Chapter 2 Outline

I. The Nervous System

The nervous system is the body’s electrochemical communication system. Neuroscience is the field of study of the nervous system. The researchers who conduct research on the nervous system are neuroscientists.

A. Characteristics of the Nervous System

Complexity

The brain is made up of billions of nerve cells, the orchestration of which allows a person to carry out a variety of activities.

Integration
Adaptation

The brain integrates information from the environment so that people can function in the world.

Each nerve cell in the brain communicates with some 10,000 other nerve cells.

As the world constantly changes, the brain and nervous system allow a person to adjust to those changes. The brain has a lot of plasticity, meaning it has a vast capacity for modification and change.

Electrochemical Transmission
Electrical impulses and chemical messenger systems allow the brain and nervous system to work as an information-processing system.

B. Pathways in the Nervous System

As people interact with and adapt to the world around them, the brain and nervous system receive and transmit incoming sensory information. The brain and nervous system integrate this information and direct the body’s motor activities.

Afferent nerves carry information to the brain.
Efferent nerves carry information from the brain out to the body.
Neural networks, made up of nerve cells, integrate sensory input and motor output.

C. Divisions of the Nervous System

The central nervous system (CNS) is comprised of the brain and spinal cord.
The peripheral nervous system (PNS) consists of the nerves that connect the brain and spinal cord to other parts of the body. The function of the PNS is to direct information to and from the brain and spinal cord. It also carries out the commands of the CNS.

The PNS is comprised of the somatic nervous system and the autonomic nervous system. The function of the somatic nervous system is to convey information from the skin and muscles to the CNS. It regulates information such as signals about pain and temperature. The autonomic nervous system’s function is to take messages to and from the body’s internal organs, thus regulating breathing, heart rate, and digestion.

The autonomic nervous system is comprised of both the sympathetic nervous system and the parasympathetic nervous system. The sympathetic nervous system prepares a person for a stressful situation; the parasympathetic nervous system calms the body down after the stressful situation.

Stress is the response of individuals to stressors, circumstances or events that threaten an individual’s well-being.
When a person experiences stress, physiological changes take place, such as sweating and an elevated heart beat.
When a person is exposed to a stressful situation this activates their sympathetic nervous system (the fight or flight response).
Acute stress, the momentary stress response, ends with the ceasing of the stressful event.
Chronic stress is stress that occurs continuously. In this type of stress the nervous system sends out corticosteroids (stress hormones) that can wear down the immune system.

II. Neurons

Neurons are the nerve cells that control the information-processing function.

Mirror neurons play a role in imitation. They are activated when we perform an action or observe others in action. These neurons are implicated in empathy and understanding others.

Glial cells provide support and nutrition to the nervous system.

A. Specialized Cell Structures

Not all neurons are alike, but they all have a cell body, dendrites, and an axon.
The cell body contains the nucleus that manufactures what neurons need for growth and maintenance.
Dendrites receive information and send it on to the cell body.
The axon carries information away from the cell body and on to other cells.
A myelin sheath, which covers the axon, is semipermeable, meaning that certain substances can pass into and out of the axon. The nerve disorder called multiple sclerosis occurs when there is a breakdown of the myelin sheath.

B. The Neural Impulse

In order for a neuron to send information to another neuron, the source neuron first sends an electrical charge.
Positive and negative ions float inside and outside the axon. The positive ions are sodium and potassium. The negative ions are chlorine.
Inside the membrane of the axon are gated pathways known as ion channels. These channels open and close, allowing the positive and negative ions to cross into and out of the axon. When a neuron is at rest and not transmitting information, the ion channels are closed and there is a negative charge on the inside of the axon and a positive charge on the outside of it.
When a neuron is inactive it is said to be at resting potential.
When an electrical impulse flows down the axon it becomes depolarized. The channels open and the positive ions move into the axon and the negative ions move outside the axon. Then the potassium channels open and the positive ions move back out and return the axon to its normal charge.
An action potential is the term given to the electrical impulses flowing down the axon.
The all-or-none principle refers to the situation that occurs when an electrical impulse reaches a certain level of intensity, then fires and moves all the way down the axon, without losing any of its intensity.

C. Synapses and Neurotransmitters

Synaptic Transmission
Synapses are the junctions between neurons. The space between one neuron and the dendrites of another neuron is called the synaptic gap.

At the end of the axon there are fibers that end in what are called terminal buttons. Neurotransmitters are stored in the terminal buttons. These carry the electrical information across the synaptic gap.

Neurochemical Messengers
There are a variety of neurotransmitters. Each plays a different role and has its own function. Some neurotransmitters excite the neuron and cause it to fire, while other neurotransmitters inhibit the neuron.

After the neurotransmitter crosses over the synaptic gap, it gets picked up by a receiving neuron. Most neurons pick up and secrete only one type of neurotransmitter.

GABA keeps many neurons from firing. Low levels of GABA are involved in anxiety.

Norepinephrineinhibits neuron firing in the CNS, but it excites the heart muscle, intestines, and urogenital tract.Low levels of dopamine are associated with Parkinson’s disease.

Serotoninis mostly an inhibitory neurotransmitter.Endorphins alleviate pain and elevate feelings of pleasure.

A drug that mimics a neurotransmitter’s effect is known as an agonist.
A drug that blocks a neurotransmitter’s effect is known as an antagonist.

Neurotransmitters

Acetylcholine sets the firing of neurons into motion and is involved in muscle action, learning, and memory.

Stress releases norepinephrine.

Dopamine is an inhibitory neurotransmitter that helps control voluntary movement.

Dopamine also affects sleep, mood, attention, learning, and the ability to recognize rewards.

Serotonin is involved in sleep regulation, mood attention, and learning.

Endorphins stimulate neuron firing.

Oxytocin plays a role in the feelings of love and human bonding.

Drugs and Neurotransmitters

D. Neural Networks

Neural networks can be altered through changes in synaptic connections.
How strongly neurons are connected determines how well a person remembers information.

III. Structures of the Brain and Their Functions

Neuron networks are not visible to the human eye; however, technology has helped neuroscientists form pictures of the structures of the neurons and the brain.

How Researchers Study the Brain and Nervous System
Much of the brain imaging available today has come from studies on patients with brain damage or injury from disease.
Brain Lesioning

Brain lesions can be the result of injury or disease.

Neuroscientists sometimes create lesions in the brains of animals to see the effect on the animal’s behavior.
Brain lesions can be made by removing brain tissue, destroying tissue with a laser, or eliminating tissue by injection with a drug.

Staining
Much of what is known about neural pathways has been found through the use of stains or dyes that are selectively absorbed by neurons.

Neuroscientists can see through high-powered microscopes which neurons have absorbed the stain.

Electrical Recording
The electroencephalograph (EEG) records the electrical activity in the brain. When electrodes are placed on a person’s scalp, they detect brain-wave activity, which is recorded on a chart.

The EEG is used to assess brain damage, epilepsy, and other problems.
Single-unit recording is used when a probe is inserted in or near an individual neuron. The probe transmits the electrical activity to an amplifier so that researchers can see the activity.

Brain Imaging
A computerized tomography or CT scan produces a three-dimensional image obtained through x-rays of the head.
A positron-emission tomography or PET scan measures the amount of glucose in various areas of the brain, and then sends this information to a computer, where it is analyzed.
A magnetic resonance image (MRI) creates a magnetic field around a person’s body and uses radio waves to construct images of the person’s tissue and biochemical activities.
A newer method of the MRI is the functional magnetic resonance image (fMRI), which allows researchers to see what is happening in the brain while it is working.

B. How the Brain Is Organized

The nervous system starts out as a long, hollow tube. Then, three weeks after conception, cells making up the tube start to differentiate into neurons. These neurons begin to develop into the three major parts of the brain: the hindbrain, the midbrain, and the forebrain.

The Hindbrain
The hindbrain is the lowest portion of the brain.
The medulla helps in controlling breathing and regulates reflexes.
The cerebellum controls leg and arm movements.
The pons is involved in sleep and arousal.
The brain stem (the oldest part of the brain) includes much of the hindbrain except the cerebellum and the midbrain. The brain stem determines alertness and regulates such basic survival functions as breathing, heart rate, and blood pressure.
The Midbrain
The midbrain is located between the hindbrain and the forebrain.
The midbrain communicates information between the brain and the eyes and ears.
The reticular formation is involved in walking, sleeping, or turning to attend to a noise. It uses the neurotransmitters serotonin, dopamine, and norepinephrine.
The brain stem encases the reticular formation. It regulates survival-type functions like breathing, heartbeat, and blood pressure.

The Forebrain

The forebrain is the highest level of the brain.

a. The Limbic System

The limbic system is important in both memory and emotion.
The amygdala is somewhat like an awareness center. It fires selectively at the sight of appropriate foods, mates, and social rivals. The amygdala is also involved in emotional awareness and expression.
The hippocampus is involved in the formation and storage of memories. People who have hippocampus damage cannot retain new memories after the damage.

b. The Thalamus
An important function of the thalamus is to sort through information and send it to the appropriate place in the forebrain.

c. The Basal Ganglia
The basal ganglia works with the cerebellum and the cerebral cortex in coordinating voluntary movements.

d. Hypothalamus
The hypothalamus monitors eating, drinking, and sexual behavior, along with emotion, stress, and reward.

C. The Cerebral Cortex

The cerebral cortex, the outer layer of the brain, controls some of the highest mental functions, such as thinking and planning.
The neocortex, the outermost part of the brain, makes up 80 percent of the cerebral cortex.

1. The Lobes of the Cerebral Cortex
The lobes are divided into two hemispheres, and each hemisphere is divided into four lobes: the occipital lobe, the temporal lobe, the frontal lobe, and the parietal lobe.
The occipital lobe, in the back of the head, involves visual stimuli.
The temporal lobe, inthe cerebral cortex just above the ears, involves hearing, language processing, and memory.
The frontal lobe, behind the forehead, is involved in the control of voluntary muscles, intelligence, and personality. Phineas Gage, a 19th-century railroad worker, during an accident had an iron rod go through his face and up into his brain. The iron rod went through his frontal lobe. After the accident, Phineas’s personality changed dramatically. He became obstinate, moody, irresponsible, selfish, and incapable of taking part in planned activities.
The parietal lobe, at the top and toward the rear of the head, involves registering spatial location, attention, and motor control.
The Somatosensory Cortex and the Motor Cortex
The somatosensory cortex processes information about body sensations.
The motor cortex processes information about voluntary movements.
The somatosensory and motor areas are associated with different parts of the body. When Wilder Penfield conducted research on the somatosensory and motor areas, he found that when he stimulated a part of one of the areas a certain part of the body would move.
The Association Cortex
The association cortex processes information about sensory input and motor output.
The association cortex is involved in thinking and problem solving.

D. The Cerebral Hemispheres and Split-Brain Research

Aphasia is a language disorder associated with brain damage.

Damage to Broca’s area will cause a person to have difficulty in speaking a language.
Damage to Wernicke’s area will cause a person to have difficulty understanding a spoken language.
The corpus callosum is a bundle of axons that connects the left and right hemispheres of the brain. If the corpus callosum is severed, the two hemispheres cannot communicate with each other. If a memory is stored in the left hemisphere it cannot communicate with the right hemisphere; therefore, the memory appears to be gone.
Speech and grammar are controlled by the left hemisphere. The right hemisphere involves the processing of nonverbal information like special perception, visual recognition and emotion.

E. Integration of Function in the Brain

There is considerable integration of function between different areas in the brain. When information, or stimuli, is noticed, the information gets sent to the correct area of the brain, where it is processed, then sent out of the brain to the correct area in the body. Along the way, from the beginning to the end, the information goes through various areas of the brain and all the areas work together to have the information processed.

IV. The Endocrine System

A. The Endocrine System’s Structures and Functions

The endocrine system consists of glands that regulate certain organs by releasing their chemical products into the bloodstream.
Hormones are chemical messengers that are manufactured by the endocrine system.
The pituitary gland involves growth and regulates other glands.
The adrenal glands are involved in regulating mood, energy level, and the ability to cope with stress. The adrenal glands secrete both epinephrine and norepinephrine.
The pancreas is involved in the digestive and endocrine functions. It secretes insulin, which controls blood sugar, which itself is implicated in metabolism and weight and obesity.
The ovaries in females and the testes in males are involved in sexual development, reproduction, and sexual characteristics.

V. Brain Damage, Plasticity, and Repair

Research has been conducted on patients with brain damage to determine how well the brain can repair itself. Recovery from brain damage depends on the age of the individual and the extent of the brain damage.

A. The Brain’s Plasticity and Capacity for Repair

Most of the human brain’s plasticity is found in young children before the age of five. For example, if a child below the age of five has brain damage to the left hemisphere, then the right hemisphere will pick up much of the language function. However, if damage occurs after the age of five, there may be permanent language disability.
Much of the brain’s ability to repair itself depends on whether the neurons in the damaged area have been completely destroyed. If these neurons were not totally destroyed, brain function may be restored over time.
Collateral sprouting is one way in which the brain can repair itself. In this process, the axons on adjacent neurons grow more branches.
Substitution of function is a second way the brain can repair itself. When this happens, another area in the brain takes over the functions of the damaged area.
Neurogenesis is the process through which new neurons are generated.

B. Brain Tissue Implants

Brain grafts are implants of healthy tissue that are placed into the damaged brain.
The most successful cases of brain grafts occur when the tissue for the implants comes from the fetal stage.
The use of stem cells has been a topic for hot debate in recent years. Stem cells are unique, because they have the ability to develop into most types of cells.

VI. Genetics and Behavior

A. Chromosomes, Genes, and DNA

The nucleus of each cell contains 46 chromosomes, which are essentially 23 pairs of chromosomes with one of each pair coming from each parent.
Chromosomes contain deoxyribonucleic acid, or DNA. DNA is the molecule that carries a person’s genetic information.
Genes are the segments of chromosomes that are composed of DNA. Genes carry the heredity information of the individual.
According to the dominant-recessive genes principle, if one of the genes of a pair is dominant over the other, the dominant gene resides over the recessive one. For example, if a person inherits the blue-eyed gene from his or her mother and the brown-eyed gene from the father and the blue-eyed gene is dominant, the person will have blue eyes.

B. The Study of Genetics

Gregor Mendel first started the research on genetics in the mid-nineteenth century when he studied heredity in pea plants.

Molecular Genetics
Molecular genetics involves the manipulation of genes.
The term genome refers to the instructions for making an organism.
Selective Breeding
Selective breeding occurs when organisms are chosen for reproduction based on how much of a particular trait they display.

Behavior Genetics

Behavior genetics is the study of the degree and nature of heredity’s influence on behavior.
In twin studies, behavior genetics studies the extent to which individuals are shaped by their heredity and the influence of the environment on them. The behavioral similarity of identical twins is compared to the behavioral similarity of fraternal twins.
Genes and the Environment
A genotype is a person’s genetic heritage.
A phenotype is a person’s observable characteristics. It refers to both the physical and psychological characteristics.