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 AnatomyCentral 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 ReflexesStretch reflex – patellar reflexTendon reflex – produces relaxation in

antagonist musclesWithdrawal reflex – touch hot objectCrossed extensor - causes opposite

motion on other side of body