Lecture 9: Spinal somatosensory pathways

Question 1

Why do some parts of the body have highly discriminative touch (eg hand) and others not (eg. back)

Answer 1

The Less discriminative sensory areas have receptors with larger sensory fields such that an objects need to be further away from each other to be distinguished as 2 separate touches.
The highly discriminative sensory areas of the body have lots of touch receptors with a small receptive field.

Question 2

How is information from the Arm, Trunk and Legs carried in the ascending sensory tracts from the spinal cord

Answer 2

The fibres run in separate bundles, with the Arm bundle most medial A–> T–> L, and in other cases, the arm is the most Anterior of the bundles

Question 3

Describe the path of somatosensory information from the face via Trigeminal nerve

Discriminative touch, vibration, proprioception

Answer 3

1. Primary sensory neurons (V1, V2, V3 cutaneous nerves for discrim touch)
   Enter through the trigeminal ganglia
2. Synapses on the primary sensory trigeminal nucleus to 2nd order neuron
3. 2nd order neuron decussates to the other side, ascends with Medial lemniscus and synapses at the Ventro posterior Medial thalamus
4. 3rd neuron travels up through internal capsule to the face part of the cortex.

Question 4

What are the 3 parts of the other nucleus for the trigeminal sensory info and what specific info is it for?

How does the path continue after that

Answer 4

In the Spinal Trigeminal nucleus

Most superior:

1. Pars Oralis: crude touch
2. Pars Interpolaris: temperature
3. Pars Caudalis: pain

After synapsing, 2nd order neuron decussates and ascends with med. lemniscus
Synapses with VP-m of thalamus, then to the sensory cortex.

Question 5

Describe the Spinoreticular pathway (maybe dnk)

Answer 5

White matter tract that travels adjacent to the Spinothalamic tract and is involved in the modulation of pain response.
It has fibres that come off to synapse with regions in the brainstem- in the reticular formation.

It also involves the Intralaminar thalamic nuclei which is involved in associated pain: being fearful of noxious/painful stimuli for the future which projects to the limbic system and other parts of the brain.

Question 6

Describe the path motor innervation of the jaw by the trigeminal nerve

(most of the facial muscles are by CN7 which synapse on upper face (50% each) and lower face muscles 100% opposite side)

Answer 6

1. An upper motorneuron from the face part of the motor cortex descends and synapses with the trigeminal motor nuclei on both sides (50% each for fine motor coordination).
2. 2nd order neuron from each of the trigeminal motor nuclei exit through the trigeminal ganglion, through V3 there