The carotid is more easily seen in this image than the vertebral artery.
Vertebral Artery
From the eMedicine site:
The typical presentation of VAD is a young person with severe occipital headache and posterior nuchal pain following a recent, relatively minor, head or neck injury. The trauma is generally from a trivial mechanism but is associated with some degree of cervical distortion.
Focal neurologic signs attributable to ischemia of the brain stem or cerebellum ultimately develop in 85% of patients; however, a latent period as long as 3 days between the onset of pain and the development of CNS sequelae is not uncommon. Delays of weeks and years also have been reported. Many patients present only at the onset of neurologic symptoms.
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From vertebralarterydissection.com
The major causes of stroke in young adults and children differ from those in older people. Dissection of the internal carotid and vertebral arteries in the neck accounts for about a fifth of strokes in the young compared with about 2.5% in older patients.
…The incidence of arterial dissection is increased in patients with fibromuscular dysplasia, migraine, or hypertension; in smokers; and in those taking oral contraceptives. It is commonly associated with trauma or manipulation to the neck.
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From the above it seems clear that care should be taken by to avoid rapid and extreme flexion, extension, and rotation of one’s partner’s head. Percussion of the neck should likewise be avoided. Those techniques that require such movements should be modified by limiting the velocity and degree of manipulation, and/or contact. Children’s necks are especially vulnerable and therefore these techniques are not appropriately practiced on them. Newer students who have not yet demonstrated their ability to use discretion in their application of force in partner work should not be encouraged or allowed to practice these kinds of techniques.
Instructors should carefully observe students when they are engaged in practicing encounters in which neck manipiulation is required, and should take seriously any complaints of headache, nausea, changes in vision, or other related symptoms.
are available here.
Fight Sciences Research Institute blog 
This is why some techniques that are allowed in freestyle wrestling are banned in high school/collegiate wrestling (folkstyle)- like the suplay/suplex.
Bob, is there any similar data of this type attributable to repeated choking, especially in a free-rolling context?
Randy,
I have not found any data that is specific enough to answer your question. There are several reports of arterial dissection following wrestling and judo, however the reports I have seen do not go into sufficient detail to determine if they were more likely to appear in people who have been exposed to multiple neck traumas over time, or to tell if there there is greater exposure to risk in “free-rolling” encounters. It does appear that even relatively moderate twisting forces when applied to the neck (as is the case with chiropractic adjustments) can precipitate vertebral arterial dissection, especially in the area around the atlas (top) vertebrae. This being the case I will be greatly surprised if the greater sensitivity by emergency room physicians to the possibility of arterial dissection following grappling and other MA activity does not eventually confirm that repeated, freestyle encounters in which the neck is subjected to trauma is particularly dangerous. Barring evidence to the contrary I think it is safe to assume that such activity does represent a greater risk than that posed by ippon kumite type encounters in which the force applied to the neck is deliberate, expected, and hopefully reasonable.
I have create a group on Facebook called ‘Carotid Artery Dissection’. Of the 60 plus members who’ve experienced a dissection, there is one 17 year old male who experienced a dissection during a wrestling match.