Wiktor Wise
Nerve impulses are electrical phenomena that occur due to differences in electrical charge across the plasma membrane of a neuron. They are similar to lightning strikes, which also occur due to differences in electrical charge. In the human body, nerve impulses are responsible for the nervous system's functioning and the control of muscle movement. The heart, for instance, contracts due to regular electrical impulses originating from the heart's sino-atrial node, commonly known as the heart's pacemaker. Electrical impulses are also used in medical procedures such as transcutaneous electrical nerve stimulation (TENS) for pain relief.
| Characteristics | Values |
|---|---|
| Definition | Electrical impulses refer to the signals transmitted through nerves and neurons. |
| Nature | Nerve impulses are electrical in nature. |
| Cause | A nerve impulse occurs due to a difference in electrical charge across the plasma membrane of a neuron. |
| Maintenance | During the resting state, the sodium-potassium pump maintains a difference in charge across the cell membrane of the neuron. |
| Transmission | Electrical impulses are transmitted through nerve cells in the brain. |
| Function | Electrical impulses are used by nerve cells to communicate with each other and carry out complex processing in the brain. |
| Application | Electrical impulses are used in transcutaneous electrical nerve stimulation, a non-invasive pain relief modality. |
| Analysis | Unit impulse signals can be used to analyze and understand the behaviour of systems and determine the output of networks and circuits. |
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What You'll Learn
Nerve impulses
When a neuron receives a chemical stimulus, it triggers a nerve impulse. This impulse travels down the axon membrane as an electrical action potential, a rapid series of changes in voltage across the cell membrane. The action potential is characterised by a sudden reversal of the electrical charge across the membrane, with the inside of the cell becoming positively charged compared to the outside. This is achieved through the inflow of sodium ions into the cell, which changes the electrochemical gradient and further increases the membrane potential.
The action potential then propagates down the length of the axon, jumping rapidly from node to node in myelinated neurons. This propagation is crucial for the transmission of the nerve impulse to the next cell. At the axon terminal, neurotransmitters are released, carrying the nerve impulse across the synapse to the next cell. This process, known as synaptic transmission, can occur electrically or chemically. In chemical synapses, the neurotransmitters bind to the postsynaptic neuron, eliciting an excitatory or inhibitory response.
The ability of the action potential to propagate effectively along the axon is vital for successful nerve impulse transmission. The speed of propagation depends on factors such as the concentration of sodium channels and the diameter of the axon. Larger axons exhibit faster nerve impulses due to reduced internal resistance to ion flow. Additionally, myelinated axons, with their insulating myelin sheaths, further enhance the speed of conduction, ensuring efficient nerve impulse transmission.
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Action potentials
An action potential is a rapid sequence of changes in the voltage across a membrane. It is a nerve impulse or "spike" when in a neuron. Action potentials are generated by special types of voltage-gated ion channels embedded in a cell's plasma membrane. These channels are shut when the membrane potential is near the (negative) resting potential of the cell. However, they rapidly begin to open if the membrane potential increases to a precisely defined threshold voltage, depolarising the transmembrane potential.
In myelinated neurons, ion flows occur only at the nodes of Ranvier. As a result, the action potential signal "jumps" along the axon membrane from node to node rather than spreading smoothly along the membrane. This is due to a clustering of Na+ and K+ ion channels at the Nodes of Ranvier. Unmyelinated axons do not have nodes of Ranvier, and ion channels in these axons are spread over the entire membrane surface.
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Synaptic signal transmission
Synaptic transmission is a specialised and regulated mechanism of neuronal communication. It involves the release and binding of neurotransmitters, which are signalling molecules, at the synapse or connection between neurons. This process was first described by Foster and Sherrington in 1897, who recognised that something unique happened at the connection between nerve cells, which was later confirmed to be a chemical process by Otto Loewi in 1921.
The process of synaptic transmission begins with the release of neurotransmitters from presynaptic terminals, which then move across the synapse to the postsynaptic neuron. This release of neurotransmitters is influenced by the interactions between ion channels, G protein-coupled receptors, second messengers, and the exocytotic machinery. The neurotransmitters then bind to the receptors on the postsynaptic neuron, generating a signal that excites, inhibits, or modulates cellular activity. This binding can result in either short-term or long-term changes in the postsynaptic neuron, such as changes in membrane potential or the activation of signalling cascades.
The transmission of a nerve impulse, or action potential, occurs due to differences in electrical charge across the plasma membrane of a neuron. This difference in electrical charge is maintained by the sodium-potassium pump, which actively transports sodium ions out of the cell and potassium ions into the cell, creating an electrical gradient or resting potential. When a neuron is stimulated, this results in a brief electrical event called an action potential, which travels along the axon and causes the release of neurotransmitters into the synapse.
Synapses play a crucial role in converting an electrical signal (the action potential) into a chemical signal through the release of neurotransmitters. Once the neurotransmitters bind to the postsynaptic receptors, the signal is converted back into an electrical form as charged ions flow into or out of the postsynaptic neuron. This process allows for the transmission of information from one neuron to another, influencing the activity of the receiving neuron.
Overall, synaptic signal transmission is a complex and dynamic process that enables the nervous system to communicate and process information with incredible sophistication. It involves the interplay between electrical and chemical signals, showcasing the intricate nature of neuronal communication.
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Electrical impulses in plants
An impulse is an electrical signal when it occurs due to a difference in electrical charge across a membrane. This is true for nerve impulses in animals, and plants also exhibit electrical impulses despite lacking a nervous system.
Plants rely on electrical forces for some of their functions. Electrical signals in plants are generated in response to touch and stress factors, such as wounds caused by herbivores and attacks on their roots. For example, the Venus Flytrap uses electrical signalling to cause the trap to snap shut when prey is sensed.
The presence of electrical signals in plant cells suggests that they, like animal cells, use ion channels to transmit information over long distances. Ion channels, the basis for action potentials, were discovered in plants in 1984. Since then, research has found that plants contain much of the same chemistry as the neuromotoric system of animals, including neurotransmitters such as acetylcholine.
The generation and propagation of various electrical signals in plants, as well as their ways of transmission within the plant body and various physiological effects, are areas of active research. Extracellular and intracellular recording methods are used to measure electric potentials in plants. Extracellular measurements are more widely used and can detect electrical potential differences over long periods, but intracellular measurements are more precise as they measure specific cells.
The recent development of a multi-electrode array technology has enabled advanced research into how plants react to their surroundings and to stress. This technology uses a thin film with electrodes that can conform to the outside of a plant's lobes to measure the electrical signal.
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Unit impulse signals
A unit impulse signal, also known as a discrete delta function, is a fundamental concept in signal processing and electrical engineering. It is a signal that is zero everywhere except at a specific point, where it has a value of one. In other words, it is a discrete representation of the Dirac delta function, which is commonly used in continuous-time systems.
The unit impulse signal is often denoted as δ [n] or u_k [n], where the subscript k denotes the index at which the value is 1. For example, δ [0] represents a unit impulse at the 0th element, with all other elements being 0. This can be generalised to higher dimensions by using tuples to represent the shape of the output. For instance, in a 2-dimensional signal, a unit impulse at (2, 2) would be represented as [[0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 1, 0], [0, 0, 0, 0]].
The unit impulse signal plays a crucial role in digital signal processing. It is used to model and analyse various physical phenomena, such as the propagation of electrical impulses in biological systems. For example, in the context of the nervous system, a stimulus elicits electrical impulses in sensory nerve cells, which then propagate along nerve fibres to the brain. These impulses are the result of differences in electrical charge across the plasma membrane of neurons, maintained by the sodium-potassium pump.
In digital signal processing literature, the unit impulse signal is often represented by the Kronecker delta. This representation allows for the expression of signals that are zero everywhere except at a specific sample, where it takes on a value of one. This discrete-time representation is analogous to the continuous-time Dirac delta function, which is commonly used in mathematical modelling and analysis of continuous-time systems.
The unit impulse signal is a fundamental tool in the analysis and design of digital filters and systems. By convolving a system's impulse response with a unit impulse signal, one can observe how the system responds to an instantaneous input. This is particularly useful in understanding the behaviour of linear time-invariant (LTI) systems, where the output is solely dependent on the input and is unaffected by the system's past state.
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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. These impulses are used by nerve cells to communicate with each other and carry out complex processing in the brain.
Electrical impulses occur due to differences in electrical charge across the plasma membrane of a neuron. This difference in charge is maintained by the sodium-potassium pump, which moves sodium ions out of cells and potassium ions into cells. The resulting electrical gradient is called the resting potential, and it is critical for the transmission of nerve impulses. When an impulse is transmitted, it travels down the axon membrane as an electrical action potential to the axon terminal, where neurotransmitters carry the nerve impulse to the next cell.
Electrical impulses are involved in various physiological processes in the human body. For example, the nervous system and the control of muscle movement are governed by electrical interactions. The heart also has its own electrical function, with regular electrical impulses originating from the heart's sino-atrial node (the heart's "pacemaker") triggering constant muscular contractions during the cardiac cycle.
