Neuroanatomy Lecture #25: Pain

Front 1

Name and describe the origin of two major classes of pain

Back 1

Nocioceptive pain -
is caused by the activation of nocioceptors

Neuropathic pain -
includes any pain syndrome where the predominating mechanism is a site of aberrant somatosensory processing in the PNS or CNS

Front 2

Name two types of pain from the body surface
- how the pain is initially recognized
- the receptors that are activated
- the fibers that transduce the signal

Back 2

• First Pain
- elicit a sharp, pricking sensation
- thermal or mechano receptors are activated
- A-delta myelinated fibers

• Second Pain
- elicits a slower onset burning sensation
- Polymodal nocireceptors are activated
- Unmyelinated C-fibers

Front 3

Because 1st and 2nd pain use different fibers, what can be said about the transduction of sensory info

Back 3

First pain fibers will transduce the info faster and would arrive in the CNS before Second pain fibers

Front 4

Name and describe the origin of two major classes of pain

Back 4

Nocioceptive pain -
is caused by the activation of nocioceptors

Neuropathic pain -
includes any pain syndrome where the predominating mechanism is a site of aberrant somatosensory processing in the PNS or CNS

Front 5

Name two types of pain from the body surface
- how they are initially recognized
- the receptors that are activated
- the fibers that transduce the signal

Back 5

• First Pain
- elicit a sharp, pricking sensation
- thermal or mechano receptors are activated
- A-delta myelinated fibers

• Second Pain
- elicits a slower onset burning sensation
- Polymodal nocireceptors are activated
- Unmyelinated C-fibers

Front 6

Because 1st and 2nd pain use different fibers, what can be said about the transduction of sensory info

Back 6

First pain fibers will transduce the info faster and would arrive in the CNS before Second pain fibers

Front 7

Visceral/Deep Pain
• How it's recognized
• The receptors that are stimulated
• The fibers that transduce the signal

Back 7

Visceral/Deep Pain
• aching or burning sensation
• Stimulation of visceral and deep somatic receptors
• Unmyelinated C-fibers tranduce the signal

Front 8

Referred Pain:
• It's cause, specify the system involved for ascension
• Is an example of this basic kind of wing mechanism
• Consequence

Back 8

Referred Pain:
• The afferent fibers of nocioceptors iNN internal organs and the afferent sensory fibers iNN the body surface enter the spinal cord through the DRG, synapsing on the same ganglion and use the same Anterolateral System (ALS)

• is an example of a convergence wiring system

• Visceral nocioceptor activation is perceived as a cutaneous painful stimulation

Front 9

The Spinal nerve pathway for pain:
• involves this system
• Primary Neuron
- the region of the spinal cord where it synapses
• 2nd order neuron
- its synaptic target and side of the body the target is located
• 3rd order neuron
- travels through these areas (2)

Back 9

The Spinal nerve pathway for pain:
• involves the Anterolateral System
• Primary Neuron
- substantia gelatinosa, the apex of the posterior horn of gray matter
• 2nd order neuron
- synapses on the VPL thalamic nuclei, contralateral side
• 3rd order neuron
• travels through the posterior limb of the internal capsule and corona radiata

Front 10

Trigeminal Pathway for pain:
• Types of sensations carried (2)
• Primary neuron
- Trajectory of its entrance into the CNS
- where it synapses

• 2nd order neuron
- trajectory
- where it synapses

• 3rd order neuron
- trajectory
- where it synapses

Back 10

Trigeminal Pathway for pain:
• Pain and temperature
• Primary neurons
- fibers first enter the brain stem at the pons and descend ipsilaterally in the Spinal Trigeminal Tract before synapsing
- synapse in the Spinous nucleus of CN V

• 2nd order neuron
- Ascends contralaterally in the ventral trigeminal thalamic tract
- synapses at the VPM Thalamic nuclei

• 2nd order neuron

• 3rd order neuron
- ascends through the posterior limb, close to the genu of the internal capsule, through the corona radiata
- synapses on S1

Front 11

Nocioceptors:
• Three ways to stimulate
• Chemosensitive type
- cause of stimulation
- 3 substances that are released and their sources

Back 11

Nocioceptors:
• Mechanically, thermally, chemically
• Chemosensitive type
- tissue damage
- 3 substances released and their sources
> K+ from damaged cells
> Bradykinin from blood
> Histamine from mast cells

Front 12

Sensitization of Nociceptors:
• Define hyperalgesia
• General process leading to sensitization
• 3 substances that are released and their sources

Back 12

Sensitization of nociceptors:
• an enhanced sensitivity and response to pain
• damaged tissue release chemical substances causing increased sensitization
• 3 substances released and their sources
- Prostaglandis and Leukotrienes from damaged cells
- Substance P from primary afferent fibers

Front 13

The Gate Control Theory:
• The goal of the pathway
• The Process
- which neurons initiate
- which neurons inhibit pain
• The transmitters discovered to be released by the interneuron and the location of the receptors

Back 13

The Gate Control Theory:
• To lessen pain
• The Process
- large myelinated neurons carrying touch perception activate inhibitory neurons
- inhibitory neurons in the dorsal horn of the spinal cord, synapse on nocioceptors, reducing their flow of information
• enkephalins, an endogenous opioid. Its receptors were found on 1st order (nociceptors) and 2nd order neurons

Front 14

Descending Pain Control Fibers:
• Have fibers originating in these parts of the brain (3), also name these fibers
• The fibers receive input from this pathway

Back 14

Descending Pain Control Fibers:
• Areas of the brain and their fibers -
- Periaqueductal area of the midbrain, spinomesencephalic fibers
- Reticular formation of pons, spinoreticular fibers
- reticular formation of medulla, spinoreticular fibers
• Anterolateral System

Front 15

In a headache, pain is due to stimulation of these pain-sensitive structures (3)
It is never due to this structure because...

Back 15

Blood vessel walls, dura mater and periosteum.

The brain parenchyma is never a source of pain since it has no nocioceptors

Front 16

Aspirin:
• inhibits this enzyme
• method of controlling pain

Back 16

Aspirin:
• inhibits cyclo-oxygenase
• it decreases the secretion of prostaglandins, which are responsible for sensitizing sensory afferent fibers

Front 17

Opioids:
• the pathway in which they control pain
• one example

Back 17

Opioids:
• Through active gate control, interacting with interneurons
• morphine

Front 18

Surgical Management of pain:
• method in which it relieves pain
• define rhizotomy

Back 18

Surgical management of pain:
• interrupts the flow of pain sensation
• transection of the dorsal roots of the spinal nerves

Front 19

Phantom Limb Pain:
• other names
• why it occurs

Back 19

In the somatotopic map, points that are in close proximity to each in reality (on the body) are also close together on the somatotopic map

With a missing limb, the cortical map has been reorganized. Touch and pain pathways that originated in the missing limb will connect with cortical neurons in a neighboring area, leading to new connections in the primary somatosensory cortex.