Somatosensory System II

Question 1

Somatosensory sensation from trunk and limbs

Answer 1

DC-ML and ALS

Question 2

Somatosensory sensation from the head

Answer 2

Proprioception & fine touch —> principal nucleus V CN
Gross touch, Tª & pain —> V spinal nucleus
Muscle spindles —> mesencephalic nucleus of trigeminal

Question 3

Trunk and limbs somatosensory information

Answer 3

DC-ML
ALS: ant & lat spinothalamic tracts

Question 4

DC-ML pathw —> relay stations

Answer 4

1st —> medulla
2nd —> thalamus
3rd —> cortex

Question 5

DC - ML conveys

Answer 5

Proprioceptive & fine touch perception

Question 6

DC - ML pathway

Answer 6

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)

Question 7

1st relay station, in the Medulla (DC -ML) - fibers

Answer 7

Thickest type + largest diameter —> Type I & Type II fibers (A-alpha and A-beta)

Question 8

1st relay station, in the Medulla (DC -ML) - pathway

Answer 8

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

Question 9

Inferior limb fibers ascend trough … (DC-ML)

Answer 9

Gracile fascicle, medial

Question 10

Superior limb fibers ascend through… (DC-ML)

Answer 10

Cuneate fascicle, lateral

Question 11

After decussating, gracile fascicle fibers from the lower limb end up being

Answer 11

Inferior

Question 12

After decussating, cuneate fascicle fibers from the lower limb end up being

Answer 12

Middle-superior

Question 13

For rostral parts of ML (once its turned horizontally), lower limb fibers are

Answer 13

Lateral

Question 14

For rostral parts of ML (once its turned horizontally), upper limb fibers are

Answer 14

Medial

Question 15

All somatosensory information from the trunk and limbs makes relay (2nd synapse) in

Answer 15

Ventral posterolateral nucleus of the thalamus (VPL)

Question 16

In the thalamus, lower limb fibers are … (DC-ML)

Answer 16

More lateral in the VPL

Question 17

In the thalamus, upper limb fibers are … (DC-ML)

Answer 17

More medial in the VPL

Question 18

The 3rd neuron will ascend from thalamic nucleus through

Answer 18

Thalamocortical tracts

Question 19

Regarding the cortex, lower limb fibres will go to … (DC-ML)

Answer 19

Medial aspect of the 1ary somatosensory cortex

Question 20

Regarding the cortex, upper limb fibres will go to … (DC-ML)

Answer 20

Dorsolateral aspect of the 1ary somatosensory
cortex

Question 21

ALS conveys

Answer 21

Gross touch, pain and Tª

Question 22

ALS pathway

Answer 22

Thick A-delta and C fibers enter laterally —> SYNAPSE
in post horn —> DECUSSATE ascending in
contralateral anterolateral column

Question 23

ALS fibers

Answer 23

Type III or A-delta fibers
Type IV or C fibers

Question 24

1st relay station: spinal cord (ALS)

Answer 24

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)

Question 25

Lesions affecting anterior commissure will be affecting (spinal cord, ALS)

Answer 25

Pain, Tª and gross touch from both hemi bodies

Question 26

Lesion in the spinal cord after the decussation will affect

Answer 26

Contralateral hemibody

Question 27

2nd relay station: thalamus (ALS)

Answer 27

End at the Ventral posterolateral nucleus (VPL)

Question 28

Lower limb fibers are … (ALS)

Answer 28

Lateral

Question 29

Arms and trunk fibers are … (ALS)

Answer 29

Medial

Question 30

In thalamus, lower limb fibers synapse … (ALS)

Answer 30

More laterally

Question 31

In thalamus, upper limb fibers synapse … (ALS)

Answer 31

More medially

Question 32

After synapsing at the VPL, 3rd neurons ascend to the cortex, to the … (ALV)

Answer 32

1ary sensory cortex

Question 33

In the cortex, lower limb fibers are … (ALS)

Answer 33

Medial

Question 34

In the cortex, upper limb fibers are … (ALS)

Answer 34

Dorsolateral

Question 35

Somatosensory inputs from the head are conveyed by

Answer 35

Trigeminal nerve

Question 36

Trigemino-thalamic pathways

Answer 36

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

Question 37

Trigeminal nerve nuclei in brainstem

Answer 37

Principal nucleus Spinal nucleus Mesencephalic nucleus

Question 38

Principal nucleus of the V CN location

Answer 38

Mid portions of the pons. Lat to motor nucleus of the V CN.

Question 39

Principal nucleus of V CN receive

Answer 39

Type I and Type II neurons (thick): proprioception + fine touch perception Thinner fibers: proprioception + fine touch from face

Question 40

Principal nucleus of V CN - after fibers arrive..

Answer 40

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)

Question 41

Principal nucleus of V CN - exception

Answer 41

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

Question 42

Fibers from the face ascend … (to principal nucleus of VCN)

Answer 42

Ventrally

Question 43

Fibers from oral cavity ascend … (to principal nucleus of VCN)

Answer 43

Dorsally

Question 44

Laterally in the VPM (ventral posteromedial nucleus)

Answer 44

Skin and mucosa form the face

Question 45

Medial in the VPM (ventral posteromedial nucleus)

Answer 45

Info from oral cavity (periodontal ligaments)

Question 46

Spinal nucleus is where

Answer 46

Gross touch, pain and Tª inputs from the face mostly reach (Type III + Type IV fibers)

Question 47

Spinal nucleus of V CN - fibers pathway

Answer 47

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)

Question 48

Mesencephalic nucleus of V CN contains

Answer 48

Cell bodies of Type IA fibers (or A-alpha) from muscle spindles of masticatory muscles

Question 49

Mesencephalic nucleus of V CN - pathway

Answer 49

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).

Question 50

Muscle spindles give rise to

Answer 50

Stretch reflexes

Question 51

Neurons in mesencephalic nucleus are

Answer 51

Afferent arm of the Mandibular reflex

Question 52

Mandibular reflex

Answer 52

Afferent fiber = muscle spindle neuron in mesencephalic nucleus Efferent branch = motor alpha neuron form motor trigeminal nucleus

Question 53

VPL and VPM are

Answer 53

sites of relay for all somatosensory information

Question 54

VPL = for

Answer 54

somatosensory info from trunk and limbs (both DC-ML and ALS)

Question 55

VPM = for

Answer 55

somatosensory info from head. Inputs from face reach lat, info from oral cavity (teeth) reach med.

Question 56

Medial most part of the VPM receives

Answer 56

Taste information

Question 57

VPM projects to

Answer 57

Ventrolateral aspects of the 1ary somatosensory cortex (info from the face processed)

Question 58

VPL ends in

Answer 58

dorsolateral and medial aspects of the 1ary sensory cortex (limb and trunk somatosensory inputs)

Question 59

1ary somatosensory cortex is in

Answer 59

Parietal lobe, in postcentral gyrus, just post to central sulcus.

Question 60

primary somatosensory cortex corresponds to

Answer 60

Brodman defined areas 3, 1 and 2

Question 61

Distinction between the three Brodman defined areas is

Answer 61

That different modalities end in each area (All the tracts that have been separately gathering info, end in the = area but separately, w/ distribution)

Question 62

Somatosensory cortices are classified as sensory due to

Answer 62

Developed layer 4 → granular cortices

Question 63

Somatosensory cortices (1ary, 2ary and associative)

Answer 63

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