Internal Spinal Cord (Gray Matter, White Matter, Funiculus) - Anatomy

Summary

The video explains the internal organization of the spinal cord, focusing on its gray matter, white matter, and the pathways that travel through the white matter.

Gray matter and white matter

• Gray matter contains many nerve-cell bodies and dendrites. Its named structures are generally called nuclei.
• White matter is rich in myelinated axons and glial cells. Its axon bundles are called tracts and are grouped into three funiculi: posterior, lateral, and anterior.
• Myelin-rich axons give white matter its pale appearance.

Gray matter: horns, zones, and nuclei

• Anterior horn: Primarily contains motor nuclei. Their axons leave the spinal cord through the anterior root of a spinal nerve.
• Posterior horn: Processes incoming sensory information. The video describes:
  • Marginal nucleus: Interneurons activated by incoming sensory signals.
  • Substantia gelatinosa: Interneurons that modulate sensory input.
  • Nucleus proprius: Processes sensory information such as pain, touch, and temperature, sending it toward higher centers.
  • Posterior thoracic nucleus: Receives unconscious proprioceptive information about body position and posture.
• Intermediate column/zone: Includes the intermediomedial nucleus, associated with unconscious proprioception, and autonomic nuclei in the lateral horn:
  • Intermediolateral nucleus: Located in the spinal segments identified in the video as C8–L2; carries sympathetic output.
  • Sacral parasympathetic nuclei: Located in S2–S4; carry parasympathetic output.
  • The video notes that some sources place the posterior thoracic nucleus in the intermediate zone rather than the posterior horn.
• Central zone: Contains the central canal, described as filled with cerebrospinal fluid and lined by ependymal cells, as well as central gelatinous substance.
• Fasciculi proprii: Thin bands of white matter around the gray matter that connect nearby gray-matter regions and spinal segments.
• Spinal reticular formation: Gray matter extending into the surrounding white matter and continuing into the brainstem. The video associates it with a network involved in basic functions such as breathing, heartbeat, and blood pressure.

Organization of spinal-cord tracts

• Ascending (afferent) tracts carry sensory information toward the brain.
  • The video distinguishes conscious sensation, which reaches the cerebral cortex, from unconscious proprioceptive information, which reaches the cerebellum.
• Descending (efferent) tracts carry motor commands from the brain toward the spinal cord.
  • Pyramidal tracts originate in the primary motor cortex and support voluntary, precise movements.
  • Extrapyramidal tracts originate elsewhere in the brain and contribute to posture, balance, and other less consciously controlled actions.

Major tracts by funiculus

Posterior funiculus

• Fasciculus gracilis: Carries conscious sensory information from the lower body and is present throughout the spinal cord.
• Fasciculus cuneatus: Carries similar information from the upper body. The video says it is present above spinal segment T6.
• Together, these pathways are associated with conscious proprioception and “epicritic” sensation, including position and movement awareness, force, vibration, fine touch, and two-point discrimination.

Lateral and anterior funiculi

• Spinocerebellar tracts: The anterior and posterior spinocerebellar tracts carry unconscious proprioceptive information to the cerebellum, supporting posture, joint stability, and related automatic responses. The video places both in the lateral funiculus and identifies different gray-matter nuclei as their sources.
• Spinothalamic tracts: The lateral tract lies in the lateral funiculus, and the anterior tract lies in the anterior funiculus. The video associates them with conscious pain, temperature, pressure, and touch, and describes them as arising from the nucleus proprius.
• Corticospinal tracts: Carry voluntary motor commands from the primary motor cortex.
  • Lateral corticospinal tract: Crosses in the medulla before descending in the spinal cord.
  • Anterior corticospinal tract: Descends without crossing initially and crosses near the spinal segment where it acts.
  • Both connect with motor nuclei in the gray matter.

Other descending pathways

• Rubrospinal tract: Originates from the red nucleus in the midbrain. The video describes it as supporting coordination and refining voluntary movement.
• Tectospinal tract: Helps coordinate eye and neck movements when orienting toward something.
• Vestibulospinal tract: Uses vestibular information to support balance and posture.
• Olivospinal tract: Presented as another pathway involved in balance and posture.
• Reticulospinal tracts: Medial and lateral pathways associated with motor control, balance, and posture, and linked to the reticular formation in the brainstem and spinal cord.
• Medial longitudinal fascicle: Located in the anterior funiculus in cervical segments, where the video says it helps coordinate involuntary movements of the head, neck, and eyes.

The video concludes with recall quizzes, asking viewers to identify gray-matter nuclei and white-matter tracts from diagrams and tables.

Speakers and sources featured

• Speaker: A single narrator who introduces himself as “Meditay.”
• Source/channel: Taim Talks Med.
• Other speakers: None identified. The video refers to a previous spinal-cord lesson and uses diagrams and animations, but no additional speakers or external sources are named.