[Paper Review] Basic Neural Units of the Brain: Neurons, Synapses and Action Potential

Jiawei Zhang|arXiv (Cornell University)|May 30, 2019

Cellular transport and secretion7 references37 citations

TL;DR

This paper provides a tutorial overview of the basic neural units—neurons, synapses, and action potentials—covering their structure, types, and signaling mechanisms.

ABSTRACT

As a follow-up tutorial article of [29], in this paper, we will introduce the basic compositional units of the human brain, which will further illustrate the cell-level bio-structure of the brain. On average, the human brain contains about 100 billion neurons and many more neuroglia which serve to support and protect the neurons. Each neuron may be connected to up to 10,000 other neurons, passing signals to each other via as many as 1,000 trillion synapses. In the nervous system, a synapse is a structure that permits a neuron to pass an electrical or chemical signal to another neuron or to the target effector cell. Such signals will be accumulated as the membrane potential of the neurons, and it will trigger and pass the signal pulse (i.e., action potential) to other neurons when the membrane potential is greater than a precisely defined threshold voltage. To be more specific, in this paper, we will talk about the neurons, synapses and the action potential concepts in detail. Many of the materials used in this paper are from wikipedia and several other neuroscience introductory articles, which will be properly cited in this paper. This is the second of the three tutorial articles about the brain (the other two are [29] and [28]). The readers are suggested to read the previous tutorial article [29] to get more background information about the brain structure and functions prior to reading this paper.

Motivation & Objective

• Introduce the cell-level composition of the brain (neurons, synapses, and neuroglia) and their roles in neural signaling.
• Explain neuron structure, classification (morphism and function), and connectivity.
• Describe synaptic structure, vesicles, neurotransmitters, and the synaptic vesicle cycle and recycling.
• Discuss membrane potential, ion channels, pumps, and the generation of action potentials.

Proposed method

• Survey and synthesis of foundational neuroscience concepts from introductory sources and existing literature.
• Detailed exposition of neuron morphology (soma, dendrites, axon, myelin, nodes of Ranvier) and supporting glial cells.
• Description of synaptic architecture, chemical vs electrical synapses, and transmission mechanisms.
• Step-by-step account of the synaptic vesicle cycle, including docking, priming, fusion, and endocytosis.
• Discussion of membrane potential maintenance, ion channels, and action potential generation.

Experimental results

Research questions

• RQ1 What are the core structural components of neurons and how do they interact to process and transmit signals?
• RQ2 How do synapses operate to convert electrical signals into chemical signals and back, and what roles do vesicles and neurotransmitters play?
• RQ3 What mechanisms underlie the generation and propagation of action potentials in neurons?
• RQ4 How do glial cells contribute to neuronal communication and plasticity?

Key findings

• Neurons consist of soma, dendrites, and a single axon, with specialized structures such as the axon hillock, myelin, and nodes of Ranvier that influence excitability.
• Synapses come in chemical and electrical forms, with synaptic vesicles and neurotransmitters mediating chemical signaling across the synaptic cleft.
• Synaptic vesicles cycle through trafficking, loading, docking, priming, fusion, and endocytosis, enabling rapid neurotransmitter release and recycling.
• Membrane potential is generated by ion gradients and channels/pumps, enabling graded potentials and all-or-nothing action potentials that propagate signals.
• Glial cells are abundant and increasingly understood to actively participate in brain signaling and plasticity, beyond mere support.
• The process of signal transmission in the brain involves a shift from electrical to chemical signaling and back, within sub-second timescales.