Spinal Cord: Anatomy, Meninges, Gray/White Matter & Tracts

Two major roles of the spinal cord

Acts as a relay station between the brain and most of the body and as a processing station capable of performing some integration independently.

Spinal cord as a relay station

Allows the brain to communicate with most of the body below the head and neck by carrying outgoing signals from the brain and incoming signals from the body.

Spinal cord as a processing station

Performs integration and processing; some spinal reflexes can occur through the spinal cord without influence from the brain.

Spinal reflex

Activity that can be processed and carried out by the spinal cord alone without influence from the brain.

Spinal meninges

Protective membranes surrounding the spinal cord: dura mater, arachnoid mater, and pia mater.

Spinal dura mater

Unlike cranial dura, spinal dura has only a meningeal layer and lacks a periosteal layer.

Denticulate ligaments

Extensions of spinal pia mater that pass through the arachnoid and attach to the dura, helping anchor the spinal cord within the vertebral cavity.

Spinal epidural space

Actual space between the meningeal dura and walls of the vertebral foramina; contains veins and adipose tissue that cushion and protect the spinal cord.

Spinal subdural space

Potential space between the dura and arachnoid; normally these two layers adhere to each other.

Spinal subarachnoid space

Space between the arachnoid and pia containing CSF; contains a larger volume of CSF inferior to the end of the spinal cord.

Epidural or spinal anesthesia

Local anesthetic is injected into the epidural space, preventing nerves below the injection level from transmitting motor or sensory impulses.

Lumbar puncture (spinal tap)

Procedure in which a needle is inserted into the subarachnoid space and CSF is withdrawn for analysis.

Lumbar puncture location

Needle is inserted between the fourth and fifth vertebrae to avoid injuring the spinal cord.

Uses of lumbar puncture

CSF may be analyzed to assess conditions including meningitis, encephalitis, and multiple sclerosis.

Spinal cord location

Spinal cord begins as an extension of the brainstem at the foramen magnum and terminates between the first and second lumbar vertebrae.

Posterior median sulcus

Narrow groove located on the posterior side of the spinal cord.

Anterior median fissure

Wider groove located on the anterior side of the spinal cord.

Conus medullaris

Tapered end of the spinal cord.

Filum terminale

Very thin extension formed by spinal pia at the first and second lumbar vertebrae that continues through the vertebral cavity and anchors to the first coccygeal vertebra.

Cervical enlargement

Bulge in the cervical region of the spinal cord where nerve roots contributing to spinal nerves serving the upper limbs attach.

Lumbar enlargement

Bulge in the lumbar region of the spinal cord where nerve roots contributing to spinal nerves serving the lower limbs attach.

Spinal nerves

PNS nerves that carry sensory and motor impulses to and from the spinal cord.

Posterior and anterior nerve roots

Nerve roots projecting from the spinal cord that merge to form spinal nerves; posterior roots are sensory and anterior roots are motor.

Cauda equina

Bundle of spinal nerve roots extending inferiorly from the conus medullaris.

Internal organization of the spinal cord

Butterfly-shaped gray matter is located internally and is surrounded by superficial white matter tracts.

Central canal

CSF-filled canal running through the center of the spinal cord.

Gray commissure

Gray matter surrounding the central canal that connects the right and left “wings” of spinal gray matter.

Anterior horn

Anterior portion of spinal gray matter containing neurons involved in somatic motor functions controlling skeletal muscle.

Posterior horn

Posterior portion of spinal gray matter containing neuron cell bodies involved in processing somatic and visceral sensory stimuli.

Lateral horn

Region of spinal gray matter present from the first thoracic vertebra into the lumbar cord; contains neuron cell bodies involved in autonomic motor control of the viscera.

Posterior root

Sensory nerve root carrying sensory information toward the spinal cord.

Anterior root

Motor nerve root carrying motor information away from the spinal cord.

Posterior (dorsal) root ganglion

Enlargement on the posterior root containing the cell bodies of sensory neurons.

Spinal white matter

Outer portion of the spinal cord containing myelinated axons organized into funiculi and tracts.

Funiculus

General region of spinal cord white matter.

Three spinal cord funiculi

Posterior, lateral, and anterior funiculi are present on each side of the spinal cord.

Tracts (columns)

Bundles of axons within the spinal cord white matter that carry information to or from specific regions of the brain.

Ascending tracts

Sensory tracts that carry stimuli from the spinal cord toward the brain.

Descending tracts

Motor tracts that carry stimuli from the brain toward the spinal cord.

Spinal tract symmetry

Ascending and descending tracts are bilaterally symmetrical, with the same tracts on the right and left sides serving their respective sides of the body.

Posterior columns

Ascending sensory tracts consisting of the fasciculus gracilis and fasciculus cuneatus; carry somatosensory information such as touch and proprioception to the brain.

Fasciculus gracilis

Medial tract of the posterior columns that carries somatosensory information toward the brain.

Fasciculus cuneatus

Lateral tract of the posterior columns that carries somatosensory information toward the brain.

Spinocerebellar tracts

Ascending tracts that transmit information about joint position and muscle stretch to the cerebellum.

Anterior and posterior spinocerebellar tracts

Ascending sensory tracts that carry proprioceptive information such as joint position and muscle stretch to the cerebellum.

Anterolateral system

Ascending sensory system that includes the spinothalamic tracts traveling in the anterior and lateral funiculi.

Spinothalamic tracts

Ascending tracts of the anterolateral system that carry pain and temperature information to the brain.

Corticospinal tracts

Largest descending motor tracts; originate mainly from motor areas of the cerebral cortex and control skeletal muscles below the head and neck.

Corticospinal tract pathway

Axons descend from the cerebral cortex through the internal capsule and brainstem; most decussate in the medullary pyramids and then travel through the lateral funiculi of the spinal cord.

Corticospinal tracts and anterior horn

Corticospinal tracts carry motor signals to appropriate locations in the anterior horn of the spinal cord.

Ascending vs. descending spinal tracts

Ascending = sensory information traveling toward the brain; descending = motor information traveling from the brain toward the spinal cord.