PNS 2

Spinal Nerves Overview

  • Total Segments in Spinal Cord: 31 segments leading to 31 pairs of spinal nerves.

Spinal Nerve Classification

  • Cervical Nerves: 8 pairs

    • Cervical Vertebrae: 7

  • Thoracic Nerves: 12 pairs

  • Lumbar Nerves: 5 pairs

  • Sacral Nerves: 5 pairs

  • Coccygeal Nerve: 1 pair (noted as C0 for differentiation)

Structure of Spinal Nerves

  • Each spinal nerve emerges from the spinal cord through the intervertebral foramen.

  • Rootlets from each segment combine to form:

    • Dorsal Root: carries sensory information; associated with dorsal root ganglia (bulge containing sensory neuron cell bodies).

    • Ventral Root: carries motor information.

  • Combined roots form the spinal nerve, which bifurcates into:

    • Dorsal Ramus (posterior branch)

    • Ventral Ramus (anterior branch)

Function of Posterior Branches

  • Carry sensory information from:*

    • Skin Sensations: includes temperature, touch, vibration, heat, and cold.

  • Each area of the body receives sensory input from a specific spinal cord segment (termed dermatome).

Clinical Relevance of Dermatomes

  • Mapping Example:

    • Sensation at nipple level corresponds with T4 segment.

    • Injury at or below T4 may result in loss of sensation below this level.

    • Sensation at the belly button level corresponds with T10; injury at T10 will lead to loss of sensation below the umbilicus.

  • C1: Not represented in dermatomes as it joins directly to the cranium.

Assessment Techniques

  • Neurological examinations historically required detailed sensory tests (e.g., applying cotton to different body areas to check sensation).

  • Modern imaging (CT scans, MRIs) helps pinpoint exact spinal injuries.

Anterior Branch Functionality

  • Anterior branches connect to form structures called plexuses.

    • Key Enlargements:

    • Cervical Plexus

    • Lumbosacral Plexus

    • The cervical plexus runs from C1 to T12 and the lumbosacral plexus runs from T12 to C0.

  • Intercostal nerves originate from T2 to T11; supply muscles between ribs, contributing to breathing mechanics.

Important Intercostal Considerations

  • The bundle of intercostal nerve, artery, and vein (VAN) runs along the inferior border of each rib, essential for anatomical understanding in thoracic regions.

Conclusion

  • The session concludes with a promise to discuss major and minor branches of spinal nerves in future meetings alongside clinical applications related to these anatomical concepts.