Spinal Cord Anatomy PDF BNU 2025

To NEURO ANATOMY Dr. Samia M. Manawy  Learning Objectives  Identify parts of nervous system  Identify structures of central nervous system  Describe anatomy of spinal cord Divisions of the Nervous System: Is divided anatomically into :  the central nervous system (CNS), consist...

To NEURO ANATOMY Dr. Samia M. Manawy  Learning Objectives  Identify parts of nervous system  Identify structures of central nervous system  Describe anatomy of spinal cord Divisions of the Nervous System: Is divided anatomically into :  the central nervous system (CNS), consisting of the brain and spinal cord  the peripheral nervous system (PNS), consisting of 12 pairs of cranial nerves and 31 pairs of spinal nerves. Is divided functionally into  the somatic nervous system, which controls voluntary activities  visceral (autonomic) nervous system, which controls involuntary activities. All of these parts Control and integrate the activity of various parts of the body. Structures of nervous system Is composed of: 1-Neurons. 2- neuroglia: (Non neuronal Cells that support neuron). As Schwann cells and satellite cells in PNS. Astrocytes and oligodendrocytes in CNS Neuron: It is the structural and functional unit of the nervous system, as it specialized for reception, integration and transmission of the nerve impulses, so known as the excitable unit. Structure of the neuron: it is formed of cell body (soma) and processes (dendrites and axons) Terms related to nervous system( definitions) Tract: fibers with the same origin, course, termination and function. Bundle (fasciculus): nerve fibers in the same site inside the CNS but with different origin, course, termination and function. Commissure: the bundle or nerve fibers connect the similar parts of CNS, in the right and left sides across the median plane. Lemnisci: ascending sensory fibers in brain stem. Central Nervous System: Peripheral nervous system (PNS): Autonomic Nervous System: 1-Brain: This part is formed of nerves and their Consists of sympathetic and Cerebrum ganglia: parasympathetic components. brain stem 12 pairs of cranial nerves that exits within the CNS and PNS. Cerebellum the skull through foramina. They supply the viscera of the body 2-Spinal cord:31 segments 31 pairs of spinal nerves that exits Cervical segments 8 the vertebral column through Thoracic segments 12 intervertebral foramina. Lumbar segments 5 (8 Cervical 12 Thoracic 5 Lumbar 5 Sacral segments 5 Sacral 1,Coccygeal) Coccygeal segments 1 Spinal cord Gross Appearance of the Spinal Cord:  The spinal cord is roughly cylindrical in shape. 42-45 cm  It begins superiorly at the foramen magnum in the skull, where it is continuous with the medulla oblongata of the brain  it terminates inferiorly in the adult at the level of the lower border of the first lumbar vertebra.  Grows more slowly than the vertebral column during fetal development, so its terminal end gradually shifts to a higher level.  It occupies the upper two-thirds of the vertebral canal of the vertebral column.  It is enveloped by the meninges.  With two enlargements: cervical and lumbosacral (lumbar). Enlargements are due to increase in size of grey matter of origin of the nerves that form brachial & lumbar plexuses that supply limbs The conus medullaris is the conical distal (inferior) end of the spinal cord. In adults, the conus ends at the L1 or L2 level of the vertebral column.  In fetus: it fills the whole vertebral canal reaching the coccyx At birth: L3Vertebra Adult: At disc between L1 and L2 Vertebra or at the level of the lower border of the first lumbar vertebra Spinal cord in cross section(internal features) by naked eye the outline of the spinal cord is circular in thoracic segments and flattened anteroposterior in cervical and lumbar segments. In cross section we see the whit matter is peripherally inclosing the gray matter. The gray matter Central part , H shaped, formed of: two anterior horns: anterior horn cells are motor. two posterior horns: post. horn cells are sensory. Two lateral horns: sympathetic T1-L 2 or L3 segments. parasympathetic S2, 3, 4 segments. Grey commissure with central canal White matter: peripheral part, formed of nerve fibers Anterior, lateral and posterior white columns. White commissure in front of grey commissure. External features: Longitudinal fissures: 1- Anterior median fissure: - Deep fissure and separate anterior white columns. - Lodge vessel called anterior spinal artery fixed by linea splendens (pia). 2- Posterior median sulcus: Shallow sulcus lies between two posterior white columns 3- postero-lateral sulcus: Lies between (post. white column) and (lateral white column). Give attachment to dorsal rootlets of spinal nerves. 4-Antero lateral sulcus: site of exit of anterior rootlets of spinal nerves. Spinal Segments: The segment is the part of spinal cord that gives origin to single pair of spinal nerves. The spinal cord is divided into approximately 31 segments —8 cervical (C) segments, 12 thoracic (T) segments ,5 lumbar (L) segments , 5 sacral (S) segments, and 1 coccygeal (Co). There are no sharp boundaries between segments within the cord itself. The segment is identified by attachment of spinal nerve rootlets Spinal nerves  A total of 31 pairs of spinal nerves leave the spinal cord and pass through intervertebral foramina  The spinal nerves are named according to the region of the vertebral column with which they are associated Parts of spinal nerves Two roots connect the nerve to the spinal cord : 1- Posterior(dorsal) root: afferent (sensory) 2- Anterior root(ventral): efferent (motor) 3-Mixed nerve trunk: By union of both roots 4- Anterior ramus: supply muscle and skin of front and form plexus. 5- Posterior ramus: supply muscle and skin of back, not form plexus. N.B: 1- Differential growth between rapidly growing vertebral column and slowly growing spinal cord leads to relative shortening of cord and terminal end shift to higher level. So  conus medullaris is displaced upward.  Spinal segments become not corresponding with the vertebral number.  Progressive elongation and obliquity of spinal nerve roots.  Lumbar, sacral and coccygeal roots become vertical form cauda equina. 2- Site of lumbar puncture -The puncture is the introduction of a cannula with needle into the space around the spinal cord ,to inject a drug ,or aspirate part of the cerebrospinal fluid (CSF) for clinical investigations. -The sites of puncture must be below the level of termination of the spinal cord. -The proper site is between the spines of lumbar 3 &4 or 4 & 5 vertebrae Spinal Meninges Consist of three layers of connective tissue membranes (pia, arachnoid, and dura mater) that surround and protect the brain and spinal cord. Contain the subarachnoid space, which is the interval between the arachnoid and pia mater, filled with CSF. 1- Spinal dura mater Def.: the thick. tough, fibrous outer most membrane surrounding the spinal cord. Structure: single layer Extent: From: foramen magnum (as continuation of of cranial dura). To: lower border of S2V where it ends as a blind sac Site (relations): - Related externally to wide space called epidural space (extradural space). - Related internally to narrow (potential) space called subdural space between it and arachnoid. 2- Spinal arachnoid mater: Def.: The middle of the meninges surrounding the spinal cord. Site: deep to dura separated from it by subdural space and from pia by subarachnoid space. - Characters: thin, avascular, and transparent (dura and pia are vascular). Extent: like dura, from foramen magnum to S2 vertebra. 3- Spinal pia mater Def: innermost & thinnest layer of spinal meninges. Characters: Forms vascular pial sheath. Extent: From: foramen magnum. To: conus medullaris (disc between L1, L2V) and continues as filum terminale to coccyx. Site (relations): - Internally it is closely surrounding the spinal cord and sends septa into its substance. - Externally it is related to a wide space called subarachnoid space between it and arachnoid. Prolongations (extensions): In ward: - in anterior median fissure forming linea splendens that fix the anterior spinal artery in anterior median fissure. Outward: 1. Around rootlets of spinal nerves. 2. Filum terminal: (20cm) which fibrous filamment. It is formed of two parts: Filum terminale Internum: 15cm Lies in subarachnoid space. Extend from conus medullaris to the end of subarachnoid space, end of (Dural sac) at S2. Pia only Filum terminale externum: 5cm Lies outside subarachnoid space Extend From the tip of the dural sac to coccyx. Pia, arachnoid and dura Filum terminale identified by thin silvery appearance. The filum terminale stabilizes the cord and dura lengthwise. 3-Denticulate ligaments: Long white pial vertical fold on each side that extends laterally between anterior and posterior roots of spinal nerves. Extent: From foramen magnum to conus medullaris (disc between L1, 2V). Action: The dentate ligament helps to stabilize the cord from side to side. Blood supply of the spinal cord Arteries of the spinal cord are: Anterior spinal arteries from vertebral Posterior spinal arteries from vertebral Radicular arteries Which of the following has motor fibers only? A- posterior root B- anterior root C- posterior ramus D- anterior ramus Filum terminal externum ends to which level A- coccyx B- S2 C- between L1 and L2 D- thoracic vertebra Test yourself Identify external and internal features of spinal cord Identify parts of spinal nerve