Neurons and Neuronal Interfaces

Neurons

• The human cerebral cortex contains approximately 20-25 billion neurons.
• Neuron cell bodies have common shapes like pyramidal and stellate.
• 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.
• Dendritic growth is associated with learning; individuals with Down's syndrome may have fewer dendritic branches.
• Most neurons have a single axon.
• Axon width typically ranges from 1-4 micrometers.
• Axons contain axoplasm (similar to cytoplasm but without ribosomes).
• Neurotransmitters are usually released from axon terminals.
• Most axons are myelinated (covered in myelin).
• Axons in the peripheral nervous system (PNS) have neurilemma, facilitating recovery after damage.

Neuronal Interfaces

• Gap junctions are characterized by membranes separated by less than 2 nanometers.
• Synapses are interfaces between the axon terminal of one neuron and a dendrite, soma, or axon of another neuron, with a space of approximately 10-15 nanometers.
• Many drugs' chemical structures mimic or interfere with neurotransmitters at synapses. For instance, LSD competes with serotonin.

Neuronal Classification

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

Glial Cells

• Glial cells outnumber neurons by approximately 5-10 times.
• Glial cell processes are connected in a vast syncytium, mainly composed of gap junctions.
• Types of glial cells include astroglia, oligodendroglia, and microglia.