Velocity of Nerve Signal Conduction, Physiology of Synapses Flashcards
1
Q
What causes Conduction Velocity to change?
A
- Resistance of Membrane (Rm)
- Capacitance of Membrane (Cm)
- Resistance of Interior (Ri)
2
Q
Resistance is …
A
resistance to flow
3
Q
Capacitance is
A
stored electrical charge
4
Q
capacitance =
A
1 / resistance
5
Q
smaller effective resistance =
A
faster velocity
6
Q
Effective resistance is proportional to
A
SQRT(RmRi)(Cm)
7
Q
membrane capacitance increases when
A
the membrane area increases
8
Q
membrane capacitance decreases when
A
the membrane area decreases
9
Q
Effective Resistance Equation
A
ER is proportional to SQRT((2/pirl)(1/pirSQ))(2pirl)
10
Q
Causes Rm decrease x2, Ri decreases x4, Cm increase x2
A
doubling the radius of a nerve
11
Q
larger diameter fibers
A
faster conduction velocities
12
Q
Myelin results in
A
faster velocity
13
Q
Why does myelin increase conduction velocity?
A
- Schwann cell membranes (decrease capacitance, increase Rm)
- Saltatory conduction (impulse jumps from one Node of Ranvier to another, less Na+/K+ ATPase and energy required)
14
Q
Schwann cell wrap of 25
A
Lowers Capacitance 50 fold, increases Rm 50 fold.
Always doubled
15
Q
Autoimmune demyelinating diseases
A
Multiple Sclerosis
ALS (Amyelotropic Lateral Sclerosis)
16
Q
close (2-3 nm), gap junction, electrical current crosses without chemicals, common in the heart
A
Electrical Synapses
17
Q
wider (30-50 nm), begins with arrival of action potential, accounts for most of delay in signal transduction (0.5 msec)
A
Chemical Synapses
18
Q
Synapses Steps
A
- Action potential impulse
- Voltage gated calcium channels open
- Calcium enters the Presynaptic Ending (down the concentration gradient)
- Release of Neurotransmitter (exocytosis)
- Neurotransmitter moves across synapse and binds to a receptor
- Transient change in postsynaptic membrane ion permeability
- breakdown of neurotransmitter by specific enzyme, recycling of products
- Membrane potential altered in Postsynaptic cell
19
Q
Causes the synapse stimulation to cease
A
- negative feedback from the Neurotransmitter at Presynapse
- degradation of neurotransmitter at receptor
20
Q
cell body to axon flow impulse 99.9% of the time
A
orthodromic
21
Q
axon to cell body flow of impulse
A
antidromic
22
Q
3 causes of synaptic delay
A
- release of the neurotransmitter
- travel of the neurotransmitter across synapse
- binding of the neurotransmitter to the post synaptic receptor
23
Q
activates neurons to fire
A
Excitatory Post-Synaptic Potential (EPSP)
24
Q
EPSP fast
A
increase in Na+ conductance
25
EPSP slow
decrease in K+ conductance
26
stops neurons from firing
Inhibitory Post-Synaptic Potential (IPSP)
27
IPSP fast
increase in Cl- conductance, hyperpolarizes cell, harder to depolarize
28
IPSP slow
increase in K+ conductance
29
2 impulses at the same time that total threshold
Spatial Summation
30
2 impulses in rapid succession that total threshold,
second comes before the first degrades
temporal summation
31
Presynaptic facilitation
simulation of Ca++ channel opening,
more neurotransmitter released
32
inhibition of Ca++ channel opening, reduces amount of neurotransmitter released
presynaptic inhibition
33
multiple nerve impulses work toward one result
Convergent neural network
34
one neural impulse works to make multiple results
Divergent neural network
35
mediated by acetyltransferase
Choline + acetyl Co A
Acetyl choline (ACh)
36
General Action of Acetyl Choline
parasympathetic stimulation (low HR, low BP, fast GI)
neurotransmitter for neuromuscular junction (nerve to muscle)
37
cholinergic receptor that is stimulated by acetylcholine located on smooth muscle, cardiac muscle, glands, and brain and stimulates the parasympathetic nervous system when activated
Muscarinic Cholinergic receptor
38
stimulated by Muscarine, blocked by atropine
Muscarinic Cholinergic receptor
39
located at neurons, skeletal muscle, and on the brain
stimulates the sympathetic nervous system when activated
Nicotinic Cholinergic receptor
40
stimulated by nicotine, blocked by curare
Nicotinic Cholinergic receptor
41
prevents degradation of ACh message, causes synapses to get stuck
1 mg is lethal
Sarin, VX Nerve Gas (AChe inhibitor, Organophosphate)
42
breaks down Acetylcholine
Acetylcholinesterase (AChe)
43
reverses Sarin, VX Nerve Gas effects
Atropine + Pralidoxime autoinjectors
43
few ACh receptors due to autoimmune degradation
Myasthenia gravis
44
decreased ACh synthesis in brain
Alzheimer's disease
45
anti-smoking drugs
nicotrol - nicotine replacement therapy
chantix - ACh agonist/antagonist
zyban - Dopamine reuptake inhibitor
46
Catecholamines
Serotonin
Histamine
Biogenic Amines
47
Norepinephrine
Epinephrine
Dopamine
Catecholamines
48
Amine synthesis
Dietary Tyrosine + Tyrosine hydroxylase = Dopa
Dopa + Dopa decarboxylase = Dopamine
Dopamine + Dopamine B- Hydroxylase = Norepinephrine
Norepinephrine + N-methyltransferase = Epinephrine
49
Norepinephrine deactivation methods
Monoamine Oxidase (MAO, in many Anti Depressants)
Catechol-O-Methyltransferase (COMT, peripheral tissues, liver, kidney, etc)
50
Nerve tracts using Epinephrine, Norepinephrine
Adrenergic Fibers
51
General Action of Epinephrine and Norepinephrine
sympathetic stimulation (HR up, BP up, GI tact slow)
E and NE have different actions depending on Receptor Types
52
Alpha Receptor
Beta Receptors
Adrenergic Receptors
53
Adrenergic Receptor with a greater affinity for NE
Alpha receptors
54
Adrenergic Receptor with a greater affinity for E
Beta receptors
55
stimulates contraction of smooth muscle, (vasoconstriction)
in vessels and the sympathetic nerve tract
IP3
Alpha 1 receptor
56
inhibition of smooth muscle contraction in GI tract
common in GI tract + pancreas
decreases cAMP
Alpha 2 receptor
57
stimulates heart rate, contractility, Kidney, fat lipolysis, increases cAMP
Beta 1 receptor
58
inhibits smooth muscle, increases cAMP
in lungs, heart, skeletal muscle blood vessels
Beta 2 receptors
59
fat exclusively, lipolysis, increases cAMP
Beta 3 receptors
60
ACh AND nicotinic receptors are present in which nervous system?
Somatic Nervous system
61
sympathetic pathways distribution
distributed in thoracolumbar area of spinal cord
ventral roots of the spinal nerves, system runs parallel to the spinal cord
62
short fibers in the ANS, use ACh as their neurotransmitter
sympathetic pathways
Preganglionic fibers
63
long fibers in the ANS, use NE as a neurotransmitter
sympathetic pathways,
adrenergic receptors on target tissue
Postganglionic fibers
64
parasympathetic pathways distribution
distribution via cranial nerves and pelvic nerves from the sacral region
cranial nerves, 3, 7, 9, and 10 have 90^ of the body's parasympathetic fibers
65
long in length use ACh as their neurotransmitter
parasympathetic pathways
preganglionic fibers
66
short in length, on target tissue, use ACh as their neurotransmitter, cholinergic muscarinic receptors are on the target tissue
postganglionic fibers
67
CNS neurotransmitter, pleasure pathways
Dopamine
68
Methamphetamine and Cocaine affect this neurotransmitter ...
Dopamine
69
Parkinsons disease in caused by a lack of this neurotransmitter ...
and is treated with this therapy ...
Dopamine
L-Dopa therapy
70
derived from Tryptophan (milk, turkey)
catabolized by MAO
excitatory for muscle
inhibitory for sensation
seratonin
71
amino acid neurotransmitters
glutamate, aspartate, glycine, GABA (Gama Amino Butyric Acid)
72
excitatory in CNS, important for learning and memory
glutamate and aspartate
73
inhibitory in CNS, anesthetic action
Glycine and GABA
74
4 modes of action for alcohol
1. Activates GABA pathways (inhibitory)
2. Activates Adenosine receptors (inhibitory)
3. Blocks Glutamate pathways (stimulatory path, inhibited)
4. Membrane soluble (inhibits/slows down second messenger pathways)
75
Neuropeptide Examples
Endogenous Opioids
Morphine (Codeine, Oxycodone, Ketamine)
Substance P
76
released in the presence of a stressor
stress, defense, repair, survival system
Vasodilator
Substance P
77
Action of Endogenous Opioids
Analgesic
Reduces Pain
78
Assists in memory and learning
Possibly protects the brain from neuronal damage in a stroke
Nitric Oxide
