Lecture 11.4 main points

Question 1

define the absolute refractory period, why does this occur (what ion channels play the main role and how)?

Answer 1

after initiating an action potential, there is a period of time called the absolute refractory period during which a cell cannot generate another AP no matter how strong the stimulus
Na channels are activated and then inactivated
inactivated Na channels must first return to the resting state before they can be opened again
not enough deactivated voltage gated Na channels to allow for another AP

Question 2

define the relative refractory period, what type of stimulus is necessary for AP during relative refractory period

Answer 2

period of time during which a second action potential can be initiated, but only by a large-than-normal (suprathreshold) stimulus
coincides with the period when the voltage gated K channels are still open after enough inactivated Na channels have returned to their deactivated resting state to allow for another AP

Question 3

list the phases of AP where the absolute and relative refractory periods take place

Answer 3

absolute refractory period - during depolarization and repolarization
relative refractive period - after hyper-polarizing state

Question 4

where does AP begin ?

Answer 4

at the trigger zone near the axon hillock

Question 5

what are the two types of methods in what AP are conducted

Answer 5

continuous conduction
saltatory conduction

Question 6

which type of AP conduction method is used by myelinated axon

Answer 6

saltatory conduction

Question 7

which type of AP conduction method is used by un-myelinated axons

Answer 7

continuous conduction

Question 8

list the three factors that affect speed of AP conduction

Answer 8

axon diameter- wider diamater = faster curren
degree of myelination - more myelination = faster
temperature - higher temp = faster (to a point) : too high or too low affects ion channels (bc they are proteins)

Question 9

what is the role of frequency of AP and number of neurons signaling for a response at the same time in perception of a stimulus

Answer 9

The frequency of AP plays a crucial role in determining the perception of a stimulus, or the extent of our response.
-In addition to this “frequency code,” a second important factor is the number of neurons recruited (activated) to the cause

Question 10

list the three types of axon fibers and their characteristics

Answer 10

A fibers - largest diameter and fast (up to 280mph), myelinated neurons that carry touch and pressure sensations; many motor neurons are also of this type

B fibers - medium size diameter and speed (up to 32mph) compromise myelinated visceral sensory and autonomic pre ganglion neurons

C fibers - smallest diameter and slowest (up to 4mph), comprise un-myelinated sensory and un-myelinated autonomic neurons

Question 11

in what direction does communication occur at a chemical synapse ? is this one way or both ways?

Answer 11

a one way transfer from a pre synaptic neuron to postsynaptic neuron

Question 12

list the events involved in the release of NT from the presynaptic cell

Answer 12

When an AP reaches the end bulb of axon terminals, voltage gated Ca channels open and Ca flows inward, triggering the release of the neurotransmitter

-in this way, the presynaptic neuron converts an electrical signal (nerve impulse) into a chemical signal (release neurotransmitter)

Question 13

what effect does the release of the NT from the pre synatic cell have on the post synaptic cell

Answer 13

the neurotransmitter crosses the synaptic cleft and binds to ligand - gated receptors in the post synaptic membrane. The post synpatic neuron receives the chemical signal and in turn generates an electrical signal (post synaptic potential)

Question 14

how does the affect of speed signaling information being relayed by the synapse

Answer 14

the time required for these processes at a chemical synapse produces a synaptic delay of 0.5 msec

Question 15

are NT receptors specific or can any molecule bind and cause an effect?

Answer 15

each neurotransmitter receptor has one or more neurotransmitter binding sites where its specific NT binds

Question 16

what are ionotropic receptors? give an example

Answer 16

receptor that has NT binding site and is an ion channel as well, when a NT binds to the receptor, it opens or closes the ion channel portion of the receptor
-nicotinic ACh receptor is an example

Question 17

what are metabotropic receptors and give an example?

Answer 17

contains NT binding site but lacks an ion channel as part of its structure
-glutamate is an example

Question 18

how do metabotropic receptors directly activate or deactivate ion channels

Answer 18

G-proteins can go on to activate/deactivate separate ion channels (direct)

Question 19

how to metabotropic receptors indirectly activate or deactivate ion channels

Answer 19

G proteins can activate other proteins that go on to activate/ deactivate ion channels

Question 20

what type of neurotransmitters are found in both the CNS and PNS

Answer 20

excitatory and inhibitory

Question 21

is an excitatory NT always excitatory?

Answer 21

no, may be excitatory in some locations and inhibitory in others

Question 22

list main chemical classifications of NTs

Answer 22

amino acids, biogenic amines, peptides (neuropeptides), purines, gases and lipids, endocannabinoids

Question 23

main ways NT effects modified

Answer 23

synthesis can be stimulated or inhibited (pre synaptic)
release can be blocked or enhanced (pre synaptic)
removal from synaptic cleft can he stimulated or blocked
receptor site can be blocked or activated

Question 24

what is a NT agonist ? example

Answer 24

any chemical that enhances or stimulates the effects of a molecule at a given receptor
-nAchrs are an example

Question 25

what is a NT antagonist? example

Answer 25

chemical that blocks or diminishes the effects of a molecule at a given receptor -atracurium besylate is a neuromuscular- blocking drug used as a paralytic agent for intubation, surgery, or ventilators

Question 26

what is the effect of a NT on the electrical state of the post synaptic cell via its receptor?

Answer 26

can cause excitatory or inhibitory graded potential

Question 27

what is an EPSP and why is it called so?

Answer 27

causes depolarization of the postsynaptic cell brings Vm closer to threshold

Question 28

is a single EPSP usually enough to reach threshold

Answer 28

no, but does make the post synaptic cell does become more excitable

Question 29

what is an IPSP and why is it called so?

Answer 29

hyperpolarizes the post synaptic cell - makes it more negative, moves Vm away from threshold

Question 30

how does spatial summation work?

Answer 30

occurs when postsynaptic potentials arrive near the same location at the same time

Question 31

how does temporal summation work

Answer 31

occurs when post synaptic potentials arrive near the same location close to the same time

Question 32

NOTE for summation

Answer 32

whether or not the post synaptic cell reaches threshold depends on the net effect after summation of all the post synaptic potentials (excitatory and inhibitory)

Question 33

what would be the effect on the post synaptic cell if the NT stayed in the synapse?

Answer 33

if stayed in the synapse, would influence postsynaptic neuron, muscle fiber, or gland cell indefinitely

Question 34

how are NT removed from the synapse

Answer 34

re-uptake degradation diffusion

Question 35

reuptake of NT from the synapse

Answer 35

removal of NT via astrocytes (in CNS) or axon terminal of release neuron

Question 36

degradation of NT in synapse

Answer 36

removal of NT by enzymes

Question 37

diffusion of NT in synapse

Answer 37

removal of NT that removes NT away from the cleft

Question 38

what is integration in reference to neuronal signaling

Answer 38

the process accomplished by the post synaptic neuron when it combines all excitatory and inhibitory inputs and responds accordingly this process occurs over and over as interneurons are activated in higher parts of the brain

Question 39

what is a neuronal network

Answer 39

may contain thousands or even millions of neurons

Question 40

what are diverging circuits in a neuronal network, provide an example

Answer 40

one input, many outputs an amplifying circuit example- a single neuron int he brain can activate 100 or more motor neurons in the spinal cord and thousands of skeletal muscle fibers

Question 41

what are converging circuits, what are they used for, provide an example

Answer 41

many inputs, one output a concentrating circuit example- different sensory stimuli can all elicit the same memory

Question 42

what are reverberating circuits, what are they used for, provide an example

Answer 42

signals travel through a chain of neurons, each feeding back to previous neurons an oscillating circuit involved in breathing, sleep wake cycle, and repetitive motor activities such as walking

Question 43

discuss parallel after-discharging circuits, what are they used for, provide an example

Answer 43

signal stimulates neurons arranged in parallel arrays that eventually converge on a single output cell impulses reach output cell at different times, causing a burst of impulses, called an after-discharge example- may be involved in exacting mental processes such as mathematical calculations

Question 44

what are neurotoxins and how do they affect neurons?

Answer 44

an extensive class of exogenous chemicals which adversely affect function in both developing and mature nervous tissue

Question 45

are neurotoxins always exogenous

Answer 45

no, some overproduction or release of endogenous NT can be neurologically toxic

Question 46

list an example and know the terminology for an endogenous neurotoxic event

Answer 46

over release of glutamate in the CNS from ischemia (low oxygen) can cause neuronal over-excitation leading to the death of the neuron (excito-neurotoxicity) this is what happens in a stroke

Question 47

what is botulinum toxin?

Answer 47

most acutely lethal toxin known. average lethal dose is 1.3-2.3ng/kg

Question 48

how does botulinum toxin work

Answer 48

it blocks the release by cutting snare proteins and blocking the release of Ach from motor neuron terminal means no stimulation of skeletal muscle fiber contraction - paralysis of skeletal muscle innervated by the neuron

Question 49

what is TTX?

Answer 49

tetrodotoxin

Question 50

list an example of where TTX can be found

Answer 50

in the viscera of a type of japanese puffer fish and many other animals

Question 51

how does TTX work

Answer 51

it is a fast voltage gated Na channel inhibitor, it binds and inhibits the opening of voltage gated Na channels in the PNS can cause paralysis in muscle and loss of sensation

Question 52

how can TTX kill you

Answer 52

can lead to paralysis in the diaphragm

Question 53

what are local anesthetics

Answer 53

drugs that block pain or other somatic sensations around the site of injection

Question 54

why are they called local

Answer 54

because they only block pain or sensation at the site of the injection

Question 55

how do most local anesthetics work

Answer 55

blocking neuronal voltage gated Na channels therefore AP are blocked

Question 56

what are examples of local anesthetics

Answer 56

lidocaine and procaine (novocaine)

Question 57

how can cooling in a neuron affect signaling

Answer 57

can slow or partially block AP conductions as well application of ice to an injury not only reduces swelling from inflammation but also decreases pain by affecting ion channel kinetics

Question 58

what are general anesthetics

Answer 58

drugs that can cause a reversible loss of consciousness

Question 59

how are general anesthetics different from that of local

Answer 59

they do not dull pain, just cause unconsciousness

Question 60

what is depression

Answer 60

a disorder in which people may feel sad and helpless, have lack of interest, and may experience suicidal thoughts

Question 61

list examples of depression

Answer 61

major depression, dysthymia, bipolar disorder, manic depressive illness, seasonal affective disorder (SAD)

Question 62

is depression caused by just one thing

Answer 62

no

Question 63

what NT may play a role in depression

Answer 63

serotonin, norepinephrine, and dopamine

Question 64

what are SSRIs and how do they work

Answer 64

inhibit the re uptake of serotonin in the synapse by the presynaptic cell therefore prolonging its duration and effects