1. Neuroscience: The Biology of Behavior
Chapter 3
Neuroscience: The Biology
of Behavior

2. Objectives
3.1 Overview: The Components of Biological Bases of Behavior
Describe how neuropsychology and neuroscience relate to the study of psychology.
Explain how the nervous system conducts signals to and from various parts of the body and brain.
3.2 Neural Communication
Identify the structural elements of the nervous system.
Recognize the types and structure of neurons.

3. Objectives 3.3 Nervous System Organization
Compare and contrast the peripheral nervous system and the central nervous system.
3.4 The Brain
Identify the different areas of the brain and the functions they control.

4. Objectives 3.5 The Endocrine System
Discuss the role of endorphins and the endocrine system as communication mechanisms in the nervous system.
3.6 Genetics
Discuss the role of genetics in psychology.

5. The Components of Biological Bases of Behavior
Neuropsychology: Studies the connection between neuroscience (the study of the brain and the nervous system) and bodily systems and behavior
Links the physical body with behavior
Explains how the brain processes thoughts/emotions
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Chapter 3: Neuroscience: The Biology of Behavior
3.1 Overview: The Components of Biological
Bases of Behavior
LO: Describe how neuropsychology and neuroscience relate to the study of psychology.
You cannot study much psychology without some understanding of biology. Biological psychology - also called neuropsychology-, is the branch of psychology that studies the connection between neuroscience (the study of the brain and the nervous system). Neuropsychology helps to link the physical body with explanations for behavior on many different levels and can help us understand how the brain processes our thoughts and emotions, as well as how our emotions are linked to the body’s physical sensations.

6. Nervous System
A collection of organs including neurons and supportive systems; consists of all the neurons in the central and peripheral nervous system
Neuron: A nerve cell
Hormones: Chemical messengers that are produced by endocrine glands
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Chapter 3: Neuroscience: The Biology of Behavior
3.1 Overview: The Components of Biological
Bases of Behavior
LO: Describe how neuropsychology and neuroscience relate to the study of psychology.
Neuroscientists are most interested in the nervous system , a network of organs, nerves, and supportive systems that send and receive neural signals to and from various parts of the body. Its main job is communication. The several million signals that the nervous system sends and receives every minute are electrochemical activity. The nervous system’s power and complexity lie in the many ways these signals are processed. Communication within the nervous system generally occurs through messages between neurons, or nerve cells, which act as instant messengers, delivering signals that activate or deactivate parts of the nervous system. Communication also occurs through long-distance messengers, such as hormones, that communicate with areas of the body beyond the nervous system. The central hub of activity, is in the brain.

7. Glia Support and protect neurons
Compose approximately 50% of the total volume of the brain
Manage and organize the nervous system by directing where neurons grow
Control how neurons communicate and connect
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Chapter 3: Neuroscience: The Biology of Behavior
3.2 Neural Communication
LO: Identify the structural elements of the nervous system
Nervous system cells fall into two major categories: glia and neurons. Glia are cells of the nervous system that support and protect neurons. Although smaller than neurons, glia are more numerous, making up about 50% of the total volume of the brain. They also manage and organize the nervous system by directing where neurons grow. They send survival signals to some neurons and perish signals to others to direct neural pruning to increase the processing speed of the nervous system. Glia also play a role in controlling how neurons communicate and forming connections between neurons. In addition, some recent research suggests that glia might send communication signals of their own.

8. Neurons Neurons communicate information throughout the nervous system.
Interneuron: A neuron that communicates only with other neurons
Afferent nerve fibers: Neurons that move information toward the brain and spinal cord
Efferent nerve fiber: A type of neuron that carries impulses away from the central nervous system
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Chapter 3: Neuroscience: The Biology of Behavior
3.2 Neural Communication
LO: Recognize the types and structure of neurons.
Neurons, or nerve cells, are the basic cells of the nervous system. Groups of neurons form nerve fibers that communicate information throughout the nervous system. Many neurons communicate with other types of cells throughout the body, such as muscle cells or gland cells. Most neurons are interneurons that communicate only with other neurons to help you do all that you do each moment of the day. Certain neurons are specialized. In the same way veins move blood away from the heart and arteries move it back, afferent nerve fibers move information toward the brain and spinal cord, and efferent nerve fibers carry impulses away from the brain and spinal cord.

9. Types of Neurons
Sensory neuron: A neuron that is responsible for carrying external stimuli to the central nervous system for processing
Motor neuron: A type of neuron that interfaces with muscles and glands
Mirror neuron: A type of neuron that fires when an individual watches an action and when performing the action
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Chapter 3: Neuroscience: The Biology of Behavior
3.2 Neural Communication
LO: Recognize the types and structure of neurons.
Different neurons are used to perform simple physical tasks. Sensory neurons, a type of afferent nerve fiber, translate external stimuli into messages to be sent to the central nervous system for processing. Motor neurons are efferent nerve fibers that send messages to muscles and glands. Mirror neurons are active both when you perform a task yourself and when you watch another person perform an action.

10. The Structure of a Neuron (slide 1 of 3)
Dendrite: A nerve cell structure that receives information from other cells
Soma: The part of the neuron that keeps the cell alive and contains the genetic material for the cell
Axon: The part of the neuron that carries the nerve impulse away from the soma
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Chapter 3: Neuroscience: The Biology of Behavior
3.2 Neural Communication
LO: Recognize the types and structure of neurons.
Most neurons have a few things in common: dendrites, a soma, and an axon. Dendrites are the nerve cell structures that receive messages from other neurons. They look a little like tree roots and funnel messages from other neurons to the soma, or cell body. The soma is the central part of the neuron. It keeps the cell alive and contains the genetic material for the cell. The axon is a long tubelike structure that carries the message away from the soma on its way to another neuron. Although axons are infinitesimally narrow, some are also infinitesimally short, while others, such as those between your spine and your toes, extend several feet.

11. The Structure of a Neuron (slide 2 of 3)
Nerves - Bundles of neurons.
Myelin sheath - A fatty substance that insulates the axon and enables efficient transmission.
Axon terminal -The part of the neuron that discharges and recycles also called the terminal button.
Terminal button - The part of the neuron that discharges and recycles neurotransmitters also called the axon terminal.
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Chapter 3: Neuroscience: The Biology of Behavior
3.2 Neural Communication
LO: Recognize the types and structure of neurons.
As a collection, the axons of neurons form cable-like bunches in the peripheral nervous system called nerves. To keep the message moving smoothly, glial cells envelop a neuron’s axon in a white fatty substance. This myelin sheath insulates and enables efficient communication along the axon. The myelin sheath also divides axons into little capsule-like sections. At the very end of the axon is the axon terminal, sometimes called the terminal button or terminal end bulb.

12. Neurotransmitters and Synapses
Neurotransmitters: Chemical messengers that transmit information from one neuron to another
Synapse: An area that includes three structures:
presynaptic neuron: The terminal button of the sending neuron
synaptic gap/cleft: The space between one neuron and the next
postsynaptic neuron: The receptor sites on dendrite of the receiving neuron
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Chapter 3: Neuroscience: The Biology of Behavior
3.2 Neural Communication
LO: Recognize the types and structure of neurons.
Although the billions of neurons are in constant communication with each other, they do not touch to communicate. Instead they use (and recycle) chemicals to bridge the incredibly tiny space between one neuron and the next. Neurons communicate messages by discharging neurotransmitters. These are molecules that act as chemical messengers that transmit, messages from one neuron to the next. Neurotransmitters can directly or indirectly influence neurons in particular areas of the brain and therefore affect behavior.
The space between neurons is part of an area called the synapse. The synapse consists of three parts: the terminal button of the sending or presynaptic neuron; the space between one neuron and the next (called the synaptic gap or synaptic cleft); and the receptor sites on the dendrites of the receiving or postsynaptic neuron.

13. Action Potentials
Depolarize: The process by which an axon becomes more positive
All-or-none law: The concept that either a neuron fires or it doesn’t.
Repolarize: The process by which a neuron’s axon will return to the resting potential
Absolute refractory period: The point after an action potential when the neuron cannot produce another action potential no matter the intensity of the stimulation
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Chapter 3: Neuroscience: The Biology of Behavior
3.2 Neural Communication
LO: Recognize the types and structure of neurons.
When a neuron is stimulated to fire, potassium channels in the first section of the axon close. Then sodium rushes into the axon and causes this section to depolarize (become more positive), which generates an action potential. Once the action potential starts hurtling down the axon, it maintains the same strength and cannot be stopped. This is called the all-or-nothing law, because an action potential either happens or it doesn’t. The action potential continues hurtling down the axon, changing the polarity of each axon section as it passes through. Once the action potential has passed, the opened channels in the axon’s membrane close, and that section of the axon repolarizes and returns to the resting potential. This reset period is called the absolute refractory period. It is the point after an action potential when the neuron cannot produce another action potential, regardless of the intensity of the stimulation. The absolute refractory period ensures that the action potential flows only in one direction.

14. Action Potentials
Synaptic vesicle: A sac that contains neurotransmitters in the axon terminal
Receptor site: An area on the dendrite that receives neurotransmitters
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Chapter 3: Neuroscience: The Biology of Behavior
3.2 Neural Communication
LO: Recognize the types and structure of neurons.
When the action potential reaches the axon terminal, it ends at synaptic vesicles (small sacs that contain the neurotransmitters), floating down to the very end of the axon terminal. There, the synaptic vesicles fuse with the terminal button. At this point, the neurotransmitters spill out into the synaptic gap where they bounce around. Some find their way to another neuron’s receptor sites. Receptor sites, located on the neuron’s dendrites, are areas that receive neurotransmitters. There, the neurotransmitters from the sending neuron bind with the receiving neuron’s receptor site and deliver the message to fire or not fire.

15. Postsynaptic Potential
Postsynaptic potential: Changes in the dendrite of the receiving neuron as the result of its binding with neurotransmitters
Excitatory Postsynaptic Potential: Causes a positive voltage shift in the resting potential of the postsynaptic neuron, triggering the neuron to fire.
Inhibitory Postsynaptic: Causes a negative voltage shift in the resting potential of the postsynaptic neuron, preventing the neuron from firing.
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Chapter 3: Neuroscience: The Biology of Behavior
3.2 Neural Communication
LO: Recognize the types and structure of neurons.
Once the neurotransmitter binds to the postsynaptic neuron’s receptor site, it can help change the voltage of the postsynaptic neuron. The postsynaptic neuron will reach its stimulus threshold, the point at which it responds by changing its voltage. This change in voltage is called a postsynaptic potential (PSP. The postsynaptic neuron may generate an action potential of its own, in which case the entire process repeats itself, and the postsynaptic neuron becomes a presynaptic neuron. There are two kinds of PSPs: excitatory and inhibitory. Excitatory postsynaptic potentials (EPSPs) cause a positive voltage shift in the resting potential of the next (postsynaptic) neuron. This triggers the channels in the axons to open and depolarize them, causing the neuron to fire. Inhibitory PSPs (IPSPs) cause a negative voltage change and make the resting potential even more negative. In this case, the neuron does not fire. It may take even more stimulation for the neuron to fire because the current resting potential may be below its usual −70 millivolts.
Postsynaptic neurons do not absorb or pass on the neurotransmitters that they receive and that bind with them so they need to either be discarded or used. Some neurotransmitters get metabolized by an enzyme called monoamine oxidase (MAO), while some others get recycled and repackaged into new synaptic vesicles by transport proteins located on the presynaptic terminal buttons. This process of reabsorbing the neurotransmitters into a presynaptic neuron is called reuptake.

16. Neural Networks
Synaptic Pruning:- The destruction of less active synapses to organize an improve efficiency of the neural connections
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Chapter 3: Neuroscience: The Biology of Behavior
3.2 Neural Communication
LO: Recognize the types and structure of neurons.
The nervous system forms more synapses than it needs, so, over time, it gradually gets rid of the less active synapses. This is referred to as synaptic pruning. Getting rid of less active connections helps to organize and improve the efficiency of the whole system. In fact, neural networks peak when a person is one year old and then begin their decline.

17. Central Nervous System
The central nervous system consists of:
Spinal cord - a collection of neurons that run from the base of the brain and down your back, protected by a spinal column
Brain
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Chapter 3: Neuroscience: The Biology of Behavior
3.3 Nervous System Organization
LO: Compare and contrast the peripheral nervous system and the central nervous system
The central nervous system consists of the brain and spinal cord, and it has a support system of its own. In addition to the bony skull and spinal column, the central nervous system is protected by cerebrospinal fluid (CSF), a clear liquid created in the brain’s ventricular system that supports and protects the central nervous system. The spinal cord is a collection of neurons that run from the base of the brain and down the back and is protected by a spinal column. The spinal cord can initiate actions all by itself. These reflexes, or involuntary motor responses, coordinated by the spinal cord are known as spinal reflexes.

18. Studying the Brain (slide 1 of 3)
Electrical stimulation: A technique used to stimulate neural networks in the nervous system (also known as deep brain stimulation)
Transcranial magnetic stimulation (TMS): A procedure that uses electromagnetic coils to activate nerve cells in the brain
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Chapter 3: Neuroscience: The Biology of Behavior
3.4 The Brain
LO: Identify the different areas of the brain and the functions they control.
The brain is an amazing organ. Weighing in at only 3 pounds, it packs in trillions of glial cells and 100 billion neurons. The brain uses about 20% of all the oxygen breathed in every day. It is staggeringly complex. Currently, there are a number of sophisticated technologies to study and treat the brain. Electrical stimulation is a technique used to stimulate neural networks in the nervous system. Also known as deep brain stimulation, it uses electrical signals to trigger areas of the brain. Transcranial magnetic stimulation (TMS) uses magnetic fields generated by electromagnetic coils to activate nerve cells in the brain. TMS can be used to activate or momentarily depress or deactivate activity in a specific area of the brain.

19. Studying the Brain (slide 2 of 3)
Electroencephalograph (EEG): A device that measures the electrical activity in the brain
Computerized tomography (CT): Uses computer enhanced X rays that are helpful at examining brain structures. Also called CT scans
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Chapter 3: Neuroscience: The Biology of Behavior
3.4 The Brain
LO: Identify the different areas of the brain and the functions they control.
The electroencephalogram (EEG) is a device that measures the electrical activity in the brain. Using electrodes on the scalp, the machine records the electrical activity or brain waves produced by the action potential of the neurons. These brain waves produce distinct images that can be analyzed. Computerized tomography scans (CT scans), another neuroimaging technique, are computer-enhanced X-rays and are good at examining structures.

20. Studying the Brain (slide 3 of 3)
Positron emission tomography (PET): Uses radioactive glucose to indicate areas of activity
Magnetic resonance imaging (MRI): Uses magnets and radio equipment to produce detailed images
Functional magnetic resonance imagining (fMRI): used to measures changes in blood flow
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Chapter 3: Neuroscience: The Biology of Behavior
3.4 The Brain
LO: Identify the different areas of the brain and the functions they control.
Positron emission tomography (PET scan), is a neuroscience imaging technique that uses radioactive glucose to indicate areas of activity. Patients are injected with glucose tagged with small amounts of radiation. The PET scan examines areas of the brain that are using more energy.
Magnetic resonance imaging (MRI) is a noninvasive imaging technique that uses magnets and radio equipment to produce detailed images. MRIs are good at producing details of soft tissue. Functional magnetic resonance imaging (fMRI) is like MRI but can examine brain activity over time.

21. The Hindbrain
The hindbrain is a central intersection for nerves that come up through the spinal cord and consists of:
The medulla
The pons
The reticular activating system (RAS)
The cerebellum
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Chapter 3: Neuroscience: The Biology of Behavior
3.4 The Brain
LO: Identify the different areas of the brain and the functions they control.
The brainstem connects the spinal cord to the rest of the central nervous system and houses many structures needed for survival. It consists of hindbrain and midbrain structures. The hindbrain is a central intersection for nerves that come up through the spinal cord. Its structures support vital bodily processes. Nerves cross over from left to right in the hindbrain. The hindbrain contains four important structures:
The medulla is the part of the hindbrain involved in breathing, heartbeat, and other essential functions. It also coordinates certain reflexive behaviors such as swallowing, coughing, vomiting, and sneezing.
The pons is the part of the hindbrain that is involved in relaying messages from the cerebral cortex and is involved in sleep and arousal.
The reticular activating system (RAS), or the reticular formation, is a network of nerve fibers critical in sleep and wakefulness. It also helps you filter out or ignore what is not important to focus on.
The cerebellum is a part of the hindbrain involved in the development and coordination of movement. About the size of two golf balls, it has a role in balance and muscle movement. It is also responsible for coordinating rhythm timing,

22. The Midbrain
Midbrain: Part of the brainstem involved in control of sensory processes
Substantia nigra: A midbrain structure that is responsible for initiation of movement
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Chapter 3: Neuroscience: The Biology of Behavior
3.4 The Brain
LO: Identify the different areas of the brain and the functions they control.
The midbrain is a major relay station for processing auditory and visual information. It is also helpful in tracking movements. An important midbrain structure is the substantia nigra, a term that means dark substance, so named because of its dark color, the substantia nigra is responsible for the initiation of movement.

23. Forebrain
The forebrain is the largest part of the brain and consists of:
The thalamus
The hypothalamus
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Chapter 3: Neuroscience: The Biology of Behavior
3.4 The Brain
LO: Identify the different areas of the brain and the functions they control.
The forebrain is the largest part of the brain, and consists of the thalamus, the hypothalamus, the limbic system, and the cerebrum.
The thalamus is a major relay station for all sensory information (except smell). It acts like a router, sorting and distributing information to other areas of the brain. In addition to this sorting function, the thalamus plays a role in how we notice and react to the sensations around us.
The hypothalamus detects need states and drives such as the fight-or-flight response and hunger. The hypothalamus controls the autonomic nervous system and pituitary hormone production. It also controls blood flow and regulates metabolic activity and reproductive activity. It helps us coordinate our responses to threats by releasing stress hormones and helps us balance the influence of our sympathetic and parasympathetic nervous systems.

24. Forebrain: Limbic System
The limbic system is a group of structures surrounding the brainstem that governs emotions
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Chapter 3: Neuroscience: The Biology of Behavior
3.4 The Brain
LO: Identify the different areas of the brain and the functions they control.
The limbic system is a group of structures surrounding the brainstem that governs emotions. It also stores and retrieves new memories. Although the limbic system has many structures, we’ll look at just two: the amygdala and the hippocampus.
The amygdala is a cluster of neurons in an area of the brain called the temporal lobe. Neurons in the amygdala are linked to emotions such as anger and fear. The amygdala integrates the emotional significance of sensory stimuli and guides our behavior.
The hippocampus is part of the limbic system that is involved in processing new memories.

25. Cerebrum and Cerebral Cortex
The cerebrum is the area most responsible for thinking and language.
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Chapter 3: Neuroscience: The Biology of Behavior
3.4 The Brain
LO: Identify the different areas of the brain and the functions they control.
The cerebrum is the area most responsible for thinking and language. It is the largest part of the forebrain and is involved in complex cognitive functioning. Containing about 90% of the brain’s volume, the cerebrum is only about ¼ of an inch thick. Its hills (gyri) and valleys (sulci) make it more compact. Without this folding, the cerebrum would be about 3 feet wide by 3 feet long. The cerebrum consists of 2 hemispheres (left and right), each of which contains 4 lobes. The 2 hemispheres are connected by a dense network of nerve fibers called the corpus callosum.
When we picture a brain, the image most of us have is of the cerebral cortex, the outside layer of the cerebrum. The cerebral cortex is the rounded mass of “gray matter” just beneath the skull. There are 4 lobes in each hemisphere of the cerebral cortex. Each lobe has been linked to different tasks:
The occipital lobes are in the rear of the cerebral cortex. At the very back of the occipital lobes is the visual cortex, which processes image information.
The temporal lobes are near the temples and contain the primary auditory cortex, which processes sounds.
The frontal lobes are at the front of the cerebral cortex and play a role in personality, organization, and planning. The frontal lobes also contain the motor cortex, an area that has a role in planning, controlling, and executing movements.
The parietal lobe is located behind the frontal lobe, at the top of the head. It contains the somatosensory cortex, which processes body sensation information such as texture, warmth, weight, and how things feel. The parietal lobes also contain association areas that are critical in the integration of information.

26. Hemispheres
The cerebrum’s hemispheres, left and right, are sometimes referred to as the left brain and right brain.
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Chapter 3: Neuroscience: The Biology of Behavior
3.4 The Brain
LO: Identify the different areas of the brain and the functions they control.
The cerebrum’s hemispheres, left and right, are sometimes referred to as the left brain and right brain. Each hemisphere is divided into the four lobes. These cerebral hemispheres operate relatively independently even though they are connected by the corpus callosum. This highway of nerve fibers allows the hemispheres to be in constant contact with each other.

27. Plasticity
Plasticity: The ability of the nervous system to adapt by creating new neural pathways
Structural plasticity: The brain’s ability to change in response to the environment
Functional plasticity: The capacity to change areas of the brain that are responsible for activities
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Chapter 3: Neuroscience: The Biology of Behavior
3.4 The Brain
LO: Identify the different areas of the brain and the functions they control.
The nervous system has an astounding ability to grow and adjust. Plasticity refers to the ability of the nervous system to adapt by creating new neural pathways. The idea that certain areas of the brain are responsible for specific processes is known as cortical localization. Because of this, scientists can predict what kind of problems a person might have due to damage to certain brain areas. The nervous system can also change and grow.
Structural plasticity is the brain’s ability to change in response to the environment.
Functional plasticity is the capacity to change areas of the brain that are responsible for activities.

28. The Endocrine System (slide 1 of 2)
The endocrine system is a separate and slower communication system that uses hormones, chemical messengers released into the bloodstream
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Chapter 3: Neuroscience: The Biology of Behavior
3.5 The Endocrine System
LO: Discuss the role of endorphins and the endocrine system as communication mechanisms in the nervous system.
While neurotransmitters work at the synapse level, other communication mechanisms transfer messages over much greater distances and over longer periods of time. The endocrine system is a separate and slower communication system that uses hormones, chemical messengers released into the bloodstream. By releasing hormones into the bloodstream, the endocrine system can exert influence not only from long distances but for a long period of time. These chemicals can also function as or influence neurotransmitters. The endocrine system and nervous system are linked via the hypothalamus and pituitary gland for communication. The endocrine system relies on the brain’s hypothalamus to regulate the production and release of hormones. It is the hormone control center for the rest of the body. The hypothalamus, in turn, relies on the pituitary gland to activate the other endocrine glands. The pituitary gland is often called the “master gland” since it influences so many other glands.

29. The Endocrine System (slide 2 of 2)
Endorphins: Chemicals linked to pain perception and reward
Adrenal glands: Important glands of the endocrine system consisting of the adrenal cortex and the adrenal medulla
Gonads: An organ that secretes sex hormones
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Chapter 3: Neuroscience: The Biology of Behavior
3.5 The Endocrine System
LO: Discuss the role of endorphins and the endocrine system as communication mechanisms in the nervous system.
Endogenous opioid peptides, or endorphins, can reduce pain and promote pleasure. During extreme exercise, pain, or even excitement, the pituitary gland and hypothalamus both pour endorphins into the bloodstream. Endorphins are neither neurotransmitters nor hormones. Rather, they are neuromodulators that influence the effects of neurotransmitters. Some endorphins function like neurotransmitters when they operate in the synapse, and most will alter the effects of neurotransmitters.
The adrenal glands are at the top of the kidneys. There are two parts to the adrenal glands: an outer adrenal cortex and an inner adrenal medulla. The sympathetic nervous system stimulates the adrenal medulla, and it releases epinephrine and norepinephrine (more commonly known as adrenaline). Hormones secreted by the adrenal glands have a broad influence over many organs in the body.
Gonads are organs that release male and female sex hormones. In women, the ovaries secrete estrogen, progesterone, and a small amount of testosterone. In men, the testes secrete testosterone. Testosterone is also produced in the adrenal glands of men and women.

30. Genetics
The nearly 6.5 feet of tightly bundled DNA in each cell of the body contains the unique list of ingredients and the specific recipe to make you you.
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Chapter 3: Neuroscience: The Biology of Behavior
3.6 Genetics
LO: Discuss the role of genetics in psychology
Genetics tell the story of an individual. The nearly 6.5 feet of tightly bundled DNA in each cell of the body contains the unique list of ingredients and the specific recipe to make you you. A genome is the sum of an organism’s hereditary information and environmental factors. Chromosomes are the parts of the cell that contain segments of DNA called genes. You got half of your chromosomes from your mother and the other half from your father back when you were a zygote . Most traits are polygenic , meaning that multiple genes influence their expression. How traits are expressed also depends on the characteristics of the genes that are linked to the traits. A dominant gene exercises its influence over other genes and overpowers recessive genes. This is called a heterozygous condition. A recessive gene’s influence will only be seen when it teams up with an identical recessive gene. When two recessive genes pair up, the trait is likely to be expressed. When genes are alike, it is called a homozygous condition. Sometimes when a trait is heterozygous, the recessive trait lurks in the background. It is genetically present but not expressed. Your phenotype, the expression of genetic influence, may not match your genotype or your personal genetic makeup.

31. Adaptation
Adaptation:- A process by which a characteristic increases in a population because it makes reproduction or survival more likely
Fitness: The contribution an individual makes to the gene pool of the next generation.
Natural selection: Varying success in reproduction resulting from the interaction of an organism with the environment
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Chapter 3: Neuroscience: The Biology of Behavior
3.6 Genetics
LO: Discuss the role of genetics in psychology
What determines which genetic are expressed? According to scientists since Darwin, it is the environment. Each time an organism produces an offspring, a unique combination of DNA from the male and female parent is passed down. By chance, some combinations of DNA cause the offspring to remain healthier in a particular environment. Therefore, these combinations live longer and are more likely to appear in future generations. In such cases, the combined DNA is an adaptation, a characteristic that increases in a population because it makes reproduction or survival more likely. These adaptations can accumulate over generations in both individuals and populations. Those who pass along the adaptive gene have the potential to increase their family’s fitness, or their contribution to the genetic pool of the next generation. As a group, this is called inclusive fitness, or kin selection, which is your family’s contribution to the entire gene pool of the population.
So what do these notions of heredity and natural selection have to do with psychology? All of human structures and molecules are mapped out by DNA. How it all comes together is influenced by the interplay of biology and the environment.

32. Heritability and Family Studies
Heritability refers to the amount of a trait or characteristic that can be attributed to genetics as opposed to environment. Several research methods are used to tease apart the influence of biology versus that of the environment.
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Chapter 3: Neuroscience: The Biology of Behavior
3.6 Genetics
LO: Discuss the role of genetics in psychology
Heritability refers to the amount of a trait or characteristic that can be attributed to genetics as opposed to environment. Several research methods are used to tease apart the influence of biology versus that of the environment.
Family studies allow researchers to test hypotheses concerning the influence of genetic factors versus that of environmental factors by examining biological relatives.
Adoption studies allow researchers to examine characteristics of children and their biological and adopted parents.
Twin studies. There are two kinds of twins: Monozygotic (MZ) (from one egg) Identical twins come from a single fertilized egg that splits apart. MZ twins share 100% of their genetic material. Only 1 in 250 births are identical twins. Dizygotic (DZ) (from two eggs) Fraternal twins. Twin studies are the gold standard, used to tease apart environmental and biological influences. Since identical twins share 100% of their genes, and twins raised together share 100% of their environment, examining twins in different families might be the ideal way to tease out the relative strength of genes versus environmental contribution.