Neurons, neuroglia and organization of the nervous system

Overview of the nervous system

Functions of the nervous system
• Sensory- detection of internal and external stimuli (sensory neurons)
• Integrative- processing of sensory information (interneurons)
• Motor- response to integrated “decision”
(motor neurons)

Structure and function of neurons
• Act through propagation of action potentials
• Vary considerably in size
• Dendrites, cell body and axons
• May be myelinated
• Synapse with other neuron or muscle cell; release neurotransmitters

Neurotransmitter action
• About 100 neurotransmitters known
• Amino acids, polypeptides, gases
• Released into synaptic cleft, bind to membrane of target cell

Structural diversity in neurons
• Multipolar- many dendrites, one axon
– Most neurons in CNS
• Bipolar- one dendrite, one axon
– Sensory organs
• Unipolar- sensory
– Axon termini extend into CNS

Neuroglial cells
• Much smaller than neurons and more numerous
• Do not propagate action potentials
• Can replace themselves

Four types of neuroglia in CNS
• Oligodendrocytes
– Myelinating cells
• Astrocytes
– Blood-brain barrier (BBB)
• Microglia
– Phagocytes (from bone marrow)
• Ependymal cells
– Line ventricles of brain; produce cerebrospinal fluid (CSF)

Neuroglia of the CNS

Neuroglia of the PNS
• Schwann cells
– Myelinating cells
– Help direct axon regeneration
• Satellite cells
– Support, protection, regulation of molecular exchange

Why myelin?
• Increases speed of nerve impulse transmission
• Myelinating cells leave gaps on axons (nodes of
Ranvier)
• Schwann cells can help regenerate axons
• Demyelination can lead to loss of function (MS)

Gray and white matter