The middle cerebral artery (MCA) supplies most of the lateral surface of the brain, including critical areas responsible for movement, sensation, language, and hearing. It is the largest branch of the internal carotid artery and the most common site of ischemic stroke, accounting for over half of all cases.
Where the MCA Originates and How It Branches
The MCA begins where the internal carotid artery splits inside the skull, then travels laterally through a deep groove called the Sylvian fissure, which separates the frontal and temporal lobes. Anatomists divide it into four segments, each named for the structure it runs along:
- M1 (sphenoidal) runs parallel to a bony ridge at the base of the skull. This first segment gives off small perforating arteries that dive down into deeper brain structures.
- M2 (insular) courses over the insula, a patch of cortex hidden inside the Sylvian fissure. Major branching happens here: the trunk most commonly splits into a superior and an inferior division, though some people have three or more trunks.
- M3 (opercular) loops over the folds of brain tissue that cover the insula.
- M4 (cortical) fans out across the outer surface of the brain, delivering blood to a wide territory of cortex.
Deep Structures: Basal Ganglia and Internal Capsule
Before the MCA ever reaches the brain’s surface, its M1 segment sends a cluster of tiny branches called lenticulostriate arteries straight down into the brain’s interior. These vessels supply the basal ganglia and the internal capsule, two structures essential for coordinating movement and relaying signals between the cortex and the rest of the body.
Specifically, MCA perforators feed the upper and outer portions of the caudate nucleus (involved in planning and executing movement), most of the putamen, part of the globus pallidus, and the superior portion of the internal capsule. The internal capsule is a dense band of nerve fibers that carries motor commands from the brain down to the spinal cord. Because the lenticulostriate arteries are small and branch at sharp angles, they are especially vulnerable to blockage or rupture, which is why strokes affecting these deep structures are so common.
Cortical Territory: The Lateral Brain Surface
The MCA’s cortical branches blanket the lateral faces of the frontal, parietal, and temporal lobes. This is a massive territory, and it includes some of the brain’s most functionally important real estate.
On the frontal lobe, the MCA supplies the primary motor cortex for the face, hand, and arm. These are the regions of the movement map (sometimes called the homunculus) that control fine motor skills like gripping objects, writing, and speaking. The leg and foot area of the motor cortex sits on the brain’s midline surface and is supplied by a different vessel, the anterior cerebral artery. That distinction matters clinically: an MCA stroke typically weakens the face and arm far more than the leg.
On the parietal lobe, the MCA feeds the primary sensory cortex for the same body parts, meaning it enables you to feel touch, pressure, temperature, and pain in the face, hand, and arm. It also supplies association areas involved in spatial awareness and integrating sensory information.
On the temporal lobe, the MCA supplies the auditory cortex, where sound is processed, along with regions that help with memory, object recognition, and emotional processing.
Language Areas in the Dominant Hemisphere
For most right-handed people and the majority of left-handed people, language is controlled primarily by the left hemisphere. Two key language regions sit squarely within MCA territory. Broca’s area, in the inferior frontal gyrus, handles speech production, the ability to form words and string them into sentences. Wernicke’s area, in the superior temporal gyrus, handles language comprehension, the ability to understand spoken and written words.
Because both regions depend on the MCA for blood flow, a left-sided MCA stroke frequently causes aphasia. A blockage affecting the superior division tends to impair speech output (the person knows what they want to say but cannot produce fluent speech), while a blockage affecting the inferior division tends to impair comprehension (the person speaks fluidly but the words don’t make sense, and they struggle to understand others). A large stroke involving the entire MCA territory can knock out both functions simultaneously.
Why the MCA Matters in Stroke
Roughly 85% of all strokes are ischemic, meaning they result from a blocked artery rather than a bleed. Over half of those ischemic strokes occur in MCA territory, making it the single most commonly affected vessel. The reason is partly anatomical: the MCA is essentially a direct continuation of the internal carotid artery, so clots traveling up from the heart or the neck tend to funnel straight into it.
The symptoms of an MCA stroke depend on which segment is blocked. A clot in the M1 segment, before any branching has occurred, can cut off blood to both deep structures and the entire lateral cortex, producing a devastating combination of one-sided weakness, sensory loss, language problems (if the dominant hemisphere is involved), and neglect of one side of space (if the nondominant hemisphere is involved). A clot further downstream, in one of the M2 or M3 branches, tends to cause a more limited deficit, perhaps just hand weakness or difficulty finding words, because only part of the territory loses blood flow.
Blood Flow Through the MCA
The MCA carries a substantial share of the brain’s total blood supply. Measured with transcranial Doppler ultrasound, blood in the MCA moves at an average velocity of about 42 to 43 cm per second, with a flow rate of roughly 170 to 180 mL per minute on each side. These values are commonly used as a baseline in clinical settings to monitor for conditions like vasospasm after a brain hemorrhage, where the artery narrows and blood velocity spikes, or for detecting reduced flow during a stroke.