Final Study Exam

Question 1

What is a gastrula?

Answer 1

gastrula, early multicellular embryo, composed of two or more germinal layers of cells from which the various organs later derive. The gastrula develops from the hollow, single-layered ball of cells called a blastula which itself is the product of the repeated cell division, or cleavage, of a fertilized egg.

Question 2

blastula

Answer 2

blastula, hollow sphere of cells, or blastomeres, produced during the development of an embryo by repeated cleavage of a fertilized egg. The cells of the blastula form an epithelial (covering) layer, called the blastoderm, enclosing a fluid-filled cavity, the blastocoel. After the blastula develops, it undergoes transition to the gastrula, a process called gastrulation.

Question 3

Gastrulationembryogenesis

Answer 3

Gastrulation is a phase early in the embryonic development of most animals, during which the single-layered blastula is reorganized into a trilaminar (“three-layered”) structure known as the gastrula. These three germ layers are known as the ectoderm, mesoderm, and endoderm.[1][2]
Gastrulation takes place after cleavage and the formation of the blastula

Question 4

embryogenesis

Answer 4

Mammalian embryogenesis is the process of cell division and cellular differentiation which leads to the development of a mammalian embryo.
A mammal develops from a single cell called a zygote, which results from an ovum (egg) being fertilized by a single sperm.
The zygote is surrounded by a strong membrane of glycoproteins called the zona pellucida which the successful sperm has managed to penetrate.
The zygote undergoes cleavage, increasing the number of cells within the zona pellucida.
After the 8-cell stage, mammalian embryos undergo what is called compactation, where the cells bind tightly to each other, forming a compact sphere.
After compactation, the embryo is in the morula stage (16 cells).
Cavitation ocurrs next, where the outermost layer of cells - the trophoblast - secrete water into the morula.
As a consequence of this when the number of cells reaches 40 to 150, a central, fluid-filled cavity (blastocoel) has been formed.
The zona pellucida begins to degenerate, allowing the embryo to increase its volume.
This stage in the developing embryo, reached after four to six days, is the blastocyst (akin to the blastula stage), and lasts approximately until the implantation in the uterus.
The blastocyst is characterized by a group of cells, called the inner cell mass (also called embryoblast) and the trophoblast (the outer cells).

Question 5

Trophoblasts

Answer 5

Trophoblasts (from Greek trephein: to feed, and blastos: germinator) are cells forming the outer layer of a blastocyst, which provide nutrients to the embryo and develop into a large part of the placenta.

Question 6

blastocyst

Answer 6

The blastocyst is a structure formed in the early development of mammals. It possesses an inner cell mass (ICM) which subsequently forms the embryo. The outer layer of the blastocyst consists of cells collectively called the trophoblast. This layer surrounds the inner cell mass and a fluid-filled cavity known as the blastocoel. The trophoblast gives rise to the placenta.

Question 7

What is the Inner Cell Mass and why is this important?

Answer 7

In early embryogenesis
is the mass of cells inside the primordial embryo that will eventually give rise to the definitive structures of the fetus. This structure forms in the earliest steps of development,
enveloped by the outer, polarized trophoblast layer of cells. The trophoblast cells form an inner cavity (blastocoele), whose formation indicates the bastocyst stage. While the trophoblast will ultimately form the outer chorionic sac and the fetal component of the placenta, the inner cell mass, will give rise to all embryonic tissues and to some of the extraembryonic membranes.

Question 8

Be familiar with the ectoderm, mesoderm and endoderm – what parts of the body originate from each?

Answer 8

ectoderm
The outer cellular layer of the developing fetus, giving rise to the skin and the nervous system.

mesoderm,
the middle of the three germ layers. gives rise to muscle, connective tissue, cartilage, bone, blood, body cavities, kidneys, ureters, gonads (sex organs),

endoderm,
the innermost layer.

Question 9

What is the neural plate, neural tube, notochord?

Answer 9

The neural plate is a key developmental structure that serves as the basis for the nervous system. in the embryo, ectodermal tissue thickens and flattens to become the neural plate. The ends of the neural plate, known as the neural folds, push the ends of the plate up and together, folding into the neural tube, a structure critical to brain and spinal cord development. This process as a whole is termed primary neurulation.

the neural tube is the embryo’s precursor to the central nervous system. The neural groove gradually deepens as the neural folds become elevated, and ultimately the folds meet and coalesce in the middle line and convert the groove into a closed tube, the neural tube

The notochord is a flexible rod-shaped body found in embryos of all chordates. It is composed of cells derived from the mesoderm and defines the primitive axis of the embryo.

Question 10

How does the brain develop from the ectoderm?

Answer 10

2 small areas divides more than others, creating ridges, because of the notochord that is releasing proteins that stimulates diferatantaion.
This forms neural tube.
The neural tube separates into functional groups.

Question 11

spina bifida

Answer 11

Spina bifida is a developmental congenital disorder caused by the incomplete closing of the embryonic neural tube. Some vertebrae overlying the spinal cord are not fully formed and remain unfused and open.

Question 12

lissencephaly

Answer 12

Lissencephaly, which literally means smooth brain, is a rare brain formation disorder caused by defective neuronal migration

Question 13

exencephaly

Answer 13

Exencephaly is a type of cephalic disorder wherein the brain is located outside of the skull.

Question 14

anencephaly

Answer 14

Anencephaly is the absence of a major portion of the brain, skull, and scalp that occurs during embryonic development.[1] It is a cephalic disorder that results from a neural tube defect that occurs when the rostral (head) end of the neural tube fails to close,

Question 15

hydrocephalus

Answer 15

Hydrocephalus[a] /ˌhaɪdrɵˈsɛfələs/, also known as “water on the brain”, is a medical condition in which there is an abnormal accumulation of cerebrospinal fluid (CSF) in the ventricles, or cavities, of the brain. This may cause increased intracranial pressure inside the skull and progressive enlargement of the head, convulsion, tunnel vision, and mental disability.

Question 16

What is a zygote?

Answer 16

is the initial cell formed when two gamete cells are joined by means of sexual reproduction. In multicellular organisms, it is the earliest developmental stage of the embryo.

Question 17

What are the six stages of neural development? Be able to describe each one. Do they occur one at a time or is there overlap between the stages?

Answer 17

Stages of Neuronal Development

1) Neurogenesis
2) Cell Migration
3) Cell Differentiation
4) Synpatogenesis
5) Neuronal Cell Death
6) Synapse Rearrangement

Neurogenesis General cells develop into neurons
Neurogenesis ends at birth

Cell Migration Via glial cells, neurons are transported to where they need to be
Cell migration ends at birth

Cell Differentiation Neurons differentiate into speciifc neurons and glial cells
Myelination occurs
Cell differentiation ends just after birth

Synaptogenesis Synapses develop between cells
Synapses develop AFTER birth

Neuronal Cell Death Apoptosis–cells die during adolescence
Hippocampus, olfactory bulb & glial cells do no undergo apoptosis

Synapse Rearrangment Connections are lost when cell die
Cell have to realign their synapses
Myelination & synapse rearrangement ends by the age of 25

Question 18

What is the difference between totipotent and multipotent stem cells?

Answer 18

A multipotent stem cell can give rise to other types of cells but it is limited in its ability to differentiate. These other types of cells are also limited in numbers. Examples of multipotent stem cells include those in the brain that give rise to different neural cells and glia or haematopoietic cells, which can give rise to different blood cell types, but they can’t create brain cells.

Question 19

What is a stem cell?

Answer 19

A cell that is undifferentiated and therefore can take on the fate of any cell that a donor organism can produce.

Question 20

What is neural proliferation, where does this occur?

Answer 20

the growth or production of cells by multiplication of parts.

The production of nerve cells is called neurogenesis. Nerve cells themselves do not divide, but the cells that will give rise to neurons begin as a single layer of cells along the inner surface of the neural tube. These cells divide (in a process called mitosis) and gradually form a closely packed layer of cells called the ventricular zone. All neurons and glial cells are derived from cells that originate from this ventricular mitosis. Eventually, some cells leave the ventricular zone and begin transforming into either neurons or glial cells.

Question 21

How do neurons migrate – two ways.

Answer 21

The movement of cells from site of origin to final location.
Neurons in the developing nervous system are always on the move. At some stage the cells that form in the ventricular layer through mitotic division move away,
Cells do not move in an aimless, haphazard manner. Cells in the developing brain move along the surface of a particular type of glial cell

Glial Spokes Guide Migrating Cells
Cells in the developing brain move along the surface of a particular type of glial cell. Like spokes (radii) of a wheel, these radial glial cells extend from the inner to the outer surfaces of the emerging nervous system. The radial glial cells act as a series of guides, and the newly formed cells mostly creep along them. Some migrating cells move in a direction perpendicular to
the radial glial cells.

The migration of cells and the outgrowth of nerve cell extensions (dendrites and axons) involve various chemicals that promote the adhesion of developing elements of the nervous system. These cell adhesion molecules (CAMs) guide migrating cells and growing axons

Question 22

What are some of the growth factors that influence neural development?

Answer 22

Nerve growth factor (NGF) is produced by targets and taken up by the axons of innervating neurons, keeping them alive. Nerve growth factor (NGF) is a small secreted protein that is important for the growth, maintenance, and survival of certain target neurons (nerve cells). Administered to
a chick embryo, NGF resulted in many more sympathetic neurons than usual.

Other factors are brain-derived neurotrophic factor (BDNF) and similar members of the neurotrophin family. There are additional neurotrophic factors, each one affecting the survival of a particular cell type during a specific developmental period. One such factor, named brain-derived neurotrophic factor (BDNF), is very similar to NGF.

Question 23

What are lammelapodia and filipodia?

Answer 23

Filopodia are the fine outgrowths of growth cones and lamellipodia are sheetlike extensions.
Both adhere to the environment and pull the growth cone in a particular direction.

Question 24

How are synapses formed?

Answer 24

At the tips of axons and dendrites alike, specialized swellings called growth cones are found. Very fine extensions, called filopodia (singular filopodium, from the Latin filum, “thread,” and the Greek pous, “foot”), extend from the growth cone (FIGURE 7.8). Just as migrating cells are guided by CAMs, the filopodia of growth cones adhere to CAMs in the extracellular environment and then contract to pull the growth cone in a particular direction (the growing axon or dendrite trailing behind). Dendritic growth cones are found in adults, mediating the continued elongation and change in dendrites that occurs throughout life in response to experience (see Chapter 17).What guides axons along the paths they take? The CAMs guiding growth cones are released by the target nerve cells or other tissues, such as muscles. The axon growth cone responds to the concentration gradients of these chemicals that provide directional guidance, as illustrated in FIGURE 7.9. Chemical signals that attract certain growth cones are called chemoattractants (Hiramoto et al., 2000); chemicals that repel growth cones are chemorepellents

Question 25

What happens to synapses that are not used? Why is neuron death important during development?

Answer 25

As strange as it may seem, cell death is a crucial phase of brain development, especially during embryonic stages. This developmental stage is not unique to the nervous system. Naturally occurring cell death, also called apoptosis (from the Greek apo, “away from,” and ptosis, “act of falling”), is a kind of sculpting process in the emergence of other tissues in both animals and plants.
Genetically interfering with
neural apoptosis in fetal mice causes them to grow brains that are too large to fit in the skull (Depaepe et al., 2005), so we can see how vital it is that some cells die.

Question 26

What is apoptosis? How does apoptosis work?

Answer 26

These cells are not dying because of a defect. Rather, it appears that these cells have “decided” to die and are ac-tively committing suicide. Your chromosomes carry death genes—genes that are expressed only when a cell undergoes apoptosis

As you may have guessed, apoptosis in vertebrates is regulated by cell-cell interactions, such as the availability of synaptic targets. Reducing the size of the synaptic target invariably reduces the number of surviving nerve cells.

Thus neurons compete for connections to target structures (other nerve cells or end organs, such as muscle). Neurons that make adequate synapses survive and grow; those that fail to form synaptic connections die. Apparently the neurons compete not just for synaptic sites, but also for a chemical that the target structure makes and releases. Neurons that receive enough of the chemical survive; those that do not, die. Such target-derived chemicals are called neurotrophic factors (or simply trophic factors) because they act as if they “feed” the neurons to help them survive (in Greek, trophe means “nourishment”). The neurotrophic factor that was the first to be identified prevents the death of developing sympathetic neurons

Question 27

How does experience/environment influence brain development?

Answer 27

Epigenetics - The study of factors that affect gene expression without making any changes in the nucleotide sequence of the genes themselves.

Amblyopia - Reduced visual acuity that is not caused by optical or retinal impairments.

sensitive period - The period during development in which an organism can be permanently altered by a particular experi-ence or treatment.

Question 28

What is neuroplasticity? neurogenesis?

Answer 28

neurogenesis The mitotic division of non-neuronal cells to produce neurons.
The production of nerve cells is called neurogenesis. Nerve cells themselves do not divide, but the cells that will give rise to neurons begin as a single layer of cells along the inner surface of the neural tube. These cells divide (in a process called mitosis) and gradually form a closely packed layer of cells called the ventricular zone. All neurons and glial cells are derived from cells that originate from this ventricular mitosis. Eventually, some cells leave the ventricular zone and begin transforming into either neurons or glial cells.

adult neurogenesis
At birth, mammals have already produced most of the neurons they will ever have. The postnatal increase of human brain weight is primarily due to growth in the size of neurons, branching of dendrites, elaboration of synapses (as we’ll see in Figure 7.6), increase in myelin, and addition of glial cells. But early reports that new neurons are added just after birth in some brain regions (Altman, 1969) have been supplemented with findings of adult neurogenesis, the generation of new neurons in adulthood, While the new neurons acquired in adulthood represent a tiny minority of neurons, there’s reason to think they are important. Enriched experience, such as learning, increases the rate of neurogenesis in adult mammals

Synapse rearrangement
Synapse rearrangement, or synaptic remodeling, refines synaptic connections.
One influence on synaptic survival is neural activity.
A neurotrophic factor may contribute.

Question 29

What is autism

What do we know about their cause, brain development and behaviour. How might they be related to neural development?

Answer 29

Autism is a developmental disorder characterized by impaired social interactions and language and a narrow range of interests and activities. The disorder is much more common in males than females. Usually autism is discovered when apparently normal toddlers begin regressing, losing language skills, and withdrawing from family interaction. Children with autism tend to perseverate (such as by continually nodding the head or making stereotyped finger movements), actively avoid making eye contact with other people, and have a difficult time judging other people’s thoughts or feelings (Senju et al., 2009). When shown photos of the faces of family members, autistic individuals display a pattern of brain activation that is different from that exhibited by controls (Pierce et al., 2001), suggesting a different brain organization for the fundamental social skill of recognizing others.
Several structural differences between the brains of people with autism and controls have been reported, including a reduction in the size of the corpus callosum and certain cerebellar regions (Egaas et al., 1995).
The amygdala has been associated with fear (see Chapter 15), so this finding suggests that children with autism avoid making eye contact with people because they find it aversive.
The underlying problem with autism may be an inability to empathize with others, as reflected in the difficulty that individuals with autism display in making “copycat” movements of the fingers or body. When people with autism do this task, a particular part of the frontal cortex is less activated than in control subjects (Villalobos et al., 2005). The same region is also underactivated when people with autism try to mimic emotional facial expressions of others

Question 30

Down Syndrome

What do we know about their cause, brain development and behaviour. How might they be related to neural development?

Answer 30

A common form of intellectual disability resulting from a chromosomal abnormality is Down syndrome (FIGURE 7.20A). People with Down syndrome usually have an extra chromosome 21, for a total of three rather than the typical two copies.

Question 31

Williams syndrome

What do we know about their cause, brain development and behaviour. How might they be related to neural development?

Answer 31

Williams syndrome A disorder characterized by fluent linguistic function but poor performance on standard IQ tests and great difficulty with spatial processing. Individuals with Williams syndrome speak freely and fluently with a large vocabulary, yet they may be unable to draw simple images, arrange colored blocks to match an example, or tie shoelaces. The individuals are very sociable, ready to strike up conversation and smile. They may also display strong musical talent, either singing or playing an instrument. The syndrome results from the deletion of about 28 genes from one of the two chromosomes numbered leads to pixielike facial features. Several of the other missing genes are thought to lead to changes in brain development and to the behavioral features of the syndrome. Difficulty with spatial memory and drawing objects

Question 32

Fragile X syndrome

What do we know about their cause, brain development and behaviour. How might they be related to neural development?

Answer 32

Probably the most frequent cause of inherited intellectual disability is the condition fragile X syndrome (FIGURE 7.20B), which is more common in males than in females. At the end of the long arm of the X chromosome is a site that seems fragile—prone to breaking because the DNA there is unstable (Yu et al., 1991). People with this abnormality have a modified facial appearance, including elongation of the face, large prominent ears, and a prominent chin. A wide range of cognitive effects—from mild to severe impairment—are associated with the syndrome (Baumgardner et al., 1994). Cortical neurons from the brains of people with fragile X syndrome, as well as mice genetically engineered to have this syndrome, possess an excess of small, immature dendritic spines (Bagni and Greenough, 2005). These findings suggest that the syndrome affects mental development by blocking the normal elimination of synapses after birth (see Figure 7.10).

Question 33

FAS

What do we know about their cause, brain development and

Answer 33

alcohol syndrome (FAS) (Abel, 1984). Prominent anatomical effects of fetal exposure to alcohol include distinctive changes in facial features (e.g., a sunken nasal bridge and altered shape of the nose and eyelids) and stunted growth. In some cases, the children may lack a corpus callosum (FIGURE 7.17). Few FAS children catch up in the years following birth. The most common problem associated with FAS is intellectual disability, which varies in severity. No alcohol threshold has yet been established for this syndrome, but it can occur with relatively moderate intake during pregnancy. Even when FAS is not diagnosed, prenatal exposure to alcohol is correlated with impairments in language and fine motor skills The brain of an infant of the same age with FAS. This brain shows microcephaly (abnormal smallness), fewer cerebral cortical gyri, and the absence of a corpus callosum connecting the two hemispheres.

Question 34

What are mirror neurons? How might they be important in the study/development of autism?

Answer 34

When control children and children with autism are asked to imitate the emotional facial expressions displayed in photographs of other people, many brain regions show activation in both groups. But the indicated region, the pars opercularis region, is less activated in children with autism than in controls. This is the region that contains “mirror neurons” (see Chapters 10 and 11). Perhaps deficits in activating brain regions underlying imitation and empathy contribute to the social impairments of autism. (After Dapretto et al., 2006; courtesy of Mirella Dapretto.)

Question 35

What are ‘green mice” and why do they matter? (in class)

Answer 35

Scientests were looking for stem cells that could groe into nerve or brain cells
They cave the mice a gene that would make them glow
They expected the brain area to glow but the whole body glowed because they where in all the hair follucals
Means there is a close relationship between hair and brain cells
Hair folucal stem cells could help nerve cells regrow
So easy to obtain

Question 36

Rasmussen’s Syndrome

Answer 36

rare inflammatory neurological disease, characterized by frequent and severe seizures, loss of motor skills and speech, hemiparesis (paralysis on one side of the body), encephalitis (inflammation of the brain), and dementia. The illness affects a single cerebral hemisphere and generally occurs in children under the age of 15.

Question 37

Synapse rearrangement

Answer 37

Synapse rearrangement, or synaptic remodeling, refines synaptic connections.
One influence on synaptic survival is neural activity.
A neurotrophic factor may contribute.

Question 38

Behavioral teratology

Answer 38

studies pathological effects of early exposure to toxic substances

Question 39

Animals with mutations are important in researching development:

Answer 39

Site-directed mutagenesis changes the sequence of a nucleotide in a gene.
Knockout organism has a gene disabled.
Transgenic has a new or altered gene

Question 40

Dementia

Answer 40

is a drastic failure of cognitive ability.

Question 41

Alzheimer’s disease

Answer 41

is a form of senile dementia.
It begins as memory loss of recent events–brains show reduced metabolism and cortical atrophy
Alzheimer’s produces cellular changes:
Senile plaques form by β-amyloid buildup, also called amyloid plaques.
Neurofibrillary tangles, including the tau protein, occur.
Basal forebrain nuclei disappear.

Question 42

Be familiar with the different types of sensory systems that I mention in class. Type, modality and stimuli.

Answer 42

Mechanical
Touch - Contact with or deformation of body surface
Pain - Tissue damage
Hearing - Sound vibrations in air or water
Vestibular - Head movement and orientation
Joint - Position and movement
Muscle - Tension

Visual
Seeing - Visible radiant energy

Thermal
Cold - Decrease in skin temperature
Warmth - Increase in skin temperature

Chemical
Smell - Odorous substances dissolved in air or water
in the nasal cavity
Taste - Substances in contact with the tongue or
Common chemical - Changes in CO2, pH, osmotic pressure
Vomeronasal - Pheromones in air or water

Electrical
Electroreception - Differences in density of electrical currents

Question 43

What is the concept of labeled lines? How does this apply to sensory systems such as the somatosensory system, pain perception, taste and olfaction?

Answer 43

Today we know that the messages for the different senses—such as seeing, hearing, touching, sensing pain, and sensing temperature—all use the same type of “energy”: action potentials. But the brain recognizes the different kinds of sensation (modalities) as separate and distinct because each modality sends its action potentials along separate nerve tracts. This is the concept of labeled lines: particular neurons are, at the outset, labeled for distinctive sensory experiences. Neural activity in one line signals a sound, activity in another line signals a smell, and activity in other lines signals touch. We can even distinguish different types of touch because some lines signal light touch, others signal vibration, and yet other lines signal stretching of the skin. You can demonstrate this effect right now. If you take your finger and gently press on your eyelid, you’ll see a dark blob appear on the edge of your field of view (it helps to look at a blank white wall). Of course, your skin also feels the touch of your finger, but why do you see a blob with your eye? The energy you applied, pressure, affected action potentials coming from your eye. Because your brain labels that line as always carrying visual information, what you experienced was a change in vision.

Question 44

Be able to describe generator potentials. How are these created in Pacinian corpuscles?

Answer 44

receptor potential
Also called generator potential. A local change in the resting potential of a receptor cell that mediates between the impact of stimuli and the initiation of nerve impulses.
The structure of a receptor determines the forms of energy to which it will respond.
The steps between the arrival of energy at a receptor cell and the initiation of action potentials in a nerve fiber involve local changes of membrane potential called receptor potentials (or generator potentials). In most instances, the receptor potential resembles the excitatory postsynaptic potentials

Pacinian corpuscle
Also called lamellated corpuscle. A skin receptor cell type that detects vibration.
One example of the generator potential can be studied in a receptor called the Pacinian corpuscle (or lamellated corpuscle; Loewenstein, 1971). This receptor, which detects vibration, is found throughout the body in skin and muscle.

Question 45

What are the different receptor types/nerve endings found in the skin (at least 7) and what type of information do they transmit to the CNS?

Answer 45

Pacinian corpuscles–vibration, fast-adapting
Meissner’s corpuscles– touch, fast-adapting
Merkel’s discs–touch, slow-adapting
Ruffini’s endings–stretch, slow-adapting

Question 46

What is sensory adaptation? How does this relate to what we do and do not perceive in our environments?

Answer 46

adaptation
The progressive loss of receptor sensitivity as stimulation is maintained.
adequate stimulus

The frequency of action potentials progressively declines, even
though the stimulus is continued (FIGURE 8.7). In terms of adaptation, there are two
kinds of receptors: Tonic receptors show little or no decrease in the frequency of ac-
tion potentials as stimulation is maintained; in other words, these receptors show
relatively little adaptation. Phasic receptors display adaptation, rapidly decreasing
the frequency of action potentials when the stimulus is maintained.
Adaptation means that there is a progressive shift in neural activity away from
accurate portrayal of maintained physical events. Thus, the sensory system may fail
to register neural activity even though the stimulus continues. Such a
striking discrepancy is no accident; sensory systems emphasize change
in stimuli because changes are more likely to be significant for sur-
vival. Sensory adaptation prevents the nervous system from becoming
overwhelmed by stimuli that offer very little “news” about the world.

Question 47

What are the levels of sensory processing?

Answer 47

Information
enters the CNS through the brainstem or spinal cord and then
reaches the thalamus. The thalamus shares the information with
the cerebral cortex; the cortex directs the thalamus to suppress
some sensations. Primary sensory cortex swaps information
with nonprimary sensory cortex. This organization is present in
all sensory systems except smell, which bypasses the thalamus,
going directly to cortex

Question 48

What is a homunculus? What does it tell us about the brain?

Answer 48

he homunculus (literally, “little man”) depicts the body
surface with each area drawn in proportion to the size of its representation in the primary
somatosensory cortex.

Question 49

How do sensory systems affect each other?

Answer 49

polymodal Involving several sensory
modalities.
Often the use of one sensory system influences perception derived from another sen-
sory system
neither sense alone may be sufficient to elicit a response (B. Stein and
Meredith, 1993). Similarly, humans detect a visual signal
more accurately if it is accompanied by a sound from the
same part of space (McDonald et al., 2000).
Many sensory areas in the brain—so-called associa-
tion areas—do not represent exclusively a single modality
but show a mixture of inputs from different modalities. Perhaps loss of input from one modal-
ity allows these cells to analyze input from the remaining
senses better, as happens, for example, in cases of people
who become blind early in life and are better than sight-
ed people at localizing auditory stimuli (Gougoux et al.,
2005). The normal stimulus convergence on such polymo-
dal cells provides a mechanism for intersensory interac-
tions (B. E. Stein and Stanford, 2008). For a few people,
a stimulus in one modality may evoke an additional per-
ception in another modality,

Question 50

What is association cortex – I mentioned two areas of your brain in class that are important for this.

Answer 50

Association cortex is the cerebral cortex outside the primary areas (Figure 1). It is essential for mental functions that are more complex than detecting basic dimensions of sensory stimulation, for which primary sensory areas appear to be necessary. In humans the association areas are by far the most developed part of the cerebral cortex, and the brain in general. These areas are necessary for perceptual activities, like recognizing objects (toasters, horses, trees, words, etc), rather than simple contours, edges or sensory qualities like color or pitch.

Sensory association areas combine this kind of information to represent complex objects. For example, the visual association area on the lower part of the temporal lobe plays a primary role in your ability to recognize faces, dogs, cars, trees, etc., whereas the primary visual cortex is required for detecting basic features of the visual world: edges, light and dark, location, etc.
the auditory association cortex (around the primary auditory cortex on the top of the temporal lobe)
the somatosensory association cortex (on the parietal lobe behind the primary somatosensory cortex)

Question 51

What is the binding problem (in class).

Answer 51

The question of how the
brain understands which individual attributes
blend together into a single object, when
these different features are processed by dif-
ferent regions in the brain.

Question 52

Be able to reconstruct the dorsal column system for somatosensory processing.

Answer 52

The Dorsal Column System Carries Somatosensory
Information from the Skin to the Brain
The touch receptors that we have described (Pacinian corpuscles, Merkel’s discs, Meissner’s corpuscles, and Ruffini’s endings) send their axons to the spinal cord, where they enter the dorsal horn and turn upward, traveling to the brain along the spinal cord’s dorsal column of white matter, which is why this is called the dorsal column system. These axons go all the way up to the brainstem, where they synapse on neurons of the dorsal column nuclei in the medulla (FIGURE 8.15). The axons of these medullary neurons then cross the midline to the opposite side and ascend to a group of nuclei of the thalamus. Outputs of the thalamus are directed to primary somatosensory cortex (S1).

Question 53

What is a dermatome? How does this relate to the spinal cord nerves?

Answer 53

The skin surface can be divided into bands corresponding to the spinal nerves that carry the axons from the different regions (FIGURE 8.16A). A dermatome (from the Greek derma, “skin,” and tome, “part” or “segment”) is the region of skin innervated by a particular spinal nerve. The pattern of dermatomes is hard to understand in an upright human, but remember that our erect posture is a recent evolutionary development. The dermatomes
overlap a modest amount

Question 54

What is plasticity in a cortical map? How does this relate to phantom limbs? What type of treatment seems to work for phantom limb pain? Speculate about why this would work (yes this is an open ended question but you can answer this )

Answer 54

Now, however, we know that cortical maps can change with experience (Merzenich and Jenkins, 1993).In one experiment, the receptive field of a monkey’s hand was mapped in detail in the somatosensory cortex (FIGURE 8.17A). Then the middle finger was surgically removed. The region of cortex that responded to each remaining, adjacent finger
expanded, so the region that had formerly responded to the removed finger now responded to the neighboring fingers (FIGURE 8.17B). In another experiment, a monkey was trained to rest two fingers on a rotating disk in order to obtain food rewards. After several weeks of training, the hand area was mapped again, and the stimulated fingers were found to have considerably enlarged representations compared with their previous areas (FIGURE 8.17C).Similar findings were noted in rats exposed to differential tactile experiences (Xerri et al., 1996). Professional musicians who play stringed instruments have expanded cortical representations of their left fingers,Brain imaging also reveals cortical reorganization in people who lose a hand in adulthood

Question 55

What is the pathway that transmits pain information?

Answer 55

1 Damaged cells release substances that excite free nerve endings that function as nociceptors.

2 Action potentials generated in the periphery can reflexively excite blood vessels and other cells to produce inflammation.

3 Information enters through the dorsal root and synapses on neurons in the dorsal horn.

4 Pain fibers release glutamate as a transmitter and substance P as a neuromodulator in the spinal cord. The dorsal horn cells then send information across the midline and up to the thalamus.

Question 56

How can the opioid system modulate the ascending spinothalamic system for pain.

Answer 56

Pain ascends the spinothalamic system to reach the brain Sensation of pain travels from its origin to the brain via the spinothalamic system, crossing the midline in the spinal cord.

anterolateral system or spinothalamic system A somatosensory system that carries most of the pa

In the central nervous system, special pathways mediate pain and temperature information. Earlier we discussed the dorsal column system that carries touch information to the brain (see Figure 8.15). The sensations of pain and temperature are transmitted separately by the anterolateral, or spinothalamic, system.

Morphine provides analgesia by stimulating the opioid receptors in this descending pain control system, in both the brainstem

Question 57

What is naloxone?

Answer 57

A potent antagonist of opiates that is often administered to people who have taken drug overdoses. It blocks receptors for endogenous opioids.

Question 58

Are their people who do not experience pain? Why would this be a problem?

Answer 58

Congenital insensitivity to pain–an inherited syndrome
Pain helps us to withdraw from its source, engage in recuperative actions, and to signal others.
Such people show extensive scarring from injuries to fingers, hands, and legs (Manfredi et al., 1981), and they tend to die young of injuries, suggesting that pain guides adaptive behavior by signaling harm to our bodies.

Question 59

Where do we process the emotional and perceptual aspects of pain?

Answer 59

cingulate cortex - Also called cingulum. A region of medial cerebral cortex that lies dorsal to the corpus callosum.

Question 60

What is the difference between the terms pain and nociception (in class)

Answer 60

“acute“ - meaning new or sudden. Acute pain often originates from nociception - the nervous systems way of detecting, transmitting and processing potential damage. This potential damage is detected by nociceptors - a kind of nerve ending (sensory receptor) found all over your body. 2

Once nociceptors are activated, they send signals through peripheral nerves to the spinal cord, which then travel to the brain. 3 The signals are processed at each stage of transmission, with the brain arguably playing the largest role in how pain is consciously experienced. 4

Question 61

Be able to describe at least one type of pain relief intervention from the four main categories listed in your textbook.

Answer 61

PSYCHOGENIC
Cognitive (learning, coping strategies) May activate endorphin-mediated pain control system. Limited usefulness for severe pain

PHARMACOLOGICAL
Opiates Bind to opioid receptors in periaqueductal gray and spinal cord. Severe side effects due to binding in other brain regions.

STIMULATION
TENS/mechanical. Tactile or electrical stimulation of large fibers blocks or alters pain signal to brain. Segmental control; must be applied at site of pain

SURGICAL
Rhizotomy (cutting dorsal root) Create physical break in pain pathway. Considerable risk of failure or return of pain

Question 62

1) Be familiar with the basic anatomy of the ear.

external ear

Answer 62

external ear
The part of the ear that we readily see (the pinna) and the canal that leads to the eardrum. The shape of the external ear is also important in identifying the direction and distance of the source of a sound.

pinna
The external part of the ear. The pinnae funnel sound waves into the second part of the external ear: the ear canal. The “hills and valleys” of the pinna modify the character of sound that reaches the middle ear. Some frequencies of sound are enhanced; others are suppressed.

ear canal
A tube leading from the pinna to the middle ear.

Question 63

1) Be familiar with the basic anatomy of the ear.

middle ear

Answer 63

middle ear
The cavity between the tympanic membrane and the cochlea.

tympanic membrane
Also called eardrum. The partition between the external ear and the middle ear.

ossicles
Three small bones (incus, malleus, and stapes) that transmit sound across the middle ear, from the tympanic membrane to the oval window.

oval window
The opening from the middle ear to the inner ear.

tensor tympani
The muscle attached to the malleus that modulates mechanical linkage to protect the delicate receptor cells of the inner ear from damaging sounds.

Stapedius
A middle-ear muscle that is attached to the stapes.

Question 64

1) Be familiar with the basic anatomy of the ear.

inner ear

Answer 64

inner ear
The cochlea and vestibular apparatus. The complex structures of the inner ear ultimately convert sound into neural activity. In mammals the auditory portion of the inner ear is a coiled, fluid-filled structure called the cochlea.

cochlea
A snail-shaped structure in the inner ear that contains the primary receptor cells for hearing. The cochlea is a coil of three parallel canals: (1) the scala vestibuli (vestibular canal), (2) the scala media (middle canal), and (3) the scala tympani (tympanic canal). The width of these canals decreases along the length of the spiral.

round window
A membrane separating the cochlear duct from the middle-ear cavity. Because these canals are filled with non-compressible fluid, movement inside the cochlea in response to a push on the oval window requires a second membrane-covered window that can bulge outward a bit. This membrane is the round window, which separates the scala tympani from
the middle ear.

organ of Corti
A structure in the inner ear that lies on the basilar membrane of the
cochlea and contains the hair cells and terminations of the auditory nerve.

hair cell
One of the receptor cells for hearing in the cochlea.

basilar membrane
A membrane in the cochlea that contains the principal structures involved in auditory transduction.

inner hair cell (IHC)
One of the two types of receptor cells for hearing in the cochlea.

outer hair cell (OHC)
One of the two types of receptor cells for hearing in the cochlea.

stereocilium
A relatively stiff hair that protrudes from a hair cell in the auditory or vestibular system.

tectorial membrane
A membrane that sits atop the organ of Corti in the cochlear duct.

tip link
A fine, threadlike fiber that runs along and connects the tips of stereocilia.

Question 65

What can we hear?

Answer 65

We perceive a repetitive pattern of local increases and decreases in air pressure as sound. Usually this oscillation is caused by a vibrating object, such as a loudspeaker or a person’s larynx during speaking. A single alternation of compression and expansion of air is called one cycle. Figure A illustrates the changes in pressure produced by a vibrating loudspeaker while it produces a single frequency of vibration. Such a sound, called a pure tone, is represented by a sine wave that plots the oscillation between the compressions (peaks) and expansions (troughs) of air in front of the vibrating cone of the speaker. A pure tone is described physically in terms of two measures: Amplitude, Frequency.

Most sounds are more complicated than a pure tone. For example, a sound made by a musical instrument contains a fundamental frequency plus one or more integer multiples of the fundamental, called harmonics. So, middle A on the piano has a fundamental frequency of 440 Hz plus some combination of harmonics at 880, 1320, 1760, and so on. When different instruments play the same note, the notes differ in the relative intensities of the various harmonics, along with subtle qualitative differences between instruments in the way they commence, shape, and sustain the sound; these differences are what gives each instrument its characteristic sound quality, or timbre. Any complex sound can be decomposed into a sum of simple sine waves
through a mathematical process called Fourier analysis.

Because the ear is sensitive to a huge range of sound pressures, sound intensity (a measure of the difference between two pressures) is usually expressed in decibels (dB), a logarithmic scale. The common reference level for human hearing is 0.0002 dyn/cm2, the smallest amplitude at which an average human ear can detect a 1000-Hz tone. A faint whisper is about ten times as intense, and a jet airliner 500 feet overhead is about a million times as intense. The whisper is about 20 dB above threshold, and the jetliner is about 120 dB above threshold. Normal conversation is about 60 dB above the reference level.

Question 66

What are the two main components of sound that we use to interpret sound information?

Answer 66

Your auditory system detects rapid changes of sound intensity (measured in decibels, dB) and frequency (measured in cycles per second, or hertz, Hz). Your ears are so sensitive to sounds in the middle of the hearing range that one of the main jobs of your powers of attention is to filter out the constant barrage of unimportant little noises that your ears detect (see Chapter 18)

Amplitude, or intensity—usually measured as sound pressure, or force per unit area, in dynes per square centimeter (dyn/cm2). Our perception of amplitude is termed loudness.

Frequency, or the number of cycles per second, measured in hertz (Hz). For example, middle A on a piano has a frequency of 440 Hz. Our perception of frequency is termed pitch.

Question 67

2) What are the ossicles? How do they transfer information from the tympanic membrane to the oval window?

Answer 67

Sound waves in the air strike the tympanic membrane and cause it to vibrate with the same frequency as the sound. The movement of the tympanic membrane moves the chain of ossicles, concentrating the tiny mechanical forces of vibrating air particles, captured from the relatively large tympanic membrane, onto the small oval window. This arrangement vastly amplifies sound pressure so that it can produce movement in the fluid of the inner ear. Two muscles vary the mechanical linkage between the ossicles to improve auditory perception and protect the delicate inner ear from loud, potentially damaging sounds. The middle-ear muscles also attenuate self-made sounds; without this system, body movement, swallowing, vocalizations, and other internally produced sounds would be distractingly loud.

Question 68

How does the basilar membrane work?

Answer 68

The principal components that convert sounds into neural activity, collectively known as the organ of Corti (see Figure 9.2D), consist of three main structures: (1) the sensory cells (hair cells) (FIGURE 9.2E), (2) an elaborate framework of supporting cells, and (3) the terminations of the auditory fibers. The base of the organ of Corti is the basilar membrane. This flexible membrane separates the scala tympani from the scala media and, most important, vibrates in response to sound. The basilar membrane is about five times wider at the apex of the cochlea than at the base, even though the cochlea itself narrows toward its apex.

When the stapes moves in and out as a result of sound waves hitting the eardum, it sets up waves or ripples in the fluid of the scala vestibuli, which in turn cause the basilar membrane to ripple, like shaking out a rug. Because the basilar membrane is tapered—it’s about 5 times wider at the apex than at the base—different parts of the basilar membrane show their strongest responses to different frequencies of sound (FIGURE 9.3). High frequencies have their greatest effect near the base, where the membrane is narrow, whereas low-frequency sounds produce a larger response near the apex, where the membrane is wider (Ashmore, 1994). The hair cells transduce movements of the basilar membrane into electrical signals.

Question 69

What are inner and outer hair cells – what do they do/how do they work?

Answer 69

hair cell
One of the receptor cells for hearing in the cochlea. The hair cells transduce movements of the basilar membrane into electrical signals. Each human ear contains two sets of hair cells within the organ of Corti: a single row of about 3500 inner hair cells (IHCs; called inner because they are closer to the central axis of the coiled cochlea) and about 12,000 outer hair cells (OHCs) in three rows (see Figure 9.2D). From the upper end of each hair cell protrude tiny hairs that range from 2 to 6 micrometers in length (see Figure 9.2E). Each hair cell has 50–200 of these relatively stiff hairs, called stereocilia (singular stereocilium; from the Greek stereos, “solid,” and the Latin cilium, “eyelid/eyelash”) or simply cilia. The heights of the stereocilia increase progressively across the hair cell, so the tops form a slope. Atop the organ of Corti is the tectorial membrane (see Figure 9.2D). The stereocilia of the OHCs extend into indentations in the bottom of this membrane.
Each IHC is associated with 16–20 auditory nerve fibers; relatively few nerve fibers contact the many OHCs. The OHCs don’t detect sound; they push
on the tectorial membrane in response to commands from the brain via the efferent nerve fibers. The OHCs change their length, thereby fine-tuning the
organ of Corti,

inner hair cell (IHC)
One of the two types of receptor cells for hearing in the cochlea.

outer hair cell (OHC)
One of the two types of receptor cells for hearing in the cochlea.

stereocilium
A relatively stiff hair that protrudes from a hair cell in the auditory or vestibular system.

tectorial membrane
A membrane that sits atop the organ of Corti in the cochlear duct.

Question 70

4) How are sound waves converted to electrical potentials that the nervous system will understand?

Answer 70

The inner parts of the ear, is where the mechanical force of sound is transduced into neural activity.

Auditory nerve fibers contact the base of the hair cells. The organ of Corti has four kinds of synapses and nerve fibers. Two of these are afferents that convey messages from the hair cells to the brain; the other two are efferents that convey messages from the brain to the hair cells. Different synaptic transmitters are active at each type of synapse.

How do IHCs transduce sound into neural activity? As sounds induce vibrations of the basilar membrane, the vibrations bend the hair cell stereocilia that are inserted into the tectorial membrane (see Figure 9.2D). Very small displacements of hair bundles cause rapid changes in ionic channels of the stereocilia.
Fine, threadlike fibers called tip links run along the tips of the stereocilia. These tip links play a key role in the generation of hair cell potentials. Sounds that cause the stereocilia to sway, even only very slightly, increase the tension on the elastic tip links and pop open the ion channels to which they are attached (Hudspeth, 1997; Hudspeth et al., 2000) (FIGURE 9.5). The channels snap shut again in a fraction of a millisecond as the hair cell sways back. The ion channels of stereocilia thus resemble trapdoors or portholes and appear to consist of the channel protein TRPA1 (transient receptor potential type A1) (Corey et al., 2004) that contains a spring like component—so in a real sense, a stereocilium ion channel is spring-loaded with a hair trigger.
Opening of the channels allows an inrush of potassium (K+) and calcium (Ca2+) ions and rapid depolarization of the entire hair cell. This initial depolarization leads to a rapid influx of Ca2+ at the base of the IHC, which causes synaptic vesicles there to fuse with the presynaptic membrane and release their transmitter contents—probably glutamate—from the base of the hair cell, which stimulates the afferent nerve fiber to trigger action potentials in these afferent axons (see Figure 9.5).

Question 71

5) How does the information from your ear get to primary auditory cortex?

Answer 71

The action potentials reach the brain via the vestibulocochlear nerve.

On each side of your head, about 30,000–50,000 auditory fibers from the cochlea make up the auditory part of the vestibulocochlear nerve (cranial nerve VIII). Recall that most of these afferent fibers are carrying messages from the IHCs, each of which stimulates several nerve fibers. Input from the auditory nerve is distributed in a complex manner to both sides of the brain, as depicted in FIGURE 9.7. Each auditory nerve fiber divides into two main branches as it enters the brainstem. Each branch then goes to separate groups of cells in the dorsal and ventral cochlear nuclei.

The output of the cochlear nuclei also travels via multiple paths. One path from each cochlear nucleus goes to both superior olivary nuclei, so they both receive inputs from both right and left cochlear nuclei. This bilateral input is the first stage in the CNS at which binaural (two-ear) effects are processed; as you might expect, this mechanism plays a key role in localizing sounds by comparing the two ears.

Several other parallel paths converge on the inferior colliculi, which are the primary auditory centers of the midbrain. Outputs of the inferior colliculi go to the medial geniculate nuclei of the thalamus. At least two different pathways from the medial geniculate extend to several auditory cortical areas.

Throughout the auditory pathways, neuronal response is frequency-sensitive, as with the vestibulocochlear nerve fibers that we discussed earlier (see Figure 9.6). This ability to discriminate frequencies is even sharper at higher stations of the auditory nervous system. At the medial geniculate nucleus and the auditory cortex, not only are neurons excited by certain frequencies, but they are also inhibited by neighboring frequencies. This interplay of excitation and inhibition further sharpens the frequency responses, allowing us to discriminate very small frequency differences.

Question 72

What is a tonotopic map?

Answer 72

tonotopic organization
A major organizational feature in auditory systems in which neurons are arranged as an orderly map of stimulus frequency, with cells responsive to high frequencies located at a distance from those responsive to low frequencies

All levels of the auditory pathway display tonotopic organization; that is, they are spatially arranged in an orderly map according to the auditory frequencies to which they respond. This organization begins with the cochlea—remember, frequency is ordered along the length of the basilar membrane (see Figure 9.3), and because the IHC fibers exiting the cochlea are organized according to their points of origin along the basilar membrane, a cross-section of the auditory projection reveals an orderly map from low to high frequencies.

Question 73

6) What is deafness (three types)? How do they occur? What types of treatment options are there?

Answer 73

deafness
Hearing loss so profound that speech perception is lost.

conduction deafness
A hearing impairment that is associated with pathology of the external-ear or middle-ear cavities. Arises when disorders of the outer or middle ear prevent vibrations produced by auditory stimuli from reaching the cochlea. Surgery to free up the ossicular chain is helpful in some cases. Hearing aids, which are simply miniaturized audio amplifiers—a microphone picks up environmental sounds, amplifies them, and plays the amplified sounds directly into the ear canal. By providing louder than usual sounds, hearing aids effectively overcome the mechanical problems inherent in conduction deafness.

sensorineural deafness
A hearing impairment that originates from cochlear or auditory nerve lesions. a condition in which auditory nerve fibers are unable to become excited in a normal manner. This hearing disorder is usually permanent. Unfortunately, amplifying sounds can’t help as effectively in sensorineural hearing loss, where the hair cells or other neural components of the inner ear are damaged or missing. But while the hair cells may be completely destroyed, the electrical excitability of the auditory nerve often remains unchanged. So one approach for circumventing deafness due to hair cell loss involves directly stimulating the auditory nerve with electrical currents. Progress in the development of cochlear implants that deliver such electrical stimulation has been rapid (FIGURE 9.17). Cochlear implants provide only a limited range of frequencies and loudness, so they do not restore normal hearing, but they nonetheless provide stimulation that the brain can interpret as sound.

central deafness
A hearing impairment that is related to lesions in auditory pathways or centers, including sites in the brainstem, thalamus, or cortex

Question 74

7) How do we localize sounds? What structure in the brain is important for localizing a sound and integrating this information with information from the visual system?

Answer 74

The auditory system accomplishes this feat by analyzing two kinds of binaural (two-ear) cues that signal the location of a sound source in the horizontal plane (this is called azimuth):

intensity differences
Perceived differences in loudness between the two ears, which can be used to localize a sound source. intensity differences occur because one ear is pointed more directly toward the sound source or because the head casts what is called a sound shadow (FIGURE 9.10A), blocking sounds located to one side (called off-axis sounds) from reaching both ears with equal loudness. The head shadow effect is most pronounced for higher-frequency sounds. Low-frequency sounds have longer sound waves that reach around the head more effectively, reducing the head shadow

latency differences
Differences between the two ears in the time of arrival of a sound, which can be employed by the nervous system to localize sound sources. They arise because one ear is always a little closer to an off-axis sound than is the other ear. Two kinds of latency differences are present in a sound: onset
disparity, which is the difference between the two ears in hearing the beginning of the sound, and ongoing phase disparity, which is the continuous mismatch between the two ears in the arrival of all the peaks and troughs that make up the sound wave

The structure of the external ear provides yet another sort of localization cue. As we mentioned earlier, the hills and valleys of the external ear selectively reinforce some frequencies in a complex sound and diminish others (FIGURE 9.12). This process is known as spectral filtering, and the frequencies that are affected depend on where the sound originates. Unlike the binaural intensity and latency cues that localize a sound in azimuth (horizontal location), spectral cues provide critical information about elevation (vertical location).

What brain systems analyze binaural cues? Both birds and mammals have highly specialized brainstem mechanisms that receive information from the two ears, and they use arrays of bipolar neurons to derive sound location from the left and right auditory signals. These bipolar neurons are capable of making very precise timing calculations by comparing the inputs to their two dendrites. The superior olivary nucleus is the primary sound localization nucleus in the mammalian brain, and its two main divisions serve different functions. The lateral superior olive (LSO) processes intensity differences. The medial superior olive (MSO) processes latency differences. Instead, sound location is encoded by the relative activity of the entire left MSO compared with the entire right MSO (Grothe, 2003; McAlpine et al., 2001). So, for example, a sound on the midline would activate the left and right MSOs equally, and the two signals would effectively cancel each other out. But a sound on the right would produce more excitation of the left MSO than the right MSO, and the converse would be true for sounds on the left. The bigger the difference between the left and right MSO is, the farther the sound source is from the midline. This disparity is passed along for further processing at other levels of the auditory system.

Question 75

auditory processing

Answer 75

Auditory cortex analyzes complex sounds encountered in everyday life.
There seem to be two main streams of auditory processing in cortex (Kaas and Hackett, 1999): a dorsal stream, involving the parietal lobe, is concerned with spatial location of sounds; a ventral stream through the temporal lobe may analyze the various components of sounds (Romanski et al., 1999), which in the human left hemisphere might include processing of speech sounds. This organization suggests the existence of separate auditory processing streams for what versus where, neatly paralleling a similar scheme that has been proposed for visual processing.

Question 76

How does experience affect auditory processing?

Answer 76

Human infants have diverse hearing capabilities at birth, but hearing for complex speech sounds in particular becomes more precise and rapid through exposure to the speech of their family and other people. Similarly, early experience with binaural hearing (via hearing aids), compared with equivalent monoaural hearing or no hearing, has a significant effect on the ability of children to localize sound sources later in life. Music is also effective in shaping the responses of auditory cortex. It might not surprise you to learn that the auditory cortex of trained musicians shows a bigger response to musical sounds than does the same cortex in nonmusicians. t the extent to which a musician’s brain is extra sensitive to musical notes is correlated with the age at which she began her serious training in music.
Certainly there are big differences by adulthood: the portion of primary auditory cortex where music is first processed, called Heschl’s gyrus, is more than twice as large in professional musicians as in nonmusicians, and more than twice as strongly activated by music

Question 77

9) What is a cochlear implant? How does this work? What did the baby in the video do when it was turned on?

Answer 77

cochlear implant
An electromechanical device that detects sounds and selectively stimulates nerves in different regions of the cochlea via surgically implanted electrodes.
But while the hair cells may be completely destroyed, the electrical excitability of the auditory nerve often remains unchanged. So one approach for circumventing deafness due to hair cell loss involves directly stimulating the auditory nerve with electrical currents. Progress in the development of cochlear implants that deliver such electrical stimulation has been rapid (FIGURE 9.17). Cochlear implants provide only a limited range of frequencies and loudness, so they do not restore nor-mal hearing, but they nonetheless provide stimulation that the brain can interpret as sound. Functional brain imaging indicates that the stimulation activates auditory cortex in a tonotopic manner, and it appears to be processed by auditory cortex in similar fashion to “natural” inputs

Question 78

11) Be familiar with the basic anatomy of the nose.

Answer 78

In humans, a sheet of cells called the olfactory epithelium (FIGURE 9.25) lines the dorsal portion of the nasal cavities and adjacent regions, including the septum that separates the left and right nasal cavities. Within the 5–10 cm2 of olfactory epithelium that we possess, three types of cells are found: supporting cells, basal cells, and about 10 million olfactory receptor cells. In many other mammals this number is an order of magnitude greater.
Each olfactory receptor cell has a long, slender apical dendrite that extends to the outermost layer of the epithelium, the mucosal surface. There, numerous cilia (singular cilium) emerge from the dendritic knob and extend along the mucosal surface. At the opposite end of each bipolar olfactory receptor cell, a fine, unmyelinated axon, which is among the smallest-diameter axons in the nervous system, runs to the olfactory bulb. olfactory receptor neurons can be replaced in adulthood.If the olfactory epithelium is damaged, it can be regenerated and will properly reconnect to the olfactory bulb.

Question 79

Where does information from your nose go?

Why do smells often evoke past memories?

Answer 79

The numerous axons of the olfactory nerve terminate in a complex structure at the anterior end of the brain called the olfactory bulb. The olfactory bulb, in relation to the rest of the brain, is much smaller in humans than in animals. The olfactory bulb is organized into many roughly spherical neural circuits called glomeruli, within which the axon terminals of olfac-
tory neurons synapse on the dendrites of the specialized mitral cells of the olfactory bulb.Output from the olfactory bulb consists of the axons from mitral cells, which extend to a variety of brain regions. These include the prepyriform and entorhinal cortex (note that smell is the only sensory modality that can synapse directly in the cortex rather than having to pass through the thalamus), the amygdala, and the hypothalamus. This close relation between olfactory inputs and limbic system structures involved in memory and emotion may help explain the potent ability of odors to evoke strong nostalgic memories of childhood

Question 80

How many different sensory elements can the nose sense?

Answer 80

The sense of smell is critical for appreciating the rich and complex flavors of individual foods but has additional important functions as well, such as signaling the presence of prey, predators, or potential mates

Our ability to respond to many odors—it is estimated that humans can detect more than 10,000 different odors and can discriminate as many as 5000 (Ressler et al., 1994)—is what produces the complex array of flavors that we normally think of as tastes.

Question 81

What are anosmia and ageusia? Anosmia is the inability to smell.

Ageusia is the loss of taste functions of the tongue

Answer 81

What are anosmia and ageusia? Anosmia is the inability to smell.

Ageusia is the loss of taste functions of the tongue

Question 82

What sensory systems send their information to the thalamus before the cortex? Which one doesn’t? note that smell is the only sensory modality
that can synapse directly in the cortex rather than
having to pass through the thalamus

Answer 82

note that smell is the only sensory modality
that can synapse directly in the cortex rather than
having to pass through the thalamus

Question 83

Be familiar with the basic anatomy of the tongue.

Answer 83

It is a common misconception that the myriad little bumps on the
tongue are taste buds, but they aren’t. They are actually papillae
(singular papilla, Latin for “nipple”) (FIGURE 9.21), tiny lumps of
tissue that serve to increase the surface area of the tongue. There
are three kinds of papillae, distributed on the tongue as shown in
FIGURE 9.22. Each of the relatively few circumvallate papillae and
foliate papillae contains many taste buds in its sides. Fungiform
papillae, which contain only about six taste buds each, resemble
button mushrooms in shape
Each papilla holds one or more taste buds, and each taste bud
consists of a cluster of 50–150 taste receptor cells (FIGURE 9.22A). At
the surface end of the taste bud is an opening called the taste pore
(FIGURE 9.22B). The taste cells extend fine cilia into the taste pore,
and these come into contact with tastants (substances that can be
tasted). Each taste cell is sensitive to just one of the five basic tastes,
and with a life span of only 10–14 days, taste cells are constantly be-
ing replaced.
As our varied experience with hot drinks, frozen flag poles, or spicy foods informs us, taste is not the only sensory capability of the tongue. Some of the sensory cells within taste buds signal heat, pain, and touch. The ability to taste many substances is already well developed in humans at birth. Even premature infants seem to show a clear preference for sweet substances, and aversion to bitter substances (Steiner, 1974). Newborns seem to be relatively insensitive to salty tastes, but a preference for mildly salty substances develops in the first few months. This preference does not seem to be related to experience with salty tastes; rather it probably indicates maturation of the mechanisms of salt perception

papilla
A small bump that projects from the surface of the tongue. Papillae contain most of the taste receptor cells.

circumvallate papillae
One of three types of small structures on the tongue, located in the back, that contain taste receptors.

foliate papillae
One of three types of small structures on the tongue, located along the sides, that contain taste receptors.

fungiform papillae
One of three types of small structures on the tongue, located in the front, that contain taste receptors.

taste bud
A cluster of 50–150 cells that detects tastes. Taste buds are found in papillae.

taste pore
The small aperture through which tastant molecules are able to access the sensory receptors of the taste bud.

tastant
A substance that can be tasted.

Question 84

Where does information from your tongue go?

Answer 84

The tastes salty and sour are evoked when taste cells are stimulated by simple ions acting on ion channels in the membranes of the taste cells.

The gustatory system (from the Latin gustare, “to taste”) extends from the taste receptor cells through brainstem nuclei and the thalamus to the cerebral cortex. Each taste cell transmits information to several afferent fibers, and each afferent fiber receives information from several taste cells. The afferent fibers run along three different cranial nerves—the facial (VII), glossopharyngeal (IX), and vagus (X) nerves (see Figure 2.9). The gustatory fibers in each of these nerves run to the brainstem. Here they synapse with second-order gustatory neurons that project to the ventral posterior medial nucleus of the thalamus. After another synapse, third-order gustatory fibers extend to the cortical taste area located in the insula, just anterior to the central sulcus. Even within the cortical taste area, a “gustatopic” map is preserved—the different tastes are represented in distinct areas within gustatory cortex

Question 85

How many different sensory elements can the tongue sense?

Answer 85

The sense of taste provides an immediate assessment of foods (Lindemann, 1995): sweet indicates high-calorie foods; savory tastes signal a protein source; salty and sour relate to important aspects of homeostasis; bitter warns of toxic constituents.

humans detect only five basic tastes: salty, sour, sweet, bitter, and umami.

The sensations uniquely aroused by an apple, a steak, or an olive are flavors rather than simple tastes; they involve smell as well as taste. Block your nose, and a raw potato tastes the same as an apple.

Question 86

12) Be able to discuss (very basic) how an odorant molecule works to stimulate ion channel opening in the CNS?

Answer 86

Odorants enter the nasal cavity during inhalation and especially during periods of sniffing; they also rise to the nasal cavity from the mouth when we chew food. The direction of airflow in the nose is determined by complex curved surfaces called turbinates that form the nasal cavity (see Figure 9.25). Airborne molecules initially encounter the fluids of the mucosal layer, which contain binding proteins that transport odorants to receptor surfaces

The odorant stimulus then interacts with receptor proteins located on the surface of the olfactory cilia and the dendritic knob of the receptor cells. These receptor proteins are members of a superfamily of G protein–linked receptors (Buck and Axel, 1991). Interactions of odorants with their receptors trigger the synthesis of second messengers, such as cyclic AMP (cAMP). Cyclic AMP opens cation channels (L. J. Brunet et al., 1996), resulting in depolarization of the olfactory receptor cell, which in turn leads to the generation of action potentials.

Question 87

1) What is the EM spectrum? How does this relate to our ability to perceive visual information? What is transduction?

Answer 87

The visual system responds to a band of electromagnetic radiation, measured in quanta.
Each quantum has a wavelength.
Quanta of light energy with visible wavelengths are called photons.

When quanta within the visible spectrum enter the eye, they can evoke visual sensations. The exact nature of such sensations depends both on the wavelengths of the quanta and on the number of quanta per second.

Question 88

What are visual fields – where is the information from the right and left visual fields go? Be able to draw this.

Answer 88

The visual field is the whole area you can see without moving your head or eyes. You may think that your vision is equally good across the visual field, but this is an illusion. Visual acuity, the sharpness of vision, is especially fine in the center of the visual field and falls off rapidly toward the periphery. We can understand this difference in visual acuity by learning more about the retina and successive levels of the visual system. FIGURE 10.5A shows a photograph of the back of the eye seen through the pupil. The central region, called the fovea (Latin for “pit”), has a dense concentration of cones. The optic disc, to the nasal side of the fovea, is where blood vessels and ganglion cell axons leave the eye. There are no photoreceptors at the optic disc, so there is a blind spot here that we normally do not notice. To locate your blind spot and experience firsthand some of its interesting features,

Question 89

What are the three pathways that carry visual information to the brain. What are these three pathways responsible for?

Answer 89

The ganglion cells in each eye produce action potentials that are con-
ducted along their axons to send visual information to the brain. These
axons make up the optic nerve (also known as cranial nerve II) that
brings visual information into the brain on each side, eventually reach-
ing visual cortex in the occipital lobe at the back of the brain

Question 90

3) What are the three main cell layers in the retina? What is meant by my comment that the retina is built backwards? How is information processed in these layers? What is a retinotopic map?

Answer 90

The first stages of visual-information processing occur in the retina, the receptive surface inside the back of the eye (FIGURE 10.2A). The retina is only 200–300 mi-crometers (μm) thick—not much thicker than the edge of a razor blade—but it contains several types of cells in distinct layers (FIGURE 10.2B). The receptor cells that detect light are called photoreceptors.
In all vertebrates, some or all of the axons of each optic nerve cross to the opposite cerebral hemisphere. The optic nerves cross the midline at the optic chiasm(named for the
Greek letter χ [chi] because of its crossover shape). In humans, axons from the half of the retina toward the nose (called the nasal hemiretina) cross over to the opposite side of the brain (see Figure 10.9A). The half of the retina toward the side of the head (the temporal hemiretina) projects its axons to its own side of the head. Having our eyes cover overlapping sections of the visual field helps us judge the distance of objects, by (unconsciously) comparing the inputs from the two eyes. In prey species such as rabbits, natural selection has sacrificed some of this binocular depth perception, favoring instead the broader visual field that results from having the eyes positioned farther apart (FIGURE 10.9B); this broader visual field helps the rabbit detect approaching predators. In such species, most of the optic nerve fibers cross the midline.
After they pass the optic chiasm, the axons of the retinal ganglion cells are known collectively as the optic tract. As FIGURE 10.10 shows, most axons of the optic tract terminate on cells in the lateral geniculate nucleus (LGN), which is the visual part of the thalamus (step 4a in Figure 10.10). Axons of postsynaptic cells in the LGN form the optic radiations (step 5), which terminate in primary visual cortex (V1) of the occipital lobe at the back of the brain (step 6). The primary visual cortex is often called striate cortex because a broad stripe, or striation, is visible in anatomical sections through this region; the stripe represents layer IV of the cortex, where the optic-radiation fibers arrive. Information from the two eyes converges on cells beyond layer IV of the primary visual cortex, making binocular, three-dimensional vision possible, as we discussed in Chapter 7.
As Figure 10.9 shows, the visual cortex in the right cerebral hemisphere receives its input from the left half of the visual field, and the visual cortex in the left hemisphere receives its input from the right half of the visual field. Some retinal ganglion cells send their optic-tract axons to the superior colliculus in the midbrain (see Figure 10.10, step 4b), to help coordinate rapid movements of the eyes toward a target.
In addition to the primary visual cortex (V1) shown in Figure 10.10, numerous surrounding regions of the cortex are also largely visual in function. These visual cortical areas outside the striate cortex are sometimes called extrastriate cortex. These different cortical regions work in parallel to process different aspects of visual perception, such as form, color, location, and movement, as we will discuss later in this chapter. In striate cortex, as well as most extrastriate regions, there is a topographic projection of the retina, which means there’s a topographic projection of the visual field, discussed next.

Question 91

4) What are rods and cones – how are they different – how do they relate to the scotopic and photopic visual systems?

Answer 91

The receptor cells that detect light are called photoreceptors. There are two kinds of photoreceptors: some are called rods because of their relatively long, narrow form; others are called cones(FIGURE 10.2C). There are several different types of cones, which respond differently to light of varying wavelengths, providing us with color vision, as described later in the chapter. Both rod and cone photoreceptors release neurotransmitter molecules (FIGURE 10.2D) that control the activity of the bipolar cells that synapse with them (see Figure 10.2B). The bipolar cells, in turn, connect with ganglion cells. The axons of the ganglion cells form the optic nerve, which carries information to the brain.

Two different functional systems arise from the two different populations of receptors (rods and cones) in the retina. One system uses the rods and works in dim light, so it is called the scotopic system (from the Greek skotos, “darkness,” and ops, “eye”). The scotopic system has only one receptor type (rods) and therefore does not respond differentially to different colors, which is the basis for the saying “at night, all cats are gray.” There is a lot of convergence in the scotopic cell, as many rods provide information to each ganglion cell. The other system requires more light and, in some species, shows differential sensitivity to wavelengths, enabling color vision. This system uses the cones and is called the photopic system (from the Greek phos, “light”). Compared with the scotopic system, the photopic system has less convergence, as some ganglion cells report information from only a single cone.

Question 92

5) What is low and high convergence – how does this relate to acuity in the scotopic and photopic systems?

Answer 92

Two different functional systems arise from the two different populations of receptors (rods and cones) in the retina. One system uses the rods and works in dim light, so it is called the scotopic system (from the Greek skotos, “darkness,” and ops, “eye”). The scotopic system has only one receptor type (rods) and therefore does not respond differentially to different colors, which is the basis for the saying “at night, all cats are gray.” There is a lot of convergence in the scotopic cell, as many rods provide information to each ganglion cell. The other system requires more light and, in some species, shows differential sensitivity to wavelengths, enabling color vision. This system uses the cones and is called the photopic system (from the Greek phos, “light”). Compared with the scotopic system, the photopic system has less convergence, as some ganglion cells report information from only a single cone. At moderate levels of illumination, both the rods and the cones function, and some ganglion cells receive input from both types of receptors. TABLE 10.1 summarizes the characteristics of the photopic and scotopic systems.

Question 93

6) What are the main visual areas of the cortex (V1, 2, 4, 5)? What do they code?

Answer 93

primary visual cortex (V1) or striate cortex Also called area 17. The region of the occipital cortex where most visual information first arrives.
Area V1 is only a small part of the portion of cortex that is devoted to vision. Area V1 sends axons to other visual cortical areas, including areas that appear to be involved in the perception of form: V2, V4, and the inferior temporal area (see Figure 10.19C). Some of these extrastriate areas also receive direct input from the LGN. The receptive fields of the cells in many of these extrastriate visual areas are even more complex than those of cells in area V1. Perception of Visual Motion Is Analyzed by a Special System That Includes Cortical Area V5

Question 94

7) What is a scotoma? How is the area a scotoma covers (the amount of damage) calculated?

Answer 94

scotoma
A region of blindness caused by injury to the visual pathway or brain.

Because of the orderly mapping of the visual field (known as retinotopic mapping) at the various levels of the visual system, damage to parts of the visual system can be diagnosed from defects in perception of the visual field. If we know the site of injury in the visual pathway, we can predict the location of such a perceptual gap, or scotoma (plural scotomas or scotomata), in the visual field. Although the word scotoma comes from the Greek skotos, meaning “darkness,” a scotoma is not perceived as a dark patch in the visual field; rather, it is a spot where nothing can be perceived, and usually rigorous testing is required to demonstrate its existence. Within a scotoma, a person cannot consciously perceive visual cues, but some visual discrimination in this region may still be possible; this paradoxical phenomenon has been called blindsight

Question 95

8) What are the dorsal and ventral streams?

Answer 95

Mortimer Mishkin and Leslie Ungerleider (1982) proposed that primates also have two main cortical processing streams, both originating in primary visual cortex: a ventral processing stream responsible for visually identifying objects, and a dorsal stream responsible for appreciating the location of objects and for guiding movement toward objects (FIGURE 10.27). These processing streams were called, respectively, the what and where streams.

The two streams are not completely separate, because there are normally many cross-connections between them. In the ventral stream, including regions of the occipitotemporal, inferior temporal, and inferior frontal areas, information about faces becomes more specific as one proceeds farther forward.

Question 96

How does this relate to the work of Mel Goodale and D.F. (A.T.)? How does this relate to prosopagnosia?

Answer 96

It was cold in the bathroom, so the young woman turned on a small heater before she got in the shower. She didn’t know that the heater was malfunctioning, filling the room with deadly, odorless carbon monoxide gas. Her husband found her unconscious on the floor and called for an ambulance to rush her to the emergency room. When she regained consciousness, “D.F.” seemed to have gotten off lightly, avoiding what could have been a fatal accident. She could understand the doctors’ questions and reply sensibly, move all her limbs, and perceive touch on her skin. But something was wrong with her sight. D.F. couldn’t recognize faces, even her husband’s, nor could she name any objects presented to her view. D.F. still cannot recognize objects today, more than 15 years after her accident. Yet she is not entirely blind. Show her a flashlight and she can tell you that it’s made of shiny aluminum with some red plastic, but she doesn’t recognize it (“Is it a kitchen utensil?”). Without telling her what it is, if you ask her to pick it up, D.F.’s hand goes directly to the flashlight and holds it exactly as one normally holds a flashlight. Show D.F. a slot in a piece of plastic and she cannot tell you whether the slot is oriented vertically, horizontally, or diagonally; but if you hand her a disk and ask her to put it through the hole, D.F. invariably turns the disk so that it goes smoothly through the slot (Goodale et al., 1991). Can D.F. see or not?

Discovery of these separate visual cortical streams helps us understand the case of patient D.F., described at the start of this chapter. Recall that after carbon monoxide poisoning, she lost the ability to perceive faces and objects while retaining the ability to reach and grasp under visual control. The investigators who studied her (A. D. Milner et al., 1991) hypothesized that D.F.’s ventral visual stream had been devastated but that her dorsal stream was unimpaired. An opposite kind of dissociation had already been reported: damage to the posterior parietal cortex often results in optic ataxia in which patients have difficulty using vision to reach for and grasp objects, yet these patients may retain the ability to correctly identify objects (Perenin and Vighetto, 1988). MRI with D.F. supports the idea that her ventral stream was damaged while her dorsal stream was relatively unaffected (T. W. James et al., 2003). High-resolution MRI of D.F.’s brain (FIGURE 10.28A) reveals damage concentrating in the ventrolateral occipital cortex. Throughout the brain, there is evidence of atrophy, indicated by shrunken gyri and enlarged sulci. FIGURE 10.28B shows the area activated in fMRI recordings when normal subjects viewed pictures of objects; it corresponds to D.F.’s lateral occipital lesion. When D.F. reached for and grasped objects, her fMRI activation in the parietal lobe was similar to that of normal subjects, indicating that D.F.’s dorsal stream is largely intact. D.F.’s intact dorsal pathway not only tells her where objects are but also guides her movements to use these objects properly. It is still puzzling that one part of D.F. knows exactly how to grasp a pencil put before her, while another part of her—the part that talks to you—has no idea whether it’s a pencil, a ruler, or a bouquet of flowers. Imagining what this disjointed visual experience must be like for D.F. allows us to appreciate how effortlessly our brains usually bind together information to give us the marvelous sense of sight.

Question 97

9) What is blindsight – Anton’s blindness? What are two reasons why a person who says they can’t see might be able to (this relates to visual system anatomy).

Answer 97

Within a scotoma, a person cannot consciously perceive visual cues, but some visual discrimination in this region may still be possible; this paradoxical phenomenon has been called blindsight. . In other cases, stimuli that cannot be seen within a scotoma affect judgments of stimuli outside it (Stoerig and Cowey, 1997). Blindsight may also be related to the phenomenon known as hemispatial neglect—neglect of the side opposite to an injured cerebral hemisphere.

Question 98

9) What is prosopagnosia? How is this relevant to visual identity of non-humans/objects? (in class)

Answer 98

prosopagnosia
Also called face blindness. A condition characterized by the inability to recognize faces. Acquired prosopagnosia is caused by damage to the brain, particularly the fusiform gyrus. Developmental (or congenital) prosopagnosia is the result of brain defects present from birth.

In contrast, the ability to recognize objects may be retained, and the patient may have no difficulty identifying familiar people by their voices.

Faces simply lack meaning in the patient’s life. No disorientation or confusion accompanies this condition, nor is there evidence of diminished intellectual abilities. Visual acuity is maintained, although the majority of patients have a small visual-field defect—that is, an area of the visual field where they are blind. Most research indicates that the right hemisphere is more important than the left for recognizing faces.

Bilateral destruction of this region leads to prosopagnosia, the inability to recognize individual faces.

Still, data from split-brain patients and functional imaging tests make it clear that both hemispheres have some capacity for recognizing faces. Thus, although damage restricted to the right hemisphere can impair face processing, the most complete cases of prosopagnosia are caused by bilateral damage. The fusiform gyrus, a region of cortex on the inferior
surface of the brain where the occipital and temporal cortices meet
(FIGURE 19.19), is crucial, and cases of prosopagnosia following brain damage almost always involve damage here. Symptoms may be exacerbated when lesions also include a nearby occipital area that performs initial face-specific visual processing and when they include the superior temporal sulcus, which has been implicated in connecting faces with speech and facial expressions.

Prosopagnosia of either type may be accompanied by additional forms of agnosia (an inability to identify items, in the absence of specific sensory impairments). Indeed, fMRI studies of healthy subjects show that the fusiform region is activated not only when people are identifying faces, but also when identifying birds, or cars (Gauthier et al., 2000). So it seems that the fusiform system may be crucial for identifying individual members of large categories (e.g., faces or birds or cars), especially when the members of the category have many things in common.

Question 99

1) What are the three major divisions of motor command at the level of the CNS? What is each responsible for? (Hint: Cortex, Basal Ganglia, Cerebellum)

Answer 99

The skeletal system and attached muscles allow for movement.

The spinal cord controls skeletal muscles.

The brainstem integrates motor commands.

Question 100

2) What is a reflex circuit? Please be able to draw and describe this.

Answer 100

reflex
A simple, highly stereotyped, and unlearned response to a particular stimulus (e.g., an eye blink in response to a puff of air).
These studies showed that some reflexes involve only short pathways in the spinal cord linking dorsal and ventral roots; others involve longer loops connecting spinal cord segments to each other, or to brain regions.

Spinal reflexes mediate “automatic” responses
A good example of automatic control at the spinal level is the stretch reflex—the contraction that results when a muscle stretches.

Question 101

What is a central pattern generator in the spinal cord?

Answer 101

central pattern generator
Neural circuitry that is responsible for generating the rhythmic pattern of a behavior such as walking.

Many such rhythmic movements are generated by mechanisms within the spinal cord. These endogenous rhythms are normally modulated by sensory feedback, but they can function independently of brain influences or afferents. The term central pattern generator is used to refer to the neural circuitry responsible for generating rhythmic patterns of behavior, as seen in walking. The central pattern generators for walking seem much the same in cats, birds, and humans (Dominici et al., 2011). This essential rhythm of walking generated by spinal cord mechanisms is activated and modulated by the brain.

Question 102

3) What are the main differences between the pyramidal and extrapyramidal systems?

Answer 102

Pathways from the brain control different aspects of movements
Some muscles are controlled directly by the brain. The cranial motor nuclei of the brainstem send their axons to innervate muscles of the head and neck (FIGURE 11.12; see also Figure 2.9). But for all the other muscles, the brain has to send commands to the spinal cord, and then the spinal cord controls the muscles. The brain sends these commands to the spinal cord through two major pathways: the pyramidal system (which we’ll discuss next) and extrapyramidal motor system (described later in this chapter).

Question 103

pyramidal systems

Answer 103

The pyramidal system (or corticospinal system) consists of neuronal cell bodies within the cerebral cortex and their axons, which pass through the brainstem, forming the pyramidal tract to the spinal cord (FIGURE 11.13A). The pyramidal tract is seen most clearly where it passes through the floor of the medulla. In a cross section of the medulla, the tract is a wedge-shaped ventral protuberance (pyramid) on each side of the midline. In the medulla the pyramidal tract from the right hemisphere crosses the midline to innervate the left spinal cord, and vice versa. Because the pyramidal tract crosses the midline (technically known as a decussation) in the medulla,
the right cortex controls the left side of the body while the left cortex controls the right. Lesions of the pyramidal system deprive the patient of the ability to move individual joints and limbs.
Many of the axons of the pyramidal tract originate from neurons in the primary motor cortex (M1), which consists mainly of the precentral gyrus, just anterior to the central sulcus (FIGURE 11.13B). The cell bodies of many of these large neurons are found in layer V of the primary motor cortex.

Question 104

extrapyramidal systems

Answer 104

In addition to the corticospinal outflow through the pyramidal tract, many other motor tracts run from the forebrain to the brainstem and spinal cord. Because these tracts are outside the pyramids of the medulla, they and their connections are called the extrapyramidal system. The two most important components of the extrapyramidal system are the basal ganglia and the cerebellum.
How do these components of the extrapyramidal system communicate with the spinal cord? Their messages are transmitted via two brainstem pathways: the reticulospinal tract, which originates in the reticular formation of the brainstem, and the rubrospinal tract, which originates from the midbrain’s red nucleus (the Latin ruber means “red”). Both tracts send axons down the spinal cord to synapse on spinal interneurons. Using these brainstem pathways, the basal ganglia and cerebellum play slightly different roles in controlling motor output, as we’ll see next.

Question 105

4) Compare and contrast the behavioural, control systems and neuroscience models of motor control.

Answer 105

behavioural
The basic units of behavior are reflexes: simple, unvarying, and unlearned responses to sensory stimuli such as touch, pressure, and pain. The motor plan, also called the motor program, is a complex set of commands to muscles that is established before the behavior starts. Feedback from movements informs and finetunes the motor program as it unfolds, but the basic sequence of movements is planned.

Control Systems
One way to look at the mechanisms that regulate and control our movements employs the language of engineering. In designing machines, engineers commonly have two goals: (1) accuracy, to prevent or minimize error, and (2) speed, to complete a task quickly and efficiently. It is difficult to accomplish both these goals at once; usually there is a trade-off between the two. Two forms of control mechanisms—closed-loop and open-loop—are commonly employed to optimize one at the expense of the other.

The Neuroscience View
We can distinguish several different levels of hierarchically organized motor control systems:

Question 106

5) How can you measure the movement of muscles?

Answer 106

We can readily analyze movements using high-speed video, which provides an intimate frame-by-frame portrait of even the most rapid events. To deal with the large amounts of data produced by image processing, methods of simplification or numerical analysis have been devised

For example, sports trainers use detailed analyses of athletic acts based on time-lapse photographs or information derived from sensors attached at joints. Computer programs process images to help quantify the performance, enabling detailed measurement of the positions of different body parts in successive instants.

Another approach to the fine-grained analysis of movements is to record the electrical activity of muscles—a procedure called electromyography (EMG). Like neurons, muscles produce action potentials when they contract, as we’ll see later in this chapter. Therefore, fine needle electrodes placed in a muscle, or electrodes placed on the skin over a muscle, can detect electrical indications of muscle activity (FIGURE 11.2). If electrodes are placed over several different muscles, we get a record of the timing and strength
of contraction of the muscles involved in a movement (Hanakawa et al., 2003). The EMGs in Figure 11.2 show that a person pulling a knob will adjust his legs just before moving his arm—another example of motor planning.

Question 107

What is the neurotransmitter that is involved in motor control?

Answer 107

acetylcholine (ACh)
A neurotransmitter produced and released by parasympathetic postganglionic neurons, by motoneurons, and by neurons throughout the brain.

Each axonal branch carries an action potential to its axon terminal, which then (in vertebrates) releases the neurotransmitter acetylcholine (ACh). Muscle fibers respond to the ACh by producing action potentials of their own.

Question 108

7) What is M1 and what does it control?

Answer 108

Many of the axons of the pyramidal tract originate from neurons in the primary motor cortex (M1), which consists mainly of the precentral gyrus,
just anterior to the central sulcus.

Question 109

What does the homunculus represent?

Answer 109

The motor cortex representation of the muscles of the body has historically been illustrated with a homunculus, like this one, in which the sizes of the figure’s body parts are proportional to the amounts of motor cortex devoted to the corresponding muscles. This sort of mapping, however, is almost certainly an oversimplification; the organization of the motor cortex is not as discrete as these maps imply

Question 110

8) What are supplementary areas of motor cortex responsible for?

Answer 110

The traditional account of nonprimary motor cortex emphasizes two main regions: the supplementary motor area (SMA), which lies mainly on the medial aspect of the hemisphere, and the premotor cortex, which is anterior to the primary motor cortex

supplementary motor area (SMA)
A region of nonprimary motor cortex that receives input from the basal ganglia and modulates the activity of the primary motor cortex.

The SMA lies mainly on the medial surface of the cerebral hemispheres.

suggesting that this region initiates movement sequences

Question 111

10) What is wrong if you have ALS?

Answer 111

amyotrophic lateral sclerosis (ALS)
Also called Lou Gehrig’s disease. A disease in which motoneurons and their target muscles waste away.
Sometimes, for reasons that remain elusive, the motoneurons of the brainstem and spinal cord spontaneously start to die and their target muscles waste away. In this disease, called amyotrophic lateral sclerosis (ALS; sometimes called Lou Gehrig’s disease after the 1930s baseball player who lost his life to the disorder), the afflicted person experiences gradually worsening paralysis until most skeletal muscle ceases to function. Although premature death is the usual outcome, some people with ALS can survive for long periods; celebrated British physicist Stephen Hawking, who was diagnosed with ALS in the early 1960s, is an example. A wide range of possible causal factors are under investigation, including premature aging, neurotoxins, viruses, immune responses, and endocrine dysfunction.

Question 112

What is wrong if you have Parkinson’s disease?

Answer 112

Parkinson’s disease
A degenerative neurological disorder, characterized by tremors at rest, muscular rigidity, and reduction in voluntary movement,that involves dopaminergic neurons of the substantia nigra.
Another feature of what is now known as Parkinson’s disease is a loss of facial muscle tone, which gives the face a masklike appearance. Patients who suffer from Parkinson’s also show few spontaneous actions and have great difficulty in all motor efforts, no matter how routine. The hands may display tremors while at rest but move smoothly while performing a task. Parkinson’s disease afflicts almost 1% of the U.S. population age 65 and older, but it sometimes unaccountably occurs in younger people, such as actor Michael J. Fox (FIGURE 11.22). Patients with Parkinson’s show progressive degeneration of dopamine-containing cells in the substantia nigra that project to the basal ganglia, particularly the caudate nucleus and putamen. The loss of cells in this area is continual, but symptoms begin to appear only after extensive cell death

Question 113

What is wrong if you have myasthenia gravis?

Answer 113

myasthenia gravis
A disorder characterized by a profound weakness of skeletal muscles; caused by a loss of acetylcholine receptors.
This disorder is characterized by a profound weakness of skeletal muscles. The disease often first affects the muscles of the head, producing symptoms such as drooping of the eyelids, double vision, and slowing of speech. In later stages, paralysis of the muscles that control swallowing and respiration becomes life-threatening.
Myasthenia gravis is an autoimmune disorder: most cases result when antibodies develop and attack a patient’s own acetylcholine receptors, disrupting neuromuscular junctions. In other cases the antibodies are directed toward other proteins that are associated with the acetylcholine receptor. Treatment often consists of prescribing drugs to suppress the immune system

Question 114

What is wrong if you have apraxia, ideomotor apraxia, or ideational apraxia?

Answer 114

apraxia
An impairment in the ability to begin and execute skilled voluntary movements, even though there is no muscle paralysis.
.apraxia (from the Greek a-, “not,” and praxis, “action”), the inability to carry out complex movements even though paralysis or weakness is not evident and language comprehension and motivation are intact.
Apraxia is a symptom of a variety of disorders, including stroke, Alzheimer’s disease, and developmental disorders of children.
Neurologists studying patients who have suffered strokes have discovered several different types of apraxia.

ideomotor apraxia
The inability to carry out a simple motor activity in response to a verbal command, even though this same activity is readily performed spontaneously.
Ideomotor apraxia is characterized by the inability to carry out a simple motor activity, either in response to a verbal command (“smile” or “use this comb”) or by copying someone else’s gesture, even though this same activity is readily performed spontaneously.

ideational apraxia
An impairment in the ability to carry out a sequence of actions, even though each element or step can be done correctly.
Ideational apraxia is an impairment in carrying out a sequence of actions, although each step can be done correctly (Zadikoff and Lang, 2005). Patients with ideational apraxia have difficulty carrying out instructions for a sequence of acts—“push the button, then pull the handle, then depress the switch”—but they can do each of these tasks in isolation