Spinal Cord, Spinal Nerves & Sensory/Motor Tracks PDF

The Spinal Cord Spinal Nerves & Sensory/Motor Tracks Ch 14 & 15 Intro While the spinal cord and brain are physically they have very distinct roles The brain is the site of processing of all information and the coordinator of all responses to stimuli The spinal cord (SC) is the transmitter of sensory...

The Spinal Cord Spinal Nerves & Sensory/Motor Tracks Ch 14 & 15 Intro While the spinal cord and brain are physically they have very distinct roles The brain is the site of processing of all information and the coordinator of all responses to stimuli The spinal cord (SC) is the transmitter of sensory & motor data to and from the brain It also integrates and processes certain levels of information on its own Gross Anatomy The adult SC extends from the foramen magnum to the first lumbar vertebrae The nerves that continue into the pelvic girdle form the cauda equina Each region of the SC (Cervical, Thoracic, Lumbar, Sacral) contains tracks (bundles of axons) that share functional similarities. The amount of gray matter increases substantially in those areas that handle sensory and motor information These areas form the: cervical Enlargement: Supplies the Pectoral Girdle and Limbs Lumbrosacral Enlargement: Supplies the Pelvic Girdle and Limbs Every spinal segment is associated with a dorsal root ganglia that contains the cell bodies of afferent sensory neurons Anterior to the dorsal root is a ventral root containing efferent axons of somatic motor neurons Distal to each ganglion, the spinal nerve forms Contains both afferent and efferent fibers Spinal Meninges Meninges cover and protect the SC and spinal nerve roots Blood vessels branching within the meninges deliver O2 and nutrients to the SC There are 3 meningeal layers: 1. Dura Mater: 2. Arachnoid Layer 3. Layer of dense irregular connective tissue Attaches to the foramen magnum, the 2nd & 3rd cervical vertebrae, and the sacrum Stabilizes the SC within the vertebral canal The outer epithelium is not connected to the vertebral column, creates the epidural space Lines the inner surface of the dura mater Subarachnoid space separates dura mater from inner most layer od the SC and contains the cerebrospinal fluid Pia Mater Firmly bonded to the underlying neural tissues Contains the blood vessels of the SC Denticulate ligaments interweave and connect the pia mater, arachnoid layer and dura mater At the inferior tip, connective tissue of the pia mater forms the filum terminale Sectional Anatomy The anterior median fissure and posterior median fissure divide the SC into left and right halves There is a central H -shaped mass of gray matter composed of the cell bodies of neuroglia and neurons The gray matter surrounds the central canal Gray matter called horns project toward the outer surface of the SC The peripheral white matter contains the myelinated and unmyelinated axons organized into tracks or columns Gray Matter Cell bodies within the gray matter are organized into groups called nuclei Sensory nuclei receive and transmit information from peripheral receptors Motor nuclei send motor commands back to the peripheral receptors The posterior horns contain the somatic and visceral sensory nuclei The anterior horns contain the somatic motor neurons Lateral horns exist only in regions T1 to L1 and contain visceral motor nuclei White Matter The overall pater of gray/white matter described is consistent throughout the SC However, the amount of white matter decreases as you move caudally White matter is divided into regions called 4 columns The anterior white column The Posterior white column 2 Lateral white columns Each column contains tracts of ascending or descending fibers A specific tract contains either sensory or motor axons Spinal Cord Tracts The ascending ( Sensory) and descending (motor) tracts each consist of a chain of neurons and associated nuclei All involve both the brain and spinal cord The name of a tract often indicated is origin: A tract beginning with Spino: begin in spine and end in brain A tract ending with Spinal: begins in the brain and ends in the spinal cord Sensory Tracts The posterior (dorsal) columns carry highly localized information from receptors in the skin and musculoskeletal system regarding proprioreception. Three neurons are involved in the transmission of information along these tracts First, second, and third order neurons First order neurons enter through the dorsal root and connect to second order neurons All second order neurons decussate (cross over) to the opposite side (Contralateral) of of the medullar Motor Tracts The CNS send motor commands in response to the sensory information it receives These efferent commands are distributed to the effectors by either the: Somatic Motor system Autonomic Motor system All descending motor tracts are two neuron systems and decussate as they reach the spinal segments The upper motor neuron originates withing the brain The lower motor neuron is found in the lateral horn of the SC Spinal Nerves There are 31 pairs of spinal nerves 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal 3 pairs of connective tissue surround each peripheral nerve 1- Epineurium-tough outermost layer 2- Perineurium-divides the nerve into compartments called fascicles 3.Endoneurium –surround individual axons All spinal nerves form 2 branches: A Dorsal and Ventral Ramus The dorsal ramus receives sensory info from, and sends motor commands to skeletal muscles of the back The ventral ramus supplies the ventrolateral body surface , structures of the body wall and limbs In adult spinal cord segments the ventral rami controlling skeletal muscle of the neck and the upper and lower limbs do not directly contact their targets: Instead, they fibers are interwoven into complex nerve trunks called a nerve plexus These include the cervical, brachial, lumbar, and sacral plexus 終了