Transcript Nervous Systems

Nervous Systems
of Animals
from Simple to Complex
Three trends in evolution of
the nervous system
• Centralization:
– Are nerves concentrated or
centralized?
• Cephalization:
– Is there a head region?
• Specialization:
– Are its sense organs complex?
Sponges
• Only multi-cellular organism with no
nervous system.
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Cnidarians
Nerve net:
• A nerve net is a collection of separate, but
"connected" neurons.
• No ganglia, no centralization.
• Some jellyfish have structure that detect
–
–
–
–
light (called ocelli)
balance (called statocysts)
chemical detection (olfaction),
touch (called sensory lappets)
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Platyhelminthes
Flatworms
• Nerve net connected by nerve cords
connected to ganglia.
• Contain some receptors to find food and
to find light so that they can avoid it.
• More cephalization than Cnidarians
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Nematodes
Roundworms
• A roundworm, the nerve
cells are even more
centralized. A
roundworm has two
nerve cords that
transmit impulses in the
roundworm.
Annelida
Segmented worms
• A earthworm has a nervous system
with a simple brain and nerve cord.
• The "brain" is located above the
pharynx and is connected to the first
ventral ganglion.
• Each segment has its own ganglia,
gets info from its own segment and
controls, muscles in its own region
• Earthworms have touch, light,
vibration and chemical receptors all
along the entire body surface.
Echinoderms
Simple nerve ring surrounds
mouth and radial nerves into
the arms
• Eyespots on each arm that
have light sensitive
pigments.
• Think back: What type of
protist had an eyespot?
Mollusks: Nervous System
•
Ganglia are organized into
a brain
• centralized brain and a
multitude of sense organs
Example:
1. Snails: 6 ganglia.
2. Bivalves: 3 pairs of ganglia
Specialization: controls
esophagus, muscles close
to the shell, and foot.
Arthropods Insecta
• Example-Grasshopper
• centralized brain and
many sense organs
• Receptors for for taste
and smell and on
antennae and legs
• Antennae can detect
odors or touch objects.
• Insects have
– simple eyes
– compound eyes.
Fish
• Well developed nervous systems, highly
developed sense organs (olfactory
bulbs), and a lateral line system that
detects water movement (That is why
we do not pound on the glass of an
aquarium)
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Amphibians
• Well developed nervous and sensory
systems, keen vision for spotting
insects, hear through their tymphanic
membranes, lateral line system in water
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Reptiles
• Similar pattern of brain as
amphibians
• Cerebrum and cerebellum in reptile
is much bigger than amphibians
• Many snakes-good sense of smell
• Simple external ear drum and single
bone conducting sound to inner ear
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Birds
• Well-developed sense organs needed
for flight
– Birds see well
– Birds hear well
Bird’s brain is large for its body size.
Possess cerebrum, cerebellum and
medulla oblongata
Birds, cont.
• Poor sense of smell but highly
developed eyes.
• Lens is highly flexible in water birds
• Ear lacks external pinna and sound still
conducted by a single bone (columella).
• Cochlea is present though not spiralled
as in mammals
Primates
• Binocular vision, welldeveloped cerebrum,
fingers and toes, and
arms that rotate around
their shoulder joint.
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Chordates
• Nonvertebrate chordates: simple
nervous system with a mass of nerve
cells that form a brain
• Vertebrates: More complex brains with
distinct regions each with a different
functions.
Sources
• http://faculty.washington.edu/chudler/inv
ert.html from Neuroscience for Kids
• Miller and Levine Biology Textbook
• Google images
Nervous System
Biologically speaking, all
thought and action results
from your nervous systems.
Question of the Day
We will go around the room and have each student
name one disease of the nervous system.
Some examples
Alzheimers
Parkinson’s Disease
Multiple Sclerosis
Tourette’s Syndrome
Amyotrophic lateral sclerosis (ALS) or Lou Gehrig’s
Epilepsy
Stroke
Brain tumors
Meningitis
Muscular Dystrophy
Tension headaches
Concussions
Migraines
How do you receive signals?
The cell body contains the
nucleus and receives signals
from other neurons on branches
called dendrites or directly on
the cell body.
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decompressor
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The axon conducts signals
away from the cell body and
divides into many branches at
the nerve terminal.
What are the parts of a nerve
cell?
Cell body
Dendrite
Axon
What do neurons
(nerve cells) do?
 receive, conduct, and transmit signals.
 http://www.youtube.com/watch?v=FZ3401XVY
ww&feature=related
 http://www.youtube.com/watch?v=AjxJabpjDG
o&feature=related
How are signals transmitted?
Impulses travel the nerve
highway
The nervous system uses
chemicals called
neurotransmitters and synapses.
How do you interpret signals?
Sense organs
Central Nervous System
How are you respond to the
signals?
9-12.IV.G.2
The student will describe how the functions of individual
organ systems are integrated to maintain a
homeostatic balance in the body.
Content Limit:
Items are limited to those which require both hormonal
and nervous regulation.
Items will be placed in scenarios that refer to body
temperature, breathing, and pulse rate as
homeostatic disruptions of the human body, or any
scenario that addresses symptoms or
disruptions of homeostasis.
Items will provide opportunities for students to describe
examples they supply.
Items will NOT address positive feedback.
Neurotransmission
ISAT 351, Spring, 2004
College of Integrated Science and Technology
James Madison University
Neuron Structure

Neurons
Signal
next
Reception
(chemical)
Signal Propagation
(electrical)
Relay to
cell
Electrical & Chemical Signal
Propagation
• Electrical Signal
– Signal propagation
within neuron
– Branched axon
terminus amplifies
signal
– Terminus makes
synapses with target
cells
• Chemical Signal
– Propagation between
cells
– Neurotransmitters
– Relay electrical
signal via exo- &
endocytosis
– Targets:
• Another neuron
• Dendrite
• Muscle cell
Types of Neurons
 Sensory neurons receive and convert
stimuli from the environment into
electrical signals
 Interneurons receive signals from neurons
and transmits signals to neurons
 Motor neurons receive signals from
interneurons and stimulate muscle or
glands
Structures are Similar
Neuron Signals
 Electric signals transmit information
within a cell from the cell body to the axon
terminus by an electric impulse called an
action potential
 Chemical signals transmit information
from sensory cells, between neurons
(synapses), and to specialized cells such
as muscle or glands
Neurons Form Circuits
Electrical Signal
 Nerve signals are changes in the electrical
potential across the neuron’s plasma
membrane (membrane potential)
 The action potential or nerve impulse can
carry a message without signal attenuation
 Action potentials actively propagate signal via
voltage-gated Na+ channels
 Explosion of activity propagated & amplified
along membrane
Electrical Signal
• Myelin sheath
insulates nerve
– Prevents signal
attenuation
– Promotes signal
propagation and
amplification
– Multiple sclerosis
involves
demyelination
Electrical Signal = Action
Potential
• Intra- & extracellular
[ion] different
– [K+] high internally
– [Na+, Cl-] high externally
• Consequences:
– Unequal distribution of
cations and anions
– Baseline membrane
potential changes when
ion distribution changes
Propagation of Action
Potential
Resting
+
+
+ + +
+ + +
+
Baseline Membrane
Potential -60mV
V1
+
+
+
+
+
+
+
+
-
Action Potential
-40mV
V2
+
+
+
+
+
+
+
+
+
-
Recovery
Propagation :
Depolarization Wave
So,
Depolarizing membrane by about
20 mV triggers action potential
Voltage-Gated Channels
Mediate Action Potential
•Depolarization causes
channels to open and an
influx of anions (Na+)
causes further
depolarization resulting
in the action potential.
•How is the membrane
repolarized?
Three Conformational States
Channel inactivated until K+ ions
repolarize membrane; speeds recovery
The Action Potential
Voltage-Gated Channel
Measurement of Potential
Propagation Measurement
• 1 electrode inside, other
outside
• Stimulate & measure as
a function of time
• V1, V2, V3 have identical
amplitudes
– Shape & intensity of
potential maintained
– Zero attenuation as
signal propagated
Consequences
• All-or-none; neurons are resting or
conducting
• Amplitude constant, so size of action potential
not important
• THE FREQUENCY OF ACTION POTENTIAL
FIRINGS CARRY INFORMATION
• RATE OF PROPAGATION FACILITATED BY
MYELIN INSULATION
Synapses Communicate
Between Neurons
• 10-100 BILLION neurons in human brain
• 10-100 TRILLION synapses
• Human forebrain: ratio of synapses:neurons
about 40,000:1
• Elastic: improve connectivity by using
neurons
• Neurons communicate via neurotransmitters:
– Electrical-to-chemical-to electrical signal
conversion
Electrical to Chemical Signal
Conversion at Synapse
Synapses
 The action potential opens voltage-gated
Ca+ channels at the nerve terminal
 The increase in Ca+ triggers the release of
neurotransmitters into the synaptic cleft
 The neurotransmitter diffuses across the
synaptic cleft, binds to the target cell, and
triggers an action potential
Conversion Back to Electrical
Signal
Neurotransmitter Tidbits
• Certain psychotic drugs (cocaine,
morphine) & venoms mimic NT
• Feel good with dopamine and serotonin
– Natural reward system appeared early in
evolution; reinforce behaviors favorable to
survival
– Prozac et al
Dopamine Malfunctions
• Parkinson’s disease
• Insufficient dopamine due to destruction of cells
that synthesize dopamine
• Motor malfunctions appear after about 70% of
neurons destroyed
• Schizophrenia hallucinations: excessive
dopamine
• Tourette’s syndrome: supersensitive
receptors
Dopamine and Addictions
• Stimulate feel good effects of dopamine using
alcohol, nicotine, marijuana, and
amphetamines
– Amphetamines stimulate secretion
– Cocaine keeps [dopamine] high
• Dopamine may be common end-point of
addictions; different mechanisms
• Addicts’ feedback mechanisms impaired
• Consequence: dopamine deficit
Use it or lose it!
Mental activity over lifetime
reinforces synaptic junctions
Learning and Memory
Thousands of nerve terminals
synapse on a neuron
Combination of synapses determines
if action potential is initiated
Synaptic pathways provide a
mechanism to store, analyze, and
recall inputs
Multiple
Multiplesclerosis
sclerosis (MS)
(MS) is
isaa disease
disease
that
thatdestroys
destroysmyelin,
myelin,an
aninsulating
insulating
material
material that
thatcoats
coatsnerve
nerve fibers
fibers and
andis
is
necessary
necessaryfor
for normal
normalelectrical
electrical
conduction
conduction in
in the
the nervous
nervous system.
system. This
This
breakdown
breakdown of
of the
the myelin,
myelin,called
called
demyelination,
demyelination,results
resultsin
inimpairment
impairmentof
of
the
the function
functionof
of the
the nerve.
nerve.
In
InMS,
MS,repeated
repeated incidents
incidentsof
of
inflammation
inflammationcause
cause scarring
scarring
(sclerosis)
(sclerosis) and
and permanent
permanent
abnormal
abnormal function.
function.
The
The name
name is
is derived
derived from
from this
this process
process
-- multiple
multiple (many)
(many) since
since it
itoccurs
occurs in
in aa number
number
of
of places
places within
withinthe
the nervous
nervoussystem
systemand
and
sclerosis
sclerosis (scars)
(scars) which
which means
means the
the hardened
hardened
tissue
tissue that
thatreplaces
replaces damaged
damaged myelin.
myelin.
During
Duringan
an MS
MSattack,
attack,myelin
myelin becomes
becomes
inflamed,
inflamed, causing
causingsymptoms
symptoms such
suchas
aslack
lack of
of
coordination,
coordination, weakness,
weakness, tingling,
tingling, impaired
impaired
sensation,
sensation, double
double vision
visionor
orbladder
bladder problems.
problems.
If
If the
the inflammation
inflammationis
is severe,
severe, the
the myelin
myelin may
may
actually
actuallybe
be damaged,
damaged,however,
however, regrowth
regrowthof
of
myelin
myelinmay
may occur
occur naturally
naturallyduring
during periods
periods of
of
remission.
remission.
MS
MSaffects
affectsabout
about 250,000
250,000
Americans
Americans and
andis
is about
abouttwice
twice as
as
common
common in
in women
womenas
as in
inmen.
men.
Multiple
Multiple sclerosis
sclerosis is
isan
an
autoimmune
autoimmune disease.
disease. Something
Something
causes
causesthe
the body
body to
tobecome
become
allergic
allergic to
toits
its own
ownmyelin.
myelin.
There
There may
may be
beaa genetic
genetic component--a
component--a predisposition-predisposition-to
to susceptibility
susceptibilityto
to MS.
MS. People
People with
withparticular
particular types
types of
of
histocompatibility
histocompatibility antigens
antigens (HLA
(HLAantigens)
antigens) develop
develop MS
MS
more
more often
oftenthan
than those
those who
whohave
have other
other HLA
HLA antigens.
antigens.
HLA
HLA antigens
antigensoften
often associated
associated with
withMS
MS are
areA3,
A3, B7,
B7,and
and
DW2.
DW2.
Common
Common symptoms
symptoms include:
include:
·Loss
·Loss of
of vision
visionin
inone
one eye
eyeor
ordouble
doublevision.
vision.
·Loss
·Loss of
of coordination
coordination and
and trembling
trembling of
of aa
hand.
hand.
·Instability
·Instabilityin
inwalking
walkingand
and spasticity.
spasticity.
·Loss
·Loss of
of bladder
bladdercontrol.
control.
·Peculiar,
·Peculiar,spontaneous,
spontaneous,nerve
nerve sensations
sensations
such
such as
as aa pins-and-needles
pins-and-needles feeling
feelingover
over
part
partof
of the
the body
body(paresthesias).
(paresthesias).
MS is notoriously hard to diagnose.
Current diagnostic tests include:
using evoked potentials (EP) to measure the rate
of nerve conduction in various parts of the
central nervous system.
Computer-assisted tomography (CT) may be used
to scan the central nervous system using an x-ray
technique which can detect areas of
demyelination.
Magnetic resonance imaging (MRI) may also be
used to detect areas of demylenation, but
without the use of x-rays.