Ch 7 - The Nervous System Part 2

-70 mV (inside if more negative than outside)

what is the resting membrane potential of neurons

1) large negatively charged molecules inside the cell

2) Na+/K+ pumps actively move 3 Na+ OUT and 2 K+ IN (more positive out than in)

3) limited permeability of the membrane to positively charged inorganic ions (ex: it’s more permeable to K+ than Na+ allowing K+ to leak out, while Na+ stays out)

what are the 3 key factors that lead to more negative inside of neuron

neurons and muscle cells

what cells can change their membrane potentials

excitability means more likely to produce action potential whereas irritability means less likely to produce action potential

excitability vs irritability in terms of membrane potential

changes in membrane permeability to specific ions which allow them to follow their electrochemical gradient and flow

what does excitability or irritability result from

concentration gradient and attraction to opposite charges (example, Na+ wants to move where it’s lower in concentration and there’s a more negative charge)

what is an electrochemical gradient a combination of

ion currents; limited areas where ion channels are located

what is flow of ions called and where does it occur

oscilloscope → have recording electrodes inside and outside the membrane to record the voltage of both and determines the difference between them

what tool is used to record changes in membrane potential and how

depolarization which is the result of excitability and stimulation

what 3 terms correspond to when the inside become more positive

hyperpolarization which is due to irritability and inhibition

what 3 terms correspond to when the inside becomes more negative

voltage-gated ion channels are only open at specific membrane potentials whereas leakage channels are always open

voltage-gated ion channels vs leakage channels

polarized; depolarization; hyperpolarization; repolarization

at rest, a neuron is ___________. when the inside of the cell becomes more positive it’s called ___________. when the inside of the cell becomes more negative it’s called ____________. when the neuron returns to its resting state following depolarization it’s called _________.

they both have voltage-gated channels, but K+ also has a leakage channel

what types of channels do K+ and Na+ have when talking about membrane potentials

1) a stimulus depolarizes the membrane potential from -70 to -50 mV reaching threshold

2) voltage-gated Na+ channels open causing Na+ to rush into the cell and further depolarize it to +30 mV

3) negative feedback kicks in and voltage-gated Na+ channels close and voltage-gated K+ channels begin to open

4) K+ leaves the cell, restoring the negative membrane potential in a process called repolarization

explain the depolarization of an axon and the process after

positive feedback → leads to Na+ rushing in and more channels opening

what type of feedback mechanism are involved with the opening of voltage-gated Na+ channels

its overshoots resting potential and gets down to -85 mV, so Na+/K+ pumps quickly reestablish resting potential and return Na+ and K+ to their correct locations

what happens during repolarization of membrane potential when K+ voltage-gated channels are open

3 milliseconds

how long does each action potential take

once threshold has been reached, an action potential will happen → conversely if it’s not met, and action potential will not happen

what does the idea of all-or-none mean in terms of action potentials?

No → it will always reach +30 mV and have the same duration (3 seconds)

does the size of the stimulus affect the size of the action potential

a stronger stimulus will make action potentials occur more frequently AND may also activate more neurons in a nerve (recruitment)

what does a strong stimulus give in terms of action potentials

1) absolute → occurs during the action potential when Na+ channels are inactivated (another action potential CANNOT be generated)

2) relative → occurs when K+ channels are still open during hyperpolarization (another action potential can be generated IF stimulus is strong enough)

absolute vs relative refractory period

the ability of neurons to conduct charges through their cytoplasm

what is a cable property of a neuron

due to high internal resistance to the spread of charges and leaking of charges through the membrane

why are cable properties of neurons poor

1) axon potentials are produced down the entire length of the axon at every patch of membrane

2) the conduction rate is slow because so many action potentials are generated, each one an individual event

3) the amplitude of each action potential is the same

explain conduction in an unmyelinated neuron

1) myelin provides insulation, improving the speed of cable properties

2) nodes of Ranvier allow Na+ and K+ to cross the membrane every 1 to 2 mm and Na+ ion channels are concentrated at the nodes

3) action potentials “leap” from node to node (saltatory conduction)

explain conduction in a myelinated neuron

1) increased diameter of the neuron because it reduces resistance to the spread of charges via cable properties

2) myelination because of saltatory conduction

what 2 things increase action potential conduction speed