscope and are divided into three types:

Did You Know? A neuron’s tree-like structure. Dendritic spines are tiny structures that accept input from neighbouring neurons’ axons. Bottom-right image: a dendritic segment from which spines grow like leaves from a tree limb. The size of a neuron is extremely small (0.001mm).

• Dendrite

A neuron’s dendrite (tree branch) is where it gets input from neighbouring cells. Dendrites are tiny filaments that convey information from neurons to the soma. They constitute the cell’s “input.” Dendrites, like tree branches, spread as they progress towards the tips, and they have leaf-like projections on them, commonly called spines.

Dendrites play an important role in synapses; it allows them to receive messages from other neurons. Some neurons have shorter dendrites, whereas others have longer dendrites.

• Axon

The axon (tree roots) is the neuron’s outlet structure, where one neuron communicates with another neuron by sending electrical signals or messages. It is a lengthy projection that transports messages from the soma to neighbouring cells. It is the cell’s “output” section. It usually concludes with many synapses linking to the dendrites of many other neurons.

The axon, also known as a nerve fibre, is a neuron’s tail-like structure that connects to the cell body at a point known as the axon hillock. The axon’s role is to transport impulses from the nerve cell to the axon terminal, where they can be transmitted to other neurons.

• Soma or Cell body

The soma (tree trunk) houses the nucleus, the neuron’s DNA, and the proteins carried throughout the axon and dendrites. It is also known as the powerhouse of the nerve cell. The soma (cell body) of the neuron receives all the information. 

The soma is surrounded by a membrane that protects and allows it to communicate with its surroundings. The soma comprises a cell nucleus, which generates genetic information and drives protein synthesis. These proteins are required for other components of the neuron to operate properly.

Neurons of various sorts are present in the spinal cord and the brain. Neurons are classified based on where they originate, where they project to, and which synapses they employ.

Curiously Enough Neurons are the cells of the nervous system. They are composed of three parts: a cell body, an axon, and dendrites. These components aid in the transmission and reception of chemical and electrical impulses.

How does an Electrical Impulse travel from Neuron to Neuron?

When a neuron receives a huge set of inputs from other neurons, the signals accumulate until they reach a certain threshold. When this threshold is reached, the neuron is stimulated to release an impulse through its axon, known as an action potential. Electrically charged atoms (ions) transported through the axon membrane generate an action potential.

The membrane potential of neurons at rest is much more negatively charged than the fluid surrounding them. Typically, it is -70 millivolts (mV).

When a nerve’s cell body absorbs enough impulses to fire, a part of the axon closest to the cell body relaxes, and the membrane potential rapidly increases and then lowers (in around 1,000ths of a second).

This change causes depolarisation (relaxation) in the axon beside it, and so on until the charge increases and the fall has travelled throughout the full length of the axon.

After each section fires, it enters a brief period of hyperpolarization in which its threshold is decreased, making it harder to be activated immediately again. The action potential is usually generated by potassium (K+) and sodium (Na+) ions. Ions enter and exit the axons via voltage-gated ion pumps and channels.

How do Neurons Connect to Other Neurons?

Learners frequently question, “how do neurons connect to other neurons?” To understand this, continue reading ahead!

Neurons are always linked with one another to transfer signals; however, they do not physically contact – there is always a space between cells known as a synapse. There always exists an electrical and chemical which connects the two neurons. These signals are sent either electrically or chemically from the first nerve fibre (presynaptic neuron) to another (postsynaptic neuron) to transfer messages.

Chemical Synapses

When a signal reaches a synapse, it causes chemicals (neurotransmitters) to be released into the distance (gap) between two neurons; this distance (gap) is known as the synaptic cleft. The neurotransmitter diffuses through the synaptic cleft and binds with receptors on the postsynaptic neuron’s membrane, causing a reaction. Chemical synapses are categorised based on the neurotransmitter they possess.

The neurotransmitters released by chemical synapses are categorised as follows:

• Glutamatergic produces glutamine. They are frequently excitatory, which means they are more likely to elicit an action potential.
• GABAergic produces GABA (gamma-Aminobutyric acid). They are frequently inhibitory, which means they diminish the likelihood of the postsynaptic neuron firing.
• Cholinergic neurons release acetylcholine. These are between sensory neurons and muscle fibres (the neuromuscular junction).
• Norepinephrine is released by adrenergic neurons (adrenaline).

Electrical Synapses

Electrical synapses are less prevalent but can be found all through the CNS. Gap junctions connect the postsynaptic and presynaptic membranes. The post- and presynaptic membranes are positioned closer together in gap junctions than chemical synapses, allowing them to conduct electric current effectively.

Because electrical synapses are far quicker than chemical synapses, they are present in regions where immediate actions are required, such as defensive reflexes.

Electrical synapses can only create simple responses, whereas chemical synapses can cause complicated reactions. They are bidirectional, unlike chemical synapses, and information or message can flow in either manner.

Curiously Enough There are millions of different types of neurons; these can be divided into three functional classes, which are motor neurons, sensory neurons, and interneurons.

Conclusion

Neurons are among the most exciting forms of human cells. They are required for every movement in the human body and allow the brain to function accurately. The intricacy of neural networks is responsible for an individual’s overall personality and intelligence. They are in charge of the most fundamental and complex actions. Neurons cover everything, from simple reflex responses to complex thoughts about the world.

Frequently Asked Questions

1. Describe the various types of neurons and their functions.

A. Different types of neurons serve various jobs. Three types of neurons are found in the human body: sensory neurons, motor neurons and interneurons. They form the network of nerve cells that transmits an impulse across the nervous system.

A sensory neuron detects and converts stimuli from the direct or indirect environment into nerve impulses. An interneuron is a type of neuron that transports nerve impulses from one neuron to the next. A motor neuron transmits input to a muscle or gland, and the muscle or gland responds.

2. What do neurons observe when they listen to the conversations of other neurons?

A. It is determined by the language or type of neurotransmitter produced in the conversation between neurons. Despite certain exceptions discovered via research, most neurons are now assumed to be unilingual. They are seen releasing only one type of neurotransmitter.

Most (80%) produce glutamate, an excitatory neurotransmitter that stimulates activity in recipient neurons, while other neurons release GABA, an inhibitory neurotransmitter that suppresses activations. Other neurotransmitters are as follows:

• Glycine
• Dopamine (the loss of which leads to Parkinson’s Disease) 
• Acetylcholine
• Serotonin                                             

 3. What is Axon Terminal?

A. The axon terminals (terminal buttons) are the end of the neuron that transfers signals to other neurons. A synapse is a gap found at the tip of the terminal button. Terminal buttons contain vessels containing neurotransmitters.

Neurotransmitters are released into the synapse from the terminal buttons and are utilised to convey signals across the synapse to neighbouring neurons. During this process, electrical signals are converted to chemical signals. The terminal buttons are then responsible for reabsorbing the extra neurotransmitters that did not transfer to the following neuron.