Week 110 Synaptic Transmission

Myelin is a substance that acts as electrical insulation for neurons. It is a fatty material that forms a protective sheath around the axons of neurons, allowing for efficient transmission of electrical signals. This insulation helps to increase the speed and efficiency of nerve impulses, allowing for rapid communication between different parts of the nervous system. Without myelin, the electrical signals would leak out and lose their strength, leading to slower and less reliable transmission of information within the nervous system.

The resting membrane potential is maintained by the Na+/K+ exchanger. This exchanger actively transports three sodium ions out of the cell in exchange for two potassium ions entering the cell. This process helps to establish the negative charge inside the cell and the positive charge outside, creating the resting membrane potential.

During the rising phase of an action potential, the ion that enters the neuron is Na+. This is because the rising phase is characterized by the depolarization of the neuron's membrane, which is caused by the influx of positively charged ions. Na+ channels open, allowing Na+ ions to flow into the neuron, resulting in a rapid increase in the membrane potential. This influx of Na+ ions is responsible for the rapid upswing of the action potential.

Schwann cells are responsible for myelination of nerves in the peripheral nervous system. Myelination is the process of forming a protective covering called myelin around nerve fibers, which helps to insulate and speed up the transmission of electrical signals. Schwann cells wrap around individual nerve fibers, forming multiple layers of myelin. This insulation allows for faster and more efficient transmission of signals along the nerves, ensuring proper functioning of the peripheral nervous system.

During the falling phase of the action potential, the ion that leaves the neuron is potassium (K+). This is because during the rising phase of the action potential, sodium (Na+) ions enter the neuron, causing depolarization. Once the action potential reaches its peak, potassium channels open and potassium ions move out of the neuron, leading to repolarization and the falling phase of the action potential. Therefore, K+ is the ion that leaves the neuron during this phase.

The influx of Ca2+ triggers neurotransmitter release. Calcium ions play a crucial role in the process of neurotransmitter release from the presynaptic neuron. When an action potential reaches the presynaptic terminal, voltage-gated calcium channels open, allowing Ca2+ ions to enter the cell. This influx of calcium triggers the fusion of synaptic vesicles containing neurotransmitters with the presynaptic membrane, leading to the release of neurotransmitters into the synaptic cleft. These neurotransmitters then bind to receptors on the postsynaptic neuron, allowing for the transmission of signals between neurons.

Resting membrane potential refers to the electrical potential difference across the cell membrane when the cell is at rest. A negative value indicates that the inside of the cell is more negatively charged compared to the outside. In most cells, including neurons, the resting membrane potential is around -65mV. This negative potential is maintained by the unequal distribution of ions, such as potassium and sodium, across the cell membrane.

Compound action potentials are measured by nerve conduction velocity tests. This is because nerve conduction velocity tests assess the speed at which electrical signals travel along a nerve. Compound action potentials, which are the summation of individual action potentials from multiple nerve fibers, can be detected and measured during these tests. Magnetic resonance imaging (MRI), angiography, computerized tomography (CT) scans, and ultrasound are imaging techniques that are used to visualize anatomical structures and blood flow, but they do not directly measure nerve conduction velocity or compound action potentials.

Oligodendrocytes are a type of cell in the central nervous system that play a crucial role in myelination of nerves. Myelination is the process of forming a protective sheath called myelin around nerve fibers, which allows for faster and more efficient transmission of electrical signals. Schwann cells, on the other hand, are responsible for myelination in the peripheral nervous system. Microglia are immune cells that protect the brain from infection and injury. Ependymal cells line the cavities of the brain and spinal cord, while astrocytes provide support and nourishment to neurons. Therefore, oligodendrocytes are the correct answer for the given question.

Multiple sclerosis is a disorder associated with the demyelination of nerves in the central nervous system. This means that the protective covering of nerve fibers, called myelin, is damaged, leading to communication problems between the brain and the rest of the body. Symptoms of multiple sclerosis can vary widely and may include fatigue, difficulty walking, numbness or tingling, muscle weakness, and problems with coordination and balance. The cause of multiple sclerosis is not fully understood, but it is believed to involve a combination of genetic and environmental factors.

Carbamazepine is a medication that is commonly used to treat epilepsy and certain types of nerve pain. One of its main mechanisms of action is blocking the firing of action potentials in neurons. Action potentials are electrical signals that allow neurons to communicate with each other and transmit information throughout the nervous system. By blocking the firing of action potentials, carbamazepine helps to reduce excessive electrical activity in the brain, which can help control seizures and alleviate nerve pain.

GABA-A receptors are ion channels that are permeable to chloride ions (Cl-). When GABA (gamma-aminobutyric acid) binds to these receptors, it opens the channel allowing the influx of chloride ions into the cell. This influx of chloride ions results in hyperpolarization of the cell membrane, making it less likely for the neuron to generate an action potential and thus inhibiting neuronal activity. Therefore, the correct answer is Cl- because it is the ion conducted by GABA-A receptors.

The correct answer is -40mV because the threshold membrane potential is the minimum level of depolarization required for an action potential to be generated. At this threshold, the voltage-gated sodium channels open, leading to an influx of sodium ions and the initiation of an action potential. Therefore, a membrane potential of -40mV is the critical point at which the neuron is able to generate and propagate an action potential.

When chloride ions (Cl-) flow into a neuron through GABA-A receptors, it causes an increase in the negative charge inside the neuron, leading to hyperpolarization. Hyperpolarization is a state where the membrane potential becomes more negative than the resting membrane potential. This makes it more difficult for the neuron to reach the threshold for an action potential, thereby reducing neuronal excitability. Hyperpolarization is an important mechanism for regulating the activity of neurons and maintaining the resting membrane potential.

Carbamazepine is a medication used primarily to treat epilepsy and neuropathic pain. It works by blocking voltage-gated sodium channels, which are responsible for the generation and propagation of action potentials in neurons. By blocking these channels, carbamazepine reduces the excessive firing of neurons, which can help control seizures and alleviate pain. It does not affect voltage-gated potassium or calcium channels, nor ligand-gated chloride or sodium channels.

Lidocaine is a local anesthetic that works by blocking voltage-gated sodium channels. These channels are responsible for the propagation of action potentials in neurons and other excitable cells. By blocking these channels, lidocaine prevents the influx of sodium ions, which inhibits the generation and conduction of nerve impulses. This results in a loss of sensation in the area where lidocaine is applied.