Pain and neural transmission Flashcards
Where are nociceptors found?
- In the periphery as simple free nerve endings
- Branches and terminates as naked, unmyelinated ending in the dermis
What does tissue damage and inflammation trigger?
Release of substances that sensitize peripheral
nociceptors → hyperalgesia
What are the different types of nociceptors, and what do they do
- Mechanical → strong pressure
- Thermal → respond to extreme heat or cold
- Chemical → respond to histamine or other chemicals
What stimuli do most nociceptors respond to
- Mechanical
- Thermal
- Chemical stimuli
How do all sensory receptors work
- Stimulus deforms and changes the nerve ending
- Alters the membrane permeability of the receptor membrane → produces receptor potential
- Triggers an action potential travelling along axon to CNS
How can sensory afferent nerves that innervate the somatosensory receptors be classified
- Conduction velocity positively correlates with axon diameter
- Large diameter: Rapidly conducting afferents
- Small diameter: Slow conducting afferents
Describe first pain
- Fast Aδ fibres
- Sharp, prickling and easily localised
- Occurs rapidly for a short duration
- Mechanical or thermal nociceptors
Describe second pain
- Slow C-fibres
- Dull ache, burning, and poorly localised
- Slow onset and persistent
- Polymodal nociceptors
What are the skin and deeper structures innervated by
A rich, vast network of peripheral nerves
Describe the primary afferents
- Feed into the spinal cord via a spinal nerve and the dorsal root
- Afferents bring information in from somatic receptors
Describe the motor afferents
- Leave the spinal cord via a ventral root and the spinal nerve
- Efferents leave the spinal cord via a ventral root and the spinal nerve
Where are the nociceptor fibre cell bodies found in the spinal cord segment
Within the dorsal root ganglion
Where do the afferent terminals enter and travel down in the spinal cord segment
- Enter the dorsal horn
- Travel down a short distance within the Zone of Lissauer
What do the afferent terminals synapse onto in the spinal cord segment
Synapse onto neurones within the superficial laminae of the dorsal horn
How do the nociceptive afferents from internal organs enter the spinal cord
- Enter through common routes and target overlapping populations of spinal neurons
- Crossover of communication leads to referred pain, where visceral pain is perceived as having a cutaneous source by the sufferer
Describe the contralateral pathway
Sensory inputs cross at level of spinal cord, ascend on opposite side
Describe the ascending pain pathways
- Processes afferent inputs from peripheral mechano-, thermal and polymodal nociceptors
- Contralateral pathway: sensory inputs cross at level of spinal cord, ascend on opposite side
- Information relayed to the thalamus and then onto the somatosensory cortex
What are the 3 components of the ascending pain pathways
- Lateral(neo-)spinothalamic tract
- Spinoreticulothalamic tract
- Anterior spinothalamic tract
Describe the trigeminal system’s role in the pathway of pain and temperature from the face and head
- Small diameter afferents descend in the spinal trigeminal tract to the brain stem
- These synapse with second-order sensory neurons in the pars caudalis
- Axons ascend contralaterally to the thalamus in the trigeminothalamic tract
- Projection to the cortex via the ventral posteromedial nucleus
What is phantom pain
Pain and touch sensations without sensory input
What is endogenous analgesia
No sensations with sensory input
What is pain modulation
Body alters the pain signal along the pathway
What are hyperalgesia (increased pain) and allodynia (touch-evoked pain) features of
Chronic pain syndromes and pathological pain
Where is the highest concentration of mu opiate receptors?
Where are intermediate levels of opiates found?
- Highest concentration in the thalamus
- Intermediate levels are in the cerebral cortex and basal ganglia
