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SPINAL CORD AND SPINAL NERVES November 2, 2011 SPINAL CORD CIRCUITRY 1. Peripheral receptors bring in sensory information from body to spinal cord –somatic from skin/muscle, visceral from organs 2. Sensory neuron enters dorsal part of spinal cord to synapse on gray matter neuron (very particular) pseudounipolar structure 3. Information integration by interneurons (not required) 4. Motor neurons exit ventral part of spinal cord 5. Effector (muscle, gland) responds SPINAL NERVE: Has both sensory and motor components Dorsal nerve root: sensory Ventral nerve root: motor Spinal nerve Trunk: BOTH Arrows indicate direction of information flow Green indicates autonomic outflow to viscera ANATOMY OF THE SPINAL CORD Ventral root: motor/efferent axons Dorsal Root: sensory/afferent axons Dorsal root ganglion: cell body of afferent Spinal nerve: sensory + motor axons SPINAL NERVES LEAVE THE SPINAL CORD IN SMALL SPACES BETWEEN THE VERTEBRAE WHY POSITION MATTERS: Partial crushing of the vertebral column leads to compression of the spinal cord, but symptoms will vary depending on which part of spinal cord is injured Epidural: sensory is deadened, but still have motor Dorsal ganglia: cell bones of sensory neurons COMPOSITION OF A PERIPHERAL NERVE Nerves contain both (sensory and motor axons and both somatic and autonomic fibers Also myelinated or unmyelinated Motor axons: myelinated=fast CONNECTIVE TISSUE COMPONENTS OF A PERIPHERAL NERVE Epineurium: -outer layer Perineurium: -middle layer -divides nerve into fascicles (axon bundles) Endoneurium: -inner layer -surrounds individual axons ANATOMY OF THE SPINAL CORD Gray matter: area containing neuron cell bodies, dendrites, synapses Central canal: ventricles of spinal cord GRAY MATTER ANATOMY: Somatic and visceral sensory areas are separated Somatic: movement of arms and legs GRAY MATTER CONSISTS OF COLUMNS OF CELLS Columns of cells: sends out axons at different levels ANATOMY OF THE SPINAL CORD: White matter: myelinated axon tracts: -ascending sensory info -descending motor info WHITE MATTER ANATOMY The white matter has: Ascending tracts carrying sensory info to the cortex and descending tracts carrying motor info from the cortex The spinal cord does not look exactly alike at all levels: More gray matter in cervical and lumbar enlargements because more motor neurons to innervate arm and leg More white matter at the cervical level because of all motor axons descending and all sensory axons ascending *C-spine injuries damage motor neurons going down and sensory going up SPINAL CORD SEGMENTS 31 pairs of spinal nerves: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal Cervical Enlargements: Upper extremity Lumbar Enlargement: Lower extremity DERMATOMES A topographic map of the body Region of skin innervated by the fibers of 1 spinal never -Arm: cervical -Leg: lumbar Spinal cord lies in dural sac (within CSF fluid) Spinal segments do not coincide with vertebral level Spinal cord ends at L1 vertebra as the conus medullaris The spinal nerves below this level form the cauda equine “horse’s tail” The conus medullaris is anchored to Dura via the filum terminale Axons that extend beyond the end of the spinal nerves travel long distances before innervating something LUMBAR PUNCTURE TO OBTAIN CSF The cauda equine is located in a sac (Dura) filled with fluid (CSF). Since there is no spinal cord, CSF can be drawn from here Some peripheral nerves (eg sciatic nerve) are formed from the union of branches of several spinal nerves = plexus NERVE PLEXUSES Complex, interwoven networks of nerve fibers Formed from blended fibers of adjacent spinal nerves Four major plexuses: 1. Cervical 2. Brachial 3. Lumbar 4. Sacral Lumbar and Sacral are often combined as lumbosacral CERVICAL PLEXUS Innervates neck, thoracic cavity, diaphragm muscles (to breath) BRACHIAL PLEXUS Innervates pectoral girdle and upper limbs LUMBAR AND SACRAL PLEXUSES Innervate pelvic girdle and lower limbs CRANIAL NERVES: 1. Head and neck 2. Diaphragm 3. Deltoids, biceps 4. Wrist extenders 5. Triceps 6. Hand THORACIC NEVERS 1. Chest muscles 2. Ab muscles LUMBAR NERVES 1. Leg muscles SACRAL NERVES 1. Bowel, Bladder 2. Sexual function