Transmission of Nerve Impulses

Transmission of Nerve Impulses: The nervous system is responsible for controlling and coordinating the activities of different organs and systems in the body. The subtopic of “Transmission of Impulses” is an important part of the chapter “Neural Control and Coordination” in CBSE Class 11 Biology. 

A vital component in our nervous system is the transmission of impulses – how we communicate messages throughout the neural network. Action potentials, or electrical signals that travel between cells known as neurons facilitate this communication efficiently. This coordinated effort across multiple cells allows us to respond quickly and with precision no matter what triggers our response.

Transmission of Impulses

The nervous system consists of specialized cells called neurons that transmit electrical signals called nerve impulses or action potentials. The transmission of impulses involves a series of events that occur in a coordinated manner.

Generation of Nerve Impulse/Action Potential

Nerve impulses are generated when a neuron is stimulated by a stimulus, which could be a change in the external environment or an internal signal from the body. This results in the opening of ion channels in the neuron’s cell membrane, leading to a rapid influx of sodium ions and an efflux of potassium ions. This generates an electrical potential difference across the neuron’s cell membrane, known as the action potential. As a result of action potential generation, the membrane of the neuron becomes depolarised, which was previously polarised in the resting state.

Propagation of Nerve Impulse

Once generated, the nerve impulse travels along the neuron’s axon in a self-propagating manner. It is aided by the presence of myelin sheath in some neurons, a fatty layer that insulates the axon and speeds up the transmission process. The impulse jumps from one node of Ranvier to another, a phenomenon is known as saltatory conduction, which helps in the faster and more efficient transmission of impulses.

Synaptic Transmission

At the end of the axon, the nerve impulse reaches a specialized structure called a synapse, where it needs to be transmitted to the next neuron or target cell. The nerve impulse triggers the release of neurotransmitter molecules from the synaptic vesicles of the presynaptic neuron. These neurotransmitters diffuse across the synaptic cleft and bind to receptors on the postsynaptic neuron or target cell, generating a new action potential and continuing the transmission process.

Termination of Nerve Impulse

After the transmission of the impulse, the neurotransmitters are either taken back into the presynaptic neuron or are degraded by enzymes in the synaptic cleft. This helps in terminating the nerve impulse and preventing continuous transmission.

FAQs on Transmission of Impulse

Q1: What are the three main events involved in the transmission of nerve impulses in a neuron?

Answer: 

The three main events involved in the transmission of nerve impulses in a neuron are a generation of nerve impulses, propagation of nerve impulses, and synaptic transmission.

Q2: How does the presence of myelin sheath in a neuron contribute to faster transmission of nerve impulses?

Answer: 

The myelin sheath insulates the axon of a neuron, allowing the nerve impulse to jump from one node of Ranvier to another in a process called saltatory conduction. This speeds up the transmission process, making it faster and more efficient.

Q3: What is the role of neurotransmitters in synaptic transmission?

Answer: 

Neurotransmitters are chemical molecules that are released from the presynaptic neuron at the synapse. They diffuse across the synaptic cleft and bind to receptors on the postsynaptic neuron or target cell, generating a new action potential and continuing the transmission of the nerve impulse.

Q4: Explain the process of propagation of nerve impulses in a myelinated neuron.

Answer: 

In a myelinated neuron, the nerve impulse propagates by jumping from one node of Ranvier to another, due to the presence of myelin sheath. This process is called saltatory conduction, which speeds up the transmission process and conserves energy for the neuron.