Nervous Tissue Flashcards
Nervous Tissue Composition
- Receptors
- Neurons
- Supporting Cells
Recepts on nervous tissue
- interacts with the outer world.. gathers info from environment and transduces it into electrochemical energy for coding information
- neurons or specialized epithelial cells
neurons
-receive, analyze, conduct, and transmit coded information
-selectively communicate with other neurons/target cells
BASICALLY: receive info from receptor and sends it to other areas in the body
Glia
specialized non-neuronal cells
supporting cells of nervous tissu
soma
- cell body of a neuron
- contains the nucleus (genetic material) and most protein synthesis capacity of the neuron + lots of other organells
- part of the receptive surface of the neuron
dendrite
extension of soma specializing in receiving input from other neurons
- major receptive surface of neuron
- ALL same organelles as some EXCEPT no nucleus and no golgi aparatus
- conduct excitatory and inhibitory postsynaptic potentials (graded electrical activity) toward the cell body
** as info travels from the dendrite through the soma, the neuronal signal degrades and is summed up before the axis
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axon
conducts information
*after info gets to the axon, no more degradation of the info
synaptic varicosities
- aka axon terminals
- the transmitting region of the neuron
- have vesicles with neurotransmitters for communication with other cells
do neurons have an external (basal) lamina?
no
bipolar neuron
one end dendrite, one end axon
pseudouniporlar neuron
1 process (all axon) looks like it is two processes but really its just one found in the dorsal cord of the spinal cord, and in PNS cells
multipolar neuron
most common neuron
it has 3+ processes (1 axon, many dendrites). having lots of dendrites increases the surface area to collect information
is nervous tissue vascularized
YES; highly, especially where there are many neuronal cell bodies.
Nervous tissue does not posses glycogen, so it need vascularization in order to supply energy
stain for nervous tissue
nissl stain (blue):
DENDRITES/AXON DO NOT APPEAR IN NISSL STAIN
-silver stain (neurofilaments make neurons argyophlic).. stain the IM and dendrites, not nucleus
neuron nucleus
centrally located, large nucleolus, mainly euchromatin (not much heterochomatin) because it uses a lot of DNA to transcribe message for proteins around it
Peryikaryon
- portion of the cell body that surrounds the nucleus (the “cytoplasm” of soma)
- contains Nissl bodies
neuropil
area that surrounds the soma: NOT EXTRACELLULAR SPACE OF CONNECTIVE TISSUE
-contains densely packed neuronal processes (dendrites/axons), glial cell bodies, and blood vessels
what does the area surrounding PNS cell bodies contain?
neuropil + good amount of CT + glial cells
nissl body/granule
- collection of free ribosomes and rough ER synthesizing the bulk of proteinaceous material used by the neuron
- located in the perikaryon
organelles in CNS vs PNS neuron
larger and more obvious in CNS; in PNS neuron appears homogenous basophilic staining o the cytoplasm of most ganglion cells
Have: lysosomes, golgi, microtubules/neurofilaments (IM)/microfilaments (actin) ,mitochondria, smooth ER
Golgi in neuron
very prominent;
needed to because lots of proteins get modified in neuron (get carb added on), also needed because lots of lysosomes etc.
“cytoskeletal” filaments of neuron
- microtubules = (donuts) contribute to cytoskeletal support and move materials throughout the cell, ESPECIALLY down the axon
- Neurofilaments = (dots) IM of neurons, function in cytoskeletal support. Stain with silver.. thus neurons are argyrophilic
- Actin microfilaments = hard to see, prominent in developing neurons and regenerating axons
smooth ER in neurons
- found throughout the neurons
- function: calcium storage for phospholipid synthesis (membrane synth)
neuronal inclusions
NO GLYCOGEN
- lipofuscin granules
- melanin
lipofuscin granules in neurons
- accumulate during aging
- breakdown products that cannot be readily disposed of by the neuron
melanin
synthesize monoamines
why are dendrites visible with a silver stain?
because they contain longitudinal arrayed microtubules and neurofilaments that are agyrophilic
(also contain sER, mitochondria, lysosomes, and ribosomes)
axon hillock
conical elevation where the electrical postsynaptic potential from all dendrites/the soma are summed
-marks the end of nissl bodies and ribosomes
initial segment
- a narrow process from the axon hillock
- where the action potential is generated (all-or-none) and conducted down the axon
axon structural composition
longitudinally arranged microtubules and neurofilaments ALL HAVE + ENDS POINTED TWARD THE AXON TERMINAL
-also have sER, mitochondria, lysosome, actin (NO nucleus or ribosomes)
axonal transport
movement of material, along the axon, that were synthesized in the cell body and that are used in the axon
-basically: axons don’t have ribosomes but they need proteins, so axonal transport is the movement of proteins and other needed material to/from the soma and terminal end
retrograde vs. anterograde axonal transport
retrograde: motor protein dynein used to move necessary proteins FROM Soma TO terminal
anterograde: motor protein kinesin used to move necessary proteins TO soma FROM terminal
* ** powered by ATP-ase. thus LOTS of mitochondria in the axon
Myelin
- spirally wound wrapping of glial cell plasma membrane
- speeds up the conduction by insulating the axon
how is the tight wrapping of glial cell PM on axon achieved?
binding of integral membrane proteins (adhesion molecules) of myelinating cels
how is the action potential conducted in myelinated axons?
it jumps between nodes of ranvier (space between myelin)
what stain is used to see myelin
- osmium tetroxide (especially in PNS)
- stains myelin dark brown/black but leaves the axon unstained; node appears as a gap
what is the conduction speed of myelinated axons depend on?
-number of turns of myelin and the conduction velocity of the action are DIRECTLY proportional to the axon diameter
myelinating cells in PNS vs. CNS
- PNS: schwann cell: YES external lamina; wrap once around and can envelop unmeylinated axon
- CNS: oligodendrocytes:NO external lamina; wrap around several segments and CANONT envelop unmyelinated axons
multiple sclerosis
demyelinating disease that may involve autoimmunity to the unique proteins
can an axon regenerate? in PNS or CNS? why
yes, in PNS, due to the presence of the external lamina
varicosity
- an axon terminal
- contains synaptic vesicles with neurotransmitters
- axon loses myelin at the target
arborize
repeated branching of UNMYELINATED axons at a varicosity/ axon terminal
synapse
- sites of neurotransmitter release at the end of a varicosity
- ONE WAY COMMUNICATION between cells
- contains proteins that help to stabilize the membrane
- has a presynaptic membrane, synaptic cleft, postsynaptic membrane
presynaptic membrane
- has neurotransmitter
- synaptic vesicles crowd at the presynaptic membrane
- appears more electron dense than a plasma membrane
synaptic cleft
extracellular space between pre/post synaptic membrane
postsynaptic membrane
- on the target cell
- contains receptors and ion channels activated by the neurotransmitter
- appears more electron dense than a plasma membrane
How does a synaptic vessel release a neurotransmitter?
- normal axonal varicosity conditions (see other card)
- AP generated causes an increase in ca2+
- causes synapsin to release the secretory vesicle
- vesicle has v-SNARE that binds to t-SNARE on the presynaptic membrane, brining fusion protein close to the presynaptic membrane
- fusion binds to the presynaptic membrane and the contents of the vesicle flood the synaptic cleft
- neurotrans binds to post-synaptic membrane ca2+ channels causes propragation of the AP
- the presynaptic membrane is removed via exoctyosis and the proteins are recycled
normal conditions of snaptic vesicle
- low ca2+
- v-SNARE on the vesicle (docking protein)
- fusion protein on the vesicle (docking protein)
- t-SNARE on the presyanptic membrane
- synapsin (cytoskeletal protein) binds the vesicle to an actin filament
neuromuscular junction neuronal vs. skeltal muscular components
neuronal: active zones (axon components)
muscular: synaptic trough, junctional fold, external lamina
synaptic trough
- in neuromuscular junction
- a depression in which the axon arborization is embedded
- in the muscle cell
active zone
in the neuromuscular junction, where the synaptic vesicles crowd near the presynaptic membrane
junctional folds
in the NMJ
- secondary series of small folds direction opposite the active zone
- lip of the fold contain Ach receptor
external lamina in NMJ
- part of the muscular component
- contains the degradative enzymes for the transmitter
- continuous through the synaptic cleft and junctional fold
satellite cells in NMJ
- schwann cells
- cover the surface of the axon arborization
myasthenia gravis
autoimmune disease where body produces antibodies to the Ach receptors, preventing Ach from binding to them, resulting in muscular weakness
CNS function
analyzes sensory information and formulates effector activity
white matter vs. gray matter in CNS
WHITE: contains mostly axons; few neuronal bodies , contain glial cells and axons
GRAY: mostly neuronal cell bodies; few axons.. WELL VASCULARIZED, contain glial cells, some axon and NUCLEI
tract
in white matter of CNS
-axons that have a common origin and destination
blood-brain barrier
endothelial cells within the CNS that form occluding zonules
3 tissue coverings of CNS
ALL COLLAGENOUS
- Dura: thick, tough, dense IRREGULAR CT
- Arachnoid: thinner, collagenous made of many trabeculae creating a space (subarachnoid space)
- Pia Mater: delicate collagenous tissue that follows all of the contours of the brain
ventricles
spaces int eh CNS that are filled with CSF and lined by ependymal cell
-produce CSF via choroid process
ependymal cells
cuboidal ciliated cell that line the ventricles of the spinal column
choroid plexus
within the ependymal cells (in ventricles); PRODUCES CSF
glial cells
supporting cells; include: oligodendrocytes, astrocytes (supportive), microglia (phagocytic), and ependymal (line ventricles)
microglial cells
a glial cell that is phagolytic and derived from monocytes
PNS function
conducts sensory information into the CNS and conducts motor signals to effectors from CNS
nerves
collection of axons in PNS
PNS nerve covering
ALL COLLAGENOUS
- epineurium; outermost sheath around large nerves, continuous with dura
- perineurium; dense CT covering individual nerve fascicles. Provide barrier and contractile properties
- Endoneurium: innermost sheath surrounding individual axons within the nerve (between myelin covering of two different axons); made of loose CT matrix with type III and type I collagen; helps anchor the EL to loose CT
nerve stain recommendation
trichrome to see the coverings (made of collagenous tissue)
sensory division of PNS
- cell bodies enter the dorsal horn of the spinal cord via its dorsal root, but travel with motor fibers peripherally
- psedounipolar cells
- cell bodies reside in dorsal root ganglia
- conduct info to the CNS (afferent)
motor division of PNS
either somatic (skeletal muscle) or visceral (autonomic; smooth muscle) -in both the motor neurons in the spinal cord exit by the ventral roots and join with sensory axons peripherally
cell bodies in CNS vs PNS
CNS: nuclei.. in gray matter
PNS: ganglia
axon bundles in CNS vs. PNS
CNS: tracts; fasciculus, lemniscus.. in white matter
PNS: nerve
is CT present? in CNS vs. PNS
CNS: very little
PNS: lots
myelinating cells in CNS vs. PNS
CNS: oligodendrocytes
PNS: schwann cells
other supportive cells in CNS vs. PNS
CNS: ependymal, astrocytes
PNS: satellite cells
phagocytic cells in CNS vs. PNS
CNS: microglia
PNS: monocyte/Schwann
