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Sensory systems (The sensory system is the major afferent input system…
Sensory systems
The sensory system is the major afferent input system taking information to the CNS regarding internal and external environments. Complex system is often broken down by sensory modalities
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'in the back door' - sensory fibres enter the dorsal horn grey matter, motor fibres leave the ventral horn grey matter
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Dorsal column pathway
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first order sensory neuron cell bodies in the dorsal root ganglion of spinal cord - travel up the gracillis/cuneatus to the medulla where they synpase with the 2nd order neuron cell bodies in their respective nuclei, then decussate to the other side. Now called medical leminicus pathway, up to vpl nucleus in thalamus - then 3rd order goes to post central gyrus - primary somatosensory cortex.
middle arcuate fibres - landmark of the pons - shows the 2nd order sensory neuron axons crossing over to the other side (contralterally) to the medial lemincus pathway on both sdes.
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the primary somatosensory cortex is the 3rd order sensory neuron target - contralateral to origin of information, part of the partietal lobe - this is the point at which we become consciously aware
Spinothalamic pathway
pain, non-discrimintive touch, temperature via spinal cord
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as soon as the first order neuron synapses with the second order neuron, it crosses immediately and rises contralterally
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