Week 1 Flashcards
Needs for a nervous system
- Allows detection of changes in external or internal environment (sensory)
- Allows rapid response to changes (motor)
- Allows integration of information and formulation of responses (central nervous system)
Neuron and what occurs in each part
At dendrites and cell body: integration of signals
At axon: transmission of action potential
At synaptic terminals: communication to next cell
Extracellular fluid
Also called internal milieu (not internal of cell, internal of body). On outside of cell
Intracellular fluid
On inside of cell
Types of structures in lipid bilayer
Integral proteins, receptors, gated channel protein, cholesterol, channel, carrier protein, glycoprotein, carbohydrates
Diffusion
Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration
0.9% NaCl to g/ml
0.9g/100ml
0.9g/100ml to g/L
9 g/L
9 g/L of NaCl into mol/L (Moles) (molar mass of NaCl is 58.44)
0.158 mol/L (M)
Aquaporin
water channel in cell membrane
Concentration gradient for sodium (Na+)
150 mM on outside
15 mM on inside
High concentration of N outside of cell
Concentration gradient for potassium (K+)
5mM on outside
140 mM on inside
High concentration of K inside cell
What causes the concentration gradient for sodium and potassium
The sodium/potassium ATPase
How the Na/K ATPase works
- Three sodium ions enter the enzyme from within cell
- ATP phosphorylates enzyme from inside of cell, causing it to pump 3 Na+ out of the cell
- Two potassium ions enter the enzyme from the outside of the cell
- The now un-phosphorylated enzyme pumps the 2 K+ into the cell
What does the ATPase need in order to function
Na+, K+ and ATP
Ouabain
Inhibits ATPase
Anions inside and outside of cell
Outside: Mostly Cl- (120mM)
Inside: Mostly large anions (100 mM) and some Cl- (10mM)
The plasma membrane is most permeable to
Potassium
Which way does Na want to go based on concentration gradient
Inside
Which way does K want to go based on concentration gradient
Outside
Is the charge on an ion large or small
very large
Inside of cell has a charge
Negative
Outside of cell has a charge
Positive
Define equilibrium potential of potassium
The potential (mV) that exists when the K+
concentration gradient is exactly matched by
the opposing electrical gradient for a given ion
(K+) in the theoretical situation of a membrane
with permeability for only K+.
Define the equilibrium potential
for sodium.
The potential (mV) that exists when the Na+
concentration gradient is exactly matched by
the opposing electrical gradient for a given ion
(Na+) in the theoretical situation of a
membrane with permeability for only Na+.
Nernst Equation
Calculates equilibrium potential
Eion = 62 mV x log ([ion]o/[ion]i)
Equilibrium potential
- Electrical “force” = - Concentration “force”
- If there were channels only for that ion, it is the voltage that would be measured across the membrane
- Calculated values based on concentration gradient between inside and outside cell
Equilibrium potential of K+
-90mV
Equilibrium potential for Na+
+62 mV
Membrane potential
Measured value that is determined by equilibrium potential for all ions and relative permeability for each ion
On most cells, including neurons, there is a
resting membrane potential with a negative
charge inside the cell. Why?
More potassium permeabity than sodium (More K+ channels than Na+ channels)
Potassium wants to leave cell due to concentration gradient
Resting Membrane Potential of a cell
- ~ -70 mV
- Due to an imbalance of ions across a cell membrane
- represents a form of energy
- measure of charge separation
Voltage
Measure of charge separation
Voltage during peak of action potential
+ 30 mV (due to open Na+ channels)
What is the electrical force on K+
70 mV pushing K+ inside of cell
Concentration force on K+
90 mV pushing K+ to outside of cell
Total force on K+
20 mV out of cell
What is the concentration force on Na+?
62 mV pushing Na+ to inside of cells
What is the electrical force on Na+?
70 mV pushing Na+ to inside of cells
Total force on Na+
132 mV into cell
How would changes in concentration affect resting membrane potential of cells
Not sure**
What determines the membrane potential
- equilibrium potential of each ion
- relative permeability for each ion
If Na+ channels open
Depolarization (cell becomes more +)
If K+ channels open
Hyperpolarization
Depolarization
Decrease in potential; membrane less negative
open Na+ channels
close K+ channels
Repolarization
Return to resting potential after depolarization
Hyperpolarization
Increase in potential; membrane more negative
Close Na+ channels
Open K+ channels
Do neurons receive information from one or multiple neurons
Most neurons receive information from many other neurons
Graded hyperpolarization
a smallish change in the membrane potential that is proportional to the size of the stimulus.
Graded potentials that make the membrane potential more negative, and make the postsynaptic cell less likely to have an action potential, are called inhibitory post synaptic potentials (IPSPs).
Graded depolarizations
Graded potentials that make the membrane potential less negative or more positive, thus making the postsynaptic cell more likely to have an action potential, are called excitatory postsynaptic potentials (EPSPs).
Summed potentials
If summed potentials reach the threshold value at the axon hillock, the membrane depolarizes and an action potential results
What is it about neurons that allows them to
produce action potentials?
Voltage-gated Na+ channels!!
At “threshold” these channels open and increase
permeability for Na+
Voltage-gated sodium channel
Has an activation gate and inactivation gate
1. Closed activation gate, capable of opening
2. Rapid opening of activation gate triggered at threshold
3. Slow closing inactivation gate triggered at threshold (when this closes, it is not capable of opening until it is restored to normal)
Voltage-gated potassium channel
Activation gate has a delayed opening triggered at threshold
Sequence for an action potential
Voltage reaches a threshold (-55 mV)
Depolarization- voltage-gated Na+ channels open
Repolarization- voltage-gated Na+ channels close, voltage-gated K+ channels open
Hyperpolarization
Return to resting membrane potential - Voltage-gated K+ channels close
Na+ at Resting (-70 mV)
Relative permeability: 1x
Direction of gradient–
Concentration: inward
Electric: inward
K+ at Resting (-70 mV)
Relative permeability: 25-30x
Direction of gradient–
Concentration: outward
Electric: inward
Na+ at Threshold (-55 mV)
Relative permeability: 600x
Direction of gradient–
Concentration: inward
Electric: inward
K+ at Threshold (-55 mV)
Relative permeability: 25-30x
Direction of gradient–
Concentration: outward
Electric: inward
