CH. 15 Brain and Cranial Nerves

Question 1

What are the 4 main regions of the brain?

Answer 1

cerebrum. diencephalon, brainstem, and cerebellum

Question 2

What are the 3 primary brain regions that develop in the embyonic stage?

Answer 2

1. Prosencephalon - forebrain
2. Mesencephalon - midbrain
3. Rhombencephalon - hindbrain

Question 3

What are the 5 secondary brain vesicles that develop in the 5th week of development?

Answer 3

■ 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.

Question 4

Differentiatie between gray and white matter.

Answer 4

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.

Question 5

What are the cranial meninges?

Answer 5

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

Question 6

What are the 3 cranial meninges and what are their characteristics?

Answer 6

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

Question 7

What are the four cranial dural septa?

Answer 7

the falx cerebri, tentorium cerebelli, falx cerebelli, and diaphragma sellae

Question 8

What are the functions of cerebrospinal fluid?

Answer 8

■ 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.

Question 9

Describe the process of CSF production, circulation, and removal.

Answer 9

1. CSF is produced in the ventricles by the choroid plexus.
2. CSF flows from the lateral ventricles and third ventricle
   through the cerebral aqueduct into the fourth ventricle.
3. 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.
4. As it travels through the subarachnoid space, CSF removes
   waste products and provides buoyancy for the brain and
   spinal cord.
5. 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.

Question 10

What is the function of the blood brain barrier (BBB)?

Answer 10

protects the nervous tissue from general circulation by regulating what substances can enter the interstitial fluid of the brain

Question 11

What is the function of the cerebrum?

Answer 11

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

Question 12

What is the main tract between the left and right hempispheres?

Answer 12

corpus callosum

Question 13

Describe hemispheric lateralization.

Answer 13

■ 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

Question 14

Describe the landscape of the cerebrum’s 5 lobes in relation to their sulcus.

Answer 14

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.

Question 15

Describe association areas.

Answer 15

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.

Question 16

What are the main association areas?

Answer 16

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.

Question 17

What are the cerebral nuclei?

Answer 17

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

Question 18

What are the components of the cerebral nuclei?

Answer 18

■ 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.

Question 19

What are the components of the diencephalon and what is its general function?

Answer 19

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

Question 20

Where is the epithalamus located and what two structures does it house?

Answer 20

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.

Question 21

What is the thalamus and what is its function?

Answer 21

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.

Question 22

What is the hypothalamus and what is its function?

Answer 22

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.

Question 23

What are the 3 regions of the brain stem?

Answer 23

midbrain, pons, and medulla oblongata

Question 24

In what 3 regions is the cerebellum partioned internally into?

Answer 24

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

Question 25

What 3 tracts link the cerebellum with the brainstem?

Answer 25

thick tracts known as peduncles;

the superior cerebellar peduncles: connect cerebellum to the midbrain

middle cerebellar peduncles: connect pons to the cerebellum

inferior cerebellar peduncles: connect cerebellum to medulla oblongata

these enable cerebellum to fine tune skeletal muscle movement and interpret all body proprioceptive movement

Question 26

What are the common brain structures of the limbic system?

Answer 26

1) The cingulate gyrus: internal mass of cerebral cortex that receives input from other components of the limbic system
2) Parahippocampal gyrus: mass of cortical tissue in temporal lobe, associated with hippocampus
3) Hippocampus: nucleus located superior to the parahippocampal gyrus that connects to diencephalon; essential as well as parahippocampal gyrus in storing memories and forming long term memory
4) Amygdaloid body: connects to hippocampus; involved in several aspects of emotion - especially fear. It helps store and code memories based on how a person emotionally perceives them
5) Olfactory bulbs, olfactory tracts, and olfactory cortex: particular odors can provoke certain emotions or be associated with certain memories
6) Fornix: thin tact of white matter that connects the hippocampus with other limbic system structures
7) Anterior thelamic nuclei, habenular nuclei, septal nuclei, and mammillary bodies: interconnect other parts of the limbic system and contribute to overall function