2017B01 Describe the visceral and somatic pain of labour with particular reference
to the anatomy of the pain pathways.



·         Types of pain

·         Pain pathways

·         Stage 1 pain

·         Stage 2&3 pain

·         Analgesia


Types of pain:

Somatic pain

·  Mainly Aδ fibres

·  Fast, sharp, well localized

·  Triggers withdrawal

Visceral pain

·  Mainly C fibres

·  Slow, dull, poorly localized

·  Elicits guarding

Referred pain

·  Pain perceived at a location distal to the site of insult

·  Due to convergence of somatic and visceral 1° afferents on same WDR projection neurons



Somatic afferent

·  Nociceptive receptor in tissues e.g. perineum

·  1° afferent: soma in dorsal root ganglion, synapse at dorsal horn (e.g. via sacral nerve roots)

·  2° afferent: decussates in anterior commissure and ascends via spinothalamic tract

·  3° afferent: to cortex (somatic) and subcortex (visceral, autonomic centres)

General visceral afferent

·  Nociceptive receptor in tissue e.g. cervix

·  1° afferent: piggybacks onto autonomic efferents

o With SNS: via white ramus communicans to spinal cord T1-L2

o With PSNS: via sacral nerves to S2-4 (also cranial)

o Direct synapse with wide dynamic range 2° afferents in deeper layers

o Convergence onto somatic nociceptive-specific 2° afferents in superficial layers

·  2° afferent:

o Decussation via anterior commissure (incomplete for older pathways)

o Ascent via multiple spinothalamic tracts

·  3° afferent:

o From brainstem or diencephalon to higher structures


Stage 1:


·  Until cervix effaced and 10cm dilated

Somatic pain

·  Minimal

Visceral pain

·  Rhythmic myometrial contraction – distension of lower segment and cervix

·  GVA pathway: T10-12 via ovarian and inferior hypogastric plexuses

·  Location: lower abdomen, sacrum, back


Stage 2&3:


·  2: Until baby is delivered

·  3: Until placenta is delivered

Somatic pain

·  Continuous stretching and tearing of perineum and outer 1/3 vagina

·  Pathway: pudendal nerve (S2-4), ilioinguinal and genitofemoral nerves (L1-2)

·  Location: perineum and vagina

Visceral pain

·  Continuous pressure on pelvic viscera

·  GVA pathway: T10-L1 via ovarian and inferior hypogastric plexuses; S2-4 via sacral plexus

·  Location: pelvis, inner thigh




·  Ascending: via non-pain modalities

o Activation of inhibitory interneurons

·  Descending: by NAd > 5-HT from brainstem nuclei (e.g. periaqueductal grey)

o Disinhibition of brainstem nuclei by endogenous opioids


·  Local anaesthetic:

o Spinal nerve roots

o Dorsal horn

o Spinal cord

·  Opioid:

o Dorsal horn

o Brain via CSF

o Systemic absorption


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