Introduction to Neurons

Definition of Neuron

  • A neuron is a specialized cell in the brain that conducts electrochemical signals to send and receive information.

  • Neurons are fundamental to all biological and cognitive processes, essentially the building blocks of the nervous system.

Importance of Neurons

  • Neurons facilitate every action we perform, from movement to sensation and memory.

  • Each movement involves neurons sending messages to muscles to contract and flex.

  • Neurons also play a critical role in dreaming and emotional experiences.

  • Learning involves the formation of new neural connections.

  • The statistics: approximately 100 billion neurons are present in the human brain, with 2/3 to 70% of those found in the brain.

  • Neurons do not regenerate significantly after they die, except in areas like the hippocampus, where some neural regeneration has been observed.

Structure of Neurons

  • Neurons can range in length from several inches to several feet.

  • They consist of various parts that work together to process and transmit information:

    • Dendrites: Branch-like structures at the neuron’s end that receive information.

    • Soma (Cell Body): Maintains the neuron's life and contains the nucleus, serving as the cell's support center.

    • Axon: A long fiber extending from the cell body that carries messages down to the axon terminal.

    • Myelin Sheath: A fatty substance that surrounds the axon; it insulates the axon, facilitating faster transmission of neural signals.

    • Nodes of Ranvier: Gaps along the axon where the myelin is absent, aiding in the rapid conduction of nerve impulses through a process called saltatory conduction.

    • Axon Terminal (Presynaptic Terminal): The end of the neuron where neurotransmitters are stored in vesicles and released into the synaptic cleft upon reaching the terminal.

Mechanism of Signal Transmission

  • Action potentials, which are electrical impulses, travel down the axon.

  • The myelin sheath and nodes of Ranvier enhance the speed of this transmission.

  • Upon reaching the axon terminal, the action potential causes vesicles to fuse with the membrane and release neurotransmitters into the synapse (the gap between neurons).

  • Neurotransmitters then cross the synaptic gap to bind to receptors on the dendrites of the subsequent neuron, completing the signal transmission process.

Practical Application

  • Students are tasked with constructing a model of a neuron that includes:

    • Dendrites

    • Soma

    • Axon

    • Myelin sheath

    • Axon terminal

    • Nodes of Ranvier (optional)

  • Each part of the model should have a corresponding key explaining its function, allowing for a practical understanding of neuronal structure and function.

Visualization

  • Diagrams or images of neurons can greatly aid understanding by providing a visual representation of the entire structure and parts.

  • Keep in mind that even though neurons appear fused under a microscope, they actually do not touch each other, with synapses creating vital communication gaps.