Neuroanatomy Sensory Paths - Nociception: Spinothalamic Tract

Spinothalamic tract

Separate system for the body using spinal nerves

Quintothalamic tract

Separate system for the head using cranial nerves

Pain stimuli participate in and can travel via

1. Local reflex paths

2. Relay paths to higher centers in both spinal and cranial systems

What do nociceptive receptors help to do?

Help determine the integrity of various localized segments in the spinal cord or brainstem, and whether that info can be transmitted to higher centers for recognition of that stimulus

What is the spinothalamic pathway function/for?

Reflex and relay for pain, temperature

What are the different kinds of spinal reflex arcs for nociception in the spinothalamic path?

1. Monosynaptic

2. Polysynaptic

Monosynaptic spinal reflex arc of spinothalamic path

Direct synapse of sensory fiber with motor neuron

Polysynaptic spinal reflex arc of spinothalamic path

Interneurons in the reflex arc

Describe how the monosynaptic spinal reflex arc works

1. Sensory fiber is picked up by a nociceptor

2. It travels to the spinal cord and synapses on a motor neuron located in the ventral horn

3. This motor neuron sends an impulse out to the periphery

4. This causes the contraction of a skeletal muscle

What is an example of the monosynaptic spinal reflex arc?

Flexor response/reflex

Flexor response/reflex application to monosynaptic spinal reflex arc

Pinching toe causes entire limb and feet to withdraw, demonstrating an intact motor response to sensory stimulus

Describe how the polysynaptic spinal reflex arc works

1. Sensory info travels into spinal cord to synapse on an interneuron, which is located on the dorsal horn

2. This interneuron then synapses on the motor neuron in the ventral horn

What exactly does the spinothalamic tract do?

Relays of nociception information to higher centers

Why is the classic pathway of the spinothalamic tract in pathways a good model?

It’s very discrete and specific as for where it’s located in primates

1st neuron in spinothalamic tract

DRG

Describe axonal movement of the 1st neuron of the spinothalamic tract

Axons ascend or descend a few segments forming the dorsolateral fasciculus (aka Lissauer’s Tract)

2nd neuron of the spinothalamic tract

Dorsal gray horn of spinal cord

Describe axonal movement of the 2nd neuron of the spinothalamic tract

Axons immediately cross and ascend contralaterally in the ventrolateral funiculus as the spinothalamic tract

3rd neuron of hte spinothalamic tract

Ventral caudal lateral nucleus of hte thalamus VCL

Describe axonal movement of the 3rd neuron of the spinothalamic tract

Axons contribute to formation of internal capsule; ascend to appropriate part of cerebral cortex

What are the differences in the spinothalamic for animals that aren’t primates?

The tract is bilateral and diffuse with many synapses

In the spinothalamic tract for animals, is the main influence contralateral or ipsilateral?

Contralateral, but info can also ascend ipsilaterally

What is the clinical significance of animal’s spinothalamic tract being bilateral?

If injury alters the primary contralateral transmission path, the animal may still receive some impulse on the ipsilateral side

What does loss of all pain sensation in a location relating to the spinothalamic tract indicate?

There’s a very serious problem in the paths traveling to the spinal cord, potentially suggesting a complete transection