RELEVANT ANATOMY AND PHYSIOLOGY
Before moving on to different types of headaches, it is important to review the relevant anatomy and physiology because the Skeletal anatomy The most important areas of the skull to be familiar with are the frontal area, or forehead region, and the occiput, or lower posterior region of the head. Many headache symptoms occur in one or both of these areas. The occiput is commonly referred to as the back of the head by headache sufferers and feels like a ridge with a bony protuberance, or “bump of knowledge,” in the middle. The upper trapezius muscle, which is prone to chronic tension, attaches on either side of this external occipital protuberance (Biel, 2001). The temporal region is likely the signature area associated with headache pain. Located on either side of the head, the temporal bone contains the mastoid process as a bony landmark found behind the ear and is the attachment site for the sternocleidomastoid muscle whose trigger point patterns refer unilaterally to the eye. The zygomatic arch, or cheekbone, is another important feature of the temporal bone. The masseter, another muscle known to contribute to headache pain, attaches to it, and the temporalis muscle passes underneath it to attach to the jaw (Biel, 2001). The brain As previously mentioned, the brain itself cannot experience pain; the structures in and around the brain are implicated in causing headaches. Three layers of meninges surround the brain, as well as the spinal cord, and function to protect it: 1. The outermost layer is the dura mater, whose main responsibility is to prevent the brain from moving. Nerves Beneath the brain sits the brainstem, which consists of the midbrain, pons, and medulla oblongata. The medulla oblongata then continues beyond the skull as the spinal cord. Within the brainstem, 10 of 12 total cranial nerves originate. Of these 10, 2 are essential to headache disorders: the cranial nerve V (CN5), also termed the trigeminal nerve, and the cranial nerve VII (CN7), known as the facial nerve . The trigeminal nerve provides motor control to the temporalis muscle and the other major muscles used for chewing. It then divides into the ophthalmic, maxillary, and mandibular nerves, which supply sensory input to the eye, nose, and face. The trigeminal nerve also receives information 2. The middle layer is the arachnoid. 3. Innermost meninx is the pia mater.
brain itself is incapable of producing pain. Because of this, a headache will be the result of structures in and around the head.
The last skeletal area of significance to headache pain is the cervical spine. It houses the spinal column and the exit point for eight cervical nerves and possesses two distinct variations from the vertebrae in the thoracic and lumbar regions. The first differentiating characteristic is the presence of transverse foramina, or openings, where the major arteries of the neck and the sympathetic nerve plexus pass through. The significance of this feature is the risk that injury or trauma to the cervical vertebrae may have on the spinal nerves. Part of what gives the cervical spine more mobility than any other region is the second distinct variation, which is the structure of the C1 and C2 vertebrae and their articulation, known as the atlantoaxial joint . C1, otherwise known as the atlas , is where the majority of flexion of the head occurs. With its ring shape, this vertebra is where the occiput of the head attaches to the spine. The atlas then rotates around the odontoid process, or pivot point, of C2 (referred to as the axis) creating the atlantoaxial joint and the location for 50% of neck rotation (Fritz, 2015; Medscape, 2017). The space between the arachnoid and pia mater is known as the subarachnoid space and is most pertinent to the study of headaches. The subarachnoid space is where all blood vessels and cranial nerves travel en route to and from the brain. The two suppliers of blood to the brain are the internal carotid and vertebrobasilar arteries that connect in the midbrain to form the circle of Willis where it then passes through the subarachnoid space as it gets distributed throughout the brain (Fritz, 2015; McCaffrey, 2014). from the facial nerve, whose main function is to innervate the muscles for facial expression. It is important to also note one of the spinal nerves in regard to headaches: the occipital nerve, which arises from the cervical plexus between the C1 and C3 vertebrae, and then splits into greater and lesser divisions. Implicated in occipital neuralgia, the greater occipital branch provides sensation to the top of the head and suboccipital region. The lesser occipital branch innervates the scalp and sternocleidomastoid muscle (Medscape, 2017).
PATHOPHYSIOLOGY
There has been much debate regarding the cause of primary headache pain. For the longest time, it was believed that migraine, sinus, and cluster-type headaches were a result of reduced blood flow in the brain followed by vasodilation that brought an influx of oxygen resulting in swelling of the meninges creating pain and, in the case of migraine, an aura. This is known as the vascular theory and was presented about 1950. Because vasoconstricting drugs were effective in easing headache pain, this theory held for some time despite the fact that some people did not experience an aura with their migraine. Then, once neuroimaging became available, researchers noticed that blood flow patterns did not support this theory (Chawla, 2017). Now the cause of primary headaches is explained by the neurovascular theory. Instead of blood vessel constriction and subsequent dilation the main reason for headaches, it is thought to be a by-product of a nervous system disorder where the
sensory neurons of the trigeminovascular system (the portions of the trigeminal nerve that stimulate the blood vessels of the brain) are easily activated by stimuli, or readily excitable. Because the trigeminovascular system receives input from the cervical structures as well as areas of the brain, the cause for this sensitization may require imaging to pinpoint (Chawla, 2017). Researchers are also looking into the role that serotonin plays in possibly causing migraine; most medications function by supporting serotonin uptake. This neurotransmitter is an antagonist to dopamine, a chemical known to cause irritability, nausea, and other headache symptoms when in excess. Several other events occur within the brain chemically that researchers continue to study in an effort to discover which one begins the cascade of others leading to headache pain. As time goes on, the neurovascular theory may be transformed to include these new research findings (Chawla, 2017).
HEADACHE CLASSIFICATION
Cephalalgia is often self-treated with over-the-counter medications or rest that most patients disregard when their symptoms first begin. It usually is not until a pattern emerges
that a patient seeks medical help out of fear of something more dire as the cause. This lapse in time makes diagnose difficult, especially because it can be enigmatic for patients to effectively
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Book Code: MLA1224
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