Interrogation of the nervous system - Ojemann Flashcards
T2 weighted image
Fluid is hyperintense (eg white)
T1 weighted image
Fluid is dark
What is an EPSP, IPSP, and an action potential?
EPSP - excitatory postsynaptic potential
IPSP - inhibitory postsynaptic potential
action potential - summation of the EPSP and IPSP
**EEG measures the summation of the EPSP and IPSP along the dendrites, but the action potential itself does not contribute much to the signal b/c is so brief. EPSP/IPSP are quite slow, comparatively
Describe the “coupling” between electrophysiologic activity in the nervous system and CNS hemodynamics.
Areas of increased electrophysiologic activity require increased blood flow.
Describe those techniques for evaluating “brain activity” that measure the electromagnetic properties of the nervous system.
EEG - electroencephalogram
ERP (Event Related Potential) - the expected signal from a given stimulus, based on many repeated stimulations**
MEG - magnetic encephalogram
**Clinically, the most commonly employed are the Auditory Evoked Potential (also called the Brainstem Auditory Evoked Response or BAER), and the Somatosensory Evoked Potential (SSEP)
Describe at a basic level the physiologic basis for the signal recorded in the EEG, the MEG, the fMRI, and the PET scan.
EEG - summation of all signals transmitted to the scalp (includes EPSP, IPSP)
MEG - measures small magnetic fields created by electromagnetic flux
fMRI - concentration of deoxyhemoglobin
PET - radioisotope tracing
Describe those techniques for evaluating “brain activity” that measure the hemodynamic properties of the nervous system.
fMRI - Oxyhemoglobin is diamagnetic, and does not cause distortion in a magnetic field, while deoxyhemoglobin is paramagnetic, and it does distort magnetic fields.
PET (15 H2O Positron Emission Tomography (H215O PET) scanning - inject a tracer compound labeled with a positron-emitting radionuclide. The radionuclide decays and the resulting positrons subsequently annihilate on contact with electrons after traveling a short distance (around 1mm) within the body. Each of the annihilations produces two photons traveling in opposite directions and these photons encounter detectors arranged circumferentially around the subject.
SPECT (single photon emission computed tomography- no details given
Describe at a basic level the method of Diffusion Tensor Imaging, or DTI.
DTI yields quantitative measures reflecting the integrity of white-matter fiber tracts, by taking advantage of the intrinsic directionality of water diffusion in human brain. By calculating the constraints on water diffusion, or fractional anisotropy arising from a given site in the nervous system, one can image the white matter pathways formed by axons passing to and from the region of interest. This allows for imaging the connectivity of the brain in normal and pathologic states, and it is becoming increasingly important in the investigation of a number of disorders.
Describe at a basic level the objectives of “Connectomics”. Understand the potential for this technique to act as a biomarker for certain disease states
The term “connectomics” was coined in 2005 to describe an effort to comprehensively describe the structural relationships within the nervous system. The “connectome” is studied as a network by means of network science and graph theory.
What is the structure and function of the pyramidal cells, and how do they participate in the generation of action potentials?
The pyramidal cells are the site of summation of the IPSP and EPSPs. The cell bodies reside deep within the cortex, with dendrites that extend longitudinally up through the layers of the cortex to receive signals.
