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What is a headache?

We all know the feeling after a long stressful day, when the tensions of the past few 415px-Tension-headachehours begin to amass in your temples, perhaps starting as a dull throb before advancing in waves to a deep pounding ache. The headache is a common malady, but what mechanisms lay behind these debilitating pains and which aspects of your life may be triggering them?

The question of why and how we experience headaches is significantly harder to answer than you might imagine. Particularly since the term ‘headache’ is in itself non-specific, being a broad term used to describe a range of common head pains, each of which may stem from a different underlying cause. Interestingly, however, one thing we do know is that the pain you experience during a headache does not originate from the brain itself. Indeed, the brain lacks pain receptors (nociceptors), therefore does not have the capacity to feel pain.

543px-Gray507But then where does the pain of a headache come from? The pain we experience during an everyday headache originates in pain-sensitive structures surrounding the skull. These include; the extracranial arteries, veins, cranial and spinal nerves, neck and pericranial muscles – all of which express pain receptors and are therefore susceptible to these sensations.

It is possible to pin down a number of simple lifestyle factors which commonly contribute to the development of headaches. These include; emotional disturbances, stress and mental tension, certain types of food, alcohol, cigarette smoke, exercise and even the way you wear your hair – hair-dos (including the tight ponytail, braids, headbands and even tight hats) can strain the connective tissue that lies across the scalp and cause headaches. So simply letting your hair down can relieve this pressure and thus the pain of the headache.

A number of the factors which lead to headaches (including certain foods, cigarette smoke and alcohol) involve the blood vessels which lie around the brain. For example, inhaling nicotine from cigarette smoke causes narrowing of blood vessels around the skull. Narrowing of these vessels can often induce extremely painful headaches. Changes in blood pressure also explain hangover and exercise headaches and why, for some people, certain foods can act as headache triggers.

6708719835_b2f15fc2e3The episodic tension headache (the type you may get after a long day at work) is the most commonly occurring type of headache. However despite the extensive research into the cause of migraines, this common type of headache remains one of the least investigated. As relief can normally be sought through over-the counter painkillers, most sufferers will not consult a doctor. The mechanisms underlying what specifically causes these headaches remains elusive, however, a number of theories regarding their pathophysiology have been proposed:

It appears that the occurrence of headaches are commonly linked to general problems of the musculoskeletal system. Skeletal muscle constitutes the largest muscle mass of the body, controlling movement, breathing, facial expressions and numerous other normal physiological functions. Each individual skeletal muscle is composed of hundreds of cells, arranged in muscle fibres. Each muscle fibre is connected to the nervous system via interactions with a single branch (an axon) of a nerve cell.

Each fibre of a muscle can relax or contract in response to signals sent from the brain via these nerves. These muscle fibres also contain sensory receptors which can feedback the health of the muscle to the brain. This helps tell you when the muscle is tired or overstretched for example. Abnormal activity in these nerves, perhaps as a consequence of injury, stress or poor posture, can therefore result in the relay of pain signals to the brain. For example, bad posture places abnormal pressure on the muscles of the neck which can result in heightened tension and the subsequent development of ‘tension headaches’.

Interestingly, tension headaches can also be induced by activation of so-called ‘trigger points’. A trigger point is defined as ‘a hypersensitive area of the body, associated with taut bands within a skeletal muscle’. Pressure or compression on these localized trigger points can cause the referral of pain along linked nerves to a nearby area. So, the presence of active trigger points in your head, neck and shoulder muscles can refer pain that will be subsequently experienced as a headache.

A number of studies have confirmed this, identifying an increased number of trigger points in the muscles of the head in patients prone to headaches, compared with patients who do not regularly experience headaches. What causes these trigger points to develop in the first place still remains unclear, however, some have speculated that they may be associated with past muscular injuries, fatigue, diet and even as a result of chronic repetitive strain, such as persistent typing.

5621720708_3e3b9c45c1Infrequent headaches, while menacing, are nothing compared to their chronic cousins. Infrequent headaches can become chronic as a result of changes that originate in the brain and spinal cord. This involves so called ‘second-order’ nerve cells which act as connectors between peripheral organs (e.g. the skin and muscles) and nerve cells in the spinal cord and brain.

A number of studies have proposed that chronic tension headaches may be triggered by changes in the sensitivity of these second order nerves, particularly those in the spinal cord and an area of the brain known as the trigeminal nucleus. This process is known as ‘central sensitization’ and can alter pain thresholds and trigger nerve cell activity. It is hypothesized that, in the presence of persistent stress or pain signals from peripheral muscles (such as that brought about through regular bad posture), nerve cells can grow forming new connections and effective contacts to low-threshold nerves that do not normally signal for pain. Furthermore, increased sensitivity can be caused by the enhanced release of chemicals that facilitate nerve cell communication. This increase in the number of pain signalling nerves and their sensitivity to strain and tension results in enhanced pain sensitivity, lower pain thresholds and the development of chronic pain states.

Chronic pain states, may be a result of prolonged stress and musculoskeletal tension, alongside central changes in the brain and spinal cord. So, if regular headaches are wearing you down you might benefit from trying to reducing your stress levels, being aware of dietary triggers, improving your posture and trying exercises to relax your muscles.

Post by: Isabelle Abbey-Vital

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The brain bank comprises a group of scientists from the North West of England eager to enthuse and entertain with their scientific banter. To learn more about who we are see the our 'about' page. You can also find us on twitter @brainbankmanc or email us brainbankmanc@gmail.com.
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