Download Nervous System Part 1

Nervous System Part 1
Organization
Resting Membrane Potential
Signaling
Graded Potentials
Action Potentials
Organization
Control
System that
receives info
about internal
and external
environment,
integrates, and
directs
activities to
respond.
Divided into
the CNS and
the PNS.
Organization
Consists of 2 classes of cells:



Neurons (20%) – communication
Neuroglia (80%) – many fnctns: structurally supporting, nurturing,
insulating, & protecting neutons
Nerves – Bundles of neurons in the PNS
Organization
3 types on neurons:
1.
2.
3.
Afferent (sensory) neurons
Interneurons
Efferent (motor) neurons
Organization
Main
parts of a
neuron:
Resting Membrane Potential
A charge
difference across
the membrane of
-70mV at rest.
Has the potential
to do work.
K+ and Na + leak
channels in the cell
membranes
establish
electrochemical
gradients.
Resting Membrane Potential
Resting
Membrane
Potential
If the cell only
had K + channels
the equilibrium
potential of the
cell would be
–90mV.
Resting
Membrane
Potential
If the cell only
had Na+ channels
the equilibrium
potential of the
cell would be
60mV.
Resting
Membrane
Potential
There are
more K+
leak
channels
so Vm is
closer to
EK than
ENa.
Resting
Membrane
Potential
Active transport
Na+/K+ pumps
maintain the ion
concentrations as
seen in table 6-2.
Signaling
Changes in a cell’s
membrane potential
produce electrical
signals.
1.
2.
Graded potentials –
signaling over short
distances.
Action potentials –
signaling over long
distances
Terms for the direction
of changes relative to
resting potential are
seen to the right.
Graded Potentials
Changes in
membrane
potential confined
to a small region of
a neuron.
They are graded,
meaning they can
vary in magnitude.
Action Potentials
If the minimum
threshold
voltage is
reached, a
graded potential
becomes an
action potential.
Action Potentials
Voltage-gated
sodium and
potassium
channels are
responsible for
the
depolarization
and
repolarization of
the membrane.
Action
Potentials
Action
Potentials
Always an
all-or-nothing
event.
Propagates
away from a
neuron’s trigger
zone.
Nervous System Part 1
(cont.)
Action Potentials Review
Synapse
Action Potentials
‘http://outreach.mcb.harvard.edu/animati
Review
ons/actionpotential.swf
Action Potentials
Review
1. A typical neuron would have a resting
membrane potential of about
(A) +70 mV
(B) +70 V
(C) -70 mV
(D) -70 V
(E) All of the above are observed at
rest.
Action Potentials
Review
2.
At the peak of the action potential, the
membrane potential is:
(A) exactly at the Na+ equilibrium potential
(B) close to but more positive than the
Na+
equilibrium potential
(C) close to but less positive than the Na+
equilibrium potential
(D) exactly at 0 mV
(E) the same as the resting membrane
potential
Action Potentials
Review
3. True or False: Threshold voltage for
opening is approximately the same for
voltage-gated Na+ and K+ channels.

Voltage-gated Na+ and K+ channels open
at the approximately the same threshold
voltage… K+ channels are just much
more slower at opening wide and closing
completely than Na+ channels.
Action Potentials
Review
Schwann cells are glia cells that that for the myelin
sheath.
They insulate the axons of neurons and increase the
rate of action potential propagation.
Synapse
Synapse: the
narrow gap b/w
1 neuron & the
next.
Neurotransmitte
r: the chemicals
that cross the
synapse
Synapse
Synapse
Response by
postsynaptic cell
depends on:





Type of
neurotransmitter
Conc. of
neurotransmitter
Type of receptor
Number of receptors
Responsiveness of
the receptors
Synapse
Many axon
terminals synapse
onto one neuron.
Excitatory and
inhibitory signals
are integrated
All synaptic
potentials are
graded potentials
Synapse
EPSP: excitatory post-synaptic potentials; depolarization
IPSP: inhibitory post-synaptic potentials; hyperpolarizing
When threshold is reached an action potential is fired down
the post-synaptic neuron.
Synapse
Neurotransmitter
s need to be
removed ASAP
after signal is
complete.
Many helpers:



Diffusion
Enzymes
Protein pumps