BME 732 - The Spinal Cord

medicineman's version from 2015-10-04 01:55

General Information

Question Answer
Communication linkBetween the brain and peripheral nerves which activate the muscles. Transfers sensory information to the brain
Segmental organization of the spinal cord30 segments and 4 groups: cervical, thoracic, lumbar, and sacral. Segments named after the vertebra adjacent to where the nerves emerge
Spinal nervesConsist of dorsal root and ventral root axons
Spinal level Motor functions
Low cervicalMovement of arms and hands
Mid thoracicRespiration
Low lumbarMovement of legs
SacralBladder, bowel, and sexual function
DermatomeArea of skin innervated by the left and right dorsal roots of a single spinal segment. One-to-one correspondence
MyotomeMotor nerve
Rexed laminaeGrey matter of the spinal cord. Laminae I-VI: mostly sensory, lamina VIII: motor interneurons, lamina IX: motor neurons
Afferent neuronCarries sensory information to the brain
Efferent neuronCarries information away from the brain
Grey MatterAppears darker than white matter because it contains neurons and cells
White MatterContains tracks (axons)
Posterior column trackCarries information that needs to travel to the brain quickly

Descending Motor Pathways

Question Answer
Lateral pathwaysVoluntary control of distal musculature
Corticospinal tract (CST) (pyramidal tract)Originates from the motor cortex
Rubrospinal tract (RST)Originates in the magnocellular portion of the red nucleus of the midbrain
Lesions in the CST and RSTUnable to make fractionated movements of the arms (independent motion of shoulders, elbows, wrists, and fingers). Voluntary movements slower and less accurate
Lesions in CST aloneSimilar deficits as lesions in both CST and RST but reversed after a few months. No recovery if RST also lesioned
Ventromedial pathwaysPosture and balance
Vestibulospinal tractKeep head balanced on shoulders
Tectospinal tractHead orientation, receives input from retina
Pontine reticulospinal tractHelps maintain posture by resisting the effects of gravity
Medullary reticulospinal tractLiberates anti-gravity muscles from reflex control. Opposite effect of pontine reticulospinal tract


Question Answer
SynergistsMuscles that work together
Antagonists Muscles that work in opposite directions (extensors and flexors)
Axial musclesMuscles that control the trunk (posture)
Proximal muscles Muscles that move the shoulder, elbow, pelvis, and knee (locomotion)
Distal musclesMuscles that move the hand, feet, and digits (object manipulation)
Muscle spindles (stretch receptors)Structures specialized for proprioception
Intrafusal fibersModified skeletal muscle fibers contained in muscle spindles
Extrafusal fibersLie outside the muscle spindle and form the bulk of the muscle
Aδ fibersMyelinated. Carry information for sharp pain
C fibersUnmyelinated. Carry information for dull pain

Spinal Control of Movement

Question Answer
High level overviewprimary motor cortex > CST > motor neurons/interneurons > muscle control
Ventral rootsFormed from bundles of axons of lower motor neurons
Spinal nerveFormed when a ventral root and a dorsal root join. Spinal nerves exit the spinal cord through the notches in between the vertebrae
Mixed spinal nervesContain both sensory and motor fibers
Alpha motor neuronsInnervate extrafusal fibers
Gamma motor neuronsInnervate intrafusal fibers
Motor unitOne alpha motor neuron and all the muscle fibers it innervates
Motor neuron poolCollection of alpha neurons that innervate a single muscle
Muscle contractionStrength of contraction is increased by recruiting more motor units and increasing firing rate


Question Answer
Epidural stimulationClinical application for pain management after spinal cord injury
Intraspinal stimulationStimulator inserted in the spinal cord below the injury. Targeting issues, stability issues, tissue trauma, electrode biocompatibility, and safety and reliability of applied stimulation

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