SPINOTHALAMIC SYSTEM

Also called anterolateral system, or ventrolateral system.

Transmits somatosensory information about pain, temperature,

and crude touch. The anterior spinothalamic tract carries information

about crude touch. The lateral spinothalamic tract

conveys pain and temperature. Consists mainly of group III & IV nerve fibers.

First-order neurons have their cell bodies in the dorsal horn and synapse on thermoreceptors & nociceptors in the skin.

The first-order neurons synapse on second-order neurons in the spinal cord.

In the spinal cord, the second-order neurons “dessucate” cross the line and ascend to the contralateral thalamus (ventral posterolateral nucleus). Decussation usually occurs 1-2 spinal nerve segments above the point of entry.

In the thalamus, second-order neurons synapse on third-order neurons, which ascend to the somatosensory cortex and synapse on fourth-order neurons.

ANTEROLATERAL SYSTEM

Spinothalamic tract (lateral and anterior): destined for thalamus; important in the localization of painful or thermal stimuli.

Spinoreticular tract: destined for reticular formation; causes alertness and arousal in response to painful stimuli.

Spinotectal tract: destined for tectum; orients the eyes and head towards the stimuli.

Fast pain: is carried on A delta, group II & III fibers, has a rapid onset & offset, and is precisely located (e.g., pin prick).

Slow pain: is carried on C fibers and is characterized as aching, burning or throbbing pain that is poorly localized (e.g., burn).

Referred pain: is of visceral origin. According to the dermatomal rule (sites on the skin are innervated by nerves arising from the same spinal

cord segments as those innervating the visceral organs). Examples: Ischemic heart pain is referred to chest & shoulder. Gallbladder pain is referred to abdomen. Kidney pain is referred to lower back.

BROWN-SÉQUARD SYNDROME

Is caused by damage to one half of the spinal cord. Resulting in: Paralysis and loss of proprioception on the same (or ipsilateral) side as the injury or

lesion. Loss of pain and temperature sensation on the opposite (or contralateral) side as the

lesion.