any ___________, _____________ particle emits ______________ radiation which can be detected
accelerating
charged
electromagnetic
producing the mri signal
- apply magnetic field
- protons line up with vertical field
- apply radio frequency pulse
- protons rotate in sync on their axis
- changing, magnetic field is produced - radio frequency pulse turned off
- protons dephase - loss of horizontal magnetism
- protons realign - gain in vertical magnetic signal
T1 weighted image
MRI image based on realignment phase
T2 weighted image
MRI image based on dephasing
do protons dephase more quickly in dense tissue or less dense tissue?
dense tissue - atoms are packed together very strongly
where are surface blood vessels located in the brain?
arachnoid membrane
why is blood flow increase to the brain slow?
takes a long time for the diameter of the arteriole to change (time lag)
what is the BOLD signal?
signal produced from MRI scanner detection of paramagnetic deoxygenated blood flowing out of a capillary bed in certain areas of the brain
why is the nature of the BOLD signal thought to be controversial?
- increased blood flow exceeds requirements of the active neurons so nothing to do with nutrition
- increased blood flow = non-specific cooling system
what is non-linear registration?
creating an average brain by morphing anatomical data from many peoples’ brains together
then overlaying bold signals
advantages and disadvantages of fMRI?
+ high spatial resolution
- low temporal resolution
GCaMP
GFP fused to m13 and calmodulin
dark conformation - not as bright as normal GFP
ca2+ present? -> m13 and calmodulin interact and stabilise GFP in bright conformation
increasing intracellular Ca2+ –> brighter GFP
active neurons = ca2+ channels open
provide an example of high resolution microscopy
confocal microscopy
how is high resolution achieved in microscopes?
pinhole rejects light not coming from the focal plane –> increases spatial resolution
halorhodopsin
cl- channel activated by yellow light
when activated, channel opens + hyperpolarises neuron –> inhibits neuron
channelrhodopsin
ion channel (k+, na+, h+) activated by blue light when activated, channel opens + depolarises neuron --> AP fires --> activates neuron
DEFINE: optogenetics
imaging and genetics involving using an ion channel activated by light
