L19 - Rootlets, roots, spinal nerves

Question 1

31 pairs of spinal nerves

Answer 1

8 - cervical (c1-7 SUPERIOR to vertebrae, c8 between c7 and T1)
12 - thoracic (T1-12)
5 - lumbar (L1-5)
5 - sacral (S1-5)
1- coccygeal (C1)

Question 2

Spinal nerves are located in…

Answer 2

intervertebral foramen

Question 3

Dorsal/ventral rootlets arise

Answer 3

Dorsal ROOTLETS combine to form dorsal ROOT, then dorsal root GANGLION (containing sensory cell bodies. (Innovate back)
- Same for ventral but ventral doesn’t have GANGLION as the motor neurons are already in the spinal cord. (Innovate front)
- Dorsal and ventral root combine to form SPINAL NERVE!
- Spinal nerve splits into dorsal (innovates back) and ventral ramus (innovates front)

Question 4

Casing

Answer 4

Endoneurium: around nerve
Perineurium: around bundle of nerves (fascicle)
Epineurium: Around whole nerve

EPE

Question 5

Dorsal root (ARRIVE = afferent, EXIT = efferent)

Answer 5

• Sensory pseudounipolar neurons
• Afferent (Towards CNS)
• Cell bodies in dorsal root ganglion
• Central process in DORSAL GREY horn

Question 6

Ventral root

Answer 6

• Motor neurons (lower)
• Efferent (away from CNS)
• Somatic lower motor bodies in VENTRAL horn
• Autonomic lower are in LATERAL horn

Question 7

Roots vs rami

Answer 7

Root = sensory OR motor
Rami = mixed

Question 8

Lower motor neurons

Answer 8

• Motor response initiated after brain processes info
• Upper motor neuron in precentral gyrus (motor cortex)
• Axon travels via:
  Internal capsule
  Brainstem
  Medullary pyramids
  Lateral corticospinal tract (in lateral funiculus)
• Synapses with lower motor neuron in ventral horn of spinal cord
• Lower motor axon exits via:
  Ventral rootlets → ventral root → spinal nerve
• Reaches and innervates forearm/hand muscles