20.7 Nerve Conduction–Electrocardiograms
3 min read•june 18, 2024
is the process by which neurons transmit electrical signals through changes in . Action potentials propagate along neurons, allowing for rapid communication within the nervous system. Myelin sheaths enhance signal transmission through .
Electrocardiograms (ECGs) graphically represent the heart's electrical activity. The ECG waveform consists of distinct components, including the , , and , which correspond to specific cardiac events. Understanding ECGs is crucial for diagnosing various heart conditions.
Nerve Conduction and Electrocardiograms
Neuron signal transmission
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- Neurons transmit electrical signals through changes in membrane potential
- Resting membrane potential maintained by differences in ion concentrations across cell membrane (, )
- actively transports ions to maintain concentration gradients
- generated when membrane potential reaches threshold value ()
- open, allowing sodium ions to rush into cell
- occurs as membrane potential rapidly rises
- open, allowing potassium ions to exit cell
- occurs as membrane potential returns to resting state
- After an action potential, there is a brief during which the cannot generate another action potential
- Resting membrane potential maintained by differences in ion concentrations across cell membrane (, )
- Action potentials propagate along length of neuron
- Local currents depolarize adjacent regions of membrane
- Voltage-gated ion channels open sequentially along
- Action potential moves in wave-like manner from cell body to axon terminal
- Examples:
- Sensory neurons transmit signals from receptors (touch, pain) to central nervous system
- Motor neurons transmit signals from central nervous system to muscles, causing contraction
Role of myelin sheaths
- Myelin sheaths are insulating layers formed by around axons
- Composed of lipids and proteins
- Act as electrical insulators
- Myelin sheaths enhance nerve signal propagation through saltatory conduction
- Action potentials "jump" from one to next
- Nodes of Ranvier are gaps in where voltage-gated ion channels are concentrated
- Saltatory conduction increases speed of signal transmission
- Reduces need for continuous regeneration of action potentials along axon
- Action potentials "jump" from one to next
- Myelination allows for faster and more efficient signal transmission
- Important for rapid communication between distant parts of body
- Damage to myelin sheaths can lead to impaired nerve function ()
- Examples:
- form myelin sheaths around axons in peripheral nervous system
- form myelin sheaths around axons in central nervous system
Synaptic transmission
- Synapses are junctions where neurons communicate with other cells
- When an action potential reaches the axon terminal, it triggers the release of
- Neurotransmitters diffuse across the synaptic cleft and bind to receptors on the target cell
- This process converts the electrical signal into a chemical signal and back to an electrical signal in the target cell
Components of ECG
- is graphical representation of electrical activity of heart
- Measures electrical potential differences between placed on skin
- P wave represents atrial depolarization
- Corresponds to contraction of atria
- Atrial systole pumps blood into ventricles
- QRS complex represents ventricular depolarization
- Corresponds to contraction of ventricles
- Ventricular systole pumps blood to lungs and body
- T wave represents ventricular repolarization
- Corresponds to relaxation of ventricles
- Ventricular diastole allows ventricles to fill with blood
- represents time from atrial depolarization to ventricular depolarization
- Reflects conduction of electrical signal through AV node
- represents time from ventricular depolarization to ventricular repolarization
- Reflects duration of ventricular systole and diastole
- The , located in the right atrium, acts as the heart's natural pacemaker, initiating each heartbeat
- Abnormalities in ECG waveform can indicate various cardiac conditions
- Arrhythmias (, )
- Conduction disorders ()
- (ST-segment elevation)
- Electrolyte imbalances (, )
Key Terms to Review (40)
Action Potential: An action potential is a rapid, transient electrical signal that travels along the membrane of an excitable cell, such as a neuron or muscle cell. It is the primary means of communication and signal transmission in the nervous system, playing a crucial role in nerve conduction and the generation of electrocardiograms.
Atrial Fibrillation: Atrial fibrillation is an irregular and often rapid heart rate that occurs when the upper chambers of the heart (the atria) experience chaotic electrical signals, causing them to quiver (fibrillate) instead of beating effectively. This disruption in the normal heart rhythm can lead to various cardiovascular complications if left untreated.
Axon: An axon is a long, slender projection of a nerve cell, or neuron, that conducts electrical signals away from the neuron's cell body to other neurons, muscles, or gland cells. Axons are a crucial component in the transmission of information throughout the nervous system, enabling the coordination of various bodily functions and behaviors.
Bioelectricity: Bioelectricity involves the electrical processes and phenomena in biological systems, primarily focusing on nerve impulses and muscle contractions. It is essential for understanding how electric currents flow within living organisms.
Depolarization: Depolarization is the process by which the electrical potential across the cell membrane of a neuron or muscle cell changes from a negative resting potential to a positive action potential. This event is crucial for the propagation of electrical signals within the nervous system and the initiation of muscle contractions.
Electrocardiogram: An electrocardiogram (ECG or EKG) is a diagnostic test that records the electrical activity of the heart. It provides information about the heart's rhythm, structure, and function, allowing healthcare professionals to detect various heart-related conditions.
Electrocardiogram (ECG): An electrocardiogram (ECG) is a medical test that measures the electrical activity of the heart over a period of time. It is used to detect and diagnose various heart conditions.
Electrodes: Electrodes are conductive devices used to establish an electrical connection between an electrical circuit and an external environment, such as the human body. They play a crucial role in various applications, including nerve conduction and electrocardiograms (ECGs).
Glial Cells: Glial cells, also known as neuroglia or simply glia, are non-neuronal cells that provide support and protection for neurons in the central and peripheral nervous systems. They are essential for the proper functioning and maintenance of nerve tissue.
Heart Block: Heart block is a condition where the electrical signals that coordinate the contractions of the upper and lower chambers of the heart (atria and ventricles) are disrupted, causing an abnormal heart rhythm. This term is particularly relevant in the context of 20.7 Nerve Conduction–Electrocardiograms, as heart block can be detected and diagnosed through electrocardiogram (ECG) readings.
Hypercalcemia: Hypercalcemia is a medical condition characterized by an abnormally high level of calcium in the blood. This imbalance can have significant impacts on the body's nerve conduction and the electrical activity of the heart, as measured by electrocardiograms.
Hypokalemia: Hypokalemia is a condition characterized by an abnormally low level of potassium in the bloodstream. Potassium is an essential electrolyte that plays a crucial role in nerve conduction and the proper functioning of the cardiovascular system, including the heart's electrical activity, which is measured by electrocardiograms (ECGs).
Membrane Potential: Membrane potential is the difference in electrical charge between the inside and outside of a cell's membrane, which is essential for various biological processes, including nerve conduction and muscle contraction.
Multiple Sclerosis: Multiple sclerosis (MS) is a chronic, autoimmune disease that affects the central nervous system (CNS), including the brain, spinal cord, and optic nerves. It is characterized by the immune system attacking and damaging the protective myelin sheath surrounding nerve fibers, which disrupts the efficient transmission of electrical signals within the CNS.
Myelin Sheath: The myelin sheath is a protective fatty layer that surrounds the axons of certain nerve cells, known as myelinated neurons. It plays a crucial role in the efficient transmission of electrical signals throughout the nervous system, particularly in the context of nerve conduction and electrocardiograms.
Myocardial Infarction: Myocardial infarction, commonly known as a heart attack, occurs when blood flow to a part of the heart muscle is suddenly blocked, often due to a blood clot. This results in damage or death of the affected heart muscle tissue, impairing the heart's ability to pump blood effectively.
Nerve conduction: Nerve conduction is the process by which electrical impulses travel along a nerve fiber. This involves the movement of ions across nerve cell membranes, creating action potentials.
Neuron: A neuron is a specialized cell in the nervous system that transmits electrical signals, known as action potentials, to other cells. Neurons are the fundamental units of the brain and play a crucial role in the processes of nerve conduction and electrocardiogram (ECG) interpretation.
Neurotransmitters: Neurotransmitters are chemical messengers that facilitate communication between neurons in the nervous system. They are released from the presynaptic neuron and bind to receptors on the postsynaptic neuron, triggering a response that propagates the signal along the neural pathway.
Node of Ranvier: The node of Ranvier is a gap in the myelin sheath that covers the axon of a neuron, allowing for the rapid transmission of electrical signals through the process of saltatory conduction. This term is particularly relevant in the context of nerve conduction and electrocardiograms.
Oligodendrocytes: Oligodendrocytes are a type of glial cell found in the central nervous system that are responsible for the production and maintenance of the myelin sheath around the axons of neurons. This myelin sheath acts as an insulator, increasing the speed of electrical impulse transmission along the neuron, which is an essential component of nerve conduction and electrocardiogram interpretation.
P Wave: The P wave is an important component of the electrocardiogram (ECG) that represents the electrical activity generated by the atrial depolarization, the first stage of the cardiac cycle. It is a crucial indicator of proper heart function and is closely linked to the processes of nerve conduction and electrocardiogram interpretation.
Potassium: Potassium is an essential mineral that plays a crucial role in nerve conduction and the regulation of heart function. It is a key electrolyte involved in maintaining the proper balance of fluids and electrical signals within the body, making it an important factor in electrocardiograms and nerve impulse transmission.
PR Interval: The PR interval is the time it takes for the electrical impulse to travel from the atria (upper chambers of the heart) to the ventricles (lower chambers of the heart) in the cardiac conduction system. It is a crucial measurement in the interpretation of an electrocardiogram (ECG) and provides information about the heart's electrical activity.
QRS Complex: The QRS complex is a characteristic feature of the electrocardiogram (ECG) that represents the electrical activity associated with the contraction of the ventricles of the heart. It is a critical component in the analysis and interpretation of the ECG, providing important information about the heart's function and health.
QT Interval: The QT interval is a measure of the time it takes for the ventricles of the heart to depolarize and repolarize, representing the duration of the ventricular electrical activity. It is an important parameter in the analysis of an electrocardiogram (ECG) and is closely related to nerve conduction in the cardiovascular system.
Refractory Period: The refractory period is a crucial concept in the context of nerve conduction and electrocardiograms, referring to the time interval during which a neuron or cardiac muscle cell is unable to generate a new action potential, even in the presence of a sufficient stimulus.
Repolarization: Repolarization is the process by which the cell membrane of a neuron or muscle fiber restores its resting potential after an action potential has occurred. It is a crucial step in the conduction of electrical signals within the body, particularly in the context of nerve conduction and electrocardiograms.
Saltatory Conduction: Saltatory conduction is a mode of signal propagation in myelinated nerve fibers, where the action potential 'jumps' from one node of Ranvier to the next, increasing the speed of signal transmission along the nerve.
Schwann Cells: Schwann cells are a type of glial cell found in the peripheral nervous system. They play a crucial role in the function and maintenance of nerve fibers, including the insulation and regeneration of axons.
Semipermeable: Semipermeable describes a membrane that allows certain molecules or ions to pass through it by diffusion and occasionally specialized processes. This selective permeability is crucial in biological and medical applications.
Sinoatrial Node: The sinoatrial (SA) node is a group of specialized cells located in the right atrium of the heart. It is responsible for generating the electrical impulses that initiate the heartbeat, making it the natural pacemaker of the heart.
Sodium: Sodium is an essential mineral that plays a crucial role in the human body, particularly in the context of nerve conduction and electrocardiograms. As an electrolyte, sodium helps maintain the balance of fluids and electrical signals within the body, making it a key component in various physiological processes.
Sodium-Potassium Pump: The sodium-potassium pump, also known as the Na+/K+ ATPase, is an active transport mechanism that maintains the electrochemical gradient across the cell membrane by continuously pumping sodium ions (Na+) out of the cell and potassium ions (K+) into the cell. This process is crucial for regulating osmosis, nerve impulse transmission, and other essential cellular functions.
Synapse: A synapse is a specialized junction between two neurons or between a neuron and another cell, where information is transmitted from one to the other through the release of neurotransmitters. It is a critical component in the process of nerve conduction and the transmission of electrical signals throughout the body, including the electrocardiogram (ECG) measurements.
T Wave: The T wave is an important component of the electrocardiogram (ECG) that represents the repolarization of the ventricles, the lower chambers of the heart. It is a crucial indicator of the heart's electrical activity and provides valuable information about the functioning of the cardiovascular system.
Threshold Potential: The threshold potential is the minimum level of depolarization required to trigger an action potential in an excitable cell, such as a neuron or muscle fiber. It represents the critical point at which the cell's membrane potential reaches a level that activates voltage-gated ion channels, leading to the rapid propagation of an electrical signal.
Ventricular Tachycardia: Ventricular tachycardia is a type of abnormal heart rhythm characterized by a rapid and uncontrolled electrical activity originating from the ventricles, the lower chambers of the heart. This condition can lead to a dangerously fast heart rate, which can impair the heart's ability to effectively pump blood throughout the body.
Voltage-Gated Potassium Channels: Voltage-gated potassium channels are specialized membrane proteins that selectively allow the passage of potassium ions across the cell membrane in response to changes in the electrical potential across the membrane. These channels play a crucial role in the generation and propagation of action potentials in nerve and muscle cells, as well as in the regulation of various physiological processes.
Voltage-Gated Sodium Channels: Voltage-gated sodium channels are specialized transmembrane proteins found in the cell membranes of neurons and muscle cells. These channels play a crucial role in the generation and propagation of action potentials, which are the electrical signals that allow for nerve conduction and the coordination of muscle contractions.