Chapter 12
Neural Tissue
deals with information
sense information
process information
respond to information
Overview of classification:
Anatomical
PNS
CNS
“nerves”
cranial
spinal
PNS
“nerves”
brain
and
spinal cord
cranial
spinal
Overview of classificaton:
Functional:
CNS
afferent
efferent
(carry to)
(bring out)
sensory
motor
receptors
somatic autonomic
cells:
neurons
processes
fig. 12-1
fig. 12-3
fig. 12-2
axonal transport
material moving
anterograde
cell
body
synapse
retrograde
neural tissue
neurons
neuroglia
(glial cells)
information
protection
nourishment
insulation
modulation
neural tissue
neuroglia (CNS)
ependymal cells
astrocytes
oligodendrocytes
microglia
neural tissue
neuroglia (CNS)
ependymal cells
line cavities of CNS
produce CSF
(cerebrospinal fluid)
neural tissue
neuroglia (CNS)
ependymal cells
astrocytes
blood-brain barrier
structural support
nourish neurons
neural tissue
neuroglia (CNS)
ependymal cells
astrocytes
oligodendrocytes
wrap around axons
myelin
neural tissue
neuroglia (CNS)
ependymal cells
astrocytes
oligodendrocytes
microglia
smallest
clean up debris
ependymal
astrocytes
oligodendrocytes
microglia
fig. 12-4
neural tissue
neuroglia (PNS)
satellite cells
like astrocytes in CNS
Schwann cells
like oligo’s in CNS
fig. 12-5
PNS
fig. 12-6
anatomy
physiology
how do the cells
send information?
cells:
neurons
processes
fig. 12-1
3 “potentials”
fig. 12-7
resting potential
ICF
=
/
ECF
K+
proteins-
Na+
Cl-
-------
+++++
chemical gradient
ICF
ECF
K+
Na+
electrical gradient
ICF
ECF
K+
Na+
-------
+++++
when at resting potential…
fig 12-9a
if membrane was freely
permeable to potassium…
fig 12-9b
when at resting potential…
fig 12-9c
if membrane was freely
permeable to sodium…
fig 12-9d
resting potential
ICF
=
/
ECF
K+
Na+
-------
+++++
membrane proteins and the
distribution and movement of ions
1.leak
channels
1.
leak
channels
2.
3.
Na+/K+ pump
gated channels:
a.
b.
c.
chemically regulated channels
voltage-regulated channels
mechanically regulated channels
membrane proteins and the
distribution and movement of ions
leak channels
K+
Na+
Na+/K+
pump
ATP
(active
transport)
Na+ leaks in
K+ leaks out
(always open)
Na+/K+ pump (ATPase)
pumps Na+
pumps K+
maintains
resting potential
back out
back in
= -70 mV
oscilloscope
millivolts
oscilloscope
0
-70
membrane
is
polarized
resting potential
time --->
membrane proteins and the
distribution and movement of ions
potentials:
1. resting potential
2. graded potentials
3. action potentials
membrane proteins and the
distribution and movement of ions
1. leak channels
2.
3.
Na+/K+ pump
gated channels:
a.
b.
c.
chemically regulated channels
voltage-regulated channels
mechanically regulated channels
a.
chemically regulated channels
signal binds
(stimulus)
channel opens
fig. 12-10a
e.g., AChR
b.
voltage-regulated channels
Na+
-70 mV
closed
-60 mV
open
1/1000 sec
+30 mV
closed
inactivated
fig. 12-10b
c.
mechanically regulated channels
closed
mechanical
stimulusopens
remove
stimulusclosed
fig. 12-10c
membrane proteins and the
distribution and movement of ions
1. leak channels
2.
3.
Na+/K+ pump
gated channels:
a.
b.
c.
chemically regulated channels
voltage-regulated channels
mechanically regulated channels
membrane proteins and the
distribution and movement of ions
potentials:
1. resting potential
2. graded potentials
3. action potentials
fig. 12-7
millivolts
oscilloscope
0
de polarized
repolarized
-70
Na+ in
time --->
fig. 12-11
fig. 12-11
fig. 12-11
fig 12-12
graded potentials
local potentials
short range
only affect a
small portion of the cell
(may trigger “events” in other cells)
action potentials
a potential that is propagated along an
axon (affects the whole cell)
? - a stimulus large enough to open
the Na voltage-gated channels
“threshold”
about -60 mV
Na+ voltage-gated channel
normally closed (activation gate)
at resting potential
most abundant in
the membrane of the
axon
Na+ voltage-gated channel
opens at -60mV
lets Na+ in
membrane
depolarizes
fig.12-10b
Na+ voltage-gated channel
inactivation gate closes
very quickly (few/10,000 sec)
stops Na+ flow
fig.12-10b
Na+ voltage-gated channel
inactivation gate closes
very quickly
remains closed
until R.P. is
restored
fig.12-10b
refractory period
from the time the Na+ voltage
sensitive channel opens until
inactivation ends
K+ voltage-gated channel
opens and closes more slowly
lets potassium flow out of cell
repolarizes membrane
fig.12-13
action potential
produced when a cell
reaches threshold
the membrane potential at
which the voltage-gated Na+
channel opens
fig. 12-13
millivolts
oscilloscope
0
threshold
-70
Na+
in
Na+ in
time --->
table 12-3
chain reaction…
…propagation
e.g., dominoes
all-or-none
propagation
• continuous
unmyelinated axons
1 meter/second
• saltatory
(L. saltare, leaping)
myelinated axons
up to 140 meters/second
continuous
fig. 12-14
continuous
fig. 12-14
nodes of Ranvier
saltatory
fig. 12-15
Myelin affects speed of AP.
So does fiber diameter
type A fibers
type B fibers
type C fibers
type A fibers
largest (4-20 µm)
have myelin
type B fibers
smaller (2-4 µm)
have myelin
type C fibers
smallest (2 µm)
unmyelinated
to 140 m/sec
~ 18 m/sec
~ 1 m/sec
type A fibers
balance, position,
delicate touch and pressure
neurons to skeletal muscle
type B and C fibers
temperature, pain
touch, pressure
axonal transport
material moving
anterograde
cell
body
synapse
retrograde
Neurons can “move” information.
How do they pass it along?
The synapse
fig. 12-16
Neurons can “move” information.
How do they pass it along?
The synapse
types
structure
function
neurotransmitter diversity
electrical synapses
direct cell-cell
communication via
gap junctions
chemical synapses
synaptic cleft (space)
between cells
electrical synapses (rare)
AP will always pass
from cell to cell
chemical synapses
AP will not always
generate an AP in
second cell
synapse anatomy
presynaptic axon terminal
synatpic vesicles
neurotransmitter
synaptic cleft
postsynaptic neuron
receptors
synapse function
AP makes it to the axon bulb
aka, synaptic knob
axon terminal
membrane depolarizes
opens voltage-gated Ca++ channels
Ca++ enters the synaptic knob
synapse function
Ca++ causes exocyctosis of
synaptic vesicles…
… release of neurotransmitter
aka nt.
nt diffuses across the cleft…
synapse function
nt bind to receptor in
postsynaptic membrane
…receptor opens ion channel…
…changes membrane potential
synapse function
one common nt:ACh
acetylcholine
receptor:
AChR
acetylcholine receptor
removal of ACh:AChE
acetylcholine esterase
fig.12-16-1
fig.12-16-2
fig.12-16-3
fig.12-16-4
AP
open
synaptic
delay
0.2 to
0.5 msec
exocytosis
diffusion
bind/open
table 12-5
synaptic fatigue
when supply of nt cannot
keep pace with nt release
neurotransmitters
many types
table 12-6
neurotransmitters
effects (2):
what kind of receptor do
they bind to?
if nt causes depolarization…
…excitatory nt
if nt causes hyperpolarization…
…inhibitory nt
excitatory nt
(stimulatory)
inhibitory nt
fig 12-12
neurotransmitter examples:
ACh
acetylcholine
cholinergic synapses
usually excitatory
used at neuromusculcar junc.
(inhibitory in cardiac muscle)
neurotransmitter examples:
Norepinephrine (NE)
aka noradrenalin
adrenergic synapses
usually excitatory
used widely in -brain
-autonomic NS
neurotransmitter examples:
Dopamine
excitatory or inhibitory
used in brain
e.g., inhibits overstimulation
of motorneurons
neurotransmitter examples:
Serotonin
CNS neurotransmitter
affects: attention
emotions
(depression?)
sleep/wake
neurotransmitter examples:
GABA
generally inhibitory nt
(20% of brain synapses)
? not well understood
reduce anxiety
neurotransmitters:
others
at least 50 identified:
amino acids
peptides
polypeptides
prostaglandins
ATP, NO, CO
Other compounds:
alter nt release
or
change postsynaptic response
neuromodulators
neuromodulators
often neuropeptides
opioids (one group):
endorphins
enkephalins
endomorphins
dynorphins
neuromodulators
often neuropeptides
opioids:
inhibit release of
substance P
(relay pain)
neurotransmitters and
neuromodulators
How do they work?
1. direct effect on
membrane potential
2. indirect effect on
membrane potential
3. diffusion into cell
neurotransmitters and
neuromodulators
How do they work?
1.
2.
3.
fig. 12-17
information processing
by postsynaptic neurons
How does a cell get
to threshold?
postsynaptic potentials
(PSP)
graded potentials
EPSP
IPSP
excitatory PSP~ 0.5 mV
inhibitory
PSP
-70 mV to -60 mV
postsynaptic potentials
Summation
temporal
spatial
Facilitation
presynaptic facilitation
presynaptic inhibition
temporal
summation
bathtub
fig. 12-18
spatial
summation
fig. 12-18
millivolts
oscilloscope
0
threshold
-70
ipsp
epsp
Na+
in
K+
out
both
time --->
2xNa+ in
see fig. 12-19
postsynaptic potentials
Summation
temporal
spatial
Facilitation
presynaptic facilitation
presynaptic inhibition
Facilitation
anything that will move the
membrane potential closer to
threshold
epsp
drugs (nicotine)
neuromodulators
hormones
fig 12-20b
postsynaptic potentials
Summation
temporal
spatial
Facilitation
presynaptic facilitation
presynaptic inhibition
fig 12-20a
rate of generation of AP
sensory receptor
several AP/sec
light touch
hundreds of AP/sec
lots of pressure
See table 12-7
EPSP’s
IPSP’s
summation
>2000 synapses
neuron
~1011 neurons
brain