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