spinal cord and spinal nerves major association,reflex and communication center conduction route to...
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Spinal Cord and Spinal Nerves
Major association,reflex and communication center
Conduction route to and from the brain
Structure of the Spinal Cord
About 18 inches longExtends from the foramen magnum
to the level of the 1st-2nd lumbar vertebrae
Very well protected by the vertebral column, meninges, CSF, vertebral ligaments
Gives rise to 31 pairs of spinal nerves
MENINGES
Pia matersub-arachnoid space
Arachnoidsub-dural space
Dura materMeningitis
External Anatomy
Cervical enlargementLumbar enlargementConus medullarisFilum terminale - extension of pia
mater that anchors to coccyxCauda equina
Internal Anatomy
Central canal containing CSFAnterior median fissurePosterior median sulcusGray matter
inner portion in the shape of a butterfly
Anterior, posterior, and lateral gray horns
White matter - 6 columns that contain ascending and descending fiber tracts
These white tracts are paired and decussate
Ascending tracts - Sensory tracts
Descending tracts - Motor tracts
Spinal Nerves
Numbered and named according to the region of cord from which they emerge
Designated by LETTER and NUMBERCoverings - endoneurium,
perineurium, epineuriumAll are mixed nervesArise from 2 roots
RootsDorsal root - is a sensory root
contains sensory nerve fibers carrying impulses toward the CNS into the cord
sensory cell bodies are located in the dorsal root ganglion
Ventral root - is a motor rootcontains motor axons carrying impulses
AWAY from the cord to the peripherymotor neuron cell bodies are located in
the gray matter of the cord
Spinal Plexuses
Cervical plexus - phrenic nerveBrachial plexus - axillary, radial,
ulnarLumbar plexus - femoral nerveSacral plexus - sciatic nerve
tibial nerve and common peroneal
Reflexes
Rapid, involuntary, automatic responses to stimuli
Reflex Arc
Receptor - distal end of a sensory neuron dendrite
Afferent sensory neuronIntegrating center - an association
neuron or the spinal cord itselfEffector neuronEffector - muscle or a gland
Types of Reflexes
Stretch reflex – patellar reflexTendon reflex – produces relaxation in
antagonist musclesWithdrawal reflex – touch hot object
Crossed extensor - causes opposite motion on other side of body