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Histo - Week 4 Tues
Terms in this set (62)
clusters of cell bodies in the PNS
protected by bone
only one that has CT, unlike CNS
brain and spinal cord
Function of CT in PNS
protect nerves from external factors
Somatic nervous system *don't care much about
all voluntary muscle systems plus reflex arcs, myelinated, important for firing AP and transmission
automatic nervous system *don't care about much
sensory nerves, myelinated
muscle spindle, nociception, propiception
example of autonomic nervous system
involuntary muscles, grandular secretion, nonmyelinated, so slower
examples of sensory system
primary visceral sensory neurons, nonmyelinated
CO2, O2, sugar in blood, arterial pressure
Three parts of neuron
1) dendrites collects input
2) axon processes info
3) output of cell to tell muscle what to do or tell other neurons to fire
Phenotype affects the ____ of a neuron
Other names for cell body
Why neurons stained?
Because they produce proteins for transmission
Nissl bodies located in ____ and stain because of ____.
stains bc of RER
tree like structures
takes in information/input from other cells or
everything in cytoplasm is in same unit/concentration
Why is axon important?
Neuron sends info thru axon
regulates what goes into axon and synaptic terminal
where action potential is initiated
action potential conduction
only when there is enough input going to input, AP is generated here at the initial segment
Two types of synapses
synaptic vesicles filled with NT
Uncommon, found in limited regions of brain and eyes for fish or others
What does calcium do?
fuse NT vesicles to the plasma membrane to dump NT into synaptic cleft
Ability for neuron to fire depends on
how fast we can clear the NT in the synaptic cleft
3 Ways to clear NT in synaptic cleft
1) Reuptake by presynaptic terminal via transporters
2) Glial cell transporters for reuptake
3) Enzymes that degrades the NT
Takes one millisecond, allows for repetitive fast movement
Possible targets of axons
dendrites, soma, axons
How many inputs can a neuron get?
the dendritic tree and soma can have thousands of synapses providing input
*can have 15,000 at once
not an action potential
only if these add up to sufficient stimulus an action potential is initiated at the axon hillock/initial
How is the threshold met?
A few episodes of sodium channels opening and letting sodium ions in
Once an action potential starts, can we stop it?
No, all or nothing
a period of inactivity after a neuron has fired
Do somas fire action potentials?
No, AP go in the direction of axons
Why does the next part of the axon continue to move the signal toward the axonal terminal and not toward the soma?
Bc the part before is in refractory period so must move toward the resting/axon terminal area
function of chemical synapse
transmit info from one cell to next
mechanism A-D for chemical synapse
A - AP moves down axon to synapse
B - Ca increases exocytosis
C - hyper or depolarization of postsynaptic cell
D - stimulus of post synaptic cells terminated by reuptake or enzymatic degradation of NT
Four characteristics of neuron cell body
very rich in ER (Nissl substance)
Cells in soma
Schwann cells or satellite cells
Edge of nucleus
rough endoplasmic reticulum
White spots in neuron cell picture
white = when treated sample with solvents, so white = ghosts of lipids gone
Why axons need to be resilient?
Because move your body, ex playing baseball
What helps for mechanical support of axons?
What helps with axonal transport in axons?
microtubules - communication device
ex when neuron needs MT, MT made and then transported
Why don't you break your axons when you overstretch?
because axon doesn't go straight, so if extend arm, you don't break it; it is squiggly
movement down the axon away from soma
movement up the axon toward the soma
common motor domain
has diff structures that bind to bring back up
motor proteins that walk along microtubules in an anterograde direction with linkers for cargo
Anterograde - speed
slow transport - brings cytoskeletal proteins, something genetic, so constant supply to build axon
fast transport - good for signaling information
retrograde - speed
What does action potential conduction velocity depend on?
1) axonal diameter
2) myelination (function of a schwann cell
Make AP faster by
1) increasing axonal diameter - less surface area to volume
prevent sodium from escaping by
thicker axon = fast conduction
2) increasing myelination to prevent sodium from escaping
nodes of ranvier
the gap between SCHWANN CELLS of myelinated nerves, speed up action potential by forcing a saltatory conduction (leaping from node to node)
Schwann cells - 4 functions
1) modulate conduction velocity
2) mechanical and metabolic (preventing Na coming in) support
3) axon regeneration after damage
4) extracellular matrix synthesis
process of myelinated axon
schwann cell rolls around axon a bunch, squeezes it to leave little room as possible
*lots of schwann cells wrapping one axon
Where does the AP regenerate?
at the node of ranvier
What are unmyelianted axons protected by and how?
schwann cells, but are not wrapped up completely
there is always one part of axon open to ECM
The axons lie in the schwann cell cytoplasm
satellite cell function
covers the soma/perikaryon/cell body
dense irregular CT, protects neurons, can put finger back and regrow axons; wraps around a bunch of bundles of axons
blood-nerve barrier: squamous cells wrapping around fascicles, tight junctions protect from exterior; wraps around a bundle of axons
similar to epithelium
loose CT, type I collagen, produced by Schwann cells, wraps around each axon
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