Nerve Impulses Flashcards
Sodium-potassium pump:
→ pumps 2 Potassium in & 3 Sodium out → negatively
charged cell
What type of channels do neurons have?
Neurons have gated ion channels (protein complexes that allow specific ions through) that open or close in response to stimuli → leading to changes in the membrane potential.
An increase in the magnitude of the membrane potential is a ______; a decrease is a ______. Changes in membrane potential that vary continuously with the strength of a stimulus are known as ____ potentials.
hyperpolarization
depolarization
graded
What is an action potential?
An action potential is a brief, all-or-none depolarization of a neuron’s plasma membrane. When a graded depolarization brings the membrane potential to the threshold, many voltage-gated ion channels open, triggering an inflow of Na+ that rapidly brings the membrane potential to a positive value.
How is a negative membrane potential restored?
A negative membrane potential is restored by the inactivation of sodium channels and by the opening of many voltage-gated potassium channels, which increases
K+ outflow. A refractory period follows, corresponding to the interval when the sodium channels are inactivated.
How does a nerve impulse travel?
A nerve impulse travels from the axon hillock to the synaptic terminals by propagating a series of action potentials along the axon.
How does the speed of conduction increase?
The speed of conduction increases with the diameter of the axon and, in many vertebrate axons, with myelination. Action potentials in myelinated axons appear to jump from one node of Ranvier to the next, a process called saltatory conduction.
In an electrical_____, electrical current flows directly from one cell to another. In a chemical synapse, ______ causes
synaptic vesicles to fuse with the terminal membrane and release neurotransmitters into the synaptic ____.
synapse
depolarization
cleft
How do neurons transmit information? (2)
- Neurons initiate action potentials → a transient alteration of the transmembrane voltage (or membrane potential *) across an excitable membrane in an excitable cell (e.g., neuron) generated by the activity of voltage-gated ion channels embedded in the membrane.
- Change in membrane potential *→ change in electrical potential associated with the passage of an impulse along the membrane of a muscle or nerve cell
What is Resting Membrane Potential?
The difference in charge between cell cytoplasm and extracellular fluid (ECF) when cell is NOT electrically active.
Caused by ionic gradients
Inside of the cell is ____ charged to the outside
- Inside: _____ ions and negatively charged proteins
- Outside: _____ ions
This creates a resting membrane potential of -70mV
The membrane potential of the neuron changes when it receives a stimulus → This is known as an ____ potential
negatively
potassium
sodium ions
action
What is the resting potential of the cell?
The resting potential of the cell is -70mV (milli volts) and is maintained by the passive diffusion of sodium and potassium and the pumping of these ions across a chemical gradient. If we put a voltmeter across the membrane we would see that it registers this voltage at rest. The resting potential is important, as once it changes
to a different voltage, we can trigger the neuron to fire and send electrical impulses.
What causes ions to move across membranes?
Ionic concentration gradients cause ions to move across cell membranes. This results in a separation of charge across the membrane, which in turn creates an electrical potential or force. A chemical form of potential energy.
Why does the ECF become more negative?
When a neuron sends an impulse, the inside of the cell now becomes more positive and the ECF becomes more negative. Cell membranes of neurons contain ion channels/proteins which make them selectively permeable, allowing for ion transport. Can be passive (facilitated diffusion) or active (gated channels). The concentration of ions differs inside + outside of neurons.
Why does the sodium-potassium pump maintain? (4)
- The sodium-potassium pump maintains a high Na+ concentration in ECF and a high K+ concentration inside the cell.
- An overall negative charge in the cell due to presence of multiple anions in cell
- Due to this concentration gradient + presence of passive Na+ (fewer channels) and K+ (more channels) transporter proteins, K+ has the tendency to leave the cell.
- This is a problem as the membrane potential would be lost.
What is the lipid bi-layer of the neuron cut with?
The lipid bi-layer of the neuron cell membrane is cut with proteins (ion channels) which only allow the exchange of one ion or the other.
There are two types, ____ channels, and_____ channels.
active
passive
What do active channels allow?
Active channels only allow ions through once stimulated to do so. The active channels only open when a ligand “tells” it to or when the voltage changes significantly. → require ATP.
Sodium-Potassium Pump:
This Co-transporter, voltage-gated ion channel fixes the above problem of K+ ions leaking.
What is its function?
Function:
- Transports 3 Na+ out and 2 K+ in
- Maintains the concentration differences
- Maintains the difference in charge between the two compartments
- Need to maintain concentration differences to maintain resting potential
*Separation of charge (voltage) results in electrical gradient that counterbalances the chemical concentration gradient of K+
Formation of the resting potential (RP): (11)
- A neuron at RP, the concentration of K+ is greater in cell while concentration of Na+ is greater in ECF.
- A negative charge inside cell (due to anions in cell)
- A positive charge outside cell
- A neuron at RP contains multiple passive K+ channels and fewer Na+ passive channels → K+ diffuses out of cell → cells are very permeable to K+ and slightly permeable to Na+
- The cell has to work to keep K+ inside cell to keep cell gradient
- Neurons have a sodium-potassium pump → only allows 3 Na+ ions to exit cell and 2 K+ ions to enter cell → 3 Na+ going out helps generate + charge outside of cell
- Sodium-potassium pump requires ATP energy (a chemical ligand which activates pump) to move Na+ and K+ against their concentration gradients and maintain gradient
- ATP hydrolysis (ATP → ADP + Phosphate) causes phosphate group to bind to pump to allow change in shape, increasing its affinity to Na+ or K+.
- As potassium binds (Na+ is transported ) and falls off (K+ is transported), shape changes.
- Glucose is needed to undergo cellular respiration to produce ATP
- Allows maintenance of (-) inside and (+) outside
Sodium Potassium Pump Mechanism: (6)
Why is the graph negative? (2)
Explanation: when the membrane potential becomes more negative so inside of cell becomes more negative
Reason: the opening of K+ passive channels increases the diffusion of K+ ions out of the cell causing the potential to approach Ek = equilibrium potential of K+ = -92 mV
Why is the graph positive? (2)
Explanation: when the membrane potential becomes more positive as the inside of the cell becomes more positive
Reason: the opening of Na+ ions increase diffusion of Na+ ions into the cell causing the potential to approach E(Na)(equilibrium potential of Na+) = + 62 mV
What is a voltage-gated channel? (2)
A voltage-gated channel is a channel that responds to changes in the electrical properties of the membrane in which it is embedded.
- Normally, the inner portion of the membrane is at a negative voltage. When that voltage becomes less negative, the channel begins to allow ions to cross the membrane
What is a ligand-gated channel? (2)
A ligand-gated channel opens because a signalling molecule, a ligand, binds to the extracellular region of the channel.
- This type of channel is also known as an ionotropic receptor because when the ligand, known as a neurotransmitter in the nervous system, binds to the
protein, ions cross the membrane changing their charge
What is a mechanically-gated channel? (3)
- A mechanically gated channel opens because of the physical distortion of the cell membrane.
- Many channels associated with the sense of touch (somatosensation) are mechanically gated.
For example, as pressure is applied to the skin, these channels open and allow ions to enter the cell. Similar to this type of channel would be the channel that opens on the basis of temperature changes, as in testing the water in the shower.
Action Potential series of Events: (5)
- Resting Potential
- Depolarization (Na+ ions move into cell)
- Repolarization (K+ ions move out of cell)
- Hyperpolarization (slow closing of K+ ion channels)
- Resting phase
AP always have a constant magnitude of about + 40 mV but Graded potentials vary.
Summary of the Action Potential: (8)
- Na+ and K+ channels open and close in response to changes in voltage
- Changes in charges at the membrane surface alter the conformation of the channel proteins.
- Depolarisation triggered by an external stimulus; rapid opening of Na+ channels → Na+ diffuses into the cell
- Action potential occurs
- Triggering of K+ channels to open, K+ diffuses out of cell (hyperpolarization)
- Depolarization phase sufficient to open voltage-gated channels in adjacent region of the membrane
- Action potential propagated along membrane
- The action potential does not propagate back up the axon – area that has just experienced action potential cannot produce another right of way.
Conduction of an Action Potential: (4)
The Na+ ions move into the cell and
depolarizes parts of the membrane.
At -40 mV, the voltage-gated Na+ channels
open to bring about AP.
An action potential starts with an inflow of
Na+. The influx of positive charges attracts
negative charges inside the cell and repulses
positive charges.
As a result, the positive charge spreads away from
the channel where the Na+ enters and
depolarizes nearby regions of the neuron.
Voltage-gated Na+ channels open in response.
The action potential leaps from node to node and conduction is so much faster.
Myelin is the ____ between the nodes.
Saves ____ energy → prevents slow inward leak
of Na+ and outward leaking of K+, maintaining membrane
potential requires ____ energy.
insulation
neuron
active
