Nerve Impulse & Blood-Brain Barrier Study Guide PDF

## 1.2 The Nerve Impulse - Resting Potential ### The Resting Potential of the Neuron - The membrane of a neuron maintains an electrical gradient (also called polarization - a difference in electrical charge between the inside and outside of the cell). - In the absence of any outside disturbance (i...

## 1.2 The Nerve Impulse - Resting Potential ### The Resting Potential of the Neuron - The membrane of a neuron maintains an electrical gradient (also called polarization - a difference in electrical charge between the inside and outside of the cell). - In the absence of any outside disturbance (i.e., at rest), the membrane maintains an electrical polarization (i.e., a difference in electrical charge between two locations) that is slightly more negative on the inside relative to the outside. - This difference in electrical potential or voltage is known as the resting potential. - The resting potential is measured by very thin microelectrodes. - A typical resting membrane potential is -70 millivolts (mV). This may vary from one neuron to another. ### Forces Acting on Sodium and Potassium Ions: - The neuron membrane is selectively permeable, which allows some molecules to pass freely (e.g., water, carbon dioxide, oxygen) while restricting others. - Most large molecules and ions cannot cross the membrane. A few important ions cross through protein channels. - During the resting potential, chloride channels (or gates) remain open along the membrane, which allows ions to pass through. - Potassium channels are mostly closed, causing potassium to cross the membrane slowly. - Sodium gates remain closed, restricting the passage of sodium ions. ### Sodium-potassium pump: - A protein complex found along the neuron membrane that transports three sodium ions outside of the cell while also drawing two potassium ions into the cell; this is an active transport mechanism (requires energy in the form of ATP to function). - The sodium-potassium pump causes sodium ions to be more than ten times more concentrated outside than inside. - ATP - energy carrying molecule found on cells. ATP captures chemical energy found in food and uses to fuel cellular processes. ### Why a Resting Potential? - The advantage of the resting potential is to allow the neuron to respond quickly to a stimulus. ## 1.1 Glia Cells - Glia (neuroglia) are the other major component of the nervous system. - Glia have many different functions but they do not transmit information like neurons. - Glia are smaller and slightly more numerous than neurons. Several types of glia exist to perform different functions. ### Image: Shapes of Various Glia Cells - This image shows a variety of glia cells, including astrocytes, oligodendrocytes, Schwann cells, and microglia. - Astrocytes have a star-like shape and are the most abundant glial cells in the brain. They play a role in supporting neurons, regulating the blood-brain barrier, and removing waste products. - Oligodendrocytes are responsible for producing myelin, a fatty substance that insulates axons and speeds up nerve impulse transmission. - Schwann cells are similar to oligodendrocytes, but they are found only in the peripheral nervous system. - Microglia are the immune cells of the brain. They are responsible for removing debris and pathogens from the brain and other nervous system tissue. ## 1.1 The Blood-Brain Barrier ### The Blood-Brain Barrier is the mechanism that keeps most chemicals out of the vertebrate brain. ### Why We Need a Blood-Brain Barrier? - The blood-brain barrier is needed because the brain lacks the type of immune system present in the rest of the body. - Because neurons generally cannot be replicated and replaced, the barrier is in place to minimize the risk of irreparable brain damage. - A wall is formed that keeps out most viruses, bacteria, and harmful chemicals. - When viruses do enter, like the rabies virus, it can infect the brain and lead to death. - A virus that enters your nervous system probably stays with you for life (e.g., chicken pox and shingles). ### How the Blood-Brain Barrier Works? - Endothelial cells form walls of the capillaries. These cells are tightly joined in the brain, blocking most molecules from passing. In the rest of the body, the endothelial cells are separated by gaps. - Small uncharged molecules (e.g., oxygen and carbon dioxide) and molecules that can dissolve in the fats of the capillary wall can cross passively (without using energy) through the blood-brain barrier. - An active transport system (a protein-mediated process that uses energy) exists to pump necessary chemicals, such as glucose, through the blood-brain barrier. - The blood-brain barrier is essential for health. - For example, in Alzheimer's disease, the endothelial cells lining the brain's blood vessels shrink and harmful chemicals can enter the brain. - The blood-brain barrier poses difficulty in medicine because it keeps out many useful medications that may be used to treat diseases like brain cancer.