CMN 548 EXAM STUDY GUIDE TEST 4 |
LATEST UPDATE WITH COMPLETE
SOLUTIONS
CMN 548 - Module 4
Section 1.2
3 Principles of Brain Organization: Cells
• The human brain contains approximately (10 to the 11 power) nerve cells,
or neurons. neurons are composed of four identified regions the cell
body, or soma, which contains the nucleus and can be considered the
metabolic center of the neuron; (2) the dendrites, processes that arise
from the cell body, branch extensively, and serve as the major recipient
zones of input from other neurons; (3) the axon, a single process that
arises from a specialized portion of the cell body (the axon hillock) and
conveys information to other neurons; and (4) the axon terminals, fine
branches near the end of the axon that form contacts (synapses) generally
with the dendrites or the cell bodies of other neurons, release
neurotransmitters, and provide a mechanism for interneuronal
communication.
• Most neurons in the human brain are multipolar in that they give rise to
a single axon and several dendritic processes.
• Projection neurons have long axons and convey information from the
periphery to the brain (sensory neurons), from one brain region to
another, or from the brain to effector organs (motor neurons). In
contrast, local circuit neurons or interneurons have short axons and
process information within distinct regions of the brain.
1
, • the brain contains several types of glial cells which are at least 10 times
more numerous than neurons. Astrocytes are the most numerous class of
glial cells and are classified as either protoplasmic or fibrous. Protoplasmic
astrocytes are large cells located exclusively in the gray matter with many
fine and elaborate processes. In contrast, fibrous
astrocytes are smaller with less complex processes and reside
exclusively in the white matter.
5Principles of Brain Organization: Connections
• Every function of the human brain is a consequence of the activity of
specific neural circuits. The circuits form as a result of several
developmental processes. First, each neuron extends an axon, either
after it has migrated to its final location or, in some cases, before. The
growth of an axon along distinct pathways is guided by molecular cues
from its
environment and eventually leads to the formation of synapses with
specific target neurons.
2
, • Second, many neuronal connections are either divergent or convergent
in nature. A divergent system involves the conduct of information from
one neuron or a discrete group of neurons to a much larger number of
neurons that may be located in diverse
portions of the brain. The locus coeruleus, a small group of norepinephrine-
containing neurons in the brainstem that sends axonal projections to the
entire cerebral cortex and other brain regions, is an example of a highly
divergent system. In contrast, the output of multiple brain regions may be
directed toward a single area, forming a convergent
system. Projection from multiple association areas of the cerebral cortex to the
entorhinal region of the medial temporal lobe (MTL) is an example of a
convergent system.
• Third, the connections among regions may be organized in a
hierarchical or parallel fashion, or both. Visual input is conveyed in a
serial or hierarchical fashion through several populations of neurons in
the retina to the lateral geniculate nucleus, to the
primary visual cortex, and then, progressively, to the multiple visual
association areas of the cerebral cortex. Within the hierarchical scheme,
different types of visual information (e.g., motion and form) may be
processed in a parallel fashion through different portions of the visual
system.
• Finally, regions of the brain are specialized for different functions. Lesions
of the left inferior frontal gyrus (Broca area) (Fig. 1.2–5) produce a
characteristic impairment in speech production. However, speech is a
complex faculty that depends not only on the integrity of Broca area but
also on the distributed processing of information across numerous brain
regions through divergent and convergent, serial and parallel
interconnections.
8 Structural Components: Major Brain Structures
• In the early stages of human brain development, three primary vesicles
can be identified in the neural tube: the prosencephalon, the
mesencephalon, and the rhombencephalon (Fig. 1.2–6). Subsequently, the
prosencephalon divides to become the telencephalon and the
diencephalon. The telencephalon gives rise to the cerebral cortex, the
hippocampal formation, the amygdala, and some components of the basal
ganglia. The diencephalon becomes the thalamus, the hypothalamus, and
several other related
structures. The mesencephalon gives rise to the midbrain structures of the
adult brain. The rhombencephalon divides into the metencephalon and the
myelencephalon. The metencephalon gives rise to the pons and the
3
, cerebellum; the medulla is the derivative of the myelencephalon.
• The cerebral cortex of each hemisphere is divided into four major regions:
the frontal, parietal, temporal, and occipital lobes (Fig. 1.2–5). The frontal
lobe is located anterior to the central sulcus and consists of the primary
motor, premotor, and prefrontal regions (Fig. 1.2–7). The prefrontal cortex
can be divided into dorsolateral and ventrolateral
regions, with each of these regions having different functional properties.
4
LATEST UPDATE WITH COMPLETE
SOLUTIONS
CMN 548 - Module 4
Section 1.2
3 Principles of Brain Organization: Cells
• The human brain contains approximately (10 to the 11 power) nerve cells,
or neurons. neurons are composed of four identified regions the cell
body, or soma, which contains the nucleus and can be considered the
metabolic center of the neuron; (2) the dendrites, processes that arise
from the cell body, branch extensively, and serve as the major recipient
zones of input from other neurons; (3) the axon, a single process that
arises from a specialized portion of the cell body (the axon hillock) and
conveys information to other neurons; and (4) the axon terminals, fine
branches near the end of the axon that form contacts (synapses) generally
with the dendrites or the cell bodies of other neurons, release
neurotransmitters, and provide a mechanism for interneuronal
communication.
• Most neurons in the human brain are multipolar in that they give rise to
a single axon and several dendritic processes.
• Projection neurons have long axons and convey information from the
periphery to the brain (sensory neurons), from one brain region to
another, or from the brain to effector organs (motor neurons). In
contrast, local circuit neurons or interneurons have short axons and
process information within distinct regions of the brain.
1
, • the brain contains several types of glial cells which are at least 10 times
more numerous than neurons. Astrocytes are the most numerous class of
glial cells and are classified as either protoplasmic or fibrous. Protoplasmic
astrocytes are large cells located exclusively in the gray matter with many
fine and elaborate processes. In contrast, fibrous
astrocytes are smaller with less complex processes and reside
exclusively in the white matter.
5Principles of Brain Organization: Connections
• Every function of the human brain is a consequence of the activity of
specific neural circuits. The circuits form as a result of several
developmental processes. First, each neuron extends an axon, either
after it has migrated to its final location or, in some cases, before. The
growth of an axon along distinct pathways is guided by molecular cues
from its
environment and eventually leads to the formation of synapses with
specific target neurons.
2
, • Second, many neuronal connections are either divergent or convergent
in nature. A divergent system involves the conduct of information from
one neuron or a discrete group of neurons to a much larger number of
neurons that may be located in diverse
portions of the brain. The locus coeruleus, a small group of norepinephrine-
containing neurons in the brainstem that sends axonal projections to the
entire cerebral cortex and other brain regions, is an example of a highly
divergent system. In contrast, the output of multiple brain regions may be
directed toward a single area, forming a convergent
system. Projection from multiple association areas of the cerebral cortex to the
entorhinal region of the medial temporal lobe (MTL) is an example of a
convergent system.
• Third, the connections among regions may be organized in a
hierarchical or parallel fashion, or both. Visual input is conveyed in a
serial or hierarchical fashion through several populations of neurons in
the retina to the lateral geniculate nucleus, to the
primary visual cortex, and then, progressively, to the multiple visual
association areas of the cerebral cortex. Within the hierarchical scheme,
different types of visual information (e.g., motion and form) may be
processed in a parallel fashion through different portions of the visual
system.
• Finally, regions of the brain are specialized for different functions. Lesions
of the left inferior frontal gyrus (Broca area) (Fig. 1.2–5) produce a
characteristic impairment in speech production. However, speech is a
complex faculty that depends not only on the integrity of Broca area but
also on the distributed processing of information across numerous brain
regions through divergent and convergent, serial and parallel
interconnections.
8 Structural Components: Major Brain Structures
• In the early stages of human brain development, three primary vesicles
can be identified in the neural tube: the prosencephalon, the
mesencephalon, and the rhombencephalon (Fig. 1.2–6). Subsequently, the
prosencephalon divides to become the telencephalon and the
diencephalon. The telencephalon gives rise to the cerebral cortex, the
hippocampal formation, the amygdala, and some components of the basal
ganglia. The diencephalon becomes the thalamus, the hypothalamus, and
several other related
structures. The mesencephalon gives rise to the midbrain structures of the
adult brain. The rhombencephalon divides into the metencephalon and the
myelencephalon. The metencephalon gives rise to the pons and the
3
, cerebellum; the medulla is the derivative of the myelencephalon.
• The cerebral cortex of each hemisphere is divided into four major regions:
the frontal, parietal, temporal, and occipital lobes (Fig. 1.2–5). The frontal
lobe is located anterior to the central sulcus and consists of the primary
motor, premotor, and prefrontal regions (Fig. 1.2–7). The prefrontal cortex
can be divided into dorsolateral and ventrolateral
regions, with each of these regions having different functional properties.
4
