Biology and Behavior Notes

Chapter 3: Biology & Behavior

Two Perspectives

  • Materialism: Behavior and cognition can be fully explained by the workings of the brain and the rest of the nervous system.

  • Dualism: The mind and body are distinct entities.

Dualism

  • The mind is not (completely) reducible to the material body or brain.

  • The mind is (partially) independent of the body.

  • The mind functions in a way that cannot be (fully) explained by physical processes.

  • This is a less radical viewpoint of dualism—with the words in parentheses added.

Materialism

  • Materialism asserts that the mind is part of the physical world.

  • Materialists believe that all mental phenomena can be explained through physical processes.

  • Consciousness arises from complex interactions within the brain.

  • The mind is not a separate substance but an emergent property of the brain’s physical structure.

  • Materialism has strong ties to scientific methodologies, particularly within neuroscience, psychology, and biology.

Psychology as a Biological Science (PSYC 200)

  • Biopsychology/Neuroscience: Area of study.

  • Perception: Area of study.

  • Learning: Area of study.

  • Thinking: Area of study.

  • Emotion: Area of study.

  • Consciousness: Area of study.

  • Memory: Area of study.

  • Motivation: Area of study.

Psychology as a Social Science (PSYC 201)

  • Social: Area of study.

  • Developmental: Area of study.

  • Personality: Area of study.

  • Mental & Physical Health: Area of study.

  • Abnormal: Area of study.

  • Lifespan Development: Area of study.

  • Therapies: Area of study.

  • Stress, Lifestyle, and Health: Area of study.

Course Connections

  • PSYC 375: Brain & Behavior

  • PSYC 369: Sensation & Perception

  • PSYC 365: Cognitive Psychology

Sensation & Perception (PSYC 369)

  • Sensation & perception is best translated into physiological explanation for perception.

  • Stimulus → Physiology → Perception

Early Psychophysics

  • Neuroscience: Correlation & Causation

  • Correlation: Research in neuroscience provides nice explanations for how this pathway works.

  • Causation: We know very little about how physiology causes perception.

Brain & Behavior (PSYC 375)

  • Brain and behavior are related

    • The brain affects behavior (e.g., hyperactivity in the dopamine system is a cause of schizophrenia).

    • Behavior affects the brain (e.g., learning can bring about long-lasting changes in the brain).

Evidence from Neuroscience Supporting Materialism

  • Advancements in neuroscience have provided substantial evidence supporting materialism.

  • Techniques such as fMRI and EEG have allowed scientists to observe brain activity in real-time, revealing correlations between specific mental states and neural patterns.

  • Changes in brain chemistry can alter mood, memory, and perception, suggesting that consciousness is deeply connected to physical processes in the brain.

  • Brain injuries and diseases like Alzheimer’s have provided further insight into the physical basis of mental functions, as they often lead to changes in personality, memory, and cognitive abilities.

Learning Outcomes

  • Examine behaviors and consciousness from the viewpoint of materialism.

  • Understand how the nervous system generates excitatory and inhibitory responses (a form of on/off binary coding).

  • Understand the physiological explanations for mental disorders like depression and schizophrenia.

  • Understand how brain damage alters consciousness in a split-brain person.

Cells of the Nervous System

  • Neurons: The basic structural & functional units of the nervous system.

  • Glial cells:

    • Outnumber neurons by about 10 to 1

    • Make up 50% of the brain volume

    • Support, nourish neurons and remove their waste.

Neuron Structure

  • Unipolar neuron: Has one axon which extends into dendrites.

  • Pseudo-unipolar neuron: Has one axon that projects from the cell body for relatively a very short distance, before splitting into two branches.

  • Bipolar neuron: Has two independent structures extending from the cell body, one is an axon, the other is a dendrite.

  • Multipolar neuron: Only has one axon extending from the cell body, but multiple dendrites grow out of it, making transmitting information easier.

Types of Neurons

  • Sensory neuron: pseudo-unipolar.

  • Interneuron: bipolar.

  • Motor neuron: multipolar.

  • Majority of Interneurons in humans are multipolar.

Neurons Based on Structure

  • Unipolar: Only one process that extends from the cell body; primary afferents of spinal and some cranial nerves in vertebrates.

  • Psuedopolar: Are unipolar neurons but appear like bipolar neuron; Most sensory neurons are pseudounipolar, dorsal root ganglia of spinal nerves.

  • Bipolar: 2 distinct processes one axon and one dendrite arising directly from the cell body; Rod and cone cells of retina olfactory system most common neurons in the CNS of invertebrates.

  • Multipolar: Most common with multiple extensions from soma. A motor neuron, Majority of neurons of CNS and PNS

Three Types of Neurons

  • The function of a neuron is to receive, integrate, and transmit information.

    • Sensory Neuron.

    • Interneuron.

    • Motor Neuron.

Neural Communication Pathway

  • Stimulus -> Receptor -> Sensory neuron -> Spinal cord -> Integrating center -> Interneuron -> Efferent neuron -> Target cell effector -> Response.

Neuron Components

  • All neurons have:

    • A cell body (also called soma).

    • Tree like dendrites specialized to receive information.

    • An axon: A long, thin fiber that transmits signals away from the cell body to other neurons, muscles, or glands.

Neuron Anatomy

  • Cell body (soma).

  • Dendrites.

  • Axon.

  • Axon terminals.

  • Nucleus

  • Schwann cell

  • Myelin sheath

  • Node of Ranvier

  • Motor End Plate

Interneurons

  • One interneuron connects to another interneuron.

  • Contains Presynaptic cell (GABA) and Postsynaptic cell (Dopamine).

Myelin Sheath

  • Many (but not all) axons are wrapped in a myelin sheath.

  • Myelin sheath: Is derived from glial cells, Speeds up signal transmission along an axon.

  • Degeneration of myelin sheath will lead to:

    • Ineffective signal transmission.

    • Multiple sclerosis.

    • Loss of muscle control.

    • Weakness & paralysis.

    • Vision difficulties.

Symptoms of Multiple Sclerosis

  • Numbness, tingling: 63.5%

  • Cognitive dysfunction: 13.4%

  • Depression: 14.7%

  • Dizziness: 23.2%

  • Vision problems: 40.2%

  • Pain: 19.3%

  • Fatigue: 40.1%

  • Bladder dysfunction: 11.1%

  • Muscle Spasms: 17.2%

  • Bowel dysfunction: 5.7%

  • Weakness: 25.3%

  • Walking difficulty: 48.9%

Axon Terminal & Synapse

  • An axon ends in a terminal button filled with neurotransmitters (a kind of chemical messengers).

  • The connection between two neurons, or a neuron and an effector, is called a synapse.

Measuring Resting Membrane Potential

  • Using a Voltmeter, Microelectrode, and Ground electrode measures about -70 mV.

The Neuron at Rest

  • Reference electrode.

  • Extracellular fluid (0 mV).

  • Cytosol (-70 mV).

  • Recording microelectrode (+70 mV).

Resting Potential

  • The cell membrane of an axon is semipermeable.

  • Na^+ & K^+ are pumped back and forth across the membrane in different rates.

  • The difference in flow rates leads to a slightly higher concentration of negatively charged ions inside the cell.

  • The resting potential of an axon is about -70 millivolts.

The Action Potential

  • When a neuron is stimulated, a brief jump occurs in the neuron’s voltage, a spike is observed on the voltmeter.

  • This sudden change in voltage is called an action potential.

  • An action potential travels along the axon like a spark traveling along a trail of gunpowder.

Action Potential Stages

  1. Resting Potential: Na^+/K^+ pump.

  2. Depolarization: Voltage-gated Na^+ channel.

  3. Repolarization: Voltage-gated K^+ channel.

  4. Resting Potential: Na^+/K^+ pump.

  • Refractory period

Detailed Action Potential Graph

  • Shows membrane potential (mV) over time.

  • Key events: Na+ influx, K+ efflux, threshold, resting potential, hyperpolarization.

Depolarization

  • In myelinated neurons, action potentials occur only in nodes of Ranvier.

  • When a neuron is stimulated, voltage-gated Na^+ channels in its cell membrane open briefly, allowing Na^+ to rush in.

  • The negativity of the membrane potential is reduced (becomes less negative).

  • The membrane is said to be depolarized.

Action Potential Threshold

  • A depolarization between -70 mV and -55 mV has no effect.

  • When the negativity of a membrane potential is reduced to less than -55 mV, an action potential occurs.

Repolarization

  • When the transmembrane potential reaches +35 mV, the voltage-gated Na^+ channels close whereas the voltage-gated K^+ channels open, allowing K^+ to rush out the membrane.

  • The negativity of the membrane potential increases (becomes more negative).

  • The membrane is repolarized.

  • The membrane potential overshoots to nearly -90 mV. At this point, the K^+ channels close.

  • The Na^+ & K^+ pump quickly brings the membrane back to its normal resting potential of -70 mV.

Ion Channel States

  • Resting: Na^+ channels closed, K^+ channels mostly closed.

  • Depolarize: Na^+ channels open, Na^+ rushes in.

  • Repolarize: Na^+ channels close, K^+ channels open, K^+ rushes out.

  • Hyperpolarize: K^+ channels remain open, membrane potential becomes more negative than resting potential.

Absolute vs. Relative Refractory Period

  • Absolutely Refractory Period:

    • After the firing of an action potential, some time is needed before the neuron can fire another action potential.

    • This downtime lasts only 1 to 2 milliseconds.

  • Relatively Refractory Period:

    • During this period, the neuron can fire, but its threshold for firing is elevated.

    • More intense stimulation is required to initiate an action potential.

Refractory Periods and Ion Channels

  • Illustrates how ion channel states (gates) influence the refractory periods.

  • Resting, Depolarize, Repolarize, Hyperpolarize.

The All-or-None Law

  • The neural impulse is an all-or-none proposition.

  • The neuron either fires or does not fire.

  • When it fires, the action potentials are all the same size.

  • Weaker stimuli do not produce smaller action potentials.

  • The strength of a stimulus is not conveyed as the size of an action potential, but as the rate of firing.

  • A stronger stimulus will cause a neuron to fire more frequently than a weaker stimulus.

  • Thicker axons transmit neural impulses more rapidly than thinner ones do.

Synaptic Transmission

  • A synapse is a connection between an end foot of the axon of one neuron and a dendritic spine of the other neuron.

Steps of Synaptic Transmission

  1. Action potentials arrive at axon terminal.

  2. Voltage-gated Ca^{2+} channels open.

  3. Ca^{2+} enters the cell.

  4. Ca^{2+} signals to vesicles.

  5. Vesicles move to the membrane.

  6. Docked vesicles release neurotransmitter by exocytosis.

  7. Neurotransmitter diffuses across the synaptic cleft and binds to receptors.

Neurotransmitter Dynamics

  • Some neurotransmitters are taken back into the axon terminal whereas others are deactivated.

Postsynaptic Effects

  • Excitatory transmitters cause depolarization.

    • Inside of a receiving neuron becomes more positive.

    • Increases the likelihood of an action potential.

  • Inhibitory transmitters cause hyperpolarization.

    • Inside of a receiving neuron becomes more negative.

    • Decreases the likelihood of an action potential.

Convergent Synaptic Transmission

  • A postsynaptic neuron receives signals from multiple presynaptic neurons.

  • Some signals are excitatory (positive); some are inhibitory (negative).

  • The summation of the strengths and directions of these signal will produce a graded (not all-or-none) postsynaptic potential.

The Postsynaptic Potentials

  • When a neurotransmitter and a receptor molecule combine, reactions in the cell membrane cause a postsynaptic potential (PSP), a voltage change at a receptor site on a postsynaptic cell membrane.

  • Postsynaptic potentials (PSP) are graded (not all-or-none) because it is a summation of many signals from the pre-synaptic neurons.

  • The size and direction of a PSP will increase or decrease the probability of a neural impulse in the receiving cell.

    • Excitatory PSP (overall positive).

    • Inhibitory PSP (overall negative).

PSP vs. Action Potential

  • Illustrates the differences in voltage change over time.

  • Action potential has a threshold and refractory period.

  • Postsynaptic potential is graded and summative.

Excitatory & Inhibitory PSP

  • Excitatory PSP (EPSP):

    • Positive voltage shift.

    • Increases the likelihood that the postsynaptic neuron will fire action potentials.

  • Inhibitory PSP (IPSP):

    • Negative voltage shift.

    • Decreases the likelihood that the postsynaptic neuron will fire action potentials.

Neurotransmitters and Their Functions

  • Acetylcholine (ACh): Enables muscle action, learning, and memory; Undersupply, as ACh-producing neurons deteriorate, marks Alzheimer's disease.

  • Dopamine: Influences movement, learning, attention, and emotion; Excess dopamine receptor activity linked to schizophrenia; starved of dopamine, the brain produces the tremors and decreased mobility of Parkinson's disease.

  • Serotonin: Affects mood, hunger, sleep, and arousal; Undersupply linked to depression; Prozac and some other antidepressant drugs raise serotonin levels.

  • Norepinephrine: Helps control alertness and arousal; Undersupply can depress mood.

  • GABA (gamma-aminobutyric acid): A major inhibitory neurotransmitter; Undersupply linked to seizures, tremors, and insomnia.

  • Glutamate: A major excitatory neurotransmitter; involved in memory; Oversupply can overstimulate brain, producing migraines or seizures (which is why some people avoid MSG, monosodium glutamate, in food).

  • You need to know only the functions and malfunctions of dopamine and serotonin.

Agonists vs. Antagonists

  • Agonist: A drug that mimics or enhances the effect of a neurotransmitter.

    • Increase neurotransmitter production.

    • Block reuptake.

    • Mimic neurotransmitter by binding to postsynaptic receptors.

  • Antagonist: A drug that blocks or reduces the effect of a neurotransmitter.

    • Decrease neurotransmitter production.

    • Destroy neurotransmitters in the synapse.

    • Block neurotransmitter binding to receptors.

Dopamine Hypothesis of Schizophrenia

  • Some forms of schizophrenia may be related to excessive dopamine activity.

  • Amphetamine and cocaine create schizophrenia-like symptoms by increasing dopamine activity at the dopamine synapses.

Examples of Agonist and Antagonist

  • Agonist: A drug that mimics or enhances the effect of a neurotransmitter (e.g., amphetamine & cocaine).

  • Antagonist: A drug that blocks or reduces the effect of a neurotransmitter (e.g., Chlorpromazine - used to reduce symptoms of schizophrenia).

Split Brain

  • Splitting the Brain Splits the Mind

  • Severing the corpus callosum affects communication between hemispheres.

Cerebral Cortex

  • Cerebral Hemispheres: Left and Right.

  • Corpus Callosum: The nerve fibers that enable communication between the two hemispheres.

Split Brain Patients of Michael Gazziniga

  • With the corpus callosum severed, objects (apple) presented in the right visual field can be named.

  • Objects (pencil) in the left visual field cannot.

Split-Brain Experiment Procedure

  • Two pictures were flashed on a screen briefly and simultaneously.

  • The experimenter asked: “What did you see?”

  • The subject typically answered: “I saw a fork.”

  • Could the person see the spoon? The subject reported verbally that he could not see the object flashed on the left visual field.

Split-Brain Interpretation Experiment

  • The left hemisphere did not see the snow scene. It interpreted the left hand’s response based on what it could see—in this case, the body parts of a chicken.

Conclusion

  • Brain and Behavior” or “the biological bases of behavior” is a research area that supports the philosophical viewpoint of materialism.

  • Materialism holds that behavior can be fully explained by the working of the brain and the rest of the nervous system, without any need to refer to the mind.

  • However, “behavior” in this research area is defined as “any kind of movement in a living organism” (e.g., reflexive movement of the hand in humans, withdrawal of the gill in a marine creature).

Textbook Readings

  • For both the 6th and the 7th editions, read sections 3.1, 3.2, 3.3, & 3.6