Histology of the Nervous System Flashcards
classifications of neurons based on morphology
unipolar
pseudounipolar
bipolar
multipolar
motor neurons
efferent neurons, multipolar with many dendrites and one long axon
somatomotor neurons and sympathetic neurons have this morphology
sensory neurons
afferent neurons
pseudounipolar with cell body in the dorsal root ganglia with a short, single process that divides into a long afferent process brining impulses from sensors in the body wall or viscera and a shorter, efferent process that enters the dorsal horn of the spinal cord via the dorsal root
interneurons
short, multipolar neurons in the spinal cord that are involved in reflexes by receiving a sensory impulse in the dorsal horn and relaying it to somatomotor neurons in the ventral horn
neurogli or glial cells
non-conducting cells that provide structural, metabolic, and functional support for neurons
supporting cells in the CNS
neuroglia and ependymal cells that form the epithelium lining the CSF-producing ventricles and central canal of the spinal cord
include oligodendrocytes, astrocytes, and microglia
supporting cells in the PNS
Schwann cells and satellite cells
Schwann cells
surround axons in both unmyelinated and myelinated nerves
produce the myelin sheaths in myelinated nerves - lipid rich, happens in nerves to muscle or sensory form body wall
does not myelinate neurons going to or from the visceral compartment
satellite cells
functions similarly to Schwann cells, but surround the nerve cell bodies instead of the axons
oligodendrocytes
the CNS equivalent of PNS Schwann cells
they produce myelin and myelinates many axons with extensions of cell processes, forms many internodal segments
astrocytes
a scaffolding in brain tissue and have cell processes that surround neuron processes and that also extend to blood vessels
microglia
phagocytic cells
What do astrocytes and oligos develop from?
neural crest
What does microglia develop from?
monocyte precursors in the bone marrow
blood-brain barrier
established by artery endothelium tight junctions
astrocyte end feet help this structure
perkaryon
the cytoplasm of neurons
Nissl bodies
compact stacks of rER that extend into the dendrites
axon hillock
the tapering of the cell body at the origin of the axon
lack of Nissl bodies is an easy way to distinguish dendrites from axons
dendritic spines
structures that increase the surface area for synapses
dendrites
relatively short and branch to varying degrees
axons synapse on dendrites
distally, dendrites contain microtubules and nuerofilaments for transport of materials in both directions
they also have free ribosomes that distinguish them form axons
autoimmune target in multiple sclerosis
myelin basic protein, helps form myelin sheaths
part of the intracellular compartment of layers calle dmajor dense lines
myelin sheaths
made by Schwann cell wrapping around the axon
cytoplasm and organelles of the Schwann cells are squeezed to the periphery to form the neurilemma or Sheath of Schwann, consists of stacked layers of Schwann cell membrane
proteins/glycoproteins with positive charges help compact the layers by connecting cell membranes
axons
carry impulse from cell body to toher neurons or effector cells like muscle, and can be many feet long
initial segment is the thinnest part betweent he axon hillock and the myelin sheath, it is the site where the axon potential is generated
most of the length of an axon contains microtubules and neurofilaments and mitochondria like dendrites, but typically lack ribosomes, required for transport of materials since most everything is manufacutred in the nucleus
slow transport
0.2-4 mm/day
only anterograde (cell body to terminal)
conveys structureal elements like tubulin, actin, neurofilament proteins and other matrix proteins and enzymes
fast transport
20-4000 mm/day
both directions
anterograde fast transport is for membrane-limited organelles, synaptic vesicles, mitochondria, and low molecular weight molecules such as amino acids, neurotransmitters, sugars, and calcium
retrograde fast transport to the cell body is for similar components plus molecules endocytosed at the terminal
nerve impulse
membrane depolariztion due to sodium ion influx, creating an action potential
synapse
specialized site of transmission of an impolse from one neuron to another or from a neuron to a muscle cell or gland cell
directions of synapses
axodendritic - axon to dendrite
axosomatic - axon to cell body
axoaxonal - axon to axon
axospinous - on dendritic spines
features of a synaptic bouton
synaptic vesicles with neurotransmitters
mitochondria and smooth ER
presynaptic density with conical dense, inward projections of the membrane
synaptic cleft, which is the EC space
postsynaptic density on the cytoplasmic side of the postsynaptic membrane
steps of impulse transmission
action potential
opens voltage-gated ion channels
calcium enters terminal
triggers neuroransmitter release through exocytosis
neurotransmitter attaches to postsynaptic receptors
conformation change opens ion channels
propagation of impulse
two consequences of impulse transmission
excitatory postsynaptic potential
inhibitory postsynaptic potential
Schmidt-Lanterman clefts
narrow bands of continuity of cytoplasm from the axon to the exterior of the sheath
Node of Ranvier
the exposed axon segment between sequential Schwann cells
action potentials exhibit saltatory conduction as they jump form one node to another, which is faster than continuous conduction
intraperiod lines
the extracellular layers of myelin sheath
protein O
a transmembrane glycoprotein that connects adjacent layers in both the intracellular and extracellular domains
a major structural component of myelin
internodal segments or internodes
the Schwann cells with their myelin sheaths
unmyelinated neurons
usually go to and from internal viscera such as the intestines
one Schwann cell surrounds many axons of unmyelinated nerves
epineurium
the connective tissue sheath enveloping the entire nerve
endoneurium
the delicate connective tissue around each individual neuron and its Schwann cell neurilemma
perineurium
surrounds groups of neurons, but is not the equivalent of connective tissue perimycium in skeletal muscle
dense fibrous layer that helps form a nerve/blood barrier in the PNS an dhas properties of connective tissue, epithelium, an dmuscle
perineurial cells produce collagen-like fibroblasts, have tight junctions wtih each other as well as contractile filaments as in muscle cells, what makes nerves contract when severed
nerve injury
only the distal segment dies
if the cut segments are realigned, the axons can regenerate and reattach to the detached segment
regenerating axons grow about 1 mm per day
