Neuroscience: Graded Membrane Potential

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Questions and Answers

What characterizes graded membrane potential (GMP)?

  • It can only increase in strength.
  • It has a defined threshold for activation.
  • Its size depends on the strength of the stimulus. (correct)
  • It is always followed by a refractory period.

What happens to graded membrane potential as the current propagates?

  • It maintains a constant magnitude.
  • It can lead to an action potential without any increase in stimulus strength.
  • It decays as it moves away from the stimulus. (correct)
  • It remains unchanged in amplitude.

How do sensory receptors contribute to graded membrane potential changes?

  • They provide a constant resistance to changes in membrane potential.
  • They only transmit signals without transduction.
  • They transform stimulus energy into electrical changes that can affect ion channel activity. (correct)
  • They initiate the process of depolarization by directly opening ion channels.

In graded membrane potential, what is the effect of the stimulus strength on the depolarization?

<p>The size of depolarization is proportional to the strength of the stimulus. (D)</p> Signup and view all the answers

Which of the following statements is false about graded membrane potential?

<p>It does not decay away from the site of stimulation. (B)</p> Signup and view all the answers

What structure of the neuron is primarily responsible for conducting action potentials?

<p>Axon (B)</p> Signup and view all the answers

Which cells are known to form the myelin sheath in the central nervous system?

<p>Oligodendrocytes (B)</p> Signup and view all the answers

What is the primary function of the Node of Ranvier?

<p>To facilitate impulse conduction (B)</p> Signup and view all the answers

In which type of neuron classification do both sensory neurons of the retina and olfactory epithelium fall?

<p>Bipolar (D)</p> Signup and view all the answers

Which disease results from the degeneration of the myelin sheath in the central nervous system?

<p>Multiple Sclerosis (D)</p> Signup and view all the answers

What type of transport in axons is mediated by Dynein?

<p>Retrograded transport (C)</p> Signup and view all the answers

Which type of neuron has multiple dendrites and a single axon, making it predominant in the nervous system of vertebrates?

<p>Multipolar (D)</p> Signup and view all the answers

What facilitates the fast transport of vesicles in axons?

<p>Kinesin (D)</p> Signup and view all the answers

What is the primary reason for the difference in resting membrane potentials between different types of cells?

<p>Electrochemical gradients of ions (B)</p> Signup and view all the answers

Which ion has the greatest permeability in a resting membrane?

<p>K+ (C)</p> Signup and view all the answers

What type of ion channel remains open and is responsible for the leakage of ions across the membrane?

<p>Non-gated ion channels (D)</p> Signup and view all the answers

What is one role of the Na+/K+ pump in maintaining resting membrane potential?

<p>It stabilizes the negative charge inside the cell by moving Na+ out (C)</p> Signup and view all the answers

Which statement about the resting membrane potential of cardiac pacemaker cells is true?

<p>It fluctuates between -40 and -60 mv. (C)</p> Signup and view all the answers

What characteristic of the plasma membrane most affects the resting membrane potential?

<p>Ionic permeability (B)</p> Signup and view all the answers

What is the primary factor for the high concentration of K+ ions inside the cell?

<p>High permeability of the membrane to K+ (B)</p> Signup and view all the answers

Which of the following ions is least permeable in a resting membrane?

<p>Na+ (D)</p> Signup and view all the answers

What contributes to the influx of Na+ ions into a cell?

<p>Chemical (diffusion) gradient favoring Na+ (C)</p> Signup and view all the answers

What helps in opposing the efflux of K+ ions from a cell?

<p>Electrical gradient (A)</p> Signup and view all the answers

What is the Nernst potential for K+ ions?

<p>-90 mV (A)</p> Signup and view all the answers

Which of the following does not represent resting membrane potential (RMP) measurements?

<p>RMP is always exactly -70 mV (A)</p> Signup and view all the answers

How is the resting membrane potential (RMP) primarily established?

<p>Leaky ion channels allowing K+ diffusion (B)</p> Signup and view all the answers

What equipment is typically used to measure membrane potential?

<p>Microelectrodes and voltmeter (A)</p> Signup and view all the answers

What maintains the concentration gradients of Na+ and K+ ions in cells?

<p>Na+/K+ ATPase pump (C)</p> Signup and view all the answers

Which cell type would most likely have an RMP of around -58 mV?

<p>Adipocytes (B)</p> Signup and view all the answers

What is the diameter of Type C fibers?

<p>Less than 2µm (B)</p> Signup and view all the answers

What is the conduction velocity of Type C fibers?

<p>1m/sec (B)</p> Signup and view all the answers

What is the primary role of Type C fibers?

<p>Carry autonomic motor and visceral sensory information (D)</p> Signup and view all the answers

Which type of synapse is considered very common?

<p>Axo-dendritic synapse (B)</p> Signup and view all the answers

What triggers an action potential (AP) in a postsynaptic cell?

<p>Multiple EPSPs added temporally or spatially (D)</p> Signup and view all the answers

What role do synaptotagmin proteins play in synaptic transmission?

<p>Sensing calcium influx (D)</p> Signup and view all the answers

What mechanism ensures that the propagation of action potentials is unidirectional?

<p>Absolute refractory period of the membrane behind the traveling impulse (D)</p> Signup and view all the answers

What happens to calcium ions during synaptic transmission?

<p>They are taken into mitochondria or released through an active calcium pump (B)</p> Signup and view all the answers

What triggers the generation of an action potential?

<p>A graded potential that reaches the threshold (C)</p> Signup and view all the answers

Which characteristic is NOT a feature of an action potential?

<p>Can be summed (C)</p> Signup and view all the answers

During the rising phase of the action potential, which ion's conductance primarily increases?

<p>Sodium (Na+) (D)</p> Signup and view all the answers

What is the term for the property of an action potential that allows it to travel long distances without losing strength?

<p>Self-propagation (B)</p> Signup and view all the answers

How does the frequency of action potentials change in response to stimuli?

<p>It increases with the intensity of the stimulus. (D)</p> Signup and view all the answers

What occurs during the repolarization phase of an action potential?

<p>Potassium conductance increases and sodium conductance decreases. (D)</p> Signup and view all the answers

What effect does hypocalcemia have on muscle contraction?

<p>May lead to tetanus due to increased frequency of action potentials. (D)</p> Signup and view all the answers

Which of the following types of graded membrane potentials involves the response from neurotransmitter release?

<p>Synaptic potentials (B)</p> Signup and view all the answers

Flashcards

What is an axon?

A long extension of a neuron that conducts electrical signals away from the cell body.

What is the axon hillock?

The specialized region of the axon where the action potential is initiated.

What is the axon terminal?

The terminal portion of the axon responsible for releasing neurotransmitters into the synapse.

What is axonal transport?

The movement of materials within a neuron, including transport of vesicles, proteins, and organelles.

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What is the myelin sheath?

A fatty substance that insulates the axon and increases the speed of signal conduction.

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What are Nodes of Ranvier?

Gaps in the myelin sheath that facilitate rapid saltatory conduction of action potentials.

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What is Multiple Sclerosis (MS)?

A disorder characterized by degeneration of the myelin sheath in the central nervous system.

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What is Guillain-Barre Syndrome (GBS)?

A disorder that affects the peripheral nervous system with destruction of myelin sheath causing muscle weakness and tingling sensations.

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Membrane Potential

The difference in electrical potential across a cell membrane, caused by the unequal distribution of ions. It represents the energy stored across the membrane.

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Equilibrium Potential

The theoretical electrical potential difference across a membrane that would be required to prevent the movement of an ion down its concentration gradient.

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Resting Membrane Potential (RMP)

The charge difference across the cell membrane when the cell is not actively signaling. It is usually negative inside the cell compared to the outside.

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Electrochemical Gradient

The movement of ions across a membrane driven by both the concentration gradient and the electrical potential difference.

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Nernst Equation

The Nernst equation is a mathematical formula used to calculate the equilibrium potential for a single ion across a membrane.

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Chemical Gradient

The movement of ions across a membrane due to their different concentrations inside and outside the cell.

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Electrical Gradient

The movement of ions across a membrane due to the electrical potential difference across the membrane.

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Microelectrode

A specialized pipette used to measure the electrical potential difference across a cell membrane.

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Resting membrane potential

The difference in electrical charge between the inside and outside of a cell membrane when the cell is at rest.

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Ion diffusion

The movement of ions across the cell membrane due to differences in concentration and electrical charge.

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Differential membrane permeability

The difference in permeability of the cell membrane to different ions. For example, the membrane is more permeable to potassium ions (K+) than sodium ions (Na+).

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Sodium-potassium pump

The active transport of sodium (Na+) and potassium (K+) ions across the cell membrane, creating an electrochemical gradient.

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Ion channels

Proteins embedded in the cell membrane that allow ions to pass through.

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Non-gated ion channels

Ion channels that are always open, allowing a continuous flow of ions.

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Gated ion channels

Ion channels that open or close in response to a specific stimulus, such as a change in voltage or binding of a chemical.

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Ion channel gating

The process of opening and closing gated ion channels, which allows for the rapid transmission of signals in the nervous system and other cells.

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What is a graded membrane potential (GMP)?

A localized and temporary change in membrane potential that can vary in magnitude depending on the strength of the stimulus. It spreads passively, with attenuation and decay, and can summate to reach a threshold for further action.

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What is depolarization?

A change in membrane potential that makes the inside of the cell more positive, bringing it closer to the threshold for an action potential.

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What is hyperpolarization?

A change in membrane potential that makes the inside of the cell more negative, moving it further away from the threshold for an action potential.

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How can GMPs be summed?

GMPs can be summed together, meaning that multiple stimuli close in time or space can add up to create a larger change in membrane potential.

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What makes GMPs different from action potentials?

GMPs lack a threshold, meaning that they can occur even with small stimuli. Unlike action potentials, they do not have a specific level of depolarization required for their initiation.

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Graded Potential

A change in membrane potential that is proportional to the strength of the stimulus. It can be either depolarizing or hyperpolarizing and decays over distance.

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Triggering Zone

The region of a neuron where an action potential is initiated. It is typically located at the axon hillock.

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What is threshold?

The minimum amount of depolarization required to trigger an action potential. This is the threshold voltage.

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What is the refractory period?

A period following an action potential during which the neuron cannot generate another action potential. This ensures that action potentials are not transmitted back towards the cell body.

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AP Generation Mechanism

The process by which a neuron generates an action potential, involving sequential influx of Na+ ions followed by efflux of K+ ions.

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Rising Phase of AP

The rising phase of an action potential, characterized by rapid depolarization due to influx of Na+ ions.

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Falling Phase of AP

The falling phase of an action potential, characterized by repolarization due to efflux of K+ ions.

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Resting State of AP

The state of the neuronal membrane after an action potential has occurred. The membrane potential returns to its resting value.

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Type C nerve fibers

Nerve fibers with a diameter less than 2 micrometers and lacking myelin sheath. They conduct impulses at a slow rate of 1 meter per second and transmit autonomic motor and visceral sensory information.

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One-way propagation of action potential

The process by which an action potential (AP) travels along a nerve fiber only in one direction, from the axon hillock towards the axon terminal.

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Chemical synapse

A junction between two neurons where communication occurs through the release of chemical messengers called neurotransmitters. These junctions are composed of a presynaptic neuron that releases the neurotransmitter, a synaptic cleft, and a postsynaptic neuron that receives the neurotransmitter.

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Presynaptic neuron

The terminal part of the axon that contains vesicles filled with neurotransmitters. These vesicles release neurotransmitters into the synaptic cleft when an action potential arrives.

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Postsynaptic neuron

A neuron that receives the neurotransmitter released by the presynaptic neuron. It has receptors that bind to the neurotransmitter, triggering a response.

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Synaptic cleft

The space between the presynaptic and postsynaptic neuron. This space allows for the diffusion of the neurotransmitter from the presynaptic neuron to the postsynaptic neuron.

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Axo-dendritic synapse

A type of synapse where the axon terminal of one neuron forms a junction with the dendrite of another neuron.

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Axo-somatic synapse

A type of synapse formed between the axon terminal of one neuron and the soma (cell body) of another neuron.

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Study Notes

Lecture Notes on Excitable Cells and Membrane Potential

  • The lecture notes are for pre-clinical I students at Addis Ababa University, Department of Medical Physiology.
  • Objectives of the lecture include discussing neuroglia, excitable cells (neurons), types of membrane potentials, action potential formation and propagation, synaptic transmission, synapse types, and correlations.
  • Excitable cells form excitable tissues (nerves and muscles) while non-excitable cells include neuroglia.
  • Neuroglia are supporting cells that outnumber neurons, proliferate throughout life, and lack synaptic potential.
  • Astrocytes maintain the blood-brain barrier, regulate electrolytes and neurotransmitters, guide neuronal development, act as buffers for potassium and neurotransmitters, and synthesize neurotransmitters GABA and glutamate.
  • Microglia are innate immune cells in the central nervous system, working with astrocytes to produce cytokines, clear cellular debris, respond to injury and stress, and proliferate, change shape, and become phagocytic, a response called gliosis.
  • Ependymal cells form the plexus (epithelium) in the wall of ventricles and regulate the blood-cerebrospinal fluid barrier, producing cerebrospinal fluid.
  • Oligodendrocytes form the myelin sheath of axons centrally, and one cell can cover multiple axons.
  • Peripheral neuroglia include Schwann cells which cover axons at the periphery and satellite cells that encapsulate dorsal root and cranial nerve ganglia, regulating autonomic ganglia.
  • Neurons are fundamental cells in the nervous system, generating and propagating electrical impulses (action potentials).
  • Neurons have longevity, consume significant energy, and cannot replicate.
  • New neurons are possible in specific brain regions, like the hippocampus and olfactory bulb, involved in memory and navigation.
  • Organization of both the central and peripheral nervous systems is discussed, including brain, spinal cord, spinal nerves, and cranial nerves.
  • Neuronal structures and functions, including dendrites, cell bodies/soma (containing organelles like nuclei, mitochondria, endoplasmic reticulum), and axons (including axon terminals with mitochondria), as well as axonal transport, are detailed.
  • Myelin sheath, consisting of fatty, lipo-protein substance, protects cells, increasing impulse conduction speed thanks to Schwann cells/oligodendrocytes. Nodes of Ranvier are also mentioned and are important for conduction of impulses.
  • Demyelination disorders like Multiple Sclerosis (MS) and Guillain-Barre Syndrome (GBS) are discussed.
  • Classifications of neurons, including based on chemical release (cholinergic, adrenergic, dopaminergic), and anatomical classification (unipolar, bipolar, multipolar) are outlined.
  • Electrical activity types in neurons (silent, pacing/beating, bursting) are presented.
  • Neuronal reactions to injury including neuronal degeneration (loss of neuronal structure, synapses, and myelin sheath), organelle rearrangement, and debris of degeneration taken by microglia are detailed.
  • Specific factors involved in neurodegeneration, including abnormal proteins, mitochondrial deficiency, and their role in Parkinson's disease, Alzheimer's disease, and Huntington's disease.
  • Neuronal regeneration in the CNS and periphery, emphasizing limited CNS regeneration, factors like glia scar formation, and inflammatory reactions, neurogenesis, and axon regrowth are covered.
  • Detailed information is provided on electrophysiology, defining membrane potential (MP), including ions' asymmetrical distribution inside and outside cells (like Na+, K+, Cl-, Ca++, HCO3-).
  • Electrochemical gradients, Nernst potential calculations, and membrane potential measurement using microelectrodes are described thoroughly.
  • Types of membrane potentials (resting membrane potential, graded membrane potential), characteristics of graded membrane potentials (e.g. depolarizations/hyperpolarizations, magnitude based on stimulus strength), and mechanisms of graded potential change and response are explained.
  • Action potential (AP) definition, propagation, characteristics (all-or-none phenomenon, threshold), mechanisms of AP generation (and trigger zone), phases of AP and responsible factors, and the refractory period are thoroughly detailed.
  • Factors influencing impulse conduction speed (myelination, membrane resistance, myelin thickness, luminal resistance, internode distance, capacitance, temperature, metabolic activity, fiber size) and the different types of nerve fibers (A, B, C) are described completely.
  • Synaptic transmission, including chemical synapses, pre-synaptic, post-synaptic cells, and clefts, multiple EPSPs, postsynaptic cell responses (EPSPs, IPSPs), the life cycle of neurotransmitters, synaptic fatigue are explored in detail.
  • Criteria for defining neurotransmitters (small chemicals vs. large peptides, direct vs. indirect action on receptors) and their functionalities via inotropic and metabotropic receptors are highlighted.
  • Synaptic plasticity (experience-based changes in neuron connectivity, short-term and long-term changes, decrease: depression, forming new structures) and factors affecting neuronal excitability (e.g., ion channel density, pH, metabolic factors, hypoxia, ischemia, drugs, and chemicals) are described.
  • Synaptic abnormalities (synaptopathology), toxins affecting transmission, and electrical synapses (gap junctions and their roles) are presented including their roles in embryonic development and cell communication.
  • Information on drug actions impacting synaptic transmission (e.g., re-uptake inhibitors, enzyme modulators, receptor agonists/antagonists, actions of toxins like curare, atropine, nicotine, and muscarine) and their impact on neuronal effects is discussed entirely.  

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