Happens At The Synapse Between Two Neurons

                                      #Structure of a synapse#

The synapse is a crucial structure in the nervous system that enables communication between neurons, the fundamental cells of the brain and spinal cord. This small but complex junction allows electrical or chemical signals to be transmitted from one neuron to another, playing a key role in everything from muscle movement to memory and thought. Understanding the events that take place at the synapse helps us understand how the nervous system functions as a whole.The synapse is a small gap or junction between two neurons. It consists of three main parts: **Presynaptic terminal**: This is the end of the neuron that sends signals. It contains synaptic vesicles filled with neurotransmitters — chemical messengers that transmit signals across the synapse. **Synaptic cleft**: This is the small gap (about 20-40 nanometers wide) between the presynaptic terminal and the next neuron. **Postsynaptic membrane**: This is the part of the receiving neuron that contains receptor proteins that are able to bind neurotransmitters and respond to the incoming signal.Most synapses in the human nervous system are **chemical synapses**, although there are also **electrical synapses**, which are less common and work differently.

      #Step-by-step events in a chemical synapse#

**Action potential arrival**This process begins when an electrical impulse, or action potential, travels down the axon of the presynaptic neuron. This action potential is generated by the sudden movement of ions across the neuron's membrane and moves toward the presynaptic terminal.**Calcium ion influx**Calcium ions then rush into the neuron from the extracellular fluid, driven by its high concentration outside the cell. **Vesicle fusion and neurotransmitter release**The influx of calcium ions triggers synaptic vesicles — tiny membrane-bound sacs containing neurotransmitters — to move toward and fuse with the presynaptic membrane. Through a process called **exocytosis**, the vesicles release their neurotransmitter contents into the synaptic cleft. **Diffusion of neurotransmitters into the synaptic cleft**Once released, neurotransmitters diffuse into the synaptic cleft. **Binding to receptors**On the postsynaptic side, specific receptors embedded in the membrane bind to the neurotransmitters. **Formation of postsynaptic potential**The binding of neurotransmitters to receptors opens or closes ion channels in the postsynaptic membrane, depending on the type of neurotransmitter and receptor. This can either:* **Excite the postsynaptic neuron**, making it more likely to fire an action potential (called an **Excitatory postsynaptic potential**, or EPSP), or* **Inhibit the neuron**, making it less likely to fire (an **Inhibitory postsynaptic potential**, or IPSP).The combined effect of multiple EPSPs and IPSPs determines whether the postsynaptic neuron will reach the threshold to fire its own action potential.

                            #Clearing the synaptic cleft#

After neurotransmitters have delivered their message, they must be cleared from the synaptic cleft to prevent continued excitation or inhibition of the postsynaptic neuron. There are three main ways this happens:**Reuptake**The presynaptic neuron reabsorbs the neurotransmitters via transporter proteins. This is a common mechanism for neurotransmitters such as serotonin and dopamine. **Enzymatic degradation**Enzymes in the synaptic cleft break down neurotransmitter molecules. For example, the enzyme acetylcholinesterase breaks down acetylcholine into inactive components. **Diffusion**Some neurotransmitters simply move away from the synaptic cleft and are eventually absorbed or broken down elsewhere.Unlike chemical synapses, **electrical synapses** involve direct physical connections between neurons through structures called **gap junctions**. However, electrical synapses are less flexible and cannot amplify or modify the signal as chemical synapses can.

Click here more site>>>>>>>>>>>>Enjoy in gurugram