Neurons and Neuronal Interfaces

Neurons

• The cerebral cortex contains approximately 20-25 billion neurons.
• Neuron cell bodies come in pyramidal and stellate shapes.
• Neuron cell bodies contain cytoplasm, a nucleus, and a nucleolus.
• Dendrites receive information from other neurons.
• Many neurons in the cerebral cortex, thalamus, and hippocampus have dendrites.
• 45 order dendrites show growth during learning, but are missing in Down's Syndrome individuals.
• Most neurons have only one axon.
• Axon width ranges from 1-4 micrometers.
• Axons contain axoplasm.
• Neurotransmitters are mostly released from axon terminals.
• Most axons are myelinated.
• Axons in the peripheral nervous system (PNS) are covered by neurilemma, allowing for better recovery after damage.

Neuronal Interfaces

• Gap Junctions: occur when membranes are less than 2 nanometers apart.
• Synapses: interfaces between axon terminals and dendrites, somas, or axons.
• Synapses are approximately 10-15 nanometers apart.
• Many drugs mimic or compete with neurotransmitters at synapses (e.g., LSD competes with serotonin).

Neuronal Classification

• Unipolar cells have one process.
• Bipolar cells have two processes.
• Multipolar cells have three or more processes.

Glial Cells

• Glial cells outnumber neurons 5-10 to 1.
• Glial cell processes are interconnected in a vast syncytium primarily composed of junctions.
• Types of glial cells include astroglia, oligodendroglia, and microglia.