BIOC32H3 Midterm: Human Phys Midterm Notes

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Published on 1 Dec 2016
Human Phys Midterm Notes
Physiology involves the mechanisms the body takes to maintain homeostasis
Changes to homeostasis:
Internal- dehydration, temperature, hunger
External- viruses, antibodies, insulin-dependent diabetes
3 experimental designs:
1. Test tube
2. Animal models
3. Humans
Taking into considerations:
1. Variability of subjects
2. Psychological bias (use placebos and double-blinded studies)
3. Ethics
Properties of Excitable Cells
Berstei’s erae theory:
1. Cells have electrolytic interior with membrane selectively permeable to ions
2. Electrical potential difference at rest
3. Selectively permeable to K at rest
4. High intracellular [K]
5. Low extracellular [K]
To measure membrane potential, voltmeter is set up with a recording electrode and a ground/reference electrode- 0mV
Muscle and neurons are excitable (dynamic potentials); RMP ~ -70mV
At RMP, only K efflux due to leak channels; Na VG channels inactive
What affects rate of K efflux through leak channels?
1. Neg harged proteis pullig the ak
2. K efflux slows thus decreasing potential until EQ reached
What generates the RMP?
1. K leak channels
2. NA/K ATPase pump
3. Properties of PM; impermeability and VG ion channels
Eion = the voltage that has to be applied to the inside of the cell to prevent ion flux
Nernst equation: used to calculated Eion for individual ions; considers ion concentration, temperature, and valency
ENa = +60mV
EK = -90mV; concentration gradient would cause K efflux while electrical gradient would cause K influx
Goldman-Hodgkin-Katz equation: used to find membrae potetial with ultiple ios ad pereaility’s to osider
The Action Potential
Steps of an AP:
1. At RMP, Na activation gates closed and inactivation gates open; also K leak channels
2. Threshold = -55mV, activation gate open FAST and Na influx is instantaneous; K gates open SLOW
3. Inactivation gate closes after 0.5 ms
4. K efflux promotes repolarization and hyperpolarization to -90mV
5. Gates and RMP restored after another 0.5 ms
Signals between neurons (down axons) are called action potentials- all or nothing
Constant amplitude; frequency may change
Signals within a soma are called graded potentials- additive
Amplitude depends on strength and distance of stimulus
Na permeability is highest at peak potential (+30m)
K permeability is highest at falling phase
Spontaneous graded potentials and action potentials are decreased i the striatu i Parkiso’s disease (PD)
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