a, b, c, d all move solutes by diffusion down concentration gradient
DESCRIPTION
a, b, c, d all move solutes by diffusion down concentration gradient. Final mechanism can work against gradient e. Active transport. Final mechanism can work against gradient e. Active transport. XXX XX XXX. X. Final mechanism can work against gradient e. Active transport. - PowerPoint PPT PresentationTRANSCRIPT
1
a, b, c, d all move solutes by diffusion down concentration gradient
2
Final mechanism can work against gradient
e. Active transport
3
Final mechanism can work against gradient
e. Active transport
XXX XXXXX
X
4
Final mechanism can work against gradient
e. Active transport
XXX XXXXX
X
5
Final mechanism can work against gradient
e. Active transport
XXX XXXXX
X
Pump Protein
6
Final mechanism can work against gradient
e. Active transport
XXX XXXXX
X
7
Final mechanism can work against gradient
e. Active transport
XXX XXXXX
X
ATP
8
Final mechanism can work against gradient
e. Active transport
XXX XXXXX
X
ATP
ADP + Pi
9
Final mechanism can work against gradient
e. Active transport
XXX XXXXX
X
10
Final mechanism can work against gradient
e. Active transport
XXXXXXXXX
Concentrates against gradient
11
Ion pumps
Uniporter (one solute one way):
I- pump in thyroid
Coupled transporters (two solutes)
Symporter (same direction):
Antiporter (opposite directions)
Na+/K+ ATPase in mitochondria
12
3. Cells can control solute distribution across their membranes by controlling:
a. Synthesis of integral proteins
b. Activity of integral proteins
c. E supply for pumps
Therefore, expect that solutes would be unequally distributed across membranes
13
4. Actual ion distributions
Squid Axon (mM):
ION [CYTOPLASM] [ECF]
Na+ 50 460
K+ 400 10
Cl- 40 540
Ca++ <1 10
A- 350 <1
Organic anions with multiple - charges
COO- on proteins, sulfates, phosphates, etc....
14
5. Reasons for unequal distribution
a. Metabolic production of organic anions
A- produced by biosynthetic machinery inside the cell
b. Membrane permeability
impermeable to A-
moderate Cl- permeability
30-50X more permeable to K+ than Na+
15
Given a and b, system passively comes to unequal ion distribution
Diffusion of ions governed not only by their concentration gradients, but also their electrical gradients
16
Permeable uncharged solutes will come to equilibrium across membranes if no other forces acting
17
1 M sucrose
Permeable uncharged solutes will come to equilibrium across membranes if no other forces acting
18
1 M sucrose
Permeable uncharged solutes will come to equilibrium across membranes if no other forces acting
19
1 M sucrose 0.5 M sucrose
0.5 M sucrose
Permeable uncharged solutes will come to equilibrium across membranes if no other forces acting
20
Permeable charged solutes will not come to concentration equilibrium across
membrane if other charged impermeable solutes are present
21
Na+
A-
Impermeable
22
Na+
A-
K+ Cl-
Permeable
23
Na+
A-
K+ Cl-
24
Na+
A-
K+ Cl-
25
Na+
A-K+
Cl-Na+
A-
K+ Cl-
26
Na+
A-K+
Cl-Na+
A-
K+ Cl-
At equilibrium: chemical force driving K+ out
27
Na+
A-K+
Cl-Na+
A-
K+ Cl-
At equilibrium: chemical force driving K+ out
is exactly balanced by the electrical force (electromotive force) holding K+ in
28
Na+
A-K+
Cl-Na+
A-
K+ Cl-
At equilibrium: chemical force driving K+ out
is exactly balanced by the electrical force (electromotive force) holding K+ in
Result: an unequal ion distribution which will be maintained passively
29
Na+
A-K+
Cl-Na+
A-
K+ Cl-
At equilibrium: chemical force driving K+ out
is exactly balanced by the electrical force (electromotive force) holding K+ in
Result: an unequal ion distribution which will be maintained passively
“Donnan Equilibrium”
30
Donnan Equilibrium resembles situation in real cell, with one exception:
cell is not maintained passively
Poison real cell and unequal distribution eventually goes away
31
c. Cells work via pumps to maintain unequal ion distribution
Na+ “leaks” in down chemical and electrical gradients
32
Na+
A-
c. Cells work via pumps to maintain unequal ion distribution
Na+ “leaks” in down chemical and electrical gradients
33
Na+
A-
c. Cells work via pumps to maintain unequal ion distribution
Na+ “leaks” in down chemical and electrical gradients
34
Na+
A-Na+Na+/K+ ATPase
c. Cells work via pumps to maintain unequal ion distribution
Na+ “leaks” in down chemical and electrical gradients
35
Na+
A-
Na+
c. Cells work via pumps to maintain unequal ion distribution
Na+ “leaks” in down chemical and electrical gradients
36
Na+
A-
Na+K+
c. Cells work via pumps to maintain unequal ion distribution
Na+ “leaks” in down chemical and electrical gradients
37
Na+
A-
Na+
K+
c. Cells work via pumps to maintain unequal ion distribution
Na+ “leaks” in down chemical and electrical gradients
38
If Na+ allowed to build up, inside becomes + , drives K+ out, and lose unequal distribution
Na+
A-
Na+
K+
c. Cells work via pumps to maintain unequal ion distribution
Na+ “leaks” in down chemical and electrical gradients
39
Therefore, cells use combination of active and passive mechanisms to maintain unequal ion distributions
REASON?
B. Membrane Potentials
1. Significance of unequal distributions
Whenever an ion is unequally distributed across a membrane, it endows the membrane with an electrical potential
“membrane potential” (EM or VM)
40
2. Membrane potential measurement
a. Voltmeter
41
2. Membrane potential measurement
a. Voltmeter
42
2. Membrane potential measurement
a. Voltmeter
43
2. Membrane potential measurement
a. Voltmeter
44
Inside is -80 mV
2. Membrane potential measurement
a. Voltmeter
45
b. Calculate with Nernst equation
EM = RT x ln[ion]outside
FZ ln[ion]inside
R = gas constant, T = abs. temperature
F = Faraday constant, Z = valance
Magnitude of the voltage due to 1 unequally distributed ion is directly proportional to the magnitude of its unequal distribution
46
BUT: can't use it for a real cell
only valid for 1 ion
only valid for freely permeable ions
Can use it to calculate voltage due to any one freely permeable ion in a mixture
e.g. K+ = -91 mV
Na+ = +65 mV
47
c. Alternative: GOLDMAN EQUATION
accounts for multiple ions
accounts for permeability of each
multiplies [ion] ratios X permeability constant for each ion, then sums
up all to get total membrane EM
48
d. CONCLUSION:
In ion mixture, each ion contributes to the overall EM in proportion to its permeability
Most permeable ions contribute the most charge
49
Which ion is most permeable?
K+
real cell: inside is -80 mV = resting EM
cell is “negatively polarized”
50
EM is due almost exclusively to the unequal distribution of K+
Changes in [K+] alter EM easily
Changes in [Na+] do not alter EM
51
All cells have resting potential due to ion distributions
Some cells can use this electrical potential to transmit information
52
C. Nervous System Components
1. Glial cells: supportive
diverse functions
support
insulation
protection
communication
up to 90% of nervous system by weight
53
2. Neurons
soma: nucleus, usual organelles
dendrites: receptive, input
axon: transmission (microm to m)
axon terminals: synapse, output
54
55
3. Integrated Function of Neurons
Generate and conduct electrical signals for communication or coordination
a. Propagation of electrical signals along individual cells (wires)
b. Communication of electrical information between cells
56
c. Model system for study:
Squid giant axon (J.Z. Young)
57
c. Model system for study:
Squid giant axon (J.Z. Young)
58
59
D. Electrical Characteristics of Neurons
1. Intracelluar Recording:Hodgkin and Huxley
60
D. Electrical Characteristics of Neurons
1. Intracelluar Recording:Hodgkin and Huxley
61
D. Electrical Characteristics of Neurons
1. Intracelluar Recording:Hodgkin and Huxley
recording electrode
62
D. Electrical Characteristics of Neurons
1. Intracelluar Recording:Hodgkin and Huxley
recording electrode
coupled with stimulating electrode
63
D. Electrical Characteristics of Neurons
1. Intracelluar Recording:Hodgkin and Huxley
recording electrode
coupled with stimulating electrode
64Can change EM by adding charge
D. Electrical Characteristics of Neurons
1. Intracelluar Recording:Hodgkin and Huxley
recording electrode
coupled with stimulating electrode
65Can change EM by adding charge
+++
D. Electrical Characteristics of Neurons
1. Intracelluar Recording:Hodgkin and Huxley
recording electrode
coupled with stimulating electrode
66
STIMULUS
67
STIMULUSmV
68
STIMULUS
RESPONSE OF CELL
mV
69
STIMULUS
RESPONSE OF CELL
EM
(mV)
mV
0
70
STIMULUS
RESPONSE OF CELL
EM
(mV)
mV
0
71
EM
(mV)
mV
-80
0
72
EM
(mV)
mV
-80
Add negative charge,
EM gets more negative0
73
EM
(mV)
mV
-80
HYPERPOLARIZATION
Add negative charge,
EM gets more negative0
74
EM
(mV)
mV
-80EM moves away from 0 HYPERPOLARIZATION
Add negative charge,
EM gets more negative0
75
EM
(mV)
mV
-80
0
76
EM
(mV)
mV
-80
0
77
EM
(mV)
mV
-80
Add positive charge,
EM gets more positive0
78
EM
(mV)
mV
-80
Add positive charge,
EM gets more positive
DEPOLARIZATION
0
79
EM
(mV)
mV
-80
Add positive charge,
EM gets more positive
DEPOLARIZATION
EM moves towards 0
0
80
EM
(mV)
mV
-80
0
81
EM
(mV)
mV
-80
0
82
EM
(mV)
mV
-80
0
83
EM
(mV)
mV
-80
0
84
2. Passive responses
a. Magnitude directly proportional to amount of current
Increase current: increase magnitude of passive depolarization
85
b. Magnitude inversely proportional to distance from stimulus
Die out locally
86
b. Magnitude inversely proportional to distance from stimulus
Die out locally
87
b. Magnitude inversely proportional to distance from stimulus
Die out locally
88
b. Magnitude inversely proportional to distance from stimulus
Die out locally
89
b. Magnitude inversely proportional to distance from stimulus
Die out locally
90
b. Magnitude inversely proportional to distance from stimulus
Die out locally
91
EM
(mV)
mV
-80
0
92
EM
(mV)
mV
-80
0
93
3. At some point, small increase in applied current triggers a membrane depolarization much greater than the stimulus current
Active response
ACTION POTENTIAL
94
Characteristics of Action Potentials:
a. Minimum stimulus necessary to elicit
“threshold” current raises membrane to threshold potential
b. Once stimulated, all-or-none event
c. Propagated over long distances without decrement
95
Characteristics of Action Potentials:
a. Minimum stimulus necessary to elicit
“threshold” current raises membrane to threshold potential
b. Once stimulated, all-or-none event
c. Propagated over long distances without decrement
96
Characteristics of Action Potentials:
a. Minimum stimulus necessary to elicit
“threshold” current raises membrane to threshold potential
b. Once stimulated, all-or-none event
c. Propagated over long distances without decrement
97
Characteristics of Action Potentials:
a. Minimum stimulus necessary to elicit
“threshold” current raises membrane to threshold potential
b. Once stimulated, all-or-none event
c. Propagated over long distances without decrement
98
Characteristics of Action Potentials:
a. Minimum stimulus necessary to elicit
“threshold” current raises membrane to threshold potential
b. Once stimulated, all-or-none event
c. Propagated over long distances without decrement
99
Characteristics of Action Potentials:
a. Minimum stimulus necessary to elicit
“threshold” current raises membrane to threshold potential
b. Once stimulated, all-or-none event
c. Propagated over long distances without decrement
100
Characteristics of Action Potentials:
a. Minimum stimulus necessary to elicit
“threshold” current raises membrane to threshold potential
b. Once stimulated, all-or-none event
c. Propagated over long distances without decrement
101
Characteristics of Action Potentials:
a. Minimum stimulus necessary to elicit
“threshold” current raises membrane to threshold potential
b. Once stimulated, all-or-none event
c. Propagated over long distances without decrement
102
4. Voltage changes during action potentials
103
4. Voltage changes during action potentials
EM
Time (msecs)
mVolts
104
4. Voltage changes during action potentials
0
-20
-40
-60
-80
EM
Time (msecs)
mVolts
105
4. Voltage changes during action potentials
EM
Time (msecs)0 1 2 3 4
mVolts
0
-20
-40
-60
-80
106
4. Voltage changes during action potentials
EM
Time (msecs)0 1 2 3 4
mVolts
1. Resting membrane before arrival
1
0
-20
-40
-60
-80
107
4. Voltage changes during action potentials
EM
Time (msecs)0 1 2 3 4
mVolts
2. Depolarization to 0 mV
1
20
-20
-40
-60
-80
108
4. Voltage changes during action potentials
EM
Time (msecs)0 1 2 3 4
mVolts
2. Depolarization to 0 mV
hyperpolarizing overshoot
1
20
-20
-40
-60
-80
109
4. Voltage changes during action potentials
EM
Time (msecs)0 1 2 3 4
mVolts
3. Repolarization back to -80 mV
1
2 30
-20
-40
-60
-80
110
4. Voltage changes during action potentials
EM
Time (msecs)0 1 2 3 4
mVolts
4. Hyperpolarizing afterpotential
1
2 3
4
0
-20
-40
-60
-80
111
4. Voltage changes during action potentials
EM
Time (msecs)0 1 2 3 4
mVolts
5. Return to resting
1
2 3
4 5
0
-20
-40
-60
-80