2.1 Structure and function of neurons and glial cells
4 min read•july 18, 2024
Neurons and glial cells are the building blocks of our nervous system. Neurons transmit electrical signals, while glial cells provide and . Together, they form the complex network that allows us to think, feel, and move.
Understanding these cells is crucial for developing neuroprosthetics. By mimicking or interfacing with neurons and glia, we can create devices that restore lost function or enhance existing capabilities in the nervous system.
Neuron and Glial Cell Structure and Function
Components and functions of neurons
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Communication Between Neurons · Anatomy and Physiology View original
Houses the nucleus and organelles essential for cellular functions (protein synthesis, energy production)
Integrates incoming signals from to generate action potentials
Dendrites
Highly branched extensions that receive and process signals from other neurons
Covered in dendritic spines, small protrusions that form with terminals
Increased surface area enhances the neuron's ability to receive and integrate multiple signals
Elongated, cable-like extension that conducts electrical signals away from the soma
Insulated by a myelin sheath formed by (CNS) or (PNS)
Myelin sheath enables faster signal propagation through saltatory conduction (nodes of Ranvier)
Specialized structure at the end of the axon that releases neurotransmitters into the synaptic cleft
Contains synaptic vesicles filled with neurotransmitters (glutamate, GABA, dopamine)
Forms synapses with dendrites or cell bodies of target neurons, or with muscle fibers or glands
Synapses
Junctions between the axon terminal of one neuron and the , soma, or axon of another neuron
Can be chemical synapses () or electrical synapses (gap junctions)
Site of information transfer and processing in neural circuits
Types and roles of glial cells
Star-shaped cells that provide structural and metabolic support to neurons
Maintain the blood-brain barrier by forming tight junctions with endothelial cells
Regulate neurotransmitter levels (glutamate uptake) and ion concentrations (K+ buffering) in the synaptic cleft
Release gliotransmitters (ATP, D-serine) to modulate and plasticity
(CNS) and (PNS)
Form the myelin sheath around axons, providing electrical insulation and increasing conduction velocity
Oligodendrocytes can myelinate multiple axons, while Schwann cells myelinate a single axon segment
Support axonal integrity and survival through trophic factor release (BDNF, NGF)
Resident immune cells of the CNS that constantly survey the brain for damage or infection
Phagocytose cellular debris, apoptotic cells, and foreign pathogens to maintain brain homeostasis
Secrete pro-inflammatory (TNF-α, IL-1β) and anti-inflammatory (IL-10, TGF-β) cytokines to regulate neuroinflammation
Contribute to synaptic pruning during development and in response to injury or disease
Cuboidal or columnar epithelial cells that line the ventricles and central canal of the spinal cord
Possess cilia that facilitate the circulation of cerebrospinal fluid (CSF) throughout the ventricular system
Form a barrier between the CSF and brain parenchyma, regulating the exchange of molecules
Contain neural stem cells in specific regions (subventricular zone) that give rise to new neurons and glia
Process and significance of neurogenesis
Neurogenesis involves the proliferation, migration, and differentiation of neural stem cells into mature neurons
Primarily occurs during embryonic and early postnatal development, establishing the basic structure of the nervous system
In adults, neurogenesis is largely restricted to the subgranular zone of the hippocampal dentate gyrus and the subventricular zone of the lateral ventricles
Hippocampal neurogenesis is associated with learning, memory formation, and mood regulation (depression, anxiety)
Subventricular zone neurogenesis generates interneurons that migrate to the olfactory bulb, contributing to olfactory learning and discrimination
Enhancing neurogenesis through exercise, environmental enrichment, or pharmacological interventions may promote brain and recovery after injury (stroke, traumatic brain injury) or in neurodegenerative diseases (Alzheimer's, Parkinson's)
Mechanisms of neuronal communication
Electrical signaling within neurons
Neurons maintain a resting membrane potential of -60 to -70 mV through the action of ion pumps (Na+/K+ ATPase) and selective ion channels
Action potentials are generated when the membrane potential reaches a (-55 mV) due to sufficient depolarization
Depolarization: Voltage-gated Na+ channels open, allowing Na+ influx and rapid rise in membrane potential
Repolarization: Voltage-gated K+ channels open, allowing K+ efflux and return to resting membrane potential
: Na+ channels are inactivated, and the neuron cannot generate another until they recover
Action potentials propagate along the axon in an all-or-none manner, maintaining their amplitude
Chemical signaling between neurons (synaptic transmission)
Action potentials arriving at the axon terminal trigger the opening of voltage-gated Ca2+ channels
Ca2+ influx causes synaptic vesicles to fuse with the presynaptic membrane and release neurotransmitters into the synaptic cleft
Neurotransmitters diffuse across the cleft and bind to receptors on the postsynaptic cell
(ligand-gated ion channels) mediate fast synaptic transmission by directly opening ion channels (AMPA, NMDA, GABAA receptors)
(glutamate) depolarize the postsynaptic cell, while (GABA, glycine) hyperpolarize it
Neurotransmitters are cleared from the synaptic cleft by reuptake into the presynaptic terminal or surrounding glial cells, or by enzymatic degradation (acetylcholinesterase)
, the strengthening or weakening of synapses in response to activity, underlies learning and memory (LTP, LTD)