9&10&11 Ion equilibrium/graded action potential

Question 1

Movement of electrolytes across semipermeable membrane is a response to:

What stops the movement? Is this a true force

Answer 1

1. electrolytes move in response to
   
   1. concentration gradient
   2. electromagnetive force
      
      1. response to electrical charge
2. net movement stops when the two forces are equl
3. diffusion=pseduoforce

ion movement is dependent on both [] and charge

Question 2

How is a charge developed and how is this measured?

Answer 2

separation of charge across membrane can be measured with a thin electrode in side the cell and compared to the outside.

1. if the charges are different, than there is a voltage on the membrane
2. Vm always refers to inside the cell in comparion the ECF (which is infinity)
   
   1. dealing with miliV=mV

Question 3

describe componenets of the nerst equation and constant.

which cells does this equation hold for?

How will the movement compare between K+ and Cl-

Answer 3

Equilibrium=EMF x [] gradient

1. Eion= equilibrium for a given ion
2. z= electric charge
   
   1. K=1+
   2. Ca=2+
   3. cl=1-
3. holds for 37degree kelvin

this equation is true for all cells that have a permebility to the ion in question

see slide 13

Question 4

What is the net movement

when Vm is in the following voltages:

1. 0mV
2. -87mV
3. -89mV
4. -88mV

explain the move towards equilibrium. How does permeability come into play?

Answer 4

1. out of the cell
2. out of the cell
3. in the cell
4. no movement

movement across the mebrane is always in the direction that move Vm toward the equilibrium potential

1. The ion must be permeable to the membrane, degree of permeability determines the speed of equilibrium achieved.

Question 5

order the following ion and label [intracellular] vs [extracellular] and Eion

Answer 5

knowing the homeostatic value allows for you to predict the movement

Question 6

what is associated eith cardiovascular events and ion equiulibrium?

Answer 6

Hypokalemia

1. 7-17% of patients with cardiovascular disease suffer from low K+ in the plasma
2. cause
   
   1. diuretics in patients with hypertension
   2. low [K+] increases mortality of patients with CD by 10x
   3. induces arrythmia by modifying the equilibrium potential

Question 7

what is resting membrane potential? How is determined and why is its value such for most cells?

Answer 7

1. resting potential
   
   1. net charge due to moement of ions across the membrane.
   2. no net movement= stabe Vm
      
      1. the amout leaking out/in are be pumped out equally
   3. -70mV for many cells
      
      1. degree of membrane permeability
         
         1. K+>Cl->Na+
         2. 1:.45:.04
      2. weighted mixture of
         
         1. Ek(-88mV)
         2. Ecl-(-63mV)
         3. Ena+(+60mV)
         4. BUT THE ONE THE MEMBRANE IS MOST PERMEABLE TO HOLDS THE MOST WEIGHT FOR DETERMINING THE Resting Potential.
            
            1. this is why the resting potential is closest to K+

Question 8

how many ions does it take to change membrane potential? how much of it is Na/K pump?

Answer 8

membrane potential needs very few ions to cross in order to change membrane potential. 100mV change occurs with 1/100000 ions moving across.

Na/K pump does not have a large affect change in membrane potential. It is a long term soluation. NOT a rapid one

Question 9

Define equilibrium, with respect to the charge differenece generated by ions

Answer 9

EqPotential=the transmembrane potential where there is no net movement of a given ion

• values determined by nerst equation

Movement across the membrane is always in the direction that moves Vm toward the equilibrium potential.

1. the membrnae must be
   
   1. permeable to the ion in question for equilibrium to be achieved
      
      1. the degree of permeability determine how quick equilibrium is achieved

Question 10

Using a beta cell for an example, describe the use of ions and how the Vm changes

finish——–

Answer 10

The permeability changes the fundamentals of the B-pandreatic cell

1. rest state
   
   1. GLUT transporter has little Glu to transport across=decrease metabolism=decrease ATP production
   2. For this cell
      
      1. the K+ gated ion channel remains open
         
         1. the reseting membrane potential is noe mostly influenced by the flux of K+
   3. The voltage gated Ca ++ channel is closed, keeping Ca++ extracellular
   4. The insulin remains in vesicles on the cytosolic side
2. secrete state
   
   1. Glucose enters via transporter by GLUT=increase glycolysis=increase ATP
   2. K+ channel “inactivation gate” phophorylated and closes.
      
      1. changing the membrane potential

Question 11

how is a membrane potentential change measured and labeled

Answer 11

changes in permebility -> change in the ion flow-> change the membrane potential

1. hyper polarization
   
   1. becomes more negative
   2. example
      
      1. release of more K+ into the extracellular enviornment
2. depolarization
   
   1. membrane becomes more positive
3. repolarization
   
   1. when cell moves from a more positive down toward resting potential

Question 12

How does conductance change? what are the pertinant gated channels and their activation? state 4

Answer 12

1. chemically gated channels
   
   1. some are opene/closed by binding of an intracellular or extra cellular compound
2. voltage gated channels
   
   1. some are opened/closed by electrical state of the cell
3. pressure
   
   1. some are opened/closed by physical force
4. temperature
   
   1. some channels stay open and close depending on the temperature
   2. this allows for temperature detection.

Question 13

what is a channels conductance? Are their selective/less selective ones?

Answer 13

channels conductance=how readily ions flow through

1. selective
   
   1. recognize a specific ion
      
      1. K+ channels
      2. Cl- channels
      3. Na+ channels
      4. Ca++ channels
2. less seletive
   
   1. monovalent-recognize single charge ions
      
      1. Na+ and K+ vs Ca++

Question 14

what disesaes may manifest from channelopathies?

Answer 14

1. Na+ channel mutation in skeletal muscle
   
   1. periodic paralysis
2. malignant hyperpyrexia
   
   1. hypermetabolic state triggered by anesthetics. Can cause bad outcome when anestetized for procedure.
      
      1. Rise in temperature, metabolic acidosis
   2. Cause
      
      1. Ca++ channel mutation
3. cystic fibrosis
   
   1. exocrine function of epithelial cell is aberrant
      
      1. thick mucous produced in lungs
   2. cause
      
      1. defective cl- channel
4. epilepsy
   
   1. seizures caused by
      
      1. mutation in 1 or more Na+ channels

Question 15

from resting describe the changes in membrane potentials as the permebility changes for the four ions

Answer 15

Question 16

What guides the diffusion of ions across a cell?

Describe the equilibrium potential

Answer 16

the diffusion of ions across a cell membrane is guided both by

1. the concentration gradient
2. the transmembrane potential

Equilibrium potential of an ion =

1. transmembrane potential when the diffusion drive (due to its concentration gradient) is balanced by that due to the electrical force.
2. look at nerst equation

Question 17

What is the process happening in excitable tisseu?

Answer 17

alteration in membrane potential underlie information processing in excitable tissue

1. they change due to changes in ion permeabilty resulting in
   
   1. hyperpolarization
   2. depolarization
   3. repolarization

Question 18

magnitude in Vm change has two factors.

Answer 18

the magnitude of Vm change, these are dependent on

1. ion species whose conductance changes
   
   1. channels conductance=how readily ions flow through
2. the magnitude of the conductance changing
   
   1. more channels= higher magnitude

changing permeability changes the Vm

1. hyperpolarized
2. depolarized
3. repolarized

Question 19

what is graded potential?

Answer 19

Vm change due to the change of [ion]

1. continuously variable
2. NOT instantaneous
   
   1. takes time to
      
      1. hyperpolarize
      2. depolarize
      3. repolarize
3. ions involved
   
   1. K+,Cl-,Na+, Ca++
4. membrane acts as a capacitor

remember the example

• injection of an aion changes Vm if Vm is not at the equilibrium potential of the ion
  
  • example
    
    • Vm at -88. So, releasing K+ will not have a
      
      • flux
      • change in Vm
• this ban be naturally or aftifically achieved both result in inducment of current
  
  • opening of an ion chnnel
  • curren injection

Question 20

diagram the affect of a signal over the length of a membrane.

Answer 20

Graded potential is a Vm change that propagates over space due to diffusion of ions, but is attenuated b/c of current leakage through the membrane and due to cytoplasmic resistance

electronic-decatying currents

Spatial decay- represented in the diagram as the weakening of the signal over the length of the membrane.

Question 21

Explain phot receptors operation and how do they rely on graded potential?

Answer 21

One source of inductin cinductance change is sensory signal where a sensory event, such as light, is transformed to a graded potential aka generator potential. The sensory transduction transforms a physical stimulus into an electric one.

1. hyperpolarization of a rod photoreceptor in the eye. These sensory cells are depolarized in the dark. When a photon stikes the cell, the cell is hyperpolarized.

Question 22

Why is Vm important in tissues? What tissue do it more?

Answer 22

the importance of Vm change is evident in excitable tissue, where electrical signaling is the basic activity

1. muscles and neurons
   
   1. modify conductance of ions in response to stimuli and this is the basis of their electrical signaling
   2. electro gradient potentials are possible in all cells with
      
      1. permeable membrane. some more than others
         
         1. neurons
         2. skeletal muscle

Question 23

What causes conductance changes in excitable tissues

Answer 23

dendrites receive connections from many other neurons. Those induce conductance changes.

1. thus electrotonic currents in the dendrite
2. signal continues over soma to the axon hillock
   
   1. the axon hillock integrates the incoming signals
3. axon transmits signal to effector neuron.

activity in the presynaptic cell translates to local conductance change in the postsynaptic cells dendrites.

Question 24

what is the length of a synaptic signal? How is this overcome?

Answer 24

1. synaptic inputs are short lasting
   
   1. conductance changes and then decays at synaptic contact
2. temporal summation
   
   1. summation of multiple depolarization at an input over time
      
      1. important because
         
         1. electronic currents decay with distance
3. sending multiple signals at timed location allows for the conductance change leading to the axon hillock.

Question 25

what is the initial segment of the trigger zone? its contents?

Answer 25

Axon hillock = the first part of the trigger zone

1. trigger zone is where the action potentials (all-or-none) self- propagating electrical signal, can be fired
   
   1. every action potential has the same membrane potential
2. cotents
   
   1. large number of voltage gated Na+ channels

Question 27

What is the action potential generting unit around the trigger zone?

describe its construct, threshold for activation (and process), process for inactivation.

How can one region of the neuron lead to such a drammatic change in conductance?

Answer 27

voltage-Gated Na+ channel-both activation and deactivation are with in the VGNa channel

1. activation gate
   
   1. charged amino acids hold the gate in the off posistion
   2. when the ions diffuse(flux), the membrane potential shifts making the inctracellular upstream more positive the the downstream side
      
      1. causing a conformation in the internal amino acid
      2. opening the activation gate
   3. Na+ rushes in
2. inactivation gate
   
   1. when the membrane potential reaches -55mV the inactivation gate is activated
      
      1. but takes time to close
         
         1. 0.5msec
         2. in the interim Na+ flows into the neuron.
            
            1. this is controlled by the opening of K+ channels.

Positive feedback allows for the self-generating all-or-none action potential.

1. think proboblaistically
   
   1. localized depolarization to threshold of a few, leads to further depolarization due to their increased conductance
      
      1. this leads to additional channels opening and porpagation of the signal
2. this is the exact opposit for repolarization
   
   1. more are closed during repolarization