Pain Pathways - NMSK

what is meant by noxious stimulus?

a stimulus that is damaging or threatens damage to normal tissues

what is meant by nociception?

the neural process of encoding noxious stimuli. Nociceptive pain (pain from activation of nociceptors)

what is meant by central sensation?

increased responsiveness of nocioceptive neurons in the CNS to their normal or subthreshold afferent input

what is meant by somatic pain?

pain experienced from skin, muscle, bone damage/disease

what is meant by visceral pain?

pain experienced because of organ pain (abdominal or thoracic)

what is meant by neuropathic pain?

pain cause by a lesion or disease of the somatosensory nervous system (in contrast to nociceptive pain)

what is meant by wind up?

wind up is a frequency-dependent increase in the excitability of spinal cord neurones, evoked by electrical stimulation of afferent C-fibres

what is the cortex?

where signals comes from - location and intensity signals come in from pelvis to spinal cord to cortex of limbic brain and signals go to limbic brain

what is the limbic brain in control of?

emotions

what is pain?

perception of whats happening - have to be conscious

what is nociception?

the signals of pain is happening - can be both conscious and unconscious and it still happens

what are the possible stimuli?

mechanical, thermal and chemical

what are nociceptors?

non-encapsulated nerve endings

what is the neuroanatomy of pain pathway?

nociceptors are stimulated

stimulates A delta and C fibres

enters grey matter in organised way

what are A fibres?

myelinated, fast conduction, well localised, sharp pain

what are C fibres?

unmyelinated, slow, dull aching pain, not well localised

what are the 2 ascending pathways?

spino(cervico)thalamic tract and spinoreticular tract

describe the spino(cervical)thalamus tract?

first order neurone (primary afferent fibre) synapses in dorsal horn of spinal cord, these synapse with second order neurones (projection nerones) which decussate (cross over) to ascend in the spinal thalamic tract. Third order neurone arises in contralateral thalamus and ascends to the cortex

what is the spino(cervic)thalamic tract?

primary pain pathway and tested by light pinch of skin

what is the difference in carnivores spin(cervico)thalamic tract?

have 2 spinal projection neurones, making a total of 4 rather than 3 neurones for this pathway

describe the spinoreticular tract?

primary afferents enter spinal cord and diverge cranially and caudally - spreads over several segments and allows intersegmental reflexes such as withdrawal

second order afferents in the dorsal horn (diffuse and bilateral) project to the reticular formation, then some pass to the thalamus

what kind of pain does the spinoreticular tract react to?

deep pain and visceral sensations

activates limbic system - emotional response

how is head pain stimulated?

3 neurones, cell bodies in trigeminal ganglion, enter pons and course along medulla

what are the non-conscious responses to pain? (5)

• cardiovascular changes

• respiratory changes

• behavioural changes

Ascending pain also connects hypothalamus:

• increasing levels of epinephrine

• increasing levels of glucocorticoids

what are the 3 modulations?

peripheral modulation

doral horn modulation

suprasegmental modulation

describe peripheral sensitisation?

inflammatory mediators trigger signalling pathways in the primary afferents, causing changes in the function/expression of receptor molecules and voltage gated ion channels which ultimately causes those afferents to become hyperresponsive to stimulation

what is dorsal horn modulation?

the gate theory of pain - one group of second-order neurons deals with the nociception

another recieves input from mechanoreceptors and may modulate the first group

explains why we rub a smack

in the grey matter of the dorsal horn there are 2 types of cells

what are the 2 types of cells of dorsal horn?

nociceptive specific

wide dynamic range

describe suprasegmental?

the PAG and the NRM and 2 important nuclei

PAG recieves input from fibres about noxious stimulation and NRM releases serotonin and norepinephrine

affects interneurons in the dorsal horn

what are the adverse effects of unrelieved pain?

neuroendocrine - hypoglycaemia, wweight loss, decreased wound healing, impaired immune system

cardiovascular - fatigue, immobility, weakness

respiratory - decreased lung volume leading to atelectasis and hypoxaemia

GIT and urinary - decreased bowel motility leading to constipation, anorexia, ileus, urinary retention

MSK - decreased muscle function and spasm leading to weakness, immobility and fatigue

Physchological - fear, anxietty leading to poor sleep, decreased coping, PTSD