10 - Ascending Pathways

Question 1

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?

Answer 1

• the dorsal column-medial lemniscal pathway, or
• the anterolateral pathway;

at the level of the thalamus

Question 2

what senses are carried by the dorsal column system?

Answer 2

fine touch, pressure, propioception

Question 3

what senses are carried by the anterolateral system?

Answer 3

pain, temperature, light touch

Question 4

which order level neuron decussates in both the dorsal column system and anterolateral system?

Answer 4

2nd order neuron

Question 5

in terms of the somatosensory pathways, for the dorsal column system, which level does decussation occur?

Answer 5

at the level of the brainstem

Question 6

in terms of the somatosensory pathways, for the anterolateral system, which level does decussation occur?

Answer 6

at the level of the spinal cord

Question 7

in terms of the somatosensory pathways, what part of the thalamus does relay information take place that then moves the signal to the cortex?

Answer 7

VPL (Ventroposterior lateral nucleus of the thalamus)

Question 8

where are the first order neurons?

Answer 8

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

Question 9

where are the second order neurons?

Answer 9

located in the spinal cord (anterolateral system) or in the brain stem (dorsal column system).

Question 10

where are the third order neurons?

Answer 10

located in one of the somatosensory nuclei of the thalamus.

Question 11

where are the fourth order neurons?

Answer 11

located in the somatosensory cortex for integration of complex information

Question 12

what are the cell layers of the neocortex in order?

Answer 12

by layers

1molecular layer
2small pyramidal layer
3medium pyramidal layer
4granular layer
5large pyramidal layer
6polymorphic layer

Question 13

what are the main connections for granular layer?

Answer 13

receives input from the thalamus

Question 14

what are the main connections for the large pyramidal layer?

Answer 14

sends output to subcortical structures other than the thalamus

Question 15

what are the main connections for the polymorphic layer?

Answer 15

sends output to the thalamus

Question 16

VPL is for face or body sensations? VPM is for face or body?

Answer 16

body; face

Question 17

describe the nerve fibers for the dorsal column system?

Answer 17

Contains large myelinated nerve fibers for fast transmission (30-110 m/sec)

Question 18

what is the level of orientation throughout the tract?

Answer 18

High degree of spatial orientation maintained throughout the tract

Question 19

how is information transmitted from the dorsal column system?

Answer 19

Transmits information rapidly and with a high degree of spatial fidelity (i.e., discrete types of mechanoreceptor information)

Question 20

what stimuli does the dorsal column system receive?

Answer 20

Touch, vibration, position, fine pressure

Question 21

why is does the Dorsal Column-Medial Lemniscal Pathway have medial lemniscus?

Answer 21

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

Question 22

in the Dorsal Column-Medial Lemniscal System, what do touch sensations require?

Answer 22

a high degree of localization of the stimulus and transmissions of fine gradations of intensity

Question 23

phasic sensations also known as?

Answer 23

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

Question 24

describe the nerve fibers of the anterolateral system?

Answer 24

Smaller myelinated and unmyelinated fibers for slow transmission (0.5-40 m/sec)

Question 25

what is the degree of spatial orientation of the anterolateral system?

Answer 25

low degree

Question 26

what types of sensations are transmitted to the anterolateral system?

Answer 26

broad spectrum of modalities like Pain, thermal sensations, crude touch and pressure, tickle and itch, sexual sensations

Question 27

Following a spinal cord hemisection at the 10th (half spinal cord cut) thorasic level on the left side, lesion not necessarily here

This pattern, together with motor weakness on the same side as the lesion is also referred as

Answer 27

Brown Sequard Syndrome