Development of CNS & Spinal Cord PDF

Dr/ Azza Abo Shanady M.D Anatomy and Embryology Lecturer of Anatomy & Embryology Faculty of Medicine- Tanta university ❑ The nervous system is a complex network of nerves and cells that carry messages to and from the brain and spinal cord to various parts of the body. ❑ The functional...

Dr/ Azza Abo Shanady M.D Anatomy and Embryology Lecturer of Anatomy & Embryology Faculty of Medicine- Tanta university ❑ The nervous system is a complex network of nerves and cells that carry messages to and from the brain and spinal cord to various parts of the body. ❑ The functional and anatomical unit of the nervous system is called neurons. ❑ The neuron consists of a nerve cell body and its processes. One process is long and called “axon” while the others are short called dendrites. 1. Cell body : contains cellular organelles. 2. Dendrites: carry nerve impulse toward the cell body. 3. Axon: carry nerve impulse away from the cell body.  Synapse is the site at which the neurological impulses are transmitted. It represents the contact between the end of an axon of one neuron with the dendrites of another neuron. ❑ The interior of the CNS is organized into white and grey matter. 1. White matter: consists of nerve fibers. 2. Grey matter: consists of nerve cells. ❑ The nervous system is derived from the ectoderm (the outermost layer of the embryonic disc). ❑ In the third week of development, the notochord appears in the mesoderm. The notochord secretes growth factors which stimulate the differentiation of the overlying ectoderm forming a thickened structure known as the neural plate. ❑ The lateral edges of the neural plate then rise to form neural folds. The neural folds move towards each other and meet in the midline, fusing to form the neural tube (precursor to the brain and spinal cord). ❑ During fusion of the neural folds, some cells within the folds migrate to form neural crest cells. They give rise to melanocytes, craniofacial cartilage and bone, smooth muscle, peripheral and enteric neurons and glia. ❑ The formation of neural tube is known as neurulation, which is achieved by the end of the fourth week of development. ❑In the fifth week of development, swellings appear at the cranial end of the neural tube. Three primitive vesicles appear first, and subsequently these develop into five secondary vesicles. ❑These vesicles will give rise to all the structures of the brain and cerebellum. ❑The caudal end develops to form the spinal cord. 1.Reception of general sensory information (touch, pressure, temperature, pain, vibration) 2.Receiving special sensations (taste, smell, vision, sounds) 3.Integration of sensory information from different parts of the body and processing them 4.Response generation (motor function). Site: ❑Occupies the upper part of the vertebral canal. ❑Extend from the foramen magnum to the lower border of the first lumbar vertebra. ❑Continuous above with the medulla oblongata at the spino-medullary junction (defined by; foramen magnum, pyramidal decussation, and the ventral rootlets of the 1st cervical nerve). Shape: ❑ Cylindrical in shape. ❑ Has two enlargements; cervical (C2- T1) and lumbar (T9-T12). ❑ Enlargements are due to an increase in the number and size of neurons to innervate the upper and lower limbs, respectively. ❑ Divided into 31 segments (8 cervical, 12 thoracic, 5 lumbar, 5 sacral and1 coccygeal). Relation Between the spinal cord and Vertebral column: ❑ During embryonic life, the spinal cord fills the whole length of the vertebral canal. Then the vertebral column grows faster than the spinal cord. This result in relative shortening of the cord. ❑ Lumbar segments lie between T9 and T12 vertebrae and the sacral segments are packed at the level of the first lumbar vertebra. ❑ In the cervical region; add one to the vertebral number to obtain the segmental level. ❑ In the upper half of thoracic region; add 2 to the vertebral number 8 months 24 months ❑ In the lower half of thoracic region; add 3 to the At birth vertebral number. Adult Spinal Nerves: ❑ 31 pairs emerge from the corresponding spinal cord segments. ❑ ❑ Leave the vertebral canal through the intervertebral foramina except: 1) C1 emerges above the posterior arch of the atlas. 2) C2 emerges between the arches of atlas and axis vertebrae. 3) From S1-S4 emerge through the sacral Sacral foramina foramina. 4) S5 and the coccygeal nerves emerge through Sacral hiatus the sacral hiatus. ❑ Spinal nerve is attached to the spinal cord by anterior and posterior roots. ❑ Each posterior root carries a posterior (dorsal) root ganglion. ❑ Spinal nerve is divided into large ventral and smaller dorsal rami. Cauda equina: Occupies the lower part of the vertebral canal below the lower end of the cord. Consists of: 1)Roots of lumbar, sacral and coccygeal nerves. 2)Filum terminale.  General Organization of Spinal Nerves ❑ The ventral rami of the upper 4 cervical nerves form the cervical plexus to supply the neck. ❑ The ventral rami of the lower 4 cervical (C 5, 6, 7 & 8) and 1st thoracic nerve (Th.1) share in formation of form the brachial plexus to supply upper limb. ❑ The ventral rami from T1-T11 form the intercostal nerves and the ventral ramus of T12 form the subcostal nerve. These nerves supply the intercostal muscles. Brachial plexuses Cervical plexuses ❑Ventral rami of upper 4 lumbar nerves form the lumbar plexus to share in the supply of anterior abdominal wall, the groin, and the lower limb. ❑The ventral rami of the 4th and 5th lumbar nerves and the ventral rami of the upper 4 sacral nerves form the sacral plexus to supply the lower limb and pelvis. ❑The dorsal rami supply the muscles and skin of the back.  Cross section of the spinal cord: Sulci : 1) Anterior median fissure 2) Posterior median sulcus 3) Two anterolateral sulci 4) Two posterolateral sulci Internal Structure: ❑ The cord is divided into two halves which are connected by the white and grey commissures. ❑ The cord is composed of: peripheral white matter and central H- shaped grey matter. ❑ The white matter contains Short tracts and Long tracts. ❑ The cells of grey matter are arranged into definite groups or nuclei (10 Rexed laminae).  I Posteromarginal nucleus mediating pain, temperature and touch sensations. II Substantia gelatinosa neurons mediating pain transmission. III & IV Proper sensory nucleus that receives inputs from substantia gelatinosa and mediating pain, temperature, and touch sensations. Concerned with unconscious preprioceptive sensations V&VI VII In the intermediate horn; autonomic fibers. VIII & IX Located in the ventral horn;innervating skeletal muscles. X Gray matter surrounding central canal Meninges of spinal cord: 3 layers: pia mater. arachnoid mater and dura mater (outward). The Epidural Space Between the ligamentum flavum and the superficial dura mater. This location contains various structures such as adipose tissue, connective tissue, nerves, the internal vertebral venous plexus, and lymphatics. It is a site commonly used for analgesic purposes and is a potential site for infection. The Dura Mater ❑ The most superficial layer of the meninges. ❑ The dura mater is the strongest of the three layers. ❑ As they make their way out of the vertebral canal, the spinal nerves are coated with dura mater as they exit into the epidural space, creating the epineurium. The Subdural Space The spinal subdural space is only a potential space. It exists between the dura and arachnoid mater. The Arachnoid Mater Between the dura and the pia mater. The arachnoid mater is avascular and primarily exists to help maintain cerebrospinal fluid (CSF) metabolism. The Subarachnoid Space Located between the arachnoid and pia mater and is filled with CSF. The Pia Mater ❑ The deepest layer of the meninges and is directly attached to the surface of the spinal cord. ❑ Composed primarily of collagen and reticular fibers. ❑ The pia mater will continue past the conus medullaris and fuse into the filum terminale, anchoring the spinal cord to the coccyx inferiorly. ❑ The spinal pia mater also contains denticulate ligaments, which extend outwards to help anchor the spinal cord to the spinal dura mater, further assisting with stabilizing the cord. Arterial supply Anterior spinal artery: ❑ Arise from the vertebral arteries, one for each side. ❑ ❑ The two arteries unite to form one anterior spinal artery. ❑ supplies anterior 2/3 of spinal cord. Posterior spinal arteries: ❑ Two arteries, one for each side. ❑ Arise from the vertebral artery. ❑ Supply the posterior 1/3 of spinal cord. Radicular arteries: ❑ Arise on each side from vertebral, ascending cervical, deep cervical, posterior intercostals, lumbar and lateral sacral arteries. ❑ Supply spinal nerve roots, posterior root ganglion. Venous Drainage six longitudinal venous channels; 1) One Anterior spinal vein. 2) One Posterior spinal vein. 3) A pair of Anterolateral veins. 4) A pair of posterolateral veins. 1.There are _____ pairs of spinal nerves. A) 12 B) 21 C) 31 D) 43 2. The deep groove on the ventral surface that extends the length of the spinal cord is the A) anterior median fissure. B) central canal. C) central sulcus. D) longitudinal fissure. 3. Which spinal nerves comprise the cauda equina? A) coccygeal B) lumbar, sacral and coccygeal C) sacral D) sacral and coccygeal 4. What two grooves extend the length of the spinal cord and partially divide it into right and left halves? A) anterior median fissure and central sulcus B) anterior median fissure and posterior median sulcus C) central sulcus and longitudinal fissure D) longitudinal fissure and posterior median sulcus 5. The fibrous strand or terminal filum that anchors the inferior end of the spinal cord to the coccyx is a continuation of the A) arachnoid mater. B) dura mater. C) epidural mater. D) pia mater.