The Ascending and Descending Tracts of the Spinal Cord

Comprehensive vocabulary flashcards covering the anatomical organization, function, and specific pathways of the ascending and descending tracts of the spinal cord.

Ascending tracts

Also known as the sensory pathways of the spinal cord (SC), these conduct afferent information that may or may not reach consciousness.

Exteroceptive information

Sensory input originating from outside the body, such as pain, temperature, and touch.

Proprioceptive information

Sensory input originating from inside the body, such as from muscles and joints.

First-order neuron

A neuron with its cell body in the posterior root ganglion whose peripheral process connects with a sensory receptor ending.

Second-order neuron

A neuron that gives rise to an axon that decussates and ascends to synapse with the third-order neuron.

Third-order neuron

Typically located in the thalamus, this neuron gives rise to a projection fiber that passes to the sensory region of the cerebral cortex.

Lateral Spinothalamic Tract

The sensory pathway mainly responsible for carrying pain and temperature sensations from the body to the brain.

Posterolateral tract of Lissauer

A region where first-order neurons of the spinothalamic tracts divide and travel $1$ or $2$ spinal cord segments before synapsing.

Substantia gelatinosa

A section of the posterior gray column where first-order neurons synapse and Substance P may act as a neurotransmitter.

Spinal lemniscus

The pathway formed in the medulla by the joining of the lateral spinothalamic, anterior spinothalamic, and spinotectal tracts.

Fast pain

Pain experienced within about $0.1$ second of stimulus, transmitted by fast-conducting delta A-type fibers.

Slow pain

Pain felt $1.0$ second or later after stimulation, transmitted by slow-conducting C-type fibers and associated with chronic, burning sensations.

The Gate Control Theory of Pain

A theory suggesting that large, myelinated sensory fibers carrying nonpainful touch can inhibit pain transmission in the posterior gray columns.

Anterior Spinothalamic Tract

The pathway responsible for carrying crude touch and pressure sensations.

Fasciculus gracilis

A posterior white column tract carrying fine touch, vibration, and conscious proprioception from the lower parts of the body.

Fasciculus cuneatus

A posterior white column tract carrying fine touch, vibration, and conscious proprioception from the upper parts of the body.

Internal arcuate fibers

Second-order neurons from the nucleus gracilis and nucleus cuneatus that cross to the opposite side during sensory decussation.

Medial lemniscus

The pathway formed after the sensory decussation that carries fine touch and proprioception to the thalamus.

Posterior Spinocerebellar Tract

A tract carrying unconscious proprioceptive information from the trunk and lower limbs to the cerebellum via Clarke's column.

Anterior Spinocerebellar Tract

Carries unconscious proprioceptive information to the cerebellum, entering through the superior cerebellar peduncle.

Spinotectal Tract

A pathway ending in the superior colliculus of the midbrain used for spinovisual reflexes.

Spinoreticular Tract

A pathway from muscles, joints, and skin to the reticular formation used to influence levels of consciousness and alertness.

Spino-olivary Tract

An indirect pathway carrying cutaneous and proprioceptive information to the cerebellum via the inferior olivary nuclei.

Descending tracts

Also known as motor pathways, these are upper motor neuron pathways from higher centers that control motor activity.

Lower motor neurons

Neurons located in the anterior gray columns whose axons form the final common pathway for innervating skeletal muscles.

Corticospinal Tracts

Pathways concerned with voluntary, discrete, skilled movements, especially of the distal parts of the limbs.

Pyramidal decussation

The crossing of most corticospinal fibers at the lower medulla to form the lateral corticospinal tract.

Reticulospinal Tracts

Pathways originating in the pons and medulla that influence alpha and gamma motor neurons to control posture and reflex activity.

Tectospinal Tract

A tract originating in the superior colliculus responsible for reflex postural movements of the head and neck in response to visual stimuli.

Rubrospinal Tract

A tract beginning in the red nucleus of the midbrain that facilitates flexor muscles and inhibits extensor muscles.

Vestibulospinal Tract

A tract that facilitates extensor muscles and inhibits flexor muscles to maintain balance and posture.

Intersegmental tracts

Short ascending and descending pathways that connect neurons across different levels of the spinal cord for intersegmental reflexes.

Reflex arc

The anatomical structure of a reflex, consisting of a receptor organ, an afferent neuron, an effector neuron, and an effector organ.

Spinal shock

A state following sudden severance of the spinal cord where segmental reflexes are depressed and muscle tone is lost.

Renshaw cells

Specialized cells that receive collateral branches from lower motor neurons and provide feedback inhibition to limit motor neuron activity.