Spinothalamic, Posterior Column/Medial Leminicus, Thalamo-cortical Pathways (9) Flashcards
What things do protopathic systems detect? (3)
Pain, crude touch, temperature
What is somethesis?
Faculty of bodily perception, including senses and proprioception
What things do epicritic systems detect? (5)
Fine touch (including form and texture), pressure, slippage, vibration, proprioception
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
Rapidly adapting skin receptor that senses light touch and vibration, found right below skin in the epidermis in glabrous skin
Meissner’s corpuscles
Slowly adapting mechanoreceptors found in fingertips and also in non-glabrous (hairy) skin
Merkel’s disks
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
What two things do free nerve endings detect typically?
Temperature and nociceptive (pain) stimuli
What is adaptation?
Reduced response in the face of a continued, constant stimulus
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
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
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
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)
Where is the cell body of the first afferent neuron in the posterior column/ medial Leminiscus pathway located?
Dorsal root ganglion
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)
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
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
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
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
Where do the 2nd order neurons traveling in the medial leminiscus synapse?
In the ventral posterolateral nucleus (VPL) of the thalamus
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
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
Via what structure do medial leminiscal fibers travel from the VPL to the primRy somatosensory cortex?
Posterior limb of the internal capsule
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
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)
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
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
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
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)
Where does the anterolateral/spinothalamic pathway decussate?
In the same level of spinal cord the 1st order neurons enter and synapse in - axons of 2nd order neurons cross via the anterior white commisure to the contralteral anterolateral funiculus (fascicle)
Where do the 2nd order neurons in the anterolateral/spinothalamic pathway go after decussating?
Ascend to the thalamus via the spinothalamic pathway (also called anterolateral funiculus)
Where do the 2nd order neurons in the anterolateral/ spinothalamic tract synapse on the 3rd order?
In the ventral posterolateral nucleus (VPL) of the thalamus
- (same as the medial leminiscal tract)
After leaving the VPL, where does the 3rd order neuron in the anterolateral / spinothalamic go to synapse? Via what structure does it get there?
To the primary somatosensory cortex (postcentral gyrus) - gets there via the posterior limb of the internal capsule
In the midbrain through the cortex, where are fibers transmitting info from lower body found?
Lower body becomes more posterior or dorsal (still partially lateral)
(Guy standing on the pyramids in lower brainstem now flipped to his head)
Why does it take 2-3 spinal levels for all protopathic axons to synapse in the dorsal horn in the Anterolateral/ spinothalamic tract?
Some axons travel in Lissauer’s tract ( posterolateral funiculus), which is composed of protopathic fibers that travel up or down 2-3 spinal levels before synapsing in the dorsal horn
What are the 2 other divisions of the anterolateral pathway (spinothalamic being the main of the three)?
- Spinothalamic
- Spinoreticular
- Spinomesencephalic
What is the overall function of the spinothalamic tract specifically? (As a division of the anterolateral, which is overall protopathic transmission)
Discriminative aspects of pain - where the pain is and what kind
*sharp object in right foot
What are the intralaminar nucleus and dorsomedial nucleus, collaterals of the spinothalamic pathway, important for? Where does each nucleus project to ultimately?
Cortical arousal (of pain)
- Intralaminar thalamic - project diffusely to the cortex
- Dorsomedial nucleus - to prefrontal cortex
What is the specific function of the spinoreticular pathway?
Tells you the stimulus actually hurts - important for the general arousal and emotional aspects of pain
(are synapses to the reticular formation in pons and medulla; come from neurons in all layers of the dorsal horn)
What is the specific function of the spinomesencephalic pathway?
Activates descending, efferent pathways that modulate pain (actions to help alleviate the pain)
(Are synapses to the mesencephalon, specifically the periaqueductal gray matter* - are from layers I and V of the dorsal horn)
As fibers are added to the anterolateral/spinothalamic tract on its way rostrally to the brain, how are axons from more cervical (superior) axons added to the tract?
Axons from cervical dorsal horn are added MEDIALLY
- contrast with the epicritic (medial leminiscal) pathway in which cervical a are added laterally to the lower
Which type of afferents specifically send out collaterals from the main anterolateral/spinothalamic path to the spinoreticular and spinomesencephalic tracts?
Fibers that project pain (some fibers conduct pain only, others are pain and temperature as well; these “mixed” fibers don’t send out collaterals to the reticular formation of periaqueductal gray)
Which types of fibers mediate “first pain”? Where do they synapse in the dorsal horn?
A delta fibers - synapse in substantia gelatinosa (rexed’s laminae I and II)
These fibers in I and II project to laminae V, which contains the cells that actually send axons across the midline and up the cord.
What is the functional importance of the substantia gelatinosa?
Is the initial site of pain (and temp) modulation and integration.
(A delta and C fibers both first synapse in the substantia gelatinosa)
What kind of pain do C fibers transmit?
“Second” pain - poorly localized, dull pain
(Axons with cells located in layer I of the dorsal horn, the marginal zone, cross the midline and ascend up the spinal cord; contrast with those form A delta fibers, which come from layer V)
Collaterals from where into layer V of the spinal cord is important in the phenomenon of referred pain?
From epicritic system; project on to the same cells in layer V that protopathicsystem is going to
Name for the axons connecting the substantia gelatinosa of different spinal cord layers
Propriospinal tract (has nothing to do with propriception)
In the cortex and thalamus the fibers relaying info on the legs is ______ and ______ within the anterolateral pathway?
Superior and medial
- correspondingly, arm and head are represented inferior and lateral
What is the function of the spinocerebellar tracts?
Relay information about limb position and movement to the cerebellum
Which spinocerebellar tract is primarily responsible for conveying information from the lower limb and body to the cerebellum
Dorsal (posterior) spinocerebellar tract
*info is from muscle spindles (Ia, II) and Golgi tendon organs (Ib)
Which spinocerebellar tract conveys information from the upper limbs and body to the cerebellum?
Cuneocerebellar tract
Cuneatus is the name for the posterior column directing sensory info from the upper, so cuneo= upper
What spinocerebellar tract integrates descending input with proprioceptive info from the lower limbs?
Ventral spinocerebellar tract
Info primarily from Golgi tendon organs (Ib)
What spinocerebellar tract integrates descending info with proprioceptive input from the upper limbs/body?
Rostral spinocerebellar tract
Like the ventral (anterior) tract, but for upper limbs; also gets info primarily from Golgi tendon organs (Ib)
Where do 1st order neurons in the dorsal spinocerebellar tract synapse? Via what structure in the spinal cord do they get there?
Clarke’s nucleus; arrive there via the fascilulus gracilis
Where is Clarke’s nucleus (or Clarke’s column) located?
In the interomedial gray matter of the spinal cord between T2-L2
*these fibers involved in unconscious proprioception
What structure do 2nd order neurons in the dorsal spinocerebellar tract pass through to reach the cerebellum after leaving Clarke’s nucleus/column?
Inferior cerebellar peduncle - travel up to the brain via the Lateral funiculus (via restiform body)
Where does the dorsal spinocerebellar tract decussate?
It doesn’t - remains ipsilateral the whole way from where fibers enter until reaching the cerebellum
Where in the cerebellum do 2nd order neurons from the dorsal spinocerebellar tract travel to?
Mainly to the anterior lobe and vermis
Where do 1st order neurons in the cuneocerebellar tract synapse first? Via what structure do they get there?
Accessory cuneate nucleus - get there via the fascilulus cuneatus
Where is the accessory cuneate nucleus located?
In the rostral medulla
What structure do 2nd order neurons in the cuneo cerebellar tract travel through to get to the cerebellum? Where in the cerebellum do they go to?
Via the inferior cerebellar peduncle - to anterior lobe, vermis, and intermediate zone
Where does the cuneocerebellar tract decussate?
It doesn’t - like the dorsal spinocerebellar, remains ipsilateral to origin all the way to cerebellum
In what layer (lamella) of the spinal cord do 1st order neurons in both the ventral (upper) and rostral (lower) spinocerebellar tracts synapse?
Layer VII (intermediate zone)
What vertebral level is the division between whether afferent fibers will travel in the ventral (lower) or rostral (upper) spinicerebellar tracts?
L3
Ventral = L3-S3
Rostral = above L3
After synapsing in the dorsal horn, what happens to fibers traveling in the ventral spinocerebellar tract? (What structure do they reach the cerebellum through, are there any decussations)
Project over to the contralateral lateral funiculus and then travel up to synapse with neurons in the superior cerebellar peduncle
After synapsing in the superior cerebellar peduncle, what happens to most neurons in the ventral spinicerebellar tract?
Most decussate again to reach the side of cerebellum ipsilateral to the original entry into spinal cord
* these cross over TWICE
After synapsing in the dorsal horn of spinal cord, via what structure do the fibers of the rostral spinocerebellar tract reach the cerebellum? Where do they decussate?
Via the inferior cerebellar peduncle to ipsilateral cerebellum - does NOT decussate
- so the ventral spinocerebellar tract is the only to go through the superior cerebellar peduncle, all 3 others go through inferior cerebellar peduncle
Which if the four spinocerebellar tracts serves as the primary input to the cerebellum from spinal cord propriceptive afferents?
Dorsal spinocerebellar tract - via Clarke’s nucleus
Which system is responsible for relaying somesthesis for the head and face?
Trigeminal system
What nucleus do the cell bodies of 2nd order neurons for the epicritic (fine touch, vibration, proprioception) system for head and face reside?
Chief sensory nucleus of V (analogous to the posterior column/medial leminiscus pathway nuclei - gracile and cuneatus nuclei)
*chief has an “E” for epicritic - mnemonic aid
Which nucleus in the trigeminal system contains cell bodies of 2nd order neurons transmitting protopathic (temp, nociceptive) information for head/face?
Spinal nucleus of V (analogous to the nuclei in the dorsal horns where the 1st order neurons of the anterolateral/spinothalamic synapse = the substantia gelatinosa)
*Spinal has a “P” for protopathic - mnemonic
What nucleus are cell bodies for 1st order afferents for muscle spindles and Golgi tendon organs from head/face found in the trigeminal system?
Mesencephalic nucleus of V (analogous to a displaced DRG, found in brainstem; maybe roughly equivalent to the spinocerebellar tracts in rest of body)
Where do the cell bodies for 1st order neurons transmitting somatosensory info for head/face reside?
In the Trigeminal (Gasserian) ganglion (analogous to the DRG for the spinal cord
Where in the thalamus do fibers from the Trigeminal system travel to?
Ventral posteromedial nucleus (VPM)
*“M” in medial; trigeminal region has the Mouth
(Compare to the other systems, which go to the VPL; these are from Limbs and body, “L” is for limb and lateral)
What is the pathway called between the chief sensory nucleus of V and the VPM in the Trigeminal system? Which neurons decussate in this pathway?
Trigeminal leminiscus - the 2nd order neurons leaving the chief sensory nucleus decussate to end up in the VPM contralateral to the 1st order afferents
*remember these are epicritic fibers
Where do trigeminal leminiscus fibers go after traveling to the VPM?
To the primary somatosensory cortex (postcentral gyrus)
What is the tract form the Spinal nucleus of V to the VPM called? Where does it decussate?
Trigeminothalamic tract - 2nd order neurons leaving the Spinal nucleus decussate to travel to the contralateral VPM from the original afferents
* recall these are protopathic fibers
Via what structure do the fibers in the Trigeminithalamic tract reach the primary somatosensory cortex (postcentral gyrus)?
Posterior limb of the internal capsule
The primary somatosensory cortex on the postcentral gyrus includes what 4 Brodmann’s areas?
3a, 3b, 2, 1
*primary somatosensory cortex is also known as S1
Where is the unimodal (somatosensory only) association cortex known as S2 located?
Parietal operculum
*areas #5 and #7 located in the superior parietal lobule are other unimodal association areas for somesthesis
Which Brodmann’s area is responsible primarily for receiving proprioceptive and pain info from the thalamus?
3A
Which Brodmann’s area receives primarily cutaneous inputs - tactile perception?
3B
In what Brodmann area does further processing of cutaneous input from 3B occur?
Area 1
Which Brodmann area integrates pain, tactile info and proprioceptive info from both areas 3A and 3B?
Area 2 - allows position and edge detection, size perception, etc
- therefore there is parallel processing and also integration b/n modalities(higher order serial processing)
What is the functional/clinical significance of Lissauer’s tract, aka posterolateral fasciculis?
Lesions at a given spinal level will result in a loss of input from segments 2-3 segments below the injury
Where epicritic fibers sensing proprioception send collateral fibers, in addition to those main ones that join and ascend in the posterior columns?
Synapse directly on alpha motoneurons in the ventral horn of spinal cord - part of the monosynaptic stretch reflex
* type 1a afferent from muscle spindles are the ones that synapse directly in the ventral horn (VIII and IX)
; others also are sent to deep layers of the dorsal horn (V-VII)
