Spinal Cord and Spinal Nerves Notes

Peripheral Nervous System (PNS)

• Includes the somatic nervous system and the motor division of the autonomic nervous system.

Anatomy of the PNS

• Peripheral ganglia
• Spinal and cranial nerves
• Associated central nervous system (CNS) structures

Spinal Cord

• Extends from the foramen magnum to the first or second lumbar vertebrae.

Regions:

• Cervical
• Thoracic
• Lumbar
• Sacral
• Coccygeal
• 31 pairs of spinal nerves.

Conus Medullaris

Meninges

• Connective tissue surrounding the brain and spinal cord.

Functions:

• Protection
• Contains cerebrospinal fluid
• Forms partitions inside the skull

Dura Mater

Subdural Space

Arachnoid Mater

Subarachnoid Space

• Contains CSF and blood vessels.

Pia Mater

• Contains many small blood vessels.

Organisation in the Spinal Cord

CNS vs. PNS

CNS

• Brain and Spinal Cord
• Grey matter: cell bodies, dendrites, unmyelinated axons, axon terminals, and neuroglia
  • Cortex of brain and nuclei
  • Outer cortex (and deep nuclei)
  • Inner
• White matter: myelinated axons
  • Nerve tracts

PNS

• Ganglion
• Nerves
• Deeper
• Outer

Sensory and Motor Pathways

• Sensory information travels through the dorsal roots.
• Motor information travels through the ventral roots.
• Spinal nerves are mixed: containing both sensory and motor neurons.

Motor Neuron Cell Bodies

• Located in the horns of the grey matter.
  • Somatic: ventral horn
  • Autonomic: lateral horn

Nerve Coverings

• Connective tissue with 3 layers.

Endoneurium

• Surrounds each axon, including Schwann cells.

Perineurium

• Surrounds a fascicle (a group of axons).

Epineurium

• Surrounds several fascicles, forming a nerve.
• A nerve is a bundle of axons and their sheaths in the PNS.

Organisation of Spinal Nerves

Vertebral Column and Spinal Nerve Pairs

• Cervical: 8 pairs, 7 bones
• Thoracic: 12 pairs, 12 bones
• Lumbar: 5 pairs, 5 bones
• Sacral: 5 pairs, 5 bones
• Coccygeal: 1 pair, 5 fused bones (= 1 bone)