Somatosensory System II Flashcards
Somatosensory sensation from trunk and limbs
DC-ML and ALS
Somatosensory sensation from the head
Proprioception & fine touch —> principal nucleus V CN
Gross touch, Tª & pain —> V spinal nucleus
Muscle spindles —> mesencephalic nucleus of trigeminal
Trunk and limbs somatosensory information
DC-ML
ALS: ant & lat spinothalamic tracts
DC-ML pathw —> relay stations
1st —> medulla
2nd —> thalamus
3rd —> cortex
DC - ML conveys
Proprioceptive & fine touch perception
DC - ML pathway
1º sensory neurons in spinal dorsal root ganglia —> Info to spinal cord - central process courses up along post funiculus of SAME side to medulla (within white matter of spinal cord)
Medulla: 1st relay / synapse —> fibers DECUSSATE = ML -> ascends along brainstem on OPPOSITE side -> neurons reach thalamus.
Thalamus: 2nd relay —> synapse w/ neurons in thalamic nuclei.
The 3rd neuron —> Thalamocortical projections - projects to cerebral cortex (area that deals w/ sensory info, mainly 1ª somatosensory cortex)
1st relay station, in the Medulla (DC -ML) - fibers
Thickest type + largest diameter —> Type I & Type II fibers (A-alpha and A-beta)
1st relay station, in the Medulla (DC -ML) - pathway
Enter medially to dorsal horn
Ascend through DC (provide some collaterals before ascending, to enable reflexes like stretch one)
Main axons
- travel on = side (Gracile (LL) / Cuneate (UL) fascicles)
- reach 1st site of relay in medulla
- enter corresponding nuclei in medulla (Gracile or Cuneate)
- synapse
- DECUSSATE
- form + continue ascending as medial lemniscus through Pons & Medulla
- reach thalamus
Inferior limb fibers ascend trough … (DC-ML)
Gracile fascicle, medial
Superior limb fibers ascend through… (DC-ML)
Cuneate fascicle, lateral
After decussating, gracile fascicle fibers from the lower limb end up being
Inferior
After decussating, cuneate fascicle fibers from the lower limb end up being
Middle-superior
For rostral parts of ML (once its turned horizontally), lower limb fibers are
Lateral
For rostral parts of ML (once its turned horizontally), upper limb fibers are
Medial
All somatosensory information from the trunk and limbs makes relay (2nd synapse) in
Ventral posterolateral nucleus of the thalamus (VPL)
In the thalamus, lower limb fibers are … (DC-ML)
More lateral in the VPL
In the thalamus, upper limb fibers are … (DC-ML)
More medial in the VPL
The 3rd neuron will ascend from thalamic nucleus through
Thalamocortical tracts
Regarding the cortex, lower limb fibres will go to … (DC-ML)
Medial aspect of the 1ary somatosensory cortex
Regarding the cortex, upper limb fibres will go to … (DC-ML)
Dorsolateral aspect of the 1ary somatosensory
cortex
ALS conveys
Gross touch, pain and Tª
ALS pathway
Thick A-delta and C fibers enter laterally —> SYNAPSE
in post horn —> DECUSSATE ascending in
contralateral anterolateral column
ALS fibers
Type III or A-delta fibers
Type IV or C fibers
1st relay station: spinal cord (ALS)
Enter dorsal part of spinal cord + lateral, closer to post horn —> synapse + decussate = ant white commissure.
Ascend via anterolateral funiculus (between lat - ant funiculi) —> some end in different areas of brainstem and others ascend directly to thalamus.
For brainstem, ALS provides collaterals: pain info and gross touch -> connected to different structures of brainstem (integrated at unconscious level for reflexes -> autonomic)
Lesions affecting anterior commissure will be affecting (spinal cord, ALS)
Pain, Tª and gross touch from both hemi bodies
Lesion in the spinal cord after the decussation will affect
Contralateral hemibody
2nd relay station: thalamus (ALS)
End at the Ventral posterolateral nucleus (VPL)
Lower limb fibers are … (ALS)
Lateral
Arms and trunk fibers are … (ALS)
Medial
In thalamus, lower limb fibers synapse … (ALS)
More laterally
In thalamus, upper limb fibers synapse … (ALS)
More medially
After synapsing at the VPL, 3rd neurons ascend to the cortex, to the … (ALV)
1ary sensory cortex
In the cortex, lower limb fibers are … (ALS)
Medial
In the cortex, upper limb fibers are … (ALS)
Dorsolateral
Somatosensory inputs from the head are conveyed by
Trigeminal nerve
Trigemino-thalamic pathways
V CN enters brainstem at the level of pons.
1st neuron has its body in trigeminal ganglion.
Central processes extend —> synapse in trigeminal nuclei (2nd neurons).
2nd neuron DECUSSATES, ascends to thalamus —> reaches contralateral thalamus, ending in VPM (post part of the complex) —> somatosensory cortex
Trigeminal nerve nuclei in brainstem
Principal nucleus
Spinal nucleus
Mesencephalic nucleus
Principal nucleus of the V CN location
Mid portions of the pons.
Lat to motor nucleus of the V CN.
Principal nucleus of V CN receive
Type I and Type II neurons (thick): proprioception + fine touch perception
Thinner fibers: proprioception + fine touch from face
Principal nucleus of V CN - after fibers arrive..
Synapse w/ 2nd neurons in the nucleus
2nd neuron exits the nucleus
Majority of fibers DECUSSATE and course medial to medial lemniscus —> thalamus.
These fibers = Ventral trigeminothalamic tract —> end in Ventral posteromedial nucleus of the thalamus (VPM)
Principal nucleus of V CN - exception
Fibers from oral cavity end in a specific area of the principal nucleus —> ascend ipsilaterally (JUST THESE) —> end in medial most part of VPM of = side!
These ipsilateral fibers = Dorsal trigeminothalamic tract
Fibers from the face ascend … (to principal nucleus of VCN)
Ventrally
Fibers from oral cavity ascend … (to principal nucleus of VCN)
Dorsally
Laterally in the VPM (ventral posteromedial nucleus)
Skin and mucosa form the face
Medial in the VPM (ventral posteromedial nucleus)
Info from oral cavity (periodontal ligaments)
Spinal nucleus is where
Gross touch, pain and Tª inputs from the face mostly reach (Type III + Type IV fibers)
Spinal nucleus of V CN - fibers pathway
Central processes enter Pons and depending on the
info they convey, they look for the corresponding area of the spinal nucleus —> form the spinal tract.
Synapse —> 2nd neuron DECUSSATES —> incorporate into Ventral trigeminothalamic tract.
(Neurons from spinal + principal nuclei will form part of this tract)
Mesencephalic nucleus of V CN contains
Cell bodies of Type IA fibers (or A-alpha) from muscle spindles of masticatory muscles
Mesencephalic nucleus of V CN - pathway
Somas in the midbrain
Mesencephalic nucleus: central process —> thin chain between periaqueductal gray substance - tectum (still 1ary sensory neurons).
Central processes go down = mesencephalic tract —> SYNAPSES in principal trigeminal nucleus!
Collaterals to spinal nucleus and motor nucleus of V (reflexes).
Muscle spindles give rise to
Stretch reflexes
Neurons in mesencephalic nucleus are
Afferent arm of the Mandibular reflex
Mandibular reflex
Afferent fiber = muscle spindle neuron in mesencephalic nucleus
Efferent branch = motor alpha neuron form motor trigeminal nucleus
VPL and VPM are
sites of relay for all somatosensory information
VPL = for
somatosensory info from trunk and limbs (both DC-ML and ALS)
VPM = for
somatosensory info from head.
Inputs from face reach lat, info from oral cavity (teeth) reach med.
Medial most part of the VPM receives
Taste information
VPM projects to
Ventrolateral aspects of the 1ary somatosensory cortex (info from the face processed)
VPL ends in
dorsolateral and medial aspects of the 1ary sensory cortex (limb and trunk somatosensory inputs)
1ary somatosensory cortex is in
Parietal lobe, in postcentral gyrus, just post to central sulcus.
primary somatosensory cortex corresponds to
Brodman defined areas 3, 1 and 2
Distinction between the three Brodman defined areas is
That different modalities end in each area
(All the tracts that have been separately gathering info, end in the = area but separately, w/ distribution)
Somatosensory cortices are classified as sensory due to
Developed layer 4 → granular cortices
Somatosensory cortices (1ary, 2ary and associative)
Sensory info —>
1ary sensory cortex
2ary sensory cortices / unimodal association cortices
- associate info from S1
- connected to higher order nuclei in thalamus
Heteromodal association cortices / Higher order association cortices
- integrate different somatosensory modalities of info)
- most common are parietal lobe and prefrontal cortex
