Blogation Numero Tres

The Hyoid bone is a horseshoe-shaped bone situated in the anterior neck between the mandible and the thyroid cartilage. It is supported by the stylohyoid ligaments, and does not articulate with any other bone (which makes it unique to the human body). The Hyoid serves as the attachment point for the anterior neck muscles, which in turn help support the movements of and provide stability to the pharynx and larynx. The Hyoid bone also maintains an open airway, and along with the attached muscles facilitates swallowing.

Fracture of the Hyoid bone is often seen in strangulation injuries when the throat is compressed. This fracturing leads to the sinkage or lowering of the hyoid bone onto the superior surface of the thyroid cartilage. Such an injury can create a difficulty in swallowing because of an inability to elevate the hyoid. It can also potentially lead to difficulty in separation of the respiratory and alimentary tracts, which can in turn lead to aspiration pneumonia (develops due to entry of foreign particles, e.g. food, into bronchi).

The phrenic nerve originates from the ventral rami of the C3, C4, and C5 vertebrae. It contains sensory, motor, and sympathetic nerve fibers. The phrenic nerve provides all of the motor innervation (and most of the sensory) to the diaphragm. It also innervates the mediastinal pleura and the pericardium. The nerve courses from lateral to medial across the anterior scalene before descending inferiorly through the thorax to the diaphragm. 

Disjuncture of the phrenic nerve will lead to a paralysis of half of the diaphragm (depending on the which is cut). Diagnosis of such a rupture can be made using radiographic imaging to observe diaphragmatic contraction. If a paralysis of one side has taken place, the dome on that side will descend during expiration as opposed to the normal ascension seen. The phrenic nerve can be purposefully blocked using anesthetic, as is the case in surgical procedures performed on the lungs. This would provide a small window of paralysis of the diaphragm for the surgeon to be better able to perform the operation on surrounding tissue.


The internal carotid arteries are major arteries of the head and neck that are terminal branches of the common carotid arteries. The proximal portion of the internal carotid artery is the location of the carotid sinus. The carotid sinus is a dilation in the artery, innervated by the glossopharyngeal nerve, which measures pressure changes in arterial blood flow. In turn, the glossopharygneal relays that information to the brain in an effort the counteract the change. The internal carotid arteries enter the cranium through the carotid canals, and then divide into the middle and anterior cerebral arteries.

Blood flow through the internal carotid arteries may be restricted or blocked by atherosclerotic thickening of the intima (innermost layer of artery). Symptoms and severity of this blockage depend on the extent of the obstruction, and the ability of the body to compensate for the lost blood flow. An incomplete blockage of the internal carotid arteries can lead to a transient ischemic attack (TIA), in which there is a temporary loss of neurological function in the area of the brain that lost blood flow. These carotid occlusions can be resolved by a procedure called a carotid endarterectomy, in which the atherosclerotic plaque is stripped off the artery it is blocking.


References
Moore et al. "Clinically Oriented Anatomy" (2010) 6th ed
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