Brain Blood Supply

The human blood circulatory system is a complex mechanism consisting of four muscular pump chambers and a lot of channels. The vessels that provide the organs with blood are called arteries.

These include the common carotid artery that carries blood from the heart to the brain. Normal functioning of the brain and the whole body is impossible without effective blood circulation, as it transmits essential elements and oxygen.

The brain blood supply functions
through 2 pairs of arteries that originate from the chest, pass through the
neck and reach the brain. These are the 2 internal carotid arteries that feed
the front of the brain, and the 2 vertebralis arteries that feed the back of
the brain (1).

Position and Structure of the Carotid Artery

People often wonder how to find the carotid artery in the neck. The answer is to address the basics of human anatomy. Furthermore, there is a common misconception that a person has only one carotid artery: in fact, there are two.

These are located on both sides of the neck and are the most important sources of blood circulation. In addition to these blood vessels, there are two additional vertebral arteries, which are much lower than the somnolent volume of the fluid being transported.

To feel the pulse, you need to find a spot in the groove below the cheekbone on one side of the so-called Adam's apple. The usual paired carotid artery originates from the chest, then flows along the neck to the skull, ending at the base of the brain. The longer right branch extends from the brachiocephalic trunk, while the left branch extends from the aorta (2).

On the exterior of the common carotid artery, there is the jugular vein, and the nervus vagus is located between them. A vascular bundle is formed. A special feature of this blood vessel is the presence of the spreading carotid sinus with a nodule adjacent to it. The external carotid canal consists of several groups of blood vessels.

The location of the branch of the internal carotid artery is considered intracranial, as it enters the cranium through a separate hole in the temporal bone. The area of the junction of the vessel with the basal artery through the anastomosis is called the Willis Circle. Internal carotid artery segments transmit blood to the visual organ, anterior and posterior parts of the brain, and cervical vertebrae. This vein consists of seven vessels.

The Function of the Carotid Artery

In addition to the blood flow, the
carotid arteries handle other tasks as well. The carotid sinus has nerve cells,
whose receptors have the following functions:

• monitor internal vascular pressure;
• respond to changes in the chemical
  composition of the blood;
• give signals about the presence of
  oxygen coming from erythrocytes;
• participates in the regulation of
  cardiac muscle activity;
• monitor the pulse;
• maintain blood pressure.

Position and Structure of the Artery Vertebralis

Vertebral arteries account for 30% of the blood supply to the brain, supplying predominantly the posterior parts of the brain. Our vertebral arteries are located within the lateral spines of the neck or cervical spine, thus being positioned along the course of the cervical vertebrae.

The vertebral arteries originate from the subclavian arteries in the upper thoracic cavity, pass into the openings of the transverse parts of the cervical vertebrae, then enter the cranial cavity, where they merge into a single basilar artery located in the lower part of the brain stem. The branches of the basilar artery provide blood to the brain stem, brain, and occipital lobes of the cerebral hemispheres.

There are 7 Vertebral Artery Branches

• spinal branches
• meningeal branches
• muscular branches
• anterior spinal artery
• posterior spinal artery
• medullary branches
• posterior inferior cerebellar artery
  (3).

The Function of the Vertebral Artery

Through their branches, the vertebral arteries and the basilar artery supply the blood to the enlarged brain, the cerebellum and the back of the cerebellum.

Now, we will talk about the function of each vertebral artery branch.

Firstly, the meningeal branches supply the falx cerebelli and the posterior cranial fossa. Secondly, the anterior spinal arteries supply the spinal cord. Likewise, the posterior spinal artery has a role in spinal cord blood supply. Similarly, the spinal branches reach the spinal cord through a segment called intervertebral foramina. These branches are also responsible for the spinal cord blood supply.

Moreover, the muscular branches supply deep neck muscles, while the posterior inferior cerebellar artery plays the key role in supplying the medulla oblongata, the inferior vermis, the 4^th ventricle choroid plexus, the cerebellar hemisphere, and the dentate nucleus. Finally, the medullary branches supply the medulla oblongata.

Diseases

Vertebrobasilar insufficiency or vertebral artery syndrome is a condition in which blood flow in the spinal and basilar arteries is reduced. The cause of these disorders may be extravasal compression, elevated spine tone (arterial circulation, vegetative-vascular dystonia), atherosclerosis, anatomical features of the body, etc.

Disorders in the volumetric and linear blood flow velocities in the spine, associated with the extravasal compression, can be detected on both sides. The most common pressure factor is muscle tissue, which is associated with anatomical localization of the vertebrae. 

Carotid artery syndrome is a disease characterized by spasm of the fibrous artery walls. Its occurrence is related to the accumulation of the cholesterol layer along the edges of the ducts, the separation of the shell into several layers, stenosis.

Stratification of the internal surface of the artery becomes the cause of ischemic stroke in different age groups. Patients over the age of 50 are especially jeopardized, but recent research shows that the percentage of young people's stroke is on the rise.

Prevention of the development of the CA syndrome implies a rejection of bad habits and an active lifestyle.

Aneurysms of the Brain

Brain aneurysms are widenings of the brain arteries. They usually have a baggy shape and dimensions of 5-15 mm. 1-10% of the population has aneurysms. Aneurysm is most commonly localized on the large arteries on the inferior surface of the brain. The chance for a closer relative to have an aneurysm is about 7-20%.

The aneurysm can be present during the whole lifetime without any symptoms. If it manifests itself, it is most often in the form of the bursting of the artery wall and bleeding. It is most commonly present in the form of subarachnoid hemorrhage - bleeding is most common on the surface of the brain base.

This is marked as SAH, standing for haemorrhagia subarachnoidalis. With or without SAH, bleeding within the brain (haematoma cerebri) is possible.

77% of all SAH cases occur due to
aneurysm bursting. Other reasons for this are injuries, vasculitis, coagulation
disorder, hypertension, etc.

Bleeding often occurs in the midst of excessive effort, stress, hypertensive crises, but also often in a state of rest, peace, even in sleep. The bleeding is usually manifested by a sudden and very intense headache.

In addition, the patient may have nausea and vomiting and be disturbed by light (photophobia). On examination, the patient tightens his/her neck (meningism). If, in addition to the subarachnoid, there is also bleeding in the brain (hematoma), then there are also various neurological outbreaks (e.g. half-body weakness - hemiparesis).

If bleeding is more severe, a comatose condition occurs. In about 50% of patients, bleeding is so difficult that they die before being admitted to the hospital.

When a patient is admitted to a
hospital, the clinical picture is usually that clear that a CT scan of the
brain is urgently needed to detect bleeding. If there is no CT scan at the
hospital or the condition is not clear, a spinal puncture is performed to
obtain the cerebrospinal fluid (lumbar puncture). In that case, the liquor is
bloody.

Conclusion

Vascularization of the head and neck is performed via the right and left carotid arteries and the two vertebral arteries. The right carotid artery is a branch of the anonimae artery, while the left carotid artery starts directly from the aortic arch.

This type of vascularization and branching is present in most cases, although there are variations in the number and localization of the aortic branches. Pair vertebral arteries are branches of the subclavian artery.

The common carotid artery branches in the middle part of the neck to the internal and external carotid arteries, and their anatomical relationship in the branching region and unique local hemodynamics are considered to be predisposing factors for the development of carotid atherosclerotic plaque.

The internal carotid artery gives the 2 terminal branches, the middle and anterior cerebral artery, which, together with the posterior cerebral artery, arising from the basilar artery (formed by joining of the vertebral arteries) at the base of the brain, form the Willis artery ring, the most significant collateral anterior posterior mesh basins of cerebral vascularization.

When flow through the internal carotid artery for its distal territory is inadequate, there are several possible sources of collateralisation. The cerebral circulation has an autoregulatory flow mechanism to provide a constant volume of flow regardless of the wide range of physiological variations in blood pressure, minute heart volume, and circulating blood volume. Stroke leads to a loss of self-regulation in the affected parts of the brain.

References

1. Purves D, Augustine GJ, Fitzpatrick D, et al., editors. Neuroscience. 2nd edition. Sunderland (MA): Sinauer Associates; 2001. The Blood Supply of the Brain and Spinal Cord.  Found online at: https://www.ncbi.nlm.nih.gov/books/NBK11042/
2. Sethi D, Gofur EM, Waheed A. Anatomy, Head and Neck, Carotid Arteries. [Updated 2019 Jul 22]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2019 Jan-. Found online at: https://www.ncbi.nlm.nih.gov/books/NBK545238/
3. Eskander MS et al. Vertebral artery anatomy: a review of two hundred fifty magnetic resonance imaging scans. Found online at: https://www.ncbi.nlm.nih.gov/pubmed/20938397