Transcript Nerve

Nerve
Action
Nerve cell
Resting
potential
membrane
is neuron,potential
100 billion neurons ± 1006
Classification
according
to conduction
velocity
and
differ
in
structure,
chemistry
&
function.
Neurons
Any
stimulus
does
not
induce
newincrease
AP at time
of
Phases
ofglia
AP
in
neurons:
Ionic
fluxes
causing
electric
phenomenon
of
RMP:
Cathodal
Types
of
stimuli,
local
responses,
&
caliber
of nerve
fiber.
From
larger
to
lowerhave
Nerve
and
muscle
cells
are
excitable
cells,
the
confer
unique
functions
of
nervous
system.
Glia
are
+
+
+
previous
depolarization
until
third
repolarization
Depolarization
phase:
Sharp
rise,
0
potential,
Ion
Extracellular
Intracellular
-Na
-K
pump:
extrude
3
Na
outside
cell,
intrude
2
decrease
Astrocytes:
with
Regulate
amplitudes
EC
space,
of
stimuli,
remove
subside
(or
restrict
after
caliber:
ability
to
reverse
the
negativity
of
their
membrane
All
living
cells
(animal
or
plant)
exhibit
potential
supporting
elements,
10
times
as
neurons.
Neurons
+
+channels,
+
+
(absolute
refractory
period:
Na
channels
cannot
overshoots,about
+35
mV
(activate
all
Na
Classification
of
nerves
K
inside,
much
positive
ions
outside
142
mEq/L
10stimulus
mEq/L velocity
Na
removal
movement
of
of)
these
neurotransmitters
stimuli.
Sufficient
raises
Accordingly,
RMP
of
nerve
cell
–70
mV,
PROTEINS¯
Aα
largest
diameter
&
fastest
conduction
potential
in
response
to
a
sufficient
external
difference
across
their
plasma
membranes
when
contain
cell
body
(soma
or
perikaryon)
&
neurites
+,previous
++
reactivated
immediately
after
activation).
inrush
of
huge
number
of
Na
PM
lose
negativity
Physioanatomic
classification:
afferent
4
mEq/L
140
mEq/L
-Na
channels
are
inactive
at
rest,
voltage
gated,
K
the
Oligodendrocytes:
membrane
potential
Myelinating
15
mV
glia
above
in
RMP
CNS,
(i.e.
form
–
3Na
skeletal
muscle
s
–90
mV,
cardiac
muscle
–85
mV
e.g.
somatic
motor
&
proprioceptive
nerve
fibers
stimulus.
The
external
stimulus
may
be
electrical,
microelectrodes
are
inserted
into
cells,
membrane
(axons
&
dendrites).
Cell
body
gives
rise
to
single
–
+
PHOSPHATES¯
From
third
repolarization
to
end
of
repolarization
Repolarization
phase:
Rapid
fall
toward
negative
103
mEq/L
4
mEq/L
ClmV);sheath
(sensory)
& phases
efferent
(motor),
subdivided
intoin
activated
by
electric
current
55
myelin
AP
(wrap
will
around
start
axons,
&
does
function
not
stop
untilto
Pump
&
smooth
muscle
isor
variable
but
nearly
–50
mV.
Aβ
e.g.
sensory
fibers
of
fine
touch
&
fine
pr.
chemical,
physical
other
types
of
stimuli.
This
interior
is
negative
in
relation
to
its
exterior.
This
is
axon
which
conducts
nerve
impulse
from
neuron
+
+
+
4
mEq/L
75
mEq/L
phase,
stronger
stimulus
induces
new,
but
weaker
Phosphates
potential
(inactivate
Na
channels,
continuous
somatic
&
visceral
neurons,
general
&gradient,
special
CHLORIDE¯
-Passive
diffusion
of
K
outside,
conc.
2K
complete
insulation),
cycle
interruptions:
occurs,
all-or-none
nodes
of
rule.
Ranvier.
Membrane
Aγ
e.g.
motor
fibers
to
muscle
spindle.
change
in
membrane
potential
is
action
potential.
resting
membrane
potential
(RMP),
due
uneven
the
next,
up
to
1
meter
length,
speed
of
impulse
is
a
+to
+
+channels
30
mg/dL
200
mg/dL
Proteins
AP
(relative
refractory
period:
fewer
Na
pumping
of
Na
&
passive
diffusion
of
K
outside)
neurons.
diffusion
potential,
major
factor
of
RMP
potential
Schwann
at
Cells:PNS,
which
AP
myelin
starts
is
sheath
threshold
&
neurolemma
or
firing
Aδ
e.g
sensory
fiber
of
acute
pain,
crude
touch
cold
Response
in
nerve
cell
is
transmission
of
nerve
+
distribution
of
ions
in
&
outside
membrane.
function
of
diameter.
Dendrites:
small
(rarely
more
2+
K
can
be
activated).
Ca
stabilize
membrane,
increase
Hyperpolarization
phase:
Decline
more
negative
-Cl
ions
still
inside,
due
to
higher
conc.
outside
potential.
Microglia:Scavenger
Subthreshold
cells
stimuli
get
rid
no
of
or
foreign
local
effects,
particle
B
e.g.2mm)&
preganglionic
autonomic
nerve
fibers.
impulse
while
response
in
muscle
cell
is
contraction
than
organized
symmetrically
(antennae).
2+:
+
threshold
potential
﴾more
positive﴿.
Lack
of
Ca
potential
than
RMP,–72
mV
(slow
closure
of
K
-Anionic
proteins
&
phosphates
stay
inside,
large
supramaximal
stimuli
the
same
effects
as
threshold
C
smallesttree:
diameter
unmyelinated
fibers
e.g.
Dendritic
all
neurites.
Neural
signals:
efferent
lower
threshold
potential,
membrane
very
excitable
channels,
after
that,
RMP
again)
size,
PM
impermeable
Home
Exit or
sensory
fibers
of
chronic
pain,
heat,
gross
pr.
and
(away)
afferent
(towards)
cell
body.
BASIM
ZWAIN
LECTURE NOTES
, continuously
firing
﴾tetanus﴿
Nerve
12-Several
Propagation
Synaptic
910-Single
11-Axon
Occlusion
collaterals
and
presynaptic
presynaptic
of
junctional
means
action
from
that
neuron
potential
neurons
transmission
postsynaptic
the sum
may
may
of
diverge
converge
activities
neurons
by its
on
of
may
singleand
axon
reverberate
several
postsynaptic
neurons
its to
collaterals
the
working
presynaptic
neuron.
into
together
several
neuron(s).
is postsynaptic
less than the
4-Synaptic
Acetylcholine:
potentials
In
neuromuscular
are
either
excitatory
junction
(NMJ),
(EPSP)
Myelin
prevents
leak,
nodes
of
Ranvier
act
as
AP
triggered
in
axon
hillock,
presence
of
large
No.
Criteria
for
classification
as
a
NT
neurons.
sum
of
their
activities
when
they
work
separately.
Properties
Classification
of
synapses:
of
neurotransmitters
11Synapses:
chemical
or
electrical:(very
rare:
e.g
gap
or
preganglionic
inhibitory
(IPSP).
ANS,
postganglionic
EPSP:
depolarization:
parasym.,
cations
basal
13Several
successive
EPSP
may
facilitate
synaptic
+
augmentation
stations,
strengthen
wave
of
depolarof
Na
channels
&
transmitted
along
axonn.formem.
same
Vesicles
fuse
with
active
zones
of
presynaptic
-Must
be
synthesized
&
stored
in
presyn.
Works
separately
on
2
neurons
1-One-way
A.
Small
molecule,
conduction
rapidly
from
acting
preto
transmitters:
post-synaptic
B.
Neuropeptide,
slowly
acting
transmitters:
junction,
current
flows
directly
through
specialized
+
CAT
in
forebrain
or
anions
&
out,
brain
while
stem
IPSP:
complexes.
hyperpolarization:
Synthesized
knob
to
depolarize
while
several
successive
IPSP
Synapse
is
junction
between
two
neurons.
The
first
ization
by
triggering
new
AP,
nodes
are
rich
in
Na
reason,
huge
number
of
positive
charges
incontains
firing
NT
diffuses
across
synaptic
cleft
to bind
its
specific
-Must
be
released
by
presyn.
n.
upon
stimulation
neurons
Class
because
I:
Acetylcholine
post
synaptic
membrane
Acetyl
coenzyme
A + knob.
choline
Acetylcholine
a-Hypothalamic-releasing
hormones.
protein
molecule:connexon,
distance
between
two
5-EPSP
from
acetylcoenzyme-A
&
IPSP
present
&
simultaneously
choline,
catalyzed
in
cleft.
by
may
inhibit
synaptic
is
presynaptic
neuron
and
the
other
is
postsynaptic
channels,
saltatory
conduction,
jumping
from
node
segment
of
membrane
is
equilibrated
by
adjacent
receptor
on
postsynaptic
mem.
Several
types
of
NT
-Application
of
NT
directly
to
target
cell
must
Temporal
summation
no
Class
synaptic
II:
vesicles.
The
amines
(adrenaline
"epinephrine",
Electrotonic
flow
of
current
Presynaptic
N
b-Pituitary
peptides.
sides
of
membrane
is
very
small:
5nM).
Chemical:
6-Synaptic
cholineacetyltransferase
potentials
are
enzyme
not
all-or-none
(CAT),
Ach
potentials.
is
14Continuous
recurrent
weak
synaptic
potentials
neuron.
Between
them
is
synaptic
cleft.
to
node,
one
direction
from
soma
to
axon
terminal
segments,
electrotonic
flow
of
current,
very
fast
available
and
each
may
have
typesdopamine,
& subtypes
of
ACE
produce
same
effects
as
NT
release
2-Synapse
noradrenaline
is
a
site
"norepinephrine",
of
neurotransduction
(from
c-Peptides
that
actbyonacetylcholinesterase
gut
and
brain.
predominant,
neurotransmitters
(NT)
synthesized
7degraded
0.5
ms
is
in
synaptic
cleft
delay
enzyme
may
cause
habituation
of
postsynaptic
neuron,
not
(orthodromic
conduction),
not
antidromic:
absolute
Acetylcholine
choline
+
acetate
Synaptic
cleft
type
of
conduction
in
solid
wires,
nerve
fiber
is
not2+
receptors.
Postsynaptic
action
depends
on
nature
of
Many
neurons
release
more
than
single
NT.
electrical
serotonine
to
and
chemical
histamine).
signal).
2+
d-Peptides
from
tissues.
Works
separately
on 2other
neurons
&
stored
in
vesicles,
AP
opens
Ca
channel
&
Ca
8(ACE),
Spatiotemporal
its
receptors
summation,
are
nicotinic(complex
additive
or
subtractof
5
α or
respond
for
similar
future
stimulations.
Recurrent
Postsynaptic
N
refractory
period,
proceeds
forward
to
resting
solid
wire,
leaky,
surrounded
by
sea
of
electrolytes,
receptor.
After
that,
NT
must
be
inactivated
by
Convergence
Neurons
that
use
acetylcholine:
cholinergic,
3-Intercellular
Class
III:
Amino
chemical
acids
messages
(γ-aminobutyric
converted
acid
into
2+
Divergence
Spatial
summation
influx,
increase
intracellular
Ca
conc.
attract
ive,
β
subunits)
numerous
or
muscarinic
synaptic
knobs
receptors.
on time
same
Nicotinic:
neuron
at
in
strong
stimulations
accompanied
by
other
weak
segment
not
backward
to
refractory
segment.
continuous
triggering
of
AP,
cost
(0.1
ms
each)
Reverberation
degradation,
reuptake,
diffusion,
or
bioconversion
catecholamines:
catecholinergic,
serotonine:
intracellular
"GABA",
glycine,
signal.
glutamate
and
aspartate).
synaptic
vesicles
(full
of
NT)
to
presynaptic
mem.,
Works
separately
on
2
neurons
same
NMJ,
time:
sym.
spatial
ganglia,
summation,
many
parts
successive
of
CNS,
Muscarinic
impulses
stimulations
may
cause
sensitization
,serotonergic
unmyelinated
nerves
slowest
conduction
velocity.
, amino
acids:
amino
acidergic
Class
IV:
Nitric
oxide
"NO".
Total
together work on 4....
neurons
signals
NT
to release
to
synaptic cleft
by exocytosis.
at smooth
in
sameTotal:
synaptic
muscles
glands.
temporal
summation.
separately
workknob:
on &
6 neurons
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BASIM ZWAIN LECTURE NOTES
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