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Welcome to 2 minute neuroscience, where I simplistically explain neuroscience topics
in 2 minutes or less.
In this installment I will discuss pain and the anterolateral system.
Pain begins at nociceptors, cutaneous receptors that are specialized to detect noxious stimuli
like extreme pressure, very hot or cold temperatures, or tissue damage.
When activated, nociceptors send a signal to the spinal cord; the signal will be sent
to the brain on pathways that make up what is known as the anterolateral system.
The anterolateral system consists of three major pathways: the spinothalamic, spinoreticular,
and spinomesencephalic tracts.
The spinothalamic tract can be considered the main pathway for transmitting pain information
to the cerebral cortex; it is involved in the awareness and recognition of where in
the body a painful stimulus is occurring.
Neurons in the spinothalamic tract carry pain information from nociceptors to the spinal
cord, then immediately synapse with a second neuron that quickly decussates, or crosses
over to the other side of the spinal cord before traveling up the spinal cord.
These fibers proceed to the ventral posterolateral nucleus of the thalamus, where they synapse
with another neuron that carries the pain information to the somatosensory cortex.
The function of the spinoreticular tract is not very clearly defined, but it may be involved
in changes in the level of attention in response to pain.
The fibers of the spinoreticular tract follow the same path as the spinothalamic tract,
but they also project to areas in the reticular formation, which is a network of neurons found
throughout the brainstem that are involved in a wide range of functions including attention
and consciousness.
The spinomesencephalic tract, also known as the spinotectal tract, plays an important
role in the control and inhibition of pain.
Fibers in the spinomesencephalic tract follow the same path as the spinothalamic tract but
they synapse in an area of the midbrain called the periaqueductal grey.
When neurons in the periaqueductal grey are stimulated, they can activate a natural pain
suppression system that involves the release of endogenous opioids, which are substances
that are produced by the body and have painkilling effects.
The release of endogenous opioids and other neurotransmitters leads to inhibition of the
pain signal in the spinal cord and naturally-produced analgesia.