Types of Neurons

Types of Neurons

Introduction

  • Review of neuron parts: dendrites, axons, cell body.
  • Focus on three basic types of neurons (though more exist).

Sensory Neurons

  • Involved in the five main senses (excluding pain): taste, touch, smell, sight, and sound.
  • Also responsible for sensing pain and temperature.
  • Sensory receptors in organs detect sensations.
  • Sensory neuron carries the signal to the spinal cord.

Interneurons

  • Located in the spinal cord.
  • Receive signals from sensory neurons.
  • Send messages to motor neurons to initiate a response.

Motor Neurons

  • Receive signals from interneurons.
  • Cause a response in muscles or glands.

Neuron Cell Bodies

  • A: Cell body of a sensory neuron.
  • B: Cell body of an interneuron.
  • C: Cell body of a motor neuron.

Sensory Receptors

  • Located on sensory neurons.
  • Receive sensations and initiate a signal if the threshold is reached.
  • Affected by external stimuli (e.g., a pin prick).
  • The pain signal travels from dendrites to the cell body, then through the axon to the interneuron.

Synapse

  • Junction between neurons.
  • The message is transmitted across the synapse to the next neuron.
  • The message received by the muscle or gland causes an effect (e.g., pulling away from pain).

Direction of Impulse

  • One-way system:
    • From sensory receptors to the central nervous system (CNS).
    • From the CNS through motor neurons to muscles or glands.

Quiz Information

  • Diagram with 12 parts to label.

Neuron Types and Functions Detailed

  • Sensory Neuron:
    • Detects stimuli.
    • Takes the impulse to the CNS.
  • Interneuron:
    • Integrates and interprets sensory information.
  • Motor Neuron:
    • Relays the impulse to effectors (glands or muscles).
  • The connection of these three is important in a protective reflex.

Neuron Structure

  • Sensory Neurons:
    • Long dendrites and short axons.
    • Cell body is close to the spinal cord in the dorsal root ganglion.
  • Interneurons:
    • Numerous processes (axons and dendrites) of various lengths.
  • Motor Neurons:
    • Long axons and short dendrites.
    • Response travels from the cell body in the CNS (spinal cord) to the destination (e.g., toes).

Neuron Location

  • Sensory Neuron:
    • Cell body located in the dorsal root ganglion.
  • Interneuron:
    • Cell body located only in the CNS.
  • Motor Neuron:
    • Cell body located mostly in the spinal cord.

Impulse Transmission

  • Sensory Neurons:
    • Transmit impulses to the CNS.
  • Interneurons:
    • Transmit impulses within the CNS.
  • Motor Neurons:
    • Transmit impulses away from the CNS.

Reflex Arc

  • Sensory neuron starts in the skin, receiving information.
  • Impulse travels down the dendrite to the cell body (in the dorsal root ganglion).
  • Interneuron is in the gray matter.
  • Motor neuron cell body is in the gray matter of the spinal cord.
  • Axon (with myelin sheath - white matter) goes to the muscles and glands.
  • Sensory neurons can have myelin sheath on both dendrites and axons.

Locating Cell Bodies

  • Sensory neuron cell body, interneuron cell body, and motor neuron cell body locations.
  • Variation in neuron types and cell body locations.

Nervous System Parts

  • Two Major Parts of the Nervous System:
    • Central Nervous System (CNS): brain and spinal cord, made of interneurons.
    • Peripheral Nervous System (PNS): nerves leading to and from the CNS.

PNS Neurons

  • Afferent neurons (sensory) lead to the CNS.
  • Efferent neurons (motor) lead from the CNS.

Nerves

  • A nerve is a bundle of neuron processes (axons and/or dendrites).
  • A nerve is not just one neuron; it contains many neurons.
  • Nerves can be mixed (sensory and motor neurons) or pure (sensory or motor).
    • Example: Optic nerve (pure sensory).
  • A nerve and a neuron are not the same thing.