Download الدكتور ليث ثامر خزعل أخصائي جراحة الجملة العصبية

Lectures on
Neuroanatomy
‫المدرس الدكتور‬
‫ليث ثامر خزعل‬
‫أختصاصي جراحة الجملة العصبية‬
‫كلية طب الكندي – فرع التشريح‬
Dr Laith Thamer
MBChB FIBMS (Neurosurgery)
Ref,
Clinical Neuroanatomy by Snell 7th ed.
Lec 1
-Introduction to Nervous System
-The Skull and vertebrae
- Spinal cord
Introduction to Nervous System:
Nervous System
Central NS
Peripheral NS
Brain Spinal Cord Spinal ns
Cranial ns
Brain:
Forebrain: telencephalon (cerebrum) and Diencephalon
(Thalamus and hypothalamus)
Midbrain Hindbrain: Cerebellum, pons and medulla oblongata -
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SKULL
Composition
The skull is composed of several separate bones united at
immobile joints called sutures. The connective tissue
between the bones is called a sutural ligament. The
mandible is an exception to this rule, for it is united to
the skull by the mobile temporomandibular joint.
The bones of the skull can be divided into those of the
cranium and those of the face. The vault is the upper
part of the cranium, and the base of the skull is the
lowest part of the cranium
The skull bones are made up of external and internal
tables of compact bone separated by a layer of spongy
bone called the diploë The internal table is thinner and
more brittle than the external table. The bones are
covered on the outer and inner surfaces with
periosteum.
The cranium consists of the following bones, two
of which are paired
• Frontal bone 1
• Parietal bones 2
• Occipital bone 1
• Temporal bones 2
• Sphenoid bone 1
• Ethmoid bone 1
The facial bones consist of the following, two of
which are single:
• Zygomatic bones 2
• Maxillae 2
• Nasal bones 2
• Lacrimal bones 2
• Vomer 1
• Palatine bones 2
• Inferior conchae 2
• Mandible 1
The Cranial Cavity
contains the brain and its surrounding meninges,
portions of the cranial nerves, arteries, veins, and
venous sinuses.
Base of the Skull
is divided into three cranial fossae: anterior, middle,
and posterior.
anterior cranial fossa is separated from the middle
cranial fossa by the lesser wing of the sphenoid,
and the middle cranial fossa is separated from the
posterior cranial fossa by the petrous part of the
temporal bone.
Anterior Cranial Fossa
lodges the frontal lobes of the cerebral hemispheres
bounded anteriorly by the inner surface of the frontal bone, and in the
midline is a crest for the attachment of the falx cerebri. Its posterior
boundary is the sharp lesser wing of the sphenoid
Middle Cranial Fossa
consists of a small median part and expanded lateral parts
The median raised part is formed by the body of the sphenoid, and the
expanded lateral parts form concavities on either side, which lodge
the temporal lobes of the cerebral hemispheres
It is bounded anteriorly by the sharp posterior edges of the lesser wings
of the sphenoid and posteriorly by the superior borders of the petrous
parts of the temporal bones. Laterally lie the squamous parts of the
temporal bones, the greater wings of the sphenoid, and the parietal
bones.
The floor of each lateral part of the middle cranial fossa is formed by the
greater wing of the sphenoid and the squamous and petrous parts of
the temporal bone.
Posterior Cranial Fossa
The posterior cranial fossa is deep and lodges the
parts of the hindbrain, namely, the cerebellum,
pons, and medulla oblongata. Anteriorly, the fossa
is bounded by the superior border of the petrous
part of the temporal bone; posteriorly, it is
bounded by the internal surface of the squamous
part of the occipital bone.
The floor of the posterior fossa is formed by the
basilar, condylar, and squamous parts of the
occipital bone and the mastoid part of the
temporal bone.
Mandible
The mandible, or lower jaw, is the largest and
strongest bone of the face, and it articulates
with the skull at the temporamandibular joint
The mandible consists of a horseshoe-shaped
body and a pair of rami. The body of the
mandible meets the ramus on each side at the
angle of the mandible.
Bones of the Skull
Summary of the More Important Openings in the Base of the
Skull and the Structures That Pass Through Them
Neonatal Skull
compared with the adult skull, has a disproportionately large cranium relative
to the face. In childhood, the growth of the mandible, the maxillary sinuses,
and the alveolar processes of the maxillae results in a great increase in
length of the face.
there being no diploë present
Most of the skull bones are ossified at birth, but the process is incomplete, and
the bones are mobile on each other, being connected by fibrous tissue or
cartilage.
separated by unossified membranous intervals called fontanelles.
Clinically, the anterior and posterior fontanelles are most important and are
easily examined in the midline of the vault.
The anterior fontanelle is diamond shaped and lies between the two halves of
the frontal bone in front and the two parietal bones behind .The fibrous
membrane forming the floor of the anterior fontanelle is replaced by bone
and is closed by 18 months of age.
The posterior fontanelle is triangular and lies between the two parietal bones in
front and the occipital bone behind. By the end of the first year, the
fontanelle is usually closed and can no longer be palpated.
The vertebral column is the central bony pillar of
the body.
It supports the skull, pectoral girdle, upper
limbs, and thoracic cage and, by way of the
pelvic girdle, transmits body weight to the lower
limbs. Within its cavity lie the spinal cord, the
roots of the spinal nerves, and the covering
meninges, to which the vertebral column gives
great protection.
Composition of vertebral body
Composed of 33 vertebrae, 7
cervical, 12 thoracic, 5
lumbar, 5 sacrasl (fused to
form the sacrum) and 4
coccygeal (the lower 3 are
commonly fused)
Intervertebral discs pads of
fibrocartilage between each
two adjacent vertebrae.
A typical vertebra composed of:
Body anteriorly and vertibral arch posteriorly
Vertebral arch composed of:
Pedicles, lamenae and seven processes - spinous process - articular process 2 sup and 2 inf - two transverse processes - sup. and inf. vertebral notch both form the intervertebral
Foramen -
Joints:
- Intervertebral disc between two bodies - Articular Joints between two vertebral arches
-
-
the atlas (C1) is the most superior (first) cervical vertebra of
the spine.
along with the Axis (C2) – forms the joint connecting the skull
and spine (the atlanto-occopital joint). The atlas and axis
are specialized to allow a greater range of motion than
normal vertebrae. They are responsible for the nodding and
rotation movements of the head.
second cervical vertebra (C2) of the spine is
named the axis
the most distinctive characteristic of this bone
is the strong odontoid process ("dens")
Spinous processes of C2
to C6 are bifid while
that of C7 are not
C7 also called vertebra
prominence (due to
palpable spinous
prosess
Vertebral artery pass
through formaina in
transverse prosesses
of C2 to C6
Intervertebral Discs
The intervertebral discs are thickest in the cervical
and lumbar regions, where the movements of the
vertebral column are greatest. They serve as
shock absorbers when the load on the
vertebral column is suddenly increased.
Unfortunately, their resilience is gradually lost
with advancing age.
Each disc consists of a peripheral part, the anulus
fibrosus, and a central part, the nucleus pulposus
The anulus fibrosus is composed of fibrocartilage,
which is strongly attached to the vertebral bodies and
the anterior and posterior longitudinal ligaments of
the vertebral column.
The nucleus pulposus in the young is an ovoid mass
of gelatinous material. It is normally under pressure
and situated slightly nearer to the posterior than to
the anterior margin of the disc. The upper and lower
surfaces of the bodies of adjacent vertebrae that abut
onto the disc are covered with thin plates of hyaline
cartilage.
With advancing age, the nucleus pulposus becomes smaller
and is replaced by fibrocartilage. The collagen fibers of the
anulus degenerate
Ligaments
The anterior and posterior longitudinal ligaments run as
continuous bands down the anterior and posterior
surfaces of the vertebral column from the skull to the
sacrum
The anterior ligament is wide and is strongly attached to the
front and sides of the vertebral bodies and to the
intervertebral discs.
The posterior ligament is weak and narrow and is attached to
the posterior borders of the discs
Other ligaments
Supraspinous ligament: This runs between the tips of
adjacent spines.
Interspinous ligament: This connects adjacent spines.
Intertransverse ligaments: These run between adjacent
transverse processes.
Ligamentum flavum: This connects the laminae of adjacent
vertebrae.
Ligamentum nuchae : the supraspinous and interspinous
ligaments are greatly thickened to form the strong
ligamentum nuchae
Nerve Supply of joints
The joints between the vertebral bodies are
innervated by the small meningeal branches of
each spinal nerve
The joints between the articular processes are
innervated by branches from the posterior rami
of the spinal nerves
the joints of any particular level receive nerve
fibers from two adjacent spinal nerves.
SPINAL CORD
Gross appearance
The spinal cord is roughly cylindrical in shape. It begins
superiorly at the foramen magnum in the skull, where it is
continuous with the medulla oblongata of the brain, and it
terminates inferiorly in the adult at the level of the lower
border of the first lumbar vertebra.
In the young child, it is relatively longer and usually ends at
the upper border of the third lumbar vertebra. Thus, it
occupies the upper two-thirds of the vertebral canal of the
vertebral column and is surrounded by the three
meninges, the dura mater, the arachnoid mater, and the
pia mater. Further protection is provided by the
cerebrospinal fluid, which surrounds the spinal cord in the
subarachnoid space
In the cervical region, where it gives origin to the brachial
plexus, and in the lower thoracic and lumbar regions,
where it gives origin to the lumbosacral plexus, the
spinal cord is fusiformly enlarged; the enlargements are
referred to as the cervical and lumbar enlargements
Inferiorly, the spinal cord tapers off into the conus
medullaris, from the apex of which a prolongation of the
pia mater, the filum terminale, descends to be attached
to the posterior surface of the coccyx.
The cord possesses a deep longitudinal fissure called the
anterior median fissure in the midline anteriorly and a
shallow furrow called the posterior median sulcus on the
posterior surface
31 pairs of spinal nerves
anterior or motor root and the posterior or
sensory root unite to form each spinal nerve
Each root is attached to the cord by a series of
rootlets
Each posterior nerve root possesses a posterior
root ganglion
Sturcture of Spinal cord
The spinal cord is composed of an inner core of gray
matter, which is surrounded by an outer covering of
white matter
Gray Matter
On cross section, the gray matter is seen as an Hshaped pillar with anterior and posterior gray columns,
or horns, united by a thin gray commissure containing
the small central canal
A small lateral gray column or horn is present in the
thoracic and upper lumbar segments of the cord. The
amount of gray matter present at any given level of the
spinal cord is related to the amount of muscle
White matter
The white matter, may be divided into anterior,
lateral, and posterior white columns or funiculi
Blood supply of spinal cord
- Arteries of the spinal cord
Posterior spinal arteries
Anterior spinal artery
Segmental spinal arteries
Feeder arteries (great anterior medullary artery of
adamkiewicz)
- Veins of the spinal cord Six tortuous longitudinal channels communicate superiorly within the skull with the veins of the brain
and venous sinuses
Meninges of the spinal cord
1- Dura Mater
Dense strong fibrous membrane that encloses
the spinal cord and cauda equina
2- Arachnoid mater
Delicate impermeable membrane separated from
the pia mater by subarachnoid space the
contain the Cerebrospinal fluid
3- Pia mater
A vascular membrane closely cover the spinal
cord
TRACTS OF SPINAL CORD
The white matter of the spinal cord consist of a mixture
of Nerve fibers and are arranged in tracts and for
purpose of description, spinal tracts are divided into:
- Ascending tracts - Descending tracts - Intersegmental tracts Considerable overlap between tracts are present
-
Transverse section of the spinal cord at the midcervical level
showing the general arrangement of the ascending tracts on
the right and the descending tracts on the left
Ascending Tracts
- On entering the spinal cord, the sensory nerve fibers of
different sizes and functions are sorted out and
segregated into nerve bundles or tracts in the white
matter
Some of the nerve fibers serve to link different segments of the spinal cord, while others ascend from
the spinal cord to higher centers and thus connect the
spinal cord with the brain
The information (of the ascending pathway) may
be divided into two main groups:
(1)
exteroceptive information, which originates
from outside the body, such as pain,
temperature, and touch.
(2)
proprioceptive information, which originates
from inside the body, for example, from
muscles and joints.
ANATOMICAL
ORGANIZATION
first-order neuron
second-order neuron
third-order neuron
- This three-neuron chain is the most
common arrangement, but some
afferent pathways use more or fewer
neurons
-
- Many of the neurons in the ascending pathways branch and give
a major input into the reticular
formation, which, in turn, activates
the cerebral cortex, maintaining
wakefulness. Other branches pass to
motor neurons and participate in
reflex muscular activity
-
Pain and Temperature Pathways
- Lateral spinothalamic tract. (contribute to posterolateral tract of Lissauer) Axons of 2nd order n. cross obliquely to the opposite
side within one spinal segment, 2nd order neuron
located at substania gelatinosa, at higher level at
medulla oblongata it accompanied with ant.
spinothalamic and spinotectal tracts to form the
Spinal lemniscus that ascending through the
posterior part of Pons then end of this neuron at
thalamus, 3rd order neuron then pass through post.
limb of internal capsule and the corona radiata to
reach the somesthetic area of precentral gyrus of
cerebral cortex
Types of pain, - fast pain and slow pain -
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Light (Crude) Touch and Pressure Pathways
Anterior Spinothalamic Tract
-
-
The axons enter the spinal cord from the posterior root ganglion
divide into ascending and descending branches travel for a distance of one or two segments of the spinal cord,
The axons of the second-order neuron cross very obliquely to
the opposite side in the anterior gray and white commissures
within several spinal segments and ascend in the opposite
anterolateral white column as the anterior spinothalamic
tract
contributing to the posterolateral tract of Lissauer form part of spinal lemniscus -
-
Transverse section of the spinal cord at the midcervical level
showing the general arrangement of the ascending tracts on
the right and the descending tracts on the left
Discriminative Touch, Vibratory Sense, and Conscious Muscle Joint
Sense
Posterior White Column: Fasciculus Gracilis and Fasciculus Cuneatus
They are separated by a septum
Ascending ipsilateraly and 2nd order n. terminate and synapse at gracilis
and cunatus nuclei
Decussation occur as sensory decussation to form medial lemniscus at
level of medulla oblongata pass to thalamus and 3rd order n. to
somesthetic area of precentral gyrus of cerebral cortex
Muscle Joint Sense Pathways to the Cerebellum
Posterior Spinocerebellar Tract (2nd order n – nucleus dorsalis (Clarke's
column)
Anterior Spinocerebellar Tract (nucleus dorsalis)
Cuneocerebellar Tract originate in the nucleus cuneatus and enter the
cerebellum through the inferior cerebellar peduncle of the same side
The fibers are known as the posterior external arcuate fibers, and their
function is to convey information of muscle joint sense to the
cerebellum
Other Ascending Pathways
Spinotectal Tract (afferent information for spinovisual
reflexes and brings about movements of the eyes and
head toward the source of the stimulation)
Spinoreticular Tract (The spinoreticular tract provides an
afferent pathway for the reticular formation, which
plays an important role in influencing levels of
consciousness)
Spino-olivary Tract (conveys information to the
cerebellum from cutaneous and proprioceptive )
Visceral Sensory Tracts
Corticospinal tracts
- Fibers of the corticospinal tract arise as axons of pyramidal
cells situated in the fifth layer of the cerebral cortex
- Pass within Corona radiata
- then pass within internal capsule (the fibers are organized so that those closest to the genu are concerned
with cervical portions of the body, while those situated
more posteriorly are concerned with the lower extremity)
- basis pedunculi of the midbrain - in pons, the tract is broken into many bundles by the transverse pontocerebellar fibers
- In the medulla oblongata, the bundles become grouped together along the anterior border to form
a swelling known as the pyramid (pyramidal tract)
At the junction of the medulla oblongata and the spinal cord, most of the fibers cross the midline at
the decussation of the pyramids and enter the
lateral white column
- lateral corticospinal tract - anterior corticospinal tract -
Reticulospinal Tracts
From a collection of nerves at the midbrain, pons, and
medulla oblongata called the reticular formation
- pontine reticulospinal tract - medullary reticulospinal tract Surve as a pathway by which the hypothalamus can control the sympathetic outflow and the sacral
parasympathetic outflow
Tectospinal Tract
Fibers of this tract arise from nerve cells in the superior colliculus of the
midbrain
These fibers are believed to be concerned with reflex postural
movements in response to visual stimuli
Rubrospinal Tract
the red nucleus is situated in the tegmentum of the midbrain at the
level of the superior colliculus
tract facilitates the activity of the flexor muscles and inhibits the activity
of the extensor or antigravity muscles
Vestibulospinal Tract
The vestibular nuclei are situated in the pons and medulla oblongata
beneath the floor of the fourth ventricle
this tract, facilitate the activity of the extensor muscles and inhibit the
activity of the flexor muscles in association with the maintenance of
balance
Olivospinal Tract
Descending Autonomic Fibers
The higher centers of the central nervous system associated
with the control of autonomic activity are situated in the
cerebral cortex, hypothalamus, amygdaloid complex, and
reticular formation
Intersegmental Tracts
Short ascending and descending tracts that originate and end
within the spinal cord exist in the anterior, lateral, and
posterior white columns. The function of these pathways is to
interconnect the neurons of different segmental levels, and
the pathways are particularly important in intersegmental
spinal reflexes
REFLEX ARC
A reflex may be defined as an involuntary
response to a stimulus. It depends on the
integrity of the reflex arc. In its simplest form, a
reflex arc consists of the following anatomical
structures:
(1) a receptor organ,
(2) an afferent neuron,
(3) an effector neuron,
(4) an effector organ
SPINAL CORD
SYNDROM
1- Complete cord transection
2- ant. cord syndrom 3- central cord syndrom
4- Brown squard syndrom
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