Corticospinal Tracts
The main pathways from the motor cortex to the brainstem and spinal cord are called the corticospinal tracts. Recall from Chapter 2 that bundles of nerve fibers within the central nervous system are called tracts outside the CNS they are called nerves. Thd term corticospinal indicates that these fiber bundles begin in the neocortex and terminate in the spinal cord. The axons of the corticospinal tracts originate mainly in layer V pyramidal cells of the motor cortex. Axons also come from the...
Table 156 Summary of Treatments of Brain and Behavior
Damage to dysfunctional area e.g., Parkinson's disease Implantation of embryonic or endogenous stem cells to regenerate lost tissue Deep brain stimulation e.g., implantation of stimulation electrode to control tremor in Parkinson's disease Removal of abnormal tissue e.g., epilepsy, tumor Repair of abnormality e.g., arteriovenous malformations Pharmacological Antibiotic or antiviral agents or both e.g., encephalitis Transcranial magnetic stimulation TMS Behavioral training e.g., speech therapy,...
The Prefrontal Cortex and Emotional Behavior
At about the same time that Kl ver and Bucy began studying their monkeys, Carlyle Jacobsen was studying the effects of frontal lobotomy on the cognitive capacities of two chimpanzees. A frontal lobotomy destroys a substantial amount of brain tissue as the result of inserting a sharp instrument into the frontal lobes and moving it back and forth. In 1935, Jacobsen reported that one of the chimps that had been particularly neurotic before being subjected to this procedure, became more relaxed...
The Cell Membrane Barrier And Gatekeeper
The cell membrane separates the intracellular from the extracellular fluid and so allows the cell to function as an independent unit. The structure of the membrane, shown in Figure 3-15A, also regulates the movement of substances into and out of the cell. One of these substances is water. If too much water enters a cell, it will burst, and, if too much water leaves a cell, it will shrivel. The cell membrane helps ensure that neither will happen. A The membrane's bilayer. B Detail of a...
How Do Any Of Us Develop A Normal Brain
When we consider the complexity of the brain, the less-than-precise process of brain development, and the number of factors that can influence it, we are left marveling at how so many of us end up with brains that pass for normal. After all, we must all have H OW D O ES T H E BRA IN D EVELO P A ND A DA P T 221 H OW D O ES T H E BRA IN D EVELO P A ND A DA P T 221 Organized normal pyramidal neurons Disorganized schizophrenic pyramidal neurons Examples from the hippocampus of pyramidal-cell...
Somatosensory Receptors and Perception
Our bodies are covered with sensory receptors. They include our skin and body hair and are embedded in both surface layers and deeper layers of the skin and in muscles, tendons, and joints. Some receptors consist simply of the surface of a sensory neuron dendrite. Other receptors include a dendrite and other tissue, such as the dendrite attached to a hair or covered by a special capsule or attached by a sheath of connective tissue to adjacent tissue. The density of sensory receptors, in the...
The Vestibular System and Balance
vestibular organs in each middle ear consist of the three semicircular canals and the otolith organs. Hair cells in the vestibular system are sensitive to movement of the head and to gravity. B A vestibular neuron is normally active and its activity increases if the cilia of its hair-cell receptors are bent in one direction but decreases if the receptors are bent in the opposite direction Nerve fibers exiting a semicircular canal vestibular organs in each middle ear consist of the three...
Neural Circuit for Implicit Memories
Hypothesizing that the basal ganglia are central to implicit memory, Mishkin and his colleagues Mishkin, 1982 Mishkin et al., 1997 also proposed a circuit for implicit memo ries.As Figure 13-15 shows, the basal ganglia receive input from the entire neocortex and Prefrontal cortex Amygdala Rhinal cortex Hippocampus Neural Circuit Proposed for Explicit Memory A General neuroanatomical areas controlling explicit memory. B Circuit diagram showing the flow of information, beginning with inputs from...
What Makes Explicit and Implicit Memory Different
One reason that explicit and implicit memories differ is that each type of memory is housed in a different set of neural structures. Another reason that they differ is that explicit and implicit information are processed differently. Implicit information is encoded in very much the same way as it is perceived and can be described as data-driven, or bottom up, processing. The idea is that information enters the brain through the sensory receptors and is then processed in a series of subcortical...
How Do We Sense Perceive and See the World
Focus on Disorders Migraines and a Case of Blindsight The Nature of Sensation and Perception Focus on New Research Testing Vision in Nonhuman Subjects Sensory Experience and Sensory Reality Light The Stimulus for Vision Structure of the Eye Focus on Disorders Optical Errors of Refraction and Visual Illuminance Location in the LGN and Cortical Region V1 Neural Activity in the Dorsal Stream Injury to the Visual Pathway Leading to the Cortex Injury to the What Pathway Focus on Disorders Carbon...
The Basis of Neural Communication in a Heartbeat
iscoveries about how neurons communicate actually stem from experiments designed to study what controls an animal's heart rate. If you are excited or exercising, your heartbeat quickens if you are resting, it slows. Heartbeat rate changes to match energy expenditure that is, to meet the body's nutrient and oxygen needs. Heartbeat undergoes a most dramat ic change when you dive beneath wat er i t almost comple tely stops. This drastic slowing, called diving bradycardia, conserves the body's...
Multiple Sclerosis
One day J. O., who had just finished university requirements t o begin work as an accountant, noticed a slight cloudiness in her right eye the cloudiness did not go away when she wiped her eye. The area of cloudiness grew over the next few days. Her opt ometrist suggested t hat she see a neurologist, who diagnosed optic neuritis, a symptom t hat could be a flag for multiple sclerosis. Although we do not ye t understand what causes MS, we do know tha t it is charact erized by a loss of myelin,...
Animal Intelligence
f undamental characteristic of intelligent animals is t hat they t hink. We begin to explore how the brain t hinks and where thinking takes place in the brain by examining thought in an intelligent nonhuman animal an African gray parrot named Alex, pictured here with Irene Pepperberg 1990, 1999 , who has been studying Alex's ability to think and use language for nearly three decades. A typical session with Alex and Pepperberg might proceed as follows Mukerjee, 1996 Pepperberg shows Alex a tray...
Enriched Experience and Plasticity
One way to stimulate the brain is to house animals in environments that provide some form of generalized sensory or motor experience. Such an experiment is described in Chapter 6 Donald Hebb took laboratory rats home and let them have the run of his kitchen. After an interval, Hebb compared the enriched rats with another group of rats that had remained in cages in his laboratory at McGill University, training both groups to solve various mazes. The enriched animals performed better, and Hebb...
Microelectrodes
The final ingredient needed to measure a neuron's electrical activity is a set of electrodes small enough to place on or into an axon. Such microelectrodes can also be used to deliver an electrical current to a single neuron. One way to make a microelectrode is to etch the tip of a piece of thin wire to a fine point and insulate the rest of the wire. The tip is placed on or into the neuron, as illustrated at the top of Figure 4-7. Microelectrodes can also be made from a thin glass tube. If the...
The Axon Hillock
The axon hillock, shown emanating from the cell body in Figure 4-21, is rich in voltage-sensitive channels. These channels, like those on the squid axon, open at a particular membrane voltage. The actual threshold voltage varies with the type of neuron, but, to keep things simple, we will stay with a threshold level of 50 mV. To produce an action potential, the summed IPSPs and EPSPs on the cell-body membrane must depolarize the membrane at the axon hillock to 50 mV. If that threshold voltage...
Lou Gehrigs Disease
Baseball legend Lou Gehrig played for t he New York Yankees from 1923 until 1939. He was a member of numerous World Series championship teams, set a host of individual records, some of which still stand today, and was immensely popular with fans, who knew him as the Iron Man. His record of 2130 consecutive games was untouched until 1990, when Cal Ripkin, Jr., played his 2131st consecutive game. In 1938, Gehrig started to lose his strength. In 1939, he played only eigh t games and then re tired...
The Oscilloscope
Hodgkin and Huxley's experiments were made possible by the invention of the oscilloscope. You are familiar with one form of oscilloscope, a conventional television set. An oscilloscope can also be used as a sensitive voltmeter to measure the very small and rapid changes in electrical currents that come from an axon. The important component of an oscilloscope is its glass vacuum tube. In the tube, from which air is removed, a beam of negatively charged electrons is projected onto the tube's...
Calcium Channels Habituate
Kandel and his coworkers measured neurotransmitter output from a sensory neuron and verified that less neurotransmitter is in fact released from a habituated neuron than from a nonhabituated one. Recall that the release of a neurotransmitter in response to an action potential requires an influx of calcium ions across the presynaptic membrane. As habituation takes place, that calcium ion influx decreases in response to the voltage changes associated with an action potential. Presumably, with...
How MotorCortex Damage Affects Skilled Movements
Scientists produced the first maps of the motor cortex in the 1930s. A number of researchers got slightly different results when they repeated the mapping procedures on the same subjects. These findings led to a debate. Some scientists held that the map of the motor cortex was capable of changing that areas controlling particular body parts might not always stay in exactly the same place and retain exactly the same dimensions. But other researchers felt that this view was unlikely. They argued...
The Nerve Impulse
Initiated by changes in voltage-sensitive sodium and potassium channels, an action potential begins with a depolarization gate 1 of the sodium channel opens and then gate 2 closes . The slower-opening potassium-channel gate contributes to repolarization and hyperpolarization until the resting membrane potential is restored. Suppose you place two recording electrodes at a distance from each other on an axon membrane and then electrically stimulate an area adjacent to one of these electrodes....
EEG Recordings
Recall your encounter with EEGs at this beginning of this chapter in connection with epilepsy. In the early 1930s, Hans Berger discovered that electrical activity in the brain could be recorded simply by placing electrodes onto the skull. Popularly known as brain waves, recording this electrical activity produces an electrical record from the head, or an electroencephalogram. EEGs reveal some remarkable features of the brain's electrical activity. The EEGs in Figure 4-25 illustrate three 1. The...
Why the Hominid Brain Enlarged
The evolution of modern humans from the time when humanlike creatures first appeared until the time when humans like ourselves first existed spans about 5 million years. As illustrated by the relative size differences of skulls pictured in Figure 1-15, much of this evolution entailed changes in brain size, which were accompanied by changes in behavior. The nearly threefold increase in brain size from apes EQ 2.5 to modern humans EQ 7.0 has been a subject of extensive research and equally...
Summary of DSMIVTR Classification of Abnormal Behaviors
Core features and examples of specific disorders Disorders usually first diagnosed in infancy, childhood, and adolescence Delirium, dementia, amnesia, and other cognitive disorders Mental disorders due to a general medical condition Schizophrenia and other psychotic disorders Mood disorders Fictitious disorders Dissociative disorders Eating disorders Sexual disorders and sexual-identity disorder Sleep disorders Other conditions that may be a focus of clinical attention Tend to emerge and...
In Review Pdk
The brain is especially plastic during its development and can therefore be molded by experience into different forms, at least at the microscopic level. Not only is the brain plastic in response to external events, it may be changed as well by internal events, including the effects of hormones, injury, abnormal genes and drugs. The sensitivity of the brain to experience varies with time. A t critical periods in development, specific parts of the brain are particularly sensitive to experience...
Habituation Response
In habituation, the response to a stimulus weakens with repeated presentations of that stimulus. If you are accustomed to living in the country and then move to a city, you might at first find the sounds of traffic and people extremely loud and annoying. With time, however, you stop noticing most of the noise most of the time. You have habituated to it. Habituation develops with all our senses. When you first put on a shoe, you feel it on your foot, but very shortly it is as if the shoe is no...
Figure 67
Neural-Tube Development Scanning electron micrographs show the neural tube closing in a mouse embryo. Reproduced with the permission of Dr. R. E. Poelman, Laboratory of Anatomy, University of Leyden. Micrographs of the neural tube closing in a mouse embryo can be seen in Figure 6-7. The cells that form the neural tube can be thought of as the nursery for the rest of the nervous system. The open region in the center of the tube remains open and matures into the brain's ventricles and the spinal...
Figure 75
Points of Influence In principle, a drug can modify seven major chemical processes, any of which results in reduced or enhanced synaptic transmission. Choline-rich diet increases available acetylcholine ACh . Black widow spider venom promotes release of ACh. Botulin toxin blocks release of ACh. Choline-rich diet increases available acetylcholine ACh . Black widow spider venom promotes release of ACh. Botulin toxin blocks release of ACh. Physostigmine and organophosphates block the inactivation...
Neuropsychoanalysis
Ddentifying the neural basis of A brain disorders and abnormal behavior has suffered from the lack of a unifying theory. Among the questions that a unifying theory of neuropsychology would answer is, How does the brain produce our concept of self, our beliefs about who we are as individuals The first coherent attempt at a theory of self is found in the writings of Sigmund Freud and other psychiatrists, beginning a century ago. Freud's theories were based on his observations of his patients and...
Deactivation Of The Neurotransmitter
Chemical transmission would not be a very effective messenger system if a neuro-transmitter lingered within the synaptic cleft, continuing to occupy and stimulate receptors. If this happened, the postsynaptic cell could not respond to other messages sent by the presynaptic neuron. Therefore, after a neurotransmitter has done its work, it is quickly removed from receptor sites and from the synaptic cleft. Deactivation is accomplished in at least four ways. One way is diffusion some of the...
Classification Of Psychoactive Drugs
Drugs with similar chemical structures can have quite different effects, whereas drugs having different structures can have very similar effects. Hence classifications based on a drug's chemical structure have not been very successful. Classification schemes based on Barbiturate. Drug that produces sedation and sleep. Antianxiety agent. Drug that reduces anxiety minor tranquillizers such as benzodiazepines and sedative-hypnotic agents are of this type. Tolerance. Lessening of response to a drug...
Mendels Principles Apply to Genetic Disorders
Some disorders caused by mutant genes clearly illustrate Mendel's principles of dominant and recessive alleles. One is Tay-Sachs disease, caused by a dysfunctional protein that acts as an enzyme known as HexA hexosaminidase A , which fails to break down a class of lipids fats in the brain. Symptoms usually appear a few months after birth. The baby begins to suffer seizures, blindness, and degenerating motor and mental abilities. Inevitably, the child dies within a few years. The Tay-Sachs...
Sound Waves The Stimulus For Audition
When you strike a tuning fork, the energy of its vibrating prongs displaces adjacent air molecules. Figure 9-2 shows that, as one prong moves to the left, the air molecules to the left compress grow more dense and the air molecules to the right become more rarefied less dense . The opposite happens when the prong moves to the right. The undulating energy generated by this displacement of molecules causes waves of chang ing air pressure sound waves to emanate from the fork. Sound waves may move...
Summary 1
There are many resources available for expanding your learning online There are many resources available for expanding your learning online Try the Chapter 3 quizzes and flashcards to test your mastery of the chapter material. You'll also be able to link to other sites that will reinforce what you've learned. http www.bioteach.ubc.ca CellBiology StudyingGeneFunction Learn more about knockout technology and gene function. Review genetics at this Web site from the Cold Spring Harbor Laboratory....
The Nature Of Sensation And Perception
As we look at the world, we naturally assume that what we see is what is really out there. Cameras and videos reinforce this impression, seeming to re-create the very same visual world that we experience first hand. But our version of the world, whether we see it directly or view it reproduced, is always a creation of the brain. What we see is not an objective reproduction of what is out there but rather a subjective construction of reality that the brain manufactures. With this in mind, we can...
Magendie Bell and Bells Palsy
Fran ois Magendie, a volatile and committed French exper-imen tal physiologist, reported in a three-page paper in 1822 t hat he had succeeded in cutting the dorsal and ventral roots of puppies, animals in which the roots are sufficien tly segre-gat ed to allow such surgery. Magendie found t hat cu tting the dorsal roots caused loss of sensation, whereas cutting the ventral roots caused loss of movement. Eleven years earlier, a Scotsman named Charles Bell had proposed functions for these nerve...
The Brain Creates A Representation Of The External World And Produces Behavior
Most animals with a multicellular brain have a common problem. They must move from place to place to eat and to reproduce. These movements, which are controlled by the nervous system, cannot be random. Rather, they must be made in response to the external world where food and mates are found. This external world is created by the nervous system through inputs from various sensory receptors. An animal's perception of what the external world is like therefore depends on the complexity and...
Explaining Drug Abuse
Why do people become addicted to drugs According to an early explanation, habitual users of a drug experience psychological or physiological withdrawal symptoms when the effects of the drug wear off. They feel anxious, insecure, or just plain sick in the absence of the drug, and so they take the drug again to alleviate those symptoms. In this way, they get hooked on the drug. Although this dependency hypothesis may account for part of drug-taking behavior, it has shortcomings as a general...
Gross Development of the Human Nervous System
When an egg is fertilized by a sperm, the resulting human zygote consists of just a single cell. But this cell soon begins to divide, and by the 15th day, the emerging embryo resembles a fried egg, as shown in Figure 6-5. It is made of several sheets of cells with a raised area in the middle called the embryonic disc, which is essentially the primitive body. By day 21,3 weeks after conception, primitive neural tissue, known as the neural plate, occupies part of the outermost layer of embryonic...
The Somatosensory Cortex and Complex Movement
This chapter began by describing the remarkable painting skills of Kamala the elephant. Kamala first needs a plan some idea of what she wants to paint. She must then execute the movements required to apply paint to her canvas, and she must use so-matosensory information to confirm that she is producing the movements that she intends. So to paint or to perform virtually any complex movement, the motor system jand the somatosensory system must work together. In this final section of the chapter,,...
Tickling
Everyone knows the effects and consequences of tickling. The perception of tickling is a curious mixture of pleasant and unpleasant sensory stimulation. The tickle sensation is experienced not only by humans but also by other primates, cats, rats, and probably most mammals. Tickling is rewarding in that people and animals will solicit tickles from others, but it is also noxious because they will attempt to avoid the stimulation when it becomes too intense. It is well known, and even described...
The Cerebellum and Movement Skill
Musicians have a saying Miss a day of practice and you're OK miss two days and you notice miss three days and the world notices. Apparently, some change must take place in the brain when practice of a motor skill is neglected. The cerebellum may be the part of the motor system that is affected. Whether the skill is playing a musical instrument, pitching a baseball, or typing on a computer keyboard, the cerebellum is critical for acquiring and maintaining motor skills. The cerebellum, a large...
Why Doesnt Everyone Abuse Drugs
Observing that some people are more prone to drug abuse and dependence than other people are, scientists have wondered if this difference might be genetically based. Three lines of evidence suggest a genetic contribution. 1. The results of twin studies show that, if one of two twins abuses alcohol, the other is more likely to abuse it if those twins are identical have the same genetic makeup than if they are fraternal have only some of their genes in common . 2. The results of studies of people...
Divergent and Convergent Intelligence
One of the clearest differences between lesions in the parietal and temporal lobes and lesions in the frontal lobes is in the way in which they affect performance on standardized intelligence tests. Posterior lesions produce reliable, and often large, decreases in intelligence test scores, whereas frontal lesions do not. One thing is puzzling, however. If frontal-lobe damage does not diminish a person's score on an intelligence test, why do people with this kind of damage often do such stupid...
Echolocation in Bats
Next to rodents, bats are the most numerous order of mammals. The two general groups or suborders, of bats consist of the smaller echolocating bats Microchiroptera and the larger fruit-eating and flower-visiting bats Megachiroptera , sometimes called flying Cell groups specialized for vocal learning Cell groups specialized for vocal learning and adult song Cell groups specialized for vocal learning Cell groups specialized for vocal learning and adult song Avian Neuroanatomy Lateral view of the...
Optimizing Connections in the Brain
s stated in Chapter 1, compared with other mammals, primates have evolved a larger brain than would be predicted from their body size. Overall, scientists believe that this increase in brain size is due to an expansion of existing structures rather than to the production of entirely new structures. As the brain has enlarged with evolution, so, too, have the number of connections among different brain regions. Connections take up space. When the fraction of the neocortex that is occupied by...
A Caution about Linking Correlation to Causation
Throughout this section, we have described research that implies that changes in the brain cause changes in behavior. Neuroscientists assert that, by looking at behavioral development and brain development in parallel, they can make some inferences regarding the causes of behavior. Bear in mind, however, that just because two things correlate take place together does not prove that one of them causes the other. The correlation-causation problem raises red flags in studies of brain and behavior,...
Neural Basis of EEG Changes Associated with Waking
A series of experiments performed on rats by Case Vanderwolf and his coworkers Vanderwolf, 1988 suggested that nuclei in the midbrain and forebrain are responsible for producing the waking EEG pattern of the neocortex. Figure 12-22 illustrates the location of these structures. Both send neural pathways into the neocortex, where they make diffuse connections with cortical neurons. The basal forebrain contains large cholinergic cells. These neurons secrete acetyl-choline ACh from their terminals...
Zeitgebers
Because Aschoff and Weber's subjects had a sleep-wake cycle of 24 hours before and after they entered the experiment and because hamsters usually have a 24-hour rhythm, we might wonder how normal rhythms are maintained. The biological clock must keep to a time that matches changes in the day-night cycle. If a biological clock is like a slightly defective wristwatch that runs either too slow or too fast, it will eventually provide times that are inaccurate by hours and so become useless. If we...
Figure 226
Cranial Nerves Each of the 12 pairs of cranial nerves has a different function. A common mnemonic device for learning the order of the cranial nerves is, On old Olympus's towering top, a Finn and German vainly skip and hop. The first letter of each word except the last and is, in order, the first letter of the name of each nerve. The somatic nervous system SNS is monitored and controlled by the CNS the cranial nerves by the brain and the spinal nerves by the spinal cord. The linkages provided...