Page 539 - First Aid for the USMLE Step 1 2020, Thirtieth edition [MedicalBooksVN.com]_Neat

Neurology aNd Special SeNSeS ` neurology—AnAtomy And Physiology Neurology aNd Special SeNSeS ` neurology—AnAtomy And Physiology SecTioN iii 495

Peripheral nerve Endoneurium—thin, supportive connective Endo = inner
tissue that ensheathes and supports individual Peri = around
Nerve trunk
myelinated nerve fibers. Epi = outer
Epineurium
Perineurium (blood-nerve Permeability
Perineurium
barrier)—surrounds a fascicle of nerve fibers.
Endoneurium
Epineurium—dense connective tissue that
Nerve fiber surrounds entire nerve (fascicles and blood
vessels).

Chromatolysis Reaction of neuronal cell body to axonal injury. Changes reflect  protein synthesis in effort to
repair the damaged axon. Characterized by:
A
ƒ Round cellular swelling A
ƒ Displacement of the nucleus to the periphery
ƒ Dispersion of Nissl substance throughout cytoplasm
Wallerian degeneration—disintegration of the axon and myelin sheath distal to site of axonal injury
with macrophages removing debris.
Proximal to the injury, the axon retracts, and the cell body sprouts new protrusions that grow
toward other neurons for potential reinnervation. Serves as a preparation for axonal regeneration
and functional recovery.

Round cellular Site of damage Myelin Microglia
swelling debris infiltration
Displacement of
nucleus to periphery
Dispersion of Nissl
substance
Chromatolysis Axonal retraction Wallerian degeneration
Injured neuron

Neurotransmitter changes with disease
loCAtion oF AnXiety dePression sChiZoPhreniA AlZheimer huntington PArKinson
synthesis diseAse diseAse diseAse
Acetylcholine Basal nucleus of   
Meynert
Dopamine Ventral    
tegmentum, SNc
GABA Nucleus  
accumbens
Norepinephrine Locus ceruleus  
(pons)
Serotonin Raphe nuclei   
(medulla, pons)

FAS1_2019_12-Neurol.indd 495 11/8/19 7:39 AM