Chapter 4

Question 1

What are the main parts common to all or most neurons, and what is the function of each
part?

Answer 1

There is the cell body that is common in all the cells, which contains the cell nucleus and the basic
machinery common to all bodily cells. There are also the dendrites that spread off from an extension of
the cell body and are responsible of collecting sensory input. The axons are also a tube-like structure
stemming from the cell body which connects to other neurons or muscle cells

Question 2

What are three types of neurons, and what is the function of each?

Answer 2

First type is the sensory neurons which are responsible for carrying nervous signals through the
peripheral nerves they have formed and transmitting them to the central nervous system. The second type
is motor neurons that carry out messages from the central nervous system through the nerves they form to
move muscles and glands. The third type is the interneuron which is responsible for collecting,
organising, integrating and carrying messages from different sources across the body. This last type only
exist within the central nervous system and vastly outnumbers the other two.

Question 3

How does the resting potential arise from the distribution of ions across the cell membrane?

Answer 3

The resting potential is the main source of action potential and is caused by the difference between the
amount of positive and negative charged ions inside and outside of the cell membrane. Depending on the
potassium or sodium channels being open, these ions enter and exit the cell to create the resting or action
potentials. Potassium channels stay open so positively charged potassium ions flow out of the cell and
join the mostly negative charged ions. This causes the imbalance between positive charges between the
insides and outside of the cell, creating an electrical tension that we call resting potential.

Question 4

How do the two phases of the action potential (depolarization and repolarization) result
from the successive opening and closing of two kinds of channels in the cell membrane?

Answer 4

In the resting state, the cell contains more potassium and less sodium inside than there is outside. During
the depolarization state, the sodium pores open up to let highly concentrated sodium into the cell. For a
moment there is an imbalance inside the cell that renders the environment temporarily positive which
pushes potassium outside, just as the potassium pores open up. This constitutes the repolarization state.
These two stages together form the action potential. To rebalance internal and external contents of the cell,
a structure called the sodium-potassium pump releases sodium outside while potassium is let back inside.

Question 5

How is an axon’s conduction speed related to its diameter and to the presence or absence of
a myelin sheath?

Answer 5

A wider axon would pose less resistance, therefore conduction speed would be higher in wider axons.
Myelin sheath, besides acting as a protective layer, also increases the conduction speed of the axon.

Question 6

How do neurotransmitters at excitatory and inhibitory synapses affect the rate at which
action potentials are produced in the postsynaptic neuron?

Answer 6

Neurotransmitters are responsible for unlocking various channels in the membrane. If this is happening

on the postsynaptic membrane of an excitatory synapse, sodium channels open and sodium flows inside
the cell. This decreases the negativity of the cell’s insides, causing depolarization which increases the rate
of action potentials in that neuron. If it is an inhibitory synapse, potassium channels open instead. The
potassium flows out which increases the negativity inside that causes the cell to hyperpolarize, causing a
decrease in the rate which action potentials are triggered.

Question 7

When are most neurons “born” and when do they begin to form synapses?

Answer 7

Most neurons are born during the third and fourth months of gestation with a rate of several hundred
thousand new neurons each minute. This process called neurogenesis lasts until adulthood, but this is the
peak of the speed in which neurogenesis occurs. Around the fifth month of conception, neurons grow in
size, produce more dendrites and axons and axon terminals start connecting to neurons, forming synapses.

Question 8

How does the metaphor of sculpting apply to brain development?

Answer 8

Brain development could be considered similar to a sculptor having a block of marble that he chiselled
down to an artistic creation that is less in amount of material but superior in aesthetic and function.
During the sculpting process, the artwork goes through a rough shaping process that involves shaping
the whole content by chiselling some away. Our brains go through a similar process, in which through
the creation and connection of new neurons and their connections, as well as some neurons and
connections dying off, it reaches its optimal state.

Question 9

What role might mirror neurons play in social learning?

Answer 9

Mirror neurons are found out to enable us to follow, memorize, learn and imitate another one’s actions as
well as recognize our own behaviour in others. This could be applied to social situations as well; our
perceptions through mirror neurons contribute to our emotional expressions, as well as constitute an
identification with others through language, expressions etc.

Question 10

How do researchers identify functions of areas of the human brain through (a) studying the
effects of brain damage, (b) using a magnetic field to interrupt normal brain activity, (c) recording
electrical activity that passes through the skull and scalp, and (d) creating images that depict
patterns of blood flow?

Answer 10

Different areas of the brain are responsible for different actions or capabilities, and researchers, by
comparing the areas of the brain that have been damaged in different patients and assessing the deficits
that have occurred, can estimate the function of a brain area. Researchers can also use magnetic field to
inactivate or activate parts of the cerebral cortex, and observe the bodily or cognitive effects of the
magnetic field on a specific portion of the cerebral cortex. Also, it is possible to use EEG to record the
electrical activity throughout the brain which is reflected onto the skull and scalp. The electrodes placed
enable the researchers to observe the activities of the brain – at least the surface – in different moments or
during the completion of different tasks. Lastly, since more brain activity means more blood flow to that
area, scientists are able to use different substances and techniques to determine the flow and accumulation
of blood throughout the brain – unlike other techniques, the whole brain – and assess the amount of work
that has been put to a specific area of the brain in any given moment.

Question 11

How do researchers damage, stimulate, and record from neurons in specific areas of
nonhuman animal brains to learn about the functions of those brain areas?

Answer 11

Researchers can determine the functions of different parts of the brain by deliberately damaging or
destroying some nerve bundles in the brain using very precise electrical and chemical instruments. They
can vary the exact location of the destruction of nerves and then compare the behavioural changes of
subjects to correlate the location of the brain with the function they seem to serve. The contrary can be
done too; different parts of the animals’ brain can be stimulated by electrical or chemicals means to
determine the effects of activation of different parts of the brain on the animal’s behaviour and drives. A
third option is not to interfere with the functions of nerves but to observe them. By placing very precise
tools inside a rat’s brain, it is possible to determine the actions of the neurons in different conditions.

Question 12

How do the autonomic and somatic motor systems differ from one another in function? How
do the sympathetic and parasympathetic divisions of the autonomic system differ from one another
in function?

Answer 12

The somatic division acts on skeletal muscles that are connected to bones and can move the skeleton
while contracting. The autonomic division, however, controls the visceral muscles and glands that are on
the insides of our body and do not move the skeleton while contracting. These visceral muscles and
glands receive two sets of neurons; the sympathetic division is responsible for managing stressful events
and increasing visceral muscle activity as well as prepare the rest of the body, including skeletal muscles,
for an upcoming event that requires action. The parasympathetic division does the opposite; it is
responsible for energy conserving and healing activities as well as the opposites of those that have been
listed for the sympathetic division.

Question 13

What are three categories of functions of the spinal cord?

Answer 13

Firstly, the spinal cord carries the somatosensory information and motor control commands through
ascending and descending tracts between the body and the brain. Secondly, it arranges and controls
simple reflexes that are not bound to the commands of the brain. Thirdly, it generates organized
rhythmic movements without the involvement of the brain.

Question 14

How is the brainstem similar to and different from the spinal cord? What role does
the brainstem play in the control of behaviour?

Answer 14

Both the brainstem and the spinal cord contain motor and sensory tracts, and they both manage some
reflexes and some species-typical behaviour patterns. However, the reflexes controlled by the brainstem
is much more complex; it manages postural reflexes such as balance and vital reflexes such as breathing.
It also manages species-typical behaviour regarding sustenance, copulation and attacking. It also manages
the speed of locomotion in the spinal cord.

Question 15

What are the functional similarities and differences between the cerebellum and the
basal ganglia?

Answer 15

Both the basal ganglia and the cerebellum act on the management of movement, however the cerebellum
acts on rapid, precise and sequential actions whereas the basal ganglia manages slow, deliberate
movements. Also, the basal ganglia manages the movements and acts accordingly as they are happening,
but the cerebellum plans ahead before the action has begun and initiates it as a completely programmed
action.

Question 16

What are the main functions of the thalamus?

Answer 16

Thalamus is generally responsible for gathering and distributing sensory and motor tracts as well as the
stimulation of the brain through the distribution of the arousal pathways.

Question 17

Why is the limbic system so named, and what function does it perform?

Answer 17

Its name comes from the Latin word “limbus” meaning “border”. It is considered as a border between
the primal and primitive parts of the brain and the new, advanced cerebral cortex above it. Through
various organs it contains, the limbic system manages emotions as well as special coordination and
encoding of memories. It also has strong connections to sensory input and their interpretations as well
as the conversions of emotions into actions.

Question 18

What are three ways by which the hypothalamus controls the body’s internal environment?

Answer 18

It influences the activity of the autonomic nervous system, it controls the release of various hormones
and it manages various drive states such as hunger and thirst.

Question 19

What are the four lobes of the cortex, and what are three functional categories of areas
within these lobes?

Answer 19

The four lobes are the occipital, temporal, parietal and the frontal lobes. The main functional categories
are the primary sensory areas, which gather and interpret signals from sensory nerves and tracts; the
primary motor area, which sends axons down the to the motor neurons; and association areas that are
made up by the rest of the cerebral cortex, interpreting sensory signals and receiving input from the
lower brain and managing the processes of thought, perception and decision.

Question 20

What does it mean to say that cortical sensory and motor areas in the cortex
are topographically organized?

Answer 20

It indicates that adjacent neurons in the brain receive sensory signals and send out motor commands
from and to adjacent neurons in another part of the body as well.

Question 21

What is the role of the prefrontal cortex in the control of behaviour?

Answer 21

The prefrontal cortex receives new information and/or retrieves information from long-term memory
and plans a proper action in accordance with the information.

Question 21

How are the movement-control functions of the nervous system summarized as a
hierarchical, top-down flow of information? How is the hierarchy illustrated by an imaginative
tour through the nervous system of a person who decides to eat some fresh cherries?

Answer 21

The limbic system and association cortex decide and plan the action that is going to be taken. They send
these signals down to the basal ganglia and cerebellum as well as premotor areas of the cortex. These
signals and the moves the command are refined in the motor nuclei of the upper brain stem and primary
motor area of cortex. Then all the commands reach motor nuclei of lower brainstem and the spinal cord to
be diffused to the skeletal muscles to produce movement. In the case of eating a cherry, the limbic system
sends a hunger message to the cortical areas that is it connected to. These areas analyse the visual input of
the cherries and conclude that they are available for consumption. The association areas also bring about
other information belonging to the cherries, such as the memory of eating cherries, the smell and the taste.
The prefrontal areas decide to make a move for the cherries and eat them. The prefrontal cortex and the

limbic system send designated action plans to the basal ganglia, the cerebellum and the premotor cortex,
as well as somatosensory information about the location of the cherries and the body parts. This
information is used to refine the movements of the body. Some programs for more direct movements are
processed and re-refined in the upper parts of the brain stem. The more delicate movements are processed
again in the motor cortex, which in turn sends its output to the brainstem and spinal cord. Finally, somatic
motor neurons receive the signal and convey it to skeletal muscles to produce movement.

Question 22

What is the difference between knowing where a brain function occurs and knowing
how it occurs?

Answer 22

Using different techniques to obstruct, activate or observe brain activity in different brain areas,
scientists can discover where a function is served within the brain, but the information of the location
does not define any internal biological or chemical reaction that would cause this particular part of the
brain to be responsible from the function that it serves. Knowing physically how an action occurs is
possible, but it is not dependant on the knowledge of this function’s place in the brain.

Question 23

What are some examples of long-term and short-term effects of hormones?

Answer 23

Some long-term effects of hormones differentiation of gender from birth and into puberty, which are
irreversible. The short-term effects can range from lasting a few minutes to a few days. These hormones
usually prepare the body for sudden events and encounters, such as preparing the body to either engage in
violence or flee the scene by pumping sugar and fat into the blood and suppressing inflammation and pain
caused by physical trauma or incisions.

Question 24

How does the brain control the release of hormones from the two lobes of the pituitary
and thereby control the release of other hormones as well?

Answer 24

The posterior lobe of the pituitary is directly connected to the brain via blood vessels and neurosecretory
cells. When stimulated by these cells, the posterior pituitary sends the hormones into bed of capillaries.
Via the bed of capillaries, the hormone diffuses into the whole bloodstream. The anterior pituitary is not
directly connected to the brain, however it is closely related to it. It is activated by the hypothalamus with
a substance called releasing factor, which is carried to the anterior pituitary by the bed of capillaries. The
releasing factor enables the anterior pituitary to produce the designated hormones and diffuse them into
the bloodstream.

Question 25

How is it possible to test each hemisphere separately in people whose corpus callosum
has been cut? How do such tests confirm that the left hemisphere controls speech and the right
hemisphere has superior spatial ability?

Answer 25

By flashing images to one half of the visual angle and having the patient both touch the object and say
what they see, scientists were able to determine where the perceived information goes through – or
doesn’t – and how it is processed. The patients can usually identify the object by touching but struggle to
say its name, and say the see the other object, that has been projected onto the right side of their vision.
These patients were also presented various images and tasks to complete with one hand, or see with one
side of their vision etc. These studies collectively conclude that verbal communication and language
related matters are usually managed by the left hemisphere whereas spatial and more abstract concepts
were better perceived with the right hemisphere.

Question 26

In what ways are the two hemispheres of the cerebral cortex symmetrical, and in what
ways are they asymmetrical?

Answer 26

Both hemispheres have almost the same motor and sensory functions, but each covers a different part of
the body – precisely the left hemisphere for the right, and the right hemisphere for the left. The left
hemisphere is more specialised in language, and the right hemisphere deals with nonverbal visuospatial
information.

Question 27

How do studies of split-brain patients tend to confirm and extend the idea about the nature
of consciousness that was developed long ago by Sigmund Freud?

Answer 27

These studies have shown that the left hemisphere and the right hemisphere could learn to cooperate,
however since language is controlled by the left hemisphere, the patients come up with seemingly
plausible but often false explanations of their seemingly contradictory actions. This has strengthened the
idea of Freud that there is an unconscious decision making process and that we act according to it.

Question 28

What are the differences between Broca’s and Wernicke’s aphasias in (a) language
production, (b) language comprehension and (c) areas of the brain damaged?

Answer 28

Broca’s area is anterior to the primary motor area. Studies have concluded that patients who suffered
Broca’s aphasia are not able to form grammatically complex sentences as well as understand them;
lacking the ability to form or decipher these sentences. Wernicke’s area, however, is near the primary
auditory area and is rather small. Patients who suffer from this type of aphasia can maintain the
grammatical integrity of the sentences but they do not convey any meaning. They also have hardship in
translating heard language into meaningful transcripts.

Question 29

How was PET used to identify brain areas involved in word perception and production?

Answer 29

The subjects were given different tasks that involved visual, auditory or linguistic activities and PET was
used to determine brain activity during these tasks. These studies showed that during the perception and
production of language, many more areas than Broca’s and Wernicke’s are involved.

Question 30

What brain changes have been observed in rats and mice caged in enriched environments?

Answer 30

The rats that have been kept in enriched environments had thicker cerebral cortices, larger cortical
neurons, more acetylcholine, more synapses per neuron, and thicker, more fully developed synapses
compared to those who have been caged in deprived environments.

Question 31

What evidence shows that practice at a skill alters neural connections so that more
neurons become devoted to the skill?

Answer 31

Scientists, by studying animals that had a specific task to complete that concerned a specific part of their
brains, or people who have been lacking in senses, discovered that often different parts of the brain
developed more depending on the kind of required task or the repeated action that was done; also that
some parts of the brain could restructure themselves to serve different purposes in order to compensate for
the lack of some senses.

Question 31

What evidence, with birds and with humans, indicates that spatial learning can result in
growth in the hippocampus?

Answer 31

With birds, those species that who buried their seeds and retrieved them later had larger hippocampi
and much better memories. Also, when these birds were allowed to collect and bury seeds their
hippocampi grew, and when they are prohibited from doing so, their hippocampi shrink again. In
humans, London taxi drivers are an example; they are able to successfully navigate themselves in that
large city which causes their hippocampi to grow, which enables them to acquire spatial proficiency.

Question 32

How has the discovery of long-term potentiation tended to confirm Hebb’s theory
about synaptic strengthening?

Answer 32

Long-term potentiation explains a neural transactions: If the connection between two neurons is weak, a
third neuron can fire and trigger one of the neurons just as the other deployed neurotransmitters onto it
and this strengthens the connection between the first two neurons. If this sequence repeats enough, the
neurons are bound more strongly from then on. This proves Hebb’s theory of synaptic strengthening.

Question 33

What evidence shows that long-term potentiation is involved in learning?

Answer 33

As results of studies conducted with mice; those that have been rendered inadequate in terms of LTP
have shown poor learning skills, even worse than their normal condition; those that have been enriched
in terms of LTP have followed the same learning patterns however were much more efficient at
remembering and repeating what they have learned.