Why Does One Side of the Body (Hand and Foot) Become Paralyzed After a Stroke?

Written By：Melody, TCM Practitioner.

Post-stroke hemiplegia means that after a stroke, one side of the body, such as one hand and one foot, becomes weak or completely unable to move. This is a very common situation, affecting almost all stroke patients to varying degrees.

To understand why this happens, we first need to know how our brain controls our body.

The Brain's "Cross-Control"

The left brain controls the right side, and the right brain controls the left side!

Imagine our brain as a sophisticated command center, divided into two halves: the left brain and the right brain.

Most of our body's movements and sensations are controlled by the "opposite side" of the brain:

🧠 Left Brain

Primarily responsible for controlling the right half of our body (right hand, right foot, part of the right side of the face). It is also responsible for our language, logical thinking, arithmetic, and so on.

🧠 Right Brain

Primarily responsible for controlling the left half of our body (left hand, left foot, part of the left side of the face). It is also responsible for our spatial awareness, artistic sense, navigation, and so on.

How does this "cross-control" happen?

This is because when the brain sends "commands" to control the body, these nerve signals "cross over" in the brainstem (the connection between the brain and the spinal cord) before reaching the body.

Stroke Hemiplegia: When the "Wiring" in the "Command Center" is Broken

A stroke, simply put, is when there's a problem with a blood vessel in the brain (it might be blocked or ruptured and bleeding), leading to the death of brain cells in a certain area due to lack of blood and oxygen.

When a specific "command area" of the brain is damaged, its controlling "wiring" is broken. Consequently, the corresponding body parts do not receive instructions and naturally become immobile or weak.

🔘 If a stroke occurs in the Left Brain

Then the right half of the body controlled by the left brain (right hand, right foot, and part of the right side of the face) will be affected, leading to hemiplegia. At the same time, because the left brain also governs language, the patient may also experience difficulty speaking or understanding others.

🔘 If a stroke occurs in the Right Brain

Then the left half of the body controlled by the right brain (left hand, left foot, and part of the left side of the face) will be affected, leading to hemiplegia. The patient may also experience impaired spatial awareness or a tendency to neglect things on the left side.

Why Does Hemiplegia Affect Both the Hand and Foot Simultaneously?

This is because in the brain regions that issue motor commands, and in the nerve pathways extending downwards to the spinal cord, the nerve fibers controlling the hand and foot are closely adjacent and interwoven.

When this area of the brain is damaged by a stroke, it's like a "regional power outage" that typically affects:

🔸The "motor command center" controlling the same side of the body

Leading to motor commands from the brain to both the hand and foot being unable to be issued normally.

🔸The "receiving station" responsible for sensation

Therefore, the paralyzed side may not only be unable to move but also feel numb or dull.

Thus, the occurrence of hemiplegia affecting both the hand and foot after a stroke is due to the brain's "cross-control" principle and the damage to the "command areas" and "wiring" in the brain responsible for movement and sensation.

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