文档介绍：Peripheral Neuropathy (周围神经病) 陶恩祥 (taoenxiang@) 中山大学孙逸仙纪念医院神经科
Peripheral Nervous System
ANATOMY OF PERIPHERAL NERVES
Axons & Myelin
1. Axons thicker than one micron in S and peripheral nervous system (PNS) are myelinated.
2. Myelin is a spiral sheet of cell membrane wrapped around the axon. In S, myelin is produced by oligodendroglial cells and in the PNS by Schwann cells.
Each oligodendrocyte makes multiple segments of myelin that wrap around many axons.
Each Schwann cell makes one segment of myelin.
This is one reason why peripheral myelin regenerates more efficiently.
Nodes of Ranvier
Nodes of Ranvier
are points of discontinuity between adjacent myelin sheaths in which the axon is not covered by myelin.
Unmyelinated axons
Unmyelinated axons are covered by Schwann cell cytoplasm, but there is no spiraling of Schwann cell membrane around them.
position of myelin
The structure of central and peripheral myelin is essentially the same. Myelin posed of 70% lipids and 30% protein.
1. some important differences in myelin proteins S and PNS.
(1) some allergic reaction against PNS myelin does not cause central demyelination and vice versa;
(2) inherited metabolic disorders of myelin proteins that affect peripheral nerves do not damage central myelin.
2. But lipids are similar between PNS S myelin.
So, metabolic disorders of myelin lipids, such as metachromatic leukodystrophy, affect both, the central white matter and peripheral nerves.
Organization of Spinal Nerves:
1. Root – inside vertebral canal
a. dorsal sensory root with a ganglion
b. ventral motor
2. Mixed spinal nerve
3. Rami
a. dorsal - mixed to skin and muscles of back
b. ventral - mixed “spinal nerve” to ventrolateral body surfaces and limbs
c. white municans motor ANS
d. gray municans motor ANS
1.
Fig 14-7
Dermatomes
Sensory innervations by specific spinal nerves Each pair of spinal nerves monitors specific region of body surface.
Clinical significance ?