Neurons Flashcards
Constitute the genetic, anatomic, trophic, and
functional units of the nervous system
Neurons
Have the capacity to receive impulses from receptor
organs or other neurons
Neurons
Have lost the capacity to undergo cell division
Neurons
Have the capacity to transmit impulses to other neurons or effector organs
Neurons
Consist of the cell body and its processes, dendrites, and a single axon
Neurons
the name given to the nerve cell and all its
processes
Neuron
excitable cells that are specialized for the
reception of stimuli and the conduction of the nerve impulse
neurons
Single neurite divides
a short distance from
cell body
Unipolar
Many dendrites and
one long axon
Multipolar
Single neurite
emerges from either
end of cell body
Bipolar
Single long axon
Golgi type I
Short axon that are
with dendrites resembling a star-
shape appearance
Golgi type II
Location of Unipolar
Posterior root
ganglion
Location of Bipolar
Retina, sensory
cochlea, and
vestibular ganglia
Location of multipolar
Fiber tracts of brain
and spinal cord,
peripheral nerves, and
motor cells of spinal
cord
Location of Golgi Type I
Fiber tracts of brain
and spinal cord,
peripheral nerves, and
motor cells of spinal
cord
Location of Golgi Type II
Cerebral and
cerebellar cortex
Also called the soma or perikaryon
NERVE CELL BODY
Contains the organelles found in other cells, including a large nucleus and a prominent nucleolus
NERVE CELL BODY
Has receptor molecules on its plasmalemmal surface that confer sensitivity to various neurotransmitters
NERVE CELL BODY
Is characteristic of nerve cells and consists of
rossettes of polysomes and rough endoplasmic reticulum
NISSL SUBSTANCE
Plays role in protein synthesis
NISSL SUBSTANCE
Is abundant throughout the cytoplasm and dendrites but is not found in the axon hillock or in the axon
NISSL SUBSTANCE
Are membrane-bound dense bodies that contain
hydrolytic enzymes and are involved in the process of
intracellular digestion
LYSOSOMES
Removes metabolized substances in the
neuron
LYSOSOMES
A genetic defect in the synthesis of lysosomal enzyme
results in a storage disease
(Tay-Sachs disease [GM2
gangliosidosis])
Lysosomes exist in 3 forms
Primary lysosomes: which have just been
formed
o Secondary lysosomes: which contain
partially digested material
▪ Eventually will be needed to
remove from the neuron
o Residual bodies: in which the enzymes are
inactive and the bodies have evolved from
digestible materials
Form an internal supportive network, the
cytoskeleton
FILAMEONTOUS PROTEN STRUCTURES
Largest among the filamentous protein structures found in the neuron
Microtubules (25nm in diameter)
Are found in the cell body, dendrites and axons
Microtubules (25nm in diameter)
Crucial in the development and maintenance of cell shape
Microtubules (25nm in diameter)
Responsible for the intracellular transport of peptide vesicles and organelles
Microtubules (25nm in diameter)
Second largest among the filamentous protein
structures
Neurofilaments (10nm in diameter)
Consists of spiral protein threads that play a role in
developing and regenerating nerve fibers
Neurofilaments (10nm in diameter)
Degenerate in Alzheimer’s disease to form
neurofibrillary tangles
Neurofilaments (10nm in diameter)
Are composed of actin
Microfilaments (5nm in diameter)
Facilitate movement of plasma membrane and
growth of nerve cell processes
Microfilaments (5nm in diameter)
Pigmented inclusions of cytoplasm that accumulate with aging
Lipofuscin (lipochrome granules)
considered residual bodies derived from
lysosomes
Lipofuscin (lipochrome granules)
A blackish pigment in the neurons of the substancia nigra and locus ceruleus
Neuromelanin (melanin)
Disappears from the substancia nigra and the locus ceruleus in Parkinson’s disease
Neuromelanin (melanin)
Are eosinophilic intracytoplasmic inclusion bodies
found in the substancia nigra in patients with
Parkinson’s disease
Lewy bodies
Are intracytoplasmic inclusion bodies found in the
hippocampus in patients with Alzheimer’s disease
Hirano bodies
Are intracytoplasmic inclusion bodies found in people
with rabies
Negri and lyssa bodies
Are processes that extend from the cell body
DENDRITES
Contain cytoplasm similar in composition to that of
the cell body, however no Golgi apparatus is present
DENDRITES
Conduct in a decremental fashion but may be capable
of generating action potentials
DENDRITES
Receive synaptic input and and transmit it toward the
cell body
DENDRITES
Arise from either the cell body or a dendrite
AXONS
Originate from the axon hillock (devoid of Nissl
substance)
AXONS
Give rise to the collateral branches
AXONS
May be myelinated or unmyelinated
AXONS
Generate, propagate, and transmit action potential
AXONS
End distally in terminal boutons in synapses with neurons, muscle cells, and glands
AXONS
Consists of axons and their glial investments
NERVE FIBERS
Are classified by function, fiber size, and conduction velocity
NERVE FIBERS
Is the name given to an axon (or dendrite) of a nerve
cell
NERVE FIBERS
Bundles of nerve fibers found in the central nervous
system are often referred to
nerve tracts
Bundles of nerve fibers found in the peripheral
nervous system are called
peripheral nerves
Diameter
Ia (Aα)
12-20
Diameter
IB (Aα)
12-20
Diameter
II (Aβ)
5-12
Diameter
III (Aδ)
2-5
Diameter
IV (C)
0.5-1
Diameter
Alpha (Aα)
12-20
Diameter
Gamma (Aγ)
2-10
Diameter
Preganglionic
autonomic
fibers (B)
<3
Diameter
Postganglionic autonomic
fibers (C)
1
CV
Ia (Aα)
70-120
CV
IB (Aα)
70-120
CV
II (Aβ)
30-70
CV
III (Aδ)
12-30
CV
IV (C)
0.5-2
CV
Alpha (Aα)
15-120
CV
Gamma (Aγ)
10-45
CV
Preganglionic
autonomic
fibers (B)
3-15
CV
Postganglioni
c autonomic
fibers (C)
2
Proprioception, muscle
spindles
Ia (Aα)
Proprioception, golgi tendon
organs
IB (Aα)
Touch, pressure, and
vibration
II (Aβ)
Touch, pressure, fast pain,
and temperature
III (Aδ)
Slow pain and temperature,
unmyelinated fibers
IV (C)
Alpha motor neurons of
ventral horn
Alpha (Aα)
Gamma motor neurons of
ventral horn
Gamma (Aγ)
Myelinated preganglionic
autonomic fibers
Preganglionic
autonomic
fibers (B)
Unmyelinated
postganglionic autonomic
fibers
Postganglioni
c autonomic
fibers (C)
Sometimes referred to as the insulator of the nerve
fiber; responsible for conducting the appropriate
nerve impulses to the different areas of the body
MYELIN SHEATH
Transmission of nerve impulses is amplified
by the myelin because it uses
saltatory
conduction
Current jumps from one node of Ranvier to
the other
Myelin sheath Is produced in the PNS by
Schwann cells
Myelin Sheath Is produced in the CNS by
by oligodendrocytes
Myelin sheath Is interrupted by the
the node of Ranvier
Consists of a spirally wrapped plasma membrane
MYELIN SHEATH
The smaller axons of the central nervous system, the
postganglionic axons of the autonomic part of the
nervous system, and some fine sensory axons
associated with the reception of pain are
nonmyelinated
In the peripheral nervous system, each axon which is
usually less than 1 nm in diameter, indents the
surface of the Schwann cell so that it lines within a
trough
In the central nervous system, nonmyelinated nerve
fibers run in small groups and are not particularly
related to the
oligodendrocytes
Are the sites of functional contact of a nerve cell with
another nerve cell, an effector cell, or a sensory
receptor cell
SYNAPSES
Consists presynaptic membrane, synaptic cleft, and
postsynaptic membrane
SYNAPSES
axons communicating with
dendrites of another neuron
Axodendritic:
axon communicating directly
with nerve cell body of another neuron
Axosomatic:
axon directly communicating to
the axon of another neuron
Axoaxonic:
dendrites communicating
to dendrites of another nerve cell body
Dendrodendritic:
Arise non-neuronal cells of the PNS and the CNS
NEUROGLIA
Neuroglia Abundant in the __
CNS
Neurons are __, while neuroglia
serve to __
Functional, support
Neuroglia arise from
the neural tube and neural crest
capable of miotic cell division throughout adult
life
NEUROGLIA
best revealed by gold and silver impregnation
stains
NEUROGLIA
Neuroglia classification
Macroglia (astrocytes and oligodendrocytes)
Microglia
Ependyma
Are the largest glial cells
ASTROCYTES
Consist of fibrous astrocytes, which are found mainly
in white matter, and protoplasmic astrocytes which
are found mainly in gray matter
ASTROCYTES
Play a role in the metabolism of certain
neurotransmitters (GABA, serotonin, glutamate)
ASTROCYTES
Buffer the potassium concentration of the
extracellular space
ASTROCYTES
Contain glial filaments and glycogen granules as their
most characteristic cytoplasmic components
ASTROCYTES
In damaged areas of the brain, form glial scars, a
condition called
gliosis
Are the processes that form the external glial limiting
membrane and the internal glial limiting membrane
ASTROCYTIC END FEET
surrounds capillaries
Perivascular end feet:
surrounds neurons
Perineural end feet:
marker
for astrocytes
glial fibrillary acidic protein (GFAP)
Like lipofuscin granules
Residual bodies of the astrocytes
GLYCOGEN GRANULES
Small glial cells with few short processes
OLIGODENDROCYTES
Lack glial filaments and glycogen granules
OLIGODENDROCYTES
myelin-forming cells of the CNS; one
oligodendrocyte can myelinate numerous (up to 30)
axons
OLIGODENDROCYTES
Do not have glycogen granules and glial filaments
o Present in astrocytes
Do not have glycogen granules and glial filaments
o Present in astrocytes
Oligodendrocyte consist of
o Interfascicular oligodendrocytes: found in
white matter
o Satellite cells: found in gray matter
Arise from monocytes, which enter the CNS via
abnormal blood vessels
MICROGLIA (HORTEGA CELLS)
Are activated by inflammatory and degenerative
processes
MICROGLIA (HORTEGA CELLS)
Are macrophages, which are migratory and
phagocytize debris of nerve tissue
o Garbage collectors among the neuroglial
cells
MICROGLIA (HORTEGA CELLS)
Line the central canal of the spinal cord and ventricles of the brain
EPENDYMAL CELLS
Possess cilia only in embryologic stages in man that
originate from blepharoplasts (basal bodies), which
can be stained by phosphotungstic acid-hamatoxylin
(PTAH)
EPENDYMAL CELLS
Include choroid epithelial cells of the choroid plexus
and tanycytes of the third ventricles; the choroid
plexus cells produce CSF and are interconnected by
tight junctions that constitute the blood-CSF barrier
EPENDYMAL CELLS
Are derivatives of the neural crest
SCHWANN CELLS (NEUROLEMMAL CELLS)
Are myelin-forming cells of the PNS; a Schwann cell
myelinates only one internode (only one peripheral
axon)
SCHWANN CELLS (NEUROLEMMAL CELLS)
Invest all unmyelinated axons of the PNS
SCHWANN CELLS (NEUROLEMMAL CELLS)
Function in regeneration and remyelination of
severed axons in the PNS
SCHWANN CELLS (NEUROLEMMAL CELLS)
Are separated from each other by the node of Ranvier
SCHWANN CELLS (NEUROLEMMAL CELLS)
Majority of the tumors in the nervous system (CNS) are arising from
neuroglial cells
Gliomas Are derived from the 3 glial cells:
astrocytes,oligodendrocytes, and ependymocytes
Result from proliferation of glioblasts, embryonic precursors
TUMORS OF THE NEUROGLIAL CELLS (GLIOMAS)
Represent 50% of primary intracranial tumors
TUMORS OF THE NEUROGLIAL CELLS (GLIOMAS)
Benign astrocytomas
Astrocytomas
Malignant astrocytomas (GBM)
Gliobastomamultiforme (most
malignant)
Developed in vestibulocochlear nerve
Schwanommas
Occurs toward the proximal end of an axon, including the cell body
RETROGRADE DEGENERATION
Reaction begins__ days or sooner after injury and
reaches a maximum in about __ days
RETROGRADE DEGENERATION
2, 20
RETROGRADE DEGENERATION Involve
o Disappearance of Nissl substance
(chromatolysis)
o Swelling of the cell body
o Flattening and displacement of the nucleus
from central location to the periphery
Occurs toward the distal end of the axon
* Takes place in both the PNS and the CNS
ANTEROGRADE (WALLERIAN) DEGENERATION
Characterized by successive fragmentation and
disappearance of axons and myelin sheaths and by
secondary proliferation of Schwann cells
ANTEROGRADE (WALLERIAN) DEGENERATION
Nerve supply towards the skeletal muscles will be
affected and may cause atrophy in the long term
ANTEROGRADE (WALLERIAN) DEGENERATION
A myelinated peripheral nerve fiber consists of an
axon, a myelin sheath and its basement membrane,
and a delicate connective sheath, the endoneurium
The severed distal nerve fiber maintains its integrity
and provides a tube of basement membrane and
endoneurium into which an axon sprout grows
REGENERATION OF THE PERIPHERAL NERVE FIBER
Schwann cells proliferate along a degenerating axon
and myelinate a new axon sprout, which grows at the
rate of
3 mm/day
If the path of regenerating axons is blocked, a
traumatic neuroma forms at the
site of obstruction
(amputation neuroma)
No basement membranes or endoneurial
investments surround axons of the CNS
REGENRATION OF AXONS IN THE CNS
Effective regeneration does not occur in the CNS
Interruption of certain CNS pathways results in
degeneration of denervated elements
TRANSSYNAPTIC (TRANSNEURONAL) DEGENERATION
Responsible for transporting all newly synthesized
membranous organelles (vesicles) and precursors of
neurotransmitters at the rate of
FAST ANTEROGRADE TRANSPORT
200-400 mm/day
FAST ANTEROGRADE TRANSPORT
mediated by
microtubules and kinesin (fast transport
is microtubule dependent)
- Facilitates the transport of mitochondria
- Occurs at the rate of
50 - 100 mm/day
FAST MITOCHONDRIA TRANSPORT
Is responsible for transporting cytoskeletal and cytoplasmic elements at the rate of
SLOW ANTEROGRADE TRANSPORT
1-5 mm/day
from cell body towards the
axon down to its terminal ends
Anterograde:
Transports neurofilaments and microtubules
SLOW ANTEROGRADE TRANSPORT
FAST RETROGRADE TRANSPORT
Returns used materials from the axon terminal to the
cell body for degradation and recycling at the rate of
100-200 mm/day
Transport nerve growth factor and neurotropic
viruses and toxins
FAST RETROGRADE TRANSPORT
FAST RETROGRADE TRANSPORT
is mediated
by microtubules and dynein
