Neuro (3) Flashcards
(84 cards)
1
Q
overall organization of the nervous system
A
NS: CNS + PNS
CNS: brain + spinal cord
PNS: afferent division + efferent division
afferent division: enteric nervous system
efferent division: ANS + somatic NS
ANS: parasympathetic NS + sympathetic NS
2
Q
what does the afferent division of the PNS regulate?
A
gastrointestinal processes
- smooth muscle
- exocrine glands
- some endocrine glands
3
Q
what type of control does the somatic NS act under
A
voluntary control
4
Q
under what types of control does the enteric NS act under
A
- autonomously OR
- controlled by the CNS via the autonomic NS of the PNS
5
Q
Types of cells of the nervous system
A
neurons and glial cells
6
Q
neurons
A
are excitable cells that generate and carry electrical signals
7
Q
glial cells
A
aka neuroglia
are NONexcitable cells that provide physical and biochemical support for neurons
8
Q
neurons vs glial cells: classification
A
neuron types are classified based on STRUCTURE and or function
glial cell types are classified based on LOCATION/function
9
Q
where are glial cells found
A
in the CNS and PNS
10
Q
4 types of glial cells found in the CNS
A
- ependymal: create barriers… BBB
- astrocytes: take up K, water and NT
- microglia: act as scavengers
- oligodendrocytes: form myelin sheaths for several cells
11
Q
what do ependymal cells and astrocytes have in common in CNS?
A
both are a source of neural stem cells
12
Q
total 4 functions of astrocytes in CNS
A
- take up K, water and NT
- secrete neurotrophic factors
- help form the BBB
- provide substrates for ATP production
13
Q
2 types of glial cells found in the PNS
A
- schwann cells: form myelin sheaths for 1 neuron, and secrete neurotrophic factors
- satellite cells: support cell bodies
14
Q
parts of neuron and functions
A
- dendrites - receive incoming signals
- cell body/soma: nucleus and axon hillock - integrate info (can also receive info)
- axon - carry outgoing info to axon terminal
(myelin sheath)
(nodes of ranvier)
(presynaptic axon terminal, synaptic cleft, postsynaptic dendrite)
15
Q
synapse
A
region where an axon terminal communicates with its postsynaptic target cell (muscles, glands, into bloodstream etc)
16
Q
neuron vs nerve
A
neuron: 1 cell
nerve: bundle of axons from multiple neurons
17
Q
what does the axon decide
A
whether an AP should be fired or not
18
Q
functional categories of neurons and differentiation
A
sensory: sensory info travels from afferent nerve fibers to sensory nerve and then CNS
interneurons: transmit info from neuron to neuron - sensory to motor… acts as middle man
efferent: carry neural impulses away from the CNS and toward muscles, glands, and organs to initiate movement.
- based on signal direction
19
Q
where are interneurons found
A
only CNS
20
Q
how to differentiate sensory vs inter vs motor
A
sensory: long dendrite, no cell body, short axon
inter: widely branched dendrites; no axon
motor: short dendrite, cell body, long axon
21
Q
how are neurons put in structural categories
A
based on location of axon relative to cell body
22
Q
structural categories of neurons
A
pseudounipolar
bipolar
anaxonic
multipolar
23
Q
pseudounipolar and bipolar neurons
A
both act as sensory neurons
pseudounipolar: has 1 process called the axon, dendrite is fused with axon during development
bipolar: has 2 relatively equal fibers extending off the central cell body
24
Q
anaxonic neurons
A
act as interneuron
has no apparent axon
25
multipolar neurons
act as interneuron and efferent neurons
int: highly branched but lacking LONG extensions
eff: has 5-7 dendrites that branch 4-6x, a singular LONG axon can branch several times at the end at enlarged axon terminals
26
what does different neuronal shapes reflect
different functions
27
where is it and what does the schwann cell nucleus tell us
pushed to the outside of the myelin sheath
tells us where we are in the PNS
28
node of ranvier
section of unmyelinated axon membrane between 2 schwann cells
*myelinated axon segment is 1-1.5mm long
29
3 diseases of demyelination
1. multiple sclerosis
- autoimmune degeneration of CNS myelin: progressive disease that results in cognitive defects
2. guillain barre syndrome
- autoimmune degeneration of PNS myelin:
sudden onset and usually temporary, results in paralysis... ZEKE VIRUS!?
30
in general, what do the diseases of demyelination lead to?
LEAD TO impaired conduction of electrical signals along axon
- loss of function depends on neurons/nerves affects
31
what are chemically gated channels important for and why?
- for a synapse as they are responsible for the open/closure to NT that could be needed for synapse
32
what are voltage gated channels important for and why?
- for an AP as they are responsible the movement of ions across neuronal membranes: propagation of AP
33
how do neurons react in response to stimulus
they rapidly propagate electrical signals in order to transmit info
34
what are electrical signals changes of
the membrane potential, generated by the movement of ions
35
2 types of electrical signals in neurons
graded potentials
action potentials
36
graded potentials: function, where, GIC involved, ions, signal, strength, signal initiation, uniqueness
function: works as an input signal
where: usually dendrites and cell body
gated ion channels involved: mechanically, chemically or voltage gates
ions involved: usually Na, Cl, Ca
type of signal: depolarizing if Na or hyperpolarizing if Cl
strength of signal: can be summed, depends on initial stimulus
signal initiation: entry of ions through gated channels
uniqueness: no minimum level needed for initiation, 2 signals coming close in time WILL SUM, initial stimulus strength is indicated by freq of a series of AP
37
action potentials: function, where, GIC involved, ions, signal, strength, signal initiation, uniqueness
function: works as a regenerating conduction signal
where: trigger zone through axon
gated ion channels involved: voltage gated
ions involved: Na, K
type of signal: depolarizing
strength of signal: all or none, NO SUMMATION
signal initiation: above threshold graded potential at trigger zone opens up ion channels
uniqueness: threshold stimulation needed for initiation, 2 signals coming close in time WILL NOT SUM
38
EPSP vs IPSP
EPSPs are excitatory signals: they make a neuron more likely to fire an action potential,
- triggered by excitatory neurotransmitters
IPSPs are inhibitory signals: they make a neuron less likely to fire an action potential
- triggered by inhibitory neurotransmitters
39
what is the initial amplitude (strength) of the graded receptor proportional to?
the strength of the stimulus AND the density of the receptor channels
**amplitude = strength of graded potential
40
if the stimulus of a graded potential increases, what happens to the activation of the channels?
activation of channels also increase because the strength of the graded potential would increase which would result in an increase in receptor density
41
what happens when there is an increase in channel density in terms of a graded potential
there is an increase in sensitivity to stimuli
42
when do graded potentials decrease in strength
when they spread out from the point in origin
43
ohms law
ion flow/current depends on the electrochemical gradient of the ion and resistance that opposes the flow
V = IR
44
In a biological convention, what is current the net movement of?
positive charges
45
2 sources of resistance to current flow in cells
Rm = membrane resistance
- varies with channel gating
- increase Rm = membrane insulation
- decrease Rm = open channels to allow ion flow
Ri = internal resistance of cytoplasm
- depends on cytoplasm composition
- inversely related to cell diameter: larger diameter = lower Ri
46
subthreshold graded potential
a graded potential that does not trigger an AP because its electrical potential is below -55mV (-60mV) when its signal is nearing the trigger zone of an axon
47
suprathreshold graded potential
a graded potential that does trigger an AP because their electric potential is above -55mV (-50mV)
48
2 types of signal integration
spatial summation
- occurs when the currents from nearly
simultaneous graded potentials combine
temporal summation
- occurs when 2 graded potentials from 1 presynaptic neurons occur close together in time
49
spatial summation: sub vs supra
sub = 1 inhib and 2 excit neurons fire, but the summed potentials are below threshold so no AP fired
supra = 3 excit neurons fire and their individual graded potentials are all below threshold but summed at the trigger zone, they create a suprathreshold signal and AP is generated
50
trigger zone, which channels live here?
voltage gated sodium channels, they can only be activated at the same time HERE
51
temporal summation: summation vs no summation
summation = AP caused by 2 subthreshold potentials arriving at trigger zone, close in time, allowing them to sum.
no summation = no AP, caused by 2 subthreshold potentials arriving at the trigger zone too far in time
52
5 steps of voltage gated Na channel gating
1. RMP -70 mV: activation gate closes the Na channel
- activation gate is closed
- inactivation gate is open
2. Depolarizing stimulus arrives (-55mV): activation gate opens
- activation gate is open, dependent on voltage
- inactivation gate is still open!!!
3. Na enters cell: since activation gate is open
- headed to +65mV
- activation gate is open
- inactivation gate is open
4. Inactivation gate closes: Na entry stops
- inactivation gate closes FEW SECS after activation gate opened
**inact gate is TIME DEPENDANT not voltage dependant
**due to the entry and stoppage of Na, we got to +30mV
5. Repolarization due to K leaving
- both gates go back to og positions: K+ leaves which causes rest again -70mV... inactivation gate opens up and activation gate closes
53
refractory periods
time period that limits how soon after an AP, another can be fired
absolute and relative
- duration of time where you cant have another AP bc Na channels are busy OR you can get an AP but need a boost: depends the Na availability
54
absolute refractory period
most Nav channels inactivated, K channels open
- no matter how big the EPSP/strength of stimulus, another AP will not fire
- excitability = 0
55
relative refractory period
some Nav channels recovered from inactivation but Kv channels are STILL OPEN
- larger than normal stimulus is needed to account for fewer available Nav channels and hyperpolarizing K efflux
- excitability is still recovering
56
local current flow and charge movement
when a part of an axon depolarizes, + charges move by the local current flow into adj parts of the cytoplasm
- on the extracellular surface, current flows towards the depolarized region
57
local current flow
= when charges move down their electrochemical gradient
current flows faster and farther along large cells (less Ri) with few leak channels
(more Rm) + myelin (more Rm)
58
AP conduction in unmyelinated axons
as current moves along an axon and activates Nav channels, AP is regenerated
- current can move backwards but AP does not due to the refractory period
- the loss of K from the cytoplasm repolarizes the membrane
59
what does myelin allow
prevents charge leakage and allows saltatory conduction
60
myelinated axons and saltatory conduction
allows an electrical impulse to skip from node to node down the full length of an axon, speeding the arrival of the impulse at the nerve terminal
- there is a high density of Na channels at the nodes of ranvier
- no Na channels present along sections of myelin covered axon
61
why does myelin enhance AP propagation?
1. increases Rm, which enhances current flow along axon
2. does not affect AP generation
3. decreases Cm which means less charge is required to be separated to cause a given voltage
- decreases Cm by increases the distance btw ECF and ICF to decrease capacitance
62
Cm
= membrane capacitance, a measure of how much charge needs to be separated across the membrane to produce a given voltage
** a capacitor is something that stores and separates charges, a strong Cap does this over a short distance: THE MEMBRANE IS A STRONG CAPACITOR!
63
membrane potential changes during an AP
1. RMP
- -70mV inside
- K leak channels
- naK
2. Depolarizing stimulus
- arrival of EPSP, reaches supra threshold
3. Membrane depolarizes to threshold
- Nav and K channels open
4. Rapid Na entry = STRONG DEPOLARIZATION
- there is max permeability to Na
- headed towards reversal potential for Na = +65mV
5. Na channels inactivate & slower K channels open
- overshoot... region above 0mV
6. K moves from cell to extracellular fluid
7. Hyperpolarization due to additional K coming
- headed towards Ek
8. Kv channels close
- now after hyperpolarization, = undershoot
9. Cell returns to resting ion permeability and RMP
- Nav channels go from being inactive to closed again
64
what drives the rising phase of AP
the rapid permeability to Na, step 4
65
what drives the falling phase of an AP
rise in permeability to potassium
66
compare and contrast Na vs K channels
Na: order = close, open, inactivate
- open and close faster (explains the sharp peak)
K: open and close, no inactive state
- slower to open and close (spread out peak)
67
explain the rising phase of an AP via feedback loop
the rapid permeability to Na, step 4 = drives the rising phase
Na enter cell
causes depolarization
Nav channels open rapidly
Na enters cell
- but depolarization also triggers slow K channels to open which causes K to leave the cell and then cause repolarization
- eventually leads to ENa, equilibrium but this doesnt happen bc they have an inactivation gate that eventually close them, thats why we got to +30 and not +65
68
Electrical junction
= a gap junction where current flows directly from a cell to another
- gap junctions are made of connexin protein and allow for fast communication and synchronization of activity within a network of cells
69
chemical synapse
= electrical signals in the presynaptic cell, converted into a chemical signal for transmission to the postsynaptic cell
70
events at the synapse (5)
1. AP arrives at axon terminal
- AP depolarizes the axon terminal
2. depolarization open Cav, Ca enters cell
3. Ca entry triggers exocytosis of synaptic vesicle contents
4. NT diffuses across synaptic clef
- NT go to bind with receptors on postsynaptic cell
5. NT binding elicits response in postsynaptic cell
- response is IPSP or EPSP
71
NT termination (3 ways)
1. Nt returned to axon terminals for reuse OR transported to glial cells
2. enzymes inactivate NT
3. NT diffuse out the synaptic cleft
2. ex: acetylcholinesterase = enzymatic breakdown of acetylcholine
72
5 requirements of a NT
1. must be found in the presynaptic neuron
2. must be released in response to presynaptic depolarization
3. must act on specific receptors on postsynaptic neuron to cause a rapid effect
4. after release, signal must be terminated
5. applying NT directly to postsynaptic membrane should have the same effect as when released by a neuron
73
NT ex: GAAALPP
G: gases - NO
A: amines - norepinephrine, epinephrine
A: aa - glutamate, glycine
A: acetylcholine
L: lipids
P: purines - ATP, adenosine
P: peptides - opioids, substance P
74
What codes stimulus intensity?
frequency of AP firing
- strong stim = more AP = more NT released
amount of NT released
- weak stim = little NT released
75
EPSP
excitatory post synaptic potential
= depolarization
= type of graded potential
76
IPSP
inhibitory post synaptic potential
= hyperpolarization
= type of graded potential
77
post synaptic response: ionotropic
fast, mediated by receptor channels
78
post synaptic response: metabotropic
slow, mediated by GPCRs
79
integration of info: divergent pathway vs convergent pathway
divergent = One presynaptic neuron branches to pass info to many downstream neurons
- muscle fibers to motor neurons
convergent = Many presynaptic neurons send input to a smaller number of postsynaptic neurons
- retina of the eye
80
presynaptic inhibition: global (def and steps)
all targets of the post synaptic neuron are inhibited equally
1. excit and inhib presynaptic neurons fire
2. summed signal in postsynaptic neuron is below threshold
3. no AP initiated at trigger zone
4. no response in any target cell
81
presynaptic inhibition: selective (def and steps)
an inhibitory neurons synapses on 1 collateral of the presynaptic neuron and selectively inhibits 1 target
1. an excit neuron fires
2. AP is generated
3. inhib neuron is fired, blocking NT release at 1 synapse
4. 1 target cell does not response
- ex: GABA... Cl?
82
Why is synaptic transmission particularly
vulnerable step in nervous signaling?
many things can go wrong
83
what are problems at the synapse good for?
act as good targets for drug therapy
- receptors are accessible to extracellular fluid
84
Synaptic disease: myasthenia gravis (def, symptoms, cause and treatment)
autoimmune disease where immune sys attacks the neuromuscular junction between somatic motor neurons and skeletal muscles
- symptoms: muscle weakness and fatigue
- muscles cannot contract
- caused by autoimmune-mediated decrease in acetylcholine receptors in post synaptic membrane
- treated with anti-cholinesterase to increase lifetime of acetylcholine in the synapse OR inhibit acetylcholinesterase
