Excitable Cells Flashcards
____, ____, and most ____ are often referred to as “excitable cells” bc their physiologic functions rely critically on electrical events in their plasma (i.e. surface) membrane
neurons (single nerve cells)
sensory cells
muscle cells
3 mechanisms of electrical events
- cell to cell (intercellular) communication
- sensing environmental changes (light, sound, temp, etc.)
- triggering intracellular events
three components of cell excitation
extracellular fluid (ECF) or interstitial fluid intracellular fluid (cytosol) membrane
extracellular fluid has a high ____ concentration
NaCl
intracellular fluid is predominantly _____
KCl
cell membrane made up of ____ and ____
phospholipid bilayer ; proteins
a characteristic of cell membranes, essential to excitation, is _____
permeability
changes in permeability, that are ____ and ____, are essential to excitation in cells
ion-specific; exquisitely timed
random diffusion down an electrical or concentration gradient; done by organic molecules or ions
simple diffusion
examples of non-polar substances
O2, CO2, fatty acids, and steroid hormones
amount of a substance crossing a surface per unit of time
flux
diffusion between 2 compartments is always _____
bi-directional
the difference between the two unidirectional fluxes
net flux
when net flux=0, the system is referred to as being in a state of ______
diffusion equilibrium
two types of mediated transport
facilitated diffusion and active transport
primary active transport
energy source is hydrolysis of ATP > transporter becomes phosphorylated > changes affinity for solute (ligand) > increases transport rate
examples of primary active transport
- transport of Na ions out of cells
2. transport of K ions into cells
secondary active transport uses energy in ____ across membrane; transporter has ____ binding sites
ion concentration gradient; two
example of secondary active transport
transport of amino acids, uses [Na] gradient
3 steps in mediated transport
- ligand binds to transporter
- transporter undergoes conformation change
- ligand is released on other side of membrane
types of channels
ligand-sensitive
voltage-sensitive
mechanosensitive
water is polar and diffuses through channels called ____; water diffuses ____ its concentration gradient
aquaporins; down
the total solute concentration in a solution
osmolarity
engulfment of fluid and particles from the extracellular space
endocytosis