Interrogating the Nervous System Flashcards
How is electrophysiologic activity in the nervous system coupled with CNS hemodynamics?
Astrocytes form links from capillaries to neurons. They sense changes in neuron activity and respond by regulating blood flow to their local region. Increased glucose and oxygen consumption by neurons results in increased blood flow, volume, and O2 content to that region.
What does the electroencephalogram (EEG) measure?
The EEG measures electrical potential fluctuations at the scalp surface. These are mostly produced by the temporal and spatial summation of relatively slow postsynaptic potentials (EPSPs and IPSPs) and NOT by action potentials (which are faster). These are generally produced by the pyramidal cells in the cortex that lie perpendicular to the scalp, as they have dendrites that span nearly the entire thickness of the cortex.
What does magnetoencephalography (MEG) measure?
MEG measures the small magnetic fields produced by electrical current flux. These fields are oriented perpendicular to the electrical fields, thus the MEG can measure activity in neurons that are not perpendicular to the scalp, such as those that lie in the sulci.
What are three methods for measuring hemodynamic changes within the CNS?
Functional Magnetic Resonance Imaging (fMRI), Positron Emission Tomography (PET), Single Photon Emission Computed Tomography (SPECT)
How can PET scanning be used to track different chemical pathways or activity levels?
Different radioisotopes can be used to track the activity of different pathways. 18-fluorodeoxyglucose will accumulate in cells that are consuming larger amounts of glucose, H2(15)O will distribute along with blood flow. 18-fluorodopa will show areas of dopamine production.
How does fMRI detect changes in blood flow?
fMRI is Blood Oxygen Level Dependent (BOLD) and detects a change in the oxygenated hemoglobin:deoxygenated hemoglobin ratio. Oxygenated hemoglobin is diamagnetic and does not affect magnetic fields, while deoxygenated heme is paramagnetic and does distort magnetic fields.
What does Diffusion Tensor Imaging measure and produce?
DTI measures the directionality of water diffusion in the brain and produces probabilistic maps of the axonal pathways. This allows for imaging the connectivity of the brain in normal and pathological states.
What is the connectome?
The connectome refers to the total assemblage of all the neural connections in the brain and body.
