Otis Singleton
Electrical signals are transmitted between neurons through two different strategies: the first is the consequence of low-resistance intercellular pathways, known as gap junctions, which allow the spread of electrical currents between the interior of two cells; the second occurs without cell-to-cell contact and is a result of the extracellular electrical fields generated by the electrical activity of neurons. Within a neuron, signals are conveyed electrically along the cell membrane, while communication between neurons involves the conversion of electrical signals into chemical signals through the release of neurotransmitters, which bind to receptors on the receiving neuron and cause a change in membrane potential, initiating an action potential in that neuron.
| Characteristics | Values |
|---|---|
| Mechanism of transmission within neurons | Conveyed along the cell membrane |
| Mechanism of transmission between neurons | Conversion of electrical signals into chemical signals |
| Medium of transmission between neurons | Neurotransmitters |
| Nature of neurotransmitters | Chemical messengers |
| Types of neurotransmitters | 100 different types, including dopamine |
| Nature of synapses | Location where two neurons are almost in contact with each other |
| Occurrence of electrical transmission between neurons | Through intercellular channels known as "gap junctions" |
| Nature of gap junctions | Groupings of tightly clustered intercellular channels |
| Function of gap junctions | Provide a pathway of low resistance for the spread of currents between cells |
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What You'll Learn
- Electrical signals within neurons are conveyed along the cell membrane
- For communication between neurons, electrical signals are converted into chemical signals
- Neurotransmitters are released from presynaptic terminals
- Neurotransmitters bind to receptors on the receiving neuron
- Gap junctions allow the spread of electrical currents between neurons
Electrical signals within neurons are conveyed along the cell membrane
Neurons are capable of both electrical and chemical communication. While chemical communication between neurons is more common, electrical synaptic interactions also occur. Electrical signals within neurons are conveyed along the cell membrane, which is made possible by the voltage differences (or potentials) between the inside and outside of the cell. This voltage difference is created by the uneven distribution of electrically charged particles, or ions, such as sodium (Na+), potassium (K+), chloride (Cl–), and calcium (Ca2+).
The electrical potential across the neuron's cell membrane arises from the different distributions of positively and negatively charged ions within and outside the cell. This potential can be altered by the redistribution of electric charge caused by the opening or closing of channels in response to neurotransmitters or changes in the cell's membrane potential. A decrease in the voltage difference, known as depolarization, can lead to an impulse or action potential travelling along the neuron.
Action potentials are brief electrical events that signal the neuron as 'active'. They are generated in the axon and travel its length, causing the release of neurotransmitters into the synapse. The synapse is the location where two neurons are almost in contact with each other and where a signal is transmitted from one neuron to the next. Neurotransmitters are chemical messengers that transmit information from one neuron to another. They are released as a result of an action potential and can excite or inhibit the target neuron.
Electrical transmission between neurons can occur through "gap junctions", which are intercellular channels that provide a pathway of low resistance for the spread of electrical currents between cells. Gap junctions are formed by the docking of two individual channels, named hemichannels or connexons, one contributed by each coupled cell. They are not exclusive to neurons and are present in various tissues. Electrical transmission can also occur without cell-to-cell contact due to the extracellular electrical fields generated by neuronal activity.
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For communication between neurons, electrical signals are converted into chemical signals
Neurons are capable of both electrical and chemical communication. While electrical signals are conveyed within a neuron along the cell membrane, communication between neurons involves the conversion of electrical signals into chemical signals. This process occurs at the synapse, a junction between the axon of one neuron and the dendrite of another.
The synapse contains a microscopic gap called the synaptic cleft, which is the site of communication between neurons. When an electrical signal, known as an action potential, travels along the axon of the transmitting neuron, it reaches the synaptic cleft and causes the release of neurotransmitters. Neurotransmitters are small messenger molecules that carry the signal across the synaptic cleft to the receiving neuron.
Neurotransmitters are released from presynaptic terminals, which can branch out to communicate with multiple postsynaptic neurons. These chemical messengers bind to receptors on the surface of the receiving neuron, initiating a response. The type of response depends on the specific neurotransmitter released, as different neurons produce and release distinct types of neurotransmitters.
Upon binding to the postsynaptic receptor, the chemical signal is converted back into an electrical signal. This occurs as charged ions flow into or out of the postsynaptic neuron, altering its membrane potential. The membrane potential, or voltage difference, between the inside and outside of the neuron is crucial for signal transmission within neurons. Thus, the electrical signal is transmitted from one neuron to another through the intermediary of chemical signals in the form of neurotransmitters.
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Neurotransmitters are released from presynaptic terminals
Neurotransmitters are small messenger molecules that carry electrical signals between neurons. They are synthesized in the cell body and then transmitted down the microtubules of the axon to the presynaptic terminal, where they are stored in presynaptic vesicles until their release. Each neuron produces and releases only a specific type or a few types of neurotransmitters, which can either excite or inhibit the target neuron.
Once released from the presynaptic terminal, neurotransmitters travel across the synaptic cleft and bind to receptors on the postsynaptic side. These receptors can be located on the postsynaptic neuron's dendrites or elsewhere on the cell. The binding of neurotransmitters to these receptors converts the electrical signal back into a chemical signal, as particular positive or negative ions flow into or out of the postsynaptic neuron.
The specific neurotransmitter released determines which ions will travel through the channels that span the membrane. For example, the release of certain neurotransmitters may result in the flow of positive ions such as sodium (Na+), potassium (K+), and calcium (Ca+), while others may lead to the flow of negative ions such as chloride (Cl-).
The release of neurotransmitters from presynaptic terminals is a crucial step in neuron communication, allowing electrical signals to be transmitted between neurons and ultimately contributing to the complex electrochemical signalling that occurs in the human brain.
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Neurotransmitters bind to receptors on the receiving neuron
Neurotransmitters are released from presynaptic terminals, which may branch to communicate with several postsynaptic neurons. They are released into the synaptic cleft, a 20-40nm gap between the presynaptic axon terminal and the postsynaptic dendrite.
Neurotransmitters carry the message across this gap and bind to specific receptors on the receiving neuron. Each type of neurotransmitter binds to a specific receptor on the target cell, much like a key that only fits and works in its partner lock. These receptors may be located on the cell's surface, or elsewhere.
The binding of neurotransmitters to receptors that act as ligand-gated ion channels causes these channels to open, leading to a redistribution of electric charge that may alter the voltage difference across the membrane. This alteration is called depolarization.
Neurotransmitters that bind to second messenger-linked receptors, such as dopamine, initiate a complex cascade of chemical events that can either excite or inhibit further electrical signals. With so many different receptors on its cell surface, some of the signals the receiving neuron receives will have excitatory effects, while others will be inhibitory.
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Gap junctions allow the spread of electrical currents between neurons
Neurons communicate with each other across microscopic gaps called synaptic clefts. Each neuron may communicate with hundreds of thousands of other neurons. The communication between neurons involves electrical and chemical signals. Within cells, electrical signals are conveyed along the cell membrane. For communication between cells, the electrical signals are converted into chemical signals conveyed by small messenger molecules called neurotransmitters.
Gap junctions are membrane channels between adjacent cells that allow the direct exchange of cytoplasmic substances, such as small molecules, substrates, and metabolites. Gap junctions electrically couple cells throughout the body of most animals. Electrical coupling can be relatively fast-acting and can be used over short distances within an organism. Gap junctions are particularly important in cardiac muscle, allowing the heart muscle cells to contract in unison.
In the context of neurons, gap junctions are sites of direct electrical connections between neurons. They are present in the primary visual cortex at many stages of life, from infancy to adulthood. Gap junctions between local, inhibitory neurons in the adult cortex have been shown to promote synchronous firing, a network characteristic thought to be important for learning, attention, and memory. In the developing visual cortex, gap junctions couple excitatory cells and potentially influence the formation of chemical synapses.
Overall, gap junctions play a crucial role in allowing the spread of electrical currents between neurons, facilitating intercellular communication and influencing various physiological processes.
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Frequently asked questions
Neurons communicate with each other through electrical and chemical signals. The presynaptic neuron releases a chemical called a neurotransmitter, which binds to a receptor on the postsynaptic neuron.
Neurotransmitters are chemical messengers that transmit information from one neuron to another. There are approximately 100 different types of neurotransmitters, and each neuron produces and releases only one or a few types.
Neurotransmitters are released from presynaptic terminals, which may branch out to communicate with several postsynaptic neurons. They bind to receptors on the postsynaptic neuron, causing a redistribution of electric charge and altering the voltage difference across the membrane.
There are two forms of electrical transmission between neurons: "gap junctions" and extracellular electrical fields. "Gap junctions" are intercellular channels that provide a pathway of low resistance for the spread of electrical currents between cells. Extracellular electrical fields are generated by the electrical activity of neurons and can induce hyperpolarization in the postsynaptic cell.
