Nerve Tissue Flashcards
Our body contains on average about how many neurons?
100,000,000
Neurons have a large, rounded usually ___ nucleus with a prominent ____
euchromatic; nucleolus
____ is the cell body which varies in size between 5-135 um
Perikaryon
The RER is extremely well-developed and forms dense structures, visible in the light microscope that are called ____ bodies. These are formed by parallel arrays of RER cisternae.
Nissl
Neurons have very few mitochondria. True or false?
false, have many
Lysosomes are never present in the cytoplasm of neurons. True or false?
false, usually present
Neurons usually lack ____. This means the cell in not capable of cell division.
centrioles
The only neurons that are replaced in an adult human body on a regular basis are the ___ neurons
olfactory
Cytoskeleton of neurons is very well developed and consists of _____, ____ and _____
nerofilaments, microfilaments, and microtubles
Each neuron has how many axons per cell?
only one
Axons begin from an elevated platform on the perikaryon called the ___ ___. Nissl bodies are absent here.
axon hillock
The axon is enclosed by the continuation of the plasma membrane called ____
axolemma
The cytoplasm of the axon does not contain either ___ ___ or ____ but has well-developed ER
Nissl bodies; ribosomes
The transport from the perikaryon to the periphery of the axon is called the _____ flow. The opposite direction is called what?
anterograde; retrograde
What is the motor used in anterograde flow?
kinesin
Slow axonal transport (1-6 mm/day) is used to move substances such as?
tubulin molecules, actin molecules, proteins that form neurofilaments
Fast axonal transport (100-400 mm/day) is used to move what?
membrane bound organelles, such as SER compartments, synaptic vesicles, and mitochondria
The fast retrograde flow provides transport of material taken up by ____ at axon terminal back to perikaryon
endocytosis
Most neurons have several dendrites per cell. Dendrites are designed to deliver the signal form the cell ____ to the ___
periphery; perikaryon
There can be up to ____ synapses in one dendritic tree
200,000
The surface of dendrites is covered with ___ ___, where synapses with axonal process of other neurons are formed. They have a mushroom shape and the head is where the most postsynaptic receptors are located
dendritic spines
Are dendrites myelinated?
no
The cytoplasmic composition of dendrites is similar to that of the perikaryon. They contain ___ and ___, but not ____
ribosomes; RER: golgi
The following describes axon or dendrite:
no nissl bodies; myelin sheath; constant diameter; restricted branching; smooth surface
axon
The following describes axon or dendrite:
nissl bodies; no myelin sheath; tapered; branches profusely; rough surface
dendrite
_____ neurons are primarily sensory neurons that have a single large process that begins from the perikaryon.
pseudounipolar
Where are pseudounipolar neurons usually found?
dorsal root galnglia and some cranial nerve ganglia
____ neurons are sensory neurons that are rather limited in their distribution. They have two processes that extend from the cell body: an axon and dendrite.
bipolar
where are bipolar neurons commonly found?
major sense organs such as: eye retina, olfactory mucosa, and cochlea and semicircular canals of the inner ear
____ neurons represent the most common type of neurons. These neurons have one axon and many dendrites
Multipolar
There are two types of multipolar neurons. Describe each one.
Golgi type I: long axon, large motor neurons found in motor nuclei of CNS
Golgi type II: short axon, interneurons found in the CNS
Nerve cells are similar to muscle cells in the fact that the plasma membrane of a nerve cell is an electric _____, like the sarcolemma of a muscle cell.
capacitor
The voltage on the inner side of the plasma membrane is negative (-70) relative to the outer side, so there is a ____ membrane potential in a resting cell
negative
The concentration of Na+ is ___ X greater outside the cell
10
Define action potential
brief positive going changes in the membrane potential that are propagated along the length of the membrane at a speed up to 120 m/sec
Electrical synapses in mammals are represented by ___ ____, which allow direct passage of ions from one cell to another to transmit the wave of depolarization.
gap junctions
_____ synapses are the principal type of synapses found in mammals. There is no protoplasmic continuity between the two cells and the signal is transmitted by release of NT by one cell.
chemical
____ synapses increase the negative potential, which hyper polarizes the postsynaptic membrane, making it less likely to generate an action potential
inhibitory
Presynaptic ____ contains synaptic vesicles that are 40-60 nm in diameter and contain the NT
knob
As the action potential reaches the presynaptic terminal it opens ___ channels briefly
Ca2+
The influx of Ca2+ into the cytoplasm does what?
causes synaptic vesicles to migrate to the presynaptic membrane and fuse with it. The NT then diffuses across the cleft
After the vesicles with NT fuse to the postsynaptic membrane, what happens to the extra plasma membrane that was formed due to the vesicles fusing?
removed by endocytosis using clathrin-coated vesicles
Up to 80% of the NTs that have been released into the cleft can be recaptured through the mechanism known as ___ ____. The NT is reincorporated by endocytosis into vesicles that are ready for repackaging
high-affinity reuptake
Enzymes associated with synaptic membrane, break down the remaining NT (ex: norepinephrine) that is left in the synaptic cleft. A drug that inhibited these enzymes would be beneficial in treating what?
depression
If the connection is between an axon and a dendrite, the synapse is called _____
axodendritic
If the connection is between an axon and perikaryon, the synapse is called _____
axosomatic
If the connection is between an axon and another axon, it is called ____
axoaxonic
______ ______ represents the neuromuscular junction and is a specialized type of synapse
motor end-plate
What 3 things do motor end-plates consist of?
- axon terminal contains presynaptic vesicles with the NT acetylcholine
- synaptic cleft is the space between the plasma membranes of the nerve cell and the muscle cell
- sarcolemma of a muscle cell forms multiple junctional folds where the sites for acetylcholine are located
Several toxins disable the chemical synapses including motor end-plates and do not allow the depolarization of the sarcolemma. The two best known toxins are the curare toxin and botulinum toxin. Describe each one.
Curare: binds to acetylcholine receptors and acts as a muscle relaxant (fun fact: used by Indians for hunting)
botulinum: produced by clostridium botulinum; prevents release of acetylcholine form the synaptic vesicles (botox is a brand name of this toxin)
Describe the autoimmune disease myasthenia gravis
affects neuromuscular junction, characterized by muscle weakness
mechanism: 1. auto-antibodies to the acetylcholine receptors are produced. 2. auto-antibodies bind to the receptor sites, which weakens the muscle response to nerve stimuli
Describe how Rabies virus works
- virus replicates in muscle after bite (1-2 weeks)
- virus finds motor-end plate and gets into cleft
- virus enters synaptic terminal and via retrograde axonal transport, reaches CNS and spreads to other neurons
- Severe inflammation in CNS - any change in light intensity or sound can cause seizure (ex: running water)
- virus spreads into the salivary glands
- after symptoms have shown up, generally there is no cure
The PNS contains two major types of support cells. What are they?
Schwann cells, satellite cells
Schwann cells form a lipid layer called ___ ____ that surrounds axons in the peripheral nerves
myelin sheath
True or false? myelin sheath is necessary for rapid conduction of electrical impulses
true
Gaps in myelin sheath are called what?
nodes of ranvier
nodes of ranvier have a high concentration of ___ channels
Na+
Action potential in myelinated nerve fibers travels via saltatory conduction, which means what?
the membrane is only depolarized at the nodes of ranvier
True or false?
Schwann cells only support myelinated nerve fibers.
false; both myelinated and unmyelinated
Action potential travels through myelinated fibers using ___ ____ (fast)
saltatory conduction
Describe action potential in unmyelinated fibers
wave-like
Satellite cells provide ___ ___ for the bodies of neurons. How are they different than schwann cells?
electric insulation; do not have myelin
All of the support cells in the CNS stain positive for GFAP, which forms the ___ ____ cytoskeleton of these cells
intermediate filament
____ are among the largest neuroglial cells and provide support for neurons and vascular structures of the CNS. They have a granular cytoplasm and large nuclei; the mitochondria are numerous in the cytoplasm
astrocytes
Astrocytes play an important role in what?
moving metabolic substances between blood and nerve cells and forming the blood-brain barrier
There are two types of astrocytes, protoplasmic and firbrous. Describe them.
protoplasmic: found in gray matter of brain, have numerous short, branching processes that form structures called perivascular feet
fibrous: have more prominent cytoskeleton, found in white matter of the brain, have fewer processes with less expressed branching
Tumors derived from astrocytes are called _____
astrocytomas
note: represent 20% of all brain tumors
Astrocytes give rise to ___% of all tumors that originate in the brain
80
____ are the most common neuroglial cells of the CNS. These are smaller cells, than astrocytes. They have small nuclei, abundant SER and prominent golgi.
oligodendrocytes
There are few tongue-like cell process that extend from oligodendrocyte cell body to wrap around the axons of the neurons of the CNS forming segments of ___ ___
myelin sheath
___ ___ is a disease that is caused by damage to the myelin sheath of the axons in the CNS done by cells of the immune system. It results in the partial loss of the myelin sheath
multiple sclerosis
What are the symptoms of multiple sclerosis?
loss of sensitivity, partial paralysis, etc. depending on the area that is damaged
Microglial cells have distinctive ___ properties.
phagocytic
Microglial cells are derived form ___ ____ and are part of the mononuclear phagocytic system. They are the smallest neuroglial cells.
blood monocytes
Microglial cells have dark indented nuclei and limited cytoplasm. They have few short twisted process that are covered with spikes. The cytoplasm of microglial cells may contain many lysosomes. What is the function of microglial cells?
remove debris from CNS
Microglial cells are abundant in patients with ____ and ____ diseases. It is possible that they are partially responsible for plaque formation, demyelination, and destruction of nerve fibers in the CNS of patients with these diseases.
Alzheimer’s; Parkinsons
The ventricles of the brain and cavities of the spinal cord are lined with ___ cells.
ependymal
Ependymal cells are responsible for what?
production and absorption of CSF
Ependymal cells are arranged in a form of ___ ___ epithelium
simple cuboidal
note: unlike true epithelium, there is no basal lamina
The nerves of the ___ are made of many nerve fibers that carry sensory and motor information between the organs and tissues of the body. They are composed of _____ and ____ axons.
PNS; myelinated; unmyelinated
____ surrounds individual nerve fibers
____ surrounds nerve fasicles
____ surrounds individual nerves
endonerium; perinerium; epineurium
____ are clusters of neuron cell bodies outside the central nervous system.
ganglia
The major types of ganglia are the sensory craniospinal ganglia and the motor ganglia of the ANS. Describe both
Sensory craniospinal ganglia: contain pseudounipolar neurons that have a single process which T-branches not peripheral and central process. The peripheral process goes to receptor organ. the central process goes to spinal cord. Satellite cells surround the neurons of these ganglia.
Motor ganglia: contain multipolar neurons and satellite cells
Special endings can be either motor or sensory. True or false?
true
Free nerve endings are branched sensory endings that do what?
mediate pain
These nerve endings include messiness’ corpuscle, pacinian corpuscle and several others
encapsulated nerve endings
Describe meissner’s corpuscle
cylindrical structure formed by the stacks of lamellae that surround one or two sensory nerve endings. These receptors provide the sense of touch and are most common in the skin of fingers and toes
Describe Pacnian corpuscle
largest encapsulated nerve ending and is most complex. it is spherical in shape and consists of up to 30 concentric sheets of connective tissue with fluid between the layers
Pacinian corpuscles respond to what? Where are they found?
respond to vibration and deep pressure; found in dermis, mesenteries, and inside internal organs
____ are designed to collect information about the angulations of joints and muscle tension
proprioceptors
Inside the muscle spindle are ___ fibers
intrafusal
The ___ nerve fibers wrap around the intrafusal fibers and transmit information about the degree of stretching. The ___ nerve fibers regulate sensitivity of the stretch receptor
sensory; motor
The CNS consists of what?
spinal cord and brain
Clusters of neurons in the CNS are called what?
nuclei
Nerve fibers are organized into ___
tracts
____ matter consists of neuron bodies and unmyelinated fibers that form dense fibrous network
gray
In the spinal cord the ___ matter is internal to the ___ matter
gray; white
note: this is opposite of brain
In the brain, the gray matter is external to the white matter and is often thrown into deep folds called gyri. In the cerebellum these folds are called what?
folia
The three main types of neurons found in the cerebrum are?
pyramidal cells, fusiform cells, and granule cells
In the cerebellum, the gray matter is organized into three layers: The molecular layer, purkinje cell layer, and granular layer. Describe each layer.
molecular layer is most external, contains few cell bodies of neurons called basket cells and numerous cell process
the purkinje cell layer is a thin layer composed of very large neurons called purkinje cells
the granular layer is the most internal layer, adjacent to the white matter. It is highly composed of small neurons called granule cells
White matter consists of what?
myelinated axons and glial cells.
True or false. The white matter has a plentiful blood supply compared to gray matter.
false; limited blood supply compared to gray matter
Generally, there are no synaptic contacts within white matter. True or false?
true
