Part 2 Flashcards
How neurons work: ion movements and electrical signals
Like all cells, neurons maintain a transmembrane potential
when the cell is at rest this is called a potential difference or an electrochemical gradient
What is a transmembrane potential?
The unequal distribution of charges inside and outside the plasma membrane
What happens if a cell is left undisturbed?
It will maintain a resting membrane potential indefinitely
the cell in this condition is said to be polarized
How do ions cross cell membranes without the use of ATP?
Leakage Channels:
- leak either Na+ or K+
Gated Channels:
- voltage gated (specific membrane potential/voltage will cause gates to open/inactivate)
- chemical (ligand) gated (certain molecules attaching to binding sites triggers gate opening)
- mechanically gated (applied pressure physically pries gates open and closes when pressure is removed)
Na+/K+ ATPase pump
- pump 3Na+ ions out of cell and 2K+ ions into cell for every ATP used
What happens to ions when an ion channel is open?
Ions move accordingly to both concentration gradients and the electrical gradient
Direction of movement due to concentration gradient:
- K+ will move out of the cell
- Na+ will move into the cell
Direction of movement due to electrical gradient:
- positive ion moves towards inside of cell (Na+ and K+)
- negative ion towards outside of cell (Cl- and protein)
What is the electrochemical gradient?
The tendency of the ions to move as a result of both concentration and electrical gradients influencing ions at the same time
Potassium ion gradients:
At a neurons resting membrane potential, the chemical and electrical gradients are opposed for potassium ions. The net electrochemical gradient tends to force potassium ions out of the cell
fk idk what its asking bluh
pg. 28
What gates are not closed at rest?
Leaky channels
there are few Na+ leaky channels
there are a few more K+ leaky channels
Na+/K+ pump moves both ions back in the opposite direction, preventing changes in concentration
- further net loss of positive charge from inside the cell
What contributes to generating the resting membrane potential?
Leaky channels, Na+/K+ pump, extracellular fluid, cytosol, proteins, etc
What are factors that can change the membrane potential from resting?
- anything that changes the permeability of the membrane to a particular ion
- i.e. opening of ion channels
- anything that changes the ion concentration on the two sides of the membrane
- normally, opening or closing of ion channels
What does it mean for a cell to be depolarized?
A cell is said to be depolarized when:
- it becomes more positive than resting potential (above -70mV)
What does it mean for a cell to be hyperpolarized?
A cell is said to be hyperpolarized when:
- it becomes more negative than the resting potential (below -70mV)
What could happen if a cell is stimulated?
If a cell is stimulated (such as having membrane potential changes from resting) and generated a current and released potential energy
changes in membrane potential act as a stimulus
How does a neuron generate an electrical impulse (action potential)
Depolarization can lead to a graded potential and the development of an action potential:
effect of neurotransmitter at a synapse between two neurons
What are the steps to a graded potential?
- resting membrane with closed chemically regulated sodium ion channels
- ligand gated channels
- Neurotransmitter binds to receptors, which is a part of the chemical (ligand) gated sodium channel
b) sodium moves into the cell, depolarizing a small area. the spread of sodium produces a local current that depolarizes adjacent portions of the cell membrane
- this small depolarization is an example of a graded potential
What are characteristics of a graded potential?
- Mostly affects locally and the effect decreases with distance = used for short distance communication
- Effect spreads passively owing to local currents
- May cause depolarization or hyperpolarization depending on which ion channels are stimulated to open
- The stronger the stimulus, the greater the change in transmembrane potential, the larger the area affected
What affects the degree of change in potential?
Varies with’
a) graded depolarization of axon hillock
b) degree of synaptic vesicles secreted
c) degree of chemical gated ion channels open
What is an action potential?
If the cell is depolarized beyond a critical threshold level, an action potential is generated
What is the difference between an action potential and graded potential?
an action potential is different from a graded potential in that it is an “all or none” event; it either occurs or does not at all
