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THE NERVOUS SYSTEM
NEURONS:
The structural components of the
nervous system…
Objectives:
Structure and mechanism of a neuron
(nervous cell).
 Types of neurons.

NEURONS:
The structural components of the
nervous system…
Structure and
mechanism of a
neuron (nervous
cell).


Types of
neurons.
Structure and mechanism of
a neuron (nervous cell).

The human body is made up of trillions of cells.
Cells of the nervous system, called nerve cells or
neurons, are specialized to carry "messages"
through an electrochemical process. The human
brain has about 100 billion neurons that carry out
the nerve impulses through a process called action
potential.
A real view showing a neuron (nerve cell)
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Structure and mechanism of a neuron (nervous cell).
Neurons are similar to other cells in
the body because:
1. Neurons are surrounded by a cell
membrane.
2. Neurons have a nucleus that contains
genes.
3. Neurons contain cytoplasm, mitochondria
and other "organelles".
4. Neurons carry out basic cellular processes
such as protein synthesis and energy
production.
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However, neurons differ from other
cells in the body because:
1. Neurons have specialized extensions called
dendrites and axons. Dendrites bring
information to the cell body and axons take
information away from the cell body.
2. Neurons communicate with each other
through an electrochemical process.
3. Neurons contain some specialized
structures (for example, synapses) and
chemicals (for example, neurotransmitters).
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Structure and mechanism of a neuron (nervous cell).
Neurons are the oldest and
longest cells in the body! You have
many of the same neurons for your
whole life. Although other cells die
and are replaced, many neurons are
never replaced when they die. In
fact, you have fewer neurons when
you are old compared to when you
are young. On the other hand, data
published in November 1998 show
that in one area of the brain (the
hippocampus), new neurons CAN
grow in adult humans.
Neurons can be quite large - in
some neurons, such as
corticospinal neurons (from motor
cortex to spinal cord) or primary
afferent neurons (neurons that
extend from the skin into the spinal
cord and up to the brain stem), can
be several feet long!
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Structure and mechanism of a neuron (nervous cell).
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A single neuron consist of:
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CELL BODY: is the metabolic center of the
neuron, contains the Nucleus and Mitochondrion.
DENDRITES: convey incoming messages to the
cell body.
AXON HILLOCK: a cone like region from where
an axon arises.
AXONS: generates nerve impulses and topically
conduct them away from the cell body." A nerve is
a group of axons”.
Presynaptic terminals: The swollen, distal end
of an axon; contains a neurotransmitter substance
within synaptic vesicles. Also called synaptic
ending or synaptic bouton.
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Structure and mechanism of a neuron (nervous cell).
There are several differences between axons and
dendrites:
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Axons
Take information away
from the cell body
Smooth Surface
Generally only 1 axon per
cell
No ribosomes
Can have myelin
Branch further from the
cell body
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Dendrites
Bring information to the
cell body
Rough Surface (dendritic
spines)
Usually many dendrites
per cell
Have ribosomes
No myelin insulation
Branch near the cell body
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Structure and mechanism of a neuron (nervous cell).
What is inside of a neuron? A neuron has many
of the same "organelles," such as mitochondria,
cytoplasm and a nucleus, as other cells in the
body.
 Nucleus - contains genetic material
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(chromosomes) including information for
cell development and synthesis of proteins
necessary for cell maintenance and
survival. Covered by a membrane.
Nucleolus - produces ribosomes
necessary for translation of genetic
information into proteins
Nissl Bodies - groups of ribosomes used
for protein synthesis.
Endoplasmic reticulum (ER) - system of
tubes for transport of materials within
cytoplasm. Can have ribosomes (rough
ER) or no ribosomes (smooth ER). With
ribosomes, the ER is important for protein
synthesis.
Golgi Apparatus - membrane-bound
structure important in packaging peptides
and proteins (including neurotransmitters)
into vesicles.
Microfilaments/Neurotubules - system of
transport for materials within a neuron and
may be used for structural support.
Mitochondria - produce energy to fuel
cellular activities.
Types of neurons.
Neurons come in many different shapes and
sizes. Some of the smallest neurons have cell
bodies that are only 4 microns wide. Some of the
biggest neurons have cell bodies that are 100
microns wide. (Remember that 1 micron is equal to
one thousandth of a millimeter!!).
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Types of neurons.
One way to classify neurons is by the number of
extensions that extend from the neuron's cell body
(soma).
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Bipolar neurons have two
processes extending from
the cell body (examples:
retinal cells, olfactory
epithelium cells).
Multipolar neurons have
many processes that
extend from the cell body.
However, each neuron has
only one axon (examples:
spinal motor neurons,
pyramidal neurons,
Purkinje cells).
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Pseudounipolar cells
(example: dorsal root
ganglion cells). Actually,
these cells have 2 axons
rather than an axon and
dendrite. One axon
extends centrally toward
the spinal cord, the other
axon extends toward the
skin or muscle.
Types of neurons.
Neurons can also be classified by the direction that
they send information:
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Sensory (or afferent) neurons: send information from
sensory receptors (e.g., in skin, eyes, nose, tongue,
ears) TOWARD the central nervous system.
Motor (or efferent) neurons: send information AWAY
from the central nervous system to muscles or
glands.
Interneurons: send information between sensory
neurons and motor neurons. Most interneurons are
located in the central nervous system.
objectives
Neuroanatomy and an
introduction to the Nervous
system.
Introduction
Neuroanatomy and an
introduction to the Nervous
system.
Neuroanatomy is the structure of the nervous
system. To learn how the nervous system functions,
you must learn how the nervous system is put
together.
the nervous system maintains body homeostasis
with electrical signals; provides for sensation, higher
mental functions, and emotional response; and
activates muscles and glands.
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the nerves system is the master controlling and
communicating system of the body. Every thought,
action and emotion reflects its activity. Its signaling
device, or means of communicating with body cells,
is electrical impulses, which are rapid and specific
and cause almost immediate responses.
Neuroanatomy and an introduction to the Nervous system.
To carry out its normal role, the nervous system has
three over lapping functions:
1) Much like a sentry, it uses its millions of sensory
receptors to monitor changes occurring both inside and
outside the body. These changes are called stimuli,
and the gathered information is called sensory input.
2) It processes and interprets the sensory input and
makes decisions about what should be done at each
moment – a process called integration.
3) It then effects a response by activating muscles or
glands (effctors) via motor output.
objectives
Structural classification
of the nervous system
Objectives:
 Central Nervous system (CNS)
 Peripheral Nervous system (PNS)
Structural classification of the
nervous system
The nervous system can be
divided into several connected
systems that function together.
Let's take the simple division:
The Nervous System is divided into:
First: The Central
Nervous System
Second: The
Peripheral
Nervous System
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Structural classification of the nervous system
The Central Nervous
System
The central nervous system is
divided into two parts: the brain
and the spinal cord. The average
adult human brain weighs 1.3 to
1.4 kg (approximately 3 pounds).
The brain contains about 100
billion nerve cells (neurons) and
trillions of "support cells" called
glia. The spinal cord is about 43
cm long in adult women and 45
cm long in adult men and weighs
about 35-40 grams. The vertebral
column, the collection of bones
(back bone) that houses the
spinal cord, is about 70 cm long.
The Central
Therefore, the spinal cord is much Nervous System
shorter than the vertebral
(Brain and Spinal
column.
Cord)
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Structural classification of the nervous system
The Peripheral Nervous System
The peripheral nervous system is divided into two major
parts: the somatic nervous system and the autonomic nervous
system.
1. Somatic Nervous System The somatic nervous system
consists of peripheral nerve fibers that send sensory
information to the central nervous system AND motor nerve
fibers that project to skeletal muscle. The picture on the left
shows the somatic motor system. The cell body is located in
either the brain or spinal cord and projects directly to a
skeletal muscle.
2. Autonomic Nervous System The autonomic nervous system
is divided into three parts: the sympathetic nervous system,
the parasympathetic nervous system and the enteric nervous
system. The autonomic nervous system controls smooth
muscle of the viscera (internal organs) and glands The
preganglionic neuron is located in either the brain or the spinal
cord. This preganglionic neuron projects to an autonomic
ganglion. The postganglionic neuron then projects to the target
organ..
Notice that the somatic nervous system has only one
neuron between the central nervous system and the target
organ while the autonomic nervous system uses two neurons.
The enteric nervous system is a third division of the
autonomic nervous system that you do not hear much about.
The enteric nervous system is a meshwork of nerve fibers that
innervate the viscera (gastrointestinal tract, pancreas, gall
bladder).
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Structural classification of the nervous system
In the Peripheral Nervous System,
neurons can be functionally divided in
3 ways:
1 Sensory (afferent) - carry information INTO the central nervous
system from sense organs.
OR
Motor (efferent) - carry information away from the central nervous
system (for muscle control).
2 Cranial - connects the brain with the periphery.
OR
Spinal - connects the spinal cord with the periphery.
3 Somatic - connects the skin or muscle with the central nervous
system.
OR
Visceral - connects the internal organs with the central nervous
system.
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Structural classification of the nervous system
Some differences between the
Peripheral Nervous System (PNS) and
the Central Nervous System (CNS):
In
the CNS, collections of neurons are
called nuclei.
In the PNS, collections of neurons are
called ganglia.
In
the CNS, collections of axons are
called tracts.
In the PNS, collections of axons are called
nerves
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Structural classification of the nervous system
The following table shows how the nervous system can be
divided. The bottom row of the table contains the names of
specific areas within the brain. Divisions of the Nervous
System
objectives
The Brain…
Although some people may
think that the brain is like a bowl of
jell-O, the brain is NOT a bowl of
jell-O. Unlike a bowl of jell-O, the
brain is not a uniform material.
Rather, the brain is made up of
many different areas, each having
a particular structure and function.
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The skull:
home of the brain
Your brain is protected
by several bones. There are
eight bones that surround
your brain: one frontal
bone; two parietal bones,
two temporal bones, one
occipital bone, one
sphenoid bone and one
ethmoid bone. These eight
bones make up the cranium.
Another 14 bones in the
face make up the entire
skull. There are also 3 small
bones in each ear. Also
protecting your brain are 3
layers of tissue called the
meninges. A few of the
bones have been colored in
the diagram to the right.
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The skull: home of the brain
There is a large opening, called the foramen
magnum, located in the back of the occipital bone. This
is where the medulla ends and projects out of the skull.
Smaller holes in the skull, called foramina, allow
nerves and blood vessels to enter and leave the
cranium. The picture in the bottom shows the base of
the skull. The places in the skull where the bones
come together are called sutures. These sutures are
flexible in young children, but become fixed as you
age.
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Divisions of the Brain
Divisions of the Brain
Major Division
Subdivision
Structures
Telencephalon
Neocortex; Basal Ganglia; Amygdala;
Hippocampus; Lateral Ventricles
Diencephalon
Thalamus; Hypothalamus;
Epithalamus; Third Ventricle
Mesencephalon
Tectum; Tegmentum; Cerebral
Aqueduct
Metencephalon
Cerebellum; Pons; Fourth Ventricle
Myelencephalon
Medulla Oblongata; Fourth Ventricle
Prosencephalon
(Forebrain)
Mesencephalon
(Midbrain)
Rhombencephalon
(Hindbrain)
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Division of the brain
Lobes of the brain
The average human brain weighs about 1,400 grams
(3 lb). When the brain is removed from the skull, it looks
a bit like a large pinkish-gray walnut. The brain can be
divided down the middle lengthwise into two halves
called the cerebral hemispheres. Each hemisphere of the
cerebral cortex is divided into four lobes by various sulci
and gyri...the sulci (or fissures) are the grooves and the
gyri are the "bumps" that can be seen on the surface of
the brain. The folding of the cerebral cortex produced by
these bumps and grooves increases the amount of
cerebral cortex that can fit in the skull. (In fact, the total
surface area of the cerebral cortex is about 324 square
inches - about the size of a full page of newspaper!).
Although most people have the same patterns of gyri
and sulci on the cerebral cortex, no two brains are
exactly alike.
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Division of the brain
Lobes of the brain
FRONTAL LOBE
 Located in front of the central
sulcus.
 Concerned with reasoning,
planning, parts of speech and
movement (motor cortex),
emotions, and problem-solving.
PARIETAL LOBE
 Located behind the central
sulcus.
 Concerned with perception of
stimuli related to touch, pressure,
temperature and pain.
TEMPORAL LOBE
 Located below the lateral fissure.
 Concerned with perception and
recognition of auditory stimuli
(hearing) and memory
(hippocampus).
OCCIPITAL LOBE
 Located at the back of the brain,
behind the parietal lobe and
temporal lobe.
 Concerned with many aspects of
vision.
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Division of the brain
A top view of the brain
From a top view, notice how the brain is divided into two
halves, called hemispheres. Each hemisphere communicates
with the other through the corpus callosum, a bundle of nerve
fibers. (Another smaller fiber bundle that connects the two
hemispheres is called the anterior commissure).
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Brain structures
Click on one of the question marks beside each
structure to view its characteristics…
hypothalamus
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Brain stem
Brain structures
Cerebral Cortex
Functions:
 Thought
 Voluntary
movement
 Language
 Reasoning
 Perception
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The word "cortex" comes from the
Latin word for "bark" (of a tree). This is
because the cortex is a sheet of tissue
that makes up the outer layer of the
brain. The thickness of the cerebral
cortex varies from 2 to 6 mm. The
right and left sides of the cerebral
cortex are connected by a thick band of
nerve fibers called the "corpus
callosum." In higher mammals such as
humans, the cerebral cortex looks like
it has many bumps and grooves. A
bump or bulge on the cortex is called a
gyrus (the plural of the word gyrus is
"gyri") and a groove is called a sulcus
(the plural of the word sulcus is "sulci").
Lower mammals, such as rats and
mice, have very few gyri and sulci.
Brain structures
Cerebellum
Functions:
 Movement
 Balance
 Posture
Return to structures
The word "cerebellum"
comes from the Latin
word for "little brain." The
cerebellum is located
behind the brain stem. In
some ways, the
cerebellum is similar to
the cerebral cortex: the
cerebellum is divided into
hemispheres and has a
cortex that surrounds
these hemispheres.
Brain structures
Brain stem
Functions:
 Breathing
 Heart Rate
 Blood Pressure
Return to structures
The brain stem is a general
term for the area of the brain
between the thalamus and
spinal cord. Structures within
the brain stem include the
medulla, pons, tectum,
reticular formation and
tegmentum. Some of these
areas are responsible for the
most basic functions of life
such as breathing, heart rate
and blood pressure.
Brain structures
Hypothalamus
Functions:
 Body
Temperature
 Emotions
 Hunger
 Thirst
 Circadian
Rhythms
The hypothalamus is composed of
several different areas and is located
at the base of the brain. Although it
is the size of only a pea (about 1/300
of the total brain weight), the
hypothalamus is responsible for
some very important functions. One
important function of the
hypothalamus is the control of body
temperature. The hypothalamus
acts as a "thermostat" by sensing
changes in body temperature and
then sending signals to adjust the
temperature. For example, if you
are too hot, the hypothalamus
detects this and then sends a signal
to expand the capillaries in your
skin. This causes blood to be
cooled faster. The hypothalamus
also controls the pituitary.
Brain structures
Thalamus
Functions:
 Sensory
processing
 Movement
The thalamus receives
sensory information
and relays this
information to the
cerebral cortex. The
cerebral cortex also
sends information to
the thalamus which
then transmits this
information to other
areas of the brain and
spinal cord.
Brain structures
Midbrain
Functions:
 Vision
 Audition
 Eye Movement
 Body Movement
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The midbrain
includes structures
such as the superior
and inferior colliculi
and red nucleus.
There are several
other areas also in
the midbrain.
Brain structures
Pons
Functions:
 Cardiovascular
and respiratory
control center.
The pons are
continuous with the
medulla
Brain structures
Medulla
Functions:
 Heart rate
 Breathing.
 Blood pressure.
 Swallowing and
vomiting
Return to structures
She brain – He brain
Bigger - Stronger - Faster...are there really any
differences between female brains and male brains?
Differences between the brains of men and women
have generated considerable scientific and public
interest. If there are differences in the way that men
and women behave, then it is reasonable to suppose
that their brains have something to do these behavioral
differences. Just what are these differences and where
in the brain might these differences be located?
For hundreds of years, scientists have searched for
differences between the brains of men and women.
Early research showing that male brains were larger
than female brains was used to "prove" that male
brains were superior to female brains. Of course, this
"proof" is NOT so simple and straight forward as you
will see. Nevertheless, even today, there is plenty of
controversy about the differences in the brains of men
and women. Not only from an anatomical point of view,
but also from a functional point of view - in other words,
just what do the differences in the brains mean?
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She brain – He brain
Hormones that are present during a baby's
development will affect the brain and determine
whether the brain will be female or male. Studies that
have looked at differences in the brains of males and
females have focused on:
Total Brain Size
The Corpus Callosum
The Hypothalamus
Women and Men - Boys and Girls
The behavioral and neurological differences between
men and women require further study. Perhaps new
studies will find neuroanatomical differences that
explain some of the complex differences between male
and female behavior. However, from a review of the
current scientific evidence, it appears that differences
in many cognitive behaviors (for example, memory) are
related more to individual differences between people
than to whether people are female or male.
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How the nervous system interacts
with other body systems.
Objectives:
 skeletal system
 cardiovascular system
 muscular system
 endocrine system
 lymphatic system
 respiratory system
 digestive system
 reproductive system
 urinary system
How the nervous system interacts
with other body systems.
All of the systems within the
body interact with one another to
keep an organism healthy. Although
each system has specific functions,
they are all interconnected and
dependent on one another. The
nervous system controls various
organs of the body directly. The
brain also receives information from
many organs of the body and
adjusts signals to these organs to
maintain proper functioning.
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