Neurophysiology Flashcards
What the ion concentrations in a cell?
Na+ and Cl- are high concentration outside the cell
K+ is high inside the cell
What gradients do we have to consider for ions?
We have to consider both concentration gradients and electrochemical gradients.
-ex: when potassium flows out of the cell, it becomes more negative. This makes it harder for the next potassium to leave the cell.
What is the charge inside the cell?
Negative
Na+/K+ pump
-uses ATP as energy source
- 3 Na+ out , 2 K+ in
- you lose one particle charge
- inside keeps becoming more negative
- 10 % contribution to membrane potential
What are leak channels?
-there job is to stay open so you can’t have too many
-K+ channels: 60% contribution comes from K+ channel ( number one contributor to membrane potential) leaks out
- Na+ channels: 30% contribution to membrane potential. Leaks in
What is a patch clamp?
Puts electrode into the cell and another outside to measure voltage difference.
-70 mV
Equilibrium potentials
Eion =(61/z) log( [ion]out/[ion]in)
Calculating equilibrium potential for each ion
Example: calculate equilibrium potential of K+
E= (61/+1) log (5mM/150mM) = -90 mV
What is the GHK equation?
Considers membrane permeability to each ion. “Contribution” of ion to potential
Changes in membrane potential
-Depolarization: inside of membrane becomes less negative
-Repolarization: inside of membrane becomes more negative (returns to resting)
-Hyperpolarization: membrane becomes more negative than resting
Graded potential
Presynaptic stimulus comes from first neuron and travels to another post synaptic neuron where it becomes more permeable to Na+ (ligand gated channel)
-like analog signal, so they decay trying to travel really long distances
-need another system to make signal travel all the way (action potential) graded potential alone won’t work
What is subthreshold?
Graded potential that is not big enough to trigger action potential
What is suprathreshold?
Graded potential that is big enough to trigger action potential (open voltage gated ion channel)
Axon hillock
Part of the neuron where it connects the axon and the cell body
Conformation of voltage gated Na+ channels
- At the resting membrane potential, the activation gate closes the channel
- Depolarizing stimulus arrives at the channel. Activation gate opens
- Influx of sodium goes through
- Inactivation gate closes and Na+ entry stops (plug)
- During repolarization caused by K+ leaving the cell, the two gates reset to their original positions
Continuous conduction
Occurs in unmyelinated axons. Slower than saltatory conduction. Action potential is propagated and conducted along the entire length of the axon
Saltatory Conduction
Occurs in axon with myelin. Action potential “jumps” to gaps in axon. Faster
-if you destroy myelin signal may not reach the end
Refractory period
Time interval required to generate another action potential.
Absolute: no stimulus can trigger another action potential
Relative: only a larger-than normal stimulus can initiate a new action potential
Axon terminal
are the fingers that “attach” to other nuerons
Neurotransmitters
-like peptide hormones
-released by exocytosis
-bind with a receptor (can be chemically gated or ligand gated)
-can trigger second messenger cascade
-can be excitatory or inhibitory
What is the second messenger that triggers release of neurotransmiiters?
Calcium (voltage gated calcium channel)
-action potential reaches axon terminal and stimulates calcium and triggers exocytosis for NT release
Acetylcholine
-common NT in brain, motor neuron, and autonomic nervous system
-don’t recycle (too many)
-mostly excitatory
Glutamate
-mostly excitatory
-glutamate is released when we learn new things
-problem is that the memory doesn’t last forever
-need repetition for the synapse to stay
Norepinephrine
-mostly excitatory
-used in autonomic nervous system (sympathetic)
-recycled
-associated with mood, motivation, and alertness
GABA = Gamma-Aminobutyric acid
-when released opens chloride channel
-primarily inhibitory
-When chloride channel is opened it flows into the cell and makes it more negative. it becomes hyperpolarized and harder to generate action potential
-sedative
Postsynaptic Potentials (graded potential)
-jobs is to make the graded potential decrease or increase
-EPSP: Excitatory postsynaptic potentials (make graded potential increase)
-IPSP: inhibitory postsynaptic potentials (make graded potential decrease) ex: chloride flows in
Temporal summation
sending multiple ESPS and adding them up so that it reaches the threshold and creates an action potential
-one synapse
Spatial summation ?
-multiple synapse
-three ESPS are fired and are added to create action potential
