homeostasis
the body’s ability to maintain stable (not constant) internal conditions within a changing environment
set point
the narrow range in which the body maintains any particular physiological parameter
negative feedback
the physiological process by which a parameter is returned to its set point
mM
millimole/L
mOsm
- for non-electrolytes, same as mM
- depends on dissociation (for NaCl, mOsm is twice mM)
colligative property
property that depends upon the number of particles in the solution (example: osmotic pressure)
higher concentration leads to…
- greater osmotic pressure
- lower freezing point
- higher boiling point
How to predict osmotic concentration of 0.9% NaCl solution
0.9% NaCl is 0.9g/100mL = 9 g/L
So 9 g/L / 58.5 g/mol (MW) = 0.15 M = 150 mM
So predicted osmolarity = 150 mM x 2 = 300 mOsm/L
isoosmotic
solute concentration inside and outside the cell are equal
isotonic
saline solution causes no change in cell volume
hematocrit
proportion of blood volume occupied by red blood cells
How to calculate % dissociation
(measured mOsm/L - half predicted mOsm/L) / (predicted mOsm/L - half predicted mOsm/L)
giant fibers
- conduct action potentials far faster than smaller ones
- allow animal to respond rapidly to threatening situations
action potential
- nerve impulse that travels along a nerve fiber
- occur when specialized V-sensitive Na channels are activated
- large increase in Na permeability results in membrane depolarization
- followed by repolarization as Na permeability returns to its baseline and K permeability is increased
Can we measure changes in cell ion concentrations during an action potential?
No, the actual numbers of ions moving are very small
absolute refractory period
first stage of refractory period during which it is impossible to initiate a second action potential
relative refractory period
second stage of refractory period during which a stimulus of greater than normal intensity can elicit a response
What was recorded by our extracellular electrodes?
a small potential difference between two points outside the axon
Which electrode was placed nearer to the stimulating electrodes?
Negative, thus, when the surface beneath it became negative, it was recorded as positive
Do the median or lateral fibers conduct faster?
Median fiber
Stimulation of the median giant fiber results in _____ withdrawal
Stimulation of the lateral giant fibers results in _____ withdrawal
median - head withdrawal
lateral - tail withdrawal
threshold voltage
stimulus strength that evokes an action potential 50% of the time
conduction velocity
distance/time
always reported in m/s
latency
time from stimulation to arrival of the action potential
