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).