Referred Pain

Question 1

Where is cardiac pain referred to and why?

Answer 1

The left arm: visceral pain fibres from the heart travel in cardiac nerves along with sympathetic afferent fibres to the superior cervical ganglion of the sympathetic trunk

As the heart develops at the same segmental level as structures within dermatome T1, pain fibres enter the spinal cord along with somatic afferents from the T1 dermatome on the LEFT side

In the spinal grey matter, visceral and somatic afferents converge on secondary fibres in the spinothalamic tracts: so the pain from the heart is perceived in the cortex as if it comes from T1; the L breast and medial portion of the L arm

Question 2

Where on the body surface would one experience pain originating in the diaphragm?

Answer 2

Visceral pain arising from the diaphragm may be felt in the costal margins and shoulder region

Question 3

Why is pain from the diaphragm referred to two different regions?

Answer 3

Because…
a) The inferior intercostal nerve (T5-T11) innervates the diaphragm’s peripheral regions AND skin over the costal margins

b) The Phrenic nerve (C5) innervates the central portion of the diaphragm and the skin over the shoulders

Question 4

Why may an amputated limb still be felt and still give pain? Where does the pain originate from in the brain and what management does NOT normally work?

Answer 4

‘Phantom sensations’ usually involve the distal structures of the limb (i.e hand or foot), where the sensory receptor density was the greatest

Originates from the somatosensory regions of the cerebral cortex, canNOT normally be managed by opiate analgesia

Question 5

In serve injury such as RTA, victims may initially feel a mild pain only. Why?

(renal tubular acidosis: accumulation of acid in the body due to a failure of the kidneys to appropriately acidify the urine)

Answer 5

The frontal cortex and somatosensory cortex can interact with the nociceptive pathway to reduce the sensation of pain in critical/stressful situations by..

Fibres from these regions release opiate like neuropeptides (i.e enkephalins and endorphins) which act on cells in the periaqueductal grey matter (PAG) of the midbrain
-Opioid receptors in the PAG are engaged by ascending nociceptive fibres (forming a pain modulating feedback loop) and by cells in the hypothalamus: so in stressful situations the release of ACTH from the anterior pituitary is often accompanied by the release of endorphin like chemicals.

Descending projections from PAG activate serotonergic fibres and NA fibres in the medulla -> which activate enkephalinergic neurons in the dorsal horn of the spinal cord and trigeminal nucleus which moderates the nociceptive pathway

Question 6

Which nerve transmits the sensation of toothache?

Answer 6

Sensory fibres carried from
V2 Maxillary branch from upper teeth
V3 Mandibular branch from lower teeth
(of the trigeminal nerve)