Download Powerpoint version

The beauty of the Na+K+ pump
 Found along the
plasma membrane of
all cells.
 Establishes gradients,
controls osmotic effects,
allows for cotransport
+
+
Na K
pump
Nerve cells have a Na+K+
pump and selective
permeability to Na+and K+
that set up a potential
Na+K+ pump transports 3
Na+ out for every 2 K+ in.
Na+–K+
pump
Cotransport
p. 61
The setup… Cotransport…the result
Cotransport
The Na+K+ pump also establishes chemical
gradients and ultimately influences electrical
gradients
Electrochemical gradient = electrical and
chemical (concentration) gradient combined
Electrochemical gradients of
neurons
Neurons and muscles are excitable cells
With stimulation, potential across membrane
changes from negative inside the cell to being
positive inside
Membrane
ECF
Concentration
gradient for K+
Electrical
gradient for K+
ICF
+
K
effects
More K+ diffuses out
compared to the
diffusion of Na+ in
K+ would diffuse until
it is balanced by its
electrical gradient
EK+ = –90 mV
+
Na
Gradient for Na+
into the cell
effects
ECF
ICF
Concentration
gradient for Na+
Na+ would
diffuse until
balanced by its
electrical gradient
Electrical
gradient for Na+
ENa+ = +60 mV
+
Na
and
+
K
passive (leak)
channels
Na+ leak channel
K+ leak channel
Na+ and K+ movement together
establish the resting potential
ECF
More K+ leak channels
Na+–K+
pump
(Passive)
Na+ channel
K+ channel
(Passive)
ICF
(Active)
(Active)
Outside
Inside
Large net
diffusion of K+
outward makes
EK+ of –90 mV
No diffusion of A–
Small net
diffusion of Na+
inward neutralizes
some of the
potential created by
K+ diffusion
Resting membrane potential = –70 mV
Cell communication
increase
decrease
Gated ion channels
Gated channels allow specific ions to pass
only when gates are open
 Note difference bw gated and leak channels
Triggered by: potential change (voltage),
chemical binding, temperature change,
stretching
Voltage-Gated Na+ Channel
ECF
Activation
gate
Inactivation
gate
Closed but capable
of opening
Slow
closing
ICF
Open (activated)
Inactivated
Voltage-Gated K+ Channel
ECF
ICF
Closed
Delayed
opening
Open
+
Na
and
+
K
gated channels
Depolarization causes:
 Na+ gates to open, then slowly close
 Delayed opening of K+ gates
First
Later
Delayed
opening
Graded potentials
Graded
potential
Resting
potential
Time
Magnitude
of stimulus
Stimuli applied
Graded potentials
Below threshold
Signal dies out
over distance
Graded potentials
Initial site of
potential change
Loss of charge
Current flow
Loss of charge
Current flow
Triggering an action potential
Na+ equilibrium
potential
At threshold, Na+ channels briefly
open, which causes a large
depolarization
K+ open during spike,
and slowly close, resting
potential returns
Threshold
potential
Resting
potential
Triggering event
K+ equilibrium
potential
1) Input zone receives incoming
signals from other neurons.
Dendrites
2) Trigger zone
initiates AP’s
Axon hillock
3) Conducting zone conducts
action potentials
Axon
terminals
4) Output zone releases
Dendrites neurotransmitter that
influences other cells.
Cell body
Axon
Conduction of signal
interstitial fluid
cytoplasm
Conduction of signal
Na+
Na+
Na+
Conduction of signal
K+
K+
K+
Na+
Na+
Na+
Conduction of signal
K+
K+
K+
Na+
Na+
Na+
K+
Na+
Action potentials
 All or nothing
 No degradation of signal
over distance
 Conduction in one
direction
Refractory period
Action potentials
travel in one
direction bc of
the refractory
period
Myelination
unsheathed node
axon
Schwann cells of a myelin
sheath
Na+
action potential
resting potential
K+
Na+
resting potential restored
action potential
resting potential
resting potential
Chemical Synapse
Voltage-gated
Ca2+ channels
Chemically gated
Na+, K+, or Cl- channels
Calcium influx
causes vesicles to
perform exocytosis
Neurotransmitters
A synapse will use only one type of neurotransmitter
Ex: dopamine, serotonin, epinephrine, GABA
Neurotransmitters are quickly removed once they bind
to receptors
Reuptake or inactivated
Neurotransmitters activate
gated ion channels
Excitatory
synapse: Na+
channels
Inhibitory
synapse: K+ or
Cl- channels
Signal at the synapse excites or
inhibits the postsynaptic neuron
Excitatory synapse:
 Causes an influx of Na+ into postsynaptic neuron.
 This produces an EPSP and depolarizes the
neuron.
Inhibitory synapse:
 Causes an outflow of K+ from the postsynaptic
neuron. It can also cause an influx of CL This produces an IPSP and hyperpolarizes the
neuron.
Excitatory synapse
Activation of synapse
Inhibitory synapse
Activation of synapse
EPSP
IPSP
PSP= Postsynaptic potential
Temporal summation: PSPs occur close
together in time from a single presynaptic
neuron.
Spatial summation: PSPs originate from
several presynaptic inputs.
Some neuron shapes
Hippocampus neuron
Purkinje neurons
Pyramidal neurons
Bipolar neurons - retina
Drug effects
If a drug affects the nervous system, it
usually changes synapse function
Drug molecules can:
mimic neurotransmitters
falsely stimulate neurotransmitter release
block neurotransmitters, or their reuptake
These drugs all mimic
natural endorphin
How stimulants and sedatives
work
In a part of the brain stem (RAS), excitatory
synapses (norepinephrine) cause wakefulness,
inhibitory synapses (GABA) cause drowsiness
How stimulants and sedatives
work
In a part of the brain stem (RAS), excitatory
synapses (norepinephrine) cause wakefulness,
inhibitory synapses (GABA) cause drowsiness
Caffeine, amphetamines, ecstasy (MDMA)
norepinephrine in RAS
Alcohol, valium, barbiturates, &
marijuana activate GABA receptors.