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Chemical synapses comprise of 3 main parts: the presynaptic neuron (in all it's vessicles and glory), the synaptic cleft, and the post synaptic neuron. From basic neurobiology, we know that the presynaptic neuron fires, and the post synaptic neuron takes it like a bitch.The main function of a synapse is to cause changes in the membrane potential of the post synaptic neuron. But what is the mechanism behind it? It largely has to do with membrane carriers. Before a synapse can fire, it has to be depolarised enough to reach threshold, so that a large proportion of ion gate channels open, ions swoop in, change the action potential and trigger the secretion of neurotransmitters. But let's start from the beginning. Membrane carriers (ion channels) that sit in between the lipid bilayer of the neuronal cell membrane allow and control the ebb and flow of certain cations, anions and proteins. Some ion channels are gated, opening and closing in response to a change in voltage (voltage-gated channels) or in response to certain neurotransmitters (ligand-gated channels). The relative internal environment inside a neuron is slightly more negatively charged than its external environment. At rest, this difference of charge, or action potential, sits at about - (50 - 80) mV. At this stage, the diffusion into and out of the cell by K+ is at equilbrium. However, the cell's membrane is not perfectly impermeable to Na+, so Na+ slowly diffuses in. If this were uncontrolled, the internal environemnt would depolarize until it reached zero, and the neuron would be unable to fire. The sodium-potassium pump actively pumps out Na+ and pumps in K+, so the equilibrium is maintained. However, if the influx of Na+ exceeds that of the capacity of the sodium-potassium pump to expel the Na+, then the inside of the cell slowly depolarises. Once the internal environment of the cell reaches -40mV, then threshold is reached. At this point, voltage-gated Na+ channels open, and a rapid influx of Na+ changes the action potential of the cell to around +40 mV. The Na+ channels close in response to the change in action potential. K+ channels open tot he same change in action potential, increasing the cell membrane's permeabilty to K+. This repolarises, and hyperpolarises the cell. At this more, all the gated channels close, and the cell returns to it's resting potential. This action potential travels down the interior of the presynaptic axon, until it reaches the presynaptic terminal. In response to the sudden depolarisation, voltage-gated calcium channels open and Ca2+ enter the axon terminal. The Ca2+ causes synaptic vessels (filled with neurotransmitter goodness) to fuse with the pre-synaptic membrane, and burst, releasing it's gooey-goodness into the synaptic cleft. The post synaptic membrane have receptor sites specifically designed for particularly neurotransmitters. Depending on the neurotransmitter released, the receptor-neurotransmitter complex either indirectly or directly opens certain ligan-gated ion channels in the post synaptic membrane. For example, Ach is a neurotransmitter that can have either excitatory and inhibitory effects depending on the synapse. At an excitatory synapse, Ach will cause ligand-gated channels to open for Na+ and K+ ions. This causes depolarisation in the postsynaptic cell, and if the depolarisation is sufficient to reach threshold, the whole process is repeated in that neuron. At an inhibitory synapse, Ach will cause ligand-gated channels to open up for Cl-. This causes a hyperpolarisation in the cell, and takes it further away from firing threshold. The remaining neurotransmitter left in the synaptic cleft is either reuptaken by the presynaptic terminal via pinoctosis, or it is broken down by enzymes. This ensures that the transmissionis brief.
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What Are The Roles Of Carbohydrates Proteins And Cholesterol In The Plasma Membrane?
Carbohydrates, proteins, and cholesterol play essential roles in the plasma membrane's structure and function. Carbohydrates, often glycoproteins or glycolipids, are involved in cell recognition and signaling, facilitating communication between cells. Proteins serve various functions, including transport, acting as channels or carriers, and enabling enzymatic activity. Cholesterol helps maintain membrane fluidity and stability, ensuring that the membrane remains flexible and less permeable to certain substances.
What do membrane proteins do in the context of cellular function and structure?
Membrane proteins play crucial roles in cellular function and structure by facilitating the transport of molecules across cell membranes, serving as receptors for signaling molecules, and helping to maintain the integrity and stability of the cell membrane.
Which molecules are often embedded within the lipid bilateral to help substances move through the membrane?
Proteins, specifically integral membrane proteins, are often embedded within the lipid bilayer to facilitate the movement of substances across the membrane. These proteins can function as channels or carriers, enabling selective transport of ions and molecules. Additionally, peripheral proteins may assist in signaling or structural roles but are not embedded like integral proteins. Together, they play a crucial role in regulating the permeability and functionality of the cell membrane.
What is meant by the statement that the protein of a membrane are distributed asymmetrically?
This means that different types of proteins are concentrated on one side of the membrane compared to the other side. Asymmetrical distribution of proteins is important for maintaining the function and integrity of the membrane, as it allows for specialized roles and interactions on each side of the membrane.
Two roles of membrane proteins?
Some membrane proteins are receptors for hormones or other chemicals. Some membrane proteins perform active transport of substances into or out of the cell.
What Molecules of what substances are stored in synaptic terminals?
Synaptic terminals store neurotransmitter molecules, which are essential for communication between neurons. Common neurotransmitters include acetylcholine, dopamine, serotonin, and glutamate. These molecules are released into the synaptic cleft during synaptic transmission, facilitating the transmission of signals across the synapse. Additionally, some terminals may store neuropeptides, which also play roles in modulating synaptic activity.
Two functions of the proteins found in the plasma membrain?
Proteins in the plasma membrane play crucial roles in cell signaling, facilitating cell-cell communication and transmitting extracellular signals into the cell. They also help transport molecules across the membrane, serving as channels, carriers, or pumps for essential substances like ions and nutrients.
The major component of the cell membrane?
The major component of the cell membrane is phospholipids. They form a lipid bilayer that acts as a barrier to control the passage of molecules in and out of the cell. Proteins embedded in this lipid bilayer also play key roles in cell membrane function.
How is a cell affected if a cell membrane doesn't have any membrane proteins?
If a cell membrane doesn't have any membrane proteins, important functions such as transport of molecules in and out of the cell, cell signaling, and cell adhesion may be compromised. Membrane proteins play crucial roles in these processes, so their absence could disrupt normal cell function and communication with the external environment.
Which is a function of a plassma membrane protein?
Plasma membrane proteins serve several essential functions, including acting as receptors to facilitate cell signaling by binding to specific ligands. They also function as transporters, helping to move ions and molecules across the membrane, thereby regulating the internal environment of the cell. Additionally, some plasma membrane proteins play roles in cell adhesion and communication, allowing cells to interact with each other and their extracellular matrix.
What is the difference between surface proteins and spanning proteins?
Surface proteins are located on the outer surface of a cell membrane and may play roles in signaling or cell recognition, often not traversing the membrane. In contrast, spanning proteins, also known as integral or transmembrane proteins, extend across the membrane, often forming channels or transporters that facilitate the movement of substances in and out of the cell. While both types are crucial for cellular function, their structural properties and roles within the membrane differ significantly.
Protein in the plasma membrane not so?
Proteins in the plasma membrane play essential roles in cell adhesion, signaling, and transport. They help regulate the passage of molecules in and out of the cell and serve as receptors for various signaling molecules. Overall, proteins in the plasma membrane are crucial for maintaining cell structure and function.
