Nervous System: Afferent and Efferent Divisions
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Questions and Answers

What is unique about the structure of first order neurons?

  • They have multiple dendrites and one axon.
  • They have two axons and one dendrite.
  • They have no axon or dendrite.
  • They have a single axon with two branches. (correct)
  • What happens when a stimulus from the outside world hits the sensory receptors?

  • Ion channels close, and ions flow out of the neuron.
  • The action potential is immediately triggered.
  • The neuron becomes hyperpolarized.
  • Ion channels open, and ions flow into the neuron. (correct)
  • What is the significance of smaller receptive fields?

  • They have no effect on the sensory input.
  • They result in higher resolution and better localization. (correct)
  • They result in lower resolution and poorer localization.
  • They only occur in the fingertips.
  • Why is two-point discrimination possible?

    <p>Because of the separation of receptive fields by at least one neuron.</p> Signup and view all the answers

    What is the function of the central branch of the first order neuron?

    <p>To transmit the action potential to the spinal cord.</p> Signup and view all the answers

    What is the primary function of the afferent division of the nervous system?

    <p>To bring sensory information from the outside world into the brain</p> Signup and view all the answers

    What type of receptors are responsible for detecting pain?

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

    What is the term for the junction between two neurons, where one neuron sends signals to another?

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

    How many neurons are involved in the somatosensory pathways?

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

    Where is the cell body of the third order neuron located in the somatosensory pathways?

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

    Study Notes

    Nervous System Divisions

    • The nervous system can be divided into afferent (sensory) and efferent (motor) divisions.

    Afferent Division

    • Brings sensory information from the outside world into the brain.
    • Involves special senses (vision, hearing, taste, smell) and general somatic senses (somatosensory system).
    • The somatosensory system is involved in the sense of touch, proprioception, pain, and temperature.

    Sensory Neurons

    • Found all over the body.
    • Have receptors classified according to the stimulus they respond to:
      • Mechanoreceptors for touch and proprioception.
      • Nociceptors for pain.
      • Thermoreceptors for temperature.

    Neuron Structure

    • Composed of a cell body (containing organelles) and nerve fibers (projections extending from the neuron cell body).
    • Nerve fibers are either:
      • Dendrites (receive signals from other neurons).
      • Axons (send signals to other neurons).

    Synapse

    • Where two neurons come together.
    • One end of an axon sends neurotransmitters to the dendrites or directly to the cell body of the next neuron in the series.

    Somatosensory Pathways

    • Made up of a relay of four neurons:
      • First order neuron (sensory neuron) with sensory receptors that convert stimuli into an impulse.
      • Second order neuron with its cell body in the spinal cord or brainstem.
      • Third order neuron with its cell body in the thalamus.
      • Fourth order neuron with its cell body in the sensory cortex of the brain.

    First Order Neurons

    • Also called pseudounipolar neurons.
    • Have only one axon that extends out from the cell body, with two branches:
      • Peripheral branch (goes from the cell body to peripheral tissues).
      • Central branch (goes from the peripheral branch to the spinal cord).

    Receptive Fields

    • The area that a first order neuron receives sensory input from.
    • Vary in size, with smaller receptive fields having higher resolution (allowing stimuli to be localized more precisely).
    • Example: smaller receptive fields in the fingertips than at the back, allowing for high resolution in reading Braille.

    Action Potential

    • Triggered when a first order neuron reaches a certain threshold of depolarization.
    • Sent through the peripheral branch and back to the central branch, and from there to the spinal cord.

    Two-Point Discrimination

    • Requires receptive fields of two sensory neurons to be separated by at least one neuron's receptive field.
    • The third neuron sends a negative signal between the two positive ones, allowing two-point discrimination.

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    Description

    Learn about the two main divisions of the nervous system, afferent and efferent, and how they process sensory information from the outside world.

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