A&P neurons Graded potential

Describe POLARITY in the membrane potential

DEPOLARIZATION- when sodium comes in it makes the cell more positive less negative *A shift in membrane potential toward 0 mV -70 to +30 HYPERBOLIZATION- the cell becomes more negative there is a decrease in change value -70 to -90 REPOLARIZATION- the return to resting potential

Describe action potential

Propagated changes in membrane potential Affect an entire excitable membrane Link graded potentials at cell body with motor end plate actions

What is a graded potential?

* local potentials *Changes in membrane potential That cannot spread far from site of stimulation *Any stimulus that opens a gated channel

Describe Relative Refractory Period

*Membrane potential almost normal *Very large stimulus can initiate action potential

Describe Absolute Refractory Period

*Sodium channels open or inactivated *No action potential possible

what occurs in a voltage gated channel ( sodium)

+when the charge across the membrane reaches +30 the channel closes and becomes (inactive it is open but inactive ) *Sodium rushes in the cytoplasm trying to reaches the equilibrium of +66 *The cell will never get to +66 at +30mv the inactive gate closes and +30 *the cells moves from negative to positive

what is the charge at threshold

-60mv

Describe the 4 characteristics of graded potential

1.The membrane potential is most changed at the site of stimulation, and the effect decreases with distance 2.The effect spreads passively, due to local currents 3.The graded change in membrane potential may involve either depolarization or hyperpolarization (the more channels open the more the stimulus ) 4.The stronger the stimulus, the greater the change in the membrane potential and the larger the area affected

Describe Initiating Action Potential

A graded depolarization of axon hillock large enough (10 to 15 mV) to change resting potential (70 mV) to threshold level of voltage-gated sodium channels (60 to 55 mV)

Describe the Effects of graded potentials

At cell dendrites or cell bodies Trigger specific cell functions For example, exocytosis of glandular secretions At motor end plate Release ACh into synaptic cleft

Describe the "all-or-none" principle:

If a stimulus exceeds threshold amount The action potential is the same No matter how large the stimulus Action potential is either triggered, or not

Describe mechanically gated channel

It opens due to a physical distortion sodium rushes in

What does you do to change the CHARGE across a membrane

STIMULUS

What is sodium and potassium resting

Sodium= +66 Potassium= -90 *potassium is more influential because it is closer than -70 there are more possum and leak channels

Four Steps in the Generation of Action Potentials

Step 1: Depolarization to threshold (The opening of the channels occurs at the membrane potential known as the threshold) Step 2: Activation of Na channels (*Rapid depolarization *Na+ ions rush into cytoplasm *Inner membrane changes from negative to positive) Step 3: Inactivation of Na channels and activation of K channels (*At 30 mV *Inactivation gates close *Na channel inactivation K+ channels open *Repolarization begins Step 4: Return to normal permeability (-70mv) *K+ channels finish closing *Membrane is hyperpolarized to 90 mV *Membrane potential returns to resting level *Action potential is over

What brings the cells back to -70mv

The sodium potassium pump pumps 3 sodium out and 2 potassium to bring the vell back to rest at -70mv

Describe the refectory period

The time period: *From beginning of action potential *To return to resting state *During which membrane will not respond *normally to additional stimuli

What does the Axolemma contain?

both voltage-gated sodium channels and voltage-gated potassium channels that are closed when the membrane is at the resting potential

what drives movement of ions in the dentries and the soma?

chemically gated channels

where on the cell does a graded deloplixation occur

on the axon hillock (threshold)

when do chemical gated,mechanically gated and voltage channels open?

only when a stimulus is present

Describe voltage gated channels

it opens when only when you change the charge across the axon. *When you there are enough chemically gated and mechanically gated channels the ions from the dendrites and the stoma float across the membrane to the axon and it opens up voltage gated channels

what is the channels that allow the ions to move

leaky channels, electrochemical gradient

what occurs in a voltage gated channel (potassium)

potassium rushes out and it reaches -90mv

what the CHARGE of the cells goes above or below -70 what bring it back to -70

the sodium potassium pump

when the cell is at rest what moves the sodium and potassium

the transmembrane

when does graded potential active

when a stimulus is present

Describe a chemically gated channel

when infor come in to attaches itself to chemically graded channel in the dendrite or the stoma. *aCh is the neurotransmitter that bind onto the receptor on the channel and opens it *When aCh binds to a sodium channel sodium rushes in and makes it more positive this causes the membrane to DEPOLARIZE *When aCh binds to a potassium recepter it pushes potassium out and makes the charge across the membrane more negative and HYPERORIZES it

At what charge is action potential over

when the charge reaches -90mv

When does threshold occur?

when there is enough neurotransmitters received onto the dendrites through mechanically and chemically channels through graded potential, the axolemma reaches threshold through graded potential from -70 to -60