Electrophysiology of Neurons (2) Flashcards
Exam 2
What is the structure of a typical neuron and what are each of them?
- neurosoma: control center
- axon hillock: mound on the neurosoma
- axoplasm: cytoplasm of axon
- dendrites: branches of neruosoma
- axon: transmits nerve impulses away form the cell body and toward other cells
What is the electrical potential?
difference in the concentration of charged particles between one point and another
What is an electrical current?
flow of charged particles from one point to another
under the right circumstances an electrical potential creates a current
As long as there’s a potential (voltage), a battery is ____
polarized
Living cells are ___
polarized
Difference in charge on each side of the plasma membrane is due to:
1) permeability of membrane
2) action of sodium-potassium pump
3) negatively charged molecules
What is the difference in charge called?
potential difference
What is the resting potential energy?
Storage of energy for conduction of nerve signals (causes the cell membrane to be polarized [charged])
What do channel proteins do?
allow solutes and water to pass through the membrane
What do Ligand-Gated Channels respond to?
chemical messengers
What do Voltage-Gated Channels respond to?
charge changes
What do Mechanically-Gated Channels respond to?
physical stress on the cell
The Resting Membrane Potential (RMP) results from the combined effect of three factors:
- ions diffuse down their concentration gradient through the membrane (permeability)
- action of Na+/K+ pumps
- Electrical attraction of cations and anions to each other (negatively charged molecules inside the cell)
What has the greatest influence on RMP?
potassium
Cytoplasmic anions cannot escape due to ___
size (too big)
Plasma is not very permeable to ___ as to ___
sodium
potassium
Na+/K+ pump moved ___ out for every ___ brought in.
3 Na+
2 K+
True or False
the sodium/potassium pump requires a lot of ATP
True
sodium/potassium pumps use ___ of the energy requirement of the nervous system
70%
highest rates of ATP consumption
Local Potentials Definition
changes in membrane potential of a neuron occurring at/near the part of the cell that is stimulated
Entry of a positive ion makes the cell ___ ____
less negative
depolarization definition
a change in membrane potential toward zero mV
Local potential is a short range change in membrane ___
voltage
What are the four properties of local potentials?
- Graded (vary in magnitude with stimulus strength/duration
- Decremental (get weaker the farther they spread from the point of stimulation)
- Reversible (if stimulation ceases, the cell quickly returns to its normal resting position)
- Either Exciting or Inhibitory (some neurotransmitters make the membrane potential more negative)
Nerve signaling is controlled by ion channels. What are the types of ion channels?
- Ligand-gated
2. Voltage-gated
Ligand-gated channels defintion
membrane protein opens/closes when ligand binds
Voltage-gated channels definition
opens/closes due to change in membrane potentials
A dramatic change in membrane polarity produced by ___ ___ ion channels
voltage-gated
What on a neuron cannot generate an action potential in the soma?
Neurosoma
Where on a neuron are action potentials generated?
trigger zone
What are the 8 steps in producing an action potential?
1) strong local potential produced (stimulus)
2) arrival of current at axon hillock depolarizes membrane
3) depolarization must reach a threshold (about -55 mV)
4) voltage-gated sodium channels to open quickly
5) membrane potential rises above 0 mV
6) slow potassium channels open – outflow repolarizes cell
7) potassium channel remain open for a time so that membrane is briefly hyper polarized (more negative than RMP)
8) RMP is restored – ion concentrations are now flipped: sodium intracellular and extracellular potasium
What are the 3 characteristics of an action potential?
1) follow all or none
2) none decremental: does not get weaker with distance
3) irreversible: once started, goes to completion (cannot be stopped)
What are the two phases of action potential- refractory period?
1) absolute refractory period (no stimulus of any strength will generate or tigger a new action potential; lasts as long as sodium gates are open, then inactivated)
2) relative refractory period (especially strong stimulus will trigger new action potential; potassium gates are still open and generally any effect of incoming sodium is opposed by the outgoing potassium; generally lasts until hyperpolarization ends)
