excitable cells Flashcards
resting membrane potential: explain how a resting membrane potential can arise across a selectively permeable membrane and recall the typical resting potential of a neuron
how are electrochemical gradients created
passive diffusion of molecules in solution from [high] to [low]
define flux
rate of transfer of molecules; number of molecules that cross a unit area per unit of time
when is there no net flux
when dynamic equilibrium reached
properties of ions
charged molecules; opposite attract; like repel
voltage: unit and generation
potential difference; volts; generated by ions to produce a charge gradient
current: unit and definition
amps; movement of ions due to a potential difference
resistance: unit and definition
ohms; barrier that prevents the movement of ions
value and calculation of resting membrane potential
-70mV (IC compared to EC); reference electrode placed outside cell (0mV) and another placed inside
what causes protein channels to open/close in facilitated specific diffusion
trans-membrane voltage, presence of activating ligands or mechanical forces
basis of generation of membrane potential
diffusion of ions through selectively permeable membrane; due to K+ moving out of cells, not ion pumps pumping K+ in; permeability of K+»>Na+ so membrane potential nearer eqm potential for K+ than Na+
if there are no channels in membrane, what would the resting membrane potential be
no diffusion across membrane despite concentration gradients → no separation of charge → 0mV
if there was only one ion channel, what would happen
direction of flux directed by concentration gradient, so where ion moves becomes more +ve and where it left becomes more -ve; eqm reached as positive charge repels movement of ion influx, reaching eqm potential
changing membrane potential: stages and mV values
depolarisation (-70 to 0); overshoot (0 to +60); hyperpolarisation (+60 to -70); hyperpolarisation (-70 to -90)
decremental spread of graded potentials: mechanism
charge dissipates across cell membrane as spread along axon
graded potentials
occur at synapses or sensory receptors; contribute to initiating or preventing action potentials
