Ch 13 The Spinal Cord and Spinal Nerves 11 04 2015 Describe the gross anatomy of the spinal cord Is it symmetrical along the entire length Gross Anatomy of the Spinal Cord About 18 inches 45 cm long 1 2 inch 14 mm wide Ends between vertebrae L1 and L2 Bilateral symmetry o Grooves divide the spinal cord into left and right Posterior median sulcus on posterior side Anterior median fissure deeper groove on anterior side Enlargements of the Spinal Cord o Caused by Amount of gray matter in segment Involvement with sensory and motor nerves of limbs o Cervical enlargement o Lumbar enlargement Nerves of shoulders and upper limbs Nerves of pelvis and lower limbs The distal end o Conus medullaris Thin conical spinal cord below lumbar enlargement o Filum terminale o Cauda equina Thin thread of fibrous tissue at end of conus medullaris Attaches to coccygeal ligament Provides longitudinal support to spinal cord Nerve roots ventral and dorsal extending below conus medullaris and into sacrum Explain how spinal nerves are numbered 31 Spinal Cord Segments Based on vertebrae where spinal nerves originate Positions of spinal segment and vertebrae change with age o Cervical nerves Named for inferior vertebra Except for cervical nerve 8 since cervical vertebra 8 does not exist o All other nerves Named for superior vertebra Describe the difference between the ventral and dorsal root Roots Two branches of spinal nerves o Ventral root Contains axons of motor neurons somatic and visceral effectors o Dorsal root Dorsal root ganglia Contains axons of sensory neurons o Contain cell bodies of sensory neurons Which carries information to the CNS Which carries information away from the CNS Where are the cell bodies of these Dorsal roots carry information to the CNS they contain sensory neurons Ventral roots carry information away from the CNS they contain motor neurons The cell bodies of the motor neurons that extend axons through the ventral root are located in the gray matter of the spinal cord Describe the meninges covering the spinal cord How is it anchored to prevent lateral movement The Spinal Meninges Specialized membranes isolate spinal cord from surroundings Continuous with cranial meninges Functions of the spinal meninges include 1 Protecting spinal cord 2 Carrying blood supply Meningitis 1 Viral or bacterial infection of meninges 2 Spinal meningitis or cerebral meningitis can disrupt CSF flow damage or kill neurons and neuroglia Later stages of meningitis affects entire meningeal system The Three Meningeal Layers 1 Dura mater o Outer layer of spinal cord o Tough and fibrous o Cranially o Caudally Fuses with periosteum of occipital bone Is continuous with cranial dura mater Tapers to dense cord of collagen fibers Joins filum terminale in coccygeal ligament o The epidural space Between spinal dura mater and walls of vertebral canal Contains loose connective and adipose tissue Adipose tissue acts as protective padding Anesthetic injection site Epidural block temporary sensory loss and possibly some motor paralysis mostly just sensory loss though Used at inferior lumbar sacral region for pain control during childbirth Only affects spinal nerves in immediate area 2 Arachnoid mater Middle meningeal layer Arachnoid membrane Simple squamous epithelia Covers outer surface of arachnoid mater The Interlayer Spaces of Arachnoid Mater Subdural space Subarachnoid space o Between arachnoid mater and dura mater Cerebrospinal Fluid CSF o Between arachnoid mater and pia mater o Contains collagen elastin fiber network arachnoid trabeculae extends to filum terminale o Filled with cerebrospinal fluid CSF o Carries dissolved gases nutrients and wastes o Lumbar puncture or spinal tap withdraws CSF o Spinal anesthesia injection of local anesthetics to subarachnoid space spreads as CSF distributes along spinal cord Breathing not affected since injection usually not at the level of upper cervical spinal nerves which controls respiration travels down 3 Pia mater Inner meningeal layer Is a mesh of collagen and elastic fibers Is bound to underlying neural tissue Blood vessels serving the spinal cord run along surface of spinal pia mater within the subarachnoid space Describe the difference between the gray and white matter found in the spinal cord 4 Gray matter Is covered by a thick layer of white matter 5 White matter Consists of ascending and descending axons Organized in columns Contains axon bundles with specific functions Explain the function of the gray horns of the spinal cord Gray matter 1 Has projections gray horns Organization of Gray Matter 1 The gray horns Posterior gray horns contain somatic and visceral sensory nuclei Anterior gray horns contain somatic motor nuclei Lateral gray horns are only in thoracic and lumbar segments contain visceral motor nuclei Explain the function of the white columns of the spinal cord Organization of White Matter 1 Posterior white columns lie between posterior gray horns and posterior median sulcus Proprioception fine touch ventral pressure vibrations 2 Anterior white columns lie between anterior gray horns and anterior median fissure Crude touch and pressure Anterior white commissure is area where axons cross from one side of spinal cord to the other 3 Lateral white columns located on each side of spinal cord between anterior and posterior columns Proprioception Describe the connective tissue layers covering the spinal nerves Three Connective Tissue Layers of Spinal Nerves 1 Epineurium 2 Perineurium Outer layer Dense network of collagen fibers Middle layer Divides nerve into fascicles axon bundles Blood vessels found outside the fascicles 3 Endoneurium Inner layer Surrounds individual axons Describe the locations and function of the major nerve plexuses The Four Major Plexuses of Ventral Rami 1 Cervical plexus 2 Brachial plexus 3 Lumbar plexus 4 Sacral plexus The Cervical Plexus 1 Includes ventral rami of spinal nerves C1 C5 2 Innervates neck thoracic cavity diaphragmatic muscles 3 Major nerve Phrenic nerve C3 5 controls diaphragm Damage to this nerve can cause you to stop breathing The Brachial Plexus 1 Includes ventral rami of spinal nerves C5 T1 2 Innervates pectoral girdle and upper limbs 3 Major nerves Musculocutaneous nerve flex arm receives sensory info on lateral surface of forearm Radial nerve extensor muscles of arm and forearm receives sensory info from posterolateral surface Median nerve flex forearm receives sensory info from Ulnar nerve flex hand receives sensory info
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