Ex Cells Flashcards
types of Excitable cells
Neurons
Sensory Cells
Most muscle cells
why are cells called excitable
Physiologic function relay critically on electrical events in their plasma membrane
what is an electrical event
A mechanism of cell-to-cell (intercellular) communication
speed of electrical events
Very rapid
what do electrical events allow
Precise timing of signals between cells
complex patterns of communication between cells
what do electrical events serve as a mechanism for
sensing environmental changes
triggering intracelular events
how can electrical events trigger intracellular events
rapid intracellular changes
accumulations over time (memory and learning)
the 3 physical components used for cell excitations
ECF
ICF
membrane
composition of the ECF
primarily ions, proteins, and other molecules
high NaCl
what is the ECF ionic concentration like
Similar to plasma in ionic composiition
Composiition of the ICF
ions
more proteins and other molecules
PRedoninant salt of the ICF
KCl
what allow cells to communicate
Inside and outside of cells are very different
what is the membrane composed of
phospholipid bilayer and proteins
equal amounts of protein and lipid with a small amount of carbs
what is premeability a characteristic of
The cell membrane
what is the permeability of a membrane to an ion
an index of the ability of the ion to cross the membrane
how does permeability affect cell excitation
Changes in permeability that are ion-specific and exquisitely timed
SImple diffusion
random diffusion down and electrical or concentration gradient
how well do non-polar molecules difuse
rapid through the membrane b/c it ids 50% lipids
how do ionspass the membrane
through channels which are proteins of several units with are ion-specific (generally)
What is flux
the amount of a substance cross a surface per unit of time
what way does diffusion occur between 2 compartments
Bi-direction
Net flux
difference between the 2 unidirection fluxes
what is something at diffusion equilibrium
when net flux equals 0
what is mediated transport
when something passes through the membrane but not directly
two types of mediated transport
Facilitaetd diffusion
active transport
energy need of facilitated diffusion
no energy
how does facilitated diffusion occur
membrane proteins serves as a carrier to translocate a molecule across the membrane
what types of molcules tend to use facilitated diffusion
large polar molecules
benifiti of facilitated diffusion
makes it hard for certain molecules to leave the cell
how does active transport work
molecule/ion bound to transporter in membrane using enegy to move up its concentration/electrical gradient
other name for active transporter
pumps
energy can affect what in active tranport
affinity of transporter for the ligant on one side of the membrane more than on the other side
rate of transporter conformational change
what happens in primary active-transport model
energy from hydrolgysis of ATP
transporter becomes phosphorylated changes affinity for solute (ligand)
increases transport rate
what happens in secondary active transport
uses energy in concetration gradient across membrane
transporter has 2 binding sites
steps in mediated transport
Ligand binds to transporter
transporter undergoes conformational change
ligand released on other side of membrane
factors that determine rate of flux
number of transporters in membrane
extrent of transporter saturation (transporter affinity,ligant concentration)
rate of transporter conformational change
types of channels
ligand-sensitive
voltage-sensitive
mechanosensitive
what is osmosis
Bulk flow of water acrosss a membrane
how does water diffuse
down its concentration gradient via aquaporins
osmolarity
the total solute concentration in a solution
osmolarity of ECF
300 mOsm
Isotonic
300 mOsm on Non-penetrating solutes in the ECF resulting in no change in cell volume
Hypotonic
less than 300mOsm of non-penetrating solutes in the ECF resulting in cell swelling
Hypertonic
greater than 300 mOsm of non-penetrating solutes in the ECF resulting in cell shrinking
difference in toniciity and osmoloarity
Toniciity is only non-penetrating
Osmolarity is non-penetating and penetrating
ligand sensitive channels
channel that binds to ligand to open
voltage-sensitive channel
changes by predominating charge diference
Mechanosensitve channels
bases on the mechanics of the envirnoment
Endocytosis
Engulfment of fluid and particles from the ECF
pinocytosis
Engulfment of small particles with or without a small volume of ECF
what does Pinocytosis
all cell types
phagocytosis
engulfment of large particels or cellular debris
what does phagocytosis
Special cells called phagocytes (usually at sites of tissue damage)
what is exocytosis
export of material from a cell (reverse of endocytosis)
what does Exocytosis lead to
replaces membrane patches internalixed through endocytosis
releases stuff from inside the cell
what is a lotinside the cell
K
Ca
Organic
w
what is a lot outside the cell
Na
Cl
where is most of the Ca inside the cell
bound or sequestered (free Ca is very low)
Voltage of a cell
Electrical charge difference between the inside and outside of a cell
why must the plasma membrane have resistance
because the voltage of a resting cell is steady
what happens when the resistance of the membrane changes
Ions cross the membrane leading to a curent
Ohm’s Law
V=IR
what is Conductance
The reciprocal of resitnace
Nernst equation
E= (58/z)log([X1]/[X2])
z=valence
what does the Nernst equation give
the hypothetical equilibtrium potention of a single ionic species
what is the equalibrium potention of a single ionic species
the votlage across a cell membrane that exactly balances the forces in the concetration gradient of a permeable ion
do diffusion potentials always stay the same
Can be transient, but also can be maintained at a steady level over time
what causes the transient property of diffusion potentials
due to asymmetric ion flow of one or many ions between 2 compartments
K and Na in and outside the cell
K higher inside
Na higher outside
what ion is the membrane permiable
most permeable to K
ratio of the permiability of K and Na
pK/PNa=60
membrane potention
-70 mV
what hold K inside
the charge (more negative inside) the cell
what does K do to create a diffusion potential
K ions move down their concentration gradient leading to the development of a diffusion potential
when is equilibrium found within the cell
when the force in the concentration gradient of K ions to move out of the cell is balanced by opposing force in electrical gradient
what does the equilibrium do to the cell
keeps K ions inside the cell
what is the equilibrium potental of K
about -100mV (close to the resting membrane potential of a cell)
why is the resting membrane potential different than that of the equalibrium potential of K
other ions must contribute to the resting potental
how does Na diffuse
Down its concetration gradient and electrical gradient
diffuse of Na leads to what
of equilibrium potential
a resting membrane potential slightly lower than Equilibium of K
is the resting membrane potential steady of transient
Steady
does instaneous movement of ions cause the resting membrane potential
Not due to the instantaneous movement (due to the fact that ions have moved across the membrane)
what keeps the resting membrane potential from decreasing (keeps homeostasis)
the Na/K ATPase pump moving K ions in and Na ions out
depolarization
towrds 0 mV
repolarization
toward resting potential
Hyperpolarization
increase in membrane potential (more negative)
how does Na/K ATPase pump do work
hydrolyzes ATP to do work(active transport)
what would happen if Na/K ATPase were to go away
resting membrane potential would go back to 0mV
Homeostasis
mechanism that have, as their goal, the maintenance of the body’s internal environment.
maintaining parameters of the internal environment at constant values
eq potential of K
-101 mV
eq potential of Na
+59 mV
eq potential of Cl
-99 mV
Action potential
A large transient change in membrane potential
4 parts of the neuron
Dendrites
Cell body
Axon
Axon terminal
stimulus leads to what in neuron
Depolarizaes membrane (dendrites)
Depolarizes cell body
AP first develops at initial segment
AP propagates along axon
where is the initial segment
where the axon meets the cell body
where the AP begins
Initial segnment
is the AP transient or steady
transient
steps of an AP
1 increased in the membrane permeability to Na ions
2 Na ions enter via channels driven by electrical and concentration gradients
3 membrane potential moves closer to 0 mV (depolarizes)
4 if depolarization reaches threshold, more Na votlage gated channels open
5 Na enters cells in a positive feed back cycle leading to the rising phase of an AP
6 eventually reaches +40mV
7 K chanells open and K leaves the cell
8 membrane potential abruptly reverses direction and returns in the falling phase of an AP
9 overshoot - hyperpolarization
what kind of channels allow Na ions to enter during an AP
Voltage regulated Na-channels
what is the movemeent of K driven by in an AP
concentration gradient and initiallly by electical gradient
why does Na channels close (Na Inactivation
Close during falling phase baecause voltage regulated channels now experience a negative change
length of depolarization and repolarization
1 ms
after polarization phase
10 ms
Do a lot of ions need to move to cause a great change in the membrane potential
no, only a few number of ions
Latnet period
Very brief period between applying stmulus and beginning of depolarization during rising phase of an AP
what occures during the latent phase
Channels are opening
what does the peak of an AP approach
the ENa( about 58 mV)
why does the Peak of an AP approach ENa
because the permiability of Na is very high during the rising phase of an AP
evnetually almost reaches where its ionic gradient is in eq with membrane potential
what does the end of the repolarization phase come close to
EK
why does the repolarization phase come close to Ek
becuase the permiability of K is high and crosses the membrane freely until its ionic gradient is in equilibium with membrane potential
when a stimulus is insufficient to take membrane to threshold
Subthreshold stimulus
when a stimultus is just sufficient to take membrane to threshold
Threshold stimulus
when a stimulus is greater than a threshold stimulus
Suprathreshold stimulus
where are subthreshold stimulus’s found
Confined to the immediate region of the membrane
small depolarization or hyperpolarizations that do not move along the membrane
Local responses
what are graded/local responses proportional to
Stimulus strenght
absolute refractor period
Brief period when a second threshold stimulus of suprathreshold stimulus cannot elicit a second AP
Relative refractory period
for a longer period after a AP suprathreshold stimulus can get an AP but threshold cannot
what does Tetrodotoxin do
Binds to sodium channels and blocks sodium influx
adaption
where 2 waves of depolarization can be applied to a cell at different rates of ramping and lead to different responses (square wave gives and AP and ramp does not)
what causes adpation
property of channels called accommodation
stimulus strength duration curve relates
less intense stimuli need more time to ilicit a response
Rheobase
Magnitude of least intense stimulus that can elicit a response
Utilization time
Duration required to elicit a response by a stimulus with a rheobase magnitude
Chronaxie
duration required to elicit response for a stimulus that has a magnitude that is twice the rheobase magnitude
use of chronaxie
compare excitability of different cells
what shape of stimuli do you need to get an AP
square wave
what kind of current are electrotonic currents
passive currents (do not propagate)
what happens if Electrotonic current are sufficient in magnitude
lead to an AP
flow in stimulating electrodes
current flows from anode through the neuron to the cathode
what does the cathode do
Causes cations to move toward it in both the ECF and inside the cells
the cations inside cell membrane are trapped in the membrane and depolarize the membane
what does the anode do
Anode attracts anions
layers of Schwann cell membrane
Myelin
roll of myelin
electrical insulation do allow AP to travel faster and farther due to the AP skipping along the axon
are large diameter axons faster or slower conducting
larger have higher velocities
Recording the AP of a periferal nerve far and close
far: gives multiple AP due to different speeds
close: one large AP due to all the AP stacking up on each other
where do AP occur in saltatory conduction
in the nodes of ranvier
