What is Stroke? Understanding Its Types and What Happens in the Brain

Introduction

Stroke is one of the major causes of death and long-term disability across the world. In 2021, stroke was estimated to be the third leading cause of combined death and disability globally.¹ India also carries a substantial stroke burden, with population-based studies showing considerable variation in stroke incidence and mortality across different regions.²

Many people have heard the word stroke, but fewer understand what it actually means. Why does someone who appeared completely normal suddenly become unable to speak? Why can one side of the body become weak within seconds? Why can vision, balance, swallowing or consciousness suddenly change?

The answer lies in the way our brain depends on a continuous blood supply. Brain cells need oxygen and glucose every moment. When blood flow is interrupted, normal brain function can fail rapidly.¹

This article explains stroke in simple language, including its different types, what happens inside the brain during a stroke, why symptoms differ from one person to another, and why reaching an appropriate hospital quickly can make such a major difference.

What is Stroke?

A stroke is a sudden neurological emergency caused by disruption of blood flow in the brain. This may occur because a blood vessel supplying the brain becomes blocked or because a blood vessel ruptures and bleeds.¹

When brain tissue does not receive enough oxygen and nutrients, neurons and other cells cannot continue functioning normally. If circulation is not restored, irreversible tissue injury can develop.

For this reason, stroke is sometimes described as a “brain attack”. The comparison with a heart attack is useful: both conditions involve sudden loss of blood supply to an important organ and both require urgent treatment.

The consequences of a stroke depend particularly on:

• the type of stroke,
• the blood vessel involved,
• the size of the affected brain region,
• which part of the brain has been injured,
• whether nearby brain tissue is still salvageable,
• the person's general medical condition, and
• how quickly effective treatment is started.

What Are the Main Types of Stroke?

There are two principal pathological types of stroke: ischemic stroke and hemorrhagic stroke.

A transient ischemic attack (TIA) can cause stroke-like symptoms because blood flow to part of the brain is temporarily disturbed. However, a TIA is better considered an important warning cerebrovascular event rather than a completed stroke. It should never be ignored.

1. Ischemic Stroke

An ischemic stroke occurs when an artery supplying the brain becomes obstructed. It is the more common pathological type of stroke in many populations.³

The blockage can develop in different ways.

Thrombotic stroke

A clot may form directly within an artery supplying the brain. This commonly occurs in association with disease of the arterial wall, such as atherosclerosis.

Embolic stroke

Material—often a blood clot—may form elsewhere and travel through the bloodstream until it becomes lodged in a cerebral artery. The heart can be an important source of emboli, particularly in conditions such as atrial fibrillation.

What happens inside the brain?

When the artery becomes blocked, blood flow to downstream brain tissue falls. The affected cells receive less oxygen and glucose.

The most severely deprived central tissue is often described as the ischemic core. Around it may be an area of threatened but potentially salvageable tissue known as the ischemic penumbra.

This concept is extremely important because modern reperfusion treatment aims to restore blood flow before potentially viable brain tissue progresses to irreversible injury.

2. Hemorrhagic Stroke

A hemorrhagic stroke occurs when a blood vessel ruptures and bleeding occurs within or around the brain.¹

Unlike ischemic stroke, where the primary problem is inadequate blood flow, hemorrhagic stroke produces injury from bleeding itself and from the pressure created by accumulating blood.

Intracerebral Hemorrhage

In an intracerebral hemorrhage, bleeding occurs directly into the brain tissue.

Long-standing high blood pressure is an important risk factor. Other causes may include vascular abnormalities, abnormalities of blood clotting, certain medications and other neurological disorders.

Subarachnoid Hemorrhage

A subarachnoid hemorrhage involves bleeding into the space surrounding the brain. Rupture of an intracranial aneurysm is an important cause.

What happens inside the brain?

Escaping blood can damage nearby tissue directly. The collection of blood may also occupy space within the rigid skull, contributing to swelling and increased intracranial pressure.

Depending on the location and severity of the hemorrhage, this may interfere with consciousness, breathing, movement and other vital neurological functions.

3. Transient Ischemic Attack (TIA): A Major Warning Sign

A transient ischemic attack, commonly called a TIA or “mini-stroke”, produces temporary neurological symptoms because blood flow to part of the brain is briefly disturbed.

The symptoms may look exactly like those of a stroke—for example, sudden weakness, facial drooping, speech difficulty or visual loss—but they resolve because the interruption in circulation is temporary.

Modern definitions therefore distinguish TIA from completed cerebral infarction rather than simply defining it by symptoms lasting less than 24 hours.

What Happens in the Brain During a Stroke?

Imagine the brain as a busy city.

The blood vessels are the roads, blood carries the oxygen and nutrients, and billions of brain cells are the workers that keep the city functioning.

During an Ischemic Stroke

A clot behaves somewhat like a major roadblock.

• Blood flow beyond the obstruction falls.
• Brain cells receive inadequate oxygen and glucose.
• Electrical activity and normal cellular function begin to fail.
• The most severely affected tissue may become permanently injured.
• Some surrounding tissue may remain salvageable if circulation is restored rapidly.

During a Hemorrhagic Stroke

Instead of a road being blocked, imagine that a major pipe suddenly ruptures.

• Blood escapes into or around brain tissue.
• Nearby cells may be directly damaged.
• A collection of blood may compress surrounding structures.
• Brain swelling may develop.
• Intracranial pressure may rise in severe cases.

Both processes can interrupt the normal communication pathways of the nervous system, which explains why stroke symptoms may appear suddenly.

Why Do Different Strokes Cause Different Symptoms?

Different regions of the brain perform different functions. Therefore, symptoms depend greatly on which part of the brain has been affected.

These patterns are useful for understanding stroke, but the human brain is complex. Symptoms cannot always be predicted simply from “left brain” versus “right brain”, and proper neurological assessment and brain imaging are essential.

Stroke in India: An Important Health Burden

Stroke represents an important public-health problem in India. A systematic review of population-based Indian studies reported substantial differences between regions, with crude annual stroke incidence estimates ranging from approximately 108 to 172 per 100,000 population in the studies included. One-month case fatality estimates also varied considerably.²

These variations remind us that India's stroke burden cannot always be summarised accurately using a single national number. Differences in population structure, risk factors, healthcare access and stroke-surveillance methods all influence the estimates.

Major modifiable contributors include high blood pressure, tobacco exposure, diabetes, abnormal blood lipids, physical inactivity, unhealthy diet, obesity, harmful alcohol use and other vascular risk factors.¹

Government initiatives

The Government of India implements the National Programme for Prevention and Control of Cancer, Diabetes, Cardiovascular Diseases and Stroke (NPCDCS), with components including health promotion, population-based screening, early diagnosis, management and referral for major noncommunicable diseases.⁴

Conclusion: What is Stroke?

So, what is stroke?

Stroke is a sudden neurological emergency in which part of the brain becomes injured because its blood supply is blocked or because a blood vessel ruptures and bleeding occurs.

The two main pathological types are ischemic stroke and hemorrhagic stroke. A transient ischemic attack can produce temporary stroke-like symptoms and should be treated as an urgent warning sign.

What makes stroke especially dangerous is its speed. A person may be talking, walking or working normally and develop major neurological symptoms moments later.

But stroke is not always the end of functional independence. Modern emergency stroke treatment, specialist stroke-unit care and structured rehabilitation can substantially influence outcomes.

Understanding what happens inside the brain also makes one message very clear: recognise stroke early, seek emergency medical care immediately and do not wait for symptoms to improve on their own.