Brain and Behavior Review

These flashcards cover key concepts related to network neuroscience, brain structure, neuron function, and synaptic plasticity, derived from the lecture notes provided.

Compare and contrast the Central Nervous System (CNS) and the Peripheral Nervous System (PNS).

1. CNS: Consists of the brain and spinal cord; acts as the primary integration and command center.
2. PNS: Consists of cranial and spinal nerves and ganglia; serves as the communication relay between the CNS and the rest of the body.

• Key Distinction: The CNS is encased in bone (skull/vertebrae) and protected by the Blood-Brain Barrier (BBB), while the PNS lacks these protections but has a higher capacity for axonal regeneration.

What are the primary structural differences between Gray Matter and White Matter?

• Gray Matter: Found in the cortex and deep nuclei; primarily consists of neuronal cell bodies (soma), dendrites, and unmyelinated axons. It is the site of information processing and computation.
• White Matter: Found in the subcortical regions; primarily composed of myelinated axons and oligodendrocytes. It functions as the infrastructure for long-range communication (connectivity) between gray matter regions.

Identify the four main types of Glial Cells and their specific physiological roles.

1. Astrocytes: Most abundant; maintain the chemical environment and form the Blood-Brain Barrier (BBB).
2. Oligodendrocytes: Provide the myelin sheath for multiple axons in the CNS.
3. Microglia: Specialized macrophages that serve as the CNS's primary immune defense.
4. Ependymal Cells: Line the ventricles and produce Cerebrospinal Fluid (CSF).

Define the Resting Membrane Potential (V_{m}) and the mechanism of its maintenance.

The resting potential is typically -70 mV, established by the unequal distribution of ions across the semi-permeable membrane. It is maintained by:

1. The Na^{+}/K^{+} Pump: Actively transports 3 Na^{+} out for every 2 K^{+} in, consuming ATP.
2. K+ Leak Channels: Allow the outward flow of potassium down its concentration gradient, making the interior more negative.

Mathematical formulation: The Goldman-Hodgkin-Katz (GHK) Equation.

The GHK equation calculates the steady-state membrane potential (V_{m}) by considering the relative permeabilities (P) of multiple ions:

V{m} = \frac{RT}{F} \ln \left( \frac{P{K}[K^{+}]{out} + P{Na}[Na^{+}]{out} + P{Cl}[Cl^{-}]{in}}{P{K}[K^{+}]{in} + P{Na}[Na^{+}]{in} + P{Cl}[Cl^{-}]_{out}} \right)

Unlike the Nernst equation, which calculates the equilibrium for a single ion, GHK accounts for the total ionic flux.

Detail the phases and ionic currents of an Action Potential.

1. Threshold: Depolarization reaches approx. -55 mV.
2. Depolarization: Rapid opening of voltage-gated Na^{+} channels (Na^{+} influx).
3. Peak: Potential reaches approx. +40 mV; Na^{+} channels begin to inactivate.
4. Repolarization: Voltage-gated K^{+} channels open (K^{+} efflux).
5. Hyperpolarization: V_{m} drops below resting potential due to slow K^{+} channel closing, followed by a return to baseline via the sodium-potassium pump.

What is the difference between the Absolute and Relative Refractory Periods?

• Absolute Refractory Period: Occurs during depolarization and early repolarization; voltage-gated Na^{+} channels are inactivated. No second action potential can be triggered, regardless of stimulus strength.
• Relative Refractory Period: Follows the absolute period; some Na^{+} channels have recovered, but lingering K^{+} efflux makes the cell hyperpolarized. A second action potential can occur but requires a significantly stronger stimulus.

Define Saltatory Conduction and the role of Myelin.

Saltatory conduction is the "jumping" of an electrical impulse from one Node of Ranvier (unmyelinated gap) to the next. This is facilitated by the myelin sheath, which acts as an insulator, drastically increasing the speed of signal transmission and reducing the metabolic energy required for repolarization.

Differentiate between Ionotropic and Metabotropic receptors.

• Ionotropic (Ligand-gated): Fast-acting; the receptor itself is an ion channel that opens upon neurotransmitter binding (e.g., Nicotinic ACh, AMPA).
• Metabotropic (G-protein coupled): Slower-acting; binding activates a G-protein and second-messenger cascades (e.g., Muscarinic ACh, GABA-B), leading to prolonged modulatory effects on the post-synaptic cell.

Identify the primary Excitatory and Inhibitory Neurotransmitters in the CNS.

• Glutamate: The primary excitatory neurotransmitter; its binding typically leads to an Excitatory Postsynaptic Potential (EPSP) through Na^{+} or Ca^{2+} influx.
• GABA (Gamma-Aminobutyric Acid): The primary inhibitory neurotransmitter; its binding typically leads to an Inhibitory Postsynaptic Potential (IPSP) via Cl^{-} influx or K^{+} efflux.

Explain Synaptic Integration: Spatial vs. Temporal Summation.

• Spatial Summation: The integration of post-synaptic potentials originating from different synapses on the dendrites/soma occurring simultaneously.
• Temporal Summation: The integration of multiple post-synaptic potentials generated by a single synapse firing in rapid succession.
• The neuron fires an action potential only if the integrated sum at the axon hillock exceeds the threshold.

Explain why the NMDA receptor is considered a 'Coincidence Detector'.

The NMDA receptor (NMDAR) requires two simultaneous events to activate:

1. Presynaptic activity: Release of Glutamate (ligand-binding).
2. Postsynaptic activity: Depolarization of the membrane to expel the Mg^{2+} block from the channel pore.
   This dual-gating mechanism makes it central to synaptic plasticity and Associative Learning (Hebb's Postulate).

Define Structural vs. Functional Connectivity in Network Neuroscience.

• Structural Connectivity: The physical mapping of anatomical connections, such as white matter tracts identified via Diffusion Tensor Imaging (DTI).
• Functional Connectivity: The statistical dependency (often temporal correlation) between the activity (e.g., BOLD signal in fMRI) of spatially segregated brain regions, regardless of physical connection.

What are the core metrics of a Brain Graph (G = (V, E)) used in network analysis?

• Nodes (V): Represent biological units (neurons, voxels, or parcellated regions).
• Edges (E): Represent the links between nodes (synapses or correlations).
• Clustering Coefficient: Measures the degree to which nodes in a graph tend to cluster together (local efficiency).
• Average Path Length: The average number of steps required to get from one node to any other node (global efficiency).

Explain why the NMDA receptor is considered a 'Coincidence Detector'.

The NMDA receptor (NMDAR) requires two simultaneous events to activate:

1. Presynaptic activity: Release of Glutamate (ligand-binding).
2. Postsynaptic activity: Depolarization of the membrane to expel the Mg^{2+} block from the channel pore.
   This dual-gating mechanism makes it central to synaptic plasticity and Associative Learning (Hebb's Postulate).

Define Structural vs. Functional Connectivity in Network Neuroscience.

• Structural Connectivity: The physical mapping of anatomical connections, such as white matter tracts identified via Diffusion Tensor Imaging (DTI).
• Functional Connectivity: The statistical dependency (often temporal correlation) between the activity (e.g., BOLD signal in fMRI) of spatially segregated brain regions, regardless of physical connection.

What are the core metrics of a Brain Graph (G = (V, E)) used in network analysis?

• Nodes (V): Represent biological units (neurons, voxels, or parcellated regions).
• Edges (E): Represent the links between nodes (synapses or correlations).
• Clustering Coefficient: Measures the degree to which nodes in a graph tend to cluster together (local efficiency).
• Average Path Length: The average number of steps required to get from one node to any other node (global efficiency).