Greg Detre
18/11/99
orientation of the columns in the spinal cord
modality specificity
connections at 4 or 5 levels ascending up the spine � brain
some fibres cross/integrate, modified by descending pathways (tracts)
somatosensory cortex � 4 sub-units, each with topographical map of body
1, 2, 3a, 3b����� differing input (from thalamus/each other)
size of area � sensitivity�������� also maps for other senses
visual system org
how study? recording particular regions with electrodes
also lesions + brain damage��������� cut the tract
retrograde pathways � back up the cell (non-metabolisable radioactive sugar)
mutants � non-binocular vision because fibres don't cross
receptor � mechanical stimulation cell changes mechanism when you press
stretch-activated channels������ let in Ca2+ ions, �/span> trigger secretion, or AP
adaptation � not aware of clothes
Pacinian � elastic membrane sacs (RA)
3 or 4 layers of membrane � if push hard, stretch activates
if push slowly, will be damped by the viscosity of the fluid
will stop firing after a while from stimulus because the sacs will be squeezed back
frequency-tuned because resonate to low vibrations
pain, heat, cold, vibration, itching?( = chemo-receptor
Brady� released locally and acts on receptors
to depolarise, responds to small peptides)
temperature sensitivity � channel in to membrane whi is temperature-sensitivity
membrane lipids will change������� some bimodality
capsaysin(???) � chili pepper, s� heal + pain kills neuron (in whole areas in dental psychology)
pain = chemical receptor to particular peptides
pressure � Pacinian (onion-like)�������� free nerve-ending� no organ on the end
flowerspray � branched axons����� dendritic
pain � Ad + C fibres������� difference in velocity (myelination)
Melzack�s gate-control theory � stimulation of cutaneous receptors � � pain � rub if you get kicked
because two sorts of ascending pathways, competing for finite capacities (TENS machines)
two sensory modalities coming together
anti-dromic, e.g. of the phys going wrong
bite then white then flare
damage to blood vessels, fluid spilling out
pain ascending travels back down to cause pain around the wound
hand receptor then up to spinal cord�������� dorsal root synapses
then to relay station (e.g. thalamus)
2 or 3 synapses on the way up
some functions cross, some don't
eye + ear
much more logical org������ columnar organisation
anti-dromic � travelling in the opposite direction
why cross over?
cortex evolved after, so it got connected laterally
growth cone driven by
apoptotic neurons to guide in development