Headache of Intracranial Origin
Pain-Sensitive Areas in Cranial Vault. The brain tissuesthemselves are almost totally insensitive to pain. Even cutting or electrically stimulating the sensory areas of the cerebral cortex only occasionally causes pain; instead, it causes prickly types of paresthesias on the area of the body represented by the portion of the sensory cortex stimulated. Therefore, it is likely that much or most of the pain of headache is not caused by damage within the brain itself.
Conversely, tugging on the venous sinuses around thebrain, damaging the tentorium, or stretching the dura at the base of the braincan cause intense pain that is rec-ognized as headache. Also, almost any type of trauma-tizing, crushing, or stretching stimulus to thebloodvessels of the meninges can cause headache. An espe-cially sensitive structure is the middle meningeal artery, and neurosurgeons are careful to anesthetize this artery specifically when performing brain operations under local anesthesia.
Areas of the Head to Which Intracranial Headache Is Referred.
Stimulation of pain receptors in the cerebral vault above the tentorium, including the upper surface of the tentorium itself, initiates pain impulses in the cerebral portion of the fifth nerve and, therefore, causes referred headache to the front half of the head in the surface areas supplied by this somatosensory portion of the fifth cranial nerve, as shown in Figure 48–9.
Conversely, pain impulses from beneath the tentorium enter the central nervous system mainly through the glossopharyngeal, vagal, and second cervi-cal nerves, which also supply the scalp above, behind, and slightly below the ear. Subtentorial pain stimuli cause “occipital headache” referred to the posterior part of the head.
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