Chapter 13
Central Nervous System
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 1
Coverings of the Brain
and Spinal Cord

Two protective coverings:

Outer covering is bone; cranial bones encase the
brain, and vertebrae encase the spinal cord

Inner covering is the meninges; the meninges of
the cord continue inside the spinal cavity beyond
the end of the spinal cord
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 2
Coverings of the Brain
and Spinal Cord

Meninges—three membranous layers

Dura mater—strong, white fibrous tissue; outer layer of meninges
and inner periosteum of the cranial bones; has three important
extensions
• Falx cerebri

Projects downward into the longitudinal fissure between the two cerebral
hemispheres

Dural sinuses—function as veins, collecting blood from brain tissues for
return to the heart

Superior sagittal sinus—one of several dural sinuses
• Falx cerebelli—separates the two hemispheres of the cerebellum
• Tentorium cerebelli—separates the cerebellum from the cerebrum

Arachnoid mater—delicate, cobwebby layer between the dura
mater and pia mater
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 3
Coverings of the Brain
and Spinal Cord

Meninges—three membranous layers (cont.)

Pia mater—innermost, transparent layer; adheres
to the outer surface of the brain and spinal cord;
contains blood vessels; beyond the spinal cord,
forms a slender filament called filum terminale; at
level of sacrum, blends with dura mater to form a
fibrous cord that disappears into the periosteum of
the coccyx
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 4
Coverings of the Brain
and Spinal Cord

Several spaces exist between and around the
meninges
• Epidural space—located between the dura mater and
inside the bony covering of the spinal cord; contains a
supporting cushion of fat and other connective tissues
(virtually absent around brain because dura is continuous
with periosteum of bone)
• Subdural space—located between the dura mater and
arachnoid mater; contains lubricating serous fluid
• Subarachnoid space—located between the arachnoid
and pia mater; contains a significant amount of
cerebrospinal fluid
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 5
Cerebrospinal Fluid


Functions

Provides a supportive, protective cushion

Reservoir of circulating fluid, which is monitored
by the brain to detect changes in the internal
environment
Fluid spaces

Cerebrospinal fluid—found within the
subarachnoid space around the brain and spinal
cord and within the cavities and canals of the brain
and spinal cord
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 6
Cerebrospinal Fluid

Fluid spaces (cont.)

Ventricles—fluid-filled spaces within the brain; four
ventricles within the brain

First and second ventricles (lateral)—one located
in each hemisphere of the cerebrum
• Third ventricle—thin, vertical pocket of fluid below and
medial to the lateral ventricles
• Fourth ventricle—tiny, diamond-shaped space where the
cerebellum attaches to the back of the brainstem
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 7
Cerebrospinal Fluid

Formation and circulation of cerebrospinal
fluid (Figure 13-5)

Occurs by separation of fluid from blood in the
choroid plexuses
• Fluid from the lateral ventricles seeps through the
interventricular foramen (of Monro) into the third ventricle
• From the third ventricle, fluid goes through the cerebral
aqueduct into the fourth ventricle
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 8
Cerebrospinal Fluid

Formation and circulation of cerebrospinal
fluid (cont.)
• From the fourth ventricle, fluid goes to two different
areas:

Some fluid flows directly into the central canal of the spinal
cord

Some fluid leaves the fourth ventricle through openings in
its roof into the cisterna magna, a space that is continuous
with the subarachnoid space
• Fluid circulates in the subarachnoid space and then is
absorbed into venous blood through the arachnoid villi
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 9
Spinal Cord

Structure of the spinal cord

Lies within the spinal cavity and extends from the
foramen magnum to the lower border of the first
lumbar vertebra

Oval cylinder that tapers slightly from above
downward

Two bulges, one in the cervical region and one in
the lumbar region

Anterior median fissure and posterior median
sulcus are two deep grooves; anterior fissure is
deeper and wider
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 10
Spinal Cord

Functions of the spinal cord

Provides conduction routes to and from the brain
• Ascending tracts—conduct impulses up the cord to the brain
• Descending tracts—conduct impulses down the cord from
the brain
• Bundles of axons compose all tracts
• Tracts are both structural and functional organizations
of nerve fibers:

Structural—all axons of any one tract originate in the same
structure and terminate in the same structure

Functional—all axons that compose one tract serve one general
function
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 11
The Brain

Structures of the brainstem (Figures 13-9 and 13-10)

Medulla oblongata
• Lowest part of the brainstem
• Part of the brain that attaches to spinal cord, located just above the
foramen magnum
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 12
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 13
The Brain

Structures of the brainstem (cont.)
 Pons
• Located above the medulla and below the midbrain
 Midbrain
• Located above the pons and below the cerebrum; forms
the midsection of the brain
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 14
The Brain

Functions of the brainstem

Performs sensory, motor, and reflex functions
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 15
The Brain

Functions of the brainstem (cont.)

Nuclei in medulla—contain reflex centers
• Of primary importance—cardiac, vasomotor, and
respiratory centers
• Nonvital reflexes—vomiting, coughing, sneezing, etc.

Pons—contains reflexes mediated by fifth, sixth,
seventh, and eighth cranial nerves and
pneumotaxic centers that help regulate respiration

Midbrain—contains centers for certain cranial
nerve reflexes
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 16
The Brain

Structure of the cerebellum

Second largest part of the brain—contains more neurons
than the rest of the nervous system

Located just below the posterior portion of the cerebrum;
transverse fissure separates these two parts of the brain

Gray matter makes up the cortex, and white matter
predominates in the interior

Arbor vitae—internal white matter of the cerebellum;
distinctive pattern similar to the veins of a leaf
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 17
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 18
The Brain

Structure of the cerebellum (cont.)


Consists of the cerebellar hemispheres and the vermis
Internal white matter—composed of short and long tracts
• Shorter tracts—conduct impulses from neuron cell bodies located in the
cerebellar cortex to neurons whose dendrites and cell bodies compose nuclei
located in the interior of the cerebellum
• Longer tracts—conduct impulses to and from the cerebellum; fibers enter or
leave by way of three pairs of peduncles

Dentate nuclei
• Important pair of cerebellar nuclei, one of which is located in each hemisphere
• Nuclei connected with thalamus and with motor areas of the cerebral cortex by
tracts
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 19
The Brain

Functions of the cerebellum

Cerebellum compares the motor commands of the cerebrum to the
information coming from proprioceptors in the muscle; impulses travel
from the cerebellum to both the cerebrum and muscles to coordinate
movements to produce the intended action

General functions
• Acts with cerebral cortex to produce skilled movements by coordinating
the activities of groups of muscles
• Controls skeletal muscles to maintain balance
• Controls posture; operates at subconscious level to smooth movements
and make movements efficient and coordinated
• Processes sensory information; complements and assists various
functions of the cerebrum
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 20
The Brain

Diencephalon

Located between the cerebrum and the midbrain

Consists of several structures located around the third ventricle:
thalamus, hypothalamus, optic chiasma, pineal gland, and several
others

Thalamus
• Dumbbell-shaped mass of gray matter made up of many nuclei
• Each lateral mass forms one lateral wall of the third ventricle
• Intermediate mass—extends through the third ventricle and joins the
two lateral masses
• Geniculate bodies—two of the most important groups of nuclei
comprising the thalamus; located in posterior region of each lateral
mass; play role in processing auditory and visual input
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 21
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 22
The Brain

Thalamus (cont.)
• Serves as a major relay station for sensory impulses on their way to
the cerebral cortex
• Performs the following primary functions:

Plays two parts in mechanism responsible for sensations:
– Impulses produce conscious recognition of the crude, less critical sensations of
pain, temperature, and touch
– Neurons relay all kinds of sensory impulses, except possibly olfactory, to the
cerebrum

Plays part in the mechanism responsible for emotions by associating
sensory impulses with feeling of pleasantness and unpleasantness

Plays part in arousal mechanism

Plays part in mechanisms that produce complex reflex movements
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 23
The Brain

Diencephalon (cont.)

Hypothalamus
• Consists of several structures that lie beneath the thalamus
• Forms floor of the third ventricle and lower part of lateral walls
• Small but functionally important area of the brain, performs
many functions of greatest importance for survival and
enjoyment
• Links mind and body
• Links nervous system to endocrine system
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 24
The Brain

Hypothalamus (cont.)
• Summary of hypothalamic functions

Regulator and coordinator of autonomic activities

Major relay station between the cerebral cortex and lower
autonomic centers; crucial part of the route by which emotions
can express themselves in changed bodily functions

Synthesizes hormones secreted by posterior pituitary and plays
an essential role in maintaining water balance

Some neurons function as endocrine glands

Plays crucial role in arousal mechanism

Crucial part of mechanism regulating appetite

Crucial part of mechanism maintaining normal body
temperature
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 25
The Brain

Diencephalon (cont.)

Pineal gland
• Involved in regulating the body’s biological clock (Figure 13-14)
• Produces melatonin as a “timekeeping hormone”

Melatonin is made from the neurotransmitter serotonin

Melatonin levels increase when sunlight is absent and decreases
when sunlight is present, thus regulating the daily biological clock

Melatonin is the “sleep hormone”
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 26
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 27
The Brain

Structure of the cerebrum

Cerebral cortex
• Largest and uppermost division of the brain; consists of
right and left cerebral hemispheres; each hemisphere is
divided into five lobes :

Frontal lobe

Parietal lobe

Temporal lobe

Occipital lobe

Insula (island of Riel)
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 28
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 29
The Brain

Cerebral cortex (cont.)
• Cerebral cortex—outer surface made up of six layers of
gray matter
• Gyri—convolutions; some are named: precentral gyrus,
postcentral gyrus, cingulate gyrus, and hippocampal
gyrus
• Sulci—shallow grooves
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 30
The Brain

Cerebral cortex (cont.)
• Fissures—deeper grooves, divide each cerebral
hemisphere into lobes; four prominent cerebral fissures

Longitudinal fissure—deepest fissure; divides cerebrum
into two hemispheres

Central sulcus (fissure of Rolando)—groove between
frontal and parietal lobes

Lateral fissure (fissure of Sylvius) —groove between
temporal lobe below and parietal lobes above; island of
Reil lies deep in lateral fissure

Parietooccipital fissure—groove that separates occipital
lobe from parietal lobes
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 31
The Brain

Functions of the cerebral cortex

Functional areas of the cortex—certain areas of the cerebral
cortex predominantly engage in one particular function
• Postcentral gyrus—mainly general somatic sensory area;
receives impulses from receptors activated by heat, cold, and
touch stimuli
• Precentral gyrus—chiefly somatic motor area; impulses from
neurons in this area descend over motor tracts and stimulate
skeletal muscles
• Transverse gyrus—primary auditory area
• Occipital lobe—primary visual areas
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 32
The Brain

Functions of the cerebral cortex (cont.)

Sensory functions of the cortex
• Somatic senses—sensations of touch, pressure, temperature,
proprioception, and similar perceptions that require complex
sensory organs
• Cortex contains a “somatic sensory map” of the body
• Information sent to primary sensory areas is relayed to
sensory association areas, as well as to other parts of the
brain
• The sensory information is compared and evaluated, and the
cortex integrates separate bits of information into whole
perceptions
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 33
The Brain

Motor functions of the cortex
• For normal movements to occur, many parts of the nervous
system must function
• Precentral gyrus—primary somatic motor area; controls
individual muscles
• Secondary motor area—in the gyrus immediately anterior to
the precentral gyrus; activates groups of muscles
simultaneously
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 34
The Brain

Integrative functions of the cortex
• Consciousness State of awareness of one’s self, one’s environment, and other
beings

Depends on excitation of cortical neurons by impulses conducted to them
by the reticular activating system

There are two current concepts about the reticular activating system:
– Functions as the arousal system for the cerebral cortex
– Its functioning is crucial for maintaining consciousness
• Language

Ability to speak and write words and ability to understand spoken and written
words

Speech centers—areas in the frontal, parietal, and temporal lobes

Left cerebral hemisphere contains speech centers in approximately 90%
of the population; in the remaining 10%, contained in either the right
hemisphere or both

Aphasias—caused by lesions in speech centers
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 35
The Brain

Integrative functions of the cortex (cont.)
• Emotions


Subjective experiencing and objective expressing of emotions involve
functioning of the limbic system
Limbic system—also known as the “emotional brain”
– Most structures of limbic system lie on the medial surface of the cerebrum; they are
the cingulate gyrus and the hippocampus
– Have primary connections with other parts of the brain, such as thalamus, fornix,
septal nuclei, amygdaloid nucleus, and hypothalamus
• Memory





One of the major human mental activities
Cortex is capable of storing and retrieving both short- and
long-term memory
Temporal, parietal, and occipital lobes are among the areas responsible for
short- and long-term memory
Engrams—structural traces in the cerebral cortex that comprise long-term
memories
Cerebrum’s limbic system plays a key role in memory
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 36
The Brain

Hemisphericity—specialization of cerebral hemispheres
• Right and left hemispheres of the cerebrum specialize in
different functions; however, both sides of a normal person’s
brain communicate with each other to accomplish complex
functions
• Left hemisphere is responsible for the following:

Language functions

Dominating control of certain hand movements
• Right hemisphere is responsible for the following:

Perception of certain kinds of auditory material

Tactual perception

Perceiving and visualizing spatial relationships
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 37
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 38
Cycle of Life:
Central Nervous System

The development and degeneration of the central
nervous system is the most obvious functional change
over the life span

Development of the brain and spinal cord begins
in the womb

Lack of development in the newborn is evidenced by
lack of complex integrative functions

Language

Complex memory

Comprehension of spatial relationships

Complex motor skills
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 39
Cycle of Life:
Central Nervous System

Complex functions develop by adulthood

Late adulthood—tissues degenerate

Profound degeneration—unable to perform
complex functions

Milder degeneration—temporary memory lapse or
difficulty with complex motor tasks
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 40
The Big Picture: The Central Nervous
System and the Whole Body

Central nervous system—ultimate regulator
of the body; essential to survival

Able to integrate bits of information from all
over the body, make sense of them, and
make decisions
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 41