action potential

physio psych

Luigi Galvani

observed that dead frog legs would occasionally move d/t being connected to house electricity

Hermann von Helmholtz

• measured speed of neuron

• timed how fast electricity moved thru frog legs ~60ft/s → slow

• animals conduct electricity in waves/pulses

Edgar Adrian

• neural code

• pulses seem to be same size, not weaker/stronger in a given nerve, just a change in frequency

• diff sensory systems had same pulses

Charles Sherrington

coined “synapse”

Julius Bernstein

membrane hypothesis begins to explain what creates neural pulses

membrane hypothesis

• PM has electrical potential across it

• when one electrode is inside the axon and the other electrode is in seawater → voltmeter reads -70mV

extracellular vs intracellular fluid composition

“special K in a bowl of salty milk” and chloride

why use a squid’s axons?

• giant axon ~1mm in width

• can see w/ eyes

• thicker axon → faster comms

PM at rest still ___ to ___ gradient

uses E, maintain

things w/ ___ form [ ] gradients

identities

things w/ ___ form voltage gradients

charges

artificial hyper and depolarization cause cell to

actively maintain membrane potential to return it to baseline

maintaining ___ req E, ___ do not spend E

membrane potential, APotentials

threshold

-45mV

resting

• VG1 Na+ closed, VG2 Na+ open

• VG K+ closed

depolarization

• VG1 Na+ opens

• influx of Na+ inside cell

repolarization

• VG2 Na+ closes

• VG K+ opens

• efflux of K+ out of cell, no more Na+ in

hyperpolarization

• VG K+ slow to close

• K+ continues to leave → too negative

return to resting

• VG K+ finally closes

• no Na or K movement

tetrodotoxin

breaks VG Na+ channels → no Na+ influx → no APotential → paralyze diaphragm → no breathing → death

dendrotoxin

breaks VG K+ channel → can fire 1 APotential → cannot recover to fire another

propagation of APotential

• dominoes

• APotential at one pt changes charge density at neighboring part of cell → primes it for an APotential

for APotential speed, ___ is better

• bigger

• i.e., bigger neurons allow ions to flow more easily

saltatory conduction

• myelin prevents ions from leaking in/out

• APotential at a pt of axon → ions flow thru myelinated areas w/o being lost → easier for APotential to occur at next node of Ranvier

myelin

• fatty tissue, white matter

• Schwann in PNS

• oligodendrocytes in CNS

ependymal cells

• create CSF

• CNS

astrocytes

• create and maintain BBB

• CNS

microglia

• resident immune cells

• CNS

satellite cells

• regulate nutrients

• PNS

oligo myelination

• grab segments of axons and wrap myelin around

• know when neurons are active → promotes inc myelination of those neurons → inc efficiency of that info processing

• neurons die → microglia clean up neuron → oligos start retracting → any new neurons do not know where to go/grow and synapse

Schwann myelination

• create myelin in one spot on neuron vs. reaching out for neurons

• neurons die → already created myelin tube → any regeneration of neurons can be directed towards the tubes and know how to grow and synapse

multiple sclerosis

• starts in periphery → attacks motor control

• immune cells attack myelin surrounding nerve fibers