Lecture 4 - Synaptic Communication Flashcards
What are the three types of voltage-gated ion channels?
Voltage-gated sodium channels, voltage-gated potassium channels, and voltage-gated calcium channels.
What is the primary function of the voltage-gated sodium channel?
The primary function of the voltage-gated sodium channel is to help start and spread the action potential in neurons.
What is the primary function of the voltage-gated potassium channel?
The primary function of the voltage-gated potassium channel is to quickly bring the membrane back to its resting state after the action potential.
What is the primary function of the voltage-gated calcium channel?
The primary function of the voltage-gated calcium channel is to trigger the release of neurotransmitters.
How do potassium ion channels selectively allow K+ ions but block Na+ ions?
The selectivity of potassium ion channels is based on a structure called the selectivity filter, which is specifically shaped to interact with potassium ions (K⁺) while preventing sodium ions (Na⁺) from passing through. When K⁺ ions enter the channel, the filter replaces the water molecules that typically surround them, known as the hydration shell, allowing them to pass easily. However, Na⁺ ions are smaller and have a different hydration shell configuration; they cannot fit through the filter properly without their surrounding water molecules. As a result, the channel preferentially allows K⁺ ions to flow through while effectively blocking Na⁺ ions.
What modern techniques have helped us understand ion channels?
X-ray crystallography and mapping DNA sequences that code for ion channel proteins.
Scientists use X-ray crystallography to determine the three-dimensional structure of ion channel proteins, revealing how they function and interact with ions. Additionally, mapping DNA sequences helps identify the genes coding for these proteins, providing insight into their structure, function, and potential mutations that affect their operation. Together, these techniques enhance our understanding of ion channels’ roles in cellular communication and physiological processes.
How can altering a DNA sequence help in studying ion channel selectivity?
By changing the amino acid coded for, researchers can determine if it affects the channel’s ability to selectively allow certain ions through.
What is a hydration shell?
A layer of water molecules that surrounds an ion when it is dissolved in water.
How many different genes in the human genome code for voltage-gated potassium channels?
40 different genes.
What are the two main types of cells in the central nervous system (CNS)?
Neurons and glia.
What is the role of astrocytes in the CNS?
They provide structural support, regulate ions, clear neurotransmitters, and control blood flow.
What do ependymal cells do?
They line the brain’s ventricles and spinal cord, circulating cerebrospinal fluid.
How do microglia function in the CNS?
They act as the brain’s cleanup crew, removing dead cells and debris and protecting against infections.
What is the function of oligodendrocytes?
They create the myelin sheath around axons, which speeds up action potentials.
What are nodes of Ranvier?
Tiny gaps in the myelin sheath where the axon’s charge can interact with the outside environment.
How much faster does myelination speed up action potentials?
It can speed up the action potential by 20 times.
What is a synapse?
The small gap between the axon terminal of one neuron and the cell membrane of another neuron.
What is the role of neurotransmitters in synaptic communication?
They are released from the axon terminal and activate receptors on the receiving neuron, which can either excite or inhibit it.
How are neurotransmitters stored before release?
They are stored in small sacs called synaptic vesicles.
What are ionotropic receptors?
Ionotropic receptors are a type of neurotransmitter receptor that acts as ion channels, opening in response to a ligand (like a neurotransmitter). They allow ions to flow into or out of the cell, leading to rapid changes in the membrane potential.
What are metabotropic receptors?
Metabotropic receptors are a type of neurotransmitter receptor that does not function as an ion channel. Instead, they activate signaling cascades inside the cell through G-protein signaling, resulting in slower, more prolonged effects on the cell’s activity.
What is the difference between ionotropic and metabotropic receptors?
Ionotropic receptors act as ion channels and respond quickly, while metabotropic receptors trigger internal signaling cascades and are slower.
What are the three methods the body uses to clear neurotransmitters?
Diffusion, enzymatic deactivation, and reuptake.
The neurotransmitter may be broken down by an enzyme, it may be sucked back up into the presynaptic neuron, or it may simply diffuse away.
What is diffusion?
Diffusion is the passive spread of neurotransmitters from areas of high concentration to areas of low concentration, gradually reducing their presence in the synaptic cleft.
