In Class Notes (2/14 and 2/17) Flashcards
Steps of Action Potential – What happens when the threshold is met?
Sodium (Na+) channels open, and Na+ rushes in rapidly. Potassium (K+) channels open slightly later, allowing K+ to leave the cell.
Steps of Action Potential – What happens at peak action potential?
Na+ channels become refractory as the inactivation gate closes.
Steps of Action Potential – What happens during repolarization?
Absolute refractory period occurs where Na+ channels will NOT reopen. K+ leaves rapidly due to positive charge and crowding.
Steps of Action Potential – What happens during hyperpolarization?
K+ channels close slowly, Na+ channels reset, and the membrane dips below resting potential before resetting.
Steps of Action Potential – How is resting potential restored?
Through diffusion, electrostatic pressure, and sodium-potassium pump activity.
Post-Synaptic Effects – What does hyperpolarization cause?
Inhibitory Post-Synaptic Potential (IPSP)
Post-Synaptic Effects – What does depolarization cause?
Excitatory Post-Synaptic Potential (EPSP)
Where does the initial action potential occur?
At the axon hillock, where sodium diffuses into the axon.
What is the role of the Node of Ranvier?
Contains voltage-gated channels that allow more sodium in to reinforce the signal.
How do myelinated axons conduct signals?
Through saltatory conduction, where electrical signals jump between nodes of Ranvier.
What is decremental conduction?
Electrical signals decrease in strength while traveling through the myelin but still trigger new action potentials at nodes
What happens when touching a hot iron (7 steps)?
Pain sensory receptors activate → Sensory neurons depolarize → Action potential starts at axon hillock → Travels to spinal cord → Depolarizes an interneuron → Motor neuron is activated → Muscle contracts
Tetrodotoxin – What is it, and how does it affect neurons?
A toxin found in puffer fish that binds to voltage-gated Na+ channels, blocking Na+ passage. Prevents action potentials, leading to muscle paralysis, including respiratory muscles.
Tetrodotoxin – Can it be used medically?
Yes, in small doses for pain management. It showed nerve-block effects in rats for 3 days without toxicity. However, blocking pain can lead to muscle injury or paralysis.
Dendrotoxins – What are they, and what do they do?
Neurotoxins found in mamba snake venom that block voltage-gated K+ channels. This prevents K+ from leaving, making neurons fire action potentials more easily and at a higher frequency.
Potassium Permeability – How does extracellular K+ affect action potentials?
When extracellular K+ is too high, it causes depolarization, triggering an action potential. K+ enters neurons via electrostatic pressure and diffusion.
Cortical Spreading Depolarization – What conditions is it linked to?
It contributes to migraine aura and certain epileptic seizures. Hypothyroidism and diabetes may cause disturbances in extracellular K+ levels, making individuals more susceptible to hyperkalemia.
How do astrocytes regulate extracellular K+?
Astrocytes help maintain homeostasis by removing excess K+ from the extracellular fluid to prevent cortical depolarization.
What are the two types of synapses?
Electrical (in the PNS) and chemical (in the CNS)
Electrical Synapses – How do they work?
Direct ion and ATP transfer between presynaptic and postsynaptic membranes through gap junction channels made of connexons. Fast and fail-safe with synchronized postsynaptic potentials
Chemical Synapses – How do they work?
Neurotransmitters are released when an action potential reaches the terminals. The neurons do not directly connect; instead, neurotransmitters cross the synaptic gap.
What is an axoaxonic synapse?
A presynaptic terminal synapses with another presynaptic terminal, which then synapses with a postsynaptic dendrite or soma.
What is an axodendritic synapse?
A presynaptic terminal directly synapses with a postsynaptic dendrite or dendritic spine.
Steps of Chemical Synaptic Transmission – What happens first when an action potential reaches the terminal?
Na+ influx causes depolarization.
