1A8 - Nociceptive Pathways Flashcards
(21 cards)
What type of axons make up the deep pain nociceptive pathways?
Thinner (0.3-1.3 um) unmyelinated (c) fibers
Which spinal tract is predominently involved in the sensation of superficial pain and temperature?
Spinothalamic tract
Which is the spinal tract that transmits deep pain in people? How is sensation of deep pain different in domestic animals?
Spinothalamic tract
In domestic animals, deep pain is transmitted only by the non-specific pathways of the ascending reticular formation
What are the three neurons involved in the spinothalamic tract, and where do their axons travel?
1) Sensory spinal nerve (dorsal root ganglion) –> axon travels to the dorsal horn of the spinal cord
2) Neuron of the dorsal horn –> axon travels cranially in the ipsilateral spinothalamic tract
3) Ventral group of the thalamic nuclei –> axons project to the primary somatosensory cortex
The ascending reticular formation forms which spinal cord tract?
The spinoreticular tract
What are the three neurons involved in the pathway for sensing of deep pain in domestic animals (spinoreticular tract), and where do their axons travel)?
1) Sensory spinal nerve (dorsal root ganglion) –> thin unmyelinated type c fibers project to the substancia gelatinosis in the dorsal horn
2) Substantia Gelatinosa (runs the length of the spinal cord dorsal horn) –> axons travel through the spinoreticular tract to the thalamic reticular formation
3) Thalamic Reticular Formation –> Forms diffuce connections to all parts of the cerebral cortex
What is the gate mechanism of deep pain and what neurons are involved?
When the gate is open, volleys of pain can pass. When the gate is closed, pain perception decreases.
The neurons of the substantia gelatinosa form an important part of the gate mechanism for pain.
What are the 5 mechanisms that can close the gate of pain?
1) Pre-synaptic inhibition of C fibers (through stimulation of cutaneous mechanoreceptions - pressure releaves pain)
2) Enkephalinergic interneurons (part of inhibitory circuit triggered through stimulation of superficial pain)
3) Raphe spinal tract (can excite enkephalinergic interneurons)
4) Endorphins from the hypothalamus (e.g. during intence exercise)
5) Hypnosis (mechanism not understood)
What two types of nerve fibers are associated with transmission of noxious stimuli?
1) Alpha delta fibers
2) C-fibers
What type of noxious sensation is transmitted by alpha delta nerve fibers? How quickly is the sensation transmitted?
Easy to localize pinprick pain
Myelinated axons means rapid conduction of pain perception
What type of noxious sensation is transmitted by C-fibers? How quickly is the sensation transmitted?
Difficult to localize dull, aching, throbbing, burning pain
Unmyelinated axons result in slow transmission of pain sensations
Why does loss of nociception only occur in extremely severe spinal cord injury/ dysfunction?
There are multiple, bilaterally represented pathways for nociception that reside in nearly all funiculi
Both alpha-delta and c-fibers will travel though the spinothalamic tract, spinoreticular tract, spinocervicothalamic tract, and spinomesencephalic tracts
What is the source of nociceptive input from the head?
All three branches of CN V (head), as well as CN VII (ear), IX & X (oral cavity)
Where do all sensory CNs that transmit nociception next synpase within the brain?
Within the spinal nucleus of cranial nerve V in the medullar
They then traval to the thalamus before traveling to the somatosensory cortex
What nerves transmit nociceptive input from the thoracic and abdominal viscera?
Sympathetic nerves
What nerves transmit nociceptive input from pelvic viscera?
Pudendal nerves
What nerve transmits nociceptive input from the respiratory tract and esophagus?
Vagus nerve
The mesencephalic nucleus of cranial nerve V is associated with perception of which sensations?
Proprioception
The pontine sensory nucleus is associated with perception of which sensations?
Touch and pressure
The spinal nucleus of cranial nerve V is associated with perception of which sensations
Pain and temperature
What are the three neurons involved in the cranial nerve pathways for nociception, and where do their axons travel?
1) Cranial Nerve (CN V, CN VII, CN IX, CN X) –> Axons travel from the cranial nerve nuclei to the spinal tract of cranial nerve V in the medulla
2) The Nucleus of the spinal tract of cranial nerve V –> Axons travel within the trigeminal lemniscus and decussate before reaching the thalamus
3) Ventral group of the thalamic nuclei –> axons project to the primary somatosensory cortex
