Otis Singleton
Electrical impulses are signals transmitted through nerves and neurons, which are excitable cells that can convert various stimuli into electrical signals. These impulses are used by nerve cells to communicate with each other and carry out complex processes in the brain. Neurons, or nerve cells, are key players in the nervous system's activity, conveying information electrically and chemically. Within a neuron, information is passed along through the movement of an electrical charge, or impulse. Communication among neurons occurs across microscopic gaps called synaptic clefts, where neurotransmitters are released from presynaptic terminals and bind to receptors on the surface of the receiving, or postsynaptic, neuron. To cross the synaptic cleft, the cell's electrical message must be converted into a chemical one.
| Characteristics | Values |
|---|---|
| What are electrical impulses? | Signals transmitted through nerves and neurons |
| How do neurons conduct electrical impulses? | Through the flow of positively charged ions across the neuronal membrane |
| What is the role of sodium and potassium ions? | Sodium channels allow sodium ions to enter the neuron, while potassium channels allow potassium ions to exit, creating a difference in concentrations that gives rise to the membrane potential |
| What is the role of myelin? | Myelin is an insulating material that coats neurons, improving the conduction of electrical impulses |
| How does myelination occur? | Electrical impulse activity stimulates oligodendrocytes to deposit myelin on neurons |
| What is the role of neurotransmitters? | Neurotransmitters are released by neurons when they generate an electrical impulse, allowing them to communicate with nearby neurons |
| What is transcutaneous electrical nerve stimulation (TENS)? | A non-invasive technique that delivers electrical impulses across the skin to activate underlying nerve structures and provide pain relief |
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What You'll Learn
Neurons and nerve cells
Neurons, or nerve cells, are the key players in the brain. They are responsible for sending and receiving signals throughout the brain and body, enabling us to perform essential functions such as breathing, talking, eating, walking, and thinking. Neurons have three basic parts: a cell body, an axon, and dendrites.
The cell body, or soma, houses the neuron's DNA and is where proteins are made and transported throughout the axon and dendrites. The axon is a long, thin structure that sends messages from the cell. It is often compared to the roots of a tree. Action potentials, or electrical impulses, are generated in the axon and travel down its length, causing the release of neurotransmitters into the synapse.
Dendrites, on the other hand, are the receiving part of the neuron, resembling the branches of a tree. They receive synaptic inputs from the axons of other neurons, with their dendritic spines acting as postsynaptic contact sites. The sum total of dendritic inputs determines whether the neuron will fire an action potential.
Neurons communicate with each other by sending chemical signals, or neurotransmitters, across the synapse between their axons and dendrites. These neurotransmitters carry messages between neurons. Additionally, neurons maintain different concentrations of certain ions (charged atoms) across their cell membranes. This difference in ion concentrations creates a membrane potential, giving the membrane a polarized state.
To prevent the dissipation of the internal depolarization in small axons, the axonal membrane is insulated with myelin. Myelin is a fatty membrane found in Oligodendroglia cells in the CNS and Schwann Cells in the PNS. It wraps around the axon, acting as an insulator and ensuring the efficient transmission of electrical impulses.
Overall, neurons play a crucial role in our bodies by sending and receiving electrical and chemical signals, allowing us to perform various functions and process complex information.
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Action potential
An action potential is a rapid sequence of changes in voltage across a cell membrane. Neurons conduct electrical impulses using this phenomenon, which is generated by the flow of positively charged ions across the neuronal membrane.
Neurons, like all cells, maintain different concentrations of certain ions (charged atoms) across their cell membranes. They pump out positively charged sodium ions and pump in positively charged potassium ions. This means there is a high concentration of sodium ions outside the neuron and a high concentration of potassium ions inside. The neuronal membrane contains specialised proteins called channels, which form pores in the membrane that are selectively permeable to particles. Sodium channels allow sodium ions through the membrane, while potassium channels allow potassium ions through.
Under resting conditions, the potassium channel is more permeable to potassium ions than the sodium channel is to sodium ions. This creates a slow outward leak of potassium ions that is larger than the inward leak of sodium ions. This difference in the concentrations of ions on either side of the membrane gives rise to the membrane potential, and the membrane is said to be polarised.
An action potential occurs when the membrane potential of a specific cell rapidly rises and falls. This is called depolarisation and causes adjacent locations to become similarly depolarised. In neurons, action potentials play a central role in cell-to-cell communication by providing for, or assisting, the propagation of signals along the neuron's axon toward synaptic boutons situated at the ends of an axon. These signals can then connect with other neurons at synapses or to motor cells or glands.
In muscle cells, an action potential is the first step in the chain of events leading to contraction. In beta cells of the pancreas, they provoke the release of insulin. In some types of neurons, the entire up-and-down cycle takes place in a few thousandths of a second. In muscle cells, a typical action potential lasts about a fifth of a second. In plant cells, an action potential may last three seconds or more.
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Voltage differences
Neurons are specialised cells of the brain and nervous system that communicate via electrical impulses and specialised molecules called neurotransmitters. Neurotransmitters are chemical precursors of the brain that transmit messages between neurons. Neurons conduct electrical impulses using the Action Potential, which is generated through the flow of positively charged ions across the neuronal membrane.
Neurons maintain different concentrations of certain ions (charged atoms) across their cell membranes. They pump out positively charged sodium ions and pump in positively charged potassium ions. This creates a high concentration of sodium ions outside the neuron and a high concentration of potassium ions inside. The neuronal membrane contains specialised proteins called channels, which form pores in the membrane that are selectively permeable to particles. Sodium channels allow sodium ions through the membrane, while potassium channels allow potassium ions through.
Under resting conditions, the potassium channel is more permeable to potassium ions than the sodium channel is to sodium ions. This creates a slow outward leak of potassium ions that is larger than the inward leak of sodium ions. This difference in ion concentrations on either side of the membrane gives rise to the membrane potential, and the membrane is said to be polarised. The inside of the membrane has a negative charge relative to the outside, as more positively charged ions flow out of the neuron than flow in.
To initiate depolarisation, a complex mechanism of ion channels (rapid channels) in the cell membrane opens momentarily, allowing a rapid entry of sodium ions into the cell through its concentration gradient. As a result, there is a flow of positively charged ions into the cell, making the cell electrically positive, while the outside of the cell becomes negative. This part of the action potential is called phase 0 (zero).
The ability of cardiac muscle cells to drive the electrical impulse that triggers contraction depends on the resting potential. Maintaining the resting potential within a narrow range of variation is crucial to prevent conduction and rhythm disturbances and reductions in cardiac pumping efficiency.
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Neurotransmitters
There are three possible actions that neurotransmitters can transmit in their messages, depending on the specific neurotransmitter: excitatory, inhibitory, and modulatory. Excitatory neurotransmitters "excite" the neuron and cause it to "fire off the message," ensuring that the message continues to be passed along to the next cell. Inhibitory neurotransmitters, on the other hand, block or prevent the chemical message from being passed any further. Modulatory neurotransmitters can either enhance or suppress the message, depending on the needs of the body.
After delivering their messages, neurotransmitters are cleared from the synaptic cleft through diffusion, reuptake, or degradation. Scientists have identified at least 100 different neurotransmitters, but it is suspected that many others remain to be discovered. These neurotransmitters are involved in most functions of the nervous system, which controls everything from our thoughts and feelings to our physical actions and organ functions.
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Myelin and insulation
Neurons are specialised cells of the brain and nervous system that communicate via electrical impulses and specialised molecules called neurotransmitters. These electrical impulses are generated by the flow of positively charged ions across the neuronal membrane. The sodium and potassium ion channels, pumps, and other mechanisms associated with action potential propagation are concentrated at sites between blocks of myelin called the Nodes of Ranvier.
Myelin is a fatty membrane of cells called Oligodendroglia (in the CNS) and Schwann Cells (in the PNS) that wraps around the axon and acts as an insulator, preventing the dissipation of the depolarisation wave. Myelin is essential for the efficient conduction of electrical impulses in neurons. Neurons conduct electrical impulses more efficiently if they are covered with an insulating material known as myelin.
Oligodendrocytes deposit myelin on neurons, and electrical impulse activity stimulates them to do so. When neurons are stimulated by electrical impulses, they release adenosine triphosphate (ATP), a high-energy molecule essential to many biological processes. The ATP binds to special sites on the surface of astrocytes, causing them to release a substance known as leukemia inhibitory factor (LIF). LIF, in turn, binds to the oligodendrocytes, stimulating them to deposit myelin around the neurons.
Human beings are born with relatively little myelin, and neurons become coated with myelin as they develop. Mental activity appears to influence myelination. For example, neglected children have less myelin in certain brain regions than other children, while raising animals in stimulating environments increases their myelin production. Additionally, mastering an activity, such as learning to play the piano, fosters myelination. Myelin is decreased in several mental disorders, including schizophrenia and bipolar disorder.
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Frequently asked questions
Electrical impulses are signals transmitted through nerves and neurons, which are excitable cells that can convert various stimuli into electrical signals.
Neurons send electrical impulses by using the Action Potential. This is generated through the flow of positively charged ions across the neuronal membrane.
Neurotransmitters are chemical messengers that carry signals between neurons. They are released by a presynaptic neuron and bind to receptors on the surface of a postsynaptic neuron.
Myelin, a fatty membrane, acts as an insulator and wraps around the axon of a neuron, preventing the dissipation of the electrical impulse. This allows impulses to travel efficiently over long distances.
One example is the electrical impulses that precede cardiac muscle contraction, which are captured and recorded in an electrocardiogram (ECG). These impulses originate in the sinus node and propagate to neighboring cells, activating the whole ventricular muscular mass.
