neurotransmission Flashcards
what do A, B, C, D, and E represent on this graph
A: resting state
B: depolarization (sodium ions in)
C: peak action potential
D: repolarization (potassium ions out)
E: hyperpolarization
what is resting action potential
the electrical potential difference across the plasma membrane when the cell is in a non-excited state
what is action potential
Action potentials are brief, rapid changes in the membrane potential that allow for the transmission of electrical signals along the neuron.
how is the membrane potential controlled
Ion channels: The cell membrane contains ion channels that selectively allow the passage of specific ions, such as sodium (Na+), potassium (K+), and chloride (Cl-). These ion channels can be either voltage-gated or ligand-gated. Voltage-gated ion channels open or close in response to changes in membrane potential, while ligand-gated ion channels open or close in response to the binding of specific molecules (ligands) to the channel.
Ion pumps: Ion pumps, such as the sodium-potassium pump (Na+/K+ ATPase), actively transport ions across the cell membrane against their concentration gradients. The sodium-potassium pump helps maintain the resting membrane potential by pumping out three sodium ions (Na+) for every two potassium ions (K+) it brings into the cell.
what does propogation of the action potential mean
Propagation of the action potential refers to the transmission of the electrical signal, or action potential, along the length of a neuron’s membrane. When an action potential is initiated at a specific site, such as the axon hillock or the initial segment of the neuron, it travels down the axon, allowing for communication between different regions of the nervous system.
The process of action potential propagation can be understood in the following steps:
Threshold and depolarization: The initial segment of the neuron receives a strong enough stimulus that brings the membrane potential to the threshold level. The threshold is the critical membrane potential at which voltage-gated sodium channels open, allowing an influx of sodium ions into the cell. This rapid influx of sodium ions causes depolarization, a change in membrane potential from negative to positive.
Generation of the action potential: The depolarization of the membrane at the initial segment triggers the opening of voltage-gated sodium channels downstream along the axon. This results in a wave of depolarization that spreads along the axon. The influx of sodium ions further depolarizes the membrane, reaching a peak potential known as the action potential.
Repolarization: After reaching its peak, the action potential enters a repolarization phase. Voltage-gated potassium channels open, allowing potassium ions to move out of the cell, leading to the restoration of the negative membrane potential.
Hyperpolarization and refractory period: In some neurons, there is a brief period of hyperpolarization following repolarization, during which the membrane potential becomes more negative than the resting potential. This is caused by the prolonged opening of potassium channels. Additionally, during this time, the neuron enters a refractory period, during which it is less responsive to subsequent stimuli.
Propagation to adjacent regions: As the action potential reaches its peak and then repolarizes, it creates a local change in the voltage of the adjacent region of the axon. This change in voltage reaches the threshold level in the adjacent region, triggering the opening of voltage-gated sodium channels and initiating another action potential. This process repeats along the length of the axon, allowing the action potential to propagate.
By propagating the action potential, neurons are able to transmit signals over long distances, ensuring effective communication within the nervous system.
how is propagation of the action potential affected by myelination
Myelination has a significant impact on the propagation of action potentials. Myelin is a fatty substance that wraps around the axons of certain neurons, forming a protective sheath. This myelin sheath is created by specialized cells called oligodendrocytes in the central nervous system (CNS) and Schwann cells in the peripheral nervous system (PNS).
The presence of myelin affects the propagation of action potentials in two main ways:
Saltatory conduction: Myelin acts as an insulating layer around the axon, preventing ion flow across the membrane. However, there are small gaps in the myelin sheath called nodes of Ranvier, where the axon is exposed. These nodes have a high density of voltage-gated sodium channels. When an action potential is initiated at the initial segment of the axon, it rapidly propagates down the axon, jumping from one node of Ranvier to the next. This skipping of the myelinated regions is known as saltatory conduction. Saltatory conduction greatly speeds up the propagation of the action potential compared to unmyelinated axons, where the action potential has to propagate along the entire length of the membrane.
Conservation of energy: Myelination reduces the energy expenditure required for action potential propagation. The depolarization and repolarization processes involved in generating and propagating action potentials require energy. In myelinated axons, since the action potential jumps from node to node, the energy needed for depolarization and repolarization is only expended at the nodes of Ranvier. The myelin sheath acts as an energy-saving mechanism by minimizing energy consumption along the axon, making neural transmission more efficient.
Overall, myelination enhances the speed and energy efficiency of action potential propagation. It allows for faster and more efficient communication between neurons, which is particularly important in facilitating rapid and precise signaling in the nervous system.
how does lignocaine (aka lidocaine) work as a local anesthetic
Blocks nerve fibre impulse propagation.
anesthetic enters the nerve cell by diffusion through the membranes. It then binds to sodium channels causing a conformational change that prevents the transient influx of sodium and therefore depolarization”
Blocks all excitable membranes although sensory first because they are thinner, unmyelinated and easily penetrated”
label
what is reuptake
reabsorption of a secreted substance by the cell after it has transmitted the nerve impulse
name the classes of receptors
Ionotropic Receptors:
Structure: Ionotropic receptors are membrane-bound receptors that are composed of multiple subunits, including the neurotransmitter binding site and an ion channel pore.
Function: When a neurotransmitter binds to the ionotropic receptor, it induces conformational changes that directly open or close the ion channel pore. This allows the flow of specific ions, such as sodium (Na+), potassium (K+), or chloride (Cl-), across the membrane. The resulting ion influx or efflux generates a rapid change in the membrane potential, leading to the generation of an excitatory or inhibitory postsynaptic potential (EPSP or IPSP), respectively. Ionotropic receptors are responsible for mediating fast synaptic transmission.
Metabotropic Receptors:
Structure: Metabotropic receptors are also membrane-bound receptors, but they consist of a single subunit that spans the cell membrane multiple times. They are coupled to intracellular signaling proteins called G proteins.
Function: When a neurotransmitter binds to a metabotropic receptor, it initiates a series of intracellular signaling events through the activation of G proteins. These signaling events can lead to the modulation of ion channels indirectly or the activation of second messenger systems. Metabotropic receptors generally have slower and more prolonged effects compared to ionotropic receptors. They can modulate synaptic transmission, regulate cellular processes, and influence neuronal excitability.
GABA and Glycine Receptors:
Function: Gamma-aminobutyric acid (GABA) receptors and glycine receptors are ionotropic receptors that mediate inhibitory neurotransmission in the central nervous system. When GABA or glycine binds to their respective receptors, they increase the permeability of the membrane to chloride ions (Cl-), leading to an influx of chloride ions into the cell. This hyperpolarizes the membrane, making it less likely for an action potential to be generated, thereby inhibiting neuronal activity.
Excitatory and Inhibitory Receptors:
Function: Excitatory receptors and inhibitory receptors refer to ionotropic or metabotropic receptors that mediate the effects of excitatory or inhibitory neurotransmitters, respectively. Excitatory receptors, such as glutamate receptors, promote depolarization and increase the likelihood of generating an action potential. Inhibitory receptors, such as GABA and glycine receptors mentioned earlier, promote hyperpolarization and decrease the likelihood of generating an action potential.
what is enymatic deactivation
mechanism that makes neurotransmitters inactive
- the enzyme changes the structure of the neurotransmitter so that it is no longer recognized by its receptor
what is excitatory post-synaptic potential (EPSP)
influx of Na causes depolarization, bringing closer the the firing action potential
what is inhibitory post synaptic potential (IPSP)
efflux of K ions causes hyperpolarization (and Cl), changing the charge of across the membrane to be further from the firing action potential
how does ketamine work as a general anesthetic
blocks the pore of the NMDA receptor (iontropic glutamate) and prevents glutamate from being transported through the channel
