Spinal Cord Chapter 1 PDF

Nervous systemspinal cord Alleko Bairamovi CNS – Central Nervous system Day 16 after fertilization → embryonal cells belong to 1 of 3 germ cell layers: Ectoderm Neurulation Differentiates into the neuro ectoderm, creating the neural plate Cell replication in the neural plate gives rise to 2 ridges (...

Nervous systemspinal cord Alleko Bairamovi CNS – Central Nervous system Day 16 after fertilization → embryonal cells belong to 1 of 3 germ cell layers: Ectoderm Neurulation Differentiates into the neuro ectoderm, creating the neural plate Cell replication in the neural plate gives rise to 2 ridges (neural crests). The depression between the crests is known as the neural fold. Mesoderm Differentiates and transforms in a tube structure called the notochord The notochord signals the neural fold to enlarge on either side of the neural groove creating the neural tube Endoderm will give rise to the lining of the GI and respiratory systems Neurulation Neurulation the differentiation and growth of the neural plate into the neural tube during the first trimester of gestation Neural crest cells migration 1st wave of the migration will form sympathetic and parasympathetic ganglia as well as the chromaffin cells of the adrenal medulla 2nd posterior root ganglia as well as Schwann and satellite cells Final wave forms melanocytes that distribute themselves throughout the epidermis and elsewhere. Neural crest cells in the head and neck Migrate the into the pharyngeal arches to contribute mesenchyme to the face, neck and into the developing heart to separate the chambers of the heart and outflow tracts Cranial neural crest cells contribute to much of the bone, cartilage, and connective tissue in the head, including most of the head skeleton and parts of the teeth. Schwann Cell and Oligodendrocytes Schwann cells surround and support axons of the peripheral nervous system; may simply cushion multiple unmyelinated axons or create myelin In this case, a single Schwann surrounds cell a small segment of a single axon. The cleft between adjacent myelinating Schwann cells is a nodeof Ranvier Do the same job in a slightly different way. A single oligodendrocyte may extend several myelinating processes around several nearby axons The Neural Tube and Ventricular System The Three Vesicle-stages The neural tube and the canal neural within it develop distinctive regions as they enlarge. Three distinct primary brain vesicles develop first: Prosencephalon (forebrain) Mesencephalon (midbrain) Rhombencephalon (hindbrain) The Five Vesiclestages Prosencephalon gives rise to: Telencephalon Diencephalon Mesencephalon stays as mesencephalon. Rhombencephalon gives rise to: Metencephalon Myelencephalon Differentiation of the Vesicles secondary brain vesicles develop into the mature brain and brainstem. Telencephalon becomes the left and right hemispheres Diencephalon becomes thalamus , cerebral cortex hypothalamus , and pineal gland Mesencephalon becomes (stays) the midbrain Metencephalon becomes the pons and cerebellum Myelencephalon becomes the medulla oblongata The rest of the neural tube develops into the spinal cord Between 3rd and 4th Interventricular foramina Between lateral and 3rd Mature Appearance of the Ventricles Mature Appearance of the Ventricles The neural canal enlarges along with the neural tube. Ependymal cells derived from the innermost layer of neuroepithelial cells, line these cavities. The left and right cerebral cortex surround the left and right lateral ventricles The thalamus, hypothalamus, and pineal gland surround the third ventricle The midbrain surrounds the cerebral aqueduct. The pons, cerebellum, and medulla oblongata all surround the fourth ventricle The spinal cord surrounds a central canal Hydrocephalus Blockage of the ventricular system or impedance the CSF’s entry to the venous blood results in a surplus of csf in or around the brain. This condition has different varieties and can be fatal. In adults, the solid bones of the skull do not allow any outlet for the increased pressure on the brain. Cerebral Aqueduct Stenosis If the cerebral aqueduct in the midbrain develops a narrow lumen, it becomes more prone to blockage when the tissues of the brain swell. Such cerebral aqueduct stenosis similar to hydrocephalus but with expansion of the lateral and third ventricles but with a normalis sized fourth ventricle. Congenital hydrocephalus and congenital aqueduct stenosis remain the most common indication for the placement of ventriculoperitoneal shunts. Up to 50% of VP shunts are placed for one of these two indications Spine Grey and white matter of the spinal cord Lateral horns in the thoracic section Spinal cord Spinal cord The most distal bulbous part of the spinal cord is called the conus medullaris, and its tapering end continues as the filum terminale. Distal to this end of the spinal cord is a collection of nerve roots, which are horsetail-like in appearance and hence called the cauda equina Spinal nerves Cervical -8 Thoracic- 12 Lumbar-5 Sacral-5 Cord ends L1/L2 Conus medullaris Cauda Equina Coccygeal nerve Spinal Cord cross section Cross section at approx. the C6–7 level (A) Left fasciculus gracilis (B) Left fasciculus cuneatus (C) Left lateral corticospinal tract (D) Left dorsolateral column (E) Left dorsomedial column (F) Right dorsomedial column (G) Right dorsolateral column (H) Right lateral corticospinal tract (I) Right fasciculus cuneatus (J) Right fasciculus gracilis Terminology Dorsal- posterior, towards back Ventral- Anterior, Towards front Rostral- towards top of the head Caudal- towards tail, away from the head Herniation of the vertebral disc Disk protrusion: protrusion of the vertebral disk nucleus pulposus Disk herniation (disk extrusion or disk prolapse): complete extrusion of the nucleus pulposus through a tear in the annulus fibrosus Disk sequestration: extrusion of the nucleus pulposus and separation of a fragment of the disk Spondylosis: a broad term used to describe degenerative changes of the spine that may result in irritation and/or damage of the adjacent nerve roots or spinal cord complete extrusion of the nucleus pulposus through a tear in the annulus fibrosus Disc protrusion Cross section of the spinal cord Posterior funiculus: contains afferent nerve tracts that convey the sensations of pressure, fine touch, vibration, and proprioception from the skin and joints. The nerves are grouped into two tracts: fasciculus cuneatus (upper limbs and neck; lateral) and fasciculus gracilis (lower limbs and trunk; medial). Anterolateral funiculus: contains afferent nerves that have decussated from the contralateral side of the body and transmit sensations of crude touch (anterior spinothalamic tract) as well as temperature and pain (lateral spinothalamic tract). Pyramidal tract: contains efferent nerve tracts (corticobulbar tract and corticospinal tract) that convey motor control impulses from the brain and cranial nerves. Nerves of the corticospinal tract decussate at the medulla oblongata and innervate the muscles of the limbs and trunk. Nearly half of the corticobulbar decussate, resulting in both contralateral and ipsilateral innervation of the facial muscles. Anterior horn of the spinal cord: contains alpha motor neurons, which initiate contraction of skeletal muscle. Contralateral: pertaining to the other side. Ipsilateral : the same side Cortex Tracts of the spinal cord Ascending Brain stem VPL : ventral posterolateral nucleus Receive all sensory info from all body parts Dorsal horn Tracts of the spinal cord Ascending UMN In white mater Tracts of the spinal cord Descending Epsilateral below medulla Contralateral above medulla Decussation Anterior horn LMN Key points Blood supply of the spinal cord Vertebral arteries Main source of blood supply to the spinal cord Arise from the subclavian artery branches Blood supply of the spinal cord Illustration of a lumbar vertebra and the adjacent spinal cord segment, showing the arterial blood supply territories. Note that the vasocorona is an anastomosis between the anterior and posterior spinal arteries.