The sphenoid bone, part 2
Part I showed us the many bones the sphenoid articulates with. Remember that any bone articulating with the sphenoid will be effected by it and will effect it. In part II we will look at one of the more common things effecting the sphenoid, the jaw. Rarely do you find someone with perfectly equal tensile force on both sides of the jaw. Generally there will be more tension on one side of the jaw. This can be due to many things; dental work, orthodontics, missing teeth, pain on one side, habit, etc. But for our purposes we are going to move away from functional reasons the jaw is misaligned and look at anatomical reasons.
One of the more common ways to achieve a misalignment of the mandible is to have a shifted hyoid bone. The mechanisms by which the hyoid bone effects the mandible are as follows: both mylohyoid and geniohyoid attach to both the hyoid and the mandible, genioglossus attaches the mandible to the underside of the tongue and the hyoid bone, and the hyoid and mandible are also attached by the mandibulo hyoid ligament.
Many things effect the position of the hyoid bone. Omohyoid muscles originate from the superior borders of the scapulas. Any movement of the scapula from a neutral position will affect the position of the hyoid bone. We could continue this for days; sternohyoid is going to connect the sternum to the hyoid, which means any shift from neutral of the sternum will also affect the position of the hyoid; the hyoid also provides attachment for the muscles of the larynx and the muscles under the tongue, either of these structures could affect the hyoid’s neutral position; etc., etc. (as a side note, a yoga teacher once told me that if the hyoid bone is out of alignment, the pelvic floor muscles will not contract properly, leading to poor posture, back pain, and bladder leakage)
Moving up into the head a little further, we know that the position of the mandible will affect the position of the temporal bones. This is simply due to the articulation at the temporomandibular joints. When the mandible shifts to one side the position of the temporal bones have to be affected. But the hyoid position will also affect the position of the temporal bones. This is due to the stylohyoid and digastric muscles attaching the hyoid to the temporal bones.
When the hyoid shifts, which happens frequently because of the various pulling forces on this small bone, it not only affects the position of the mandible, but also of the temporal bones. How does this then affect the position of the sphenoid? The sphenoid articulates directly with the temporal bones through the sphenosquamosal sutures. An immobilization of one or both temporal bones has a direct effect on the mobility of the sphenoid bone.
The mandible is connected to the sphenoid by the sphenomandibular ligaments. As the mandible shifts and tightens on one side, the sphenomandibular ligament on that side also tightens. The tightened spenomandibular ligament then pulls the sphenoid to that side, creating a misalignment of the sphenoid bone. Additionally, the medial pterygoid muscles originate on the lateral pterygoid plate of the sphenoid bone and insert on the medial angle of the mandible. So, as the jaw shifts to one side, one of the medial pterygoid muscles will tighten more than the other, again leading to a shift of the sphenoid in that direction.
This began with a shift to the hyoid, which shifted the mandible, then both of these shifted the temporal bones, then the shift at the mandible and temporal bones shifted the sphenoid. The shift in the neutral position of the sphenoid can have a multitude of affects. Anatomical effects can include a misalignment of the sphenobasilar joint, leading to a sub-occipital or eye orbit headache, or an immobilization of the frontal bone, leading to a frontal or temporal headache.
Physiological effects are caused by the location of the pituitary inside the sella turcica. As the sphenoid moves from its neutral position and/or becomes immobile on one side, it inhibits the communication between the pituitary and the hypothalamus. This can lead to depression, hypothyroid symptoms, fatigue, and more. In addition to this, immobilization and shifting of the sphenoid effects the flow of the cerebrospinal fluid. This can lead to general sluggishness, slow thinking, headaches, and exhaustion.
To relieve these symptoms, both anatomical and physiological, it is important to know how to work on the anterior neck, and how to work with the cranial bones. In part III of the sphenoid bone, we will look at the affects of misaligned cervical vertebrae on the position of the sphenoid.