Anatomy

Lectures on Neuroanatomy

المدرس الدكتورليث ثامر خزعلأختصاصي جراحة الجملة العصبيةكلية طب الكندي – فرع التشريحDr Laith ThamerMBChB 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


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


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 H-shaped 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


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


- 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
Ascending Tracts


The information (of the ascending pathway) may be divided into two main groups: exteroceptive information, which originates from outside the body, such as pain, temperature, and touch. proprioceptive information, which originates from inside the body, for example, from muscles and joints.


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

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 SensePosterior White Column: Fasciculus Gracilis and Fasciculus CuneatusThey are separated by a septumAscending ipsilateraly and 2nd order n. terminate and synapse at gracilis and cunatus nucleiDecussation 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 CerebellumPosterior 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 sideThe 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

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

1- Complete cord transection 2- ant. cord syndrom 3- central cord syndrom 4- Brown squard syndrom