lecture 6 Flashcards
ions
ions- electrically charged particles
anions- negatively charged ex. Cl
cations- positively charged ex. Na, K
concentration gradient
differences in concentration of a substrate b/w 2 regions
- substances diffuse from high to low
voltage gradient
difference in charge b/w 2 regions
- ions move from high charge to low charge
resting potential
stored energy in electrical charge across membrane in absence of stimulation
cells have negative intra and positive extra
around -70 mV
which 4 ions produce resting potential (3 main)
Na, K, large anions and some Cl
how is the resting potential maintained
through an active process of gates, channels and pumps
large protein anions
made inside the cell, cannot leave
- negative charge isnt large enough to produce resting potential
- cells need to balance negative charge
potassium
balance large anions
- high concentration inside cell, K is drawn outwards
Na
high concentration outside
gate is mostly closed so no entry of Na allowed
- blocked by voltage gated channels
resting potential summary
large anions cannot leave, make inside -
concentration gradient pushes K out through channels
gated channels prevent Na from entering
Na/K pumps eject Na and inject K
graded potentials
small voltage fluctuations across the cell membrane
- happen if concentration of any ions changes
2 types of graded potentials
- hyperpolarization- increase in electrical charge
becomes more negative due to inward flow of Cl or outward flow of K - depolarization- decrease in electrical charge
becomes more positive due to inward flow of Na
action potential
large brief reversal in polarity of axon for approx 1ms
- reverses to become positive then returns to negative
basic mechanism for action potential
voltage sensitive ion channels open or close at specific membrane voltages
- Na channels open quick and close quick
k channels open after and close slowly
refractory periods
absolute- tip of AP, can be no AP generated
relative- during hyperpolarization, requires a strong depolarizaiton to initiate another AP
nerve impulse
propagation of AP on the membrane of an axon
- how neurons signal
why dont impulses travel backwards
refractory periods
all or none law
size and shape of AP remains constant along the axon
myelin
produced by oligodendroglia in CNS and schwann cells in PNS
- wrap around to produce insulating sheath
- AP cannot occur under sheath
node of ranvier
gaps in sheath rich in ion channels
saltatory conduction
propagation of AP at successive nodes of ranvier
- makes nerve impulses metabolically cheaper and much faster
