page 320-329 Flashcards
Lesion on one side causes
Ipsilateral motor loss (corticospinal).
■ Ipsilateral touch/sensory loss.
■ Contralateral pain and temperature loss (spinothalamic).
https://drive.google.com/open?id=0B8uJUY-tie8GU1RKaGFxb05MTzQ
https://drive.google.com/open?id=0B8uJUY-tie8GRENDaFRSdWZnakk
——– set up across the resting nerve membrane.
■ Due to separation of charged particles (ions and proteins) between
extracellular and intracellular fluids.
Charge differential or voltage set up across the resting nerve membrane.
■ Due to separation of charged particles (ions and proteins) between
extracellular and intracellular fluids.
Polarized membrane■ ).
More positive ions (cations) outside (extracellular).
■ More negative ions (anions) inside (intracellular
Charge separation occurs because:
xxx leak (resting K+ conductance)
yyyyy charges leave cell down electrochemical gradient.
■zzzz zzzz determinant of RMP.
Charge separation occurs because:
■ K+ leak (resting K+ conductance)
■ + charges leave cell down electrochemical gradient.
■ Most important determinant of RMP.
Na+/K+ pump
■ Using ATP, establishes the x and y gradient; creates gradient to
allow zz leak to occur.
■ Pump is electrogenic: a K+ in for every b Na+ pumped out = net loss
of c charges from the cell.
Na+/K+ pump
■ Using ATP, establishes the Na+ and K+ gradient; creates gradient to
allow K+ leak to occur.
■ Pump is electrogenic: 2 K+ in for every 3 Na+ pumped out = net loss
of + charges from the cell.
RMP: ranges between a and b
■ RMP in humans (most cells) is xxxx (close to K), skeletal muscle
yyyyy, cardiac muscle zzzz
■ Threshold for depolarization: ~ tttt
RMP: ranges between –40 and –85 mV.
■ RMP in humans (most cells) is ~ –70 mV (close to K), skeletal muscle
–90 mV, cardiac muscle –90 mV
■ Threshold for depolarization: ~ –50 mV
Initiated by depolarizing stimulus (depolarization).
AP
RMP becomes more positive (less negative).
■ Ion channels open.
■ Positive ions move from outside to in.
■ As positive ions go intracellularly, RMP becomes positive.
Na+ (sodium)
■ Na+ entry initially causes more Na+ channels to open.
■ Membrane potential approaches that of sodium equilibrium potential.
■ Once threshold reached, the action potential (AP) will fire.
■ Threshold = 20 mV+.
All or none phenomenon.
■ If don’t reach threshold, don’t get AP.
■ AP is same with supra threshold and threshold stimuli
REFRACTORY PERIOD
■ Period of time after an AP that the membrane cannot again be stimulated,
ie, another AP cannot be initiated
ABSOLUTE REFRACTORY PERIOD
■ No stimulus, no matter how large, will stimulate an AP (corresponds to
close of voltage-sensitive Na+ channel).
RELATIVE REFRACTORY PERIOD■
A larger than usual stimulus will stimulate an AP, ie, the threshold is
increased (due to increased permeability to K+ channel).
Repolarization (Figure 10–5)
■ Membrane potential returns to normal following an AP.
■ ↓ Na+ permeability (rapid).
■ Block Na+ entry.
■ ↑ K+ permeability (in to out)(slower).
■ K+ leaks out of the cell.
https://drive.google.com/open?id=0B8uJUY-tie8GaXBwV21SRWRNTEU
https://drive.google.com/open?id=0B8uJUY-tie8GaG55MVVkcWJXUjg
Hyperpolarization
■ During repolarization there is an overshoot in the more negative direction.
■ Membrane potential briefly becomes more negative than RMP before
returning to RMP.
■ This is because of ↑ K+ conductance.
This is because of ↑ K+ conductance.
■ K+ channels stay open.
■ K+ efflux is greater than in resting.
hyperpol.
Note: Hyperpolarization is responsible
for the relative refractory period (cell
remains hypoexcitable). Influx of Cl– will also hyperpolarize and make AP
more difficult to generate.
Block sodium channels (↓ Na+ permeability).
■ Bind to inactivation gates of fast, voltage-gated Na+ channels,
■ keeping them closed and
■ prolonging absolute refractory period.
↓ Membrane excitability → cannot generate AP → no nerve impulse
conduction.
■ Reversible.
■ K, Cl, Ca conductances are unchanged
LA
Affect small myelinated fibers first (size rule).
Unmyelinated C-fibers (slow, dull, long lasting) (smallest)
↓
Small myelinated nerve fibers (pain, temp)
↓
Larger A-fibers (touch proprioception, Golgi tendon)
Depolarize (more positive) the postsynaptic membrane potential.
■ Brings it closer to threshold.
■ ↑ probability of AP in postsynaptic neuron
excitability
Creates an excitatory postsynaptic potential (EPSP).
■ Glutamate is the major excitatory neurotransmitter.
excitability
Inhibitory
■ Hyperpolarize (more negative) the postsynaptic membrane potential.
■ Moves it away from threshold.
■ ↓ probability of AP in postsynaptic neuron.
Creates an inhibitory postsynaptic potential (IPSP).
■ Result of ↑ membrane permeability to either Cl– or K+.
inh
glycine
GABA.
■ Both bind receptors and open Cl– channels (↑ Cl– permeability
inh
Spatial Summation
■ Two excitatory inputs arrive at a postsynaptic neuron simultaneously.
■ Converging circuit.
■ Arrival of impulses from multiple presynaptic fibers at same time.
Temporal Summation
■ Two excitatory inputs arrive at a postsynaptic neuron in rapid succession.
■ ↑ frequency of nerve impulses from a single presynaptic fiber.
Nerve impulse =
action potential spreads along plasma membrane.
Occurs in myelinated fibers (remember: Schwann cells (periphery) and
oligodendrocytes (CNS)).
■ ↑ velocity of nerve transmission along myelinated fibers.
Salt conduction
salt conduction
Conserves energy because:
■ Only the Ranvier node depolarizes.
■ Less energy for Na+/K+ ATPase to reestablish resting ion gradients.
■ Na+/K+ pumps reestablish concentration gradient only at Ranvier
nodes.
■ Allow repolarization to occur with less transfer of ions.
Electrochemical basis behind saltatory conduction is xx membrane
capacitance (yyyy distance between charges; zzz charges necessary).
Electrochemical basis behind saltatory conduction is ↓ membrane
capacitance (increase distance between charges; less charges necessary).
