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examBoard: AQA
examType: GCSE
lessonTitle: Motor and Sensory Areas
Your brain is like the control centre for your entire body. It processes all the information from your senses and controls all your movements. Two crucial parts of this system are the motor areas (which control movement) and the sensory areas (which process information from your senses). Today, we'll explore how these areas work and why they're so important for everyday functioning.
Key Definitions:
These parts of your brain control all your voluntary movements, from walking and running to writing and speaking. The primary motor cortex is located in the frontal lobe, just in front of the central sulcus (a deep groove that runs across the brain).
These regions receive and interpret information from your senses. The primary somatosensory cortex (which processes touch) is located in the parietal lobe, just behind the central sulcus. Other sensory areas include the visual cortex (for sight) and auditory cortex (for hearing).
The primary motor cortex is a strip of brain tissue that runs from the top of your head down to just above your ear. It's responsible for controlling voluntary movements throughout your body.
Scientists have mapped which parts of the motor cortex control which body parts, creating what's called a "motor homunculus" - a distorted representation of the human body based on how much brain space is devoted to controlling each part. Parts of your body that need fine motor control (like your hands and face) have larger areas of the motor cortex dedicated to them than parts that need less precise control (like your torso).
A large portion of the motor cortex is dedicated to controlling your hands and fingers, allowing for precise movements like writing, typing, or playing an instrument.
Your lips, tongue and facial muscles also have large areas of the motor cortex devoted to them, enabling speech and facial expressions.
Less motor cortex space is dedicated to your torso, as these movements tend to be less complex and require less precision.
When you decide to move, your brain goes through several steps:
One of the most famous cases in neuroscience involves Phineas Gage, a railway worker who survived an iron rod passing through his skull in 1848. The rod damaged his frontal lobe, including areas involved in motor planning. While he could still move his body, his personality changed dramatically, suggesting these brain areas are involved in more than just physical movement - they also help regulate behaviour and decision-making.
The somatosensory cortex is the main area for processing touch sensations. Located in the parietal lobe, it receives information about touch, pressure, pain, temperature and body position from all over your body.
Like the motor cortex, the somatosensory cortex has been mapped to create a "sensory homunculus" - a distorted representation of the human body based on sensitivity. Areas with greater sensitivity (like fingers and lips) have more brain space devoted to them.
Your fingertips, lips and tongue have many sensory receptors and large areas of the somatosensory cortex dedicated to them. This is why you can feel very small details with these body parts.
Your back and legs have fewer sensory receptors and smaller areas of the somatosensory cortex, making them less sensitive to touch.
When you touch something, the information follows this path:
People who have had limbs amputated often report still feeling sensations from their missing limb - a phenomenon called "phantom limb sensation." This happens because the area of the somatosensory cortex that processed sensations from that limb is still intact and can be activated. Neuroscientist V.S. Ramachandran developed a "mirror box" therapy that helps reduce phantom limb pain by providing visual feedback that tricks the brain into thinking the missing limb is moving.
Located at the back of the brain in the occipital lobe, the visual cortex processes information from your eyes. Different parts process different aspects of vision, such as colour, movement and shape recognition.
Found in the temporal lobe (near your ears), the auditory cortex processes sounds. It can distinguish between different tones, volumes and complex patterns like speech and music.
Damage to the motor cortex (such as from a stroke) can cause paralysis or weakness on the opposite side of the body. This condition is called hemiplegia (complete paralysis) or hemiparesis (partial weakness). Rehabilitation often focuses on helping the brain rewire itself through neuroplasticity.
Damage to the somatosensory cortex can cause numbness or altered sensation on the opposite side of the body. People might be unable to feel touch, temperature, or pain, which can be dangerous as they might not notice injuries.
Understanding which brain areas control which functions is crucial for medical treatments. Before brain surgery, doctors often use electrical stimulation to map a patient's brain, ensuring they don't damage critical areas for movement or sensation. This has led to "awake brain surgery," where patients remain conscious and perform tasks while surgeons operate, allowing immediate feedback if an important area is affected.
Canadian neurosurgeon Wilder Penfield pioneered brain mapping in the 1930s and 1940s. During epilepsy surgeries, he stimulated different parts of patients' brains with small electrical currents while they were awake (the brain itself has no pain receptors). When he stimulated the motor cortex, patients' bodies would move involuntarily. When he stimulated the sensory cortex, patients reported feeling sensations. His work created the first detailed maps of the motor and sensory homunculi that are still used today.
The motor and sensory areas of your brain work together to help you interact with the world. The motor areas control your movements, while the sensory areas process information from your environment. Both are organized in a systematic way, with more brain space devoted to body parts that need finer control or have greater sensitivity. Understanding these brain regions helps us comprehend how we move and sense the world around us and how damage to these areas affects behaviour.
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