Download Chapter 4 Answers to Before You Go On Questions Describe how

Chapter 4
Answers to Before You Go On Questions
1. Describe how studies of people with brain damage and EEGs have contributed to our
knowledge of the brain and nervous system. Patients with localized brain damage often
experience the loss of some function, which gives researchers clues about what certain brain
regions do when they are undamaged. Using electroencephalograms (EEGs), scientists can
take a broad look at the activity of patients’ brains and compare an injured to an uninjured
brain to learn what certain regions of the brain do.
2. What are the main advantages of neuroimaging methods over earlier neuroscience research
methods? Neuroimaging enables researchers to identify what parts of the brain are
neurochemically active during certain tasks. Researchers have the advantage of obtaining
visual images in both healthy and unhealthy humans functioning typically or atypically.
These techniques, including positron emission tomography (PET) and functional magnetic
resonance imaging (fMRI), allow for the detection of uptake molecules so that the brain areas
of increased activity can be identified (Phelps, 2006).
3. What are the two types of cells in the nervous system? Neurons, or nerve cells, are the
fundamental building blocks of the nervous system. Glia, non-neuronal cells in the nervous
system, actually outnumber neurons by a factor of 10 in certain parts of the human brain
(Laming et al., 2011), and are now thought to serve many purposes that are critical for
normal functioning of neurons in the nervous system.
4. What are the three major types of glia and the functions of each type? There are three major
categories of glia: astroglia, oligodendroglia, and microglia. Astroglia are shaped like stars
and are important for creating the blood–brain barrier (a system that tracks the passage of
molecules from the blood to the brain) and for regulating the flow of blood into regions with
increased neuronal activity (and thus which require more nutrition support or oxygenation)
(Iadecola & Nedergaard, 2007). Oligodendroglia are important for providing a protective
fatty sheath called myelin that wraps around the axons of neurons, insulating them from
nearby neuronal activity. Microglia, so named because they are very small, are important for
cleaning up debris of dead cells so that brain regions can continue with their normal
functioning. These tiny microglia are important in the brain’s defence against infection and
illness.
5. How do neurons work? Neurons send messages to one another via electrochemical actions; a
sudden change in the electrical charge of a neuron’s axon causes it to release a chemical that
can be received by other neurons, thereby passing a signal along from one neuron to the next.
6. What happens in the axon of a neuron during an action potential? During an action potential
a sudden positive change in the electrical charge of a neuron’s axon occurs. Also known as a
spike, or firing, action potentials rapidly transmit an excitatory charge down the axon. This
occurs through the opening of ion channels that allow for an in-rush of sodium into the axon,
changing its electrical charge or polarity. This starts a chain reaction that moves the electrical
charge down the neuron’s axon.
7. When an action potential reaches the axon terminal, what happens? When the spike reaches
the presynaptic axon terminal, it causes the release of neurotransmitter molecules into the
synapse. The neurotransmitter then diffuses across the synapse and binds to neurotransmitter
receptors on the dendrite of the receiving, or postsynaptic, neuron.
8. How does a postsynaptic neuron receive and respond to messages from other neurons?
Molecules of neuron transmitter substances fit into receptor sites on the dendrites of the
postsynaptic neurons. If the receptor sites are thought of as locks, then the neurotransmitter
substances that enter them can be thought of as keys. If enough of the proper kind of
neurotransmitter substances enter receptor sites on a neuron they can cause that neuron to
“fire.”
9. What are the two parts of the central nervous system? The two main parts of the central
nervous system are the spinal cord and the brain.
10. What happens when the sympathetic nervous system is operating? How does that compare to
the operation of the parasympathetic nervous system? When the sympathetic nervous system
is operating we develop a rapid heart rate and dry mouth. This is our “fight-or-flight”
response, which enables us to respond to potentially life-threatening situations. The
parasympathetic nervous system, on the other hand, is important for controlling basic
functions that occur when a person is not at immediate risk and for cutting back on the
effects of the sympathetic nervous system, thus returning us to a baseline or balanced state.
For example, digestion is a function under the control of the parasympathetic nervous
system. When stressful situations occur, our digestion stops, thus diverting energy from
digestion to other functions (such as increased blood flow to our leg muscles) so that we can
escape a threatening situation.
11. How do the brain and spinal cord work together? Our spinal cord is important for gathering
information from our bodies and sending it to our brains, as well as for enabling the brain to
control body movement. So the spinal cord gathers information, which it passes along to the
brain; the brain responds to that information and passes commands back down through the
spinal cord to initiate movement and other functions.
12. What neuron types are important for simple reflexes? Simple circuits can control pain
reflexes without any communication with the brain. They consist of three neurons: (1) a
sensory neuron, whose cell body is located in the periphery but whose axon travels into the
spinal cord; (2) a connecting neuron, called an interneuron; and (3) a motor neuron, whose
cell body is located in the spinal cord and whose axon travels out to the body.
13. What determines how much disability will result from a spinal cord injury? The higher up the
spinal cord the damage occurs (i.e., the closer it occurs to the brain), the larger the proportion
of the body that is afflicted. This is because when the spinal cord is damaged, the flow of
information to and from the brain is disrupted; thus individuals become paralyzed and are
incapable of noticing touch or pain sensations on the body.
14. Which part of the brain is essential to basic functioning, such as breathing? The brainstem,
or medulla, is essential for basic bodily functions, including respiration and heart rate
regulation, making this part of the brain critical for survival and normal functioning. Most of
the actions of the brainstem occur without our conscious knowledge or involvement. Damage
to the brainstem is often fatal.
15. Describe the role of the brain in regulating hormones throughout the body. The
hypothalamus, aptly named because this collection of nuclei sits beneath the thalamus, is
critical for the control of the endocrine, or hormonal, system. The endocrine system controls
levels of hormones throughout the body.
16. Which part of the brain has been linked with our fear responses? The region of the brain
linked to our fear responses is known as the amygdala. It is involved in recognizing, learning
about, and responding to stimuli that induce fear (LeDoux, 2007). In addition, the amygdala
is thought to be involved in the development of phobias, or abnormal fears.
17. What behaviour is most closely linked to the hippocampus? Memory is most closely linked to
the hippocampus. Neuroscientists have extensively studied individuals with damage to the
hippocampus and found that they are incapable of forming new episodic memories, or
memories about events and personal experiences. It is thought to store information about
events only temporarily (Squire et al., 2004).
18. Which of our senses is linked primarily with the occipital cortex? Which with the temporal
cortex? Which with the parietal cortex? The occipital cortex, the cortical area at the back of
the skull, contains primary sensory regions important for processing very basic information
about visual stimuli, such as orientation and lines. The temporal cortex is located on the sides
of the head within the temporal lobe. It wraps around the hippocampus and amygdala and
includes areas important for processing information about auditory stimuli, or sounds.
Finally, the parietal cortex, localized on the top of the brain, is critical for processing
information about touch or somatosensory stimuli—our sense of touch, pressure, vibration,
and pain.
19. What are the primary functions of Broca’s and Wernicke’s areas, and where are they
located? Broca’s area, located in the frontal lobe, is critical for speaking (speech production),
and Wernicke’s area, located in the temporal lobe, is critical for understanding language or
spoken communication.
20. What mental functions are associated with the frontal cortex? The frontal cortex, located at
the front of the brain (behind the forehead), is a relatively large cortical region and is
proportionately larger in humans compared to less complex animals. The frontal cortex is
important for planning and movement; voluntary movements begin in the frontal cortex, in
part referred to as the primary motor strip. Recent research suggests that parts of the motor
cortex are not only involved in contracting specific muscles, but also in coordinating the use
of these muscles in complex movements (Graziano, 2006). The frontal cortex is involved in
inhibiting or limiting our responses and is thus involved in planning. Planning involves
thinking about what the best reaction is before responding.
21. How do the two hemispheres of the brain communicate? The brain can be broken down into
two relatively equal halves, called hemispheres, which are not completely symmetrical.
Communication from one side of the brain to the other occurs via a bundle of axons that
make up a large structure called the corpus callosum. However, the hemispheres do not quite
work the way you may expect. There are many crossed connections to and from the primary
cortex, leading to differences in function between the hemispheres. Input from our visual,
auditory, and somatosensory systems is at least partially crossed, for example. The left part
of the somatosensory cortex receives tactile input from the right part of the body, and vice
versa. And to cloud the situation even further, not everybody’s hemispheres are identical.
There are actually some rather fascinating individual differences in the two halves of our
brains.
22. What are Darwin’s four observations and one inference, and how are they important for our
understanding of how to breed domestic animals, such as cats, dogs, and dairy cows, for
specific traits? Darwin’s four observations are as follows: (1) Darwin noticed that there were
observable, subtle changes in the forms of fossilized animals, suggesting they were changing
over time; (2) despite looking different on the surface, there are similarities in the structures
of things like the human hand, a cat’s paw, and a bat’s wing; (3) selective breeding of captive
animals leads to changes in the appearance of the resulting offspring; and (4) not all animals
that are born survive to maturity and reproduce. Darwin’s inference was that those animals
that survive to reproduce are the ones best equipped to adapt to and survive in their current
environment. For breeders of animals, Darwin’s observations and inference mean that certain
traits can be bred into resulting offspring by selecting parents that exhibit the desirable traits.
For instance, if a dog breeder wants to breed sport dogs that are fast and energetic, he or she
should select parents that exhibit those qualities; the resulting litter of puppies is more likely
to have dogs who also exhibit those traits and who therefore will make great hunting
companions. However, caution should be taken about which traits we selectively breed for,
as the resulting animals may not be viable or adaptive.
23. Describe how mate selection in humans has been influenced by our evolutionary history.
Evolutionary theory suggests we will be drawn to mates who exhibit qualities that imply they
are in good reproductive health (like hip-to-waist ratios in females) or will be able to
contribute to parental care (to ensure children survive), thus ensuring that our genes will be
more likely to go forward into a future generation.
24. What does research show about “right-brained” spatial thinking versus “left-brained”
logical thinking? Though there has been work done with patients showing that there is indeed
some localization of function in one or the other of our hemispheres, the possibility that one
side of our brain is in charge and dominates the functioning of the other side of our brain is
not supported by neuroscience research, despite being a useful way for artists to account for
their dislike of logical reasoning and mathematics (Hines, 1987). Overall, the research shows
that, aside from the language areas, the two hemispheres are more similar than they are
different. Even when right–left differences are detected in function, these differences are
usually small and relative. For example, the left brain can accomplish the same things that
the right brain can accomplish, it’s just less efficient at some tasks and more efficient at
others.
25. On which side of the brain do most people have their language-related areas? What about
left-handed people? The language production area (Broca’s area) is located in the left
hemisphere of the brain, and this does not change for left-handed people.
26. Does overall brain size matter in how well brains function? On average, the brains of women
are smaller than those of men. However, this does not mean that men are smarter than
women on average. The overall size of the brain appears to be more closely related to the size
of the body than to function. A relationship between brain size and intelligence does not
actually exist (Tramo et al., 1998), except at the two extreme ends of the spectrum—people
with abnormally small or abnormally large brains are both more likely to exhibit mental
deficiencies than those with brains whose size falls within the normal range.
27. What goes wrong in the nervous system to cause multiple sclerosis, ALS, Parkinson’s
disease, and Huntington’s disease? Neurological illnesses are thought to be structural,
generally involving the degeneration of neurons. Multiple sclerosis involves the
demyelination, or loss of myelin, of the axons of neurons. This leads to the inefficient
transmission of electrical information among neurons. Amyotrophic lateral sclerosis (ALS, or
Lou Gehrig’s disease) is caused by the degeneration of motor neurons in the spinal cord.
People with ALS typically die when the motor neurons that control basic functions, including
breathing, die. Parkinson’s disease is a neurological condition that involves the death of
dopaminergic neurons—those that rely on the neurotransmitter dopamine—in the substantia
nigra. Huntington’s disease is an inherited condition that results in the death of neurons in the
striatum. Like ALS and Parkinson’s disease, Huntington’s disease is progressive and, as yet,
there is no cure.
28. What have neuroscientists learned to date about transplants of brain tissue as a way to treat
neurological diseases? Early work ruled out the possibility of transplanting fully
differentiated brain tissue into a damaged region, as these transplants did not survive or
integrate properly into the existing circuitry. Subsequent attempts to transplant fetal brain
tissue into brains of adults suffering from Alzheimer’s or Parkinson’s disease also met with
limited, if any, success. Fetal tissue may integrate into the damaged brain, but it remains
foreign and often does not function normally for extended periods of time (Freed, 2000).
Thus, modern science has focused primarily on the possibility of restoring damaged circuits
by transplanting stem cells.