bmed 3100 L4

bmed 3100 L4 - Neurophysiology
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Unformatted text preview: Neurophysiology
1:
 Nervous
system
basics,
autonomic
 nervous
system,
sensory
system
 Sept.
1,
2011
 Nervous
System
Organiza>on
 •  Two
categories
of
dis>nc>on:
 –  Anatomical
 •  Central
nervous
system
(brain,
spinal
cord)
 •  Peripheral
nervous
system
(sensory
nerves,
Rs,
ganglia)
 –  Direc>on
of
informa>on
 •  Sensory
(afferent):
info
into
nervous
system
 –  Sight,
touch,
etc
 •  Motor
(efferent):
info
out
of
nervous
system
 –  Control
of
muscle
 Basics
 •  Neuron
 –  –  Cell
body
(soma)
 Dendrites
 •  •  –  Axon
(nerve
fiber)
 •  •  –  NeurotransmiPer
release
 Axonal
transport
 –  –  •  Carries
output
to
target
cell
 Collaterals
 Axon
terminal
 •  •  Receive
info
from
other
neurons
 Increase
SA
of
neuron
 Anterograde
 Retrograde
 Classes
of
neurons
 –  Afferent
 –  Efferent
 –  Interneurons
 •  •  •  Sends
informa>on
from
>ssues/organs
to
CNS
 Sends
informa>on
away
from
CNS
to
>ssues/organs
 Connect
neurons
within
CNS
 Groups
of
neurons
in
CNS:
nucleus
 Groups
of
neurons
in
PNS:
ganglion
 Basics
 •  Glial
cells
 –  –  •  Types
 –  –  –  –  Schwann
cells
 –  •  Forma>on
of
>ght
junc>ons
in
endothelial
cells
of
CNS
 capillary
walls
 Microglia
 •  Makes
myelin
in
CNS
 Makes
myelin
in
PNS
 Helps
regulate
ECF
composi>on
in
CNS
 Forma>on
of
blood‐brain‐barrier
 –  Oligodendrocyte
 •  Astrocyte
 •  •  Surround
cell
body,
axon,
dendrites
 Provide
physical/metabolic
support
 Macrophage‐like
(immune
func>ons)
 Ependymal
cells
 •  •  Line
fluid‐filled
cavi>es
within
brain
and
SC
 Regulate
produc>on
and
flow
of
CSF
 Nervous
System
Organiza>on
 •  Two
categories
of
dis>nc>on:
 –  Anatomical
 •  Central
nervous
system
(brain,
spinal
cord)
 •  Peripheral
nervous
system
(sensory
nerves,
Rs,
ganglia)
 –  Direc>on
of
informa>on
 •  Sensory
(afferent):
info
into
nervous
system
 –  Sight,
touch,
etc
 •  Motor
(efferent):
info
out
of
nervous
system
 –  Control
of
muscle
 Central
Nervous
System
 Brain
 •  4
subdivisions
 –  Cerebrum
 –  Diencephalon
 –  Brainstem
 –  Cerebellum
 Forebrain
 •  Cerebrum:
right
and
le\
 hemispheres
 •  Hemispheres:

 a)  b)  •  Cerebral
cortex
 •  Gray
maPer
(cell
bodies)
 White
maPer
(myelinated
fiber
 tracts)
 Cerebral
Cortex:

 –  –  Most
complex
integra>ng
area
of
 CNS
 Receives
and
processes
sensory
 info
and
integrates
motor
 func>ons
 1.  2.  3.  4.  Frontal
 Parietal
 Occipital
 Temporal
 Forebrain
 Subcor>cal
Nuclei
in
cerebral
hemispheres:
 •  Basal
ganglia
 –  Receives
input
from
all
lobes
of
cerebral
 cortex
 –  Control
of
movement
and
posture
and
 complex
aspects
of
behavior
 –  Division:
 •  Caudate
nucleus
 •  Putamen
 •  Globus
pallidus
 •  Hippocampus
 –  Memory
 •  Amygdala
 –  Emo>ons
 –  Communicates
with
ANS
via
hypothalamus
 Forebrain
 Diencephalon:
 •  Thalamus
 –  Several
large
nucleisynap>c
relay
 sta>ons
 –  Processes
all
sensory
info
going
into
 cerebral
cortex
 –  Processes
almost
all
motor
info
 coming
from
cerebral
cortex
to
 brain
stem
and
spinal
cord
 •  Hypothalamus
 –  Master
command
center
for
neural
 and
endocrine
coordina>on
 •  Regulates
body
temperature,
food
 intake,
water
balance
 Limbic
System:
func>onal
system
 responsible
for
learning,
emo>ons,
behavior,
 and
some
visceral/endocrine
func>ons
 Cerebellum
 –  Coordina>on
of
 movement,
 maintenance
of
posture,
 head
and
eye
 movements
 –  Integrates
sensory
info
 about
posi>on
from
 spinal
cord,
motor
info
 from
cerebral
cortex,
 and
balance
info
from
 inner
ear
 Brain
Stem
 –  10
of
12
cranial
nerves
 •  Carry
sensory
informa>on
to
brain
 stem
and
motor
info
away
from
it
 1.  Medulla
 •  2.  Pons
 •  •  3.  Autonomic
centers
for
breathing,
BP,
 swallowing,
coughing,
vomi>ng
 With
medulla

balance,
 maintenance
of
posture,
breathing

 Relays
info
from
cerebral
 hemisphere
to
cerebellum
 Midbrain
 •  Control
of
eye
movements
 •  Par>cipates
in
auditory
&
visual
 systems
 Spinal
Cord
 •  Gray
MaPer
 –  Interneurons
 –  Cell
bodies
&
dendrites
of
 efferent
neurons
 –  Entering
axons
of
afferent
 neurons
 –  Glial
cells
 •  White
MaPer
 –  Groups
of
myelinated
axons
 *
31
pairs
of
spinal
nerves
(both
sensory
and
motor)
 
Info
can
also
travel
up
and
down
spinal
cord:
 Ascending
(lower
to
higher
levels
of
CNS)


 Descending
pathways
(higher
to
lower
levels
of
CNS
 Peripheral
Nervous
System
 Peripheral
Nervous
System
 •  43
pairs
of
nerves
 –  12
pairs
of
cranial
nerves
 –  31
pairs
of
spinal
nerves
 •  8
cervical:
neck,
shoulders,
 arms,
hands
 •  12
thoracic:
chest,
upper
abs
 •  5
lumbar:
lower
abs,
hips,
legs
 •  5
sacral:
genitals,
lower
GI
 •  1
coccygeal:
tailbone
 Organiza>on
of
Nervous
System
 •  Two
categories
of
dis>nc>on:
 –  Anatomical
 •  Central
nervous
system
(brain,
spinal
cord)
 •  Peripheral
nervous
system
(sensory
nerves,
Rs,
ganglia)
 –  Direc>on
of
informa>on
 •  Sensory
(afferent):
info
into
nervous
system
 –  Sight,
touch,
etc
 •  Motor
(efferent):
info
out
of
nervous
system
 –  Control
of
muscle
 Motor
Nervous
System
 •  Soma>c
(voluntary)
 –  Skeletal
muscle
innerva>on
 –  One
motoneuron
and
the
muscle
 fibers
it
innervates
 •  Autonomic
(involuntary)
 –  Visceral
organ
innerva>on
 –  Two
neurons:
 1.  Preganglionic
neuron
 •  •  –  Cell
body
of
motoneuron
located
in
 CNS
 –  Axons
synapse
directly
on
skeletal
 muscle
 –  ACh

nico>nic
receptors
 •  2.  Cell
body
resides
in
CNS
 Axons
synapse
on
cell
bodies
of
 postganglionic
neurons
in
ganglia
 Secrete
ACh
 Postganglionic
neuron
 •  •  •  Located
outside
CNS
 Axons
travel
to
periphery
where
 they
synapse
on
visceral
effector
 organs
(heart,
vasculature,
GI,
 bladder)
 Release
either
ACh
or
 norepinephrine
 Autonomic
Nervous
System
 •  Two
major
anatomic
divisions:
 –  Sympathe>c
 •  Preganglionic
neurons
originate
in
 thoracolumbar
spinal
cord
 •  Ganglia
lie
close
to
SC
in
a
chain
(sympathe>c
 chain)
 –  Parasympathe>c
 •  Preganglionic
neurons
originate
in
brain
stem
 and
sacral
spinal
cord
 •  Ganglia
lie
close
to
effector
>ssue
 •  Two
types
of
neurons:
 –  Adrenergic
 •  Release
norepinephrine

adrenoreceptors
 (may
also
be
ac>vated
by
epinephrine
secreted
 from
adrenal
medulla)
 –  Cholinergic
 •  Release
ACh

cholinoreceptors
 All
preganglionic
neurons
are
cholinergic.


 Postganglionic
neurons
can
be
either
cholinergic
or
 adrenergic.
 ‐ Most
in
the
parasympathe>c
system
are
cholinergic
 ‐ Most
in
the
sympathe>c
system
are
adrenergic
 Sympathe>c
Nervous
System
 Mobilize
the
body
for
ac>on
 •  Preganglionic
neurons
originate
in
thoracolumbar
 spinal
cord
 •  Postganglionic
neurons
originate
in
1
of
2
places:
 1.  2.  •  Sympathe>c
chain
ganglia
 One
of
the
prevertebral
ganglia
 Preganglionic
axons
follow
1
of
3
courses:
 1.  2.  3.  Synapse
with
postganglionic
neurons
in
ganglion
it
 enters
 Pass
upward
or
downward
in
chain
and
synapse
in
 another
ganglion
 Pass
through
chain
and
terminate
in
one
of
 prevertebral
ganglia
 •  Origin
of
preganglionic
neurons
are
anatomically
 consistent
 •  The
loca>on
of
the
ganglia
are
anatomically
 consistent
 •  Postganglionic
neurons
are
adrenergic
(except
in
 the
thermoregulatory
sweat
glands)
 •  Preganglion
nerves
are
short;
postganglionic
nerves
 are
longer
 paravertebral
 prevertebral
 Adrenal
Medulla
 •  Part
of
adrenal
gland
 •  Some
preganglionic
neurons
pass
all
the
way
from
 spinal
cord
to
adrenal
medulla
 •  S>mula>on
of
chromaffin
cells
by
sympathe>c
 preganglionic
nerves

release
of
large
amounts
of
 norepinephrine
and
epinephrine
into
circula>on
 •  Similar
ac>on
as
direct
sympathe>c
s>mula>on
 except
longer‐ac>ng
effects
 •  Direct
and
indirect
ac>ons
support
each
other
or
can
 subs>tute
for
each
other.
 Parasympathe>c
Nervous
System
 Conserving
energy
 •  Preganglionic
neurons
originate
in
either
the
 brain
stem
or
sacral
spinal
cord
(craniosacral)
 •  Preganglionic
neurons
leave
cranial
region
pass
 through
cranial
nerves
 –  75%
of
all
parasympathe>c
nerve
fibers
are
in
vagus
 nerves
(cranial
nerve
X)
 •  Preganglionic
neurons
leave
sacral
region
 though
pelvic
splanchnic
nerve
 •  Origin
of
preganglionic
neurons
are
 anatomically
consistent
 •  Ganglia
are
located
near,
on,
or
in
effector
 organs
 •  Preganglionic
nerves
are
long;
postganglionic
 nerves
are
very
short
 •  Most
postganglionic
nerves
are
cholinergic
but
 ac>vate
muscarinic
Rs
 Signal
Transduc>on
 Neuroeffector
Junc>ons
 •  Compared
to
NMJ:
 1.  Postganglionic
neurons
innervate
effector
>ssue
 through
diffuse
branching
networks
 •  Varicosi>es:
sites
of
neurotransmiPer
synthesis,
storage,
 and
release
 2.  Effector
>ssues
may
be
innervated
by
many
 postganglionic
neurons
 3.  Postsynap>c
Rs
widely
distributed
on
effector
>ssues
 (no
motor
end
plate)
 Autonomic
Innerva>on
 Reciprocal
Func>ons
 •  Urinary
Bladder
 –  Micturi>on
reflex
 –  Sympathe>c
 •  Bladder
filling

relaxa>on
of
detrusor
muscle
and
 contrac>on
of
internal
sphincter
 –  Parasympathe>c
 •  Bladder
is
full

fullness
sensed
by
mechanoreceptors
in
 bladder
wall

contrac>on
of
detrusor
muscle
and
 relaxa>on
of
internal
sphincter
 Autonomic
Innerva>on
 Pupil
 •  Size
of
pupil
controlled
by
 radial
and
constrictor
 muscles
in
iris
 •  Sympathe>c
 –  Constric>on
of
radial
 muscle

dila>on
 •  Parasympathe>c
 –  Constric>on
of
constrictor
 muscle

constric>on
 Excep>ons:
sweat
glands,
vascular
smooth
muscle,
pilomotor
muscles
of
 skin,
liver,
adipose
>ssue,
kidney
 Autonomic
Receptors
 •  Loca>ons
 1.  2.  •  Cell
bodies
of
 postganglionic
 neurons
 In
effector
organs
 G
protein‐linked
 receptors
 –  Coupled
to
G
proteins
 •  Bind
GTP
 •  Heterotrimeric
 –  α
subunit
 »  Binds
 GDP/GTP
 –  β
subunit
 –  γ
subunit
 –  Coupled
to
enzymes
 •  Adenyl
cyclase
 –  cAMP
 •  Phospholipase
C
 –  IP3
 Autonomic
Receptors
 •  Adrenoreceptors
 –  α1

 •  Contrac>on
 •  Vascular
smooth
muscle
 of
skin/
skeletal
muscle/ splanchnic
region,
 sphincters
of
GI
tract
and
 bladder,
radial
muscle
of
 iris
 –  α2

 •  Inhibitory
 •  GI
tract
 •  Two
forms:
 –  Autoreceptors
 »  Sympathe>c
 postganglionic
 nerve
terminals
 –  Heteroreceptors
 »  Parasympathe>c
 postganglionic
 nerve
terminals
 Autonomic
Receptors
 •  Adrenoreceptors
 –  Β1
 •  Contrac>on
 •  SA
node,
AV
node,
 ventricular
muscle,
 salivary
glands,
 adipose
>ssue,
kidney
 –  Β2
 •  Relaxa>on
 •  Vascular
smooth
 muscle
of
skeletal
 muscle,
walls
of
GI
 tract
and
bladder,
 bronchioles 

 Autonomic
Receptors
 •  Cholinoreceptors
 –  Nico>nic
Rs
 •  Motor
end
plate,
all
postganglionic
neurons
of
both
sympathe>c
and
 parasympathe>c
systems,
chromaffin
cells
in
adrenal
medulla
 –  Muscarinic
Rs
 •  All
effector
organs
of
parasympathe>c
nervous
system
(heart,
GI
tract,
 bronchioles,
bladder,
male
sex
organs)
 Organiza>on
of
Nervous
System
 •  Two
categories
of
dis>nc>on:
 –  Anatomical
 •  •  –  Central
nervous
system
(brain,
spinal
cord)
 Peripheral
nervous
system
(sensory
nerves,
Rs,
ganglia)
 Direc>on
of
informa>on
 •  Sensory
(afferent):
info
into
nervous
system
 –  •  Sight,
touch,
etc
 Motor
(efferent):
info
out
of
nervous
system
 –  Control
of
muscle
 Sensory
Systems
 Receive
info
from
environment
and
transmit
to
CNS
 General
steps
of
the
sensory
system:
 1.  A
s>mulus
ac>vates
a
sensory
R
 2.  S>mulus
is
converted
into
a
receptor
 poten>al
(sensory
transduc>on)
 3.  The
produced
current
flows
along
axon
to
a
 region
of
the
membrane
capable
of
ac>on
 poten>als
(nodes
of
Ranvier)
 Sensory
Receptors
 •  Types
of
Receptors:
 1.  Mechanoreceptors
 •  •  2.  Photoreceptors
 •  •  3.  Ac>vated
by
chemicals
 Involved
in
olfac>on,
taste,
breathing
 Thermoreceptors
 •  5.  Ac>vated
by
light
 Involved
in
vision
 Chemoreceptors
 •  •  4.  Ac>vated
by
pressure
or
stretch
 Touch,
blood
pressure,
muscle
tension
 Ac>vated
by
temperature
 Nociceptors
 •  •  Specialized
nerve
endings
 Ac>vated
by
extremes
of
pressure,
temperature,
or
noxious
chemicals
 Differen>al
sensi>vity:
Each
type
of
R
is
highly
sensi>ve
to
one
type
of
s>mulus
but
almost
 nonresponsive
to
other
s>muli.
 Sensory
Transduc>on
 •  Environmental
s>mulus

 Receptor
Poten>al
 •  Steps:
 1.  S>mulus
causes
change
in
R
 depending
on
kind
of
R
 2.  Change
causes
ion
channels
to
 open
or
close

 depolariza>on
or
 hyperpolariza>on
 3.  APs
are
generated
 downstream.
 4.  The
higher
the
RP,
the
more
 frequent
the
APs
 Dura>on
of
S>mulus:
 Adapta>on
of
Sensory
Rs
 Adapta>on
of
Sensory
Rs
 •  Slowly
adap>ng
Rs:

 Tonic
Receptors
 –  Almost
con>nuous
signal
 •  Rapidly
adap>ng
Rs:
 Phasic
Receptors
 –  React
strongly
while
 change
is
taking
place
 (ini>a>on
AND
 termina>on
of
s>mulus)
 Sensory
Coding
 •  Conversion
of
s>mulus
 energy
into
signal
that
 conveys
relevant
sensory
info
 –  –  •  Sensory
unit:
a
single
 afferent
neuron
with
all
its
 receptor
endings
 Recep>ve
field:
area
of
body
 that
when
s>mulated
leads
 to
ac>vity
in
par>cular
 afferent
neuron
 Things
that
affect
coding:
 1.  S>mulus
modality
 •  2.  3.  Pathways
dedicated
to
one
 modality
(ex:
vision,
heat,
 cold,
sound,
pressure)
 Intensity
of
s>mulus
 Spa>al
loca>on
 S>mulus
Intensity
 •  The
higher
the
RP,
the
more
 frequent
the
APs
 •  Increase
intensity
of
s>mulus

 increase
#
Rs
ac>vated
(spa>al
 summa>on)
 •  Also,
increase
intensity
of
s>mulus
 
increase
different
types
of
Rs
 that
can
be
s>mulated
 S>mulus
Loca>on
 •  Recep>ve
field:
 –  Area
of
body
that
when
 s>mulated
changes
the
 firing
rate
of
a
sensory
 neuron
 –  Affects
acuity
based
on:
 •  Size
 •  Receptor
density
 •  Overlap
 Lateral
Inhibi>on
 •  Helps
enable
localiza>on
of
 s>mulus
 –  Rs
at
edge
of
 s>mulus=inhibitory
 –  Rs
at
center
of
 s>mulus=excitatory
 •  Enhances
contrast
between
 center
and
periphery
of
 s>mulated
region
 Sensory
Pathway
 Ascending
Pathways
 •  Afferent
sensory
pathways
are
formed
by
 chain
of
3
or
more
neurons
connected
by
 synapses
 •  Carries
info
to
cerebral
cortex
 •  Steps:
 –  First
order
sensory
afferent
neurons:
 •  Primary
sensory
afferent
neuron
 •  Cell
body
in
dorsal
root
or
spinal
cord
ganglion
 –  Second‐order:
 •  First
order
neuron
processes
synapse
on
second
 order
neuron
at
Relay
nucleus
in
spinal
cord
or
 brain
stem
 –  Third‐order:
 •  Second
order
neuron
processes
synapse
on
third
 order
neuron
at
relay
nuclei
in
thalamus
 –  Fourth‐order:
 •  Third
order
neuron
processes
synapse
on
fourth
 order
neuron
in
appropriate
sensory
area
of
 cerebral
cortex
 ...
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