biopotencial 1. potencial de repouso prof. sérgio
TRANSCRIPT
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BIOPOTENCIAIS
1. Potencial de Repouso
Prof. Sérgio Francisco Pichorim
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Fig. 2.2. Cortical nerve cell and nerve endings connected to it.
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Fig. 2.3. A sketch illustrating how the phospholipid molecules behave in water. The cell
is enclosed by a cell membrane whose thickness is about 7.5 - 10 nm. It consists of
phosphoric acid and fatty acids called glycerides. The head of this molecule is
hydrophilic (attracted to water). The fatty acids have tails consisting of hydrocarbon
chains which are hydrophobic (repelled by water). .
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Fig. 2.4. The construction of a cell membrane. The main constituents are two lipid
layers, with the hydrophobic tails pointing inside the membrane. The macromolecular
pores in the cell membrane form the ionic channels through which sodium, potassium,
and chloride molecules flow through the membrane and generate the bioelectric
phenomena.
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POTENCIAL DE REPOUSO
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MICROELETRODO
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Micropipeta
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CONCENTRAÇÕES IÔNICAS INTRA E EXTRACELULAR
EXEMPLO 1
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Exemplo 2 – Célula Muscular
Concentrações
em mMol/l Intracelular Extracelular
Na+ 12 145
K+ 155 4
Cl- 4 120
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BOMBA SÓDIO-POTÁSSIO
• Sequência de reações químicas (cf. Okuno)
• Exemplo didático
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• Outro
exemplo
didático
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Determinação da Tensão de
Membrana (Vm)
• Tensão através de membrana com diferença
de concentrações.
VOLTÍMETRO
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Movimento Browniano (Einstein, 1905)
• Real, em Vídeo e Simulação matemática
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• Energia Térmica = Energia Cinética
• Coeficiente de Difusão de uma partícula (D)
• Mobilidade do Íon (m)
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• Relação de EINSTEIN
D / m = k.T / q
• Equilíbrio de DONNAN
Jc + Je = 0
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• Lei de FICK
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• Lei de OHM
Je = s E
E = - dV / dx
Je = - m C dV/dx
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Equação de NERNST
• V = Tensão elétrica
• R = Cte Universal dos Gases 8,3144 J/K/mol
• F = Constante de Faraday 96.485,3 C/mol
• z = valência do íon
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Exercício – Calcular a Tensão de Nernst para
cada íon da célula muscular (rã a 16oC)
Concentração
em mMol/l Extracelular Intracelular
Tensão de
NERNST (mV)
K+ 2,25 124
Na+ 109 10,4
Ca++ 2,1 4,9
Mg++ 1,25 14
Cl- 77,5 1,5
HCO3- 26,6 12,4
Potencial de Repouso (Vm) é de – 98 mV.
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Respostas da Tensão de Nernst para cada íon
da célula muscular (rã a 16oC)
Concentração
em mMol/l Extracelular Intracelular
Tensão de
NERNST (mV)
K+ 2,25 124 -99,8
Na+ 109 10,4 58,5
Ca++ 2,1 4,9 -10,6
Mg++ 1,25 14 -30,1
Cl- 77,5 1,5 -98,2
HCO3- 26,6 12,4 -19,0
Potencial de Repouso (Vm) é de – 98 mV.
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Equação de Goldman-Hodgkin-Katz
(1943-1949)
• Para 3 íons
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Equação de Goldman-Hodgkin-Katz
• Exemplo: Axônio de Lula Gigante (19ºC) tem as
permeabilidades com a seguinte relação:
PK:PNa:PCl = 1 : 0,03 : 0,1 ou seja
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• Modelo elétrico para o Potencial de Repouso
• Cálculo da Tensão de Membrana (Vm)
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Três Tipos de Membrana
• Igualmente permeável
• Igualmente não-permeável
• Membrana seletiva