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Week II - more nervous system basics


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Which cranial nerves have components that lie outside the CNS?
III, VII, IX and X
List the three connective tissue sheaths found in a peripheral nerve from the outside in.
1. Epineurium-surrounds nerve
2. Perineurium - surrounds nerve fascicle
3. Endoneurium - surrounds individual exon
Which CT layer of the nerve behaves like a blood-nerve barrier?
The Perineurium
Do the CT sheaths surrounding the nerve have a blood supply or are they avascular?
They have a blood supply
There are two distinct areas seen in a myelinated axon. name them and describe which cellular side they are on.
1. major dense line - cytoplasmic side (dark due to squished proteins in cell)
2. intraperiod line - extracellular side
What are the 2 main proteins found in myelin of peripheral nerves?
1. MBP (myelin basic protein)
2. Po
Charcot-Marie-Tooth disease is a mutation of what? (mutated thing pertains to myelin)
mutation of the Po protein
What is the analog of Po in the CNS? What about MBP?
PLP (proteolipid protein)
MBP has no analog; it is present as itself in the CNS
define the following nerve-nerve synapses: axodendritic, axosomatic, axoaxonic, dendrodendritic
axodendritic: axon synapses on dendrite
axosomatic: axon synapses on soma (cell body)
axoaxonic: axon synapses on another axon
dendrodendritic: dendrite synapses on another dendrite
List the 3 types of ganglia
1. sensory
2. sympathetic
3. parasympathetic
There are 2 types of sensory ganglia. What are they?
dorsal root ganglia
cranial ganglia
autonomic ganglia are characterized by _________ (multi/uni/pseudouni polar) neurons.
In what type of ganglia are neuron-neuron synapses found?
In what type of ganglia are no neuron-neuron synapses found?
Found in autonomic ganglia
not found in sensory ganglia
* What type of nerve cell damage results in cell death?
* What type of nerve cell damage results in regeneration?
* Damage to the perikaryon results in cell death
* Damage to the axonal processes can result in regeneration
What are the three findings observed with perikaryon damage?
1. chromatolysis
2. eccentric nucleus
3. perikaryon swells
Define primary and secondary degeneration. Where does this occur?
occurs in the axon after damage.
1. primary degeneration - degeneration of axon proximal to cut. (minor)
2. secondary degeneration - degeneration of axon distal to cut (complete)
T/F: Schwann cells do not degenerate when the axon they are associated with degenerates.
FALSE. Schwann cells degenerate along with the axon.
What happens to the endoneurium after axonal damage? Why is this critical for regeneration?
The endoneurium remains as a hollow tube and is now called the endoneurial tube. Schwann cells eventually proliferate and fill the tube.
What are Bugner Bands? What is their function?
endoneurial tubes filled with Schwann cells. Axon sprouts grow along these bands.
Distinguish between inter- and intra- cellular signalling.
intercellular - between cells
intracellular - within cells (from one end to another)
What are the advantages of utilizing electrical intracellular transport vs. the other types of transport?
FAST transmission
MODIFIABLE - can increase or decrease signal very easily
diffusion and transport are slow mechanisms and are not modified easily.
neuronal electrical potentials are dependant on 2 things:
1. DIFFERENT ION CONC. on the inside and outside
2. SELECTIVE PERMEABILITY of the plasma memb. to different ions
the electrochemical gradient is formed by two separate forces. what are they?
1. concentration gradients
2. electrical charges
when determinig the voltage potential of a neuron, what is the reference point?
the outside of the neuron is assumed to have a charge of 0.
*What is the resting membrane potential for most neurons?
*What does this mean in regards to charge differences across the membrane?
-60 to -75 mV
*the inside of the cell is more negative than the outside.
what is the difference between an ion channel and an ion transporter?
*ion channel - passive, specific; ions flow down concentration gradient
*ion transporter - active, specific; ions move against concentration gradient & create gradients
which ion is responsible for maintenance of the resting membrane potential?
K+ (flows out of the cell leaving the inside very negative)
At RMP: which ions are very permeable? which ions are not?
Very permeable: K+, Cl-
Not: Na+, Ca++
* K+ and Cl- follow concenration gradient
T/F: at electrochemical equilibrium K+ is moving outside of the cell
FALSE: by the time electrochemical equil. is reached the [K+] on the inside and outside are equal.
the equilibrium potential of K+ is -120 mV. Why is the RMP of a neuron only -60 mV?
This is due to a slight influx of Na+ that makes the RMP more (+)
What is the neuron membrane potential of Na+?
+56 mV
What are two types of graded potentials (which are a subcategory of slow potentials)?
1. Spatial
2. Temporal
Which ion has the greatest influence on the RMP? How about the AP?
RMP -> K+
AP -> Na+
in an AP, what phases does Na+ control and what phases does K+ control?
Na+ controls: rising phase and overshoot phase
K+ controls: undershoot phase and termination
What [exactly] is the factor that initiates the AP?
an increase in Na+ permeability; hence Na+ rushes into the cell
Describe the membrane permeability changes throughout the AP.
Rising and Overshoot phases -membrane very permeable to Na+
Undershoot phase - Na+ permeability turned off, K+ perm. increased
Termination phase - K+ permeability decreases and cell returns to resting state
Describe the changes in the voltage gated ion channels during an AP.
1. RMP - both closed
2. early depolarization - Na+ channels open
3. later depolarization and early hyperpolarization - Na+ channels inactivated; K+ channels open
4. later hyperpolarization - both closed, return to RMP
Why is there a refractory period after an AP?
Na+ channels take a while to "reset."
What is essential for neurons to maintain RMP?
ATP to run their Na+/K+/ATPases
T/F: an AP degrades as it moves along an axon.
FALSE: an AP does not degrade as it moves down the axon. An AP in one area induces an AP in another area, kind of like passing a baton in a relay race.
Why does an AP not spread in both directions down the axon?
The refractory period from where the AP just came from prevents that.
in what part of a neuron does the AP usually start?
the axon hillock
is passive current flow fast or slow?
fast: it is almost instantaneous and is used between the nodes of Ranvier.
Which is faster: saltatory conduction or sequential conduction?
saltatory conduction. sequential conduction occurs in an unmyelinated axon.
List the 3 types of ion channels.
1. voltage gated (only open within a certain voltage range)
2. ligand gated (ion channel opened by specific chemical signal)
3. stretch & heat activated (sensory receptors that generate receptor potentials)
What are the two active transporters that return a cell to RMP?
ATPase pumps
Ion Exchangers
Why are myelinated axons more energy efficient than unmyelinated axons?
myelinated axons have fewer ATPases (only at nodes of Ranvier), therefore they use less ATP.
There are two types of electrical synapses: what are they and how does each type work?
1. Ephatic transmission (ion flow in one axon influences other axons)
2. Gap junctions (pores that connect adjacent cells)
What are the special structures (2) for chemical neurotransmission called and where is each found?
1. terminal boutons (at axon terminal)
2. en passant boutons (along the axonal length)
which is slower: chemical or electrical synapses?
chemical synapses are slower (neurotransmitter must cross synaptic cleft and act on receptors). electrical synapses are virtually instant
Which ion is essential for presynaptic transmission?
Ca++ (rushes into neuron and causes vesicles to fuse w/plasma membrane)
What happens once the neurotransmitter binds to its postsynaptic receptor?
Ion channels open, ions flow in and alter membrane potential in postsynaptic cell. (this may initiate or inhibit an AP here)
in a neuromuscular junction: what is the presynaptic neuron and what is the postsynaptic cell?
presynaptic neuron: a-motor neuron
postsynaptic cell: skeletal muscle
What neurotransmitter is used exclusively by the NMJ and is it (+) or (-)?
ALWAYS Acetylcholine
Where are neuron-neuron chemical synapses found? Are they (+) or (-)
In both the CNS and PNS. May be either (+) or (-)
What is a postsynaptic potential? Is it (+) or (-)
a slow potential that sums temporally and spacially to sometimes form a postsynaptic AP. Can be either (+)EPSP or (-)IPSP
EPSPs are due to the influx of what ion?
What about IPSPs?
EPSPs: due to influx of Na+ or Ca++ (depolarize)
IPSPs: due to influx of Cl- (hyperpolarize)
T/F: EPSPs and IPSPs can sometimes cancel eachother out.
TRUE. When an EPSP and an IPSP occur at the same time the net effect is 0. (they cancel eachother out)
what is presynaptic inhibition of a postsynaptic potential?
when presynaptic axon terminals are inhibited there is no terminal depolarization: therefore no postsynaptic depolarization
Mini end plate potentials sum up to form ___________, which are a form of postsynaptic potential.
end plate potentials
what is the result of a miniature end plate potential?
results in a spontaneous release of one synaptic vesicle worth of neurotransmitter (1 quantum)
What is the difference between secretory vesicles and synaptic vesicles?
secretory vesicles: contain neuropeptides, open anywhere along axon
synaptic vesicles: contain neurotransmitters, open only at terminal or passant boutons.
What is a docking complex?
a specialization in the presynaptic membrane that binds synaptic vesicles.
T/F: synaptic vesicles are recycled. Why/why not?
TRUE - this cuts down on time (otherwise vesicles have to come from neuronal soma)
What determines the number of vesicles released during one AP?
amount of Ca++ influx into cell
What 2 proteins prime the vesicle for fusion to the docking complex of the presynaptic membrane?
SNAP and NSF regulate ___________.
the assembly of SNAREs (SNAP receptors)
what is the name of the protein that binds Ca++ upon its influx into the presynaptic terminal? What is it's other function?
synaptogogmin: also senses Ca++ levels and triggers vesicle fusion
Name the 3 protiens involved in vesicle recycling. what are their specific functions?
1. clathrin - buds recycled vesicles from plasma membr.
2. dynamin - pinches off membranes after budding
3. synapsin - keeps vesicles tethered to cytoskeleton for a reserve pool.
define: neurotransmitter
neural signalling molecules that can act alone
what is the difference between a neurotransmitter and a neuromodulator/neuroeffector?
neurotransmitters act alone (primary signaling molecule)
neuromodulators are secondary neurotransmitters as they modify the signal of the primary neurotransmitter
Give an example of:
1. a neurotransmitter and
2. a neuromodulator/effector.
1. acetylcholine
2. neuropeptides
Give an example of:
1. a small molecule neurotransmitter
2. a neuropeptide
3. a gas neurotransmitter
1. classic transmitters: Ach, glutamate, aspartate, GABA, glycine, ATP, DA, NE
2. any peptide 3-26 aa long
3. NO, CO
small neuropeptides are synthesized in ____________, whereas peptide neurotransmitters are synthesized in ___________.
neuron terminals
cell body
What are the 3 ways a neurotransmitter is removed from the synaptic cleft?
1. diffusion
2. reuptake in neuron or glia
3. degradation
When would a cotransmitter be observed?
when a neuron makes and releases more than 1 neurotransmitter
What decides the neurotransmitter action (whether the AP is (+) or (-))?
type and location of neurotransmitter receptors.
what is the difference between:
1. cell-permeant (intracellular) receptors
2. cell-impermeant (transmembrane) receptors?
1. A lipophilic neurotransmitter crosses the p.m. to access the receptors inside.
2. neurotransmitter binds to receptors found on the membrane.
What are 3 types of transmembrane (cell-impermeant) receptors?
2.enzyme linked - alters intracellular target proteins
3. metabotropic (G-protein coupled), initates GTP-mediated cascade.
which receptor is faster: an ionotropic or metabotropic receptor?
ionotropic - msec response
(vs. metabotropic, sec->min response)
what is the advantage of a metabotropic receptor?
these receptors can amplify signals by activating signal transduction: signal is also long lasting
What is the basic pathway through a metabotropic receptor (binding to eventual physiological response)
NT binds,(+) G-protein,(+) 2nd messenger, this (+) enzymes that alter the phosphorylation of protiens, which alters RNA and protein synthesis.
give an example of 4 second messengers used by metabotropic receptors.
1. Ca++
2. cAMP, cGMP
3. IP3, DAG
4. NO
Regarding Ach:
1. where found?
2. Precursor?
3. Removal mechanism?
4. classes of receptors?
1. NMJ, glands, (+) in CNS
2. acetyl CoA & choline
3. AchE(acetylcholinesterase)
4. nicotinic, muscarinic
nicotinic receptors:
1. type?
2. usually (+) or (-)
3. Agonist?
4. Antagonist?
1. ligand-gated
2. (+) because open to all cations
3. nicotine
4. curare
muscarinic receptors:
1. type (class)
2. two kinds of muscarinic receptors, name&where found?
3. Agonist?
4. Antagonist?
1. metabotropic, in CNS & PNS
2. M1-CNS, M2-peripheral
3. muscarine, pilocarpine
4. atropine, scopolamine
Neurotransmitter used by 95% of ecitatory neurons in brain?
1. where made?
2. precursor?
3. types (classes) of receptors?
1. nerve terminals
2. glutamine (from glia), or glucose (via TCA cycle)
3. both ionotropic and metabotropic
Does glutamate cross the BBB?
NO (therefore it must be synthesized in within the CNS)
PCP and ketamine are antagonists at which receptors? What neurotransmitter normally binds here?
*NMDA receptors
*glutamate normally binds to NMDA receptors
What are the two major inhibitory neurotransmitters of the CNS and, more specifically, where are they found?
GABA (brain)
Glycine (spinal cord)
why is strichnine toxic?
b/c it blocks glycine receptors
catecholamines, seratonin and histamine can all be classified as _____________.
biologic amines
Where is NE made in the CNS?
what is the precursor?
in the locus ceruleus (precursor - tyrosine)
What are the 2 enzymes that remove catecholamines?
Where are they found?
Both found in neurons & glia
what type of receptors do catecholamines use?
metabotropic receptors (that are G protein coupled)
what type of receptors do histamines use?
metabotropic (H1-H4)
which H receptor do antihistamines and anti-nausea medications work against?
1. Where is seratonin made?
2. Precursor?
3. what is the name of the only ionotropic seratonin receptor?
1. main Raphe nucleus
2. tryptophan
3. 5-HT3
what type of receptors are 5-HT1 and 5-HT2 receptors? function?
*metabotropic seratonin receptors
*implicated in higher functions and motor behaviors
What is the source of ATP, AMP and adenosine in the CNS?
comes from mitochondrial oxidative phosphorylation and glycolysis
Purines have what type of receptors?
both ionotropic(+) and metabotropic(-)
how does coffee work?
blocks adenosine metabotropic(-) receptors in the CNS; therefore stimulates
morphine and other narcotics are _________ neurotransmitters. (class) They act at __________ receptors.
m-opiod receptors are what type of receptor? The fact that morphine can act at such a low concentration classifies it as_________ action.
T/F: peptides can be found & released anywhere along an axon. Release is slow
slow release, however, do not need docking complexes to coordinate exocytosis.
What are the 5 terminal branches of CN VII?
what three muscles make up the "nasal group?"
1. nasalis
2. procerus
3. depressor septi
name the four deep muscles of the face
1. buccinator
2. levator anguli oris
3. depressor labii inferiorus
4. mentalis
Name the 8 superficial muscles of the face.
orbicularis oris, zygomaticus major and minor, levator labii superioris, levator labii superioris aleque nasi, depressor anguli oris, platysma, risorius
what muscle is found in the temporal fossa?
Where are the branches of the anterior division of the mandibular branch of CN V going?
motor: to temporalis, masseter, lateral and medial pterygoids
sensory: buccal
What are the branches of the posterior division of the mandibular branch of CN V?
motor: to mylohyoid and ant. belly of digastric
sensory: auriculotemporal n., lingual n, inferior alveolar n.

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