Chapter 4 Flashcards
Neurons and electrical signaling
What is a positively charged ion called?
Cation
What is a negatively charged ion called?
Anion
Cation
Positively charged ion
Anion
Negatively charged ion
Concentration gradient
the relative abundance of a substance in a space (ions in this case)
Concentration gradients flow due to…
Diffusion
Diffusion
the movement of a substance from a high concentration to a place with low concentration
Does diffusion require energy?
No
Voltage gradient
the difference in charge between 2 areas
How do ions flow in a voltage gradient?
from a place of higher charge to a place of lower charge
What is the voltage of an axon during resting potential?
-70mv (avg.)
What four charged particles take part in producing resting potential and where are they concentrated (intra- or extracellular)?
Na+ (extra-), K+ (intra-), Cl-(extra-), A- (intra-)
What three features contribute to the cell’s resting potential?
- A- (protein anions) can’t pass out of the cell (keeps negative voltage).
- channels allow K+ and Cl- to flow freely in and out of cell (along concentration/voltage gradient)
- Na+-K+ pumps extrude Na+ and inject K+ (3 Na+ for 2 K+, keeping voltage difference).
Why don’t sodium ions diffuse freely across the cell membrane?
Gated channels.
What does the sodium-potassium pump do?
Pumps 3 sodium ions out of the cell and take in 2 potassium ion. For when sodium ions leak in the cell.
How do chloride ions travel across the cell membrane?
Open channels. Still, because of the voltage gradient and concentration gradient, there are more chloride ions outside of the cell.
What is a graded potential?
A small voltage fluctuation across the cell membrane
What is hyperpolarization?
An increase in the charge inside the cell.
Less likely for an action potential to occur.
What ions contribute to hyperpolarization
Efflux of K+ (outside becomes more positive)
Influx of Cl-
What is depolarization?
A decrease in the charge inside the cell.
More likely for an action potential to occur.
What ions contribute to depolarization?
Na+ (inlfux inside the cell)
Where on the cell do graded potentials occur?
Soma and neuronal dendrites - where there are gated channels
What is the threshold potential of a cell?
-50mv
How much does a cell depolarize during an action potential?
to 30mv (100mv change)
What is a voltage-activated channel?
a gated protein channel that opens or closes only at specific membrane voltages
The voltage change due to what ion channel takes place first when voltage-gated channels open?
Na+
What is the absolute refractory period?
The state of an axon in the repolarizing period, during which a new action
potential cannot be elicited (with some exceptions) because gate 2 of
sodium channels, which are not voltage activated, are closed.
What phase(s) of the action potential are a part of the absolute refractory period?
Depolarization and repolarization (with few exceptions)
What is the relative refractory period?
The state of an axon in the later phase of an action potential, during which
higher-intensity electrical current is required to produce another action
potential; a phase during which potassium channels are still open.
What phase(s) of the action potential are a part of the relative refractory period?
Hyperpolarization
What sodium gate is time-sensitive?
Gate 2
What is a nerve impulse
The propagation of the action potential along an axon.
How long is the refractory period of an axon and how often can an action potential occur?
5ms, 200 action potentials per second.
What are glial cells called in the PNS and the CNS
Schwann cells in the PNS and oligodendroglia in the CNS
What is the function of glial cells (Schwann and oligodendroglia)?
To wrap around and insulate the axon
What is the myelin sheath?
The glial cells that wrap around and insulate the axon.
What are the gaps between myelin called where the action potential propogates?
Nodes of Ranvier
What is saltatory conduction?
Fast propagation of an action potential at successive nodes of Ranvier
What are 2 consequences of myelin on the axon?
Metabolically cheaper - uses less energy
Increases conduction speed
What happens to myelin when someone has MS
Myelin in the CNS deteriorates
(myelin formed by oligodendroglia)
What is an EPSP?
Excitatory post synaptic potential
Depolarizes cell
Increases likelihood for action potential to occur.
What is an IPSP
Inhibitory post synaptic potential
Hyperpolarizes cell
Decreases likelihood for action potential to occur.
The opening of what ion channel(s) is associated with EPSPs
Sodium channels - influx of Na+
The opening of what ion channel(s) is associated with IPSPs
Potassium channels - efflux of K+
What is the initial segment?
Area rich in voltage-gated channels;
Area near or overlapping the axon hillock; where the action potential begins
What is temporal summation?
The summation of multiple inputs (at the exact same location) occurring near or at the same time.
What is spatial summation?
The summation of multiple inputs occurring near each other on the membrane at the same time.
What impulses are usually created close to the initial summation - where they are more influential?
IPSPs
Where do giant depolarizing potentials occur and what is thought to be their purpose?
Developing hippocampus - aiding in neural circuitry
What is back propogation?
Reverse movement of an action potential into the soma and dendritic field of a neuron
What is the role of back propagation?
plays a role in the plastic changes that underlie learning
- Can signal the presynaptic neuron to fire more or less, for example
