Nervous System and Neuron Vocabulary Flashcards

Nervous System Intro

  • The nervous system uses electricity to speed communication.
  • How cells communicate and move things inside themselves:
    • Diffusion
    • Motor proteins
    • Cytoskeleton
  • Three Functional Types of Neurons
    • Sensory neurons → sensor
    • Interneuron → processor
    • Motor neuron → effector (outward signals) to muscle or other targets
  • Five Structural Types of Neurons
    • Anatomic (anatomical)
    • Unipolar
    • Bipolar
    • Pseudo-unipolar
    • Multipolar

Neuron Structure and Basic Anatomy

  • Generic Neuron Structure:
    • Soma (cell body)
    • Dendrites: Receive information from other neurons
    • Axon Hillock: Starts the action potential (AP)
    • Axon: Transmits outbound information
    • Axon terminal: Communicates with other neurons; where AP ends
  • Myelin Sheath and Nodes of Ranvier
    • Myelin sheath insulates the axon to speed electrical transmission
    • Nodes of Ranvier are gaps in the myelin where ion exchange occurs, facilitating faster conduction

Action Potentials: Mechanism and Properties

  • The Membrane as a selective barrier: It doesn't let ions through freely
  • Resting membrane potential:
    • Inside of neuron is negative when at rest: Vrest = −70 mVV_{rest} \,=\, -70\ \text{mV}
  • Ions involved:
    • Sodium (Na extsuperscript{+}) ions: More outside than inside
    • Potassium (K extsuperscript{+}) ions: More inside than outside
  • Ion channels and pumps:
    • Voltage-gated Na extsuperscript{+} channels with three possible states: open, closed, inactive
    • Na extsuperscript{+} entry depolarizes the membrane (cell becomes more positive)
    • Na extsuperscript{+} channels eventually inactivate after opening
    • Na extsuperscript{+}/K extsuperscript{+} pump maintains ion concentration gradients
    • Voltage-gated K extsuperscript{+} channels: open to allow K extsuperscript{+} to exit, aiding repolarization
    • K extsuperscript{+} channels eventually close
  • Key voltage ranges:
    • Threshold region around V≈− 55 mVV\approx -\,55\ \text{mV} to −40 mV-40\ \text{mV}
    • Resting to threshold involves movement from V≈−70 mVV\approx -70\ \text{mV} toward the threshold range
  • Sequence of events during an action potential:
    1. Depolarization: Stimulus opens Na extsuperscript{+} channels; Na extsuperscript{+} ions enter; the membrane potential becomes positive
    2. Na extsuperscript{+} channels inactivate after a short time
    3. K extsuperscript{+} channels open; K extsuperscript{+} ions exit; the membrane repolarizes
    4. K extsuperscript{+} channels close; the membrane potential returns toward the resting level
  • AP properties:
    • All APs have the same size (All-or-Nothing principle)
    • Information is encoded in the timing and frequency of APs, rather than their amplitude
    • Refractory period: period after an AP during which another AP is more difficult or impossible to fire
  • Additional clarifications:
    • The resting potential is maintained by ion concentration gradients and the Na extsuperscript{+}/K extsuperscript{+} pump
    • APs propagate along the axon to reach synapses at the axon terminals
  • Conceptual note on signaling speed:
    • The nervous system uses electrical signaling to speed communication compared to purely chemical diffusion alone
    • Myelin and nodes of Ranvier contribute to rapid, saltatory conduction, allowing signals to travel faster along the axon
  • Simple conceptual metaphor (for study):
    • Think of an AP as a digital-like all-or-nothing event that travels along the axon; the info is carried by how often and when these bursts occur, not by varying their height

Connections to Core Principles

  • Intracellular transport mechanisms (diffusion, motor proteins, cytoskeleton) enable movement of materials within neurons and are foundational for neuron function and maintenance
  • Membrane potential dynamics integrate inputs from many sources at the soma and dendrites to determine whether an AP is initiated at the axon hillock
  • The all-or-nothing nature of APs provides a reliable signaling mechanism over long distances in the nervous system
  • Myelin-based speeding of transmission exemplifies how structure-function relationships optimize neural communication

Quick Reference: Key Terms and Values

  • Resting membrane potential: Vrest=−70 mVV_{rest} = -70\ \text{mV}
  • Threshold potential range: between V≈−70 mVV \approx -70\ \text{mV} and V≈−55 mVV \approx -55\ \text{mV}, with depolarization occurring toward −55 mV-55\ \text{mV} to reach threshold
  • Action Potential characteristics: All-or-nothing amplitude; information carried by timing and frequency; includes a refractory period
  • Ionic movements:
    • Na extsuperscript{+} influx during depolarization
    • Na extsuperscript{+} channel inactivation followed by K extsuperscript{+} efflux during repolarization
  • Structural features critical for speed and signaling: Myelin sheath and Nodes of Ranvier; axon hillock as AP initiator; axon terminal as synaptic output site