26.1

  • organisms to highly complex and centralized systems in vertebrates.

Structure and Function of the Nervous System

  • Fundamental Unit: Neuron

    • Specialized cell that receives and transmits chemical or electrical signal information.

    • Structure:

      • Dendrites: tree-like structures that receive signals from other neurons at synapses 

      • Cell Body (soma): contains the central nucleus ->genetic information; processes information, maintains neuron’s structure, and provides energy 

      • Axon: tube-like structure that transmits signals.

    • Types:

      • Sensory: Detect external/internal signals.

      • Motor: Initiate movement (organs and muscles)

      • Interneuron: Connect sensory and motor neurons.

  • Supporting Cells

    • Schwann Cells (glial cells): Produce myelin sheath, enhancing signal transmission speed.

    • Glial Cells: Play crucial roles in neuron development, protection, and support, outnumbering neurons.

  • Disorders: Diseases can arise from the loss of myelin sheath, affecting the nervous system's functionality.

  • How signals are transmitted: dendrites first receive the signal → cell body contains an axon hillock that helps process information and also serve as a junction between the axon → axon sends the signal to specialized endings called axon terminals which releases chemicals that allows signals to be communicated→ signal is transmitted to other neurons, muscle, or target organs at synapses 



  • Nodes of Ranvier: gaps along the axon where the signal is “recharged”.



Detailed Neuron and Glia Overview

  • Neurons:

    • Serve as the nervous system's primary signal transmitters.

    • Share common structures but are highly specialized in form and function.

    • Most share same cellular components but different sizes and shapes related to their roles 

    • 4 basic types based on number and placement of axons include unipolar, bipolar, multipolar, and pseudounipolar, reflecting their diverse roles.

  • Unipolar: found in insects 

  • Bipolar: one axon and one dendrite extending from soma. Ex> retinal bipolar cell

  • Multipolar: found in brain and spinal cord

  • Pseudounipolar: share characteristics of unipolar and bipolar cell; have an axon that branches into two extensions: one connected to dendrites and another that transmits information.  Ex: sensory neurons 

  • Glia:

    • Cells that provide support functions for neurons by playing an information processing role 

    • Essential for neuron support, outnumbering neurons significantly.

    • Types include Astrocytes (nutrient support and regulate concentrations of ions and chemicals in the extracellular fluid), Microglia (defense; scavenge and degrade dead cells), Oligodendrocytes (myelin production in CNS), Schwann Cells (myelin production in PNS), and Satellite glia (structural and nutrient support in PNS).

Neurogenesis - process  by which new neurons are generated 

  • Contrary to previous beliefs, new neurons can form in adulthood, playing a role in learning and memory.

  • Neurogenesis is influenced by factors like exercise and stress