Molly Ayala
The human brain is a complex organ, with about 85 billion neurons and 86 billion non-neuronal cells. Neurons are cells that use electrical charges and chemicals called ions to communicate with each other. This communication is facilitated by the flow of sodium and potassium ions across the neuron's cell membrane, creating electrical activity. Electrical impulses in the brain foster myelination, speeding up communication between brain cells. Researchers have developed new techniques to measure and understand this electrical activity, including using fluorescent molecules and light-sensitive proteins that emit signals indicating the voltage a cell is experiencing. These advancements are helping to uncover the mysteries of the brain's electrical activity and its impact on our thoughts, behavior, and perception of the world.
| Characteristics | Values |
|---|---|
| Number of neurons in the brain | 85 billion |
| Number of connections or synapses between neurons | 10 quadrillion |
| Number of non-neuronal cells in the brain | 86 billion |
| Type of cell membrane in neurons | Made up of molecules called phospholipids |
| Cell membrane function | Separates everything inside the cell from everything outside |
| Cell membrane creation | Long chains of carbon that interact with each other creating an internal environment inside the membrane that repels water (a hydrophobic environment), and surface molecules capable of interacting with water (a hydrophilic environment) |
| Electrical activity in the brain | Flow of sodium and potassium ions across the neuron's cell membrane |
| Brain cell function | Rapid electrical impulses |
| Brain cell function underlying | Thoughts, behavior, and perception of the world |
| Brain cell function underlying | Thoughts, feelings, understanding, sensation, behavior, emotion |
| Brain cell activity measurement | Using electrodes |
| Brain cell activity measurement | Multielectrode arrays |
| Brain cell activity measurement | Calcium imaging |
| Brain cell activity measurement | Voltage-sensing molecule that fluorescently lights up when brain cells are electrically active |
| Brain cell activity measurement | Light-sensitive protein that can be embedded into neuron membranes |
| Brain cell activity measurement | Imaging technique using a voltage-sensing molecule |
| Brain cell activity measurement | Transcranial direct current stimulation (tDCS) |
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What You'll Learn
The flow of sodium and potassium ions across the neuron's cell membrane
The cell membrane is like a "skin" that separates the inside of the cell from the outside. The flow of sodium and potassium ions across the neuron's cell membrane is a crucial process in the generation of electrical activity in the brain. This flow of ions is facilitated by the sodium-potassium pump, which actively transports ions against their concentration gradients, creating a polarized membrane with a slightly negative inner surface.
At rest, neurons maintain a negative membrane potential due to the uneven distribution of ions across the membrane. Sodium ions are concentrated outside the cell, while potassium and other anions are concentrated inside. This resting state is established and maintained by the sodium-potassium pump, which works to keep the ion concentrations stable as ions cross the membrane. The pump operates by transporting three sodium ions out of the cell while allowing two potassium ions to enter, creating an unequal transfer of positive charge and contributing to the polarized state of the membrane.
When the neuron becomes active and generates a nerve impulse, there is a sudden movement of ions across the membrane. Specifically, there is an influx of sodium ions (Na+) into the cell through open channels, resulting in a depolarization of the membrane potential. This initial depolarization opens voltage-gated sodium channels, allowing a large influx of positive sodium ions and further increasing the positivity of the cell interior. This movement of sodium ions is crucial for the generation of electrical activity in the brain.
Following depolarization, there is an outward flow of potassium ions (K+) through channels such as the delayed rectifier channel (IDR). This efflux of potassium ions counteracts the effect of sodium influx by allowing the discharge of potassium, thereby repolarizing the membrane. This process restricts the duration of the nerve impulse and regulates the repetitive firing of the neuron. The balance between the influx of sodium and the efflux of potassium is essential for maintaining the proper functioning of neurons.
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Myelination and insulation of brain cells
The brain is a complex network of about 85 billion neurons in a typical adult human brain, with about ten quadrillion connections or synapses between them. Myelination is a process that insulates these neurons, and it is essential for the proper functioning of the brain.
Myelin is a protective membrane that wraps around certain nerve cells, forming a sheath made of protein and fat (lipids). This sheath acts as an insulator, strengthening and speeding up electrical signals in the nerve pathways that connect neurons. The myelin sheath is made up of individual sections called internodes, separated by small gaps known as the nodes of Ranvier. These nodes are rich in positive sodium ions, which help recharge the electrical signal as it travels along the axon, ensuring it doesn't lose its charge or signal strength.
The process of myelination is dynamic and can change in the healthy adult brain. It is formed during early development by brain cells called oligodendrocytes, which wrap around the axons of certain neurons. Myelination increases the speed and efficiency of signals passing along axons, influencing electrical signaling patterns within neural networks.
Research has shown that myelination plays a crucial role in learning and memory formation. Studies on mice have revealed that forming long-lasting memories is accompanied by increased myelination. This suggests that myelination helps reinforce and stabilize newly formed neural connections, making certain memories more persistent.
Damage to the myelin sheath can have significant consequences for brain function. Diseases such as multiple sclerosis are known for attacking the myelin sheath, leading to a loss of muscle control. Researchers are actively exploring ways to protect, repair, and regenerate myelin through various approaches, including stem cell therapy and drugs like ibudilast and phenytoin.
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Electrical brain stimulation
Electrical impulses in the brain are caused by the flow of sodium and potassium ions across the cell membrane of neurons, creating an electric potential. These electrical impulses encode all the information in the brain, including thoughts, feelings, and understanding.
EBS can be delivered directly through electrodes implanted in the brain or indirectly through electrodes placed on the scalp. The latter method is known as transcranial magnetic stimulation (TMS) and involves creating a magnetic field to induce weak electrical currents that stimulate neurons and neural circuits. TMS has been FDA-cleared for various conditions, including treatment-resistant depression, OCD, migraines, anxiety, and smoking dependence.
Another form of EBS is deep brain stimulation (DBS), which involves the use of deeply implanted electrodes in localized areas of the brain. DBS has been shown to elicit both pleasurable and aversive responses in laboratory animals and humans, including the stimulation of ritualistic motor responses of sham rage in cats and more complex emotional and behavioral components of "true rage" in experimental animals and humans.
In addition to its therapeutic applications, EBS is also used in neurosurgical procedures to treat conditions such as Parkinson's disease, focal epilepsy, and psychosurgery. The same electrode used for stimulation can also be used to probe the brain for defective functions before passing a lesioning current.
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Electrodes inserted into the brain
The brain is a complex organ, with billions of electrical impulses flying through it at any given moment. These electrical impulses are the building blocks of our thoughts, feelings, and understanding. They are mediated by the flow of sodium and potassium ions across neuron cell membranes, which ultimately encode all the information in our brains.
One way to study and treat the brain is through the use of electrodes inserted directly into the brain tissue. This method is known as deep brain stimulation (DBS) and is a neurosurgical procedure that uses implanted electrodes and electrical stimulation to treat various neurological conditions. DBS is often used when medications have become less effective or their side effects interfere with a patient's daily life.
During DBS surgery, the patient is awake, and their head is stabilised with a frame. Local anaesthesia is administered to numb the head, and a small hole is drilled into the skull. A thin insulated wire, or electrode, is then inserted into the brain, guided by CT or MRI scans to ensure accurate placement. The patient may be asked to move their face, arm, or leg to test the electrode's position.
The electrode is attached to a small pulse generator, usually implanted in the chest, which delivers mild electrical stimulation. This stimulation can help to decrease a patient's need for medication and improve their quality of life. DBS does not fully resolve symptoms, but it can be an effective treatment option for movement disorders associated with Parkinson's disease, essential tremors, dystonia, and other conditions.
Another form of brain stimulation therapy is electroconvulsive therapy (ECT), where electrodes are used to induce a brief seizure in the brain. This therapy is often used to treat depressive episodes, and patients typically resume normal activities within an hour of the procedure.
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Fluorescent molecules and imaging techniques
Traditionally, measuring electrical activity in the brain has involved inserting an electrode into the brain, a process that is time-consuming, labour-intensive, and often only allows for the recording of one neuron at a time. To overcome this, researchers have developed a fluorescent probe that lights up when brain cells are electrically active. This probe can be genetically inserted into neurons and becomes embedded in the cell membrane. The brightness of the probe corresponds to the voltage of the cell, and this fluorescence can be seen with a standard light microscope.
This technique, known as directed protein evolution, was developed by Boyden and colleagues at MIT and Boston University. They engineered a molecule called Archon1, which they used to image electrical activity in the brains of transparent worms, zebrafish embryos, and mouse brain slices. They then modified the probe to target a specific region of the neuron membrane, creating SomArchon, which provides clearer images by preventing interference from neighbouring neurons.
The use of fluorescent molecules and imaging techniques has provided a new way to study electrical activity in the brain, allowing researchers to visualise the activity of circuits within the brain and link it to specific behaviours. This has applications in understanding diseases such as Parkinson's and depression, as well as in developing treatments for brain diseases and neurological disorders. For example, researchers have used fluorescent probes to detect and image hyaluronidase in cancer cells and to monitor ATP in the healthy brain.
Fluorescence imaging has also been combined with other techniques such as optogenetics, which uses light-sensitive proteins to silence or stimulate neuron activity. This combination of techniques has allowed researchers to stimulate one neuron and then measure the resulting effect in connected neurons. Overall, the development of fluorescent molecules and imaging techniques has provided a powerful tool for understanding electrical activity in the brain and its implications for behaviour and health.
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Frequently asked questions
Electrical activity in the brain is caused by neurons communicating via electrical impulses or charges.
Neurons are cells in the brain that use electrical charges and chemical ions to communicate with each other.
The flow of sodium and potassium ions across the neuron's cell membrane creates electrical activity in the dendrites, which ultimately encodes all the information in the brain.
Electrical activity in the brain fosters myelination, the insulation process that speeds up communication among brain cells. This process has been linked to treating demyelinating diseases, such as multiple sclerosis. Additionally, electrical brain stimulation can be used to alter brain activity and help people with brain damage or disorders resolve potentially problematic patterns of brain activity.
