BIOL 105 - LECTURE 4

Structure and Function of Cells of the Nervous System

  • Nervous System Overview

    • The primary organ is the brain, responsible for muscle movement and behavior.

    • Composed of two main types of cells: neurons and supporting cells (glia and Schwann cells).

    • The blood-brain barrier (BBB) protects the brain by regulating substances that enter it.

Neuron Classification

  • Neurons are categorized based on the structure of their axons and dendrites:

    • Multipolar Neurons

      • Characterized by one axon and multiple dendrites.

      • Most common type of neuron in the central nervous system (CNS).

    • Bipolar Neurons

      • Feature one axon and one dendrite.

      • Often sensory neurons that transmit sensory information to the CNS.

    • Unipolar Neurons

      • Have a single axon that splits into two branches: one for receiving sensory information and the other for sending it to the CNS.

Internal Structure of Neurons

  • Cell Membrane

    • Forms the boundary of the cell, composed of lipid bilayers.

  • Cytoplasm

    • Jelly-like substance within the membrane that surrounds the nucleus, containing organelles.

  • Mitochondria

    • Converts nutrients (like glucose) into energy (ATP), crucial for cell functions.

  • Nucleus

    • Houses hereditary material (chromosomes), composed of DNA packaged around histones.

  • Cytoskeleton

    • Provides cell structure and shape, assists in cell movement and division.

Additional Definitions in Neuroscience

  • Enzymes

    • Catalysts for biochemical reactions within cells.

  • Axoplasmic Transport

    • Active process transporting substances along axons.

      • Anterograde Transport: Movement from soma to terminal buttons.

      • Retrograde Transport: Movement from terminal buttons back to soma.

  • Microtubules

    • Protein structures facilitating axoplasmic transport, guiding the movement of materials.

Supporting Cells (Glia)

  • Represent half of CNS volume, crucial for neuron support.

    • Functions of Glia:

      • Surround and hold neurons in place, regulate nutrient supply, insulate neurons, and assist in neuron cleanup.

    • Types of Glial Cells:

      • Astrocytes: Support neurons and clean debris; regulate nutrient levels.

      • Oligodendrocytes: Produce myelin sheath around CNS axons, insulating them.

      • Microglia: Smallest glial cells; act as phagocytes, responding to brain damage.

Myelination in the Nervous System

  • Myelin Sheath:

    • Composed of 80% lipids and 20% proteins, produced by oligodendrocytes in CNS and Schwann cells in PNS.

    • Segmented nature allows effective insulation; nodes of Ranvier are gaps in the sheath where action potentials can be generated.

Schwann Cells**

  • In PNS, Schwann cells myelinate axons, with each cell wrapping around a single axon.

  • Significant role in regenerating nerves after injury and maintaining axon health.

Implications in Disorders

  • In conditions like Multiple Sclerosis (MS), the immune system targets myelin in the CNS, affecting oligodendrocytes but sparing Schwann cells in the PNS.