3.1 Nervous System: Spinal Cord Topography

3.1 Nervous System: Spinal Cord Topography

Divisions of the Nervous System

• CNS - Central Nervous System:

  • Brain

  • Spinal Cord

• PNS - Peripheral Nervous System:

  • Sensory Division:

  • Visceral Sensory Division

  • Somatic Sensory Division

  • Motor Division:

  • Visceral Motor Division

  • Somatic Motor Division

  • Sympathetic Division

  • Parasympathetic Division

Overview of Spinal Cord

• Importance: The spinal cord links the brain to the body.

• Length/Size: Extends from the foramen magnum to L1-L2 level; 40-50 cm long and 1-1.5 cm in diameter.

• Structure: 31 pairs of spinal nerves emerge from the spinal cord.

Spinal Cord Organization

The spinal cord is divided into four different regions:

• 8 Cervical

• 12 Thoracic

• 5 Lumbar

• 5 Sacral

• 1 Coccygeal

• Enlargements:

  • Cervical enlargement (C3 to T2)

  • Lumbar enlargement (L1 to S3)

  • The spinal cord constitutes only about 2% of the central nervous system (CNS)

  • Spinal Cord - Contained in epidural space - Network of sensory and motor
    nerves – a firm, cord-like structure

Spinal Nerve Topography

• Organization:

  • 31 segments corresponding to 31 pairs of spinal nerves: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal.

• Roots: Dorsal (sensory) and ventral (motor) roots leave through intervertebral foramina.

Protective Membranes of the Spinal Cord

• Meninges:

  • Dura Mater

  • Arachnoid Mater

  • Pia Mater

• Spaces:

  • Epidural Space (fatty tissue)

  • Subarachnoid Space (contains cerebrospinal fluid)

  • Subdural Space (potential space)

Internal Structure of the Spinal Cord

• cross-section:

  • White Matter on the outside

  • Gray Matter (H-shaped) on the inside

  • Central Canal filled with cerebrospinal fluid (CSF)

• Horns:

  • Anterior Horn: Contains lower motor neurons that innervate skeletal muscles (motor neurons).

  • Posterior Horn: Contains sensory neurons that receive input from the body and transmit signals to the brain (sensory neurons).

• Major Sulci:

  • Anterior median fissure: A deep groove that runs along the ventral midline of the spinal cord, separating the two halves.

  • Posterior median sulcus: A shallow groove that runs along the dorsal midline of the spinal cord, also separating the two halves.

  • Lateral sulci (anterolateral and posterolateral): These grooves separate different regions of the spinal cord and mark the locations of emerging spinal nerves

Blood Supply to the Spinal Cord

• Arteries:

  • Anterior Spinal Artery (supplies anterior 2/3)

  • Posterior Spinal Arteries (supply posterior 1/3)

  • Segmental Spinal Arteries (radicular and feeder arteries like the Adamkiewicz artery)

• Supply Regions: Cervical, thoracic, lumbar

Venous Drainage of the Spinal Cord

• Plexus Formation: Formed from spinal cord veins, draining into a plexus(nurves bundle) in the pia mater; interconnected channels along anterior median fissure and posterior median sulcus.

• The spinal cord veins derived from the nervous tissue terminate in a plexus in the
  pia mater, often forming plexiform longitudinal channels, along the anterior
  median fissure, posterior median sulcus, and further behind and in front of the
  ventral and dorsal roots.

• They communicate freely with one another

Dermatomes and Plexus

• Dermatome: Region of skin supplied by sensory fibers from a single spinal nerve root.

• Plexus: Networks of nerves that originate from ventral rami from spinal nerves, including:

  • Cervical Plexus (C1-C4)

  • Brachial Plexus (C5-T1)

  • Lumbar Plexus (L1-L4)

  • Sacral Plexus (L4-S4)