CH. 15 Brain and Cranial Nerves Flashcards
What are the 4 main regions of the brain?
cerebrum. diencephalon, brainstem, and cerebellum
What are the 3 primary brain regions that develop in the embyonic stage?
- Prosencephalon - forebrain
- Mesencephalon - midbrain
- Rhombencephalon - hindbrain
What are the 5 secondary brain vesicles that develop in the 5th week of development?
■ The telencephalon (tel-en-sef′ă-lon; tel = head end) arises
from the prosencephalon and eventually forms the cerebrum.
■ The diencephalon (dī-en-sef′ă-lon; dia = through) arises
from the prosencephalon and eventually forms the thalamus,
hypothalamus, and epithalamus.
■ The mesencephalon is the only primary vesicle that does not
form a new secondary vesicle. It is renamed the midbrain.
■ The metencephalon (met′en-sef′ă-lon; meta = after) arises
from the rhombencephalon and eventually forms the pons and
cerebellum.
■ The myelencephalon (mī′el-en-sef′ă-lon; myelos = medulla)
also derives from the rhombencephalon, and it eventually forms
the medulla oblongata.
Differentiatie between gray and white matter.
The gray matter houses
motor neuron and interneuron cell bodies, dendrites, terminal
arborizations, and unmyelinated axons. (Origin of gray color described
in section 14.2a.) The white matter derives its color from the myelin in
the myelinated axons.
What are the cranial meninges?
three connective tissue layers that separate
the soft tissue of the brain from the bones of the cranium, enclose and
protect blood vessels that supply the brain, and contain and circulate
cerebrospinal fluid. In addition, some parts of the cranial meninges
form some of the veins that drain blood from the brain
What are the 3 cranial meninges and what are their characteristics?
Pia Mater
The pia mater (pē′ă mah′ter, pī′ă mā′ter; pia = tender, delicate,
mater = mother) is the innermost of the cranial meninges. It is a
thin layer of delicate areolar connective tissue that is highly vascularized
and tightly adheres to the brain, following every contour
of the surface.
Arachnoid Mater
The arachnoid (ă-rak′noyd) mater, also called the arachnoid
membrane, lies external to the pia mater (figure 15.4). The term
arachnoid means “resembling a spider web,” and this meninx is
so named because it is partially composed of a delicate web of
collagen and elastic fibers, termed the arachnoid trabeculae. Immediately
deep to the arachnoid mater is the subarachnoid space.
The arachnoid trabeculae extend through this space from the arachnoid
mater to the underlying pia mater. Between the arachnoid mater
and the overlying dura mater is a potential space, the subdural space.
The subdural space becomes an actual space if blood or fluid accumulates
there, a condition called a subdural hematoma
Dura Mater
The dura mater (dū′ră mā′tĕr; dura = tough) is an external tough,
dense irregular connective tissue layer composed of two fibrous
layers. As its Latin name indicates, it is the strongest of the meninges.
Within the cranium, the dura mater is composed of two layers. The
meningeal (mĕ-nin′jē-ăl, men′in-jē′ăl) layer lies deep to the periosteal
layer. The periosteal (per′ē-os′tē-ăl; peri = around, osteon =
bone) layer, the more superficial layer, forms the periosteum on the
internal surface of the cranial bones
What are the four cranial dural septa?
the falx cerebri, tentorium cerebelli, falx cerebelli, and diaphragma sellae
What are the functions of cerebrospinal fluid?
■ Buoyancy. The brain floats in the CSF, which thereby
supports more than 95% of its weight and prevents it from being crushed under its own weight. Without CSF to support it, the heavy brain would sink through the foramen magnum.
■ Protection. CSF provides a liquid cushion to protect delicate
neural structures from sudden movements. When you try to
walk quickly in a swimming pool, your movements are slowed
as the water acts as a “movement buffer.” CSF likewise helps
slow movements of the brain if the skull and/or body move
suddenly and forcefully.
■ Environmental stability. CSF transports nutrients and
chemicals to the brain and removes waste products from the
brain. Additionally, CSF protects nervous tissue from chemical
fluctuations that would disrupt neuron function. The waste
products and excess CSF are eventually transported into the
venous circulation, where they are filtered from the blood and
secreted in urine in the urinary system.
Describe the process of CSF production, circulation, and removal.
- CSF is produced in the ventricles by the choroid plexus.
- CSF flows from the lateral ventricles and third ventricle
through the cerebral aqueduct into the fourth ventricle. - Most of the CSF in the fourth ventricle flows into the
subarachnoid space by passing through openings in the roof of
the fourth ventricle. These ventricular openings are the paired
lateral apertures and the single median aperture. CSF also
fills the central canal of the spinal cord. - As it travels through the subarachnoid space, CSF removes
waste products and provides buoyancy for the brain and
spinal cord. - As CSF accumulates within the subarachnoid space, it exerts
pressure within the arachnoid villi. This pressure exceeds the
pressure of blood in the venous sinuses. Thus, the arachnoid
villi extending into the dural venous sinuses provide a conduit
for a one-way flow of excess CSF to be returned into the
blood within the dural venous sinuses.
What is the function of the blood brain barrier (BBB)?
protects the nervous tissue from general circulation by regulating what substances can enter the interstitial fluid of the brain
What is the function of the cerebrum?
The cerebrum is the location of conscious thought processes and the
origin of all complex intellectual functions. It is readily identified as
the two large hemispheres on the superior aspect of the brain (see
figure 15.1a, b). Your cerebrum enables you to read and comprehend
the words in this textbook, turn its pages, form and remember ideas,
and talk about your ideas with your peers. It is the center of your
intelligence, reasoning, sensory perception, thought, memory, and judgment,
as well as your voluntary motor, visual, and auditory activities
What is the main tract between the left and right hempispheres?
corpus callosum
Describe hemispheric lateralization.
■ The two hemispheres appear as anatomic mirror images, but
they display some functional differences, termed hemispheric
lateralization. For example, the portions of the brain that
are responsible for controlling speech and understanding
verbalization are frequently located in the left hemisphere.
These differences primarily affect higher-order functions,
which are addressed in section 17.4.
■ With few exceptions, both cerebral hemispheres receive their
sensory information from and project motor commands to
the opposite side of the body. The right cerebral hemisphere
controls the left side of the body, and vice versa
Describe the landscape of the cerebrum’s 5 lobes in relation to their sulcus.
The frontal lobe (lōb) lies deep to the frontal bone and forms
the anterior part of the cerebral hemisphere. The frontal lobe ends
posteriorly at a deep groove called the central sulcus that marks the
boundary with the parietal lobe. The inferior border of the frontal
lobe is marked by the lateral sulcus, a deep groove that separates
the frontal and parietal lobes from the temporal lobe. An important
anatomic feature of the frontal lobe is the precentral gyrus, which
is a mass of nervous tissue immediately anterior to the central sulcus.
The frontal lobe is primarily concerned with voluntary motor
functions, concentration, verbal communication, decision making,
planning, and personality.
The parietal lobe lies internal to the parietal bone and forms
the superoposterior part of each cerebral hemisphere. It terminates
anteriorly at the central sulcus, posteriorly at a relatively indistinct
parieto-occipital sulcus, and laterally at the lateral sulcus. An
important anatomic feature of this lobe is the postcentral gyrus,
which is a mass of nervous tissue immediately posterior to the central
sulcus. The parietal lobe is involved with general sensory functions,
such as evaluating the shape and texture of objects being touched.
The temporal lobe lies inferior to the lateral sulcus and underlies
the temporal bone. This lobe is involved with hearing and smell.The occipital lobe forms the posterior region of each hemisphere
and immediately underlies the occipital bone. This lobe is
responsible for processing incoming visual information and storing
visual memories.
The insula (in′sū-lă; inland) is a small lobe deep to the lateral
sulcus. It can be viewed by laterally reflecting (pulling aside)
the temporal lobe. The insula’s lack of accessibility has prevented
aggressive studies of its function, but it is apparently involved in
interoceptive awareness, emotional responses, empathy, and the
interpretation of taste.
Describe association areas.
The primary motor and sensory cortical regions are connected to
adjacent association areas that either process and interpret incoming
data or coordinate a motor response (see figure 15.11). Association
areas integrate new sensory inputs with memories of past experiences.
What are the main association areas?
The premotor cortex, also called the somatic motor association
area, is located in the frontal lobe, immediately anterior to the precentral
gyrus. It permits us to process motor information and is primarily responsible
for coordinating learned, skilled motor activities, such as moving the
eyes in a coordinated fashion when reading a book or playing the piano.
The somatosensory association area is located in the parietal
lobe and lies immediately posterior to the primary somatosensory
cortex. It interprets sensory information and is responsible for
integrating and interpreting sensations to determine the texture,
temperature, pressure, and shape of objects. The somatosensory
association area allows us to identify objects while our eyes are
closed.
The auditory association area is located within the temporal
lobe, posteroinferior to the primary auditory cortex. Within this area,
the cortical neurons interpret the characteristics of sound and store
memories of sounds heard in the past.
The visual association area is located in the occipital lobe
and surrounds the primary visual area. It enables us to process visual
information by analyzing color, movement, and form, and to use this
information to identify the things we see
A functional brain region acts like a multi-association area
between lobes for integrating information from individual association
areas. One functional brain region is the Wernicke area
(see figure 15.11), which is typically located only within the left
hemisphere, where it overlaps the parietal and temporal lobes. The
Wernicke area is involved in recognizing, understanding, and comprehending
spoken or written language. As you may expect, the
Wernicke area and the motor speech area must work together in order
for fluent communication to occur.
Another functional brain region, called the gnostic (nō′stik;
gnōsis = knowledge) area (or common integrative area), is composed
of regions of the parietal, occipital, and temporal lobes. This region
integrates all sensory, visual, and auditory information being processed
by the association areas within these lobes. Thus it provides
comprehensive understanding of a current activity.
What are the cerebral nuclei?
paired, irregular masses
of gray matter buried deep within the central white matter in the basal
region of the cerebral hemispheres inferior to the floor of the lateral
ventricle
What are the components of the cerebral nuclei?
■ The C-shaped caudate (kaw′dāt; caud = tail) nucleus has
an enlarged head and a slender, arching tail that parallels the
swinging curve of the lateral ventricle. When a person begins
to walk, the neurons in this nucleus stimulate the appropriate
muscles to produce the pattern and rhythm of arm and leg
movements associated with walking.
■ The amygdaloid (ă-mig′dă-loyd; amygdala = almond) body
(often just called the amygdala) is an expanded region at the
tail of the caudate nucleus. It participates in the expression of
emotions, control of behavioral activities, and development of
moods (see section 15.7 on the limbic system).
■ The putamen (pū-tā′men; puto = to prune) and the globus
pallidus (pal′i-dŭs; globus = ball, pallidus = pale) are two
masses of gray matter positioned between the bulging external
surface of the insula and the lateral wall of the diencephalon.
The putamen and the globus pallidus combine to form a
larger body, the lentiform (len′ti-fōrm; lenticula = lentil,
forma = shape) nucleus, which is usually a compact, almost
rounded mass. The putamen functions in controlling muscular
movement at the subconscious level, whereas the globus
pallidus both excites and inhibits the activities of the thalamus
to control and adjust muscle tone.
■ The claustrum (klaws′trŭm; barrier) is a thin sliver of gray
matter formed by a layer of neurons located immediately
internal to the cortex of the insula and derived from that cortex.
It processes visual information at a subconscious level.
What are the components of the diencephalon and what is its general function?
The components of the diencephalon include the epithalamus,
the thalamus, and the hypothalamus (figure 15.15). The diencephalon
provides the relay and switching centers
for some sensory and
motor pathways and for control of visceral activities
Where is the epithalamus located and what two structures does it house?
partially forms the posterior roof of the diencephalon and covers the third ventricle; posterior portion of the epithalamus houses the pineal gland and the habenular nuclei.
What is the thalamus and what is its function?
paired oval masses of gray
matter that lie on each side of the third ventricle (figure 15.16). The
thalamus forms the superolateral walls of the third ventricle;
Each part of the thalamus is a gray matter mass composed of
about a dozen major thalamic nuclei that are organized into groups;
axons from these nuclei project to particular regions of the cerebral
cortex
The thalamus is the principal and final relay point for sensory
information that will be processed and projected to the primary somatosensory
cortex.
What is the hypothalamus and what is its function?
anteroinferior region of the diencephalon;
- Master control of the autonomic nervous system. The
hypothalamus is a major autonomic integration center. In
essence, it is the “president” of the corporation known as the autonomic nervous system (see section 18.6). It projects
descending axons to autonomic nuclei in the inferior brainstem
that influence heart rate, blood pressure, digestive activities,
and respiration.
■ Master control of the endocrine system. The hypothalamus
is also “president” of another “corporation”—the endocrine
system (see section 20.2)—overseeing most but not all of that
system’s functions. The hypothalamus secretes hormones that
control secretory activities in the anterior pituitary gland. In
turn, subsequent normal secretions from the pituitary gland
control metabolism, growth, stress responses, and reproduction.
Additionally, the hypothalamus produces two hormones that
are transported through axons in the infundibulum and then
stored and released in the posterior pituitary: Antidiuretic
hormone reduces water loss at the kidneys, and oxytocin
stimulates smooth muscle contractions in the uterus, mammary
gland, and prostate gland.
■ Regulation of body temperature. The body’s thermostat
is located within the hypothalamus. Neurons in the preoptic
area detect altered blood temperatures and signal other
hypothalamic nuclei, which control the mechanisms that heat
or cool the body (shivering and sweating, respectively).
■ Control of emotional behavior. The hypothalamus is located
at the center of the limbic system, the part of the brain that
controls emotional responses, such as pleasure, aggression, fear,
rage, contentment, and the sex drive.
■ Control of food intake. Neurons within the ventromedial
nucleus monitor levels of nutrients such as glucose and amino
acids in the blood and produce sensations of hunger.
■ Control of water intake. Specific neurons within the anterior
nucleus continuously monitor the blood solute (dissolved
substances) concentration. High solute concentration
stimulates both the intake of fluid and the production of
antidiuretic hormone by neurons in the supraoptic nucleus and
paraventricular nucleus (see section 20.2).
■ Regulation of sleep–wake (circadian) rhythms. The
suprachiasmatic nucleus directs the pineal gland when to
secrete melatonin. Thus, both work to regulate circadian
rhythms.
What are the 3 regions of the brain stem?
midbrain, pons, and medulla oblongata
In what 3 regions is the cerebellum partioned internally into?
an outer gray matter layer of cortex, an internal region of white matter, and the deepest gray matter layerl which is composed of cerebellar nuclei
white matter of cerebellum is called arbor vitae because it has a distribution pattern that resembles a tress
