Psych 118 - Lecture 6

Important Announcements

  • Exam 1: Scheduled for Thursday on takeithome.com.

    • Review session led by Kaylee today at 04:00 via Zoom (same link as office hours).

    • All three sets of study questions due by midnight tomorrow.

    • Students can attempt the study questions multiple times to achieve a perfect score.

Overview of Today's Material

  • Unit 4: Beginning today, covering the evolution of the nervous system.

    • Note: Material covered in this unit will not be included in Thursday's exam (relevant for Exam 2).

Evolution of the Nervous System

Significance of Nervous Systems in Animals

  • Animals possess a nervous system primarily to facilitate movement through their environments.

  • Movement entails sensory input and motor output, allowing organisms to react to stimuli.

Key Concepts in Nervous System Evolution

  • Neurons: Fundamental building blocks of the nervous system.

    • Evolutionary origin links to precursors in non-animal life forms.

    • Neurons first evolved in unicellular eukaryotes, eventually leading to behavioral complexities in multicellular organisms.

Eukaryotes vs. Prokaryotes

  • Eukaryotes: Organisms with DNA enclosed in a nucleus (higher complexity).

  • Prokaryotes: Organisms lacking a nucleus (e.g., bacteria).

Example Studies with Plants

  • Venus Flytrap: Responds to touch via modified leaves that trap insects when stimulated.

  • Mimosa Plant: Closes leaves reflexively to avoid predation, showcasing a basic response mechanism.

  • Action Potentials in Plants: Recorded using electrophysiological techniques.

    • Plant action potentials similar in principle to animal neurons.

Experiment on Action Potentials and Anesthetics

  • Researchers tested diethyl ether’s effect on Venus flytraps and mimosa plants to determine action potential response.

    • Results show anesthetic application leads to temporary inhibition of action potentials, showcasing similarities with animal neurons.

Functionality of Nervous Systems in Multicellular Organisms

  • Nervous systems help coordinate various physiological actions:

    • Mechanical events (e.g., heartbeat).

    • Glandular processes (e.g., digestion).

    • Movement.

  • Sophisticated neural networks lead to complex behaviors such as perception, learning, and cognition.

Methods to Study Nervous System Evolution

  1. Fossil Record: Analyzes past organisms; difficulty due to the decomposing nature of nervous tissue.

    • Paleontologists use fossilized behavioral traces to infer nervous system properties.

  2. Comparative Analysis: Examines living organisms’ neural circuitry and behaviors to reconstruct evolutionary pathways.

    • Helps clarify neural development trends through phylogenetic relationships.

Example of Using Fossil Evidence

  • Stone Tools and Cut Marks: Indicative of early human activity, providing insights into the evolution of hominids (e.g., Homo habilis, dated around 2.4 million years ago).

  • Footprints and Fossilized Evidence: Footprints in volcanic ash provide evidence of bipedalism in early ancestors like Australopithecus, noting similarities to modern human locomotion.

Footprints of Dinosaurs

  • Fossilized footprints provide crucial data on locomotion patterns, showing the distinction in movement styles between mammals/birds and reptiles.

Rare Brain Tissue Preservations

  • Example of trilobite brain discovered in China, showing a tripartite brain similar to modern crustaceans, indicating ancient complex nervous systems.

Comparative Method in Modern Research

  • Modern invertebrates (e.g., sponges, jellyfish, mollusks) are studied to understand early nervous system evolution.

  • Phyla Example: Study involves analyzing animals like sea sponges, cnidarians, echinoderms, and arthropods to understand neural characteristics and evolutionary progression.

Sponges and Basic Nerve Responses

  • Porifera (sponges):

    • Simple organisms lacking true neurons; cells can communicate and function individually.

    • Exhibit basic behavioral responses without a centralized nervous system.

Cnidarians and True Neurons

  • Cnidarians (e.g., jellyfish):

    • Possess true neurons organized into a rudimentary nervous system.

    • Neurons operate in networks, capable of sensory and motor functions but lacking centralized control (no brain).

    • Action potentials can be bidirectional, a unique feature among neural systems.

Reflex Arc and Instinctual Behaviors

  • Reflexes: Basic unit of behavior; often categorized through simple reflex arcs.

  • Study Example: Aplysia (sea slugs) are used to investigate reflexes and learning due to their simpler nervous systems and identifiable neurons.

    • Gill Withdrawal Reflex: Unconditional reflex where stimulation leads to gill withdrawal.

  • Researchers have extensively mapped the neural circuitry involved, examining both monosynaptic (direct) and polysynaptic (indirect) connections.

Habituation and Sensitization

  • Habituation: Decrease in response strength with repeated exposure to a stimulus (e.g., gill withdrawal diminishes over time).

  • Sensitization: Increased response strength following exposure to a strong or noxious stimulus.

Example of Crayfish Escape Reflex

  • Crayfish study details motor systems involved in escape responses, emphasizing two neural circuits (giant fibers for rapid reflexes and non-giant fibers for more flexible responses).

    • Reflexes may have different latencies based on the nature of the stimulus.

Learning as a Behavioral Modifier

  • Learning induced changes in behavior beyond instinctive reflexes, encompassing habituation (decreasing response) and sensitization (increasing response).

    • Example of sensitization discussed with the effect of shocks on subsequent responses.

Closing Notes

  • Reminder: Exam is on Thursday and questions can be submitted on the forum. Review session today at 04:00. Study questions are due midnight tomorrow.