Flashcards in Spinothalamic, Posterior Column/Medial Leminicus, Thalamo-cortical Pathways (9) Deck (86)
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What is somethesis?
Faculty of bodily perception, including senses and proprioception
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What things do protopathic systems detect? (3)
Pain, crude touch, temperature
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What things do epicritic systems detect? (5)
Fine touch (including form and texture), pressure, slippage, vibration, proprioception
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Receptors that detect gross pressure and vibratory skin stimuli; found in subq skin joints, muscle and mesentery
Pacinian corpuscles - are the ones that have lamellae, fire APs when stimulus begins and again when it ends
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Rapidly adapting skin receptor that senses light touch and vibration, found right below skin in the epidermis in glabrous skin
Meissner's corpuscles
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Slowly adapting mechanoreceptors found in fingertips and also in non-glabrous (hairy) skin
Merkel's disks
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Mechanoreceptors found in deep skin that respond to sustained pressure and skin stretch; responsible for detecting objects slipping along the skin
Ruffini organs - also cont. position sense
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What two things do free nerve endings detect typically?
Temperature and nociceptive (pain) stimuli
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What is adaptation?
Reduced response in the face of a continued, constant stimulus
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What pathway is responsible for detecting pain, temperature, and crude touch?
Anterolateral pathway - Spinothalamic tract
Is a protopathic type tract; protopathic info travels in the anterolateral funiculi in the spinothalamic tract; spinothalamic has a "P" for protopathic
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What pathway is responsible for detecting fine discriminative touch, proprioception, and vibration?
Posterior columns/ Medial Leminiscus
(Tract is called Medial Leminiscus above the caudal medulla, after the posterior columns decussate); carries epicritic info - Leminiscus has an "E" for epicritic
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Which groups of neurons are from the muscle receptors (muscle spindle and Golgi tendon organs)? Where do they project?
A alpha - project to ventral horn and deep layers of dorsal horn
Muscle spindles are subtype 1a; *Golgi tendon organs are classifies as A beta 1b, according to text, but notes say this
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What group of neurons send afferent info from cutaneous and joint receptors and primarily project to dorsal horn?
A beta; subtypes 1b (joints) and II (skin receptors)
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Where is the cell body of the first afferent neuron in the posterior column/ medial Leminiscus pathway located?
Dorsal root ganglion
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Where does the first neuron in posterior column pathway synapse? (General name for the two potential places)
Synapse in the posterior column nuclei in the lower medulla (nucleus gracilis and nucleus cuneatus)
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Which part of the spinal cord do the first neurons in the posterior column pathway travel if from lower part of body? If from upper? At what spinal level does this change?
Fasciculus gracilis - lower body
Fasciculus cuneatus - upper body
* switch is made at the level of T6
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Which posterior column tract is the most medial in the spinal cord?
Fasciculus gracilis is most medial; cuneatus more lateral
(this is the same arrangement for the same named posterior column nuclei in the lower medulla)
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Where does the posterior column/leminiscal pathway decussate? What are the fibers called that actually cross the midline?
In the medulla; the second neurons leaving the posterior column nuclei then decussate - are called internal arcuate fibers
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What do the second order neurons of the posterior column pathway travel in after decussating?
In the Medial Leminiscus - is the same thing as the posterior columns, but they join to form this one common fasciculi above the level of the lower medulla (after decussating)
*medulla = metencephalon
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Where do the 2nd order neurons traveling in the medial leminiscus synapse?
In the ventral posterolateral nucleus (VPL) of the thalamus
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Where the third neurons in the posterior column/medial leminscus pathway synapse after leaving the thalamus (where they originate)?
In the primary somatosensory cortex, located in the postcentral gyrus
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How many times does the posterior column/ medial leminscal path decussate?
Just the one time in the caudal medulla after fibers synapse in the posterior column nuclei located there
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Via what structure do medial leminiscal fibers travel from the VPL to the primRy somatosensory cortex?
Posterior limb of the internal capsule
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In the rostral medulla, in what part of the medial leminscus are fibers from the lower body found?
Lower is anteriorly; upper body is posterior
(Imagine a person standing upright on the ventral surface of the spinal cord if you are facing it)
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In the caudal pons, where are the fibers located in the medial leminscus that transmit the info from the lower half of body?
Lower is now lateral and upper medial (medial leminscus rotates laterally)
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Where do touch and pressure afferents send collaterals to in the spinal cord?
Primarily to dorsal horn
* both touch/pressure (A beta) and propriceptive (A alpha) also send axons up ipsilateral spinal cord as part of the posterior columns of course
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What type of fibers detect non discriminative touch? (i.e. Intense mechanical stimulation that does not result in tissue damage)
A delta fibers
Transmit fast, localized pain info; C fibers are more slow and transmit more generalized pain
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What fibers detect chemical damage, itch, and temperature change?
C fibers (are unmyelinated)
* A delta and C fibers part of the anterolateral/spinothalamic pathway - are attached to free nerve endings in the periphery
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Where is the cell body located for the first order neurons in the anterolateral/spinothalamic pathway? Where do these neurons first synapse?
Dorsal root ganglia
Neurons (protopathic) first synapse in the dorsal horn of the spinal cord (I - V)
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