Question

A list of events occurring in the transmission of nerve inpulk across the synapse is given below in a random order. (i) Opening of specific ion channels allows the ento d ions, a new action potential is generated in the poos. synaptic neuron. (ii) Neurotransmitter binds to the receptor on post synaps: membrane (iii) Synaptic vesicle fuses with pre-synaptic membrane, neurotransmitter release into synaptic cleft. iv) Depolarization of pre-synaptic membrane. v) Arrival of action potential at axon terminal.

Short answer

The correct sequence is: (v) Arrival of action potential at axon terminal, (iv) Depolarization of pre-synaptic membrane, (iii) Synaptic vesicle fuses with pre-synaptic membrane releasing neurotransmitter, (ii) Neurotransmitter binds to receptors on post-synaptic membrane, and (i) Opening of ion channels resulting in a new action potential in the post-synaptic neuron.

Step-by-step solution

Arrival of the Action Potential

Identify the event that initiates the process at the synaptic terminal. The arrival of an action potential at the axon terminal is the first step in the sequence.

Depolarization of Pre-synaptic Membrane

Determine what happens immediately after the action potential arrives. Depolarization of the pre-synaptic membrane is the second step, triggered by the action potential.

Fusion of Synaptic Vesicles with Pre-synaptic Membrane

After depolarization, synaptic vesicles containing neurotransmitters fuse with the pre-synaptic membrane, releasing their contents into the synaptic cleft.

Neurotransmitter Release

Clarify that the neurotransmitter release into the synaptic cleft is part of the vesicle fusion process. It is the continuation of Step 3, where neurotransmitter molecules are released into the synaptic gap.

Binding of Neurotransmitter to Post-synaptic Receptors

Once neurotransmitters are in the synaptic cleft, they bind to specific receptors on the post-synaptic membrane. This is the next event in the sequence.

Ion Channel Opening and Generation of New Action Potential

The binding of neurotransmitters to the receptors results in the opening of specific ion channels. This leads to the entry of ions and generation of a new action potential in the post-synaptic neuron, completing the sequence.

Key concepts

Synaptic Cleft

The synaptic cleft plays a pivotal role in the communication between neurons in the nervous system. It is the small gap, approximately 20 nanometers wide, that separates the pre-synaptic neuron from the post-synaptic neuron. Think of it as the space where an important conversation takes place—the conversation being the chemical signals that convey information.

When an action potential arrives at the axon terminal of the pre-synaptic neuron, it sets the stage for this critical discourse. The synaptic cleft ensures that neurons do not physically touch; instead, the communication occurs through the release of chemical messengers. This elegant design allows for precise control over where and when neurons activate, providing the brain with its complex functionality.

Neurotransmitter Release

The release of neurotransmitters is akin to sending a letter through a pneumatic mail tube—it's quick, targeted, and efficient. Neurotransmitters are the chemical messengers produced by neurons that relay signals across the synaptic cleft to the post-synaptic neuron.

The process commences when an action potential depolarizes the pre-synaptic membrane. This triggers synaptic vesicles inside the neuron to move towards and fuse with the pre-synaptic membrane—a step that's essential for the contents, the neurotransmitters, to spill into the synaptic cleft. Without this release, the crucial information would be confined within the neuron, unable to influence the next neuron in line. It is this release that ensures the continuation of the neural conversation, one synapse at a time.

Post-Synaptic Receptors

Upon reaching the other side of the synaptic cleft, neurotransmitters encounter post-synaptic receptors—specialized proteins embedded in the membrane of the post-synaptic neuron. These receptors are like mail slots for the neurotransmitters, designed to bind selectively to specific messenger molecules.

Once the neurotransmitter and receptor pair up, the downstream effects are initiated. It's as if the receptor unlocks a door, allowing specific ions to flow into the post-synaptic cell. This results in changes in the post-synaptic neuron's electrical charge, a process crucial for the propagation of the neural signal. The diversity of receptor types and functions in the brain contributes to the vast array of neural communications and responses, influencing everything from muscle contractions to mood regulation.

Action Potential

The action potential is the foundation of nerve impulse transmission. It's an electrical phenomenon that occurs when a neuron 'fires' and sends a signal down its axon. You can imagine it as a wave of electrical charge rushing along the neuron's membrane—this is what ultimately leads to the communication between neurons.

An action potential is initiated when a neuron's membrane potential reaches a certain threshold. Thanks to a complex ballet of ion channels opening and closing, positively charged ions rush in and out of the neuron. This change in electrical charge moves down the axon until it reaches the terminal, where it triggers the release of neurotransmitters, thus connecting the cycle of neural communication. Without action potentials, our ability to move, think, feel, and react would simply be non-existent.