8 - Central Somatosensory Pathways

Question 1

Relationship between where afferent fibres enter spinal cord and spatial location of these afferents within the spinal cord

Answer 1

The lower down an afferent enters the spinal cord, the closer to the midline it is.

Question 2

*Ascending mechanosensory pathway

Answer 2

Question 3

Where does the ascending mechanosensory tract cross sides?

Answer 3

At dorsal column nuclei primary sensory afferents synapse with a secondary afferent, which travels contralaterally. Then travels upwards in the medial lemniscus.

Question 4

Path of medial lemniscus

Answer 4

Medial lemniscus begins centrally, travels laterally as it ascends until afferents in it synapse with those in thalamus

Question 5

Three neuron mechanosensory afferent pathway.

Answer 5

First cell body in dorsal root ganglion Second cell body in dorsal column nuclei Third is in the thalamus

Question 6

Path of afferents from muscle spindles

Answer 6

Ascend contralaterally and ipsilaterally in dorsal columns (spinocerebellar tracts). Travel to cerebellum

Question 7

Part of thalamus that mechanosensory pathways travel to

Answer 7

Information from the body travels to the ventral posterior thalamus, lateral part. Information from face travels through trigeminal nerve to the ventral posterior thalamus, medial part

Question 8

Where does the ventral part of the thalamus project to? 1 2 3

Answer 8

1) The post-central gyrus of the cortex (ridge behind the central sulcus). AKA primary somatosensory cortex (S1). 2) Secondary somatosensory area 3) Posterior parietal cortex

Question 9

What occurs in posterior parietal cortex?

Answer 9

High-level synthesis of space (hence tactile information from ventral thalamus projects here)

Question 10

*Subdivisions of primary somatosensory cortex

Answer 10

Question 11

Which side of the body does one lobe of the primary somatosensory cortex map?

Answer 11

Contralateral. Four parallel maps (one for each subdivision - 1, 2, 3a, 3b)

Question 12

Subdivision of primary somatosensory cortex that receives most information

Answer 12

3b

Question 13

Role of subdivision 1 of primary somatosensory cortex

Answer 13

Texture differentiation

Question 14

Parts of the brain that subdivisions of primary somatosensory cortex project to 1 2

Answer 14

1) Secondary somatosensory cortex (conscious cognition of object). Projects to amygdala, hippocampus. 2) Parietal areas 5, 7. Projects to motor, premotor cortical areas

Question 15

* Projections from the primary somatosensory cortex

Answer 15

Question 16

Example of parcellation in the cerebral cortex

Answer 16

Ocular dominance columns

Question 17

Effect of amputation of a digit on cortical mapping of digits

Answer 17

Neuroplasticity demonstrated. Region is remapped, neurons that were receiving input from removed digit receive input from adjacent digits (after only a few months). Not known where exactly this cortical plasticity comes from

Question 18

Limit of central plasticity

Answer 18

Can’t change identity of signal (EG if swap over radial and ulnar nerves, these won’t remap to supply respective areas)

Question 19

Implication of phantom limbs

Answer 19

Map of the body is cortical, not just from receiving input from mechanoreceptors.