Flashcards in Methods for studying the nervous system Deck (45):
Why are methods for studying the nervous system important?
“Science only as good as its methods”
Have to be constantly revised
New methods provide new information
What other disciplines does neuroscience use fir their methods?
Physiology, anatomy, biochemistry, psychology, molecular biology
What are the 5 foundation methods of neuroscience?
Light microscopic (LM) methods
Electron microscopic (EM) methods
What does the method of dissection involve?
Flemish anatomist, Vesalius (1543), made some of the first accurate drawings of the brain
Latin and Greek names for structures in the CNS originate from this time, e.g. hippocampus= seahorse
How are microscopic features studied in light microscopy?
1. Golgi method
2. Nissl staining
3. Myelin staining
What is the Golgi method in light microscopy?
Silver stain that stains cell bodies and dendrites
What is Nissl staining in light microscopy?
For labelling cell bodies (soma of neurons, shape and collection of cell bodies)
What is Myelin staining in light microscopy?
Myelinated axons (fatty substance in white matter of the brain, surrounds axons)
What can these light microscopic features determine?
The six layers of the human cerebral cortex
How were connections studied in light microscopy?
By cutting/severing axons which form tracts and allowing cells origin to degenerate
When connections are severed in light microscopy what two things degenerate?
What is cell body degeneration?
What is axon degeneration?
Anterograde degeneration (stains used to detect change, usually silver stains)
What are electron microscopes used to examine?
What did the introduction of electron microscopes allow?
Subcellular elements of neurons can be investigated
Confirmation of existence of synapses and synaptic connections
What are the two types of lesion study?
Observational functional disturbances following experimental lesion in animals
Relate disorders in man to lesions of the CNS e.g. language areas of the brain
What are the problems with lesions studies?
Lesions are seldom specific and compensation may occur
No control over lesions
Nervous system has a capacity to compensate for loss or damage (e.g. when someone has a stroke, some function returns, brain finds an alternative way)
How is electrical stimulation applied to the CNS?
On the tracts or nuclei of the CNS
e.g. stimulation of the motor cortex results in contraction of muscles on the opposite side of the body
What did electrical stimulation show about the brain?
Represented by 'maps' i.e. Homunculus
What are the problems with electrical stimulation?
Approach is limited
Reveals nothing about complex connections of the CNS
What are the modern anatomical methods in neuroscience?
In situ hybridization
What is the tract-tracing method?
Selective tracer substances are transported by axonal transport
Tracers are placed in the CNS close to the cell bodies or axon terminals of cells and are selectively taken up and transported along the axon
What are the two types of tract-tracing methods?
What is anterograde tracing?
Used to identify axon terminals, i.e. tracer is placed in the vicinity of cell bodies, taken up, transported along the axon and accumulates in the axon terminals
What is retrograde tracing?
Used to identify cell bodies, i.e. tracer is placed in the vicinity of axon terminals, taken up, transported along the axon and accumulates in cell bodies
What are the 3 types of tracers?
Radio active amino acids
Horseradish peroxidase (HRP)
Phaseolus vulgaris leucoagglutinin (PHAL)
What is radio active amino acid tracer used for?
Made by proteins, detected by autoradiography. A technique which employs the use of photographic emulsions on histological slides (anterograde and retrograde tracing)
What is horseradish peroxidase (HRP) tracer used for?
Very good retrograde tracer
What is Phaseolus vulgaris leucoagglutinin (PHAL) tracer used for?
Lectin extracted from red kidney bean
Excellent anterograde tracer
What does immunocytochemistry involve?
Antibodies to detect molecules in the CNS
E.g. neurotransmitters, receptors
What is the process of immunocytochemistry?
Bound antibodies in tissue are detected by attaching a fluroescent probe or an HRP molecule to the antibody
What is in situ hybridization used to detect?
mRNA sequences produced in neurons
E.g. for peptides or receptors
What is the process of in situ hybridization?
Complimentary DNA probes (identified by autoradiography) are used to detect mRNA (DNA binds/hybridises with mRNA)
RNA sequences are obtained from a library (massive data bank)
What are the 3 electrical recording methods?
What is the process of extracellular recording?
Metal electrode is placed on the surface of the nerve or in the CNS
Connected to amplifier and cathode ray tube
Electrical activity can be observed on the screen of the cathode ray tube (original method)
Now observed on computers (recorded)
What are the problems with extracellular recording?
Only recording global activity than individual cells
What is the process for intracellular recording?
Glass micropipettes (inserted into neuron) containing an electrolyte solution are inserted into a neuron or axon
Connected to an amplifier and a cathode ray tube
Markers (e.g. dyes/enzymes) may also be injected (by pressure or electrical impulse) through micropipettes to label recorded neurons
Individual cell recording (inside the cell itself)
What is the process for patch clamping?
Small piece of cell membrane is attached to a micropipette and current flow through ion channels in the membrane is recorded
E.g. ion channels in a rod of the retina responding to a flash of light
What are the 3 types of computer imaging methods?
Computerized tomography (CT)
Magnetic resonance imaging (MRI)
Positron emission tomography (PET)
What do CT scans show?
X-rays are beamed at many angles through the head and the amount of radiation absorbed is measured by a detector
Computer determines the density of tissue
CT scan is produced (2D scan)
Denser colours in warmer colours, less dense= cooler colours
What are the problems with CT scans?
Spatial resolution poor (no accurate anatomical picture of the brain)
What so MRI scans show?
Magnetic fields used to generate signals from protons in tissue
What are the advantages of MRI scans?
Method has good spatial resolution of the brain
Non-invasive (i.e. drugs, X-rays etc. aren’t used)
Considered to by safe
3-D images of the brain can be generated with modern computer technology
What do PET scans show?
Tracers or drugs containing positron-emitting radio nucleotides are injected into blood supply (radioactive glucose) or are inhaled as a gas (radioactive oxygen)
Substances are taken up by the active regions of the brain
Positrons are converted into photons which are detected by the PET scanner and active regions of the brain can be visualises e.g. language areas during reading or spoken tasks