Nervous Systems of Animals from Simple to Complex

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Nervous Systemsof Animals from Simple to
Complex

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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?

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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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PlatyhelminthesFlatworms

• 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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NematodesRoundworms

• A roundworm, the nerve cells are even more
  centralized. A roundworm has two nerve cords that
  transmit impulses in the roundworm.

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AnnelidaSegmented 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.

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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?

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Mollusks Nervous System

• Ganglia are organized into a brain
• centralized brain and a multitude of sense organs
• Example
• 1. Snails 6 ganglia.
• Bivalves 3 pairs of ganglia
• Specialization controls esophagus, muscles close
  to the shell, and foot.

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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.

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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
• Birds brain is large for its body size.
• Possess cerebrum, cerebellum and medulla oblongata

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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

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Primates

• Binocular vision, well-developed 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.

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Sources

• http//faculty.washington.edu/chudler/invert.html
  from Neuroscience for Kids
• Miller and Levine Biology Textbook
• Google images

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Nervous System

• Biologically speaking, all thought and action
  results from your nervous systems.

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Question of the Day
We will go around the room and have each student
name one disease of the nervous system.
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Some examples
Alzheimers Parkinsons Disease Multiple
Sclerosis Tourettes Syndrome Amyotrophic lateral
sclerosis (ALS) or Lou Gehrigs Epilepsy Stroke Br
ain tumors Meningitis Muscular Dystrophy Tension
headaches Concussions Migraines
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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.
• The axon conducts signals away from the cell body
  and divides into many branches at the nerve
  terminal.

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What are the parts of a nerve cell?

• Cell body
• Dendrite
• Axon

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What do neurons(nerve cells) do?

• receive, conduct, and transmit signals.
• http//www.youtube.com/watch?vFZ3401XVYwwfeature
  related
• http//www.youtube.com/watch?vAjxJabpjDGofeature
  related

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How are signals transmitted?
Impulses travel the nerve highway The nervous
system uses chemicals called neurotransmitters
and synapses.
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How do you interpret signals?
Sense organs Central Nervous System
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How are you respond to the signals?
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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.
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Neurotransmission

• ISAT 351, Spring, 2004
• College of Integrated Science and Technology
• James Madison University

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Neuron Structure

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Neurons

• Signal Signal Propagation Relay to
  next
• Reception (electrical)
  cell (chemical)

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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

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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

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Structures are Similar
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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

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Neurons Form Circuits
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Electrical Signal

• Nerve signals are changes in the electrical
  potential across the neurons 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

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Electrical Signal

• Myelin sheath insulates nerve
• Prevents signal attenuation
• Promotes signal propagation and amplification
• Multiple sclerosis involves demyelination

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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

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Propagation of Action Potential
Resting V1
V2

- - -
- - -
- - - -
- - -
- - - -
Recovery
Baseline Membrane Action Potential
Propagation Potential -60mV
-40mV Depolarization Wave
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So,

• Depolarizing membrane by about 20 mV triggers
  action potential

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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?

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Three Conformational States

• Channel inactivated until K ions
• repolarize membrane speeds recovery

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The Action Potential
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Voltage-Gated Channel
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Measurement of Potential
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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

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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

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Synapses Communicate Between Neurons

• 10-100 BILLION neurons in human brain
• 10-100 TRILLION synapses
• Human forebrain ratio of synapsesneurons about
  40,0001
• Elastic improve connectivity by using neurons
• Neurons communicate via neurotransmitters
• Electrical-to-chemical-to electrical signal
  conversion

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Electrical to Chemical Signal Conversion at
Synapse
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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

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Conversion Back to Electrical Signal
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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

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Dopamine Malfunctions

• Parkinsons disease
• Insufficient dopamine due to destruction of cells
  that synthesize dopamine
• Motor malfunctions appear after about 70 of
  neurons destroyed
• Schizophrenia hallucinations excessive dopamine
• Tourettes syndrome supersensitive receptors

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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

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Use it or lose it!

• Mental activity over lifetime reinforces synaptic
  junctions

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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

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