so in this slide in the next what we're going to do is draw the pathway for fine tight
reception and then as we're going we'll kind of compare and contrast with gross touch and
then we'll talk a little bit about some of these differences and why they're important so to begin
so fine touch hmm let me see here's a penny and well and here's a dime dimes are rough pennies
are smooth you can feel the difference between a penny and a dime because of your fine touch sense
proprioception again is knowing where your limbs are in space and that travels with fine touch so
there's a dorsal root so you have a finger and a thumb you know well you know me am i drawing
so anyway so here's the dorsal root ganglion neuron which is number one in the chain and
it enters the dorsal horn it may kind of give a sidebar chat with some of the neurons here
but for the most part it doesn't really it's not as big as synapse and it travels in this dorsal
horn in the dorsal fist in the dorsal columns if it's from the leg it is in the gracilis if
it's from the arm it's in the cuneatus it comes up to the medulla oblongata and synapses
appropriately either in the gracilis nucleus or the cuneatus nucleus okay based
on whether it was traveling in which of these parts of the dorsal columns these
neurons cross the midline and now they're called this fiber tract is called the medial lemniscus
these fibers of these and secondary neurons that have crossed the midline a send to the thalamus
where they synapse again on a thalamic neuron which goes to the primary somatosensory cortex
so what I hope you do is get a piece of paper you don't have to draw in pretty spinal cords
you can just draw boxes or circles or whatever you want to draw and practice drawing fine touch
and proprioception and practice drawing gross touch so you remember where the second order
the second neuron in the chain crosses because remember the first neuron is very simple it's
always going to be the drg neuron the third neuron is also simple it's always going to be
the thalamus neuron it's this second neuron that can cause some consternation and some
confusion but once you get that down you've got the sensory system down so in the next slide
we're gonna go over it in boxes because boxes are even easier than brains so again another
way of you know another schema to look at fine touch and proprioception is to remember that
there's a stimulus the first neuron is in the dorsal root ganglion that dorsal root ganglion
neuron then goes into the spinal cord and rut goes through either the fasciculus cuneauts
or the fasciculus gracilis it then synapses in the medulla in the nucleus Kenyatta's or
the nucleus gracilis these are the second-order neurons they cross the midline and we call them
arcuate fibers when they cross the midline and then they ascend or go to up towards the brain
via the medial lemniscus they synapse in the thalamus and then that third neuron projects
to the somatosensory cortex where it comes to since perception so again the first neuron and
the third neuron are where they always are in the drg and in the thalamus the second neuron
for gross touch is going to be in the spinal cord and it's axons cross for fine touch and
proprioception the second neuron is in the medulla those are the neurons that cross so it's always
the second neuron that crosses the midline so to summarize again I mean how many neurons does
it take to relay fine touch and proprioception to the primary sensory cortex where are these neurons
located which of axons crossed the midline where does that axon cross the midline and then where
does this axon travel as it ascends towards the brain so where does it travel in the spinal cord
where does it travel in the brainstem once you understand these things you'll be ready for the
assessment practice drawing doesn't matter how pretty or how ugly the the your own illustrations
are but once you draw it you'll understand it and you'll be ready for the assessment