[Biology Class Notes] on Neurons and Nerve Impulse Pdf for Exam

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 –

1. Dendrite

2. Axon

3. Axon terminal

4. Soma

5. Node of Ranvier

6. Schwann cell

7. Myelin Sheath

8. 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: 

1. Which part of a neuron receives a nerve impulse first?

2. What is Axoplasm?

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