BIOL 388 Midterm Lab Practical
What is a compound muscle potential?
An AP generated by MANY muscle fibers within the muscle
What is a compound action potential?
An AP that simultaneously occurs in a collection of individual cells; normally powerful enough to be recorded using extracellular electrodes
Why do the readings appear to be straight lines rather than parabolas like in the past?
Each amplitude exhibits how many motor units are being recruited at that particular time; there are none that recruit over a long period of time to create a parabola
Does this experiment protocol demonstrate a requirement for sodium in action potential generation?
No because we are not sure which variable is causing this: no Na+ or because the resting membrane potential is hyperpolarized
What is the command potential required for activation of the current?
~40mV
What is the Neuron Model?
A computation tool for learning about membrane potentials, ion channels, and ion currents while conducting virtual experiments
What is (RT/ZF)?
A constant; don't worry because it will be provided to you somehow
What is a PowerLab?
A recording instrument that measures electrical signals, usually through the inputs on its front panel; can also generate output signals
What is an involuntary movement?
A reflex; follows the stretch reflex pathway
How does the frequency of motor unit activity change as the contractions get stronger?
Frequency increases as the contraction gets stronger (directly related)
Why does the muscle potential appear to be more complex than the nerve potential?
Nerves are more compact and have myelination; however, muscle fibers are larger and there are more opportunities for the acetylcholine (neurotransmitter) to get "lost"
Does the amplitude of the action potential of the median giant axon vary with stimulus voltage?
Yes, the amplitude of the action potential in the median giant fiber varied within the stimulus voltage; as the stimulus voltage was raised, the resulting amplitude of the median giant axon's action potential increases, as well
Does verbal encouragement while your eyes are closed enable one to increase their strength again? How is this possible if the muscle is fatigued?
Yes, the encouragement gives the subject adrenaline, in addition to it being another form or biofeedback
Are the amplitudes of the signals the same in all three recordings (different sampling rates)?
Yes, the voltage of the beats is not changing based on how many samples per second are being taken
Does the worm still possess small nerves along with giant fibers?
Yes, they just do not run the full length of the body
Were you able to maintain a 50% contraction with our eyes shut, and if so, why?
Yes, this is an example of proprioception; your body gives brain signals of where it is in space
Would one be able to sustain a contraction better if brief rest periods are allowed and if so, why?
Yes; O2, ATP, and nutrients would all able to be replenished at least a little bit and there would be less lactic acid build up
What is the physiological basis of biofeedback?
You are able to better control your movements and possibly fight/hesitate a reflex
What do "p(ion)" and "g(ion)" mean?
p(ion): ion permeability g(ion): channel conductance
Typical permeation ratio in a glial cell
pK leak = 1, pNa leak = 0
Typical permeation ratio in a neuron
pK leak = 1, pNa leak = 0.06
If action potentials are all-or-nothing events, why is the pulse height of the compound action potential graded (varying with stimulus strength)?
Since the sciatic nerve is constructed on many axons, it creates a compound action potential. CAPs are generated by impulses flowing through each axon collectively and every neuron, while similar, can have differing characteristics. Another explanation: APs within single axons are all or nothing events; however the number of these occurring within a compound action potential causes the amplitudes of the action potentials to vary with differing stimuli.
What do motor units vary in based on muscle function?
Size Explanation: with the SAME NUMBER of motor units recruited, smaller motor units will generate a smaller contraction than a contraction generated by larger motor units
How can you tell which side of the worm is the anterior region?
Slightly larger with a clitellum
What are oxidative muscles?
Small, slow to fatigue, produce less force, aerobic, sustain contraction for a long time Ex: good for marathon runners (a low amount of energy for a long period of time)
How do we set up the frog nerve to collect the data necessary?
1 set of stimulating electrodes and 2 of recording electrodes
What causes a compound muscle action potential (chemically)?
1) Ach is released from the axon terminal of a motor neuron and binds to receptors in the motor end plate. This binding elicits an end-plate potential, which triggers an AP within the muscle cell 2) AP propagates along the sarcolemma and down the T-tubules
What is the purpose of the PowerLab?
To acquire, store, and analyze data
What is the horizontal threshold bar used for?
To separate the true peaks from any unnecessary noise
Is 0.003 seconds a reasonable measure for a synaptic delay?
Yes because it takes a little bit of time for the whole process of generating the action potentials to occur; however, it still happens VERY quickly. Think about how quickly you're able to move in response to a stimulus
What does each giant fiber act like (in general)?
A giant axon (due to gap junctions)
What is a glial cell?
A passive cell only, no action potentials occur (reason for no Na+ channels being open)
What impact does a low pass filter have on the signal?
A smaller frequency results in a smaller amplitude of the waves than a larger frequency
What is a pair of muscles called?
Antagonistic muscles
What are the two views in LabChart?
Chart View and Scope View
What colors do the overlay options cause the waves to be?
Clear --> blue (unselected) Clear --> red (selected)
What is a leakage current?
Current flow that comes through resting or passive channels
Is the voltage change caused by injections a hyperpolarization or a depolarization and why?
Depolarization; the cell started negative so it would not have become more negative, it would have become more positive
If the current changes from 0 to 3, how has the membrane response changed?
Depolarized more and quicker
In what direction is the first flow of current detected and why?
Downward current
What does the phrase "downward current" mean?
Ions are flowing INTO the cell
Do more or less fibers cause MORE tension?
MORE fibers cause MORE tension (direct relationship)
What are the 5 steps of the diagrammatic summary of the PowerLab's data acquisition?
Raw input --> amplification --> filtering --> sampling --> display
What is a motor unit?
One motor axon in addition to the muscle fibers it innervates
What does a stimulation of the medial giant fiber result in?
Rapid head withdrawal
What does a stimulation of the lateral giant fibers result in?
Rapid tail withdrawal
What is Henneman's Size Principle?
Smaller motor units are recruited BEFORE larger ones
What is the soma?
The cell body
How can you tell which side of the worm is the dorsal side?
The darker side
What do extracellular electrodes detect?
The difference in charge between two locations on the outside of the nerve; reason for displaying a biphasic wave
What is the efferent neuron?
The motor unit
What does excitation-contraction coupling involve (chemically)?
The muscle AP inducing calcium release from stores within the sarcolemma and consequently, conformational changes in the cytoskeletal filaments
Why do we not want to stretch, cut, or pinch the nerve?
The neuron could be unattached from the muscle
How does this differ from the same change in the neuron (as opposed to the glial cell)?
The same change in the neuron will result in an exponential change in resting membrane potential due to the Na+ leak channels being relevant now
What is the afferent neuron?
The sensory unit going to the muscle spindle in the leg (?)
What is the distal segment of one's finger?
The tip
What comes first: opening the program or turning on the PowerLab?
Turning on the PowerLab
Where do you always want to pickup the prep?
Achilles tendon
What is a neuromuscular junction (NJM)?
Chemically transmitting synapse found between a neuron and a muscle fiber
What is the NJM susceptible to?
Fatigue
Where is the on/off signal on the PowerLab?
On the back
What is the scientific name for a bullfrog?
Rana catesbeiana
How is the Vm (rest) of the glial cell different from its EK+?
There is only potassium acting upon the cell, not sodium
What are skeletal muscles?
Those attached to the bones
How do you calculate conduction velocity?
V = (distance between electrodes)/(change in time)
What is the Nernst equation?
(RT/ZF) * log(ions in/ions out) = E
What is the cell's resting membrane potential in a glial cell?
-100mV (specifically -99.97mV)
What are the steps (not the diagrammatic summary) of how the PowerLab obtains data?
1) A transducer causes a mechanical signal to be triggered 2) An electrode records this signal and turns it into an analog signal 3) The PowerLab transforms the analog signal into a digital signal 4) The digital signal is shown on the computer screen
What are TWO anatomical properties of nerve fibers that influence conduction velocity?
1) Diameter of nerve fibers -- direct relationship 2) Degree of myelination -- direct relationship
What are the two different types of muscles?
1) Oxidative 2) Glycolytic
What is the stretch reflex pathway?
1) Sensory neurons stimulated 2) SN relay impulses to motor neurons 3) Motor neurons activate contraction of muscle to resist stretch
What are the three types of electrodes used?
1) Stimulating electrodes 2) Recording electrodes 3) Muscle recording electrodes
How might that ^^ problem be corrected?
1) could modify K+ concentrations 2) want to change the resting membrane potential back to -65mV by altering the base current -- what we did to determine this is the cause!!
What biochemical changes are occurring in your muscles when they become fatigued?
1) depleting O2 2) depleting ATP 3) depleting nutrients 4) lactic acid build up
Why does the neuron's Vm(rest) more closely resemble its EK+ and not its ENa+?
1) higher concentration of K+ than Na+ 2) K+ is a lot more permeable (flow out faster than Na+ can flow in)
What are the three basic steps that are being measured between the motoneuron and the muscle contraction?
1) the motoneuron AP triggers acetylcholine release at the NJM 2) this in turn, triggers the muscle action potential 3) a latent period follows which eventually triggers a muscle contraction
At about what current did an action potential finally occur?
1.65
How did we anesthetize the earthworm?
10% ethanol in earthworm saline; continuously adding a little to ensure the worm stays moist and anesthetized
What is the holding potential of the clamped neuron?
100mV (K+ equilibrium)
How do you calculate your heart rate in beats per minute?
60 / time value measured between peaks (both in seconds)
What is the (RT/ZF) for mammals?
61 (58 is a squid)
When does the 1st command occur?
65mV (resting membrane potential)
When would a faster sampling rate be ideal?
A faster sampling rate would be ideal when measuring a fast heart rate so that you can actually see everything. It is always idea to have a sampling rate as close to the rate of what you're measuring, as possible
Without an action potential, what does the graph look like?
A horizontal line (slope of zero) at -70mV
What does a 500mV range mean?
A signal that extends from -500mV to +500mV will produce a full-scale deflection of the trace
What is the waveform cursor?
A tool that can be used to read amplitude and time values directly from a waveform on the screen (shaped like a plus sign)
How is a compound action potential seen by paired extracellular electrodes?
A traveling wave of negative potential
What is resting membrane potential?
About -65mV or -70mV
What are active membrane properties?
Action potentials
What are electrical signals?
Action potentials or excited states
What is one advantage and disadvantage of having a high sampling rate?
Advantage: More accurate Disadvantage: Farther apart so it's harder to analyze
What is the relationship between stimuli, action potentials, and stimulated axons?
All directly related; as the stimulus is increased, a larger action potential occurs due to a larger amount of stimulated axons within the compound action potential
What is the role of giant fibers?
Allow the animal to respond rapidly to threatening situations; conduct action potentials far faster than smaller nerves
What does myelination do and where can it be seen fully developed?
Allows conduction velocities of similar speed in nerves of a much smaller size; Chordates, in general
What are Digital Voltmeter Mini-windows (DVMs)?
Allows you to see the numbers clearly if you are recording data away from the monitor; creates mini windows of rate/time and range/amplitude
What is a low pass filter?
Alters the frequency of the waves; filter out everything above the set number of Hz
What is the physiological basis of this antagonistic muscle function?
Antagonistic muscles aid in homeostasis by returning bones to their original positions and smoothing/slowing/stopping movements When one is contracting, it enables the other one to relax, and vice versa
Where do you always want to place the marker?
As close to the top, as possible
What is the physiological basis for the answer to the question above?
As more and more neurons are passing through an axon, the larger the action potential (in amplitude) it is going to create within the worm; can be explained by the number of ion channels along the axon's membrane, which increase along with diameter, which is why the medial giant fiber has more
What does "auto scale channel" do?
Automatically adjusts the amplitude axis so the maximum value is just larger than the maximum value of visible data in this channel
What mechanism is responsible for the increased magnitude of contraction with the increase in stimulating current?
Because of the larger stimulus, more muscle fibers are being recruited, causing larger motor units to be recruited (thinner and larger/equal lines on graph)
Why do the graphs have rounded corners?
Because of the lipids in the membrane; cause it to have capacitance until reaches max depolarization
What is different about extracellular recordings on the display screen (waveform)?
Biphasic waveform, different than intracellular
Which color is plugged into which port on the PowerLab (BNC outputs)
Black --> negative Red --> positive
What color is the power button when it's turned on?
Blue
How does an axon in an earthworm nerve cord compare to that of the sciatic nerve of a frog?
Both axons in earthworms and sciatic nerves in frogs carry APs caused by stimuli throughout the body. Axons in earthworms are constructed of three nerve fibers (one medial and two lateral), whereas the sciatic nerve is made of many. The single axon of an earthworm is more easily excitable than those in a frog. The axon of an earthworm runs throughout its ENTIRE body (due to gap junctions), whereas the sciatic nerve runs from the lower back to the foot (still the largest nerve a frog has!)
What does changing the mV of the range do?
Changes the sensitivity of the recording system; **Does NOT change the signal from the pulse transducer!!
What is a voluntary movement?
Conscious intent to generate a specific skeletal muscle contraction
What is resting membrane potential a product of?
Current flow through open ion channels in the cell's membrane
What experiment shows the dependence of Na+ for action potentials?
Decreasing extracellular sodium with a base current of 2.25 and seeing what happens (NO AP!)
What do extracellular electrodes do?
Detect the difference in charge between two locations on the outside of the nerve
Why do we not want the metal probe to touch the nerve?
Different ions will be transferred to the nerve and throw off the potential or readings
What might be the reason for latency and velocity differences among the subjects in your lab section?
Differing heights and muscle strengths
How many individual motor units can you detect during a weak contraction? How do you distinguish them?
Distinguish them by counting how many different amplitudes there are; each different amplitude constitutes another motor unit
What is an alternative to using the insertion of intracellular electrodes into neurons since majority of animals do not have large enough neurons?
Electrical activity of neurons can be studied in excitable cells of vertebrates by activating an action potential simultaneously in a collection of individual cells
How does a 10-fold change in [K+]o (from 3.1mM to 31mM) affect the Vm(rest) of your glial cell?
Every change in concentration is going to cause a decrease in membrane potential of about 60mV; affects the same way, just over and over again
What does the display window show if you move the overlay slider all the way to the right?
Every page of data that has been collected overlaid atop one another
What is an electromyogram (EMG)?
Extracellular recoding of electrical activity in a whole muscle
Why could nobody sustain the 100% contraction?
Fatigue in the muscles
What equation estimates the equilibrium potential for a neuron?
Goldman Equation (includes ALL ions, therefore it can find the equilibrium using BOTH K+ and Na+)
What are the antagonistic muscles that we experimented and focused on?
Gastrocnemius (calf) and tibialis anterior (shin)
What does it mean if the signal is single-sided?
Has only values above zero on the data display
How does the overlay slider being slid to the right (more pages overlaid) affect the record?
Having a larger sample size (ex: 10 v. 3) makes the average more accurate
What are permeation ratios?
How easy ions move in and out of leak channels; K+ generally moves out more than Na+ moves in
How many motor units does a human calf muscle have (general ballpark)?
Hundreds
What does a permeation ratio mean?
If Na is 0.06 and K is 0.1, that means that for every 6 Na molecules that flow through, 100 K flow through, as well
What explanations are there for pseudo-fatigue?
If there is no biofeedback occurring; the only feedback you have is that you know how tightly contracted your muscle is but other than that, you don't know what is going on
What is the relationship between stimulation duration (ms) and voltage (V)?
Indirect; as stimulation duration increases, the voltage decreases
How does the intensity of electrical activity relate t the locomotor behavior?
Intensity of electrical activity increases along with a contraction during a locomotor behavior (MORE electrical = STRONGER contraction, directly related)
Why were invertebrate animals chosen for this experiment rather than vertebrates?
Invertebrates are generally simpler organisms than vertebrates. If research canbe done on a simpler animal before aplying it to a more complicated one, that is what scientists will do. In addition to this, invertebrates are studied instead of vertebrates specifically in neurology because vertebrates have nerves made o MANY fibers, making it more difficult to trace and research APs
Why should you not stretch your earthworm?
It can bring damage to the nerve cord
Why is it important to not hit the table or vibrate the device during recordings?
It could cause unnecessary noise to be collected within our data
How does the neuron's EK+ differ from the glial cell's EK+?
It does not differ; the concentrations of the K+ ion specifically did not change; ignores permeability and other ion channels (E of all ions togther is different)
What does it mean if a signal is bipolar?
It has positive and negative values
How does a current stimulate muscle contraction?
It is applying an electrical current to trigger synapse at a neuromuscular junction
Why is it important to calculate the average of several individual measurements before drawing a conclusion about BPM?
It is important to calculate individually instead of overlaying because using the overlay feature to obtain an average will cause it to overestimate the measurements
How can the lowest threshold event occur without the other?
It is possible to hit the nerve threshold (lowest threshold event) without hitting the muscle threshold, thus exciting the nerve and not the muscle
Median giant fiber v. lateral giant fiber, conduction velocity
LGFs conduct slower than MGFs (reaches action potential recording later and creates a peak there instead)
Median giant fiber v. lateral giant fiber, thresholds
LGFs have higher stimulus thresholds than MGFs
What software do we use to analyze and interpret the PowerLab's data?
LabChart 7
What is an action potential?
Large electrical signals that travel along an axon
What is each giant fiber comprised of?
Large, individual cells (ONE per segment) that are electrically coupled to one another through gap junctions
What are glycolytic muscles?
Large, quick to fatigue, produce greater amounts of force, anaerobic, build up lactic acid so do not sustain contractions for long Ex: good for sprinters (a lot of energy in a short period of time)
Why did the latency period differ between the median and lateral fibers?
Latency periods are those that occur between the stimulus artifact and the action potential. Median fibers have a larger diameter than lateral fibers, allowing it to conduct APs quicker due to more ion channels being able to cover the fiber's membrane. This causes the latent period for the median fiber to be smaller than that of the lateral fibers due to its AP occurring first.
What is the refractory period?
Longest stimulus interval between two pulses where no second action potential was seen
What is the scientific name for the common earthworm?
Lumbricus spp. or Annelids
What does a force transducer do?
Measure muscle contraction; allows comparison between the compound muscle potential and changes in muscle tension, the contraction (BNC plug connects it to the frog in place of the neural recording electrodes)
What are the two types of fibers in earthworms?
Medial and lateral
Which action potential shows up first and larger on graphs of the two giant fiber types?
Median shows up first, then lateral
Which part has the rounded corners and which has the sharp corners: membrane potential or injection of current?
Membrane potential - rounded corners (top) Current injection - sharp corners (bottom)
What does the input amplifier do?
Modify signals so they are displayed optimally when you start recording
What is Ringer's solution?
Moistens the preparation and contains the same ions that inside the frog possesses to keep the neuron "alive"
What is the antagonistic muscle function?
Muscles are deactivated by the CNS while their antagonistic muscle contracts; by activating the gastrocnemius muscle, the tibialis anterior muscle is inhibited
Why does the AP repolarize so abruptly near 0mV?
Na+ channels become inactive and K+ channels become active. Less Na+ flowing in and more K+ flowing out causes abrupt repolarization as the membrane becomes more positive (refractory period). Do not see APs until Na+ channels are activated again!!
What current ALWAYS flows first and why?
Na+ current flows first (inward) but once it reaches equilibrium (~ +41mV), Na+ channels begin inactivating as K+ channels open (Na+ flow stays flat)
What leakage currents underlie your neuron's resting potential?
Na+, K+ leak channels (sometimes Ca++, also)
Are Na+ and K+ currents transient or sustained?
Na+ = transient; voltage gated ion channels inactivate and the flow of ions eventually stops K+ = sustained
Why isn't the flow of sodium into the cell simultaneously compensated for by the movement of potassium out of the cell?
Na+ activates first and then K+ activates. If this happend at the same time, the membrane potential would stay constant instead of generating APs
What equation estimates the equilibrium potential for K+ (EK+) in this cell?
Nernst Equation: estimates equilibrium potential for ONE ion at a time
Are all neurons the same within a compound nerve fiber?
No, they may differ in myelination, diameter, threshold, etc.
Does the giant axon conduct equally well in both directions?
No; although it has a preferred direction, both ways are possible.
What is a stimulus artifact?
Noise within the collected data; does not tell us anything about the physiology of the organism
When should you take the average using overlay?
ONLY if all of the waves appear to be as equal as possible (on the x AND y axes)
What physical law explains the relationship between current and voltage?
Ohm's Law: V = IR **Current and voltage are directly related
Why does the late-activated current switch to an outward current flow?
Only K+ channels are open and activated now so the ions are flowing out of the cell (Na+ ions eventually completely stop flowing inward so only outward flow remains)
What directions do the earthworm's medial and lateral fibers conduct naturally generated impulses (same direction or opposite)?
Opposite
How do you adjust the number of pages that are overlaid?
Overlay adjustment bar (under overlay options, the contrast can be adjusted, as well)
Why is the glial cell's Vm at rest greater than that of the neuron?
Positive ions are flowing out without any positive ions flowing inside to "replace" them
What's the specific type of PowerLab?
PowerLab 26T: a four channel recording instrument with built-in-front-ends that allow simultaneous recording of up to four different biological signals and provide safe stimuli for humans **Useful because it can stimulate and record at the same time, not to mention it can record at multiple locations and pickup data for each
What does orthodromic mean?
Preferred natural direction of conduction (always away from the soma); this direction is determined mainly by interconnections (synapses) between neurons
What is another name for the threshold voltage in LabChart?
Pulse height
What is another name for the stimulus duration in LabChart?
Pulse width
What do these gap junctions allow?
Rapid conduction of action potentials from cell to cell
What does intracellular mean in terms of animal physiology lab?
Record/manipulate voltage across the cell membrane (an electrode inside and an electrode outside the cell)
What does extracellular mean in terms of animal physiology lab?
Record/manipulate voltage from the outside of the cell (a positive and a negative electrode)
Why must the finger pulse transducer strap NOT be too TIGHT?
Reduce blood flow to the finger, weakening the signal and causing discomfort to the subject
How does one perceive that their muscles are fatigued?
They become too tired to continue the physical activity at hand
How can the resistance of a membrane be determined from this kind of experiment?
Resistance: how easily ions can flow in The longer it takes for an action potential to occur, the more resistance it has (inverse relationship)
What are passive membrane properties?
Resting potentials
During which movement (rising up onto tiptoes or rocking back on heels) is the most electrical activity observed?
Rising up on tiptoes; the recording electrodes are measuring the muscle contraction of the gastrocnemius muscle, which is the one used during rising onto your tiptoes
Does reflex latency vary along with different stimulus strengths?
They do NOT vary; the stimulus changes the amplitude (# of motor units) instead of the speed because the action potentials are not fired faster, the number of motor units being recruited is different
Why do the peaks of the evoked action potentials repolarize when they reach voltages slightly greater than 0mV?
The K+ channels are activated (opened) later on; they open after an influx on Na+ depolarizes the membrane (1st part of AP). When the Na+ ions stop flowing completely, we will witness a steep repolarization curve
What does a strength-duration curve tell us?
Stimulus strength (y) vs. duration (x)
What has the squid giant axon allowed us to do?
Study the electrical events underlaying the all-or-none, self-propagating nature of an action potential in a single cell
What is biofeedback?
Subject's visualization of their own muscle electrical activity or their own data being collected
What is the chemical that blocked potassium channels so only sodium channels were flowing?
TEA (competitive antagonist of K+ channels)
What is the chemical that blocked sodium channels so only potassium channels were flowing?
TTX (pufferfish venom)
What is a good way to demonstrate a reflex?
Tap on the Achilles tendon with a rubber mallet, should cause a reflex of the gastrocnemius muscle
Why doesn't the action potential bounce back down the fiber when it reaches the end?
The AP doesn't bounce back due to the refractory period due to the region behind it still depolarizing
Why is the distance measured doubled?
The action potential must travel to the spinal cord AND BACK
In what part of the neuron is the generation initiated in?
The axon hillock; the Na+ channels open and allow a LOT of Na+ ions to flow through
What is important to note about the biphasic waveform during NJM APs?
The biphasic wave here does mean depolarization or hyperpolarization
Why is the resting membrane potential a negative value?
The cell is more negative to its surroundings
What is the shortest onset latency?
The closest together that is possible for the two recording electrodes
Where does the needle hook of the force transducer go?
The distal portion of the Achilles tendon
What are Annelids' ventral nerve cord analogous to?
The dorsal spinal cord of Chordates
What is the latent period?
The elapsed time between the application of the stimulus and observation of the resulting action potential
What is the duration of the injection pulse?
The entire line From the onset point to the offset point = smaller than the duration of the injection pulse
Why is the sciatic nerve the one that is studied as opposed to one in the central nervous system (CNS)?
The frog sciatic nerve-gastrocnemius NJM is much more accessible than other synapses in the CNS
What is the significance of the green trace when overlaid is being selected?
The green trace is the sample of data that is being selected
What provides the safe stimuli within the PowerLab?
The isolated stimulator
What allows the lateral giant fibers to function together as a single unit?
The lateral giant fibers are extensively linked to each other by cross-connections, and therefore function as a single unit
What is excitation-contraction coupling?
The mechanism by which a muscle potential is transduced into a contraction of muscle fibers
If gK = 0 and NaK = 0, what does this mean?
The membrane/cell is passive; still have leak channels of 0.06mM and 1mM
What is the rheobase?
The minimum stimulus intensity that will elicit a response at infinite directions; found where the line begins to asymptote; Y-AXIS VALUE
What is the difference between the waveforms recording in the three blocks (changing sampling rate)?
The more samples that are collected causes the waves to be more spread out, thus making them more accurate and easier to read **sampling rate should be pretty close to the rate we're actually measuring
Why could we not use 310mM instead of 200mM within this program?
The neuron would explode!
How do you measure the latent period between the muscle potential and the muscle contraction?
The onset of the contraction minus the peak of the AP from the muscle
How do we measure the ECC time?
The onset of the peak recorded by the force transducer (top) minus the top of first peak within the muscle (bottom)
What do you see on the recordings of antagonistic muscles?
The recordings are opposite of one another; when one is contracting, the other is relaxing
What is the effect of decreasing extracellular sodium?
The resting membrane potential dropped to about 99.97mV from ~65mV. We also do not see any APs.
Why must you subtract 2 milliseconds from the reflex pathway time for an accurate estimation of conduction velocity?
These two seconds account for the synaptic delay
How are the nerve and muscle action potentials and muscle contraction affected by increasing the stimulus strength?
They all increase due to their direct relationships
What is important to note about the sampling rate so that the PowerLab is recording accurate data?
The sampling rate must be set high enough to where the signal does not vary too much between samples
Why do you not see a second action potential from . the median giant axon when the stimulus interval is generally pretty short?
The second action potential takes longer to appear since the cell needs to repolarize, meaning it must have time to close its Na+ ion channels and open its K+ channels along the axon. **This must occur before the second action potential can be sent!
Why must the finger pulse transducer strap NOT be too LOOSE?
The signal will be weak, intermittent, or noisy
What does comparing two chronaxie values tell us?
The smaller the chronaxie value, the more excitable the nerve is and the faster it will hit its rheobase value
Describe the MOST important way in which the median giant fiber action potential can be distinguished from a stimulus artifact.
The stimulus artifact has a larger amplitude and has a much larger hyper-polarization than the MGF AP
What is the chronaxie?
The stimulus duration required at a stimulus strength of 2x the rheobase; X-AXIS VALUE
When currents are injected, why does the neuron sometimes not generate an action potential in response to the injection and membrane depolarization?
The stimulus threshold has not been reached yet
What is the simplified definition of a CAP (compound action potential)?
The sum of all action potentials in many axons traveling within the same nerve
What is reflex latency?
The time it takes for the action potential to reach the spine and return to the muscle (onset of stimulus to onset of muscle contraction)
What is synaptic delay?
The time required for action potential-evoked transmitter release at the nerve terminal to be transduced into a membrane potential change in the postsynaptic cell AKA: time between onset of action potential in nerve cell and the onset of the action potential in the muscle cell
What is excitation-contraction coupling time?
The time required for excitation-contract coupling to occur
Why do motor units vary in size?
Their size is dependent upon how many muscle fibers they can innervate; innervating MORE causes a LARGER motor unit due to INCREASED tension (all directly related)
What is obvious about the "size recruitment" of new motor units with increasing contraction strength?
There are more with a larger amplitude than those with smaller amplitudes; remember, smaller motor units exhibit a smaller contraction strength than larger motor units
Explain how larger motor units can be recruited before smaller motor units, a process that contracts the size principle.
This can be done using biofeedback and learning how to move the muscle to generate different amplitudes or recruit differing motor units; can make a quick contraction as opposed to a slow and steady contractions (ex: like Gaston showed us in the lab)
Where do the biological signals come from?
Through the Bio Amplifier
What are the typical chart measures?
Time - horizontal axis Event (electrical signal or voltage) -- vertical axis
Why is it not necessary to have a large puddle of solution to keep the worm moist?
Too much liquid may interfere with the recording
How do you measure conduction velocity?
Total length of reflex pathway (distance) divided by the reflex latency MINUS TWO MILLISECONDS
In data collected, what is considered the true data and what is considered to be noise?
True data -- the signal we are interested in Noise -- smaller, non pulse peaks
Why don't we stick the electrodes straight into the worm?
We do not want to puncture the nerve fiber
In the voltage clamp, what do the upward and downward deflections mean?
Upward- represents positive ions leaving or negative ions entering the cell (repolarization) Downward- represents negative ions leaving or positive ions entering (depolarization)
Assume that the frog sciatic nerve conducts at a velocity of approximately 20m/s. How could you use this velocity to generate a better estimate of synaptic delay in your preparation?
Using the equation V=distance/time to measure conduction velocity, if the velocity and distance variables are known, the time can be mathematically predicted. How? 1) convert centimeters to meters 2) plug in given velocity and measured distance to solve for time in seconds (time = synaptic delay)
What is Ohm's Law?
V= IR = resistance * current We are either changing I and measuring V or changing V and measuring I (R does not change)
Which is found on the top and which is found on the bottom?
Voltage-top Curent-bottom
What is the purpose of using a semi log plot?
We are collapsing the linear information so it is more visual; otherwise, it would look like two very similar and close together lines
Is there any reason to exclude any of the traces from the average calculation?
We should exclude values that cause the average to skew, such as different signal artifacts or "noise"
Why does the sodium current become upward (outward) at command potentials above +50mV?
We will see a value of zero and there will be no movement. About +50mV, flows outward. Below +50mV, it flows inward.
When do the sodium channels become inactivated and begin allowing potassium out of the cell?
When the resting membrane potential is ~10mV
What is signal conditioning?
When the signal is amplified and filtered (modified) so it is easier to read as the voltage is monitored by the hardware
What does the required command potential correspond with in regards to physical biochemistry of the membrane?
When this happens, we begin to see deflection in the graph, which is when K+ channels begin to open up (remember that Na+ channels open first)
What are small motor units good for?
When you need less strength but more control (such as your hand)
What is a voltage-clamp?
Where membrane potential is manipulated and CURRENT is RECORDED
What is a current-clamp?
Where the current is manipulated and the VOLTAGE is RECORDED
How do you measure synaptic delay on a graph?
Zoom in as much as possible and measure the time from the onset of the neuron action potential to the onset of the muscle potential
