Download General layout of the Nervous System

Topic 2
The Anatomy of the
Brain (Nervous System)
Systems, Structures, and Cells
That Make Up Your Nervous
System
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Outline of topic
1.
2.
3.
4.
5.
General layout of the Nervous system
Cells of the Nervous system: Anatomy of
Neuron
Spinal Cord
Major structure of the Brain
Central Nervous System
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General layout of the Nervous System

The brain is a large mass of neurons, glia, and other supporting
cells. It is the most protected organ of the body, encased in a
tough, bony skull and floating in a pool of cerebrospinal fluid.

The brain receives a copious supply of blood and is chemically
guarded by the blood–brain barrier.

The brain receives approximately 20 percent of the blood flow
from the heart, and it receives it continuously.

Other parts of the body, such as the skeletal muscles or
digestive system, receive varying quantities of blood,
depending on their needs (relative to those of other regions).
But the brain always receives its share.
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1) General Layout of the
Nervous System
a) Central Nervous System (CNS)


Brain (in the skull)
Spinal Cord (in the spine)
b) Peripheral Nervous System (PNS)

Located outside of the skull and spine

Connects the central nervous system to all other
parts of the body

Serves to bring information into the CNS and carry
signals out of the CNS
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How do you differentiate CNS and PNS?
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General Layout of the Nervous
System Continued
b) Peripheral Nervous System
i) Somatic Nervous System


Afferent nerves (sensory)
Efferent nerves (motor)
ii) Autonomic Nervous System


Sympathetic and parasympathetic nerves
Both are efferent
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ii) Autonomic Nervous System



All nerves are efferent
Sympathetic and parasympathetic nerves
generally have opposite effects
Two-stage neural paths, neuron exiting the
CNS synapses on a second-stage neuron
before the target organ
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Autonomic Nervous System
Continued

Sympathetic




Thoracic and lumbar
“Fight or flight”
Second stage neurons
are far from the target
organ
Parasympathetic



Cranial and sacral
“Rest and restore”
Second stage
neurons are near the
target organ
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FIGURE 3.2 The major divisions of the
nervous system.
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Meninges, Ventricles, and
Cerebrospinal Fluid (CSF)

CNS encased in bone and covered by
three meninges




Dura mater – tough outer membrane
Arachnoid membrane – web-like
Pia mater – adheres to CNS surface
Cerebrospinal fluid (CSF)

Fluid serves as cushion
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FIGURE 3.3 The cerebral ventricles.
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Protecting the Brain

Chemical protection


The blood-brain barrier – tightly-packed
cells of blood vessel walls prevent entry
of many molecules
Physical protection



Skull
Meninges
Cerebrospinal fluid (CSF)
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2) Cells of the Nervous
System: Anatomy of Neurons

Neurons


Specialized cells for the reception, conduction,
and transmission of electrochemical signals
Many sizes and shapes
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FIGURE 3.5 The major external
features of a typical neuron.
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FIGURE 3.6 The major
internal features of a
typical neuron.
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FIGURE 3.7 The cell membrane is a
lipid bilayer with signal proteins and
channel proteins embedded in it.
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FIGURE 3.8 A unipolar neuron, a
bipolar neuron, a multipolar neuron,
and an interneuron.
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Glial Cells:
The Forgotten Cells


Glial cells
 Outnumber neurons 10:1
 Support neurons
 Recent evidence for glial communication and modulatory
effects of glia on neuronal communication
Four classes of Glial cells:
 Oligodendrocytes – extensions rich in myelin create myelin
sheaths in CNS
 Schwann cells – similar to function of oligodendrocytes but in
PNS, can guide axonal regeneration
 Astrocytes – largest glia, star-shaped, many functions
 Microglia – involved in response to injury or disease
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FIGURE 3.9 The myelination of CNS axons by
an oligodendrocyte and the myelination of PNS
axons by Schwann cells.
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Terminology Note
CNS
PNS
Myelin-providing
glia
Oligodendrocytes
Schwann cells
Clusters of cell
bodies
Nuclei
(singular nucleus)
Ganglia
(singular ganglion)
Bundles of axons
Tracts
Nerves
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Neuroanatomical Techniques
and Directions



Golgi stain – allows for visualization
of individual neurons
Nissl stain – selectively stains cell
bodies
Electron microscopy – provides
information about the details of
neuronal structure
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FIGURE 3.11 Neural tissue that has
been stained by the Golgi method.
(Ed Reschke © Peter Arnold, Inc.)
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FIGURE 3.12 The Nissl stain.
(Courtesy of Carl Ernst and Brian
Christie, Department of Psychology,
University of British Columbia.)
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FIGURE 3.13 A color-enhanced scanning
electron micrograph of a neuron cell body
(green) studded with terminal buttons
(orange). Courtesy of Jerold J. M. Chun,
M.D., Ph.D.
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Neuroanatomical Tracing
Techniques


Anterograde (forward)
 tracing to where axons project
away from an area
Retrograde (backward)
 tracing from where axons are
projecting into an area
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FIGURE 3.14 Anatomical directions
in a representative vertebrate (cat).
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FIGURE 3.15 Anatomical directions
in a human.
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Directions in the Vertebrate
Nervous System Continued


Anatomical directions ignore the fact that
humans walk upright. Therefore, top of
the head is both “dorsal” (back) and
“superior” (top)
Other directions:




Medial – toward the middle
Lateral – toward the side
Proximal – close
Distal – far
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Sections of the Brain
How can you examine a brain?
 Cross Section - with respect to the central
nervous system, a slice taken at right angles
to the neuraxis
 Horizontal – a slice parallel to the ground
 Frontal (coronal) – slicing bread or salami
 Sagittal – a midsagittal section separates the
left and right halves

See figure 3.16 & 3.2.
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FIGURE 3.16 Horizontal, frontal
(coronal), and sagittal planes in the
human brain and a cross section of
the human spinal cord.
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Midsagittal view
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3) Spinal Cord

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Gray matter – inner component, primarily cell
bodies
White matter – outer area, mainly myelinated
axons
Dorsal – afferent, sensory
Ventral – efferent, motor
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The Spinal Cord

The spinal cord is a long, conical structure,
approximately as thick as one’s little finger. The
principal function of the spinal cord is to distribute
motor fibers to the effector organs of the body
(glands and muscles) and to collect
somatosensory information to be passed on to the
brain.

The spinal cord also has a certain degree of
autonomy from the brain; various reflexive control
circuits.
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The Spinal Cord

Spinal Cord


the cord of nervous tissue that extends caudally from
the medulla
Spinal Root

a bundle of axons surrounded by connective tissue that
occurs in pairs, which fuse and form a spinal nerve
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The Spinal Cord

Cauda Equina (ee kwye na)


a bundle of spinal roots located caudal to the end of the
spinal cord
Caudal Block

the anesthesia and paralysis of the lower part of the
body produced by injection of a local anesthetic into the
cerebrospinal fluid surrounding the cauda equina.
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Figure 3.21, page 91
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The Spinal Cord

Dorsal Root
 the spinal root that contains incoming (afferent) sensory fibers

Ventral Root
 the spinal root that contains outgoing (efferent) motor fibers

Spinal Nerve
 a peripheral nerve attached to the spinal cord
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The Spinal Cord

Afferent Axon


Dorsal Root Ganglion


an axon directed toward the central nervous system,
conveying sensory information
a nodule on a dorsal root that contains cell bodies of
afferent spinal nerve neurons
Efferent Axon (eff ur ent)

an axon directed away from the central nervous system,
conveying motor commands to muscles and glands
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FIGURE 3.17 The dorsal and ventral
roots of the spinal cord.
FIGURE 3.18 A schematic cross
section of the spinal cord.
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Section Summary

The outer part of the spinal cord consists of
white matter: axons conveying information up
or down.

The central gray matter contains cell bodies.
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FIGURE 3.19 The early development
of the mammalian brain illustrated in
schematic horizontal sections.
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FIGURE 3.20 The divisions of the
adult human brain.
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The Central Nervous System –
Brain
The
brain consists of three major divisions, organized around the
three chambers of the tube that develops early in embryonic life:
the forebrain, the midbrain, and the hindbrain.
Although
the basic development of the nervous system is
genetically controlled, sensory stimulation plays a role in refining
the details.
In
addition, the neural circuitry of even a fully mature brain can
be modified through experience.
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The Central Nervous System

The large size of the human brain, relative to the
brains of other primates, appears to be accomplished
primarily by lengthening the first and second periods
of brain development.

The FOREBRAIN, which surrounds the lateral and
third ventricles (hollow, interconnected chambers –
little bellies), consists of the telencephalon and
diencephalon.

The telencephalon contains the cerebral cortex (like
the bark of a tree), the limbic system, and the basal
ganglia.
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The Central Nervous System

The cerebral cortex is organized into the frontal,
parietal, temporal, and occipital lobes.

The central sulcus divides the frontal lobe—which
deals specifically with movement and the planning
of movement—from the other three lobes (p,t,o),
which deal primarily with perceiving and learning.

The limbic system—which includes the limbic
cortex, the hippocampus, and the amygdala—is
involved in emotion, motivation, and learning.
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The Central Nervous System

The basal ganglia in the forebrain participate in
the control of movement.

The diencephalon consists of the thalamus, which
directs information to and from the cerebral cortex,
and the hypothalamus, which controls the
endocrine system and modulates species-typical
behaviors.
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


MIDBRAIN – also called mesencephalon,
contains two main parts: tectum and
tegmentum
Tectum – involve in the auditory and visual
system such as visual reflexes and reactions
to moving stimuli.
Tegmentum – play a role in sleep, arousal,
attention, muscle tonus, movement (specific
movements includes fighting & mating).
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The Central Nervous System
Section Summary

The HINDBRAIN surrounds the fourth ventricle—
contains the cerebellum, the pons, and the medulla.

The cerebellum plays an important role in integrating
and coordinating movements.

The pons contains some nuclei that are important in
sleep and arousal.

The medulla oblongata, too, is involved in sleep and
arousal, but it also plays a role in control of movement
and in control of vital functions such as heart rate,
breathing, and blood pressure.
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4) Major Structures of the Brain
Major divisions:
a) Hindbrain
b) Midbrain
c) Forebrain
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4) Major Structures of the Brain
a) Hindbrain
1) Myelencephalon = medulla


Composed largely of tracts
Origin of the reticular formation
2) Metencephalon



Many tracts
Pons – ventral surface
Cerebellum – coordination
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FIGURE 3.21 Structures of the
human myelencephalon (medulla)
and metencephalon.
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Major Structures of the Brain
Continued

Mesencephalon = midbrain

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tectum has inferior and superior colliculi
tegmentum has periaqueductal gray,
substantia nigra, and red nucleus
Diencephalon


thalamus
hypothalamus
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FIGURE 3.22 The human
mesencephalon (midbrain).
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FIGURE 3.23 The human
diencephalon.
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Telencephalon – Cerebral
Cortex



Convolutions serve to increase
surface area
Longitudinal fissure – a groove that
separates right and left
hemispheres
Corpus callosum – largest
hemisphere-connecting tract
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FIGURE 3.25 The major fissures of
the human cerebral cortex.
FIGURE 3.26 The lobes of the
cerebral hemishphere.
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Telencephalon – Subcortical
Structures

Limbic system – regulation of motivated
behaviors


Mammillary bodies, hippocampus, amygdala,
fornix, cingulate, septum
Basal ganglia motor system

Amygdala, striatum (caudate nucleus +
putamen), globus pallidus
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FIGURE 3.28 The major structures of
the limbic system: amygdala,
hippocampus, cingulate cortex,
fornix, septum, and mammillary
body.
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FIGURE 3.29 The basal ganglia:
amygdala, striatum (caudate plus
putamen) and globus pallidus.
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FIGURE 3.30 Summary of major
brain structures.
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