Neuroscience Chapter: Synaptic Diversity
87 Questions
0 Views

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the effect of EPSP in synaptic transmission?

  • Hyperpolarization of the post-synaptic cell
  • Complete closure of ion channels
  • Inhibition of neurotransmitter release
  • Depolarization of the post-synaptic cell (correct)

    • Which neurotoxin is known to block nicotinic ACh receptors?

  • Botulinum toxin
  • Bungarotoxin (correct)
  • Calcicludine
  • Neurotoxin A

    • What role does the hypothalamus serve in synaptic transmission?

  • It exclusively processes electrical signals
  • It blocks synaptic transmission
  • It directly initiates action potentials
  • It regulates hormone release affecting synaptic activity (correct)

    • What is one possible outcome of disrupted synaptic transmission?

    <p>Symptoms of neurological disorders</p> Signup and view all the answers

    Which statement about ionotropic and metabotropic pathways is true?

    <p>Ionotropic pathways directly affect ion channels</p> Signup and view all the answers

    Which of the following ions is typically associated with EPSP?

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

    How do pharmacological agents affect synaptic transmission?

    <p>They can modulate synaptic activity either positively or negatively</p> Signup and view all the answers

    Which of the following is NOT a function of synapses in neural communication?

    <p>Completely isolating signals from adjacent neurons</p> Signup and view all the answers

    What type of receptors are chemically gated ion channels classified as?

    <p>Ionotropic receptors</p> Signup and view all the answers

    Which of the following describes the function of metabotropic receptors?

    <p>They activate second messenger pathways.</p> Signup and view all the answers

    What is the primary effect of excitatory neurotransmitters on the postsynaptic cell?

    <p>Depolarize the membrane</p> Signup and view all the answers

    Which of the following best characterizes slow synaptic potentials?

    <p>They can have long-term effects.</p> Signup and view all the answers

    What change occurs in the presynaptic axon terminal that affects synaptic signaling?

    <p>Modification of existing ion channels</p> Signup and view all the answers

    Which statement accurately describes the action of inhibitory neurotransmitters?

    <p>They typically hyperpolarize the postsynaptic membrane.</p> Signup and view all the answers

    Which of the following pathways is primarily involved in the activation of metabotropic receptors?

    <p>Second messenger pathways</p> Signup and view all the answers

    What aspect of synaptic transmission can be altered by metabotropic receptor activation?

    <p>The permeability of the postsynaptic membrane</p> Signup and view all the answers

    What is one of the primary functions of the hypothalamus?

    <p>Regulating body temperature</p> Signup and view all the answers

    Which part of the brain is specifically associated with auditory processing?

    <p>Auditory cortex</p> Signup and view all the answers

    What type of information is primarily processed by the dorsal root ganglion in the spinal cord?

    <p>Sensory information</p> Signup and view all the answers

    Which structure is involved in coordinating movement?

    <p>Cerebellum</p> Signup and view all the answers

    What is the role of the medulla oblongata in the autonomic nervous system?

    <p>Controlling involuntary functions</p> Signup and view all the answers

    In the spinal cord, what does the descending tract primarily do?

    <p>Relay motor commands from the brain</p> Signup and view all the answers

    What type of response is described as a short and fast reaction that does not require feedback?

    <p>Reflex response</p> Signup and view all the answers

    What primarily distinguishes spinal reflexes from homeostatic reflexes?

    <p>Spinal reflexes are fast and involuntary, whereas homeostatic reflexes are slower.</p> Signup and view all the answers

    Which of the following is NOT a function of the hypothalamus?

    <p>Processing visual stimuli</p> Signup and view all the answers

    Which of the following statements about the autonomic nervous system (ANS) is correct?

    <p>The control centers for the two branches of the ANS within the CNS are spatially segregated.</p> Signup and view all the answers

    What is the primary function of the hypothalamus in the brain?

    <p>Secreting hormones through the pituitary gland.</p> Signup and view all the answers

    Which part of the brain is primarily responsible for processing visual information?

    <p>Occipital lobe</p> Signup and view all the answers

    What is the main distinction between gray matter and white matter in the nervous system?

    <p>Gray matter consists of cell bodies and dendrites, while white matter contains myelinated axons.</p> Signup and view all the answers

    Which spinal nerves correspond to the lumbar region?

    <p>Lumbar spinal nerves</p> Signup and view all the answers

    Which area of the brain is responsible for somatic sensory processing?

    <p>Parietal lobe</p> Signup and view all the answers

    What is the role of the pituitary gland in the endocrine system?

    <p>It secretes hormones that influence other glands.</p> Signup and view all the answers

    What is the primary function of the sympathetic division of the autonomic nervous system?

    <p>To initiate 'fight or flight' responses</p> Signup and view all the answers

    Which of the following is NOT controlled by the autonomic division?

    <p>Skeletal muscle movement</p> Signup and view all the answers

    In terms of effect, what is the primary role of the parasympathetic division?

    <p>Promote 'rest and digest' processes</p> Signup and view all the answers

    Which neurotransmitter is typically associated with the sympathetic nervous system?

    <p>Epinephrine</p> Signup and view all the answers

    Which structure is involved in the autonomic control of heart rate?

    <p>Hypothalamus</p> Signup and view all the answers

    What is the role of the adrenal medulla in the autonomic nervous system?

    <p>Releasing neurotransmitters directly into the blood</p> Signup and view all the answers

    Which of the following accurately describes the nature of parasympathetic pathways?

    <p>They initiate responses mainly during restful states.</p> Signup and view all the answers

    What is the significance of nicotinic receptors in autonomic pathways?

    <p>They facilitate communication in ganglionic synapses.</p> Signup and view all the answers

    Which category of membrane receptors involves ligand binding to open or close a channel?

    <p>Receptor-channel</p> Signup and view all the answers

    What type of signaling involves the release of molecules that affect the same cell that released them?

    <p>Autocrine signaling</p> Signup and view all the answers

    The endocrine system utilizes rapid signaling for communication.

    <p>False</p> Signup and view all the answers

    Which mechanism allows peptide hormones to alter existing proteins?

    <p>Signal transduction activation</p> Signup and view all the answers

    What type of hormones can diffuse across cellular membranes?

    <p>Steroid hormones</p> Signup and view all the answers

    Hormones produced by glands, specialized cells, or neurons are known as ______.

    <p>hormones</p> Signup and view all the answers

    What type of receptor is involved in cholinergic signaling?

    <p>Cholinergic receptor</p> Signup and view all the answers

    Match the following hormones to their characteristics:

    <p>Polypeptide hormones = Not lipid soluble Steroid hormones = Lipid soluble Peptide hormone synthesis = Pre-synthesized &amp; stored in vesicles Steroid hormone synthesis = Synthesized on demand</p> Signup and view all the answers

    What does acetylcholinesterase (AChE) do?

    <p>Breaks down acetylcholine</p> Signup and view all the answers

    What role do trophic hormones play in the endocrine system?

    <p>Regulation of hormonal release</p> Signup and view all the answers

    What are the two pathways through which chemical synapses affect postsynaptic cells?

    <p>Both A and B</p> Signup and view all the answers

    Synapses can either be electrical or chemical.

    <p>True</p> Signup and view all the answers

    What is the primary role of neurotoxins in synaptic transmission?

    <p>To disrupt synaptic transmission</p> Signup and view all the answers

    Define osmolarity.

    <p>The number of solute particles per volume</p> Signup and view all the answers

    What is tonicity?

    <p>A physiological feature of a fluid that determines whether fluid will move into or out of a cell</p> Signup and view all the answers

    What does Fick's Law describe?

    <p>The rate of diffusion</p> Signup and view all the answers

    What components affect the rate of diffusion through a cell membrane?

    <p>All of the above</p> Signup and view all the answers

    Which type of transporters can facilitate diffusion?

    <p>Both A and B</p> Signup and view all the answers

    What are the effects of growth hormones?

    <p>All of the above</p> Signup and view all the answers

    Hypersecretion refers to deficient hormone secretion.

    <p>False</p> Signup and view all the answers

    What is the role of trophic hormones in the endocrine system?

    <p>They regulate the release of other hormones.</p> Signup and view all the answers

    The hypothalamus-anterior pituitary axis is involved in _____ regulation of hormonal release.

    <p>endocrine</p> Signup and view all the answers

    Which of the following is a function of the nervous system compared to the endocrine system?

    <p>Rapid but short lasting shifts in physiology</p> Signup and view all the answers

    Match the following hormones with their primary functions:

    <p>Growth Hormone = Growth and metabolism ACTH = Stress response TSH = Regulates metabolism Prolactin = Milk production</p> Signup and view all the answers

    What is the charge inside the cell at resting membrane potential?

    <p>-70 mV</p> Signup and view all the answers

    Changes in membrane permeability to Na+ and K+ lead to _____ potentials.

    <p>action</p> Signup and view all the answers

    Local communication regulates the state of distant cells.

    <p>False</p> Signup and view all the answers

    What functions does the cell body of a neuron serve?

    <p>Integrating center</p> Signup and view all the answers

    What determines whether an action potential will fire?

    <p>The sum of graded potentials in the cell body</p> Signup and view all the answers

    Graded potentials can only be excitatory.

    <p>False</p> Signup and view all the answers

    What is true about the absolute refractory period?

    <p>Both A and C</p> Signup and view all the answers

    Match the disorders with their effects:

    <p>Multiple Sclerosis = Myelin degeneration Meylitis = Inflammation of myelin Leukodystrophy = Genetic disorder affecting myelin Myelin Degeneration = Loss of neuron function</p> Signup and view all the answers

    What increases the speed of action potential propagation?

    <p>Myelination and larger axon diameter</p> Signup and view all the answers

    What are the two types of synapses?

    <p>Electrical and chemical</p> Signup and view all the answers

    Neurotransmitters are released from the _____ terminal of the presynaptic neuron.

    <p>axon</p> Signup and view all the answers

    What role does calcium (Ca2+) play at the synapse?

    <p>Triggers exocytosis of neurotransmitters</p> Signup and view all the answers

    How are ionotropic and metabotropic synapses different?

    <p>Ionotropic synapses are fast, metabotropic are slow.</p> Signup and view all the answers

    What primarily determines the resting phase of an action potential?

    <p>K+ permeability</p> Signup and view all the answers

    Which phase of the action potential involves high permeability for Na+?

    <p>Rising phase</p> Signup and view all the answers

    What happens during the falling phase of an action potential?

    <p>K+ flows out of the cell, causing repolarization.</p> Signup and view all the answers

    What is the recovery phase of an action potential characterized by?

    <p>K+ channels closing and slowly restoring the membrane potential.</p> Signup and view all the answers

    The Na+ channels remain open during the falling phase.

    <p>False</p> Signup and view all the answers

    What is the effect of myelination on action potential propagation?

    <p>Increases resistance to current loss</p> Signup and view all the answers

    The __________ phase sees Na+ inactivation gates close and K+ channels open.

    <p>Overshoot</p> Signup and view all the answers

    Name one disease associated with myelin degeneration.

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

    What is the impact of the diameter of an axon on the speed of action potential?

    <p>Larger axons are faster</p> Signup and view all the answers

    The threshold is reached during the __________ phase of an action potential.

    <p>Rising</p> Signup and view all the answers

    Study Notes

    Chemical Synaptic Diversity

    • Ionotropic receptors are fast-acting and directly affect ion channels.
    • Metabotropic receptors are slow-acting and use G-protein coupled receptors to indirectly affect ion channels.

    Variation in Postsynaptic Responses

    • Excitatory postsynaptic potentials (EPSPs) result in depolarization and increased likelihood of an action potential.
    • Inhibitory postsynaptic potentials (IPSPs) result in hyperpolarization and decreased likelihood of an action potential.

    Synaptic Transmission: Possibilities for Modulation

    • Neurotoxins can disrupt synaptic transmission.
    • Botulinum toxin prevents vesicle docking.
    • Bungarotoxin blocks nicotinic acetylcholine receptors.
    • Calcicludine blocks voltage-gated calcium channels.

    Review

    • Synapses are junctions between neurons and other cells, including muscle cells.
    • Synapses can be electrical or chemical, with chemical synapses using neurotransmitters.
    • Chemical synapses can activate ionotropic or metabotropic receptors.

    Lecture 5 Learning Objectives

    • The hypothalamus plays a vital role in maintaining homeostasis.
    • Spinal reflexes are rapid, involuntary actions not requiring brain integration.
    • Homeostatic reflexes are slower and often involve the autonomic nervous system.
    • The autonomic nervous system has two branches: parasympathetic and sympathetic.
    • Control of the autonomic nervous system branches is spatially segregated within the CNS.
    • The two branches of the autonomic nervous system interact with different cellular receptors in target cells.

    Organization of the Nervous System

    CNS Architecture

    • The central nervous system (CNS) consists of the brain and spinal cord, which are protected by the cranium and vertebrae, respectively.
    • The brain includes the cerebral hemispheres, cerebellum, and brainstem (pons and medulla oblongata).

    Gray & White Matter

    • Gray matter in the CNS contains neuronal cell bodies, dendrites, and unmyelinated axons.
    • White matter in the CNS contains myelinated axons.

    Control Centers of the Brain

    • The hypothalamus controls vital functions including body temperature, osmolarity, reproduction, food intake, and hormone release.
    • The thalamus acts as a relay center for sensory and motor information.
    • The cerebellum coordinates movement.
    • The medulla oblongata controls involuntary functions like breathing, coughing, and sneezing.

    Hypothalamus

    • Activates the sympathetic nervous system.
    • Regulates body temperature, osmolarity, reproductive functions, and food intake.
    • Regulates hormone release from the pituitary gland.

    Spinal Cord: Anatomy

    • The spinal cord is organized into gray and white matter, with distinct dorsal (sensory) and ventral (motor) regions, and lateral horns for autonomic neurons.
    • The dorsal root ganglion contains the cell bodies of sensory neurons.
    • The ventral root contains axons of motor neurons.
    • Ascending tracts carry sensory information to the brain.
    • Descending tracts carry motor commands from the brain.

    Response to Stimulus

    • Reflex responses are rapid and happen directly in the spinal cord without brain involvement.
    • Homeostatic responses are slower, often involving the brain and hypothalamus.

    Autonomic Division

    • The autonomic nervous system controls smooth muscle, cardiac muscle, exocrine glands, endocrine glands, lymphoid tissue, and adipose tissue.
    • The parasympathetic nervous system promotes "rest and digest" functions.
    • The sympathetic nervous system promotes "fight or flight" responses.

    Autonomic Pathways

    • The autonomic nervous system uses two-neuron pathways.
    • The sympathetic nervous system uses acetylcholine (ACh) at the preganglionic synapse and norepinephrine (NE) at the postganglionic synapse.
    • The parasympathetic nervous system uses ACh at both preganglionic and postganglionic synapses.
    • The adrenal sympathetic pathway bypasses ganglia and directly stimulates the adrenal medulla to release epinephrine (adrenaline) and norepinephrine.

    Neuron Communication

    • Neurons communicate with each other and other cells using synapses.
    • Synapses can be electrical or chemical.
    • Chemical synapses convert electrical information to chemical information.

    Chemical Synapses

    • Chemical synapses are more prevalent than electrical synapses.
    • There are two types of chemical synapses:
      • Ionotropic: These synapses are fast.
      • Metabotropic: These synapses are slow.

    Synaptic Transmission

    • Synaptic transmission can be altered by neurotoxins or pharmacological agents.

    Graded vs. Action Potentials

    • Action Potentials:
      • all or none
      • have a threshold
      • involve Na+ and K+
      • have voltage gated channels
      • are depolarizing
      • have refractory periods
      • signals cannot sum
    • Graded Potentials:
      • do not have a threshold
      • involve Na+, K+, Ca2+, Cl-
      • have voltage, ligand, and mechanically gated channels
      • can be depolarizing or hyperpolarizing
      • do not have refractory periods
      • signals can sum

    Neuron Anatomy

    • Dendrites: Receive input signals
    • Cell body: Integrates signals
    • Axon hillock: Trigger zone for action potentials
    • Axon: Transmits output signals
    • Myelin sheath: Insulates axons
    • Axon terminal: Releases neurotransmitters

    Integration

    • The cell body of a neuron acts as an integrating center.
    • Graded potentials entering the cell body can be excitatory (+) or inhibitory (-).
    • The sum of these graded potentials determines whether an action potential will fire.

    Integration: Spatial Summation

    • Spatial summation occurs when multiple presynaptic neurons release neurotransmitters simultaneously, converging upon a single postsynaptic neuron.
    • If the sum of the excitatory postsynaptic potentials (EPSPs) is greater than the threshold, an action potential will be generated.

    Integration: Temporal Summation

    • Temporal summation occurs when a single presynaptic neuron releases neurotransmitters repeatedly in quick succession.
    • The summation of these EPSPs can reach the threshold and trigger an action potential.

    Events at the Synapse and Exocytosis

    • An action potential arriving at the axon terminal causes voltage-gated Ca2+ channels to open, and Ca2+ enters the cell.
    • Ca2+ entry promotes the fusion of synaptic vesicles with the presynaptic membrane, releasing neurotransmitters into the synaptic cleft.
    • Neurotransmitters diffuse across the synaptic cleft and bind to receptors on the postsynaptic membrane.
    • The binding of neurotransmitters to receptors initiates a response in the postsynaptic cell.

    Synthesis and Recycling of Neurotransmitters

    • Neurotransmitters are synthesized and packaged in the presynaptic terminal.
    • Once released, neurotransmitters are either broken down by enzymes, reuptaken back into the presynaptic terminal, or diffuse away from the synapse.
    • Recycling of neurotransmitters ensures efficient communication at the synapse.

    Membrane Proteins

    • Structural proteins help maintain cell shape and integrity
    • Enzymes catalyze biochemical reactions within the cell
    • Membrane receptor proteins receive and process signals from the cellular environment
    • Transporters facilitate movement of molecules across the cell membrane:
      • Channel proteins create pores that allow specific molecules to pass through
      • Carrier proteins bind to specific molecules and transport them across the membrane

    Facilitated Diffusion

    • Movement of molecules across a membrane down their concentration gradient with the help of a transporter protein
    • This process does not require energy expenditure
    • Equilibrium can be reached, but conversion maintains the gradient

    Co-transport: SGLT

    • Sodium-glucose linked transporter (SGLT) is a type of co-transporter that moves both sodium and glucose across the membrane simultaneously
    • Sodium binds to the carrier protein, creating a high affinity site for glucose to bind.
    • Binding of both sodium and glucose changes the conformation of the carrier, allowing molecules to pass through to the intracellular fluid
    • Sodium is released first due to a lower concentration in the cytosol, followed by glucose

    Signaling Pathways

    • Signaling pathway starts with a signal molecule binding to a cell membrane receptor protein
    • This binding triggers a cascade of intracellular signal molecules that amplify and propagate the signal within the cell
    • These intracellular signaling molecules can alter target proteins or create new ones, ultimately leading to a cellular response

    Four Categories of Membrane Receptors

    • Channel-linked receptors: Ligand binding opens or closes ion channels
    • Receptor-enzymes: Ligand binding activates an intracellular enzyme
    • G protein-coupled receptors: Ligand binding opens an ion channel or alters enzyme activity
    • Integrin receptors: Ligand binding alters the cytoskeleton

    Membrane Properties

    • Membrane properties are influenced by the lipid bilayer and membrane proteins.
    • Membrane proteins facilitate transport and communication.

    Signal Transduction

    • Extracellular signals initiate signal transduction cascades.
    • Signal transduction cascades regulate cellular processes.

    Feedback Regulation

    • Feedback loops control physiological processes.
    • Negative feedback loops maintain homeostasis.

    Local Communication

    • Contact-dependent signaling involves direct cell-to-cell contact.
    • Autocrine/paracrine signals act on nearby cells.

    Long-distance Communication

    • Endocrine communication occurs via hormones released into the bloodstream.
    • Nervous system communication utilizes electrical signals.

    Hormone Production

    • Hormones are produced by glands, specialized cells, and neurons.
    • Hormones regulate various body functions.

    Hormone Mechanisms of Action

    • Peptide hormones alter existing proteins.
    • Steroid hormones alter gene expression.

    Hormone Classification

    • Peptide hormones are water-soluble, pre-synthesized, and have short half-lives.
    • Steroid hormones are lipid-soluble, synthesized on demand, and have long half-lives.

    Peptide Hormone Synthesis, Packaging, and Release

    • Messenger RNA directs the synthesis of a preprohormone.
    • Enzymes in the ER cleave the signal sequence to form a prohormone.
    • The prohormone is packaged into secretory vesicles in the Golgi complex.
    • Secretory vesicles release hormones through exocytosis.

    Peptide Hormone Action

    • Peptide hormones activate membrane receptors.
    • Activation initiates signal transduction, often via second messenger systems.
    • Cellular responses are rapid due to the modification of pre-existing proteins.

    Steroid Hormone Synthesis

    • Cholesterol is the precursor for steroid hormone synthesis.
    • Enzymes modify cholesterol to produce specific steroid hormones.

    Steroid Hormone Action

    • Steroid hormones diffuse through the cell membrane.
    • Receptors are located in the cytoplasm or nucleus.
    • Hormone-receptor complexes bind to DNA and regulate gene expression.
    • New proteins are synthesized, leading to cellular responses.

    Hormone Interactions

    • Permissiveness enhances responses to other hormones.
    • Synergism produces a combined effect greater than the sum of individual effects.
    • Antagonism reduces the response to another hormone.

    Hormone Regulation

    • Trophic hormones control the release of other hormones.
    • The hypothalamus-anterior pituitary axis regulates hormone release.

    Hypothalamus-Anterior Pituitary Axis

    • Hypothalamic neurons release trophic hormones into the portal system.
    • Trophic hormones travel to the anterior pituitary, stimulating the release of anterior pituitary hormones.
    • Anterior pituitary hormones circulate throughout the body, affecting target organs and tissues.

    Hypothalamus-anterior pituitary axis

    • The hypothalamus synthesizes and releases trophic hormones into the portal system.
    • These trophic hormones are transported to the anterior pituitary via portal vessels.
    • The anterior pituitary then releases its own hormones into the general circulation.
    • This axis regulates the release of hormones from the anterior pituitary, which in turn regulate the function of target organs throughout the body.

    Hormone Regulation

    • Trophic hormones are hormones that regulate the release of other hormones.
    • The hypothalamus-anterior pituitary axis is a good example of trophic hormone regulation.

    Endocrine Pathologies

    • Hypersecretion is an excess of hormone secretion.
    • Hyposecretion is a deficiency of hormone secretion.
    • Target cell pathologies can occur due to loss or down-regulation of target cell receptors or issues with signal transduction.

    Review: homeostasis and communication in the body

    • Negative feedback control loops regulate physiological function.
    • Local communication influences the state of nearby cells.
    • The nervous system provides rapid but short-lived changes in physiology, while the endocrine system produces slower but longer-lasting effects.
    • Membrane permeability of peptide and steroid hormones affects their actions.
    • Endocrine responses involve complex cascades that can be regulated at multiple levels.

    Organization of the Nervous System

    • Sensory neurons (afferent) transmit information from the periphery to the central nervous system.
    • Motor neurons (efferent) transmit information from the central nervous system to the periphery.
    • Interneurons integrate information within the central nervous system.

    Cells of the Nervous System

    • Glial cells support and protect neurons.
    • Astrocytes maintain the extracellular environment and clean up debris.
    • Oligodendrocytes produce myelin in the central nervous system.
    • Schwann cells produce myelin in the peripheral nervous system.
    • Stem cells can differentiate into different types of neurons and glial cells.
    • Neurons are responsible for transmitting signals.
    • Dendrites receive input signals.
    • The cell body integrates signals.
    • The axon transmits output signals.

    Chemical Disequilibrium

    • Ions are unequally distributed across the cell membrane.
    • This creates a charge difference called the membrane potential.
    • The Nernst equation calculates the equilibrium potential for a given ion.
    • Membrane permeability affects the membrane potential by determining the ease with which ions can cross the membrane.

    Resting Membrane Potential

    • The resting membrane potential is around -70 mV, with the inside of the cell being more negatively charged than the outside.
    • This is mainly due to the permeability of the membrane to potassium ions (K+), which are more concentrated inside the cell.

    Phases of the Action Potential

    • The action potential is a rapid change in membrane potential that travels along the axon.
    • Resting Phase: The membrane potential is at rest (-70 mV).
    • Rising Phase (depolarization): The membrane becomes more positive due to an influx of sodium ions (Na+). This is caused by the opening of voltage-gated sodium channels.
    • Overshoot Phase: The membrane potential reaches its peak (positive values) as sodium channels inactivate.
    • Falling Phase (repolarization): The membrane potential becomes more negative due to an efflux of potassium ions (K+). This is caused by the opening of voltage-gated potassium channels.
    • Recovery Phase (undershoot): The membrane potential briefly becomes more negative than the resting potential due to the delayed closing of potassium channels.

    AP initiation through positive feedback

    • The action potential is initiated by a local depolarization that reaches the threshold potential.
    • This triggers a positive feedback loop, where the influx of sodium ions further depolarizes the membrane, leading to the opening of more sodium channels.
    • This process continues until the peak of the action potential is reached.
    • Once the peak is reached, sodium channels inactivate, and potassium channels open, leading to the repolarization of the membrane.

    Changes in Permeability

    • The action potential is generated by changes in membrane permeability to sodium and potassium ions.
    • The opening and closing of voltage-gated sodium and potassium channels control these changes.
    • These changes in permeability are responsible for the different phases of the action potential.

    Action Potential Propagation

    • The action potential propagation process is a critical element in the nervous system, allowing for communication between neurons.
    • The process begins with depolarization, which triggers the opening of fast sodium channels, leading to increased Na+ permeability and a rapid influx of sodium ions.
    • This positive feedback loop further amplifies depolarization, ultimately resulting in a rapid rise in membrane potential.
    • As the membrane potential reaches its peak, the sodium channels begin to inactivate, halting the influx of sodium ions.
    • At the same time, slow potassium channels open, allowing potassium to flow out of the cell.
    • This efflux of potassium ions leads to repolarization, restoring the membrane potential to its resting state.
    • Throughout this process, the opening and closing of sodium and potassium channels are tightly regulated, ensuring a precise and efficient nerve impulse transmission.

    Refractory Periods

    • The refractory period is a critical element in the action potential propagation process, ensuring that the signal travels in one direction.
    • The absolute refractory period is characterized by the closure of both sodium and potassium channels, rendering the membrane completely unresponsive to any stimulus, regardless of its strength.
    • This ensures that the action potential travels in one direction, preventing it from traveling backward along the axon.
    • Following the absolute refractory period, the relative refractory period commences, as the sodium channels recover and become responsive once again.
    • During this phase, a stronger than usual stimulus is required to trigger a new action potential.
    • These refractory periods are crucial for the efficient and unidirectional propagation of action potentials along the axon.

    Propagation Rates/Graded Potentials

    • The propagation rate of action potentials, or how quickly they travel, depends on the resistance of the axon to current loss.
    • A higher resistance to current loss allows the signal to maintain its strength over a longer distance, improving the efficiency of the signal transmission.
    • Factors like the diameter of the axon and its myelination status significantly influence this resistance.

    Propagation Rates & Factors Affecting Them

    • The speed of action potential conduction in a neuron is directly influenced by several factors.
    • One critical factor is the diameter of the axon. Larger axons have lower resistance to current flow, allowing for faster conduction speeds.
    • Another important factor is the resistance of the axon membrane to ion leakage. Myelinated axons, covered in a layer of myelin sheath, significantly reduce ion leakage and enhance the conduction velocity.
    • These factors work in concert to determine how quickly action potentials travel along the axon, which in turn impacts the speed of neuronal communication.

    Saltatory Conduction

    • Saltatory conduction refers to the "jumping" pattern of action potential propagation in myelinated axons.
    • The myelin sheath acts as an insulator, preventing current leakage and allowing the action potential to jump between the unmyelinated gaps called "Nodes of Ranvier".
    • This "jumping" mechanism significantly increases the speed of action potential conduction, making myelinated axons far more efficient for transmitting information.

    Myelin Degeneration

    • Myelin degeneration, a condition characterized by the deterioration of the myelin sheath, can severely compromise the efficiency of action potential propagation.
    • This degeneration can lead to significant loss of function, impacting various neurological processes.
    • Several diseases, including multiple sclerosis, meylitis, and leukodystrophy, are associated with myelin degeneration, highlighting its crucial role in maintaining healthy neurological function.

    Review

    • The establishment of membrane potential in cells is governed by the interplay of ion concentration gradients and membrane permeability.
    • Dynamic changes in membrane permeability, particularly for sodium and potassium ions, are key for the generation of action potentials, the fundamental units of communication within the nervous system.
    • The initiation of action potentials is triggered by local current flow, also known as graded potentials, which are localized changes in membrane potential.
    • Interestingly, the strength of graded potentials is determined by the resistance to current flow, highlighting the importance of factors like axon diameter and myelination for signal propagation.
    • Myelination plays a crucial role in enhancing the speed of action potential propagation by reducing current leakage and enabling "saltatory conduction" in myelinated axons.

    Studying That Suits You

    Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

    Quiz Team

    Related Documents

    E109 Lecture 5: Nervous System III PDF
    E109 Lecture 4: Nervous System II Fall 2024 PDF

    Description

    Explore the intricacies of synaptic transmission in neuroscience. This quiz covers ionotropic and metabotropic receptors, the effects of excitatory and inhibitory postsynaptic potentials, and the modulation of synaptic responses by neurotoxins. Test your understanding of synapses and their roles in neural communication.

    More Like This

    Neurotransmisores y respuestas postsinapticas
    18 questions

    Neurotransmisores y respuestas postsinapticas

    AuthenticFairy avatar
    AuthenticFairy
    Synaptic Transmission
    30 questions

    Synaptic Transmission

    IrreplaceableDenver avatar
    IrreplaceableDenver
    Transmisión Sináptica y Axon Terminal
    12 questions

    Transmisión Sináptica y Axon Terminal

    IdolizedHolmium avatar
    IdolizedHolmium
    Use Quizgecko on...
    Browser
    Open
    Browser
    Browser