Chapter 4 - Electrical Signalling Flashcards
Where is dendritic activity summated?
- At the axonal initial segment (AIS), found shortly after the soma
Define the terms electricity, battery, voltage, and current.
- Electricity - the flow of electrons from a body that contains a higher charge to a lower charge
- Battery - Source of potential energy
- Voltage - the difference in charge between two points (measured in volts)
- Current - movement of charged particles (measured in amps)
T/F: Polar molecules diffuse across the membrane.
- FALSE
- Non-polar molecules diffuse across the membrane because of the hydrophobic tails.
- Polar molecules require protein channels
What’s the difference between a concentration gradient and a voltage gradient?
- Concentration gradient - substances move from areas of high concentration to areas of low concentration
- Voltage gradient - ions move from areas of high charge to areas of low charge
What does the term electrochemical gradient signify?
- When the chemical and electrical gradients are equal in magnitude (i.e., when the neuron is resting)
What electrical term is a neuronal membrane synonymous with?
- Acts as a dam, or rather a charged battery
- The flow of charged particles acts as the water (i.e., the current)
What’s the resting potential of a neuron?
- -70mv (more negative on the inside)
Which ions are in higher concentration inside and outside the cell?
- Outside: High sodium, high chloride
- Inside: High potassium, high negatively charged proteins
How are sodium and potassium ions moved across the neuronal membrane?
- Potassium - Has a leak ion channel and is free to move in and out of the cell when needed
-Sodium - Has a gated-ion channel with a closed gate (on top) and an activation gate (on bottom). Closed at rest to maintain resting voltage of -70mV
What’s the purpose of the sodium-potassium pump?
- Maintains high sodium outside the cell and high potassium inside the cell
- Expels 3 sodium ions for every 2 potassium ions
What does a voltmeter do?
- Device that measures the strength of electrical voltage by recording the difference in electrical potential between two points
- One electrode is inside, the other is outside
What animal is commonly used to measure neuronal mechanisms?
- A giant squid axon kept in a saline solution
- Discovered by Hodgkins and Huxley in the 1930s
- Won a Nobel prize for discovering the neurons ionically-based electrical activity
Where are ion channels highly concentrated along the neuron?
- At the Nodes of Ranvier
What are the confirmational states of potassium voltage-gated ion channels?
1) Closed at resting potential
2) Start to open at -50mV where potassium efflux occurs
What are the confirmational states of sodium voltage-gated ion channels?
1) Activation gate Closed at resting potential
2) Opens at -50mV where sodium influx occurs
3) non-activation gate closes at +30mV
What are the main causes of depolarization and hyperpolarization?
- Depolarization - due to the inward flow of sodium ions due to an action potential
- Hyperpolarization - due to the outward flow of potassium ions or inward flow of chloride ions when a neuron is trying to return to a resting state.
T/F: An action potential is an all or none response.
- TRUE
- The action potential has the same amplitude every time no matter the stimulus
- Can only increase the frequency of action potentials occurring at one time, never the amplitude
What are the general steps during an action potential?
1) Neuron initially at -70mV resting potential
2) Stimulus triggers membrane potential to increase to -50mV
3) Sodium ion channels open, causing a sodium influx
4) Rapid depolarization occurs and membrane potential shoots up to +30mV
5) The sodium activation gate closes and the potassium channels finally open, causing a potassium efflux
6) Hyperpolarization occurs, and both sodium gates close
7) Neuron returns to resting state as both channels close
Why does potassium efflux occur after depolarization occurs?
- Even though potassium channels are triggered to open at -50mV, they just take longer to open
- They are mainly responsible for repolarization
What’s the difference between the relative refractory and absolutely refractory period?
- Absolutely refractory period - a new AP cannot be elicited (found during ascending and descending peak on graph)
- Relatively refractory period - During the hyperpolarization phase, a higher intensity stimulation is required to produce another action potential (potassium channels still open but you’re below the resting potential)
How does an electrical signal propagate down the neuron?
- AIS > axon terminals
- Influx of sodium ions in one segment triggers the depolarization of the following segment
What’s saltatory conduction?
- The “jumping” of ions from one node of Ranvier to another, critical for speeding up the propagation of action potentials
What’s multiple sclerosis (MS)?
- Most common autoimmune disease
- Due to loss of myelin formed by oligodendroglia due to a poor immune response
- Plaques form at the sites of myelin loss, making it difficult to propagate signals properly.
- Starts with loss of sensation in motor control in hands and feet
T/F: AIS is sparse in terms of ion channels
- FALSE
- It’s rich in voltage-gated ion channels
- These channels help generate the initial action potential
What exactly is the AIS summating?
- Excitatory postsynaptic potentials (EPSPs) and Inhibitory postsynaptic potentials (IPSPs)
- Thousands occurring all at once at the dendrites
Temporal summation vs. Spatial summation?
- Temporal - Inputs on the same dendritic spine occurring in rapid succession
- Spatial summation - Inputs on different spines that occur at the same time, will summate if the inputs are close in space
