Spinal cord/brainstem #2

Question 1

WHat combination is need for a CONTROLLED muscle reflex

Answer 1

Higher thinking Reflex action **if it went to the cortex this would take too long.

Question 2

Pars Basalaris

Answer 2

enlargement of pons that contains the facial neurons

Question 3

Where does the Pyramidal/corticospinal tract cross over?

Answer 3

Medullary pyramids, means that one side of the brain controls the other side of the body!

Question 4

Describe the pathway of DISCRIMINATIVE/sensory sensation (periphery > inwards)

Answer 4

Dorsal-column Medial Lemniscal pathway

1. Encapsulated nerve endings travels in via the dorsal root ganglion to enter the spinal cord
2. Input synapses at the gracile (LL) or cuneate (UL) fusiculus in the dorsal funiculi/column, and some go into Lamina 3/4
3. At Lamina 3/4 the fibres converge, and 50% in conveyed up into the dorsal column
4. These ALL travel up the dorsal column to a region just behind the medullary pyramids in the tegmentum, ‘Gracile and Cuneate Nuclei’
5. This is where the decussation occurs as internal arcuate fibres into the medial Lemniscus of the tegmentum
6. Travel a medial path up the white matter tract of the ML, to sit just behind the substantia Nigra of the midbrain
7. From here they travel up into the thalamus and synapse in VP
8. Go out via the Internal capsule to the area with the specific homonculus rep. in the primary sensory cortex.

Question 5

Internal arcuate Fibres

Answer 5

Big, myelinated fibres that course over from one side to another as cell bodies into a white matter tract (medial lemniscus)

Question 6

Describe the pathway of pain and temperature .

“Lateral spinothalamic tract”

Answer 6

1. Slow conducting, unmyelinated free nerve endings travel into the spinal cord via the dorsal root ganglion, in the Dorsal Tract of Lissauer synapsing on lamina 1 and 2
2. They then synapse with neurons that travel through tje Anterior white commisure and into the ventral funniculus as the “spinothalamic tract”.
3. These fibres dessucate immediately at the spinal segmental level of the dorsal ganglion!
4. They ventrally travel a little further back in the tegmentum, the STT merging in the pons with the medial lemniscus.
5. By the midbrain the STT is just a dot within the medial lemniscus.
6. Travels also to the VP > internal capsule > sensory cortex

Question 7

From looking at the spinothalamic tract and the dorsal medial lemniscus pathway what are the similarities?

Answer 7

Although the start and dessucate differently, the medial lemniscus and the STT merge within the pons and then continue to the primary sensory cortex on the same path.