Chapter_14_-_Spinal_Cord_and_Nerves_Student

Chapter 14: Spinal Cord and Spinal Nerves

Overview

  • Author: Kenneth S. Saladin

  • Edition: Sixth Edition

  • Publisher: McGraw-Hill Education (2020)


Surface Anatomy of the Spinal Cord

Regions

  • Cervical

  • Thoracic

  • Lumbar

  • Sacral

Enlargements

  • Cervical Enlargement: Responsible for innervating the arms.

  • Lumbosacral Enlargement: Responsible for innervating the lower limbs.

Key Structures

  • Medullary Cone: Tapered end of the spinal cord.

  • Cauda Equina: Bundle of spinal nerve roots extended beyond the spinal cord.

  • Terminal Filum: Fibrous extension anchoring the spinal cord.


Spinal Meninges

Layers of Meninges

  • Dura Mater (Dural Sheath)

    • Tough, outer layer.

    • Contains the epidural space.

  • Arachnoid Mater

    • Middle layer.

    • Subarachnoid Space: Contains cerebrospinal fluid (CSF).

  • Pia Mater

    • Delicate, inner layer, supports blood vessels to the spinal cord.

    • Denticulate Ligaments: Anchors spinal cord to vertebrae.


Cross-Sectional Anatomy of the Spinal Cord

Gray Matter

  • Regions:

    • Posterior Horn

    • Lateral Horn (only in thoracic region)

    • Anterior Horn

  • Gray Commissure: Connects left and right sides.

  • Characteristics: Contains few myelinated axons.

White Matter

  • Columns (Funiculi):

    • Posterior Funiculus

    • Lateral Funiculus

    • Anterior Funiculus

  • Contains the myelinated axons; connected by the white commissure.


Spinal Tracts

Types of Tracts

  • Ascending Tracts: Carry sensory information to the brain.

  • Descending Tracts: Carry motor information from the brain.

    • Decussation: Many tracts cross midline, which means origin and destination are on opposite sides of the body.

    • Some tract connections remain ipsilateral (same side).


General Anatomy of Nerves and Ganglia

Structure of Nerves

  • Components:

    • Epineurium: wraps the entire nerve.

    • Perineurium: wraps a fascicle of axons.

    • Endoneurium: wraps around a single axon.

Anatomy of a Ganglion

  • Ganglion: Cluster of cell bodies outside of the CNS.


Spinal Nerves

Overview

  • Total of 31 pairs:

    • Cervical: C1–C8

    • Thoracic: T1–T12

    • Lumbar: L1–L5

    • Sacral: S1–S5

    • Coccygeal: Co1

Proximal Branches

  • Posterior Dorsal Root: Sensory input.

  • Dorsal Root Ganglion: Contains sensory neuron cell bodies.

  • Anterior Ventral Root: Motor output.

Distal Branches

  • Posterior Dorsal Ramus: Innervates deep muscles and skin of the back.

  • Anterior Ventral Ramus: Larger, innervates front and limbs, gives rise to plexuses, especially intercostal nerves.


Spinal Nerve Plexuses

Major Plexuses

  • Cervical Plexus: Includes innervation of neck and diaphragm (phrenic nerve).

  • Brachial Plexus: Supplies upper limbs (includes musculocutaneous, radial, median, and ulnar nerves).

  • Lumbar Plexus: Innervates lower back and legs (includes femoral and obturator nerves).

  • Sacral Plexus: Supplies lower body, includes sciatic nerve.

  • Coccygeal Plexus: Innervates lower sacrum and coccyx.


Specific Plexuses

Cervical Plexus

  • Nerves:

    • Hypoglossal, Lesser Occipital, Great Auricular, Transverse Cervical, Phrenic Nerve.

Brachial Plexus

  • Complexity of branches serving shoulder and arm:

    • Dorsal Scapular, Suprascapular, Musculocutaneous, Median, Ulnar, Radial Nerves.

Lumbar Plexus

  • Important branches include:

    • Iliohypogastric, Ilioinguinal, Genitofemoral, Obturator, Femoral Nerves.

Sacral and Coccygeal Plexuses

  • Key Nerves: Sciatic nerve (Common Fibular and Tibial branches), pudenal nerve.


Cutaneous Innervation and Dermatomes

  • Dermatome: Area of skin innervated by specific spinal nerve.

  • Maps show the skin areas corresponding to spinal nerves.


Clinical Terms to Know

  • Paraplegia: Paralysis of both lower limbs (lesions from T1 to L1).

  • Quadriplegia: Paralysis of all four limbs (lesions above C5 requiring ventilation support).

  • Hemiplegia: Paralysis on one side of the body, often due to stroke.


Conclusion

  • End of Chapter 14: Comprehensive overview of the anatomy and functions of the spinal cord and spinal nerves.

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