Topic 2- Neurophysiology Intro & Review Flashcards
What is resting potential?
Resting potential is a stable, negative electrical charge across a neuron’s cell membrane when it’s not actively transmitting signals, typically around -70mV.
What is the threshold for excitation in a neuron?
The threshold for excitation in a neuron is around -55mV. To initiate an action potential, the membrane potential needs to reach -55mV.
What sets neurons apart from other cells?
Neurons are different from other cells because they are excitable. Their ability to change membrane potential, especially from resting potential to the threshold, allows them to respond to stimuli and transmit signals
Membrane Potential
Difference in electrical charge across the cell membrane.
What is the tendency of ions regarding concentration and voltage gradients
Ions tend to move down concentration and voltage gradients.
What is the role of active transporter proteins in maintaining the membrane potential?
Active transporter proteins create and maintain ion gradients, ensuring that there are more positively charged ions outside the cell than inside, contributing to the membrane potential.
What does the sodium-potassium (Na+/K+) pump do to maintain the resting membrane potential?
The Na+/K+ pump actively transports 3 sodium ions (Na+) out of the cell for every 2 potassium ions (K+) it pumps into the cell, contributing to the negative charge inside the cell.
How does potassium (K+) contribute to the resting membrane potential?
Potassium ions leak out of the cell through potassium ion channels, allowing some positive charge to leave the cell and helping to establish the negative resting membrane potential.
What is hyperpolarization and explain how it is inhibitory?
It makes the neuron’s membrane potential even more negative than its resting state, moving it farther away from the threshold needed to trigger an action potential.
Depolarization
Process that makes the neuron’s electrical state more positive, which is exciting because it brings the neuron closer to the action potential threshold
Four Types of Ion Channels
Leak (non-gated)
Ligand-gated
Mechanical (modality gated)
Voltage-gated
Leaky Channels (ex. K+ ion channel)
Allow for passive diffusion of ions in and out of the cell (selectively permeable)
Mechanical Channels
sensitive to physical changes in the cell membrane, such as stretching, pressure, or deformation.
Voltage Gated Ion Channels
Membrane proteins that respond to changes in the electrical potential (voltage) across the cell membrane.
Ligand Gated Ion Channels
Respond to the binding of specific chemical signaling molecules, called ligands, to their receptor sites.
Ligand Gated ion Main Function
Convert chemical signal to electrical signal and play a crucial role in synaptic transmission, where neurotransmitters bind to receptors on postsynaptic neurons to initiate an electrical signal.
Where are mechanical channels found?
Sensory receptors, like touch receptors, and play a role in transducing mechanical stimuli into electrical signals.
Steps of an Action Potenital
1) Resting Membrane Potential
2) Depolarization
3) Rising Phase
4) Repolarization
5) Overshoot and Hyperpolarization
6) Return to Resting Potential
7) Refractory Period
First Step: Resting Membrane Potential
Neurons’ resting potential is around -70 mV due to ion imbalance, with K+ inside and Na+ outside the cell.
Second Step: Depolarization
When a stimulus reaches the threshold, voltage-gated Na+ channels open, causing an influx of Na+ ions and making the membrane potential more positive.
Third Step: Rising Phase of an action potential`
During this phase, more Na+ ions flow into the neuron, leading to a continuous increase in membrane potential (more positive), reaching approximately +30 mV.
4) Repolarization
After reaching its peak, voltage-gated Na+ channels close, and voltage-gated K+ channels open, allowing K+ ions to exit, making the membrane potential more negative.
5) Overshoot and Hyperpolization
The membrane potential briefly goes below the resting level (overshoot) due to the efflux of potassium ions, followed by a temporary hyperpolarization where it becomes more negative due to open K+ channels.
How does a neuron Return to Resting Potential after an action potential?
The sodium-potassium pump (Na+/K+ pump) actively moves Na+ ions out and K+ ions in, restoring the original ion balance, and resetting the membrane potential to around -70 mV
What is the Refractory Period in an action potential?
It’s a period when the neuron is less responsive to stimuli. This refractory period consists of two phases: the absolute refractory period, during which another action potential cannot be triggered because voltage gated sodium channels are closed , and the relative refractory period, during which a stronger stimulus is required to initiate a new action potential.
How can different cells can have different types of APS
Due to different types and densities of ion channels
What is the function of the axon in a neuron?
The axon acts like a cable, transmitting the electrical signal (action potential) from the cell body to the presynaptic terminals, where communication with other cells occurs.
Why are neuronal membranes not good insulators?
Neuronal membranes allow ions like sodium (Na+) and potassium (K+) to leak across them, which makes them poor insulators and challenges the maintenance of electrical signals over long distances
How is the signal strength boosted in neurons?
Neurons use nodes of Ranvier along their axons. At these nodes, the action potential is regenerated or “boosted” by the opening of voltage-gated ion channels, ensuring the signal remains strong during transmissio
What is the major challenge in neuronal communication?
The major challenge is speed. Neurons often need to transmit signals quickly for rapid responses. The leakiness of neuronal membranes can slow down signal propagation, but the continual regeneration of the action potential at nodes of Ranvier helps maintain signal speed.
What are oligodendrocytes, and where are they found?
Oligodendrocytes are glial cells found in the central nervous system (CNS), including the brain and spinal cord.:
What is the primary function of oligodendrocytes?
The primary function of oligodendrocytes is to provide insulation to axons by producing myelin, which speeds up the transmission of electrical signals in the CNS.
What are Schwann cells, and where are they located?
Schwann cells are glial cells found in the peripheral nervous system (PNS), which includes nerves outside the brain and spinal cord
What is the role of Schwann cells?
Schwann cells play a role in myelinating axons in the PNS, helping in rapid nerve signal transmission and supporting nerve regeneration.
What creates the small gaps known as Nodes of Ranvier along the axon?
Nodes of Ranvier are small gaps where myelin-forming glial cells (oligodendrocytes in the CNS or Schwann cells in the PNS) do not cover the axon, creating spaces between adjacent glial cells along the axon’s length
Primary difference in function between oligodendrocytes and Schwann cells
Oligodendrocytes myelinate multiple axons and Schwann cells myelinate (wrap around) single axons.
What characterizes Nodes of Ranvier in terms of ion channels?
Nodes of Ranvier are characterized by a high density of voltage-gated sodium (Na+) channels on the axonal membrane, which open in response to changes in membrane potential and are crucial for the rapid initiation of action potentials.
What distinguishes Nodes of Ranvier from myelinated axonal segments in terms of potassium (K+) channels?
Nodes of Ranvier lack voltage-gated potassium (K+) channels, unlike myelinated axonal segments where K+ channels are abundant. This absence prevents the early repolarization phase of the action potential in these regions.
What is the term for the mode of rapid nerve signal propagation that occurs at Nodes of Ranvier?
“Saltatory” conduction refers to the rapid transmission of action potentials where the signal “jumps” or “skips” from one Node of Ranvier to the next along a myelinated axon, significantly increasing signal speed and efficiency.
How does a lack of myelin impact the propagation of action potentials in neurons?
A lack of myelin slows down and disrupts the smooth transmission of nerve signals, making them less efficient, leading to symptoms and issues with motor control, sensation, and coordination as seen in MS
What does lambda represents and affect?
Represents (how far a current can go) and what affects it (how thick myelin is…goes farther!…and how low axon resistance is
