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This is a cross-sectional diagram of the spinal cord, showing the gray matter nuclei in the center and the white matter tracts surrounding them. Here is a full breakdown:
Overview of the Diagram
The spinal cord in cross-section has a butterfly-shaped central gray matter (containing neuronal cell bodies) surrounded by white matter (containing myelinated axon tracts). The diagram is oriented with Posterior (Dorsal) at the top and Anterior (Ventral) at the bottom.
GRAY MATTER - Cell Body Nuclei
The gray matter is divided into horns, each containing specific nuclei:
Posterior (Dorsal) Horn - Sensory Processing
These receive incoming sensory signals from the body:
| Nucleus | Function |
|---|---|
| Substantia Gelatinosa | Processes pain and temperature signals (gate control of pain) |
| Nucleus Proprius | Main sensory relay nucleus; processes touch, pressure |
| Visceral Afferent Nucleus | Receives sensory input from internal organs |
| Nucleus Dorsalis (Clarke's Column) | Relays proprioception to the cerebellum via spinocerebellar tracts |
Lateral Horn - Autonomic Neurons
Present only in thoracic (T1-L2) and sacral (S2-S4) segments:
- Lateral Nucleus - preganglionic sympathetic (or parasympathetic) neurons
- Medial Nucleus - part of the intermediate zone
Anterior (Ventral) Horn - Motor Neurons
These send signals OUT to skeletal muscles (Lower Motor Neurons):
| Nucleus | Muscles Innervated |
|---|---|
| Lateral Nucleus | Distal limb muscles (fine movements) |
| Intermediate Nucleus | Intermediate limb muscles |
| Medial Nucleus | Axial/trunk muscles (posture) |
WHITE MATTER - Ascending (Sensory) Tracts
These carry sensory information upward to the brain:
Posterior Funiculus (Dorsal Column)
Carries fine touch, vibration, and proprioception to the thalamus and cortex:
- Fasciculus Gracilis - carries signals from the lower body (below T6): legs, pelvis
- Fasciculus Cuneatus - carries signals from the upper body (T6 and above): arms, chest
Lateral/Anterior Funiculus - Spinocerebellar Tracts
Carry proprioception to the cerebellum for coordination:
- Dorsal Spinocerebellar Tract - ipsilateral; carries unconscious proprioception from the lower limb
- Ventral Spinocerebellar Tract - crosses twice (net ipsilateral); carries proprioception from the lower limb
Spinothalamic Tracts
Carry pain, temperature, crude touch to the thalamus:
- Lateral Spinothalamic Tract - pain and temperature (crosses at each spinal level)
- Ventral (Anterior) Spinothalamic Tract - crude touch and pressure
Other Ascending Tracts
- Spinotectal Tract - carries pain/touch signals to the superior colliculus (visual reflexes)
- Spinoolivary Tract - carries proprioception to the inferior olive (cerebellar learning)
WHITE MATTER - Descending (Motor) Tracts
These carry motor commands downward from the brain:
Lateral Column - Voluntary and Postural Motor Control
| Tract | Origin | Function |
|---|---|---|
| Lateral Corticospinal Tract | Motor cortex | Voluntary fine movement of limbs; crosses in the medullary pyramids |
| Rubrospinal Tract | Red nucleus (midbrain) | Assists with limb flexion; less prominent in humans |
| Lateral Reticulospinal Tract | Reticular formation (pontine) | Facilitates extensor tone; postural control |
Anterior Column - Postural and Reflex Control
| Tract | Origin | Function |
|---|---|---|
| Ventral (Anterior) Corticospinal Tract | Motor cortex | Voluntary control of axial/trunk muscles; crosses at segmental level |
| Vestibulospinal Tract | Vestibular nuclei | Maintains balance and posture; activates extensor muscles |
| Ventral Reticulospinal Tract | Reticular formation (medullary) | Inhibits extensor tone; modulates reflexes |
| Tectospinal Tract | Superior colliculus | Head and neck reflexes in response to visual stimuli |
Clinical Relevance - "Which tract tells me what is damaged?"
| Symptom | Damaged Structure |
|---|---|
| Loss of fine touch + vibration on same side | Posterior funiculus (ipsilateral) |
| Loss of pain + temperature on opposite side | Lateral spinothalamic tract (contralateral) |
| Spastic paralysis on same side | Lateral corticospinal tract (ipsilateral) |
| Loss of coordination | Spinocerebellar tracts |
| Horner's syndrome | Lateral horn (T1-T2 disruption) |
This pattern of combined findings helps identify classic cord syndromes like Brown-Sequard syndrome (hemisection), central cord syndrome, or anterior cord syndrome.
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