Internal Structure

Introduction

Introduction to Spinal Cord Neuroanatomy

The spinal cord is a vital component of the central nervous system (CNS), serving as the primary conduit for sensory and motor information between the brain and the peripheral nervous system. It extends from the foramen magnum of the skull to the level of the first or second lumbar vertebra, housed within the vertebral canal. The spinal cord is organized into distinct regions—cervical, thoracic, lumbar, sacral, and coccygeal—each corresponding to the vertebral segments and giving rise to spinal nerves that innervate specific body regions.

Functional Overview

Functionally, the spinal cord integrates reflexive and voluntary motor responses while relaying sensory input to higher CNS centers. Its internal structure is characterized by gray matter, containing neuronal cell bodies, and white matter, composed of myelinated axons. This organization underpins the cord’s role in processing and transmitting neural signals critical for movement, sensation, and autonomic regulation.

Study

Gross Anatomy and External Features

The spinal cord exhibits two enlargements: the cervical enlargement (C4–T1) and the lumbosacral enlargement (T11–L1), which correspond to the origins of the brachial and lumbosacral plexuses, respectively. These regions contain a higher density of motor neurons to innervate the upper and lower limbs. The cord tapers distally into the conus medullaris, from which the filum terminale extends to anchor the cord to the coccyx. Spinal nerves emerge laterally via intervertebral foramina, with dorsal and ventral roots uniting to form mixed nerves.

Internal Organization: Gray Matter

The gray matter of the spinal cord is arranged in an H-shaped configuration, divided into dorsal (posterior) horns, ventral (anterior) horns, and lateral horns (present in thoracic and upper lumbar segments). The dorsal horns contain sensory neurons that receive afferent input from peripheral receptors via dorsal root ganglia. The ventral horns house lower motor neurons that project axons through ventral roots to skeletal muscles. Lateral horns contain preganglionic sympathetic neurons, which are part of the autonomic nervous system.

Internal Organization: White Matter

White matter surrounds the gray matter and is organized into three funiculi: dorsal, lateral, and ventral. These funiculi contain ascending and descending tracts that transmit sensory and motor information. Key ascending tracts include the dorsal columns (proprioception and fine touch), spinothalamic tracts (pain and temperature), and spinocerebellar tracts (unconscious proprioception). Descending tracts, such as the corticospinal tracts, convey motor commands from the brain to spinal motor neurons, enabling voluntary movement.

Spinal Cord Tracts and Pathways

The dorsal column-medial lemniscus pathway transmits discriminative touch, vibration, and proprioception from the body to the somatosensory cortex. Fibers ascend ipsilaterally in the dorsal columns and decussate in the medulla. The spinothalamic tract carries pain, temperature, and crude touch sensations, with fibers decussating at the level of entry in the spinal cord. The corticospinal tract, critical for voluntary motor control, originates in the motor cortex and decussates in the medullary pyramids, descending contralaterally to synapse with lower motor neurons.

Blood Supply and Clinical Correlates

The spinal cord is vascularized by the anterior spinal artery and paired posterior spinal arteries, supplemented by segmental arteries such as the artery of Adamkiewicz. Ischemia or infarction in these vessels can result in devastating neurological deficits, such as anterior cord syndrome, characterized by loss of motor function and pain/temperature sensation below the lesion, with preserved proprioception. Understanding the vascular supply is essential for diagnosing and managing spinal cord injuries and vascular pathologies.

Summary

Key Takeaways

The spinal cord is a segmented structure with cervical and lumbosacral enlargements, housing gray matter organized into dorsal, ventral, and lateral horns. White matter is divided into dorsal, lateral, and ventral funiculi, containing ascending and descending tracts critical for sensory and motor function. Major pathways include the dorsal column-medial lemniscus, spinothalamic, and corticospinal tracts, each with distinct functional roles and decussation patterns.

Clinical Correlate

Lesions in the spinal cord can result in characteristic syndromes based on the affected tracts. For example, damage to the dorsal columns leads to ipsilateral loss of proprioception and fine touch, while spinothalamic tract lesions cause contralateral loss of pain and temperature sensation. Corticospinal tract injuries result in ipsilateral motor deficits below the lesion. Recognizing these patterns is crucial for localizing spinal cord pathology and guiding clinical management.

Functional Integration

The spinal cord integrates reflexive activity through local circuits, such as the stretch reflex, while also serving as a conduit for higher-order processing. Autonomic functions, including sympathetic and parasympathetic regulation, are mediated by specific spinal segments. A thorough understanding of spinal cord neuroanatomy is foundational for interpreting neurological deficits and designing therapeutic interventions.