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Glial Cells Protect and Assist Neurons

  • Glial cells support neuronal activity by providing raw materials, chemical signals, and structure; they also participate in information processing.
  • Two types wrap around axons to provide a fatty insulation layer called myelin:
    • Oligodendrocytes form the myelin sheaths in the brain and spinal cord.
    • Schwann cells provide myelin to neurons outside the brain and spinal cord.
  • Nodes of Ranvier – gaps between sections of myelin where the axon is exposed.

Glial Cells: Astrocytes and Microglia

  • Astrocytes: star-shaped cells with many processes that stretch around and between neurons and, sometimes, blood vessels; secrete chemicals; help form the outer membrane around the brain.
  • Microglial cells (microglia): tiny, mobile cells that remove debris from injured or dead cells.
  • In the figure, Capillary, Astrocyte, Neuron, Microglia; Microglia engulf and destroy debris.

Information Is Transmitted through Synapses

  • Flow of information (diagram label).
  • Structural components at the synapse:
    • Presynaptic axon terminal
    • Mitochondrion
    • Synaptic vesicles
    • Presynaptic membrane
    • Neurotransmitter molecules
    • Synaptic cleft
    • Postsynaptic membrane
    • Dendritic spine
  • Synaptic vesicles: small spheres in presynaptic axon terminals that contain a neurotransmitter, a specialized chemical.
  • Neurotransmitters are released in response to electrical activity in the axon.
  • Neurotransmitter receptors in the postsynaptic membrane are specialized proteins that react to neurotransmitter molecules.
  • Neural plasticity refers to the continual remodeling of neuronal connections.

Nervous System Extends throughout the Body

  • The central nervous system (CNS) consists of the brain and spinal cord.
  • The peripheral nervous system includes all other parts of the nervous system outside the brain and spinal cord.

Peripheral Nervous System and Nerves

  • The peripheral nervous system consists of nerves, or bundles of axons.
  • Sensory nerves convey information from the body to CNS (afferent neurons).
  • Motor nerves transmit information from the spinal cord and brain to muscles and glands (efferent neurons).