Anatomy
Central Nervous System
The basilar artery is formed from which of the following blood vessels:
Answer:
The basilar artery is formed by the joining of the two terminal vertebral arteries.Arterial Supply of Brain
Anatomy / Central Nervous System
Last Updated: 30th March 2020
The brain receives its arterial supply from two pairs of vessels, the vertebral arteries and the internal carotid arteries.
![By Rhcastilhos (Gray519.png) [Public domain], via Wikimedia Commons](https://mrcemsuccess.com/wp-content/uploads/2017/01/Circle-of-Willis-643x1024.png)
Cerebral Blood Supply. (Image by Rhcastilhos (Gray519.png) [Public domain], via Wikimedia Commons)
Internal Carotid Arteries
The two internal carotid arteries arise from the common carotid arteries at the level of vertebra C4 and enter the cranial cavity through the carotid canal in the temporal bone. Entering the cranial cavity, each internal carotid artery gives off the following paired branches:
- The ophthalmic artery (supplying structures in the orbit and giving rise to the central retinal artery supplying the retina)
- The posterior communicating artery (joining the posterior and middle cerebral arteries)
- The anterior choroidal artery (supplying parts of the optic pathway, the internal capsule, the midbrain and the choroid plexus)
- The anterior cerebral artery (supplying the medial cerebral hemisphere)
- The anterior communicating artery (joining the two anterior cerebral arteries)
- The middle cerebral artery (supplying the lateral cerebral hemispheres)
Vertebral Arteries
The two vertebral arteries, branches of the subclavian arteries, ascend through the transverse foramina of the upper six cervical vertebrae before entering the cranial cavity through the foramen magnum.
The vertebral arteries give rise to the following branches:
- The single anterior spinal artery (supplying the anterior portion of the spinal cord)
- The posterior inferior cerebellar arteries (supplying the cerebellum)
- The posterior spinal arteries (supplying the posterior portion of the spinal cord) - either a direct branch of the vertebral artery or of the posterior inferior cerebellar artery
The basilar artery is formed by the joining of the two terminal vertebral arteries inferior to the pons.
The basilar artery gives rise to the following paired branches:
- Pontine arteries (supplying the pons and adjacent structures)
- Labyrinthine artery (supplying the vestibular apparatus and cochlea)
- Anterior inferior cerebellar artery (supplying the cerebellum)
- Superior cerebellar artery (supplying the cerebellum)
- Posterior cerebral artery (supplying the occipital lobe and the inferior temporal lobe)
Clinical Effects of Occlusion of the Cerebral Arteries
The middle cerebral artery is the largest branch of the internal carotid artery and supplies the largest area of the cerebral cortex. It is the most commonly involved artery in stroke. Pure anterior cerebral artery infarcts are rare because of the collateral circulation provided by the anterior communicating artery.
Table: Clinical Effects of Occlusion of the Cerebral Arteries
| Blood Vessel | Territory of Supply | Clinical Effects of Occlusion |
|---|---|---|
| Anterior cerebral artery | Medial cerebral hemisphere including the frontal lobe, superior parietal lobe and the anterior corpus callosum | FRONTAL LOBE: contralateral weakness in lower limb, dysarthria/dysphasia, apraxia, urinary incontinence, personality change
PARIETAL LOBE: contralateral somatosensory loss in the lower limb CORPUS CALLOSUM: dyspraxia and tactile agnosia |
| Middle cerebral artery | Lateral convexity of cerebral hemisphere including the frontal lobe, superior temporal lobe, inferior parietal lobe and the basal ganglia and internal capsule | FRONTAL LOBE: contralateral weakness (face/arm > leg), contralateral somatosensory loss (face/arm > leg), conjugate deviation of the eyes to affected side, expressive dysphasia, change in judgement, insight and mood
TEMPORAL LOBE: deafness (if bilateral), receptive dysphasia, auditory illusions and hallucinations, contralateral superior quadrantanopia PARIETAL LOBE: loss of sensory discrimination, hemineglect, apraxia, contralateral inferior quadrantanopia N.B. contralateral homonymous hemianopia will occur if the entire optic radiation is affected, and global dysphasia will occur if both the Broca and Wernicke speech areas are affected |
| Posterior cerebral artery | Occipital lobe, inferior temporal lobe (including hippocampal formation), thalamus and the posterior aspect of the corpus callosum and internal capsule | OCCIPITAL LOBE: contralateral homonymous hemianopia with macular sparing (the macular area is additionally supplied by the middle cerebral artery), cortical blindness (if bilateral)
TEMPORAL LOBE: confusion, memory deficit OCCIPITOTEMPORAL REGION: prosopagnosia, colour blindness |
![By derivative work: Frank Gaillard (talk) Brain_stem_normal_human.svg: Patrick J. Lynch, medical illustrator (Brain_stem_normal_human.svg) [GFDL 1.3 (www.gnu.org/licenses/fdl-1.3.html), GFDL 1.3 (www.gnu.org/licenses/fdl-1.3.html), CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0) or CC BY 2.5 (http://creativecommons.org/licenses/by/2.5)], via Wikimedia Commons](https://primary-cdn.frcemsuccess.com/wp-content/uploads/2017/01/Cerebral-Vascular-Territories-1-1.jpg)
Cerebral Blood Supply. (Image by derivative work: Frank Gaillard (talk) Brain_stem_normal_human.svg: Patrick J. Lynch, medical illustrator (Brain_stem_normal_human.svg) [GFDL 1.3 (www.gnu.org/licenses/fdl-1.3.html), via Wikimedia Commons)
Circle of Willis
The arterial circle of Willis is positioned around the optic chiasm and is composed of the following (left and right) arteries:
- Anterior cerebral artery (branch of the internal carotid)
- Anterior communicating artery (branch of the internal carotid)
- Internal carotid
- Posterior cerebral artery (branch of the basilar artery from the vertebral artery)
- Posterior communicating artery (branch of the internal carotid)
Cerebral Aneurysm
Berry aneurysms tend to arise from the vessels in and around the circle of Willis. The most frequent location is the anterior communicating artery (35%), followed by the internal carotid artery (30%-including the carotid artery itself, the posterior communicating artery, and the ophthalmic artery), the middle cerebral artery (22%), and finally, the posterior circulation sites, most commonly the basilar artery tip.
Aneurysm of the anterior communicating artery may compress the optic chiasm and cause a bitemporal hemianopia. Aneurysm of the posterior communicating artery may cause an oculomotor nerve palsy. Rupture of berry aneurysm is a common cause of spontaneous subarachnoid haemorrhage.
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
