Methods of studying the CNS Flashcards
Nissl staining reveals
‘Nissl bodies’ which are dark patches in the staining where patches of RER, ribosomes and golgi are.
What is an example of a basic Nissl dye?
Cresyl violet
What is a stain used to reveal myelinated fibre tracts within the CNS?
Luxol fast blue and weigert staining
What staining reveals the cytoarchitecture of the brain?
Nissl stains
Reticular theory
The reticular theory, (Golgi) stated that the nervous system consisted of a diffuse nerve network formed by anastomosing branches of nerve processes.
Neuron doctrine
The “Neuron Doctrine” (Cajal) includes descriptions of synapses and their proposed function.
Neurons are individual cells, which are not continuous to other neurons, neither anatomically nor genetically;
The neuron has three parts: dendrites, soma (cell body) and axon.
Why is doctrine an oversimplification?
Doctrine is an over-simplification of how a neuron functions
In addition to synaptic contacts there are gap junctions, modulatory receptors on pre-synaptic elements, and the modulatory action of transmitters, hormones and gaseous messengers in the local environment which affect neuronal activity.
Golgi staining
Impregnation of the cell cytoplasm with a silver chromate precipitate.
Luxol blue myelin appears
Blue myelin, pink neuropil, purple nerve cells
Cresyl violet RNA appears
Violet (Nissl bodies darkest)
Weigert stain myelin appears
Darkest
What method gives a direct measure of the activity of nerve cells?
Two-photon calcium imaging
HRP staining
HRP is an enzyme that associates with nerve cells. DAB substrate is oxidized by horseradish peroxidase (HRP). The oxidized DAB forms a brown precipitate, at the location of the HRP, which can be visualized using light microscopy.
What enables imaging areas of functional activity in the CNS?
fMRI
What enables activity of neurons to be increased or decreased?
Optogenetics or chemogenetics
CT
Computed tomography - combinations of multiple X-ray measurements taken from different angles to produce tomographic (cross-sectional) images (virtual “slices”) of a body, allowing the user to see inside the body without cutting.
Bone clearly white air and fat black
MRI scanners
Use strong magnetic fields, magnetic field gradients, and radio waves to generate images of the organs in the body.
Contrast provided between grey and white matter
Fat underneath the skin or reservoirs of water in the body can be either white or dark in appearance, depending on the pulse sequence.
Bones often black, fat is bright
Functional MRI (fMRI)
Functional magnetic resonance imaging (fMRI) measures brain activity by detecting changes associated with blood flow.
This technique relies on the fact that cerebral blood flow and neuronal activation are coupled. When an area of the brain is in use, blood flow to that region also increases
PET
Positron emission tomography (PET is a functional imaging technique that uses radioactive substances known as radiotracers to visualize and measure changes in metabolic processes, and in other physiological activities including blood flow, regional chemical composition, and absorption.
MEG
Magnetoencephalography (MEG) is a functional neuroimaging technique for mapping brain activity by recording magnetic fields produced by electrical currents occurring naturally in the brain, using very sensitive magnetometers.
MEG uses
Research into perceptual and cognitive brain processes, localizing regions affected by pathology before surgical removal, determining the function of various parts of the brain, and neurofeedback.
EEG vs MEG
Magnetic fields are less distorted than electric fields by the skull and scalp, which results in a better spatial resolution of the MEG.
EEG can detect activity both in the sulci and at the top of the cortical gyri, whereas MEG is most sensitive to activity originating in sulci.
EEG is, therefore, sensitive to activity in more brain areas, but activity that is visible in MEG can also be localized with more accuracy.
Extracellular recordings
Give information about the electrical excitement and action potentials of neurons
Single unit extracellular recordings
An electrode inserted into the brain detects electrical activity that is generated by the neurons adjacent to the electrode tip.
Very similar (but smaller) results to intracellular recordings
Multi-unit extracellular recordings
f the electrode tip is slightly larger, then the electrode might record the activity generated by several neurons (multi-unit recording).
Field potential
Electrode tip is very large, in general the activity of individual neurons cannot be distinguished but the electrode will still be able to record a field potential generated by the activity of many cells.
Electroencephalography (EEG)
Non-invasive recordings of electrical activity of the brain.
Electrodes placed along the scalp
EEG measures voltage fluctuations resulting from ionic current within the neurons of the brain.
EEG is used in clinical circumstances to determine changes in brain activity that might be useful in diagnosing brain disorders, especially epilepsy or another seizure disorder.
What enables the imaging of neurotransmitter vesicles at a synaptic cleft?
EM
What is used to study patterns of electrical activity within the entire brain?
EEG
What method could specifically stain astroglia?
GFAP stain determine whether cells contain glial fibrillary acidic protein, a protein found in glial cells.
Immunohistochemistry
What method gives a direct measure of the activity of large populations of nerve cells?
Field potentials
