What is the structure and function of neurons and how does nerve impulse transmission occur
A Brief Introduction to Neurons & Nerve Impulse
The nervous system is responsible for generating a response to external stimuli. In a broad sense, the nervous system has three components, namely, the brain, spinal cord and neurons.
In this article, you will find information about neurons and generation and conduction of nerve impulse. In turn, it will help you understand related concepts more effectively.
That being said, read on to find more!
What is Neuron?
A neuron is a structural and functional unit of the nervous system. Collectively, neurons can identify, receive and transmit different kinds of stimuli.
So, in case you are wondering, “what is an impulse in Biology?” Remember that nerve impulse in biology is simply how neurons communicate with one another. It occurs owing to a disparity in electrical charges in a neuron’s plasma membrane.
Notably, neurons interact with one another at designated junctions known as synapses. Now, they are either chemical (interacting through chemical messengers) or electrical.
These are the Components of Neurons –
Dendrite
Axon
Axon terminal
Soma
Node of Ranvier
Schwann cell
Myelin Sheath
Nucleus
This figure below offers a pictorial representation of a neuron and its components.
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State as True or False: There are 3 parts in a Neuron.
Generation and Conduction of Nerve Impulse
Generation of nerve impulse is dependent on the strength of a stimulus, which in turn, triggers both chemical and electrical changes in neurons. Notably, the neural membrane harbours several ion channels which are selectively porous to different ions.
For instance,
A. Generation of Nerve Impulse: Resting Membrane
When a specific neuron is resting, its axonal membrane is relatively porous to potassium ions. Alternatively, it is quite non-porous to sodium ions (Na+) and other negatively charged proteins in axoplasm.
This axoplasm comprises a high concentration of potassium ion (K+), negatively charged ions and also a low concentration of sodium ion. Likewise, the fluid present outside axon comprises a low concentration of potassium ion but a high concentration of sodium ion.
Resultantly, it forms a concentration gradient. Now, these ionic gradients in a resting membrane are kept stable through the active transmission of ions.
As the sodium-potassium exchange pump transmits 3Na+ out to draw 2 K+ into the cell, the interior of the axonal membrane becomes negatively charged. Similarly, the membrane’s exterior becomes positively charged and through the course gets polarised.
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B. Generation of Nerve Impulse: Active Potential
Regardless in the event of generation of nerve impulse, the porousness of the cell membrane changes. The above mentioned sodium ions now flow inside, while the potassium ions flow outside. This reserves the charges and depolarises the cell.
In turn, an action potential occurs which further drives the nerve impulse across the axon. Also, the said depolarisation takes place throughout the nerve.
It is noteworthy that a series of reactions take place where sodium ions flow out and potassium ions move into a cell. Consequently, the process again leads to the polarisation of cells with the restoration of their initial charges.
Subsequently, neurotransmitters release chemicals when a nerve impulse makes its way at the end of the axon. These chemicals diffuse in the synaptic gap and may be transmitted either by the chemical synapse or the electrical synapse.
This figure below represents the generation conduction of nerve impulse.
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Test Your Knowledge:
Which part of a neuron receives a nerve impulse first?
What is Axoplasm?
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FAQs on Neurons and Nerve Impulse Structure and Transmission
1. What is a neuron and what is its function?
A neuron is a specialized nerve cell that transmits electrical and chemical signals in the body. It is the structural and functional unit of the nervous system and is responsible for communication between the brain, spinal cord, and other body parts.
- Receives signals through dendrites
- Processes information in the cell body (soma)
- Transmits impulses along the axon
- Passes signals to other cells at the synapse
Neurons enable thinking, movement, sensation, and reflex actions.
2. What are the main parts of a neuron?
The main parts of a neuron are the dendrites, cell body, and axon. Each part has a specific role in nerve impulse transmission.
- Dendrites – receive incoming signals from other neurons
- Cell body (soma) – contains the nucleus and integrates signals
- Axon – carries nerve impulses away from the cell body
- Myelin sheath (if present) – insulates the axon and speeds up impulse conduction
- Axon terminals – release neurotransmitters at the synapse
These structures work together to ensure efficient signal transmission in the nervous system.
3. What is a nerve impulse?
A nerve impulse is a rapid electrical signal called an action potential that travels along a neuron’s axon. It occurs due to changes in electrical charge across the neuron’s membrane.
- Triggered by a stimulus reaching threshold
- Involves movement of sodium (Na⁺) and potassium (K⁺) ions
- Travels in one direction along the axon
- Ends at the synapse to transmit the signal
Nerve impulses allow rapid communication within the nervous system.
4. How does a nerve impulse travel along a neuron?
A nerve impulse travels along a neuron through a sequence of membrane depolarization and repolarization known as an action potential. This process involves ion movement across the axon membrane.
- Resting potential – neuron is polarized at about −70 mV
- Depolarization – Na⁺ channels open and sodium enters
- Repolarization – K⁺ channels open and potassium exits
- Propagation – the impulse moves forward along the axon
In myelinated neurons, the impulse jumps between nodes in a process called saltatory conduction.
5. What is the role of the myelin sheath in nerve impulse transmission?
The myelin sheath is an insulating layer around the axon that increases the speed of nerve impulse conduction. It prevents ion leakage and allows impulses to jump between gaps called nodes.
- Formed by Schwann cells (PNS) or oligodendrocytes (CNS)
- Creates gaps known as Nodes of Ranvier
- Enables saltatory conduction
- Greatly increases transmission speed
Damage to myelin, as in multiple sclerosis, slows nerve impulse transmission.
6. What happens at a synapse?
At a synapse, a nerve impulse is transmitted from one neuron to another using chemical messengers called neurotransmitters. This ensures communication between neurons or between a neuron and a muscle or gland.
- Impulse reaches the axon terminal
- Neurotransmitters are released into the synaptic cleft
- They bind to receptors on the postsynaptic membrane
- A new impulse may be generated in the next cell
Synaptic transmission is usually one-way and ensures controlled signal flow.
7. What is the difference between sensory, motor, and interneurons?
The difference between sensory, motor, and interneurons lies in the direction and function of impulse transmission.
- Sensory neurons – carry impulses from receptors to the central nervous system
- Motor neurons – transmit impulses from the CNS to muscles or glands
- Interneurons – connect neurons within the CNS and process information
Together, these neuron types coordinate reflex actions, movement, and complex thinking.
8. What is the resting potential of a neuron?
The resting potential of a neuron is the electrical charge difference across its membrane when it is not transmitting an impulse, typically about −70 mV. It results from unequal ion distribution.
- Maintained by the sodium-potassium pump
- More Na⁺ outside and more K⁺ inside the cell
- Inside of the neuron is negatively charged relative to outside
Resting potential is essential for generating an action potential.
9. Why does a nerve impulse travel in one direction?
A nerve impulse travels in one direction because of the refractory period that follows depolarization. During this time, the recently activated region cannot generate another impulse immediately.
- Na⁺ channels become temporarily inactivated
- The membrane undergoes repolarization
- Prevents backward propagation
This ensures that action potentials move forward from the cell body toward the axon terminals.
10. What is saltatory conduction?
Saltatory conduction is the rapid transmission of a nerve impulse in which the action potential jumps between Nodes of Ranvier in a myelinated axon. It significantly increases conduction speed.
- Occurs only in myelinated neurons
- Impulse jumps from node to node
- Reduces energy use by limiting ion exchange
Saltatory conduction makes nerve impulse transmission faster and more efficient compared to unmyelinated fibers.
