excitable cells Flashcards
voltage-gated channel
respond to changes in potential by changing conformation
- allows ion influx/efflux
ligand-gated channel
bind neurotransmitters and ions
- opens in response to ligand binding
ion distribution
- large amounts of Na+ outside the cell
-large amounts of K+ inside the cell - intracellular proteins (A-) are negatively charged and unable to leave the cell
- ICF is more negatively charged than the ECF
ion permeability
cell membrane is more permeable to potassium than sodium
(K+ is King of the Kastle)
concentration gradient
Na+ wants to enter the cell
K+ wants to leave the cell
electrical gradient
Na+ wants to enter the cell
K+ wants to stay in the cell
membrane potential
separation of positive and negative charges across the plasma membrane
resting membrane potential
the membrane potential of ells in non-excitable tissues and also excitable tissues at rest
what is the average resting membrane potential
-70 mV
equilibrium potential
electrical gradient balances with the concentration gradient, no net movement
nernst equation
E= 61 log [outside]/[inside]
potassium equilibrium potential
-90mV
(if the membrane potential were to reach -90mV, the electrical and concentration gradients would be balanced and there would be no net movement of K+)
sodium equilibrium potential
61mV
(if the membrane potential were to reach 61mV, the electrical and concentration gradients would be balanced and there would be no net movement of Na+)
which ion is resting membrane potential determined by?
POTASSIUM
hypokalemia
Low ECF [K+]
- concentration gradient: increases
- electrical gradient: increases in magnitude
- equilibrium potential for K+: more negative
- RMP: more negative (harder to reach threshold= less excitable)
hyperkalemia
High ECF [K+]
- concentration gradient: decreases
- electrical gradient: decreases in magnitude
- equilibrium potential for K+: less negative
- RMP: less negative (easier to reach threshold= more excitable)
excitatory graded potentials
brings the membrane potential closer to the threshold (hypopolarizes)
inhibitory graded potentials
brings the membrane potential further from threshold (hyperpolarizes)
action potentials
an excitable cell membrane that is depolarized to threshold potential (-50mV)
get less negative ;)
graded potentials
hyperpolarize
get less negative ;)
-can turn into an action potential if it hyperpolarizes an excitable cell membrane to threshold
threshold
caused by graded potentials - triggers opening of voltage-gated channels
depolarization
rapid influx of Na+- membrane become less negative
repolarization
rapid efflux of K+ - membrane becomes more negative
hyperpolarization
membrane potential drops below RMP (caused by slow closure of voltage gated K+ channels)
how do action potentials propagate
they go in ONE direction and they do NOT diminish
absolute refractory periods
the period in which a cell cannot undergo another action potential
- starts at threshold and ends whenever sodium gates reset
relative refractory periods
a cell can undergo an action potential but it is harder than usual because the membrane potential is below RMP
- refractory periods ensure one-way propagation of action potentials
contiguous conductions
conduction in unmyelinated fibers that begins at the axon hillock
- the action potential spreads along every portion of the membrane
myelin
thick layers of lipids that cover axons at regular intervals
purpose: insulator that prevents leakage current
myelin-forming cells are
schwann cells (PNS) and oligodendrocytes (CNS)
nodes of ranvier
a bare patch of membranes that are between myelinated regions
- current can flow or jump across nodes
saltatory conduction
(saltatory = to jump)
- in myelinated nerve fibers
- an action potential at one node produces an action potential at the next node (the impulse “jumps” from node to node skipping over the myelinated section of the axon)
- 50 x faster than contiguous
conduction velocity of small unmyelinated fibers
SLOW
- seen in digestive tract
- pain fibers- Slow C type- lingering pain
conduction velocity of large myelinated cells
FAST
- skeletal fibers
- pain fibers- fast A type- part of reflex, sharp pain
regeneration fibers of the PNS
schwann cells guide the peripheral axon to re-establish connection
which type of cells can regenerate and repair neurons
schwann cells in the PNS
regeneration fibers of the CNS
oligodendrocytes retract their arms, losing the neuronal pathway
examples of demyelinating diseases
guillain-barre syndrome and MS
what is lost in MS and guillain- barre syndrome
loss of saltatory conduction and loss of axonal action potential conduction due to their being no myelin sheath
synapse
the junction between neurons
electrical synapses
neurons connected directly by gap junctions
chemical synapses
chemical messenger transmitted across the junction separating neurons
(most common)
when does the neurotransmitter combine with a glutamate receptor?
excitatory post synaptic potentials
what happens during excitatory post synaptic potentials
ligand gated Sodium channel opens
- sodium goes into the cell and the cell becomes more positive (hypOpolarization)
when does the neurotransmitter combine with a GABA receptor?
inhibitory post synaptic potentials
what happens during inhibitory post synaptic potentials
ligand gated potassium channel opens
- potassium goes out if the cell and the cell becomes more negative
ligand gated chlorine channel opens
- chlorine goes into the cell and the cell becomes more negative
(hypERpolarization)
temporal summation
EPSP or IPSP from a single and repeatedly firing presynaptic input that occur close together in time so they add together
*one kid repeating mom over and over
spatial summation
EPSP or IPSP simultaneously firing from different presynaptic inputs
*multiple kids saying mom at the same time
what happens if an excitatory input dominates during summation
the cell is brought closer to threshold
what happens if an inhibitory input dominates during summation
the cell is taken further from threshold
what happens if inhibitory and excitatory input is balanced during summation
the membrane potential remains close to resting
summation of all inputs
grand post synaptic potential
neuropeptides
large molecules made up of 2 to 40 amino acids
neuromodulator
act slowly to produce long-term changes at the synapse
where are neuropeptides synthesized
golgi
where are classical neurotransmitters synthesized
cytosol
