10 - Ascending Pathways Flashcards
from the entry point into the cord and then to the brain, the sensory signals are carried through one of two alternative sensory pathways, what are these pathways? where do these two systems come back together?
- the dorsal column-medial lemniscal pathway, or
- the anterolateral pathway;
at the level of the thalamus
what senses are carried by the dorsal column system?
fine touch, pressure, propioception
what senses are carried by the anterolateral system?
pain, temperature, light touch
which order level neuron decussates in both the dorsal column system and anterolateral system?
2nd order neuron
in terms of the somatosensory pathways, for the dorsal column system, which level does decussation occur?
at the level of the brainstem
in terms of the somatosensory pathways, for the anterolateral system, which level does decussation occur?
at the level of the spinal cord
in terms of the somatosensory pathways, what part of the thalamus does relay information take place that then moves the signal to the cortex?
VPL (Ventroposterior lateral nucleus of the thalamus)
where are the first order neurons?
located in the primary afferent neuron whose cell bodies are in the dorsal root or cranial ganglia, and their axons synapse on somatosensory receptor cells
where are the second order neurons?
located in the spinal cord (anterolateral system) or in the brain stem (dorsal column system).
where are the third order neurons?
located in one of the somatosensory nuclei of the thalamus.
where are the fourth order neurons?
located in the somatosensory cortex for integration of complex information
what are the cell layers of the neocortex in order?
by layers
1molecular layer 2small pyramidal layer 3medium pyramidal layer 4granular layer 5large pyramidal layer 6polymorphic layer
what are the main connections for granular layer?
receives input from the thalamus
what are the main connections for the large pyramidal layer?
sends output to subcortical structures other than the thalamus
what are the main connections for the polymorphic layer?
sends output to the thalamus
VPL is for face or body sensations? VPM is for face or body?
body; face
describe the nerve fibers for the dorsal column system?
Contains large myelinated nerve fibers for fast transmission (30-110 m/sec)
what is the level of orientation throughout the tract?
High degree of spatial orientation maintained throughout the tract
how is information transmitted from the dorsal column system?
Transmits information rapidly and with a high degree of spatial fidelity (i.e., discrete types of mechanoreceptor information)
what stimuli does the dorsal column system receive?
Touch, vibration, position, fine pressure
why is does the Dorsal Column-Medial Lemniscal Pathway have medial lemniscus?
because this is where the transition occurs of the signal moving from the rostral medulla to the pons together with nucleus gracilis and nucleus cuneatus
in the Dorsal Column-Medial Lemniscal System, what do touch sensations require?
a high degree of localization of the stimulus and transmissions of fine gradations of intensity
phasic sensations also known as?
vibratory sensations
note also sensations that signal movement against the skin, position sensations from the joints, pressure sensations having to do with fine degrees of judgment of pressure intensity
describe the nerve fibers of the anterolateral system?
Smaller myelinated and unmyelinated fibers for slow transmission (0.5-40 m/sec)
