Lec. 4/5

Question 1

Describe primary somatic sensory neurons’ unique morphology (3)

Answer 1

• unipolar (no dendrites)
• long axon starts in skjn/muscle then projects to spinal cord

Cell body sits outside spinal cord and form stalks

Question 2

What are dorsal root ganglion?

How many pairs of them do we observe?

Answer 2

Cell bodies of primary somatic sensory neurons sitting right outside the spinal cord.

There are 31 pairs along the spinal cord

Question 3

What are neuronal cell body clusters called in the PNS vs CNS?

Answer 3

Ganglion - PNS

Nucleus - CNS

Question 4

What are the segments of the spinal cord?

Answer 4

31 segments in total:

• 8 cervical (arms)
• 12 thoracic
• 5 lumbar (legs)
• 5 sacral
• 1 coccygeal

Question 5

What are the enlargements observed in the spinal cord?

Answer 5

Cervical and lumbar enlargements, corresponding to limb innervating fibers.

Question 6

What is particular about the lumbar segment?

Answer 6

The lumbar cistern! An empty CSF filled space in the spine, in which all lumbar fibers must project up into (don’t enter on sides and join spinal cord, for there isn’t a spinal cord en tant que tel).

These projections form the cauda equina (horse’s tail)

Question 7

What kind of ‘matter’ do we see in the nervous system?

Answer 7

Gray matter -> cell bodies

White matter -> axons

Question 8

In terms of spinal cord anatomy, where do sensory vs motor neurons enter/exit

Answer 8

Primary somatic sensory afferents enter through dorsal roots

Motor neurons project to muscle fibers by exiting the ventral roots

Question 9

What are the regions innervated by spinal neurons called?

Answer 9

Dermatome

Question 10

There is a distinction of where sensory afferents enter depending on the stimulus. Explain.

Answer 10

Fine touch/proprioception afferents enter more medially (closer to middle)

Vs

Pain/temperature afferents that enter more laterally

Question 11

What is the organization of sensory vs motor neurons vs interneurons/autonomic neurons within the spinal cord?

Answer 11

Dorsal horn -> somatic sensory

Ventral horn -> motor

In between -> interneurons/autonomic

Question 12

What tract do pain/temp afferents enter through? What do these connected neurons then do?

Answer 12

They enter through the Lissauer tract, synapse to dorsal horn neurons. These neurons then crossover to ascend the anterolateral column.

Question 13

What is the somatotopic organization of the sensory columns? Describe each.

Answer 13

Map of the body plan!

Dorsal column (sensory/proprioception)

• > Medial -> legs
• > lateral -> arms

Anterolateral column (pain/temp)

• > Medial -> arms
• > lateral -> legs

Question 14

What’s the somatotopic significance of the posterior intermediate sulcus in the spinal cord

Answer 14

It’s the dividing line between the arms and leg in the ascending fine touch/proprioception tracts