PNS Lecture 1: Structural Components and Spinal Nerves

structural components of the peripheral nervous system

-sensory receptors

-nerves

-motor endings

-ganglia

sensory receptors

respond to stimuli and initiate signals in sensory axons

nerve

bundle of nerve fibers (peripheral axons)

motor endings

axon terminals of motor neurons

-innervate effector organs

ganglia

clusters of cell bodies

nerves- structural overview

-contain myelinated and unmyelinated axons

-mostly mixed (contain sensory and motor)

-connective tissue coverings: endoneurium, perineurium, epineurium

endoneurium

layer of loose connective tissue surrounding each axon

perineurium

dense connective tissue surrounding a bundle of axons (nerve fascicle)

epineurium

dense connective tissue sheath surrounding whole nerve

types of nerves in peripheral nervous system

-spinal nerves (31 paired), 4 nerve plexuses (cervical, brachial, lumbar, sacral)

-cranial nerves (12 paired)

spinal nerves of the body

-each nerve contains thousands of nerve fibers

-named according to the spinal cord segment they are attached to

-cervical nerves: C1-C8 (C1 exits above C1 vertebra, the rest all exit below corresponding vertebrae)

-thoracic nerves: T1-T12

-lumbar nerves: L1-L5

-sacral nerves: S1-S5

-coccygeal nerve: CO1

structure of spinal nerves

-connect to the spinal cord via a dorsal and ventral root

-roots formed via rootlets

-spinal nerve branches into a dorsal and ventral ramus

-rami communicantes connect to the base of the ventral ramus, lead to the sympathetic chain ganglia (thoracic region)

dorsal root

contains sensory fibers (from dorsal horn)

-cell bodies located in dorsal root ganglion

ventral root

contains motor fibers (from ventral horn)