Action Potential 2024 DRKF PDF

Action Potential & Resting Membrane Potential Action Potential: Nerve Impulses or Action Potentials are the means or the language of communication among the human cells; in other words, nervous and muscle cells of the body do understand each other by a language of transduction of any type of energy,...

Action Potential & Resting Membrane Potential Action Potential: Nerve Impulses or Action Potentials are the means or the language of communication among the human cells; in other words, nervous and muscle cells of the body do understand each other by a language of transduction of any type of energy, i.e., heat, light, sound, pressure.. etc., into nerve impulses and neurotransmitter …. Tools of communication Loading… Resting Membrane Potential : The unequal distribution of ions across the cell membrane gives a negatively charged membrane called a resting membrane potential in an unexcited cell. This resting membrane potential changes if the excitable cell is stimulated and creates nerve impulses or action potential. gap between a muscle neuron and cell. Synapse Synapse: The neurons or neurons and muscle cells come in close contact via synapses (gaps), but they do not stick or come into direct contact to each other. Electrical and Concentration Gradients Electrical and Concentration Gradients Two forces drive ion movement through the cell membrane: 1) Concentration or Chemical gradient: ions move from high concentration to low. 2) Electrical gradient: ion of negative charge moves towards positively charged ions. Loading… Two types of lon forces I concentration or electrical gradient : high to low concentration 2 electrical gradient : lons negative charged move to posite charged long Overview Of The Nervous System Nervous system – Allows the communication between cells through sensory input, integration of data and motor output The nervous system is responsible for the reception and processing of sensory information from both the external and internal environments. Divisions of Nervous System The nervous system has two major divisions: A) The Central Nervous System (CNS) which consists of the brain and the spinal cord. AND B) The Peripheral Nervous System (PNS) consists of nerves that lie outside the CNS and also consists of GANGLIA (cell bodies) Peripheral Nervous System Within the PNS, major divisions are the somatic nervous system and the autonomic nervous system, which has two branches: the parasympathetic and the sympathetic branches. Relationshi p between the central and peripheral nervous systems Relationshi p between the central and peripheral nervous systems PNS CNS Loading… CNS = brain + spinal cord; all parts of interneurons are in the CNS. PNS = consists of afferent neurons going into the CNS and efferent neurons projecting out of the CNS or exiting out of the CNS: transferring the nerve impulses to muscles or glands causing movement, secretion, etc.) Nervous Tissue Nervous tissue contains two types of cells: Neurons Neuroglia (neuroglial cells). Neurons are the cells that transmit nerve impulses between parts of the nervous system. Neuroglia are cells that support and nourish neurons. There are different types of neuroglia in the CNS, each with specific function. Microglia are phagocytic cells that help remove bacteria and debris Astrocytes provide metabolic and structural support directly to the neurons Schwann cells in PNS form the myelin sheath whereas oligodendrocytes form the myelin sheath in the CNS 2 types of nervous system Peripheral nervous central nervous Brain Espinal cord nerves that lay outside CNS & ganglia autonomic Somatic nervous system 2 types of nervous system nervous tissue Neurolgia neurons cells that cell body transmit Cells that support nerve impulses and nourish neurons microlgia remove help bacteria debris astrocyte Provides metabolic Structural support to the neurons schwann cell In PNS form the. myelin sheath Oligondrocytes form myelin sheath In CNS Types of neurons Neurons are classified according to their functions into three types: to (NS Sensory neurons or afferent neurons (going at CNS). Take nerve signals from a sensory receptor to the CNS. Interneurons: lie entirely within the CNS. They receive input from sensory neurons & from other interneurons in the CNS. Therefore, they sum up all the information received from other neurons before they communicate with motor neurons. from CNS Motor neurons or efferent neurons (exit out of CNS) take impulses away from the CNS to an effector( muscle fiber, organ, or gland) 1 Sensory. motor 2. 3 (afferent) (efferent) Interneurons (lie entirely in CNS Structure of a neuron Neurons have three distinct structures: A cell body: contains the nucleus as well as other organelles. Dendrites: are short extensions protruding from the cell body that receive signals from sensory receptors or other neurons. Axon: is the portion of a neuron that conducts nerve impulses. Individual axon are termed NERVE FIBERS, collectively , they form a NERVE. The nervous system has three specific functions 1) 2) The nervous system receives sensory input. Sensory receptors in skin and other organs respond to external and internal stimuli by ①recieves generating nerve signals that travel by way of the PNS to the CNS. For example, if you smell baking cookies or bread , smell receptors in the nose use the PNS to transmit that information to the CNS. The CNS perform information processing and integration, summing up the input it receives from all the body. The CNS reviews ② the information, stores the information as memories, and creates the appropriate motor responses. sensory inputs cus reviews , stores the information as memories 3) The CNS generates motor output. Nerve signals from the CNS go by way of the PNS to the muscles, glands and organs, all in response to the cookies. Signals to the salivary glands make you salivate; Your stomach produces the acid and enzymes needed to digest the cookies –even before you’ve had a bite. Myelin Sheath Many axons are covered by a protective myelin Sheath. The myelin sheath develops when Schwann cells (PNS) or oligodendrocytes (CNS) wrap their membranes around an axon many times. Each neuroglial cell covers only a portion of an axon, so the myelin sheath is interrupted. The gaps where there is no myelin sheath are called nodes of Ranveir. The myelin sheath plays an important role in the rate at which signals move through the neurons. Long axons tend to have a myelin sheath, but short axons do not. nodes of ranreir : gaps with no myelin sheath Myelin Sheath The myelin sheath Schwann cells form myelin on peripheral neuronal axons. Oligodendrocytes form myelin on central neuronal axons. Among all types of neurons, myelinated neurons conduct action potentials most rapidly. The myelin sheath ↑pathat inces a A lipid covering on long axons that acts to increase the speed of nerve impulse conduction, insulation and regeneration of neurons in the PNS Schwann cells – neuroglia that make up the myelin sheath in the PNS Nodes of Ranvier – gaps between myelination on the axons Saltatory conduction – conduction of the nerve impulse from node to node. Multiple sclerosis MS is a nervous disease where the myelin is destroyed in CNS and conduction of impulses becomes difficult. Neuronal Signaling and the Structure of the Nervous System neuron communication is based in membrane's on - changes Permeability. - Two 1.. 2 - types of membrane potential Action Potential graded Typical. axonal 2 Potential neuron has : 1. dendritic : : Communication by neurons is based on changes in the membrane’s permeability to ions. Two types of membrane potentials are of major functional significance: graded potentials and action potentials. recieve information deliver information A typical neuron has a dendritic region and an axonal region. The dendritic region is specialized to receive information whereas the axonal region is specialized to deliver information. Transmission of nerve signals (action potentials) Resting Membrane Potential If you separate positively charged ions from negatively charged ions by a membrane, then you will get a polarized membrane with a potential energy separating these differently charged ions. This energy is called resting membrane potential. The cell membrane is polarized: positively charged ions are stashed outside the cell, with negatively charged ions inside. Although all cells have a membrane potential, only a few types of cells have been shown to alter their membrane potential in response to stimulation. Neurons and muscle cells have the ability to produce and conduct these changes in membrane potential. Such an ability is termed excitability or irritability. > potential energy seperating differently charged ins & neurons &, muscle have ability cells to produce and conduct in membrane changes potential ClNa+ Na+ Cl- Na+ K+ Na+A- Cl- Na+ Na+ AK+ AClClK+ AClK+ K+ AANa+ K+ ClK+ A- K+ Na+ Na+ Na+ K+ ClNa+ A- K+ AClClANa+ Na+ K+ Cl- Only a very thin shell of charge difference is needed to establish a membrane potential How does this separation of ions occur? The inside of the cell is negatively charged in relation to the exterior of the cell because of the presence of large, negatively charged proteins and other molecules that remain inside the cell because of their size. large negatively charged The outside of the cell is positive because positively charged sodium ions (Na+) gather around the outside of the cell membrane. charged Inside is negative due to proteins outside is positive because positively sodium lons are around the cell membrane At rest, the neuron’s cell membrane is permeable to potassium (K+) but not to sodium. Therefore, the resting cell is thus more permeable to K+ than to Na+. Thus, positively charged potassium ions contribute to the positive charge, outside, by diffusing out of the cell to join the sodium ions. The inside of a nerve cell has a voltage or stored energy of -70 millivolt. At rest, the neuron cell’s voltage is always negative resting cell is more permeable than sodium to potassium How does this separation of ions occur? But this membrane potential tends to change due to two following facts: Potassium is more concentrated inside the cell than outside, so potassium is leaking out under the influence of its concentration gradient ( from high to low concentration) so it tends to go outside under the influence of its concentration gradient. Sodium ions tend to diffuse down their concentration gradient as sodium is more concentrated outside the neuronal cell than inside, and it also tends to be attracted by the negatively charged proteins inside the cell, i.e. down its electrical gradient. These two diffusions tend to change the membrane resting potential. diffusions Potassium Sodium of Potassium more more and sodium. concentrated inside concentrated outside How does this separation of ions occur? Neurons must maintain their resting membrane potential at around minus or negative 70mv to be able to work and function properly. To do so, neurons actively transport Na+ ions out of the cell and return K+ ions back into the inside of the cell. This is the function of a protein carrier in the basolateral membrane of the cell, called sodium-potassium pump, pumps sodium ions out of the neuron and pumps potassium ions back into the neurons, in order to correct the changes in voltage and always keeps the resting membrane potential at -70 mV. Loading… The nerve impulse: resting potential (RP) RP : more Potassium inside Resting potential – when the axon is not conducting a nerve impulse More positive ions outside than inside the membrane There is a negative charge of -70 mV inside the axon More Na+ outside than inside More K+ inside than outside Action Potential (AP) or Nerve Impulse The resting potential energy of the neuron can be used to perform the work of the neuron: conduction of nerve signals. action potential : - process of The process of conduction is termed action potential, and it occurs in the axons of neurons. A stimulus activates the neuron and begins the action potential. However, the stimulus must be strong enough to cause the cell to reach threshold, which is the voltage that will result in an action potential, (which is about -55mV). An action potential is an all-or-nothing event; meaning that once the threshold is reached, the action potential happens automatically and completely. If the threshold is not reached, the action potential does not occur. - happens conducting in axon The nerve impulse: The steps of generating action potential Action potential – rapid change in the axon membrane that allows a nerve impulse to occur Sodium gates open letting Na+ in Depolarization occurs Interior of axon loses negative charge (+40mV) Sodium in Potassium out Potassium gates open letting K+ out Repolarization occurs Interior of axon regains negative charge (-65mV) Wave of depolarization/repolarization travels down the axon Resting potential is restored by moving potassium inside and sodium outside by the Na+/K+ pump. Steps of Generation The Nerve Impulse or The Action Potential Generation of action potential A) resting membrane potential: Na+ outside the axon, K+ and large anions inside the axon. Separation of charges polarizes the cell and causing the resting membrane potential. B) Stimulus causes the axon to reach its threshold” the axon potential increases from -70 mV to -55 mV, the action potential has begun. C) Depolarization continues as Na+ gates open and Na+ moves inside the cell. D) Action potential ends: repolarization occurs when K+ gates open and K+ moves to outside the axon. E) The sodium-potassium pump returns the ions to their resting position. Forces acting across the cell membrane Two forces drive ion movement through the cell membrane: 1) Chemical gradient: ions move from high concentration to low. 2) Electrical gradient: ion of negative charge moves towards positively charged ions. So, the main two ions will move as follows: Na+ goes inside the cell because 1) Na is positive and inside is negative, and 2) Na concentration is higher outside K+ goes outside because K concentration is higher inside than outside, but the electrical gradient tends to keep the K inside as it’s positive and inside is negative. But the concentration gradient is bigger the electrical gradient and it will overcome the attraction force, thence leaves the cell. In resting potential, only K+ channels are open Types of Channel with Gates Involved in Action Potential Sodium Channels: Protein channels specific for sodium ions are located in the cell membrane of the axon. When an AP begins in response to a threshold stimulus, these protein channels open, and sodium ions rush into the cell, causing the inside of the axon to be positive. This change is called depolarization. Because depolarization the charge or polarity inside changes from negative to positive. repolarization Potassium Channels : Almost immediately after depolarization, the sodium channels close and a separate set of potassium channels open. Potassium ions leave the cell, and the inside of the cell becomes negative again. This change in polarity from positive to negative is called repolarization. Finally, the Na+/K+ pump complete the AP by transporting K+ back to the inside and kicking Na+ out of the cell, and resting potential is restored.. : : sodium inside Potassium outside. Overshoot refers to the development of a charge reversal. A cell is “polarized” because its interior is more negative than its exterior. Repolarization is movement back toward the resting potential. Depolarization occurs when ion movement reduces the charge imbalance. Hyperpolarization is the development of even more negative charge inside the cell. Depolarization +35 0 - Repolarization -55 -70 Hyperpolarization The propagation of the action potential from the dendritic to the axon-terminal end is typically one-way Saltatory Conduction: Action potentials jump from one node to the next as they propagate along a myelinated axon. Saltatory conduction Insulated with myelin for speeding up 1. Unmyelinatd axons speed of AP is 10 meter/s. 2. Myelin sheath has spaces= Nodes of Ranvier. The AP jumps from node to next node (speed 120 meter/s). Continuous Conduction Occurs in unmyelinated axons. In this situation, the wave of depolarization and repolarization simply travels from one patch of membrane to the next adjacent patch. Action Potentials moved in this fashion along the sarcolemma of a muscle fiber as well. Analogous to dominoes falling. Continuous Conduction The synapse receiving sending A small gap between the sending neuron (presynaptic membrane) and the receiving neuron (postsynaptic membrane). Transmission of signals is accomplished across this gap by a neurotransmitter (e.g. Acetylcholine, dopamine and serotonin) Neurotransmitters are stored in synaptic vesicles in the axon terminals How does transmission across the synapse occur? When nerve impulse reaches the axon terminal, calcium ions enter the axon terminal. This will stimulate the synaptic vesicles to fuse with the presynaptic membrane Neurotransmitters are released on diffuse across the synapse and bind with the postsynaptic membrane to inhibit or excite the neuron. Inactivation of Ach is by the enzyme Acetylcholine esterase The synapse Neurotransmitters Acetylcholine ACh,Dopamine, GABA, Glutamate Norepinephrine: Autonomic nervous system, wakefulness, dreaming, mood. Serotonin: thermoregulation, sleeping, emotion Depression (Serotonin & Epinephrine. Theory- Antidepressive drugs are serotonergic drugs) Excitatory signal, and Inhibitory signal