AP Notes
Biological Bases of Behavior
Module 4: Neural Processing & the Endocrine System
Keep in mind that the following units will also rely heavily on a thorough understanding of bases of behavior:
Unit: Sensation & Perception
Unit: States of Consciousness
Unit: Memory
Unit: Emotions, Stress & Health
Unit: Abnormal Psychology
Unit: Treatment of Psychological Disorders
While there are no prominent names featured in this unit, one key study you may want to be familiar with in order to
appreciate the science of behavior & mental processes was conducted in 1972. Rosenzweig, Bennet, and Diamond
conducted research with rats that showed that enriched environments contributed to more complex neuronal
connections in the cortex. This study shows that neural complexity could be influenced by environment factors, showing
how nature and nurture interact.
**This unit is organized form a micro level (neuron) to a macro level (nervous/endocrine system). If you can keep this in
mind, it will be easier to keep the information straight.
Neuroglia are another category of neural cells that provide the support network of cells surrounding the neurons and
blood vessels of the brain and nervous system. They are thought to outnumber typical neurons 10 to 1. There are three
types of neuroglia in the body:
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Oligodendroglia are cells found in the central nervous system (CNS) that produce myelin, a protective covering of
axons that speed neural transmissions.
Schwann cells perform the same function as oligodendoglia, but are found in the peripheral nervous system
(PNS). Aside from location, the main difference between Schwann cells and oligodendroglia is that only Schwann
cells can help axons regenerate.
Astrocytes are the star-shaped and form most of the matrix in which neural cells are embedded and envelop
blood vessels in the brain. They also absorb dead neural cells.
Many students often fail to appreciate the complexity of the neural network in the nervous system. The neural chain
presented in your text is the simplest way neurons communicate. For the vast majority of the nervous system, multiple
neurons connect with each other, creating a complex network capable of almost endless combinations of neurons
communicating. Please keep in mind that this simple presentation does not capture the true complexity of neural
communication.
The following explanations may help you to better understand the concept of action potential:
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Ions have a charge, either positive or negative. When these particles move, they create electricity, which is what
action potential is.
The natural tendency for matter is to move from a more crowded situation to a less crowded situation. The
neuron is packed with negatively charged ions, with positively charged ions packed on the outside of the cell.
The neuron’s membrane is normally impermeable, but neurotransmitters weaken it, allowing the ions to move
according to the principle above.
Demo: flushing toilet!! I will explain in class—but it will exemplify: all-or-none law, threshold, refractory period
The sodium-potassium pump is the mechanism by which ions are allowed to pass through the membrane of the neural
cell. Named for the two primary elements present in the ion exchange, this pump brings positively charged ions into the
cell & then pumps them back out when the action potential is over. This term may show up on the AP Exam.
ANALOGY: POTATO CHIP—again I WILL explain in class!!
The importance of the myelin sheath cannot be emphasized enough. Myelin, produced by glia cells, helps make neural
communication more efficient. Without myelin, neurons would not communicate as quickly, making behavior and mental
processes occur more slowly or perhaps not occur at all. Multiple sclerosis is a disorder in which myelin is attacked by the
body’s immune system, and people who have this disorder find movement increasingly difficult.
The Nodes of Ranvier are the spaces in between the myelin cells that encircle the axon. These spaces are important to
keeping the charge going through the relatively long axon. Without these spaces, the charge might lose its intensity
before reaching the end of the cell.
Neurotransmitter (I refer to as neuro-ts (!)) are the key component for all behavior and mental processes. The
neurotransmitters carry the messages for all that we do. Neuro-ts send messages to be happy or sad, to move or to stay
still. Neuro-ts can function differently depending on where they are located in the nervous system. Scientists are still
discovering how these chemicals work, so you should be aware that the information in this unit in now is comprehensive
or definitive—it’s the tip of the iceberg!!
From the diagram on How neurons communicate (4.3), it may seem that only one neuron and one neuro-t act on each
synapse. However, some neurons can house more than one neuro-t, and usually more than one neuron is present at any
given synapse. This diagram is intentionally simplified to help communicate the basic idea of the process involved in
neural communication, but that the reality is amazingly complex.
The function of the neuro-t depends on which part of the brain it acts upon:
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If the neuro-t is acting in the brainstem, it affects basic functions like breathing & heartbeat.
If it acts on areas in the midbrain, it affects functions like memory & emotion.
Finally, if it acts on areas in the cortex, higher functions like memory integration, problem solving & perception
are affected
If you can see this hierarchical organization of the brain & how neur-ts play a role in that will help you gain a better
understanding of neuroanatomy.
(Another fact—not on AP test, but this is MY favorite unit!!, myasthenia gravis is a neurological disorder resulting
from the depletion of acetylcholine. Without ACh, the muscles do not move properly. People with this disorder
experience extreme fatigue since it takes enormous effort to move muscles at all)
Each of the neuro-ts featured in Table 4.1 is chemically similar to a drug or other chemical that affects behavior,
cognition, and emotion. Here are some similarities the chart does not point out:
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Dopamine is similar to cocaine.
Serotonin is similar to LSD and Ecstasy.
Just as our bodies produces its own painkillers, so too, does it produce the chemicals necessary for energy,
euphoria, and even hallucinations. In healthy people, these chemicals are balanced to produce normal
experiences. Taking illegal or non-prescribed drugs disrupts this balance, causing abnormal levels of energy,
emotion, and sensor experience.
Another neuro-t not described in the table is Substance P, the body’s pain neuro-t. It works in opposition with endorphins
to regulate pain. Substance P signals that the body is in pain, and endorphins are triggered to inhibit the pain signal.
Also VERY important is understanding the difference between agonist and antagonist when these terms pertain to drugs.
These terms are often confused, so knowing them will help you if they show up on the AP Exam—which they have!!
(English teacher mode—think of antagonist like the literature term!!)
In order for drugs to have an effect on the body, there must be an accompanying receptor site on a neuron that matches
the structure of that drug. So the body produces naturally chemical substances that are similar to many of the drugs that
affect the body. When we introduce drugs into our bodies, we are either increasing the amount of these substances in
the body or blocking substances that are supposed to work in a specific way.
But not all substance can pass through the body’s blood-brain barrier, which protects the brain from pathogens
and harmful substances. For example, Parkinson’s patients cannot simply take dopamine to alleviate their symptoms.
They must take a precursor of dopamine called L-dopa that will metabolize into dopamine once it reaches the brain.
Some people (hopefully not those of you who took Anatomy!) have trouble understanding that the nervous system is an
integrated network. The divisions discussed in this mod were created to recognize the executive function of the brain &
spinal cord and the delivery function of the peripheral nerves. These two systems work seamlessly together, even though
they have been separated here to understand them better.
The autonomic nervous system is a key player for emotions, STRESS, & health. The “fight or flight” response is governed
by the autonomic ns (nervous sys.), and this response plays a role in how we respond to stress or environmental cues
(unfortunately, as we’ll discuss, as the human species has evolved, this system remains the same from our hunter &
gather days which does not correspond to our modern lives & chance of being pounced on by a large predatory animal!).
Therapeutic processes, discussed in Modules 48 like biofeedback, relaxation & systematic desensitization use knowledge
of how this system works to treat mood & anxiety disorders.
Be sure to remember the difference between the nervous systems with these mnemonics:
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Central Nervous System (CNS): the brain & spinal cord are located in the CENTER of the body.
Peripheral Nervous System (PNS): fingers and toes lie in the outermost areas of the body from the center, or the
PERIPHERY of the body.
Somatic Nervous System (SNS): volunteer work is done by choice, so the body’s or SOMA’S (Greek for body!!)
voluntary actions are controlled by this nervous system.
Autonomic Nervous System (ANS): AUTONOMIC sounds similar to the word AUTOMATIC, and the body’s
automatic actions (breathing, heartbeat, etc.) are controlled by this nervous system.
The sympathetic and parasympathetic nervous systems together make an opponent process system. Opponent
processes work in opposition of each other, with one system performing the exact opposite role. In this case, the
sympathetic nervous system causes the body to rise to the challenge it faces and the parasympathetic nervous system
causes the body to calm after the challenge has been addressed. This opposition creates homeostasis, or balance in the
body.
Remember what the sympathetic nervous system does by thinking about what we do when we feel SYMPATHY—we try
to help actively be comforting and consoling others. We have to act to help others, so the sympathetic nervous system
will kick in, giving us the energy we need to accomplish our goals.
The dendrites of neurons contribute significantly to the complexity of the neural network. The more dendrites a neuron
has, the greater the # of connections that one neuron can make with other neurons, increasing the likelihood its message
will get passed along this change.
Sensory neurons connect to the spinal cord dorsally, or in the back. Motor neurons connect in the anterior of the spinal
cord, or in the front. Therefore, it is possible to lose feeling in lower portions of the body in a spinal cord injury but retain
the ability to move if the spinal cord is not completely severed.
Have you ever jerked away from a hot surface only to feel the burn after a delay? Interneurons make reflexes happen.
These cells in the spinal cord process motor responses quickly to protect the body from harm. Without interneurons, you
would experience severe burns if you left your hand on that hot surface long enough to process both the heat and the
pain before jerking away!
The movement for reflexes occurs before the brain has a chance to process the incoming sensory information. Reflexes
enable us to respond to stimuli before they have a chance do us harm. It’s almost as if the spinal cord is a brain itself,
having the ability to process danger before the brain has to do so.
Some important endocrine glands and the hormones they secrete are listed below:
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Anterior pituitary: secretes growth hormone. Too little produces dwarfism; I think you can figure out what too
much does!
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Posterior pituitary: secretes vasopressin and oxytocin. Vasopressin constricts blood vessels thereby raising blood
pressure. Oxytocin in women sparks labor during pregnancy, will discuss more in class.
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Thyroid: releases thyroxine and triiodothyronine, increasing metabolic rate growth & maturation, will discuss
more in class.
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Parathyroids: release parathyroid hormone, increasing blood calcium & decreasing potassium—vital to heart &
nerve functioning.
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Pancreas: secrets insulin, regulating the level of sugar in the bloodstream, will also discuss more in class.
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Ovaries: secrete estrogen, promoting ovulation & female sexual characteristics.
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Testes: release androgens, promoting sperm production & male sexual characteristics.
Exocrine glands secrete substances outside the body. Examples include salivary glands, tear glands & sweat glands.
Endocrine means “within”; endocrine glands secrete from within the body into the bloodstream.
You need to realize that hormones and neuro-ts are the same. They are only different based on where they are
manufactured and located in the body. Neuro-ts are manufactured in neurons & other nervous system cells and located
w/in the nervous system, while hormones are manufactured by glands & based in the body and the bloodstream.