Biology 233 Lecture 14

Front 1

Transmembrane Potential

Back 1

The potential difference, measured across a plasma membrane and expressed in millivolts, that results from the uneven distribution of positive and negative ions across the plasma membrane

Front 2

Five main membrane Process in Neural Activities

Back 2

1) Resting potential

2) Graded potential

3) Action potential

4) Synaptic activity

5) Information processing

Front 3

Resting Potential

Back 3

The transmembrane potential of resting cell

Front 4

Graded Potential

Back 4

1) Temporary, localized change in resting potential

2) Caused by stimulus

Front 5

Action Potential

Back 5

1) Is an electrical impulse

2) Produce by graded potential

3) Propagates along surface of axon to synapse

Front 6

Synaptic Activity

Back 6

1) Releases neurotransmitters at presynaptic membrane

2) Produces graded potentials in postsynaptic membrane

Front 7

Information Processing

Back 7

Response (integration of stimuli) of postsynaptic cell

Front 8

Three requirements for transmembrane potential:

Back 8

1) Concentration gradient of ions (Na+, Cl-, K+)

2) Selectively permeable through channels

3) Maintains charge difference across membrane

(Resting potential -70mV)

Front 9

Passive forces acting across the membrane; Chemical gradients:

Back 9

Concentration gradients of ions (Na+ & K+)

Front 10

Passive forces acting across the membrane; Electrical gradients:

Back 10

1) Separate charges of positive & negative ions

2) Result in potential difference

Front 11

Electrical currents and Resistance

Back 11

1) Electrical currents; movement of charges to eliminate potential difference

2) Resistance; How much the membrane restricts ion movement

Front 12

Electrochemical Gradient

Back 12

For a particular ion (Na+ & K+) is the sum of chemical and electrical forces acting on the ion across a plasma membrane. A form of potential energy.

Front 13

Equilibrium Potential

Back 13

The transmembrane potential at which there is no net movement of a particular ion across the cell membrane

Front 14

Equilibrium Potential values:

Back 14

K+ = -90mV

Na+ = +66 mV

These values are in the membrane were freely permeable, but it is not!

Front 15

Active forces across the membrane

Back 15

Sodium-potassium ATPase (exchange pump)

1) Is powered by ATP

2) Carries 3 Na+ out & 2 K+ in

3) Balances passive forces of diffusion

Front 16

Resting Potential

Back 16

Plasma membrane is highly permeable to K+ ions, so resting potential is fairly close to -90mV

(this represents the equilibrium potential for K+

Front 17

Resting potential, even though the electrochemical gradient for Na+ ions is very large, membrane permeability to these ions is very low.

Back 17

1) Therefore Na+ has a small effect on normal resting potential

2) This makes it just slightly less negative than it would normally be

Front 18

Resting potential Na+/K+ exchange pump ejects 3 Na+ ions for every 2 K+ ions it brings in.

Back 18

Thus stabilizing resting potential when ration of entry/exit

Front 19

At normal resting potential, these passive and active mechanisms are in balance.

Back 19

Resting Potential

Front 20

Resting potential varies widely depending on the cell type

Back 20

Typical neuron has resting potential of -70mV

Front 21

Changes in Transmembrane potential , transmembrane potential rises or falls in response to?

Back 21

Temporary changes in membrane permeability, resulting from opening or closing specific membrane channels.

Front 22

Transmembrane potential Sodium & Potassium channels

Back 22

Membrane permeability to Na+ and K+ determines transmembrane potential

Front 23

Transmembrane Potential are either, what?

Back 23

Passive or Active

Front 24

Transmembrane Potential passive channels also called leak channels are?

Back 24

Always open and permeability changes with conditions.

Front 25

Transmembrane Potential active channels also called gated channels are?

Back 25

Open and close in response to stimuli & at resting potential, most gated channels are closed

Front 26

The conditions of gated channels are?

Back 26

1) Closed, but capable of opening

2) Open (activated)

3) Closed, not capable of opening (inactivated)

Front 27

Three classes of gated channels are?

Back 27

1) Chemically gated channels

2) Voltage gated channels

3) Mechanically gated channels

Front 28

Chemically gated channels

Back 28

Open in presence of specific chemical (ACh) at a binding site and found on neuron cell bodies and dendrites

Front 29

Voltage gated channels

Back 29

1) Respond to changes in transmembrane potential

2) Have activation gates (opens) and inactivation gates (closes)

3) Characteristic of excitable membrane

4) Found in neural axons, skeletal muscle sarcolemma & cardiac muscle

Front 30

Mechanically gated channels

Back 30

1) Respond to membrane distortion

2) Found in sensory receptors: Touch, Pressure & Vibration

Front 31

Transmembrane potential exists across plasma membrane because?

Back 31

1) Cytosol and extracellular fluid have different chemical/ionic balance.

2) The plasma membrane permeability in response to chemical or physical stimuli

Front 32

Graded potential also called local potentials:

Back 32

1) Changes in transmembrane potential (That cannot spread far from site of stimulation

2) Any stimulus that opens a gated channel (Produces a graded potential)

Front 33

The resting state, opening sodium channel produces graded potential such as:

Back 33

1) Resting membrane exposed to chemical

2) Sodium channel opens

3) Sodium ions enter the cell

4) Transmembrane potential rises

5) Depolarization occurs

Front 34

Depolarization is a shift in transmembrane potential toward 0mV:

Back 34

1) Movement of Na+ through channel

2) Produces local current

3) Depolarizes nearby plasma membrane (graded potential)

4)change in potential is proportional to stimulus

Front 35

Repolarization

Back 35

When the stimulus is removed, transmembrane potential returns to normal.

Front 36

Hyperpolarization

Back 36

1) Increasing the negativity of the resting potential

2) Result of opening a potassium channel

3) Opposite effect of opening a sodium channel

4) Positive ions move out, not into cell

Front 37

Transmembrane potential is most affected at the site of stimulation:

Back 37

The effect decreases with distance and spreads passively (owed to local currents)

Front 38

Effects of graded potentials at cell dendrites or cell bodies:

Back 38

Trigger specific cell functions