Spinal Cord and Meninges Overview

Spinal Cord

• The spinal cord is a hollow tube within the vertebral column, extending from the foramen magnum to the second lumbar vertebra.
• It acts as a sophisticated neural superhighway.
• The spinal cord has 31 segments, each with a pair of spinal nerves.
• It ends at L2 in the conus medullaris, where the cauda equina extends.
• Spinal nerves float in cerebrospinal fluid (CSF).
• Cervical and lumbar enlargements are widened areas of the spinal cord.
• The spinal cord extends from the brain to the coccygeal region, with the following sections: cervical, thoracic, lumbar, sacral, and coccygeal.

Meninges

• Meninges are protective coverings for the brain and spinal cord.
• They provide cushioning and shock absorption.
• Dura mater: Thick fibrous outer layer.
• Arachnoid mater: Middle, wispy layer resembling a spiderweb, composed of collagen and elastic fibers. It acts as a shock absorber and transports dissolved gases, nutrients, and chemical messengers.
• Pia mater: Innermost layer, fused to the neural tissue, containing blood vessels.

Meningeal Spaces

• Epidural space: Situated between the dura mater and the vertebral column, filled with fat and blood vessels.
• Subdural space: Between the dura and arachnoid mater, containing a small amount of fluid.
• Subarachnoid space: Between the arachnoid and pia mater, filled with cerebrospinal fluid (CSF), acting as a fluid cushion; this is where lumbar puncture can be performed.
• Together, the meninges and their fluid-filled spaces, along with skull and vertebral column bones, form a strong protective system for CNS injury.

Internal Spinal Cord Structure

• The spinal cord is divided into anterior median fissure (deep groove) and posterior median sulcus (shallow groove).
• Internal spinal cord also divided into white matter columns, and gray matter horns.
• The horns contain nerve cell bodies.
  • Dorsal horn: Sensory function
  • Ventral horn: Motor function
  • Lateral horn: Autonomic function
• White matter columns are tracts (pathways/axons) running up and down the spinal cord to/from the brain.

Ascending Tracts

• Dorsal column tract: Carries fine-touch and vibration information to the cerebral cortex.
• Spinothalamic tract: Carries temperature, pain, and crude touch information to the cerebral cortex.
• Spinocerebellar tract: Carries information about posture and position to the cerebellum.

Descending Tracts

• Corticospinal tract: Carries orders from the cerebral cortex to motor neurons in the ventral horn of the spinal cord.
• Corticobulbar tract: Carries orders from the cerebral cortex to motor neurons in the brainstem.
• Reticulospinal and rubrospinal tracts: Carry information from various brain regions to the brainstem and ventral horn, coordinating movements.

Spinal Cord Commissures

• Commissures (gray and white) connect the left and right halves of the spinal cord, allowing communication between their sides.
• Central canal: A cavity in the center of the spinal cord, filled with cerebrospinal fluid (CSF).

Spinal Nerves

• Spinal nerves connect the CNS to the outside world (part of PNS).
• They consist of bundles of axons, blood vessels, and connective tissue.
• Spinal nerves carry information to/from the CNS.
• Thoracic spinal nerves project directly to the thoracic body wall, without branching.
• All other spinal nerves branch extensively before reaching peripheral structures (plexuses).

Interneurons

• Interneurons modulate sensory information and coordinate movement patterns.
• They regulate autonomic function.

Reflexes

• Monosynaptic reflexes (tested by doctors) involve a single synapse between afferent and efferent neurons (e.g. knee-jerk).
• Polysynaptic reflexes (e.g. withdrawal reflex) involve reciprocal inhibition (involves multiple synapses).

Primitive Reflexes

• Babinski reflex, Grasp reflex, and Glabellar Tap reflex are associated with specific brain damage.

Spinal Cord Injuries

• Anterior cord syndrome, Central cord syndrome, Brown-Sequard syndrome, and Cauda Equina are categorized spinal cord damage effects.

Additional Information and Concepts

• White matter consists of axons.
• Gray matter encompasses cell bodies.
• Dorsal root is sensory, ventral root is motor.
• Sensory neurons are in the dorsal root ganglion which is outside the cord.