Nerve Impulses PDF - Biology Lesson

Nerve Impulses: The Electrical Language of the Nervous System The nervous system is the body's intricate communication network, responsible for everything from reflexes to thoughts. Nerve impulses, also known as action potentials, are the electrical signals that travel along neurons, enabling this c...

Nerve Impulses: The Electrical Language of the Nervous System The nervous system is the body's intricate communication network, responsible for everything from reflexes to thoughts. Nerve impulses, also known as action potentials, are the electrical signals that travel along neurons, enabling this communication. This presentation delves into the fascinating world of nerve impulses, exploring their fundamental principles and clinical implications. What is a Nerve Impulse? Electrical Signal Communication Information Transmission A nerve impulse, or action potential, is It's the primary means by which a rapid electrical signal that travels neurons communicate with each other Nerve impulses transmit information along the axon of a neuron. and with target cells. about stimuli, both internal and external, throughout the body. Types of Nerve Impulses Nerve impulses are classified into two main types: Action Potentials Graded Potentials They are rapid, short-lived They are localized changes in electrical signals that travel along membrane potential that vary in axons. strength and duration.  Polarized State Resting Potential of  Messages in a neuron develop from disturbances of the Neurons resting potential.  All parts of a neuron are covered by a membrane with about 8 nanometers (nm) thick. That is about one ten- thousandth the width of an average human hair.  The membrane is composed of two layers (free to float relative to each other) of phospholipid molecules (containing chains of fatty acids and a phosphate group). Embedded among the phospholipids are cylindrical protein molecules through which certain chemicals can pass.  When at rest, the membrane maintains an electrical gradient, also known as polarization—a difference in electrical charge between the inside and outside of the cell.  The electrical potential inside the membrane is slightly negative with respect to the outside, mainly because of negatively charged proteins inside the cell. This difference in voltage is called the resting potential.  Researchers measure the resting potential by inserting a very thin microelectrode into the cell body. Resting Potential of Neurons 1 Polarized State 2 Sodium-Potassium Pump In its resting state, a neuron maintains a potential difference The resting potential is across its membrane. This is established and maintained by known as the resting potential, the sodium-potassium pump, where the inside of the neuron is which actively transports negatively charged compared to sodium ions out of the cell and the outside. potassium ions into the cell. 3 Ion Channels The neuron's membrane also contains ion channels that allow specific ions to pass through. In the resting state, these channels are mostly closed, contributing to the potential difference. Sodium-Potassium Pump  A protein complex, repeatedly transports three sodium ions  When the neuron is at rest, two forces act out of the cell while drawing two potassium ions into it. on sodium, both tending to push it into the a) An active transport that requires energy. cell. Consider the f f: b) Effective only because of the selective permeability of the membrane, which prevents the sodium ions that were 1. ELECTRICAL GRADIENT pumped out of the neuron from leaking right back in  Sodium is positively charged, and the again. inside of the ell is negatively charged.  The resting potential is established and maintained by the  Opposite electrical charges attract, so sodium-potassium pump, which actively transports sodium the electrical gradient tends to pull ions out of the cell and potassium ions into the cell. sodium into the cell.  POTASSIUM – subject to competing forces; positively charged 2. CONCENTRATION GRADIENT and the inside of the cell is negatively charged, so the  The difference in distribution of ions electrical gradient tends to pull potassium in. across the membrane.  Sodium is more concentrated outside WHY A RESTING POTENTIAL? than inside, so just by the laws of probability, sodium is more likely to  The body invests much energy to operate the sodium– enter the cell than to leave it. potassium pump, which maintains the resting potential.  The resting potential prepares the neuron to respond rapidly.  Excitation of the neuron opens channels that allow sodium to enter the cell rapidly. Sodium-Potassium Pump Depolarization and the Action Potential The nerve impulse is initiated by a change in the neuron's membrane potential, a process known as depolarization. Sodium Influx Threshold Potential Depolarization occurs when the If the depolarization reaches a neuron's membrane becomes certain threshold, an action more permeable to sodium ions, potential is triggered. allowing them to rush into the cell. The nerve impulse is initiated by a change in the neuron's membrane potential, a process known as depolarization. Action Potentials – message sent by axons.  We can measure a neuron’s potential with a microelectrode.  When an axon’s membrane is at rest, the recordings show a negative potential inside the axon.  The change is called hyperpolarization, which means increased polarization.  When the stimulation ends, the charge returns to its original resting level.  Any subthreshold stimulation produces a small response that quickly decays.  Any stimulation beyond the threshold, regardless of how far beyond, produces a big response like the one shown, known as the action potential.  HYPERPOLARIZATION - an exaggeration of the usual negative charge within a cell (to a more negative level than usual).  DEPOLARIZATION - a decrease in the amount of negative charge within the cell. Depolarization and the Action Potential Stimulus When a neuron receives a stimulus, it triggers a change in the membrane's permeability to 1 ions. Sodium Influx 2 Sodium channels open, allowing sodium ions to rush into the cell, making the inside more positive. Action Potential This rapid change in potential, known as depolarization, generates an 3 action potential, a brief electrical signal that travels along the neuron. The Propagation of Nerve Impulses Depolarization The action potential travels along the axon, the neuron's long extension, by Refractory Period depolarizing neighboring sections of the membrane. This process continues in a There is a brief refractory period after each action potential, preventing the impulse wave-like manner. from traveling backward and ensuring unidirectional propagation. 1 2 3 Repolarization After depolarization, the membrane rapidly repolarizes as potassium channels open, allowing potassium ions to flow out of the cell, restoring the negative potential. Propagation of Action Potential - describes the transmission of an action potential down an axon.  The propagation of an animal species is the production of offspring.  In a sense, the action potential gives birth to a new action potential at each point along the axon.  As an action potential occurs at one point on the axon, enough sodium enters to depolarize the next point to its threshold, producing an action potential at that point.  In this manner the action potential f lows along the axon, remaining at equal strength throughout.  Behind each area of sodium entry, potassium ions exit, restoring the resting potential. THE ALL-OR-NONE LAW 3. At the peak of the action potential, the sodium channels close.  States that the amplitude and velocity of an action potential are independent of the intensity  A neuron’s membrane contains cylindrical of the stimulus that initiated it, provided that the proteins. Opening one of these proteins allows a stimulus reaches the threshold. particular type of ion to cross the membrane.  A protein that allows sodium to cross is called a THE MOLECULAR BASIS OF THE ACTION sodium channel (or gate), and one that allows POTENTIAL potassium to cross is a potassium channel.  The axon channels regulating sodium and potassium are voltage-gated channels The chemical events behind the action potential may seem complex, but they make sense if you  Action potentials require the flow of sodium and remember three principles: potassium.  Local anesthetic drugs, such as Novocain and Xylocaine, attach to the sodium channels of the 1. At the start, sodium ions are mostly outside the membrane, preventing sodium ions from entering neuron, and potassium ions are mostly inside. 2. When the membrane is depolarized, sodium and potassium channels in the membrane open. Myelination and Saltatory Conduction Myelin Sheath Many neurons in the nervous system are covered in a fatty substance called myelin, which acts as an insulator, preventing ion leakage and speeding up impulse transmission. Myelinated Axons those covered with a myelin sheath.  found only in vertebrates, are covered with layers of fats and proteins.  The myelin sheath is interrupted periodically by short sections of axon called nodes of Ranvier. Saltatory Conduction The action potential jumps from node to node, a process called saltatory conduction, making the signal travel much faster than in unmyelinated neurons, from the Latin word saltare, meaning “to jump”. THE REFRACTORY PERIOD Remember, at the peak of the action potential, the sodium gates snap shut. As a result, the cell is in a refractory period during which it resists the production of further action potentials. The refractory period depends on two facts: a. The sodium channels are closed, b. and potassium is flowing out of the cell at a faster-than-usual rate. LOCAL NEURONS  Axons produce action potentials. However, many small neurons have no axon.  Neurons without an axon exchange information with only their closest neighbors. We therefore call them local neurons. Because they do not have an axon, they do not follow the all-or-none law.  Neurons without an axon exchange information with only their closest neighbors.  When a local neuron receives information from other neurons, it has a graded potential, a membrane potential that varies in magnitude in proportion to the intensity of the stimulus.  Local neurons are difficult to study because it is almost impossible to insert an electrode into a tiny cell without damaging it.  Most of our knowledge, therefore, has come from large neurons, and that bias in our research methods may have led to a misconception. Nerve Impulse Speed The speed at which a nerve impulse travels along an axon can vary depending on several factors, including the diameter of the axon and the presence of myelin. Axon Diameter Myelination Larger axons generally conduct Myelin, a fatty sheath that impulses faster than smaller axons insulates axons, speeds up due to less resistance to the flow conduction by allowing the of ions. impulse to "jump" between nodes of Ranvier, a process called saltatory conduction. Factors Affecting Nerve Impulse Transmission Temperature pH Temperature can affect the rate of The pH of the surrounding fluid can nerve impulse transmission. Higher also influence nerve impulse temperatures generally increase the transmission. Extreme pH values can speed of conduction, while lower disrupt the function of ion channels temperatures slow it down. and affect the electrical properties of the neuron. Drugs and Toxins Drugs and toxins can interfere with nerve impulse transmission. Some drugs can block the action of neurotransmitters, while others can enhance their effects, leading to various physiological and behavioral changes. Clinical Implications and Nerve Disorders 1 2 3 Neurological Disorders Treatment Research Disruptions in nerve impulse transmission can Understanding the mechanisms of nerve Ongoing research focuses on understanding the lead to a wide range of neurological disorders, impulse transmission is crucial for developing causes of neurological disorders and developing such as multiple sclerosis, Parkinson's disease, effective treatments for these conditions. new therapies to improve patient outcomes and and Alzheimer's disease. Medications, therapies, and lifestyle enhance the quality of life. modifications can be employed to manage neurological symptoms.