Sensory systems and pain Flashcards
Where do primary sensory nerves enter the spinal cord?
Via the dorsal root ganglia
Which sensory fibres decussate? (cross over the midline)
Secondary fibres
Which tract transmits fine touch, conscious proprioception and is responsible for two-point discrimination?
The dorsal column
Where do the primary fibres of the dorsal column synapse with secondary fibres? Where do these secondary fibres decussate?
Brainstem
Which tract transmits crude touch, temperature and localising pain?
The spinothalamic tracts (anterolateral)
Where do the primary fibres of the spinothalamic tract synapse? Where do the secondary fibres decussate?
In the dorsal horn
Secondary fibres decussate in the spinal cord, a few levels superior to where the primary nerve entered the cord
Describe the role of the spinocerebellar tract
Unconscious proprioception
Sends information about the length and tension of muscle fibres from the periphery to the cerebellum via the spinal cord
Describe the role of the spinoreticular tract
Where does it decussate?
Involved in the emotional aspects of pain
Sends collateral neurones to the reticular formation in the brainstem
Decussates in the spinal cord and ascends with the spinothalamic tract
Which types of nerve fibre conduct pain?
A-delta fibres - conduct rapid, sharp, localised pain
C fibres - conduct slow, dull, diffuse main
Which types of nerve fibre conduct sensation from non-noxious stimuli, i.e. light touch, pressure and vibration
A-beta fibres (large myelinated fibres - very fast)
Which types of nerve fibres transmit sensory information from muscle spindles and golgi tendon organs? For what is this information used?
A-alpha and A-beta fibres
Proprioception
Describe the types of peripheral pain sensitisation
Hyperalgesia - exaggerated responde to normal and supranormal stimuli. Changes occur in the nociceptor because of inflammatory mediators
- primary; at the site of injury
- secondary; in the surrounding tissues
Allodynia - decreased threshold for nociceptor response
What are the three types of central pain sensitisation?
WInd-up: progressive increase in response of secondary afferent neurotransmitters
Classical: the opening of new synapses in the dorsal horn
Long term potentialtion: pain continues on a long term basis
Describe the mechanism of wind-up sensitisation, including the neurotransmitters involved
Progressive increase in response of secondary afferent neurones
Only involves activated synapses
Manifests over the course of the stimuli and terminates with the stimuli
Mediated by neurotransmitters; higher-intensity stimulus = more neurotransmitter release
- substance P
- CGRP
Describe the mechanism of classical sensitisation and the neurotransmitters involved
New synapses open in the dorsal horn Neurones that do not normally receive input start to receive input and record nociception Outlasts the stimuli Maintained even at low levels of stimuli Uses glutamate
Describe the mechanism of long-term potentiation and the neurotransmitters and receptors involved
Pain continues on a long term basis Involves mainly the activated synapses Occurs primarily for very intense stimuli Uses glutamate as a neurotransmitter Uses AMPA and NMDA receptors
Which parts of the brain are responsible for descending control of pain?
Periaquaductal Grey (PAG) complex Rostroventromedial medulla (RVM) complex
Which substances are involved in descending control of pain?
Enkephalins and endorphins (“endogenous opioids”)
What are the four parts of the pain pathway that can be targeted with therapy to reduce pain?
Transduction
Transmission
Perception
Descending modulation
Where in the pain pathway do opioids affect?
Transmission and descending modulation
What is neuropathic pain?
Pain initiaited or caused by a primary lesion of dysfunction in the somatosensory nervous system
