Generation, Conduction And Transmission Of Nerve Impulse: Process & Types

What Is a Nerve Impulse?

A nerve impulse is an electrical wave that sweeps down the length of a neuron. These impulses are how the nervous system communicates as the waves are how the information can travel to and from the body, through the brain and spinal cord. They allow for anything from a muscle to contract to perception.

Neuron Structure Relevant to Nerve Impulse

The neurons are the basic building blocks of the nervous system, particularly specialized for the communication of nerve impulses. The different parts primarily constituting one single neuron are described as follows.

• Cell Body (Soma): It contains the nucleus and other organelles that maintain the health and functioning of the neuron.

• Dendrites: The branches are supported extensions, specifically those that allow the receiving of signals by activity conducted through neurone transmissions towards the cell body.

• Axon: The second type of long and thin cellular projection that conducts impulses away from the cell body towards the neurons or the effectors.

• Myelin Sheath: A fatty layer that insulates the cell body from the axon, serving to increase speed during conduction.

• Nodes of Ranvier: gaps in between the myelin sheath, the action potentials will cause the signal to jump along the axon quickly.

Mechanism of Nerve Impulse

The generation of a nerve impulse includes a series of electrical changes across the membrane of the neuron. The resting neuron initiates the process, and subsequently, several unique phases occur as an impulse is transmitted.

Resting Potential

• The voltage across the neuronal membrane in the neuron is not conducting an impulse.

• Average value is -70 mV.

• Ion distribution, outside the neuron, there is a high concentration of Na+; while inside the neuron contains a high concentration of K+.

Action Potential

• Depolarisation: opening of Na+ channels and entry of Na+ make the membrane potential positive.

• Repolarisation: The opening of K+ channels and the exit of K+ make the potential negative.

• Hyperpolarisation: a momentary increase in negativity before the membrane potential returns to the resting potential.

• Refractory Period: A period in which the neuron is not able to initiate another action potential

Conduction Of Nerve Impulse

After the nerve impulse is initiated, it needs to be conducted through the length of the neuron to properly send the message. A nerve impulse can be conducted down the length of a neuron in one of two ways, which depends on whether a neuron is myelinated or un-myelinated.

Saltatory Conduction (Myelinated Fibres)

• Happens in myelinated neurons.

• Action potential jumps from one Node of Ranvier to the other.

• Raises the speed of impulse induction

Continuous Conduction (Unmyelinated Fibres)

• Happens in un-myelinated neurons.

• Action potentials propagate along the axon without decremental

Transmission Of Nerve Impulse (Synase)

The generation of the nerve impulse is an organized process of electrical changes across the membrane of the neuron. It is a process that initiates with the smallest and moves across all the degrees before a neuron is ready to send an electrical signal.

Structure of Synapse

• Presynaptic Neuron: Neuron sending the signal.

• Synaptic Cleft: Gap between neurons.

• Postsynaptic Neuron: The neuron receiving the signal.

Chemical Synaptic Transmission

• When the action potential reaches the axon terminal.

• When Ca2+ enters through calcium channels.

• The neurotransmitters are released by the vesicles into the synaptic cleft.

• The neurotransmitters bind with the receptors present on the postsynaptic membrane.

• The ion channels either open to lead to the depolarisation or hyperpolarisation of the postsynaptic neuron.

Types Of Neurotransmitters

The two types of neurotransmitters are:

Factors Affecting Nerve Impulse Transmission

The factors affecting nerve impulse transmission are:

• Temperature: Higher temperatures increase speed.

• Axon Diameter: Larger diameters conduct faster.

• Myelination: Myelinated axons conduct impulses more rapidly.

Nerve Impulse-Related Disorders

Neurological disorders alter the process of impulse transmission:

Multiple Sclerosis

• Disorder of demyelination and improper nerve conduction

Epilepsy

• Results from unusual electrical activity in the brain.

Neuropathies

• Conditions come in the way of the normal function of the nerve, and this can often lead to pain, weakness, or numbness.

Nerve Impulse NEET MCQs (With Answers & Explanations)

Important questions asked in NEET from this topic are:

• Mechanism of nerve impulse

• Factors affecting nerve impulse

Practice Questions for NEET

Q1. Axolemma is selectively permeable for

1. Complex proteins

2. Simple organic molecules

3. Inorganic molecules

4. Both b and c

Correct answer: 4) Both b and c

Explanation:

Axolemma is selectively permeable for simple organic and inorganic molecules. The axolemma's permeability is regulated by ion channels and transporters in the membrane. These channels are specific to certain ions such as sodium, potassium, calcium, and chloride. Being selectively permeable, it also helps in maintaining the resting membrane potential.

Hence, the correct option is d. both b and c.

Q2. What is the function of the axon in a neuron?

1. To receive signals from other neurons

2. To support and protect the cell body

3. To transmit signals to other neurons

4. To synthesize neurotransmitters

Correct answer: 3) To transmit signals to other neurons

Explanation:

The function of the axon in a neuron is to transmit signals to other neurons or other cells such as muscles or glands. The axon is a long, slender projection of the neuron that carries electrical signals away from the cell body and toward the axon terminals, where neurotransmitters are released to communicate with other neurons or cells. The axon is covered by a myelin sheath, which helps to insulate and speed up the transmission of electrical signals.

Hence, the correct answer is option 3) To transmit signals to other neurons.

Q3. Resting membrane potential is maintained by

1. Hormones

2. Neurotransmitters

3. Ion pumps

4. None of the above

Correct answer: 3) Ion Pumps

Explanation:

The sodium-potassium pump and leak channels are examples of ion pumps and channels that preserve a cell's resting membrane potential:
For every ATP molecule, this pump transports two potassium ions into the cell and three sodium ions out of it. The potassium ion gradient produced by this action adds to the resting membrane potential. The electrical potential across a cell's plasma membrane when it is not activated is known as the resting membrane potential. Because more cations are released than are absorbed, the inside of the cell stays negatively charged in relation to the extracellular fluid.

Hence, the correct answer is option 3) Ion pumps.

Also Read:

• MCQs on Introduction to Nerve Impulse

• Mechanism of Vision

• Lobes of Cerebrum

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