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Lecture: 1
Introduction and Organization of the
Nervous System,
Anatomy of the Spinal Cord
Dr. Eyad M. Hussein
Ph.D of Neurology
Consultant in Neurology Department,
Nasser Hospital,
Assistant Professor,
Faculty of Medicine, Islamic University
Faculty of Dentistry, University of Palestine
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‫مع الشكر‬
Nerves System Terminology
1. Neurone: is a nerve cell and its processes.
2. Nucleus: is a group of nerve cells located in the CNS.
3. Ganglia: is a group of nerve cells located out the CNS.
4. Nerve fiber: is an axon or dendrite.
5. Nerve: is a bundle of nerve fibers in the PNS.
6. Tract: is a group of nerve fibers in the CNS which have the
same origin, termination and function. The tract may be
ascending (sensory or afferent) or descending (motor or
efferent).
7. Bundle: is a group of nerve fibers which have different origin ,
termination or function.
8. Fasciculus: is a small bundle.
9. Peduncles: are large nerve tracts that emerge from certain region
of the brain.
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10. Commissure: is a group of nerve fibers which connect right
and left parts of the brain.
11. Association fibers: are nerve fibers which connect parts of
the nervous system on the same side.
12. Synapse: is the site of contact (without continuity) of the
axon of one neurone with the dendrites or cell body another
neurone.
13. White matter: consists of nerve fibers (myelinated axons of
neurons in the CNS) supported by neuroglia.
14. Gray matter: consists of nerve cells and the proximal part
of their processes (unmyelinated portion of neurons in the
CNS) supported by neuroglia.
15. Ventricles: are interconnected cavities in the brain.
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Introduction of the Nervous System
 The nervous system (NS) is one of the two main control
system in the body. The other system is endocrine system.
 The NS is the system of communication, the aim of
communication is to keep body homeostasis.
 The NS differs from endocrine system in that controls the
rapid activities of the body (e.g. muscle contraction).
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Functions of the Central Nervous System
1. Sensory function: perception of the various
sensation.
2. Motor function: production and control of
muscular activity.
3. Integrative function: this is processing “analysis”
of the information and intellectual function
“learning, memory, thinking, behavior, emotion,
and speech”.
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Organization of the Nervous System
A. Central nervous system (CNS):
a. Brain (intracranial part).
b. Spinal cord (extracranial part).
B. Peripheral nervous system (PNS):
1. Somatic (cranio-spinal) NS:
a. Cranial nerves: 12 pairs
attached to the brain.
b. Spinal nerves: 31 attached to
the spinal cord.
2. Autonomic NS:
a. Sympathetic NS.
b. Parasympathetic NS.
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Organization of the NS According the Function
1. Afferent Division:
a. Somatic sensation.
b. Special senses.
2. Efferent Division:
a. Somatic NS: motor neurons.
b. Autonomic NS: sympathetic and parasympathetic NS.
The somatic nervous system supplies the skeletal muscles,
while the autonomic nervous system supplies the glands,
smooth and cardiac muscles.
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The Development of the NS
The Entoderm: gives rise to the gastrointestinal
tract, the lung, and the liver.
The Mesoderm: gives rise to the muscles,
connective tissue, and the vascular system.
The Ectoderm: gives rise to the nervous system.
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The Development of the NS
The Ectoderm: in the first four weeks after conception
the nerve tissue called Neural plate that can be seen at
about the 16th day of development → Neural groove →
Neural tube by the 21st day of development.
 Neural tube differentiates into the:
Forebrain
Midbrain
Hindbrain
Spinal cord
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Brain Development
Primary Brain Vesicles: three cavities form during the
early embryonic development of the brain at the end of fourth
week. These are forebrain, midbrain and hindbrain vesicles
By the 7th week of development, the three primary vesicles
develop into primary divisions an secondary divisions
(subdivision) this process is called encephalization and finally
give adult structures (8-28 weeks)
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The Development of the Brain
Primary Vesicle
Forebrain vesicle
Midbrain vesicle
Primary Division
Prosencephalon
(forebrain)
Mesencephalon
(midbrain)
Subdivision
Adult Structures
Telencephalon
-Cerebral
hemisphere,
basal nuclei.
Diencephalon
-Thalamus,
hypothalamus,
epithalamus,
pituitary gland,
mammillary bodies
Mesencephalon
-Midbrain
Metencephalon
-Pons, cerebellum
Hindbrain vesicle Rhombencephalon
(hindbrain)
Myelencephalon -Medulla blongata
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Prenatal brain development video
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The Nervous Tissue
The CNS (Brain) consists of:
1. Gray Matter (outer): consists of nerve cells and
the proximal part of their processes supported by
specialised tissue called Neuroglia.
2. White Matter (inner): consists of nerve fibers
supported by neuroglia.
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The Nervous Tissue
The nervous tissue is made up of two types of cells:
1. Neuron: also called nerve cells, which generate
action potentials and transmit nerve impulses to
another neuron.
2. Neuroglia: they act as supportive and
nourishment cells, which do not generate action
potentials.
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Structure of the Nerve Cell
Neurone: is the name give to the nerve cell and all its
process. The neuron is responsible for sending and
receiving impulses or signals.
Each nerve cell consist of:
1. Cell body (Soma): which contains the nucleus and
the other organelles necessary for cellular function.
2. Several short processes called dendrites: are the
region where one neuron receives connections from
other neurons
3. One long process called axon: which information
is transmitted from one part of the neuron (e.g., the
cell body) to the terminal regions of the neuron
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Structure of the Nerve Cell Body
1. Nucleus.
2. Cytoplasm: it is formed of
the following structures:
• Nissl substance
• The Golgi complex
• Mitochondria
• Microfilaments
• Microtubules
• Lysosomes
• Centrioles
•Lipofuscin, Melanin,
lipid, and glycogen.
3. Plasma membrane.
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The Nerve Fibers
Definition: it is an axon or a dendrite of a nerve cell.
Structures of the Nerve Fiber:
1. Schwann cell.
2. Node of Ranvier.
3. Myelin sheath.
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Classification of the Neurons
Morphological
Structure
Location
Classification
One short process that
1. Unipolar
immediately divides into Posterior root ganglion
two very long process
2. Bipolar
Single axon and a single
Retina, sensory cochlea,
dendrite
and vestibular ganglia
Fibers tracts of brain and
3. Multipolar
Many dendrites and one
spinal cord, peripheral
long axon
nerves, and motor cells of
the spinal cord
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Bipolar Neuron
Unipolar Neuron
Multipolar Neuron
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Comparison of Variations in the Structure of Neurons
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Neuroglial Cells
The most numerous cellular constituents of the CNS are
the non-neuronal ”Neuroglial cells” that occupy the
space between neurons.
The functions of neuroglial cells:
• Support
• Protect against microorganisms
• Nutrition
• Maintain homeostasis, blood-brain barrier function
• Formation of myelin
• Production of CSF
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Types of Neuroglial Cells
Neuroglia are divided into two major categories based on size:
I.
Macrogliacells: are of ectodermal origin and consist of:
- Astrocytes (Astroglia).
- Oligodendrocytes.
- Ependymal cells.
II. Microglia cells: cells are probably of mesodermal origin.
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Types of Neuroglial Cells
1. Astrocytes (Astroglia): are found in the brain’s capillaries
and form the blood-brain barrier that restricts what
substances can enter the brain.
2. Oligodendrocytes: are CNS structures that play important
role in formulation of myelin sheath. Oligodendrocytes and
Schwann cells indirectly assist in the conduction of
impulses.
3. Microglial cells: are extremely small cells of the CNS that
remove cellular waste and protect against microorganisms.
4. Ependymal cells: are found in choroidal plexuses of
ventricular system, the main function is production of CSF.
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The Spinal Cord
The spinal cord (SC) is an
extracranial part of the central
nervous system enclosed inside
the vertebral column
Anatomy of the Spinal Cord (SC)
Shape: compressed cylindrical column.
Number of neurons in human SC: about 13,500,000
Length of human SC: about 45 cm (male); 43 cm
(female).
Weight of human SC: about 35g.
Diameter: about 1 cm.
Location: It is located in the spinal (vertebral) canal.
Beginning: the SC is continuation of the medulla.
oblongata which begin from the foramen magnum
downward.
Termination of the Spinal Cord
At the third month of
intrauterine life: the SC fills the
whole spinal canal.
At birth: it ends at the level of
L3 vertebra.
In the adult: it ends at the level
of lower border of the first
lumbar vertebra.
Termination of the Spinal Cord According to Age
3rd month of intrauterine life
At Birth
Function of the Spinal Cord
1. Conduction function: from and to the brain:
a. Ascending tracts: conduct sensory impulses
from the SC to the brain.
b. Descending tracts: conduct motor impulses
from the brain to SC.
2. Reflexes center: the gray matter of the SC is the
integrative area for all spinal reflexes.
Meninges of the Spinal Cord
The spinal cord is covered by 3 membranes (meninges),
from inside to outside they are:
1. Pia Matter.
2. Arachnoid Matter.
3. Dura matter.
Meninges of the Spinal Cord
 Dura matter: ends at the level of the second sacral
vertebra.
 Arachnoid: ends at the level of the second sacral
vertebra.
 Pia matter: ends at the level of SC termination
(lower border of the first lumbar vertebra in adult).
Meningeal Spaces of Spinal Cord
1. Epidural Space: it is located between the dura matter
and vertebral periosteum. It contains semiliquid fat.
2. Subdural Space: it is located between the dura matter
and arachnoid matter. Contains thin film of serous
fluid.
3. Subarachnoid Space: it is located between the
arachnoid and pia matter. Is a wide space contains:
• CSF.
• Spinal blood vessels.
• Roots of spinal nerves.
External Structure of the Spinal Cord
 Anterior median fissure
 Anterior lateral sulci
(Rt. & Lt.).
 Posterior median sulcus.
 Posterior lateral sulci
(Rt. & Lt.).
The Spinal Cord Segments
There are 31 segments:
8 – Cervical segments.
12 – Thoracic (dorsal).
5 – Lumbar segments.
5 – Sacral segments.
1 – Coccygeal segments.
Epiconus: it is the L4, 5 and S1, 2
segments of the SC.
Conus medularis: the lower end
of the SC. It is the S3, 4, 5
segments of the SC.
Cauda equina:
It is located below the lower border
of the first lumbar vertebra, the
spinal canal is filled by the
collection of lumbo-sacral roots
which descends in this space to their
corresponding intervertebral canal.
Relationship between the Spinal Cord
Segment and the Vertebra
№
Spinal Cord
Vertebra
1
From C1 - C4 segments
Opposite C1 - C4
2
From C5 - C8 segments
Subtract 1
3
From T1 - T6 segments
Subtract 2
4
From T7 - L2 segments
Subtract 3
5
L3 - L4 segments
Opposite T12
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L5 and all sacral segments
Opposite L1
The Roots of the Spinal Cord
Each segment has four roots : two posterior & two anterior.
1. Two posterior (dorsal) roots: there are sensory fibers
(afferent fibers). Each dorsal root has spinal or dorsal root
ganglion.
2. Two anterior (ventral) roots: there are motor and autonomic
fibers (efferent fibers).
 The anterior and posterior roots will join to form a single
mixed nerve called the spinal nerve → 31 pairs of spinal
nerves (right and left).
 Each spinal nerve emerges from the intervertebral foramen.
Exit of Spinal Nerve Roots
 Through
 C1
pass horizontally above C1 vertebra.
 Roots
 C8
the inter vertebral foramina.
C2- C7 above their vertebra.
pass below C7 vertebra.
 Thoracic
lumbar and sacral nerves pass below
corresponding vertebra.
 Lower
lumbar , sacral and ccocygeal nerves descend
vertically as cauda equina pass below corresponding
vertebra.
Enlargement of the Spinal Cord
1. Cervical enlargement.
2. Lumbar enlargement.
Cervical Enlargement of the Spinal Cord
It is the C5, 6, 7, 8 and D1 segments
of the SC, corresponding to the
region from which the brachial
plexus arises → give spinal nerves
that supply the upper limbs.
Lumbar Enlargement of the Spinal Cord
It is the L1, 2, 3, 4, 5 and
S1, 2 segments of the SC
(extends from T9-T12),
corresponding to the region
from which the lumbar and
sacral plexuses arises →
give spinal nerves that
supply the lower limbs.
Internal Structure of the Spinal Cord
A transverse section in the
SC is formed of:
• White matter (outer).
• Gray matter (inner).
• Central canal (1 mm in
diameter): is present in
gray matter.
The Gray Matter of the Spinal Cord
Structure: it consist of nerve cells.
Shape: the grey matter resembles the letter “H” and
formed of:
1. Anterior horns (right and left: Consist of motor
cells.
2. Posterior horns (right and left): Consist of
sensory cells.
3. Lateral horns (right and left): In the thoracicand
upper two lumbar segments. They contain
sympathetic nerve cells.
4. Central canal: The central canal contains C.S.F.
5. Gray commissure: anterior and posterior gray
commissure.
The White Matter of the Spinal Cord
• The white matter surround the gray matter and contains
ascending and descending tracts.
• It is divided into three column (fasciculus) of SC on each
side:
a. Anterior column (AC): lying between the anterior
median fissure & the attachment of anterior spinal root.
b. Lateral column (LC): lying between attachment of
anterior and posterior spinal roots.
c. Posterior column (PC): lying between the posterior
median fissure & the attachment of dorsal spinal root.
Structure of White Mater
The white mater contains 3 types of nerve fibers (tract):
1. Ascending tracts of the SC:
Carrying sensory impulses from the SC to the brain:
e.g. lateral spinothalamic tract.
2. Descending tracts of the SC:
Carrying motor impulses from the brain to the SC:
e.g. pyramidal tract “corticospinal tract”.
3. Associative tracts:
Containing short ascending & descending fibers
which coordinate the function of the different
regions of spinal cord.
Classification of the Tracts
The tracts are divided into:
1. Short Tracts:
- They begins and end in the spinal cord.
- They are found close to the gray matter.
- They are associative in function.
2. Long Tracts:
- Ascending tracts.
- Descending tracts.
Blood Supply of the Spinal Cord
1. Anterior (ventral) spinal
artery: supplies anterior and lateral
columns and anterior horn cell. Is the
longest artery in the body.
2. Posterior spinal arteries (right
and left): supply posterior horns and
posterior columns
3. Radicular arteries:
a. Cervical radicular arteries.
b. Thoracic radicular arteries.
c. Lumbar radicular arteries.
d. Great radicular artery of
Adamkiewicz.
e. Ascending sacral arteries.