Spinal Cord
The spinal cord is a cylindrical cord of nervous tissue about 45 cm long and about 1 cm in diameter, located in the spinal canal. It starts from the medulla oblongata at the level of the foramen magnum and ends with the conus medullaris** at the level of the I–II lumbar vertebrae.
External structure
The spinal cord has two thickenings - cervical (C4-Th1) and lumbosacral (L1-S2), which correspond to the origin of nerves to the upper and lower extremities. Below the conus medullaris in the spinal canal is the cauda equina (cauda equina) - a bundle of roots of the lumbar and sacral nerves.
31 pairs of spinal nerves depart from the spinal cord: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal. Each nerve is formed by the fusion of the anterior (motor) and posterior (sensory) roots.
Internal structure
The cross section shows:
- Gray matter is a butterfly-shaped structure in the center containing the cell bodies of neurons. The anterior horns contain motor neurons, the posterior horns contain sensory neurons, and the lateral horns (in the thoracic region) contain autonomic neurons.
- White matter - surrounds the gray matter, consists of myelinated axons that form pathways.
- Central canal is a narrow cavity in the center of the gray matter, filled with cerebrospinal fluid.
Pathways
Ascending (sensitive) pathways carry information from receptors to the brain:
- Thin and wedge-shaped beams - deep sensitivity (position of joints, vibration)
- Spinothalamic tract - pain and temperature
Descending (motor) pathways transmit commands from the brain to the muscles:
- Corticospinal (pyramidal) tract - voluntary movements
- Rubrospinal, vestibulospinal - involuntary regulation of tone and posture
Reflex arc
The spinal cord is the center of the simplest reflexes. The classic example is the knee reflex: blow to the patellar ligament → sensory neuron → motor neuron in the anterior horn → extension of the lower leg. The entire journey takes less than 50 milliseconds.
Spinal cord injuries
Spinal cord injury results in impairment of all functions below the level of injury. Injury to the cervical spine causes tetraplegia (paralysis of all four limbs), and injury to the thoracic spine causes paraplegia (paralysis of the legs). Knowledge of segmental innervation allows the neurologist to accurately determine the level of damage based on clinical signs.
The Humio](/) app offers an interactive 3D model of the spinal cord - you can view the segments, roots and membranes by rotating the model in any direction.