Sensory systems and pain

Question 1

Where do primary sensory nerves enter the spinal cord?

Answer 1

Via the dorsal root ganglia

Question 2

Which sensory fibres decussate? (cross over the midline)

Answer 2

Secondary fibres

Question 3

Which tract transmits fine touch, conscious proprioception and is responsible for two-point discrimination?

Answer 3

The dorsal column

Question 4

Where do the primary fibres of the dorsal column synapse with secondary fibres? Where do these secondary fibres decussate?

Answer 4

Brainstem

Question 5

Which tract transmits crude touch, temperature and localising pain?

Answer 5

The spinothalamic tracts (anterolateral)

Question 6

Where do the primary fibres of the spinothalamic tract synapse? Where do the secondary fibres decussate?

Answer 6

In the dorsal horn

Secondary fibres decussate in the spinal cord, a few levels superior to where the primary nerve entered the cord

Question 7

Describe the role of the spinocerebellar tract

Answer 7

Unconscious proprioception

Sends information about the length and tension of muscle fibres from the periphery to the cerebellum via the spinal cord

Question 8

Describe the role of the spinoreticular tract

Where does it decussate?

Answer 8

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

Question 9

Which types of nerve fibre conduct pain?

Answer 9

A-delta fibres - conduct rapid, sharp, localised pain

C fibres - conduct slow, dull, diffuse main

Question 10

Which types of nerve fibre conduct sensation from non-noxious stimuli, i.e. light touch, pressure and vibration

Answer 10

A-beta fibres (large myelinated fibres - very fast)

Question 11

Which types of nerve fibres transmit sensory information from muscle spindles and golgi tendon organs? For what is this information used?

Answer 11

A-alpha and A-beta fibres

Proprioception

Question 12

Describe the types of peripheral pain sensitisation

Answer 12

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

Question 13

What are the three types of central pain sensitisation?

Answer 13

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

Question 14

Describe the mechanism of wind-up sensitisation, including the neurotransmitters involved

Answer 14

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

Question 15

Describe the mechanism of classical sensitisation and the neurotransmitters involved

Answer 15

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

Question 16

Describe the mechanism of long-term potentiation and the neurotransmitters and receptors involved

Answer 16

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

Question 17

Which parts of the brain are responsible for descending control of pain?

Answer 17

Periaquaductal Grey (PAG) complex
Rostroventromedial medulla (RVM) complex

Question 18

Which substances are involved in descending control of pain?

Answer 18

Enkephalins and endorphins (“endogenous opioids”)

Question 19

What are the four parts of the pain pathway that can be targeted with therapy to reduce pain?

Answer 19

Transduction
Transmission
Perception
Descending modulation

Question 20

Where in the pain pathway do opioids affect?

Answer 20

Transmission and descending modulation

Question 21

What is neuropathic pain?

Answer 21

Pain initiaited or caused by a primary lesion of dysfunction in the somatosensory nervous system