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Evolution Of The Nervous System
Evolution Of The Nervous System
Evolution Of The Nervous System
Evolution Of The Nervous System
Evolution Of The Nervous System
Evolution Of The Nervous System
Evolution Of The Nervous System
Evolution Of The Nervous System
Evolution Of The Nervous System
Evolution Of The Nervous System
Evolution Of The Nervous System
Evolution Of The Nervous System
Evolution Of The Nervous System
Evolution Of The Nervous System
Evolution Of The Nervous System
Evolution Of The Nervous System
Evolution Of The Nervous System
Evolution Of The Nervous System
Evolution Of The Nervous System
Evolution Of The Nervous System
Evolution Of The Nervous System
Evolution Of The Nervous System
Evolution Of The Nervous System
Evolution Of The Nervous System
Evolution Of The Nervous System
Evolution Of The Nervous System
Evolution Of The Nervous System
Evolution Of The Nervous System
Evolution Of The Nervous System
Evolution Of The Nervous System
Evolution Of The Nervous System
Evolution Of The Nervous System
Evolution Of The Nervous System
Evolution Of The Nervous System
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Evolution Of The Nervous System

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  • 1. Evolution of the Nervous System
  • 2. Unifying Principles <ul><li>Uniformity in how nerve cells function through out the animal kingdom </li></ul><ul><li>Great diversity in how nervous systems are organized </li></ul><ul><li>All nervous systems must allow for stimulus and response </li></ul>
  • 3. The Simplest Nervous Systems <ul><li>The simplest nervous systems are found in some cnidarians </li></ul><ul><ul><li>(example: Hydra) </li></ul></ul><ul><li>Have a nerve net </li></ul><ul><ul><li>A loosely organized system of nerves with no central control </li></ul></ul><ul><ul><li>Most synapses are electrical </li></ul></ul><ul><ul><li>Impulses are bi-directional </li></ul></ul><ul><ul><li>Stimulation at any point spreads to cause movement of entire body </li></ul></ul><ul><li>Many radially symmetric animals such as ctenophora (jelly fish) and echinoderms (star fish) are similar </li></ul>
  • 4. First Nervous System Centralization <ul><li>Some cnidarians show the first signs of centralization </li></ul><ul><li>Clusters of nerve cells control the ability to perform more complex motor tasks requiring coordination, such as swimming </li></ul>
  • 5. Centralization in the Jellyfish <ul><li>The jellyfish ( Medusa ) is a cnidarian that exhibits basic centralization </li></ul><ul><li>The nervous system forms an undifferentiated network and serves primarily to coordinate the animal's swimming motions. </li></ul><ul><ul><li>Jellyfish's skirt must open and contract in a coordinated manner for the animal to move through the water. </li></ul></ul><ul><ul><li>Nervous system serves as a simple communications network so all parts of the skirt open and then contract at the same time. </li></ul></ul>
  • 6. Increasing Cephalization <ul><li>Bilateral animals tend to be more active </li></ul><ul><ul><li>require sense organs and feeding structures </li></ul></ul><ul><li>Cepahlization : </li></ul><ul><ul><li>concentration of sensory organs & feeding structures at the head or forward-moving portion of an animal </li></ul></ul><ul><li>Enlargement of the anterior ganglia that receive this sensory input and control feeding gave rise to the first brains </li></ul><ul><li>An anterior brain connected to a nerve cord is the basic design for all organisms with central nervous systems </li></ul>
  • 7. Invertebrate Nervous Systems <ul><li>Invertebrates show increasing cepahalization up the evolutionary ladder </li></ul><ul><li>Flatworms have diffuse, ladder-like nervous systems </li></ul><ul><li>Annelids (segmented worms) & arthropods (insects, crustaceans) have a well defined ventral nerve cord with a brain at the anterior end </li></ul><ul><ul><li>May contain ganglia in each segment to control movement of that segment </li></ul></ul>
  • 8. Worms <ul><li>The simplest organisms to have a central nervous system. </li></ul><ul><li>More complicated nervous system allows worms to exhibit more complex forms of behavior. </li></ul><ul><li>Although there is a separate brain in worms, the brain is not the sole control of action. </li></ul><ul><ul><li>even with its brain removed, worms are able to perform many types of behaviors, including locomotion, mating, burrowing, feeding, and even maze learning </li></ul></ul>
  • 9. Mollusks <ul><li>Nervous system complexity correlates with habitat as well as phylogeny </li></ul><ul><li>Slow moving mollusks (e.g. clams) have little or no cephalization and simple sense organs </li></ul><ul><ul><li>Nervous system is a chain of ganglia circling the body </li></ul></ul><ul><li>Cepahalopods </li></ul><ul><ul><li>most sophisticated invertebrate nervous systems </li></ul></ul><ul><ul><li>Octopus – large brain & large image forming eyes </li></ul></ul><ul><ul><li>Rapid conduction along giant axons </li></ul></ul>
  • 10. Insects <ul><li>Increased complexity of the brain and nervous system. </li></ul><ul><li>Giant fiber systems (also found in worms and jellyfish) allow rapid conduction of nerve impulses </li></ul><ul><ul><li>connect parts of the brain to muscles in legs or wings. </li></ul></ul><ul><li>Brain divided into three specialized segments: </li></ul><ul><ul><li>Protocerebrum, deutocerebrum, tritocerebrum. </li></ul></ul>
  • 11. Variation & Adaptation in Insects <ul><li>Insects possess a greater variety of sensory receptors than any other group of organisms, including vertebrates. </li></ul><ul><ul><li>sensitive to the odors, sounds, light patterns, texture, pressure, humidity, temperature, and chemical composition </li></ul></ul><ul><ul><li>concentration of sensory organs on the head provides for rapid communication with the brain located within. </li></ul></ul><ul><li>Remarkable variety of behaviors </li></ul>
  • 12. Study of Invertebrate Systems <ul><li>Provide unique opportunities for study of nerve cells </li></ul><ul><li>Small nervous systems </li></ul><ul><ul><li>approximately 1000 neurons (10 7 fewer than humans) </li></ul></ul><ul><li>Large neurons </li></ul><ul><ul><li>easy to study electrophysiologically </li></ul></ul><ul><li>Identifiable neurons </li></ul><ul><ul><li>can be cataloged and recognized from animal to animal </li></ul></ul><ul><li>Identifiable circuits </li></ul><ul><ul><li>neurons make the same connections with one another from animal to animal </li></ul></ul><ul><li>Simple genetics </li></ul><ul><ul><li>small genomes, short life cycles allow genetic manipulation </li></ul></ul>
  • 13. Squid Giant Axon An Important Example <ul><li>Giant axons in the mantle of the north Atlantic squid, Loligo pealei , first noted by L.W. Williams in 1909 </li></ul><ul><li>The giant axon is actually a fusion of several hundred smaller axons </li></ul><ul><li>The electrical properties of this structure are, however, the same as other neurons. </li></ul><ul><li>The accessibility of several centimeters of giant axon up to 1 mm in diameter & its viability for several hours in physiological solution made many neurophysiology experiments possible </li></ul>
  • 14. Research on Squid Giant Axons <ul><li>1936 – </li></ul><ul><li>The first measurement of the resting potential in any living cell. </li></ul><ul><li>1943 – </li></ul><ul><li>Goldman equation derived using squid giant axons. </li></ul><ul><li>1945 – </li></ul><ul><li>First recording of resting potential in a living cell. </li></ul><ul><ul><li>A section of squid giant axon several cms long was dissected free and placed in a physiological solution. </li></ul></ul><ul><ul><li>A minute capillary tube filled with KCl was inserted down the central axis of one end of the axon and the voltage was recorded relative to the bath. </li></ul></ul>
  • 15. And More Research <ul><li>1952 – </li></ul><ul><li>Hodgkin & Huxley propose equations to describe currents measured with voltage clamps in squid giant axons. </li></ul><ul><ul><li>These equations could account for the action potential. </li></ul></ul><ul><ul><li>This turned out to have very wide applicability for neurophysiological phenomena in many species </li></ul></ul>
  • 16. Vertebrate Nervous Systems <ul><li>Simplest vertebrates: </li></ul><ul><ul><li>fish, reptiles & amphibians </li></ul></ul><ul><li>Brain: </li></ul><ul><ul><li>becomes much larger and more complex </li></ul></ul><ul><ul><li>composed of a series of swellings of the anterior end of the spinal cord </li></ul></ul><ul><li>The spinal cord </li></ul><ul><ul><li>protected by the vertebrae </li></ul></ul><ul><ul><li>Serves as a two-way path of communication </li></ul></ul><ul><ul><li>fibers segregated into descending motor pathways and ascending sensory pathways </li></ul></ul>
  • 17. Evolution of the Vertebrate Brain <ul><li>The vertebrate brain began as 3 bulges at the anterior end of the spinal cord: </li></ul><ul><ul><li>Prosencephalon (forebrain) </li></ul></ul><ul><ul><li>Mesencepahlon (midbrain) </li></ul></ul><ul><ul><li>Rhombencephalon (hindbrain) </li></ul></ul><ul><li>These are present in all vertebrates </li></ul><ul><li>In more complex brains, they are further subdivided for integration of complex tasks </li></ul><ul><li>Complex behaviors due to increased brain complexity </li></ul>
  • 18. Comparing Vertebrate Brains Fish Amphibian Reptile Mammals
  • 19. Three Trends in Brain Evolution <ul><li>Relative size of the brain increases </li></ul><ul><ul><li>Brain size is a constant proportion of body weight in fishes, amphibians, and reptiles </li></ul></ul><ul><ul><li>Increases relative to body size in birds & mammals </li></ul></ul><ul><li>Increased compartmentalization of function </li></ul><ul><li>Increasing complexity of the forebrain </li></ul><ul><ul><li>Transition from water to land of amphibians & reptiles made vision & hearing more important, favoring enlargement of the midbrain & hindbrain </li></ul></ul><ul><li>More complex behaviors parallel growth of cerebrum </li></ul>
  • 20. Convolutions <ul><li>Convolutions increase surface area </li></ul><ul><li>Surface area is more important than volume in determining complexity because cell bodies are in the cortex </li></ul><ul><li>Greatest in primates & cetaceans (whales & porpoises) </li></ul>
  • 21. Convolutions in Mammals
  • 22. Increase in Relative Brain Size
  • 23. Mammals <ul><li>Brain keeps its three major components </li></ul><ul><li>Two new structures: </li></ul><ul><li>Neocerebellum (&quot;new cerebellum&quot;) added to the cerebellum, at the base of the brain </li></ul><ul><li>Neocortex (&quot;new cortex&quot;) at the front of the forebrain. </li></ul><ul><ul><li>In most mammals, these structures are not particularly large relative to the brain stem. </li></ul></ul><ul><ul><li>In primates they are much larger </li></ul></ul>
  • 24. The Brainstem <ul><li>Present in all mammalian brains </li></ul><ul><li>Oldest part of brain </li></ul><ul><li>Evolved ~ 500 million yrs ago </li></ul><ul><li>Called “reptilian brain” because it resembles the entire brain of a reptile </li></ul><ul><li>Handles basic functions for survival : breathing, heart rate, etc. </li></ul><ul><li>Determines alertness & detects incoming info </li></ul>
  • 25. Limbic System <ul><li>Group of structures located between the brainstem and the cortex </li></ul><ul><li>Evolved between 200 & 300 million years ago </li></ul><ul><li>Called the “mammalian brain” because it is most highly developed in mammals </li></ul>
  • 26. The Human Brain <ul><li>Continues four major evolutionary trends: </li></ul><ul><li>Increasingly centralized in architecture </li></ul><ul><li>Trend toward Encephalization (concentration of neurons at one end of the organism) </li></ul><ul><li>Size, number, and variety of elements of the brain increased </li></ul><ul><li>Increase in plasticity </li></ul><ul><li>Humans have the largest ratio of brain weight to body weight of any of earth's creatures. </li></ul>
  • 27. Centralized Architecture <ul><li>Evolved from a loose network of nerve cells (as in the jellyfish) to a spinal column and complex brain with large swellings at the hindbrain and forebrain. </li></ul><ul><li>Increasingly hierarchical </li></ul><ul><ul><li>Newer additions to the human brain are involved in control </li></ul></ul><ul><ul><li>The initiation of voluntary behavior, the ability to plan, engage in conscious thought, and use language depend on neocortical structures. </li></ul></ul>
  • 28. Plasticity <ul><li>Increase in plasticity </li></ul><ul><li>The brain's ability to modify itself as a result of experience </li></ul><ul><li>Makes memory and the learning of new perceptual and motor abilities possible. </li></ul>
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