Physiological mechanisms of brain trauma and headache

Primary mechanisms of brain trauma

A number of anatomic structures of the head and neck can be involved in the generation of pain. A headache following injury to the head, jaw, and neck can be explained by the damage to extra-cranial features including bones, arteries, skin and discs. Injuries causing pain can affect intra-cranial features such as the dura at the brain base, the venous sinuses and a number of cranial nerves such as the optic, oculomotor, trigeminal, glossopharyngeal and vagus nerves. The upper cervical spine, as well as neurological pathways in the spinal cord and brain stem, can also trigger pain.

Causes of headache following mild brain trauma

Figure 1.3 Causes of headache following mild brain trauma.

Example: headache generated by activation of the trigemino-cervical complex

An external injury to the head and neck triggers pain sensitive receptors and activates a pain pathway associated with the trigeminal neurovascular system. This can lead to the spreading of the pain sensation known called “referred pain,” i.e., pain originating from an injured location that is perceived in a different area.

The trigeminal nerve, as one of the major pain-transmitting pathways, contains afferent nociceptive fibres from the anterior scalp and cranium, face, mouth, teeth, temporomandibular joints, sinuses, cranial blood vessels and meninges. A rich network of nociceptive fibres originates in the trigeminal ganglion and innervates the blood vessels of the meninges and a range of large cerebral arteries.

The occipital nerves, arising from cervical spinal roots (C2, C3), connect pain stimuli from the posterior head and scalp. Trigeminal and cervical nociceptive neurons merge in the upper cervical spinal cord (Figure 1.4). Neurons in this region can perceive afferent pain signals from cervical and trigeminal sources. As a result, the peripheral activation of one area can stimulate the central pain systems of the other and vice versa. It is thought that the trigemino-cervical complex explains how injuries to the neck cause head pain and how the activation of trigeminal pathways is linked to neck and posterior headache.

Trigemino-cervical complex

Figure 1.4 Trigemino-cervical complex.

 
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