Lecture 11.4 main points Flashcards
define the absolute refractory period, why does this occur (what ion channels play the main role and how)?
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
define the relative refractory period, what type of stimulus is necessary for AP during relative refractory period
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
list the phases of AP where the absolute and relative refractory periods take place
absolute refractory period - during depolarization and repolarization
relative refractive period - after hyper-polarizing state
where does AP begin ?
at the trigger zone near the axon hillock
what are the two types of methods in what AP are conducted
continuous conduction
saltatory conduction
which type of AP conduction method is used by myelinated axon
saltatory conduction
which type of AP conduction method is used by un-myelinated axons
continuous conduction
list the three factors that affect speed of AP conduction
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)
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
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
list the three types of axon fibers and their characteristics
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
in what direction does communication occur at a chemical synapse ? is this one way or both ways?
a one way transfer from a pre synaptic neuron to postsynaptic neuron
list the events involved in the release of NT from the presynaptic cell
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)
what effect does the release of the NT from the pre synatic cell have on the post synaptic cell
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)
how does the affect of speed signaling information being relayed by the synapse
the time required for these processes at a chemical synapse produces a synaptic delay of 0.5 msec
are NT receptors specific or can any molecule bind and cause an effect?
each neurotransmitter receptor has one or more neurotransmitter binding sites where its specific NT binds
what are ionotropic receptors? give an example
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
what are metabotropic receptors and give an example?
contains NT binding site but lacks an ion channel as part of its structure
-glutamate is an example
how do metabotropic receptors directly activate or deactivate ion channels
G-proteins can go on to activate/deactivate separate ion channels (direct)
how to metabotropic receptors indirectly activate or deactivate ion channels
G proteins can activate other proteins that go on to activate/ deactivate ion channels
what type of neurotransmitters are found in both the CNS and PNS
excitatory and inhibitory
is an excitatory NT always excitatory?
no, may be excitatory in some locations and inhibitory in others
list main chemical classifications of NTs
amino acids, biogenic amines, peptides (neuropeptides), purines, gases and lipids, endocannabinoids
main ways NT effects modified
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
what is a NT agonist ? example
any chemical that enhances or stimulates the effects of a molecule at a given receptor
-nAchrs are an example
what is a NT antagonist? example
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
what is the effect of a NT on the electrical state of the post synaptic cell via its receptor?
can cause excitatory or inhibitory graded potential
what is an EPSP and why is it called so?
causes depolarization of the postsynaptic cell
brings Vm closer to threshold
is a single EPSP usually enough to reach threshold
no, but does make the post synaptic cell does become more excitable
what is an IPSP and why is it called so?
hyperpolarizes the post synaptic cell - makes it more negative, moves Vm away from threshold
how does spatial summation work?
occurs when postsynaptic potentials arrive near the same location at the same time
how does temporal summation work
occurs when post synaptic potentials arrive near the same location close to the same time
NOTE for summation
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)
what would be the effect on the post synaptic cell if the NT stayed in the synapse?
if stayed in the synapse, would influence postsynaptic neuron, muscle fiber, or gland cell indefinitely
how are NT removed from the synapse
re-uptake
degradation
diffusion
reuptake of NT from the synapse
removal of NT via astrocytes (in CNS) or axon terminal of release neuron
degradation of NT in synapse
removal of NT by enzymes
diffusion of NT in synapse
removal of NT that removes NT away from the cleft
what is integration in reference to neuronal signaling
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
what is a neuronal network
may contain thousands or even millions of neurons
what are diverging circuits in a neuronal network, provide an example
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
what are converging circuits, what are they used for, provide an example
many inputs, one output
a concentrating circuit
example- different sensory stimuli can all elicit the same memory
what are reverberating circuits, what are they used for, provide an example
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
discuss parallel after-discharging circuits, what are they used for, provide an example
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
what are neurotoxins and how do they affect neurons?
an extensive class of exogenous chemicals which adversely affect function in both developing and mature nervous tissue
are neurotoxins always exogenous
no, some overproduction or release of endogenous NT can be neurologically toxic
list an example and know the terminology for an endogenous neurotoxic event
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
what is botulinum toxin?
most acutely lethal toxin known. average lethal dose is 1.3-2.3ng/kg
how does botulinum toxin work
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
what is TTX?
tetrodotoxin
list an example of where TTX can be found
in the viscera of a type of japanese puffer fish and many other animals
how does TTX work
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
how can TTX kill you
can lead to paralysis in the diaphragm
what are local anesthetics
drugs that block pain or other somatic sensations around the site of injection
why are they called local
because they only block pain or sensation at the site of the injection
how do most local anesthetics work
blocking neuronal voltage gated Na channels therefore AP are blocked
what are examples of local anesthetics
lidocaine and procaine (novocaine)
how can cooling in a neuron affect signaling
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
what are general anesthetics
drugs that can cause a reversible loss of consciousness
how are general anesthetics different from that of local
they do not dull pain, just cause unconsciousness
what is depression
a disorder in which people may feel sad and helpless, have lack of interest, and may experience suicidal thoughts
list examples of depression
major depression, dysthymia, bipolar disorder, manic depressive illness, seasonal affective disorder (SAD)
is depression caused by just one thing
no
what NT may play a role in depression
serotonin, norepinephrine, and dopamine
what are SSRIs and how do they work
inhibit the re uptake of serotonin in the synapse by the presynaptic cell therefore prolonging its duration and effects
