Spinal Cord Anatomy Overview PDF

Neuro Organization of the Nervous System: 1. Central nervous system (CNS): i. Brain (cerebrum and cerebellum). ii. Brain stem (midbrain, pons and medulla oblongata). iii. Spinal cord. 2. Peripheral nervous system (PNS): i. Cranial nerves (12 pairs, connected to under surface of cerebrum and br...

Neuro Organization of the Nervous System: 1. Central nervous system (CNS): i. Brain (cerebrum and cerebellum). ii. Brain stem (midbrain, pons and medulla oblongata). iii. Spinal cord. 2. Peripheral nervous system (PNS): i. Cranial nerves (12 pairs, connected to under surface of cerebrum and brain stem). ii. Spinal nerves (31 pairs arise from spinal cord and are divided into; 8 cervical, 12 thoracic, 5 lumber, 5 sacral and one coccygeal). 3. Autonomic nervous system (ANS): i. Parasympathetic (craniosacral) division: - Cranial part: related to cranial nerves III, VII, IX and X. - Sacral part: related to sacral spinal nerves 2, 3 and 4. ii. Sympathetic (thoracolumber) division: - Arises from the spinal cord (T1-L3). - Forms the sympathetic trunk with its ganglia. 1 Spinal cord I. External features - Site: It occupies the upper 2/3 of the vertebral canal. - Length: It is about 45 cm in length in males and 42 cm in females. - Extent: a- Above: It begins as a continuation of the medulla oblongata at the lower border of foramen magnum at the level of 1 st cervical nerve. b- Below: the lower end of the cord tapers forming conus medullaris. It ends at the following levels : 1. By the 3 rd month of intra-uterine life, it occupies the whole vertebral canal. 2. At birth, it ends at the level of L3 vertebra. 3. In adult, it ends at the level of the disc between L1/2 vertebrae. These changes are due to differential growth between the spinal cord (slower) and vertebral column (faster). - Shape: The spinal cord is cylindrical and shows two enlargements: a- Cervical enlargement: from C5-T1 spinal segments, where the spinal cord gives origin to the brachial plexus of the upper limb. b- Lumbar enlargement: from L1-S3, where the spinal cord gives origin to lumbar and sacral plexuses of the lower limb. - External features: The external surface of the spinal cord shows 6 longitudinal grooves or sulci: Anterior median fissure or sulcus: is the deepest. Posterior median sulcus. Two anterolateral sulci: for exit of the ventral (motor) roots. Two postero-lateral sulci: for entry of the dorsal (sensory) roots. 2 3 -Segmentation The spinal cord is divided into 31 segments, each segment gives origin to a pair (right and left) of spinal nerves which are (8 cervical, 12 thoracic, 5 lumbar segments, 5 sacral segments and 1 (one) coccygeal). Each spinal nerve is attached to the side of its corresponding spinal segment by two roots: a. Ventral root (motor): It contains somatic efferent (motor) fibers. b. Dorsal root (sensory): It consists of general somatic afferent (sensory) fibers. Each dorsal root carries an oval swelling called the dorsal root ganglion. At the corresponding intervertebral foramen, the two roots (ventral and dorsal) unite together forming the spinal nerve trunk (mixed) which is very short and divides immediately after leaving the foramen into two primary rami (anterior and posterior). Both rami are mixed and supply the anterior and posterior aspects of the body respectively. Vertebral levels of the spinal cord segments: Spinal cord segments are present higher than their corresponding vertebrae. The rule 1,2,3 is applied to the vertebral spines : a) Cervical region: Add one to the spine.C5 spine is opposite to C6 segment. b) Upper thoracic region: Add 2 to the spine. T3 spine is opposite to T5 segment. c) Lower thoracic region: Add 3 to the spine. T10 spine is opposite toL1 segment. d) T11 spine is opposite to L2 to L5 segments. e) T12 and L1 spines are opposite to all sacral segments N.B. Each cervical nerve from C1 to C7 emerges above its corresponding vertebra. i.e. C1 nerve emerges above atlas and C8 emerges above T1. Each of the remaining spinal nerves from T1 emerges below the corresponding vertebra. 4  The gap in the length between the spinal cord and vertebral canal results in, gradual lengthening of the lumbar and sacral nerve roots which have to descend downward to reach their exit foramina as a leash of fibers called cauda equina. 5 6 Coverings of the spinal cord (Spinal Meninges): The spinal cord is surrounded by three membranes called the meninges; from inside outwards; pia, arachnoid and dura maters. 1) Spinal Pia Mater: It is a delicate membrane which is closely adherent to the spinal cord. Prolongations : Outwards: forming sheaths around spinal nerve roots. Inwards: forming sheaths around blood vessels of spinal cord. Thickenings : i. Denticulate ligaments: Two lateral extensions which arise from the pia mater pierce arachnoid mater and finally anchor to dura mater. Each ligament extends midway between the ventral and dorsal spinal nerve root, from the foramen magnum (above) down to the level of L1 vertebra (below). The lateral edge of each ligament is serrated and has 21 processes. ii. Subarachnoid septum: Is a backward extension arising from the pia mater at the posterior median sulcus to get attached to the dura mater. iii. Linea splendens: Is a median glistening band of pia mater that extends along the anterior median fissure. iv. Filum terminale: - It is a silvery glistening fibrous band of pia mater which extends downward from the tip of conus medullaris among the roots of cauda equina. - At the level of S2 vertebra it pierces the arachnoid and the dural tubes, and acquires a dural investment to get finally attached to the back of coccyx. 2) Spinal Arachnoid Mater: It is a delicate membrane which lies between pia and dura maters above, it is continuous with the arachnoid mater of the brain and below; it ends at the level of the S2. It is separated from the pia mater by the subarachnoid space, while it is separated from the dura mater by a narrow subdural space. 7 The subarachnoid space contains: Cerebro-spinal fluid (CSF). Spinal blood vessels. Spinal nerve roots. 3) Spinal Dura Mater: It is thick tough fibrous membrane representing the outermost of the three meninges, extending from the foramen magnum (above) down to the level of (S2) vertebra. Prolongations: forming (sheaths) around 1) Spinal nerve roots 2) Spinal nerve trunks in the intervertebral foramina. 3) Around filum terminale It is separated from the arachnoid mater by the subdural space, and separated from the periosteal lining of the vertebral canal by the extradural (epidural space) which lodges the internal vertebral venous plexus and spinal nerve roots. (i.e. the spinal dura mater is related to two spaces). Fixation of the Spinal Cord: i. Filum terminale which attaches the spinal cord down to the back of the coccyx. ii. Denticulate ligaments which anchors the spinal cord to the dura mater on either side. iii. Subarachnoid septum that attaches the spinal cord to the dura mater posteriorly. iv. The dura mater itself which is attached above to the margin of the foramen magnum and on either side to the margins of the intervertebral foramina. - Lumbar cistern It is the lower part of spinal subarachnoid space (devoid of spinal cord) Extends from L2 to S2 Contents: CSF, cauda equine and filum terminale 8 Clinical Importance : important site for lumbar puncture 9 10 Blood Supply of the spinal cord A- Arterial Supply 1. Single Anterior Spinal Artery: It is formed by the union of 2 anterior spinal arteries, which arises from the 4th part of each vertebral artery. It descends to leave the skull through the foramen magnum and continues downwards along the anterior median fissure of the spinal cord. It gives central branches to supply the anterior 2/3 of the spinal cord (ventral, lateral horns as well as the anterior and most of the lateral white funiculi). 2. Two Posterior Spinal Arteries: Each artery arises inside the skull as a branch from the 4 th part of the vertebral artery or its posterior inferior cerebellar branch. Each artery descends to leave the skull through the foramen magnum and continues downwards along the dorsal nerve roots (the posterolateral sulcus). They supply the posterior 1/3 of the spinal cord (the dorsal horn and the posterior \white funiculus). Anastomosis between anterior and posterior spinal arteries occurs around the conus medullaris. 3. Radicular Spinal Arteries: (Transverse arteries) They arise from the vertebral arteries, the posterior intercostal arteries, lumbar arteries, and lateral sacral arteries on either side. They enter the vertebral canal through the intervertebral foramina and divide into anterior and posterior branches which run along the ventral and dorsal spinal nerve roots; they are main source of blood supply to the lower 1/3 of the spinal cord. They end by anastomosing with both anterior and posterior spinal arteries. One of the lower radicular arteries is very large and supplies the lumbar enlargement (the arteria radicularis magna). B-Venous Drainage - They are 6 longitudinal venous channels : Anteromedian and posteromedian channels. Right and left anterolateral channels. Right and left posterolateral channels. 11 The channels are drained by radicular Veins which drain into the internal vertebral venous plexus present in the epidural space. 12