ANAT 6. Nervous System Histology.docx

Learning objectives: (LOTS of PRACTICE CONTENT at END of CHAPTER IN BOOK) - - - - - - - CNS PNS ----------------------------------------------------------- -------------------------------------------------------------------...

Learning objectives: (LOTS of PRACTICE CONTENT at END of CHAPTER IN BOOK) - - - - - - - CNS PNS ----------------------------------------------------------- ------------------------------------------------------------------------------- Neurons: transmit rapid electrical signals, long distance Neurons Oligodendrocytes: wrap axons in fatty myelin. Schwann cells Microglia, Astrocytes, Ependymal. Satellite cells: metabolically/chemically support soma in peripheral ganglia. Multipolar: Motor(Efferent), somatic(skeletal) & autonomic. (soma in CNS) Bipolar: Sensory, retina/olfactory/inner-ear. (soma in DRG) Pseudounipolar: Sensory(Afferent), somatic/visceral body sensory, taste. (soma in DRG) DRG Histology: PNS sensory soma(large), Nissi bodies(rER)-basophilic, axons, satellite cells. Nissl bodies: granular substance in cytoplasm of neurons, filled with rER/ribosomes creating proteins from mRNA. Its the RNA that stains. \*Lack of Nissl bodies in an area, suggests beginning of axon. Axonal transport: microtubules allow protein transport between distant locations in a neuron. - - \*Other histologically relevant axon components: Neurofilament(intermediate filaments), microfilaments, mitochondria(especially at axon terminal). Myelination of PNS axons, ↑ speed of electrical signal. (schwann cells wrap axon \~100x at end) Nodes of Ranvier: small gaps in myelination, help signal NOT die out. - - \*Myelination of PNS begins \~11wks, CNS in 3rd trimester. Continuous postnatally in the 1st year of life. "Mostly" humans complete myelination after 2nd year postnatal life. Unmyelinated axons: some w/ small diameter, e.g. 1 type of nociceptive neurons(pain). Small fiber neuropathy. Still supported by Schwann cells metabolically/ionically to keep the cell alive.  Peripheral Nerve Anatomy: 50-90% of mass is CT. - - - - - - - - - - - - - - - In nerves, axons= "nerve fibers" Nerve make-up, E.g. Musculocutaneous N. \~26k axons, only \~1,700 motors, rest is sensory. Chemical synapse: primary type in PNS. Histological expectations: neurotransmitter vesicles in presynaptic terminal, mitochondria, dense cell membranes at synapse(lots of proteins).  Clinical case: \*Bands of Fontana: alternating light & dark bands along nerves. Shown to be nerve fibers running in phase in a sinusoidal pattern down length of nerve. ??