Neuroscience Quiz: Glial Cells and Neural Circuits

Nervous System Overview

• The nervous system is comprised of neurons and glial cells
• Neurons transmit signals; glial cells provide support
• Neurons are the primary signaling units

Neuron Structure

• Dendrites: Highly branched extensions receiving signals from other neurons; contain neurotransmitter receptors
• Cell Body (Soma): Contains the nucleus and organelles; site of protein synthesis
• Axon: Single, long extension transmitting action potentials to other neurons or target cells; can be myelinated or unmyelinated
• Myelin Sheath: Insulates axons, speeds up signal transmission; produced by oligodendrocytes (CNS) and Schwann cells (PNS)
• Nodes of Ranvier: Unmyelinated gaps in the myelin sheath increasing signal speed through saltatory conduction

Synapses

• Synapses are the sites where neurons communicate
• Presynaptic terminal (terminal bouton): Releases neurotransmitters stored in vesicles
• Synaptic cleft: The space between neurons where neurotransmitters diffuse
• Postsynaptic terminal: Contains receptors that bind neurotransmitters

Glial Cells

• Support and regulate the function of neurons
• Astrocytes: Maintain blood-brain barrier, regulate ion and neurotransmitter concentrations, secrete chemicals essential for synaptogenesis
• Oligodendrocytes: Myelinate axons in the CNS
• Microglia: Act as the immune cells of the CNS
• Schwann Cells: Myelinate axons in the PNS

Signal Transmission

• Neurons are polarized (distinct input/output regions)
• Proteins and organelles move along axons via microtubules
• Signal types include excitatory, inhibitory, and modulatory (depending on the neurotransmitter)

Neuronal Circuits

• Afferent neurons carry sensory information toward the CNS
• Efferent neurons carry motor commands away from the CNS
• Interneurons facilitate local processing in circuits

Neural Circuit Example: Knee-Jerk Reflex

• Sensory neurons detect stimulus
• Sensory neurons synapse with and excite motor neurons in the spinal cord
• Interneurons synapse to inhibit motor neurons of opposing muscles
• Motor neurons trigger muscle contraction (extension)

Techniques for Studying Neural Activity

• Calcium Imaging: Calcium-sensitive dyes used to monitor neuronal activity
• Optogenetics: Using light to control neuronal activity via light-sensitive proteins (opsins)

Structural Analysis of Neural Systems

• Lesion studies: Damage specific brain areas to study information flow
• Labeling proteins: Visualize gene expression and areas of activity

Organization of the Nervous System

• Central Nervous System (CNS): Brain and spinal cord (processing sensory input, generating motor output)
• Peripheral Nervous System (PNS): Connects the CNS to the body (sensory and motor pathways)

Genomics and the Nervous System

• Genomics: Analysis of complete DNA sequences
• Role of the Genome: Human genome has genes regulating brain organization and function; a significant proportion expressed exclusively in the brain
• Model Organisms: Used to study neural systems. Examples include humans, mice, zebrafish, fruit flies, and nematodes

Genetic Engineering Techniques

• Knock-in/Knock-out Models: Modify specific genes in organisms to study their effects
• Cre-LoxP System: Alter specific DNA regions in controlled manner, typically in mice; used to control gene expression

CRISPR-Cas9 System

• Components: Cas9 endonuclease and guide RNA
• Process: The CRISPR-Cas9 system is used to modify specific DNA regions by introducing double-stranded breaks
• This allows for: inducing mutations, insertions, or deletions facilitating gene function studies and creating animal models of diseases