Chapter 3 Flashcards
Neuronal membrane at rest
Foot+Tack response pathway
pinch skin-sensory neuron (into dorsal root)-spinal cord (CNS)-brain-spinal cord (out of ventral root)-motor neuron-mechanical/motor response
Cytosol and Extracellular fluid
key ingredient (polar water molecule is solvent)
Ions
contain spheres of hydration when ionized
lipids
hydrophobic and contribute or resting and action potentials (dont dissolve in water due to even electrical charge)
proteins/structure
enzymes, cytoskeletal elements, receptors, special transmembrane proteins (that control resting and action potentials)
R-group+alpha carbon+amino acid tails (peptide bonds form polypeptides)
four levels of protein structures
primary
secondary
tertiary
quaternary
Channel Proteins
contain polar R groups and nonpolar R groups across phospholipid bilayer (subunits make the whole); purpose is ion selectivity and gating
Ion pumps
formed by membrane spanning proteins, ATP using, neuronal signaling
Diffusion
Ionic flow down concentration gradient; channels permeable to specific ions, concentration gradient is across the membrane
electrical conductance (g)
g=1/R
Resistance (R)
R=1/g
Electrical current flow across a membrane
Ohm’s law: Current=(conductance)(potential)
I=gV
resting potential
Inside (-ve)vs relative outside (+ve); -65mV
Equilibrium potential (Eion)
equilibrium reached when K+ channels inserted into the phospholipid bilayer; electrical potential difference that exactly balances ionic concentration gradient
Equilibrium potentials (4 important notes)
- Large changes in Vmemb=miniscule changes in ionic concentrations
- Net difference in electrical change inside and outside of membrane surface
- Rate of movement of ions across membrane is proportional to Vmemb-Eion
- if Concentration difference is known: equilibrium potential can be calculated
nernst equation
used to calculate the exact value of equilibrium potential for EACH ION separately in mV: Considers: 1.charge of ion 2. Temperature 3. Ratio of the external and internal ion concentrations
K+ (ratio of out:in/Eion)
1:20/-80mV
Na+(ratio of out:in/Eion)
10:1/62mV
Ca2+(ratio of out:in/Eion)
10 000:1/123mV
Cl-(ratio of out:in/Eion)
11.5:1/-65mV
At rest, which ions are more concentrated outside, which ions are more concentrated inside?
outside: sodium, calcium, chloride
inside: potassium
Sodium potassium pump
enzyme breaks down ATP when Na+ is present
Calcium pump
actively transports Ca2+ out of cytosol
Goldman equation
takes into account permeability of membrane to different ions
determinant of membrane potential
membrane permeability determines membrane potential (since neurons are permeable to more than one type of ion)
Key determinant in resting membrane potential
Potassium channels
potassium channels(Lily and Yuh Nung Jan)
Shaker potassium channel
Mackinnon (2003 nobel prize)
neurological disorders due to mutations of specific potassium channels are inherited
How many subunits in potassium channels?
4
channel selectivity in potassium channels
K+ ions
Why is Resting membrane potential close to Ek
Because it is mostly permeable to K+, membrane potential is sensitive to extracellular K+
What happens when an increase of extracellular K+ ions/what regulates external potassium concentration?
depolarizes membrane potential/blood brain barrier and potassium spatial buffering (astrocyte)
Sodium potassium pump
works against the concentration gradient: 3 potassium back in for 2 sodium back out to restore the large K+ concentration gradient
