Somatic Motor Neurons homework 3 lab

Nov 5, 2024

Lecture Notes: Somatic Motor Neuron Model

Classification

  • Multipolar Neurons
    • Have many projections off the soma (cell body).
    • Classified as motor neurons or interneurons.
    • Interneurons are in central nervous system (CNS) gray matter.

Myelination

  • Myelin presence indicates white matter.
  • Since myelin is present, this neuron is a motor neuron, not an interneuron.

Parts of the Motor Neuron

Soma (Cell Body)

  • Contains the nucleus.
  • Nissl Bodies: Analogous to rough ER, produce proteins.

Dendrites

  • Thickened projections off of the soma.
  • Receive information from other neurons.
  • Contain ligand gates (mechanical gates are for sensory neurons).

Synaptic End Bulbs

  • Belong to a presynaptic neuron.
  • Do not touch the soma or dendrites due to a synaptic cleft.

Axon Hillock

  • Cone-shaped area off of the soma.
  • Contains the trigger zone with sodium voltage gates.
  • Action potential begins here if threshold (-55 mV) is reached.

Axon

  • Covered by myelin sheath.
  • Myelin formed by Schwann cells in the peripheral nervous system (PNS).
  • Schwann Cells: Multiple cells wrap around the axon, forming the myelin sheath.
  • Neurolemma: Outer layer of Schwann cell's myelin sheath.
  • Node of Ranvier: Indentations on axon lacking myelin, allowing action potential to "jump" (saltatory conduction).

Structural Support

  • Neurofibrils: Provide structure and support for the neuron shape.

Conduction

  • Myelin blocks voltage gates; action potential jumps between nodes, speeding conduction (saltatory conduction).
  • Endoneurium: Connective tissue layer protecting delicate Schwann cells and myelin.

Summary

  • Motor neuron, somatic type, targets skeletal muscle.
  • Function: Sends information to glands and muscles to prompt action.
  • Structure: Multipolar, distinguished by soma, Nissl bodies, dendrites, axon hillock, myelinated axon, and nodes of Ranvier.

Key Terms

  • Soma: Another term for cell body.
  • Nissl Bodies: Blue rough areas for protein production.
  • Dendrites: With ligand gates for receiving signals.
  • Axon Hillock: Trigger zone for action potential.
  • Schwann Cells: Form myelin sheath in PNS.
  • Neurolemma: Outer membrane of Schwann cells.
  • Node of Ranvier: Indentations for saltatory conduction.