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Practical Anatomy LEC.1 Dr. Firas M. Ghazi Vertebral Canal and Spinal

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Practical Anatomy LEC.1 Dr. Firas M. Ghazi Vertebral Canal and Spinal Practical Anatomy LEC.1 Dr. Firas M. Ghazi Vertebral canal and Spinal Cord Lecture Objectives: By the end of this lecture students are expected to be able to 1. Describe the vertebral canal and its content 2. Discuss the meningeal coverings and spaces surrounding the spinal cord 3. Recall various external features of spinal cord 4. Summarize the blood supply of spinal cord 5. Draw a diagram showing the main topographical features of spinal cord section 6. List the major descending and ascending tracts within white matter of spinal cord 7. Summarize the topographical distribution, connections, and functions of the above tracts 8. Differentiate between upper and lower motor neuron disease A) Vertebral canal Vertebral canal A tubular cavity along the vertebral column (vertebral foramina lying above each other) Boundaries: o Anteriorly: 1. Vertebral bodies (from C1 to sacral hiatus) 2. Intervertebral discs (IVDs) 3. Posterior longitudinal ligament o Posterolaterally 1. Vertebral arch 2. Ligamenta flava 3. Intervertebral foramena It is continuous above with cranial cavity Content: 1. Internal vertebral venous plexus 2. Spinal meninges 3. Spinal cord with its nerve roots and blood vessels. The sacral canal is considered as its lower part which ends at the sacral hiatus Intervertebral foramens (IVFs) For boundaries and content/ Refer to lab checklist IVFs change size during movement of vertebral column so spinal nerves exiting through IVFs can be compressed causing back pain & pain radiating to upper or lower extremities B) Meningeal coverings of spinal cord Epidural space Lies between the spinal dura and the periosteum lining the vertebral canal. Content 1. Loose areolar tissue 2. Spinal radicular arteries 3. Internal vertebral venous plexus Further assistance on: Page 1 University website: http://staff.uobabylon.edu.iq/site.aspx?id=93 Facebook page: Anatomy For Babylon Medical Students Practical Anatomy LEC.1 Dr. Firas M. Ghazi Spinal radicular arteries: Enter the vertebral canal through IVFs along the spinal nerve roots. Unite with (Augment) anterior and posterior spinal arteries Arise from different arteries at different parts of vertebral column 1. Cervical region: ascending cervical and deep cervical arteries 2. Thoracic region: posterior intercostal arteries 3. Lumbar region: lumbar arteries 4. Sacral region: lateral sacral arteries Internal vertebral venous plexus Is a network of veins extending along the length of vertebral canal within epidural space It is continuous with dural venous sinuses of cranial cavity through the foramen magnum Drain venous blood from the vertebrae, spinal meninges and spinal cord. Communicate with regional veins outside the vertebral canal Act as a bypass when venous flow through inferior or superior vena cava is obstructed Has no valves; therefore the direction of drainage is posture and respiration dependent Clinical note: Inferiorly this plexus is continuous with the prostatic venous plexus of the male. Therefore prostatic cancer may metastasize to vertebra and to the meninges and brain Dura Attached above to foramen magnum and close inferiorly at S2 Separated from the vertebrae by the epidural space Arachnoid Continues above with cranial arachnoid and closed inferiorly at S2 Thecal sac: is a term used to refer to dura and arachnoid together. It extends from foramen magnum to S2 and contains the CSF. Subarachnoid space Filled with CSF At various locations it becomes enlarged, forming regions called cisterns. lumbar cistern lies between the conus medularis (L1) and (S2), it contains the CSF and the spinal nerve roots forming the cauda equina. Clinical note: CSF can be collected by introducing a needle into the subarachnoid space without risk of injuring the spinal cord. The procedure is called lumbar puncture. Pia Thin vascular membrane closely applied to spinal cord Continues above with cranial pia mater Filum terminale: thin filament of pia extending below the lower end of spinal cord, surrounded by cauda equina. It passes through the sacral hiatus and gets attached to the dorsal surface of CX1 vertebra Further assistance on: Page 2 University website: http://staff.uobabylon.edu.iq/site.aspx?id=93 Facebook page: Anatomy For Babylon Medical Students Practical Anatomy LEC.1 Dr. Firas M. Ghazi C) Spinal cord The spinal cord serves two main functions: 1. Transmit information between body and brain. 2. Execute simple reflexes. External features Begins at the foramen magnum as the continuation of medulla oblongata Ends opposite the intervertebral disc between L1 and L2 vertebrae In the fetus, the spinal cord reaches the level of S2 vertebra. Cauda equina is formed by lumbar (except L1), sacral, and coccygeal nerve roots. Spinal segments: is the portion of spinal cord which gives origin to a pair of spinal nerves (They are not visible on the surface). Thus spinal cord consists of 31 spinal segments. Approximate vertebral levels of the spinal segments Cervical 1 8 <<<>>> Foramen magnum to C6 vertebrae Thoracic 1 6 <<<>>> C6 T4 vertebrae Thoracic 7– 12 <<<>>> T4 T9 vertebrae Lumbar and– sacral <<<>>>– T10 L1 vertebrae – – Spinal enlargements: at certain segments the spinal cord enlarges due to increased mass – of motor cells in the anterior horns of grey matter. 1. Cervical enlargement: In the region of C5 T1 spinal segments. The nerves arising from these segments form brachial plexus. 2. Lumbar enlargement: In the region of L2–S3 spinal segments. The nerves arising from these segments form the lumbar plexus. – Note: Vertebral levels of these enlargements do not correspond to their spinal segments, cervical enlargement lies opposite C3 to T1 vertebrae and lumbar enlargement lies opposite T9 to L1 vertebrae. Internal structures a) The Grey matter is made up of nerve cell bodies Transverse grey commissure connect both sides of grey matter Central canal: passes through the center of the grey commissure. The amount of grey matter, shape of its horns, and amount of white matter varies at different levels of spinal cord Types of neurons 1. Motor neurons: present in the anterior and lateral horns Anterior horn cells: supply skeletal muscle Lateral horn cells: preganglionic sympathetic neurons (T1-L2) Note: preganglionic parasympathetic neurons are found within grey matter of spinal segments S2-S4 giving rise to the sacral parasympathetic outflow Further assistance on: Page 3 University website: http://staff.uobabylon.edu.iq/site.aspx?id=93 Facebook page: Anatomy For Babylon Medical Students Practical Anatomy LEC.1 Dr. Firas M. Ghazi 2. Sensory neurons: Present in the posterior horn Relay sensory information to: Different parts of the brain forming ascending tracts Other segments of spinal cord forming intersegmental tracts. 3. Interneurons (association neurons): Small neurons present throughout the grey matter Connect different types of neurons b) White matter Made up mainly of fiber tracts (ascending to or descending from brain) In each half of spinal cord, it is divided into three parts called columns: 1. Posterior white column, between posterior median septum and posterior horn 2. Lateral white column, between anterior and posterior horns 3. Anterior white column, between anterior median fissure and anterior horn Tracts: Collections of nerve fibers within the central nervous system Have same origin, course, and termination. Other names: fasciculus (= bundle) or lemniscus (= ribbon) Their names are derived from the names of masses of grey matter they connect. The names usually consist of 2 parts; the first denotes the origin and second the termination of the tract. Examples: 1. Corticospinal tract: originate from cerebral cortex & terminate at spinal cord. 2. Spinothalamic tract: originate from spinal cord and terminate at the thalamus Specific tracts a) Corticospinal (pyramidal) tract: Descending tract Origin: most fibers take origin from primary motor area in precentral gyrus . The remaining fibers arise from other areas of cerebral cortex Course: cerebral cortex, corona radiate, posterior limb of internal capsule, crus of≈40% the midbrain, pons, and pyramid of medulla oblongata. Further course of the tract will vary as described below: 1. 80% of fibers cross the midline in pyramidal decussation, descend through contralateral side of spinal cord as lateral corticospinal tract. 2. 10% of fibers do not cross, but descend directly downward as the anterior corticospinal tract, which occupies the anterior column at cervical and upper thoracic levels, these fibers cross later within the white commissure to reach the contralateral anterior horn 3. 10% enter the lateral corticospinal tract on same side (do not cross) Termination: motor neurons of anterior horn at various levels of the spinal cord Function: transmits information regarding voluntary motor activity of limbs & trunk Further assistance on: Page 4 University website: http://staff.uobabylon.edu.iq/site.aspx?id=93 Facebook page: Anatomy For Babylon Medical Students Practical Anatomy LEC.1 Dr. Firas M. Ghazi Upper and lower motor neurons: neurons of the motor cortex and their axons forming the corticospinal tracts are referred to as upper motor neuron while motor neurons of anterior horn and their axons (forming spinal nerves) constitute the lower motor neurons Lesion: upper motor neuron (UMN) lesions lead to loss of voluntary movements of the body below the level of the lesion. The muscles are not actually paralyzed but the tone of muscles is increased leading to spastic
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