Essay Question 9 - Ascending and descending spinal nerve tracts

Descending (motor) tracts

-conduct motor impulses down brainstem and spinal cord -involves 2 motor neurons

Lower motor neuron

-in brainstem or spinal cord -axon of this neuron leads the rest of the way to the muscle or other target organ

Gracile fasciculus

-major ascending tract -posterior, in medulla -senstaions of limb and trunk position and movement, deep touch, visceral pain -below level T6

Posterior spinocerebellar

-major ascending tract -lateral -feedback from muscles

Medial lemniscus

-major ascending tract -lateral and anterior, in spinal cord -sensations of light touch, tickle, itch, temperature, pain and pressure

Spinothalimic

-major ascending tract -lateral and anterior, in spinal cord (some fibers) -sensation of pain from tissue injury

Anterior spinocerebellar

-major ascending tract -lateral, in spinal cord -same as posterior spinocerebellar

Cuneate fasciculus

-major ascending tract -posterior, in medulla -same as gracile fasciculus, from level T6 up

Medial reticulospinal

-major descending tract -anterior -same as lateral reticulospinal

Lateral vestibulospinal

-major descending tract -anterior -balance and posture

Medial vestibulospinal

-major descending tract -anterior, in medulla (some fibers) -control of head position

Tectospinal

-major descending tract -anterior, in midbrain -reflexive head turning in response to visual and auditory stimuli

Anterior corticospinal

-major descending tract -anterior, in spinal cord -fine control of limbs

Lateral reticulospinal

-major descending tract -lateral -balance, posture, regulation of awareness of pain

Lateral corticospinal

-major descending tract -lateral, in medulla -fine control of limbs

Decussation

as the fibers pass up or down the brainstem and spinal cord they cross over from the left to the right side and vice versa

Third-order neuron

carries the signal the rest of the way to the cerebral cortex

Ascending (sensory) tracts

carry sensory information up the cord -sensory signals typically travel across 3 neurons from their origin in the receptors to their destination in the brain

Second-order neuron

continues as far as a "gateway", the thalamus, at the upper end of the brainstem

First-order neuron

detects a stimulus and transmits a signal to the spinal cord or brainstem

Upper motor neuron

originates in cerebral cortex or brainstem and terminates on a lower motor neuron

Contractile

when the origin and destination of a tract are on opposite sides of the body

Ipsilateral

when the origin and destination of a tract are on the same side of the body; does not decussate