Neurophysiology of nociception Flashcards
Define pain
Unpleasant sensory and emotional experience associated with actual or potential tissues damage
Define nociception
Mechanism that provide notice of potential noxious substance/stimuli or injury
The mechanism that provides the notice of pain
Define ganglion
An encapsulated neural structure containing a collection of neuronal cell bodies
Define afferent nerve
Sensory nerve conveying signals from receptor to CNS
Define efferent nerve
Motor nerve conveying signals from CNS to effector
What nerve provides the majority of sensory innervation to the face?
Trigeminal nerve (CN 5)
What is the only feature of the face in which the trigeminal nerve does not provide sensory innervation?
What is this supplied by?
Angle of the mandible
Upper cervical nerves
What are the 3 branches of the trigeminal nerve?
Opthalmic, maxillary, mandibular
How is the mandibular division of the trigeminal nerve divided?
Anterior and posterior
What is the function of the thalamus?
Processes and relays sensory information to varying parts of the brain
What part of the brain is responsible for memory, language skills, consciousness and governing of voluntary control?
Cerebral cortex
What is the function fo the cerebral cortex?
Responsible for memory, language, consciousness and governing of voluntary control
What are algogenic substances?
Substances released after tissue damage associated with pain, the brain interpreters these as pain
Name 2 algognenic substances that can be inhibited by analgesics
Substance P
Prostaglandin
What detects algogenic substances?
Nociceptors
What are nociceptors?
Receptors on a neurone that detect the actual/potential noxious stimuli
What kind of stimuli can nociceptors respond to?
Chemical, thermal or mechanical
Name the 2 main types of nociceptive axons (fibres)
A delta
C fibres
What are the difference between A delta and C fibres
a) speed
b) myelination
c) stimuli they respond to
d) type of pain
e) location in the tooth
f) diagnosis of tooth depending on pain they feel
a) a delta = fast (act first) C = slower b) A delta = myelinated, C = unmyelinated c) a delta = mechanical C = mechanical, thermal and chemical d) A delta = short sharp C = dull ache e) A delta = periphery of pulp C = centre of pulp f) A delta = reversibel pulpitis C = irreversibel pulpitis
Algogenic substances are released and stimulate nociceptors on A delta or C fibres, where are these nociceptors found (in terms of facial pain)?
Trigeminal ganglion
Algogenic substances are released and stimulate …… on ……. or …….. fibres.
Nociceptors
A delta
C
From the trigeminal ganglion, where are pain signals transmitted?
Brianstem
Via what pathway are pain signals transmitted from trigeminal ganglion to brainstem?
Sensory root
What part of the brainstem do the pain signals from the trigeminal ganglion enter?
Pons
Why is dental pain relatively well localised?
The pain signal is carried along one signal axon from the tooth to the brainstem = very little cross over
From the brainstem, where do the primary afferents of the trigeminal nerve go?
Sensory nuclei of the trigeminal nucleus caudalis (TNC)
What is to note about the structure of the TNC (trigeminal nucleus caudalis)?
Multiple different nucleic within the TNC that are responsible for different types of pain
What structure within the TNC receives the majority of nociception from the primary afferents of the trigeminal nerve?
Spinal nucleus
What kind of neurones will synapse with the primary afferents of the trigeminal nerve in the TNC?
Second order neurones
Second order neurones that have synapsed with primary afferents in the spinal nuclei (TNC) can feedback to the spinal nuclei as they ascend, what is the advantage of this?
This can be used to modulate pain
How can second order neurones help to modulate pain?
They can feedback to the spinal nuclei as they ascend
Where do second order neurones synapse?
Thalamus
What do second order neurones synapse with?
Where do these go?
Third order neurones
Higher centres of brain which allow individual to interpret pain
What is the pathway termed as from tissue damage to interpreting pain?
Ascending (sensory) pathway
What is the pathway that is sent out by the brain once it has interpreted the signals?
Descending (motor) pathway
List 2 mechanisms of modulating nociception we can control outside the body?
Altering stimuli
Pharmacological intervention
Name 2 mechanisms of nociception modulation that occur in the body
Descending impulses
Sensitisation
How can descending impulses from the brain modulate nociception? (2)
Endogenous chemical messengers can effect transmission of impulses from primary afferents
Gate theory - touch pressure activates A beta fibres which are faster than A delta - generates descending impulse and closes the gate at TNC
Describe the gate theory?
A beta fibres are activated from touch - hoses are faster than A delta or C fibres, clsoingthe gate to the TNC so the TNC finds it harder to relay the nociceptive fibres
What is sensitisation?
Increase in pain response
In what 2 was can sensitisation occur?
Hyperalgesia - increase in painful signal
Allodynia - a previously neutral stimuli is now interpreted as painful
How can sensitisation be classified?
Peripheral and central
How is sensitisation helpful?
It has a protective role. It ensures you do not damage the area more
How can sensitisation be harmful?
Chronic pain
What is peripheral sensitisation?
Peripheral nociceptors have increased responsiveness or respond at lower thresholds (hyperalgesia)
What causes peripheral sensitisation?
Constant chronic tissue damage releasing continual allogenic substances causing: the recruitment of sleeping nociceptors, making nociceptors prone to spontaneous activity, lower threshold
What is central sensitisation?
When second order neurones receive prolonged stimulus of nociceptive input.
Increase strength fo pain sensation (hyperalgesia)or allodynia
What causes both hyperalgesia and allodynia?
Central sensitisation
What causes only hyperalgesia?
Peripheral sensitsation
What causes central sensitisation?
Nerve trauma
Hormonal, genetic and environmental factors
peripheral sensitisation
Psychological factors
What is convergence? What does it cause
Brain struggles to tell which area an impulse came from- causes referred pain
What is divergence?
Radiation of pain
What causes divergence?
Primary afferents synapse several other second order neurones - signals come from a large area
How can central sensitisation be exploited?
Can be caused by psychological factors, so can be treated with this
What is persistent idiopathic dentoalveolar pain?
Persistent pain derived from a tooth that has been removed or a root has been removed
What are the warning signs of persistent pain?
Difficulty localising pain No obvious pathology Burning/electric shock pain LA does not reduce pain Pain fro longer than healing process Does not respond to further treatment Unusual triggers and abnormal response Doesn't disturb sleep
What are the 3 features of biopsychosocial model of pain?
Biological, psychological, sociological
How does the BSP model link to management of persistent pain?
Multidisciplinary management
persistent pain has same effect as depression - psychological
Aim to improve pt management of pain with cognitive techniques
