Language
Country/Area
No result found
Chemical vs. electrical synapses: Which do dominate in the brain?
In the brain, neurons connect through synapses, which can be divided into chemical synapses and electrical synapses. Chemical synapses are the primary form of information transmission between the vast majority of neurons, while electrical synapses are less common and represent direct electrical conduction. Together, they form the brain's complex neural network, which is essential for perception and behavior.
In the interaction of neurons, nerve impulses can be either facilitatory or inhibitory. When excitatory signals at a synapse outweigh inhibitory signals, the neuron generates a new action potential at its axon hillock, transmitting the information to another cell. This is called an excitatory postsynaptic potential (EPSP).
The most common neurotransmitter at excitatory synapses is glutamate, which diffuses into the dendritic spines of the postsynaptic neuron and binds to specific transmembrane receptors, triggering cell depolarization.
Comparison of electrical and chemical synapses
There are significant differences between electrical and chemical synapses. Electrical synapses enable the direct, active flow of electrical current through specialized intercellular connections called gap junctions. These connections enable electrical signals to be transmitted instantaneously between neurons and can travel in both directions. Their main goal is to synchronize the electrical activity between neurons.
In contrast, chemical synapses involve the transmission of neurotransmitters or neuropeptides, which are released from the presynaptic axon into the synaptic cleft. This mode of transmission involves multiple steps to complete the transmission of signals due to the presence of a 15 to 25 nanometer space called the synaptic cleft.
The process of synaptic transmission
In neurons with chemical synaptic transmission, neurotransmitters are synthesized either in the neuron cell body or in the presynaptic terminal, depending on the type of neurotransmitter. These neurotransmitters are stored in synaptic vesicles, and when a nerve impulse reaches the presynaptic terminal, calcium ion cell membrane channels open, causing calcium ions to enter the presynaptic terminal, ultimately triggering the release of neurotransmitters.
This calcium entry is necessary for the release of neurotransmitters, which then enhance or inhibit neuronal activity at receptors on the postsynaptic membrane.
Postsynaptic neuron response
When excitatory neurotransmitters reach the postsynaptic neuron, they bind to specific receptors clustered in the postsynaptic cytoskeleton. Depending on the receptor, this binding can rapidly change the electrical potential of the cell membrane, thereby affecting the probability of an impending action potential.
Types of excitatory neurotransmitters
Different excitatory neurotransmitters have different functions in the human body. For example, acetylcholine plays an important role in both the central and peripheral nervous systems, while glutamate is the primary excitatory neurotransmitter and is directly involved in signaling at most synapses.
In addition to glutamate, neurotransmitters such as catecholamines (such as norepinephrine), serotonin and histamine also play important roles in the nervous system, affecting mood, emotion and behavior.
Disease-related links to excitatory synapses
Excitatory synapses play a fundamental role in information processing in the brain and peripheral nervous system. Unfortunately, loss of synaptic stability can lead to disruptions in neural circuits and trigger various neurodegenerative diseases. For example, symptoms of Alzheimer's disease are related to problems with signal transmission, and dysfunction of current circuits is often closely associated with pathologies caused by AD and PD at the excitatory synapses.
Excitotoxicity: A pathological mechanism
Excitotoxicity is a process involving abnormal stimulation of the neurotransmitter glutamate, leading to the death of neurons. In the presence of high concentrations of glutamate, neurons become overstimulated, eventually triggering a process called apoptosis. This is an unfavorable factor for the development of many neurodegenerative diseases, and related research and exploration need to continue.
ConclusionWhen discussing the impact and function of chemical and electrical synapses, it is clear that each has advantages and disadvantages in the workings of the brain, especially as their roles may vary in different contexts. When these synapses function abnormally, a range of neurological diseases may occur. Are there new treatments that could be effective in improving our understanding of the nervous system?
