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?

The size of depolarization is proportional to the strength of the stimulus. Signup and view all the answers

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

It does not decay away from the site of stimulation. Signup and view all the answers

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

Axon Signup and view all the answers

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

Oligodendrocytes Signup and view all the answers

What is the primary function of the Node of Ranvier?

To facilitate impulse conduction Signup and view all the answers

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

Bipolar Signup and view all the answers

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

Multiple Sclerosis Signup and view all the answers

What type of transport in axons is mediated by Dynein?

Retrograded transport 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?

Multipolar Signup and view all the answers

What facilitates the fast transport of vesicles in axons?

Kinesin Signup and view all the answers

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

Electrochemical gradients of ions Signup and view all the answers

Which ion has the greatest permeability in a resting membrane?

K+ Signup and view all the answers

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

Non-gated ion channels Signup and view all the answers

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

It stabilizes the negative charge inside the cell by moving Na+ out Signup and view all the answers

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

It fluctuates between -40 and -60 mv. Signup and view all the answers

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

Ionic permeability Signup and view all the answers

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

High permeability of the membrane to K+ Signup and view all the answers

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

Na+ Signup and view all the answers

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

Chemical (diffusion) gradient favoring Na+ Signup and view all the answers

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

Electrical gradient Signup and view all the answers

What is the Nernst potential for K+ ions?

-90 mV Signup and view all the answers

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

RMP is always exactly -70 mV Signup and view all the answers

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

Leaky ion channels allowing K+ diffusion Signup and view all the answers

What equipment is typically used to measure membrane potential?

Microelectrodes and voltmeter Signup and view all the answers

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

Na+/K+ ATPase pump Signup and view all the answers

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

Adipocytes Signup and view all the answers

What is the diameter of Type C fibers?

Less than 2µm Signup and view all the answers

What is the conduction velocity of Type C fibers?

1m/sec Signup and view all the answers

What is the primary role of Type C fibers?

Carry autonomic motor and visceral sensory information Signup and view all the answers

Which type of synapse is considered very common?

Axo-dendritic synapse Signup and view all the answers

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

Multiple EPSPs added temporally or spatially Signup and view all the answers

What role do synaptotagmin proteins play in synaptic transmission?

Sensing calcium influx Signup and view all the answers

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

Absolute refractory period of the membrane behind the traveling impulse Signup and view all the answers

What happens to calcium ions during synaptic transmission?

They are taken into mitochondria or released through an active calcium pump Signup and view all the answers

What triggers the generation of an action potential?

A graded potential that reaches the threshold Signup and view all the answers

Which characteristic is NOT a feature of an action potential?

Can be summed Signup and view all the answers

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

Sodium (Na+) 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?

Self-propagation Signup and view all the answers

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

It increases with the intensity of the stimulus. Signup and view all the answers

What occurs during the repolarization phase of an action potential?

Potassium conductance increases and sodium conductance decreases. Signup and view all the answers

What effect does hypocalcemia have on muscle contraction?

May lead to tetanus due to increased frequency of action potentials. Signup and view all the answers

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

Synaptic potentials Signup and view all the answers

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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Description

This quiz focuses on graded membrane potentials and their roles in neuronal function. It covers concepts such as sensory receptor contributions, myelin sheath formation, and related neurological diseases. Test your understanding of how graded potentials influence depolarization and action potential propagation.