Second lecture and Third lecture Flashcards
What is the blood-brain barrier?
Selectively permeable barrier between blood and the brain through tight junctions in the walls of cells of the brain’s capillaries.
What is the primary function of the blood-brain barrier?
Regulate and maintain the composition of the extracellular fluid in the brain.
How do astrocytes contribute to the function of the blood-brain barrier?
They actively transport wanted nutrients across the walls for most chemicals.
What problem can arise from the function of the blood-brain barrier?
It can be a problem for drugs that we want to get into brain tissue.
What does the blood-brain barrier restrict?
Entry of chemicals or toxins that would interfere with the transmission of information between neurons.
What does the blood-brain barrier actively transport back to the bloodstream?
Waste.
What is the area postrema?
A region of weakness in the blood-brain barrier located in the medulla.
What can be detected in the area postrema?
Poisons.
What is the wall of the axon made of?
A special cell membrane
What can we measure across the axon cell membrane?
Relative voltage difference (electrical potential)
What is the electrical charge inside the axon at rest?
Negative
What is the Resting State Potential when the axon is at rest?
Negative
What is transmitted along the axon from soma to axon terminals?
Axonal Transmission (conduction) of signals
What are the electrochemical signals sent by neurons called?
Action Potentials (APs)
Where are Action Potentials usually triggered in a neuron?
Near the soma
What do Action Potentials trigger at the axon’s terminals?
Release of neurochemicals
What influences the behavior and neurobiology of recipient neurons?
Neurochemicals released from Action Potentials
What is the electrochemical basis of the Action Potential easily measured as?
An extremely brief reversal of the voltage difference
What ensures that the Action Potential travels in one direction along the axon?
Nature of the axon membrane and its local environment
What is the ‘code’ used by the neuron to convey information?
Temporal pattern and sequence of many Action Potentials
What does the All-or-none Law state about Action Potentials?
Firing of AP depends on a threshold
How is the size of the Action Potential described?
Fixed in size for a given neuron
What does the Rate Law explain about variations in axon transmission?
Variations in the rate of AP propagation represent variations in stimulus intensity
Fill in the blank: The Action Potential is propagated at this exact, full voltage potential without _______.
decrement
True or False: All Action Potentials are of different sizes.
False
What is the resting potential of an axon?
-70mV
The resting potential is the membrane potential of a neuron when it is not being altered by other neuronal activity.
What happens during depolarization?
Membrane potential moves towards being more positive
This is part of the process of action potential where the charge inside the axon becomes more positive.
What is hyperpolarization?
Membrane potential becomes more negative than in resting state
This occurs when the membrane potential dips below the resting potential.
Define Action Potential (AP).
Brief electrical impulse that provides the basis for conduction along an axon
The AP is characterized by a rapid reversal of polarity and a return to a negative state.
What is the threshold of excitation?
Value of the membrane potential that must be reached to produce an action potential (e.g. -60mV)
Without reaching this threshold, no action potential occurs.
True or False: The action potential can be stopped once the threshold of excitation is reached.
False
Once the threshold is reached, the action potential is generated and self-regenerates down the axon’s length.
How long does the action potential process take?
3-5ms
This is the rapid duration of the action potential process.
What is diffusion force?
Molecules distribute themselves evenly when dissolved, moving from high concentrations to low concentrations
This principle explains how substances spread out in solution.
What is electrostatic pressure?
Electrical force when substances are dissolved in water and split into charged particles (ions)
This pressure affects the movement of ions in biological systems.
What are cations?
Carry positive charge
Cations are one type of ion that plays a critical role in action potentials.
What are anions?
Carry negative charge
Anions are the other type of ion that contributes to electrical activity in cells.
What happens to ions with the same charge?
They repel each other
This principle is fundamental to understanding ionic interactions.
What happens to ions with opposite charges?
They attract each other
This attraction is crucial for the formation of ionic bonds and electrical activity.
What keeps Na+ levels high outside the axon?
Sodium-potassium pumps continuously pump out Na+ and pump in K+
This process helps maintain the concentration gradient necessary for action potentials.
What primarily influences the movement of Na+ into the cell?
Both diffusion and electrostatic pressure
These forces would normally push Na+ into the cell, but the resting membrane is not very permeable to Na+.
What happens when the membrane becomes permeable to Na+?
The sodium channels open, allowing Na+ to rush inside the axon
This influx leads to a rapid change in membrane potential, creating an action potential.
What is the threshold in the context of action potentials?
The level of depolarization where the closed sodium gates open
At this point, the process becomes all or nothing, allowing ions to transfer rapidly across the membrane.
What occurs first once the threshold of excitation is reached?
Na+ channels open, allowing Na+ to rush inside the axon
This initiates the action potential.
What happens after the Na+ channels open during an action potential?
Voltage-dependent K+ channels open later, allowing K+ to leave the cell
This is due to diffusion out of the cell.
What occurs when the Na+ channels become refractory?
They block and won’t open again until the membrane repolarizes to a negative inside
This is critical for resetting the action potential cycle.
What causes the membrane to return to resting potential?
Diffusion of K+ out of the cell
This happens as the K+ channels remain open.
What is the role of the Na+/K+ transporter after an action potential?
It removes new Na+ that leaked in and retrieves K+ that leaked out
This helps restore the resting state of the neuron.
How does action potential propagation differ in myelinated versus non-myelinated axons?
In non-myelinated axons, the AP regenerates along the axon; in myelinated axons, it jumps from node to node
This is known as saltatory conduction.
What are the advantages of myelination?
Faster conduction and more economic use of energy
Myelin allows for action potentials to jump between nodes, reducing energy expenditure.
Where do action potentials start in a neuron?
At the axon hillock
This is the part of the axon next to the cell’s soma.
What happens at the terminal branches of the axon?
Action potentials influence synapses and neurotransmitter release
This affects the neurobiology of recipient neurons.
Fill in the blank: The electrical disturbance along the myelinated segment of the axon is ______.
decremental
The voltage change gets smaller as it passes under the myelin.
True or False: Action potentials can travel backwards along the axon.
False
They only propagate forwards due to the refractory state of Na+ channels.
