Organization of the Nervous System
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Questions and Answers

What is the function of myelin sheaths in neurons?

  • To destroy the axon
  • To facilitate ion movement across the cell membrane
  • To prevent almost all ion movement across the cell membrane (correct)
  • To slow down action potential generation along the axon

    • Which type of cells forms myelin sheaths in the PNS?

  • Glial cells
  • Oligodendrocytes
  • Schwann cells (correct)
  • Neurons

    • What is the purpose of nodes of Ranvier in myelinated axons?

  • To decrease the speed of action potential generation
  • To increase the speed of action potential generation
  • To destroy the axon
  • To allow ion movement across the cell membrane (correct)

    • What is the effect of myelination on action potential generation?

    <p>Increases the speed and efficiency of action potential generation</p> Signup and view all the answers

    What is the typical composition of a small nerve?

    <p>More unmyelinated axons than myelinated axons</p> Signup and view all the answers

    What is the site where unmyelinated axons rest?

    <p>In indentations of oligodendrocytes or Schwann cells</p> Signup and view all the answers

    What is multiple sclerosis?

    <p>A disease of the myelin sheath</p> Signup and view all the answers

    What is the effect of multiple sclerosis on muscle function?

    <p>Causes loss of muscle function</p> Signup and view all the answers

    What is the main function of neurons in the nervous system?

    <p>To conduct action potentials and transmit signals to other neurons or effector organs</p> Signup and view all the answers

    What is the role of glial cells in the nervous system?

    <p>To provide structural support and maintain normal conditions within nervous tissue</p> Signup and view all the answers

    What is the function of the dendrite in a neuron?

    <p>To receive information from other neurons and transmit it to the cell body</p> Signup and view all the answers

    What is the function of the axon in a neuron?

    <p>To conduct sensory signals to the CNS and motor signals away from the CNS</p> Signup and view all the answers

    What is the characteristic feature of multipolar neurons?

    <p>They have many dendrites and a single axon</p> Signup and view all the answers

    What is the structure that contains the nucleus of a neuron?

    <p>Cell body</p> Signup and view all the answers

    What is the location where the axon leaves the cell body?

    <p>Axon hillock</p> Signup and view all the answers

    What is the function of the cell body in a neuron?

    <p>To contain the nucleus and maintain cellular functions</p> Signup and view all the answers

    What is the primary location where voltage-gated Na+ channels open during an action potential?

    <p>Axon hillock</p> Signup and view all the answers

    What is the result of the opening of voltage-gated Na+ channels during an action potential?

    <p>600-fold increase in membrane permeability to Na+</p> Signup and view all the answers

    What happens to the inside of the cell membrane relative to the outside during an action potential?

    <p>The inside becomes more positive</p> Signup and view all the answers

    What is the purpose of the sodium-potassium pump in relation to the action potential?

    <p>To restore the resting membrane potential</p> Signup and view all the answers

    What is the term for the brief reversal of charge during an action potential?

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

    What is the characteristic of action potentials in terms of their occurrence?

    <p>All-or-none</p> Signup and view all the answers

    What is the main difference in the conduction of action potentials between unmyelinated and myelinated axons?

    <p>Speed of conduction</p> Signup and view all the answers

    Where do action potentials occur along the membrane of unmyelinated axons?

    <p>Along the entire membrane</p> Signup and view all the answers

    What is the term for the pattern of action potential conduction in myelinated axons?

    <p>Saltatory conduction</p> Signup and view all the answers

    What is the location of action potentials in myelinated axons?

    <p>At the nodes of Ranvier</p> Signup and view all the answers

    What is the characteristic of action potential conduction in unmyelinated axons?

    <p>Slow and continuous</p> Signup and view all the answers

    What is the main difference between action potential conduction in unmyelinated and myelinated axons?

    <p>Speed of action potential</p> Signup and view all the answers

    What happens to the concentration of substances in the synaptic cleft?

    <p>They decrease rapidly through breakdown or reuptake</p> Signup and view all the answers

    What is the function of acetylcholinesterase?

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

    What is the primary purpose of reflexes?

    <p>To allow a person to react to stimuli more quickly</p> Signup and view all the answers

    What is the typical location of reflex occurrence?

    <p>Spinal cord or brainstem</p> Signup and view all the answers

    What is the term for the neuronal pathway by which a reflex occurs?

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

    What is the role of interneurons in a reflex arc?

    <p>To communicate with two other neurons</p> Signup and view all the answers

    What is the component of a reflex arc that responds to stimuli?

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

    What is the type of neuron that transmits signals from sensory receptors?

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

    Study Notes

    Organization of the Nervous System

    • The nervous system consists of neurons and glial cells
    • Neurons receive stimuli, conduct action potentials, and transmit signals to other neurons or effector organs
    • Glial cells are supportive cells of the CNS and PNS, enhancing neuron function and maintaining normal conditions within nervous tissue

    Neurons

    • A neuron has a cell body, dendrite, and axon
    • Cell body contains a single nucleus
    • Dendrite receives information from other neurons and transmits it to the cell body
    • Axon conducts sensory signals to the CNS and motor signals away from the CNS

    Types of Neurons

    • Multipolar neurons have many dendrites and a single axon

    Glial Cells

    • Types of glial cells include oligodendrocytes in the CNS and Schwann cells in the PNS
    • Oligodendrocytes and Schwann cells form myelin sheaths around axons

    Myelin Sheath

    • Myelin sheath is a specialized layer that wraps around the axons of some neurons
    • Formed by oligodendrocytes in the CNS and Schwann cells in the PNS
    • Myelin is an excellent insulator that prevents almost all ion movement across the cell membrane
    • Gaps in the myelin sheath, called nodes of Ranvier, occur about every millimeter
    • Ion movement can occur at the nodes of Ranvier
    • Myelination of an axon increases the speed and efficiency of action potential generation along the axon

    Unmyelinated Neurons

    • Unmyelinated axons lack the myelin sheaths
    • Axons rest in indentations of oligodendrocytes in the CNS and Schwann cells in the PNS
    • Typical small nerve contains more unmyelinated axons than myelinated axons

    Action Potential

    • Action potential occurs when voltage-gated Na+ channels open, causing a massive increase in membrane permeability to Na+
    • Voltage-gated K+ channels also begin to open
    • As more Na+ enters the cell, depolarization continues, causing a brief reversal of charge
    • Charge reversal causes Na+ channels to close and Na+ stops entering the cell
    • K+ channels continue to open, resulting in repolarization
    • At the end of repolarization, the charge on the cell membrane briefly becomes more negative than the resting membrane potential (hyperpolarization)
    • Action potentials occur in an all-or-none fashion
    • Sodium-potassium pump assists in restoring the resting membrane potential

    Unmyelinated and Myelinated Axon

    • Action potentials are conducted slowly in unmyelinated axons and more rapidly in myelinated axons
    • Action potentials along unmyelinated axons occur along the entire membrane
    • Action potentials on myelinated axons occur in a jumping pattern at the nodes of Ranvier (saltatory conduction)

    The Synapse

    • The synapse is the gap between the terminal end of one neuron and the beginning of another
    • Neurotransmitters are released from the presynaptic terminal and bind to receptors on the postsynaptic terminal
    • Neurotransmitters are either broken down by enzymes or transported back into the presynaptic terminal

    Reflex

    • A reflex is an involuntary reaction in response to a stimulus applied to the periphery and transmitted to the CNS
    • Reflexes allow a person to react to stimuli more quickly than is possible if conscious thought is involved
    • Most reflexes occur in the spinal cord or brainstem rather than in the higher brain centers
    • A reflex arc is the neuronal pathway by which a reflex occurs and has five basic components:
      • A sensory receptor
      • A sensory neuron
      • Interneurons
      • A motor neuron
      • An effector organ (muscles or glands)

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    Learn about the structure and function of the nervous system, including neurons and glial cells, and how they work together to transmit signals.

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