PNB Practical 2
What is the parallel conductance equation?
-GHK/resting membrane potential -Na+, K+ and Cl- are all permeable -ENa+=60mv -ECl=-70mV G=conductance/how much the membrane conducts ions: 1. depends on the number of channels in the membrane for that ion 2. depends on the number of open ion channels E=E(Na)G(Na) +E(K)G(K) +E(Cl)G(Cl)/ G(Na)+G(K)+G(Cl)
Explain what happens when you stimulate different sensory spines?
-If you stimulate one spine, a subset of sensory neurons will be activated -Size of nerve and proximity to electrode can alter AP
Explain the placement of the electrodes on the earthworm.
-Stimulating electrodes placed near head -Ground electrode placed in between recording electrodes and stimulating electrodes -2 recording electrodes (negative then positive) are put through the worm'Es body to catch the voltage changes extracellularly
What is the structure and function of the adrenal gland?
-adrenal glands->located on top of each kidney -adrenal medulla->inner -adrenal cortex->outer
What is the affect of Batrachotoxin?
-after depolarization, the membrane potential remained positive for an extended length of time, and the repolarization was often extremely delayed -with higher concentrations of the toxin, you found cases when the cell could not repolarize at all, or if it began to repolarize, it would immediately depolarize again
When does muscle fatigue occur?
-after tetanus
What is an ECG recording?
-an electrocardiogram
What are the parts of the adrenal cortex?
-from outer to inner 1. Zona Glomerulosa 2. Zona Fasiculata->secretes cortisone 3. Zona Reticularis->secretes sex hormones
What is the structure of the cockroach?
-from top to bottom -coxa, femur, tibia, tarsus
Explain the electrode placement in the cockroach:
-ground electrode in the coxa -positive electrode in the femur
What are the structures of the oxyphil cells?
-larger cell type -contains abundant mitochondria
Where is the thyroid gland located and what is its structure?
-located in neck between larynx and trachea -left and right lobes of thyroid gland connected by isthmus glands
During lethal injection, K+ is added to the EC fluid. What happens the membrane potential?
-more depolarized
What are the structures of chief cells and what is their funciton?
-most numerous cell types -small round cell with a central nucleus secrete Parathyroid hormone(PTH)->serves to increase the levels of calcium in the blood
What is summation?
-multiple stimuli in a short duration of time will summate the response and result in an increased contractile force
Why is tetanus tension so much greater than twitch tension?
-relative timing of availability of Ca2+
What is stretch?
-the tension or force generated is proportional to the number of cross bridges made between thick and thin filaments
What are the key characteristics of the median and lateral giant nerve fibers?
1. Giant fibers composed of large individual cells that are electrically coupled to each other through gap junctions 2. Giant fibers can be stimulated by placing electrodes-> single action potential can be recorded using this model and the responses can be recorded extracellularly from the animal surface 3. Small nerves do not run long so electrical activity is not recorded
How can you analyze data using a histogram? How does varying bin size effect your interpretation?
1. Make a histogram of the amplitudes observed Vary bin sizes for action potential amplitude 2. At large bin size(less bins), many different size spikes/amplitudes will fall into a single bin giving false impression that they originate from a single axon 3. At small bin size(more bins), the variability of action potentials and background noise makes data be separated across several bins -AP originating from a single axon could be erroneously rejected as belonging to more than one axon
What are the gland parts of the anterior pituitary gland?
1. Pars Distalis 2. Pars Intermedias 3. Pars Tuberalis
What is the set up for an EMG recording?
1. Put two ECG electrodes(white and black/positive and negative) on the subjects biceps 2. Put one electrode(green/ground) on the back of the wrist for the same arm
How do you increase muscle contractile force if AP are all or none events?
1. Recruitment -twitch 2. Stretch -tension 3. Summation -tetanous
Explain the procedure and key takeaways of the stimulating different spines experiment for the cockroach.
1. Start recording and touch a sensory spine 2. measure amplitude of AP for each spine that was stimulated
Explain how to find the threshold value for the lateral giant axon in the earthworm.
1. Stimulate the earthworm with the threshold for the median giant axon 2. Increase the stimulus voltage by 0.05 V steps until you observe the threshold and a 2nd response with a longer latency for the lateral giant fibers 3. latency-measure the time from the stimulus artifact to the start of the AP
Explain the waveform for an EC recording of an earthworm. For example, when you see the stimulus artifact.
1. Stimulus artifact(highlighted): Peak immediately after stimulus administered and is not AP -Always occurs even when your stimulating voltage isn't high enough to generate AP 2. Median Giant Fiber generates AP->as shown by bump 3. At higher voltage, Lateral Giant Fiber generates AP->as shown by bump
What are factors that influence the amplitude of action potentials?
1. The size of the axon - larger diameter axons produce greater amplitude action potentials. 2. The proximity of the axon to the recording electrodes - those that lie closer produce greater amplitude action potentials. -AP with different amplitudes rise from different axons!!!!
What are other differences between sheep and human brains?
1. size of olfactory bulb 2. number and size of mammillary bodies 3. size->human brain is larger than sheep 4. human brain has many more sulci and gyri 5. human brain has deeper sulci->increases SA of human brain
What is the optimal sarcomere length for max force generation in muscles? a. completely contracted b. intermediate length c. fully stretched
b. intermediate length
What is the longitudinal fissure?
separates the two cerebral hemispheres
What's an alternative way to ask stretch?
twitch tension
How do you calculate the total volume of oxygen consumed by the mice?
(3/5)=15mL/total length of time required for each of the 3 trials(seconds/60) -3 trials, 5 mL moved for the soap bubble
Explain the structure of the cerebral cortex.
-6 layers -giant pyramidal cells are most numerous in layer 5(most medial)
What occurs in twitch tension in relation to Ca2+ availability?
-Ca2+ is saturated to bind to troponin so all tropomyosin binding sites are available for myosin to bind to initially -Cross bridge takes time so Ca2+ gets pumped back into SR -In this time, the troponin-tropomyosin complex might become reblocked binding sites limiting cross bridging
What is the set up of an extracellular recording and what kind of information do you receive?
-Does not have direct access to membrane potential action potential -Instead places one electrode in close proximity to excitable cell and the other cells are a little bit of distance away -Study potential changes of the membrane surface -NOT to see the changes across the cell membrane of excitable cell
Explain the thyroid experiment and the mouse set up.
-Effects of Thyroid Hormones on Mouse Metabolism -Mice have different levels of thyroid hormone -Measure oxygen consumption rate on mouse to observe the effect of thyroid hormones in mouse on metabolic rate -CO2 absorbent(lime) placed in chamber which will absorb the carbon dioxide produced as a result of oxygen consumption -Place mouse in metabolic chamber and close chamber -Insert bubbles into chamber(at end of pipette)-as oxygen is consumed by the mouse, CO2 is produced and absorbed inside the chamber -As CO2 is absorbed by material, the bubbles will move closer to the chamber -Record time for all 5 mL of bubbles to pass through pipette. -Repeat for 3 recordings
Explain the triphasic waveform when measuring AP in tactile spines of cockroaches.
-Extracellular Recording shows triphasic(bottom figure is blow up of top figure) action potential with negative, positive, and negative waveform
Explain the fast sensory adapting of tactile neurons in cockroaches.
-Movement of spine produced bursts of action potentials -even if movement of spine is maintained, the neuron will stop or decrease its firing rate significantly within 1 second
What type of signal data should you use for calculations?
-RMS/integrated activity should be used for measurments -place the pointer selector at the peak/amplitude of a waveform in the RMS Biceps Channel->will appear in the RMS Value channel
What is the relationship between stimulus strength and response amplitude in a single axon?
-Remember single axon so a greater stimulus strength CANNOT recruit -In a single axon, it doesn't necessarily matter how strong or weak the stimulus is because it will be an all-or-none response. This means that either the stimulus will be strong enough for the response amplitude to reach the threshold to fire an action potential, or the stimulus won't be strong enough to trigger an action potential and nothing will happen.
What are the structural differences between the sheep's mammillary body and the human mammillary body?
-Sheep have a 1 larger mammillary body -Humans have 2 mammillary bodies
What is a hormone?
-a blood-borne chemical agent -travels by blood and binds to receptors on specific target cells -target cells respond to specific hormones
What is the relationship between stimulus rate and contraction?
-as stimulus rate increases, tension/force increases
Describe how the isolated muscle responded as it was stretched progressively.
-as stretch or tension increased as you increased the height of the force transducer, the amplitude of twitch force exhibited by the muscle increased. However the net force, or the difference between the resting force and twitch force increased then decreased
What should you observe in the EMG trace for co-contraction?
-as you increase the weight(ex. books) the force exerted by both muscle will increase -both bicep and tricep(agonist and antagonist) muscles will contract -in the RMS Bicep and Tricep trace, you will see a similar shape but DIFFERENT AMPLITUDE signal at the same time -the height of the signal in the RMS Bicep trace correlates with the force produced by the muscle
At what stimulus interval do you observe tetanus?
-at an interval where the stimulus has summated and resulted in the max contraction force
What's unique to the trace seen for co-contraction?
-both muscle ARE contracting -the bicep and triceps are BOTH activated BUT exert a different force so have a different amplitude
What is the function of the marker in software?
-by placing marker at the baseline, the value panel readout becomes a relative amplitude
What occurs in Tetanous Tension in relation to Ca2+ availability?
-continuous stimuli and continuous action potentials allow sufficient Ca2+ to saturate troponin all the time -the troponin-myosin complex is always readily unblocked -myosin can readily bind to actin and more force can be generated
What is the affect of the PTU hormone?
-decreased thyroid function (hypothyroidism) as indicated by decreased food intake, growth, and =decreased O2 consumption
Explain the twitch recruitment Experiment.
-determine the threshold stimulus for muscle contraction by progressively increasing the strength of stimulus and record the effects on muscle contraction 1. muscle must be moist and in contact with stimulating electrodes 2. Set stimulus to 500 mV->single stimulus will be delivered and contractile response of muscle at the time that the stimulus was delivered will be shown in force panel 3. Continue to increase the stimulus amplitude by 200 mV until you have 3 successive stimuli that do not produce an increase in the amplitude of the muscle contraction
What does the value panel tell you?
-displays the data values(mv or amplitude) for the action potential at the time selected by the pointer selector
What is the function of the cerebellum?
-dorsal brain stem structure responsible for control of movement
What is the resting membrane potential?
-electrical potential difference between the exterior and interior of the cell(found by placing the electrode on inside and outside of cell) - (-70mV) -potential is maintained through the constant action of ATP consuming pumps to reestablish the gradient -hydrophobic lipid bilayer->ions diffuse through ion channels
What is the Reversal/Nernst/Equilibrium Potential?
-electrochemical gradient create a driving force moving ions across the cell membrane to reach equilibrium -Eion=voltage at which that ion is at equilibrium -ion brings Vm to its Ex -chemical concentration gradient: down gradient by diffusion -electrostatic force: ion attracted by side of opposite charge Eion=[RT/zF] ln[ion, out]/[ion, in] *****Anion is in over out
Explain the tetanus experiment.
-examine muscle's response to a series of stimuli at a different frequency 1. stimulate the muscle with the supramaximal stimulus voltage at an interval of 400 ms and number of frequency to 60 2. repeat by decreasing the stimulus interval to 200 ms etc.
Explain the fatigue experiment.
-examine muscle's response to a sustained series of stimuli at high frequency 1. stimulate the muscle with supramaximal stimulus voltage at an interval of .02 seconds
What does the exocrine tissue in the pancreas consist of?
-exocrine tissue is most abundant -secretes and synthesizes digestive enzymes
Why are intracellular and extracellular recordings biphasic? Define biphasic.
-have a positive and negative deflection -Negative phase of action potential recorded extracellularly is due to how it is recorded
What is conduction velocity and what are the two methods used to calculate it?
-how fast the AP travels down the axon 1. Absolute Method 2. Difference Method
What is incomplete tetanus?
-if a relaxing stage is allowed in between stimuli and contractile force
What is the optimal sarcomere length for max tension generated?
-intermediate length in between completely contracted and fully stretched -allows for numerous cross-bridges during contraction
What is the function of the autoscale button?
-it adjusts the height of the scaled data to display the minimum and maximim data
Why is the EMG waveform irregular?
-it is recording the unsynchronized electrical activity of many muscle fibers
What should you observe on the EMG trace for reciprocal activation?
-large scale alternation of activity in the biceps and triceps
What is the set up of an intracellular recording and what kind of information do you receive?
-measures single transmembrane potential by inserting glass pipette into one cell and recording potential changes with respect to extracellular reference electrodes -Used to directly study the resting membrane potential or an action potential of the excitable cell
How do we calibrate the force transducer?
-must calibrate because raw output from the transducer is in mV and must be converted to N
What is the affect of the thyroid hormone on the mice?
-normal metabolism, growth, and development =increased O2 consumption
What are the cells in the Pars Distalis?
-pars distalis is a part of the anterior pituitary gland 1. Acidophils->growth hormones and prolactin 2. Basophils->secrete gonadotropins like FSH and LH 3. Chromophobes->secrete MSH and ACTH
Where is the pituitary gland located?
-pituitary gland is in close relationship with the hypothalamus -hormones secreted by the hypothalamus into the posterior pituitary gland -anterior and posterior pituitary gland
Where do you attach electrodes to your triceps?
-place a brown and red electrode(positive and negative) in addition to the existing electrodes, on your tricep
Explain the stretch experiment.
-progressively increase the stretch on the muscle and record the effects on the force of muscle contraction 1. stimulate the muscle with the supramaximal stimulus voltage with one pulse at length reference position 2. raise the force transducer and continue the recording as you increase stretch
What is a twitch?
-response to a single stimulus above the threshold that results in a single contraction-relaxation muscle cycle -one muscle unit can only respond with ONE twitch per stimuli -Note: muscles have multiple motor units-> contraction!
Explain the procedure and key takeaways of the sensory adaptation recording experiment for the cockroach.
-sensory adaptation: where the response to a constant stimulus gradually declines. 1. hold a spine for ten seconds while recording 2. the frequency of action potentials eventually declines as time continues
What is a sensory spine, what is its function and what are the types of spines?
-sensory spine: distributed along the femoral and tibial segments of the leg -contains sensory receptors for tactile and audovibratory stimuli -small hairs respond to air puffs and other gentle stimuli -at the base of each spine is a single sensory neuron 1. tibial spines->highly abundant(>20), diverse orientation 2. femoral spines-> lesser abundance, two rows on ventral surface 3. Femoral Tactile Spine: a single spine that projects dorsally
Where is the central sulcus and what is its function?
-separates the frontal and parietal lobe -separates motor cortex and somatosensory cortex
Where is the lateral sulcus and what is the function?
-separates the frontal and parietal lobe from the temporal
Explain the key takeaways of the spontaneous recording experiment for the cockroach.
-spontaneous recording that has been digitally filtered to remove very high or low frequencies -measure the amplitudes of the AP: from flat baseline of AP to trough
Explain the summation experiment.
-stimulate muscle with twin pulses at different pulse intervals and observe the effect on muscle contraction. 1. Stimulate the muscle with your supramaximal pulse height at 2 pulses for an interval between the pulses of 400 ms 2. Decrease the interval of time between the 2 pulses
What is tetanus?
-stimulus frequency increases, the average contractile force remains constant
What is the difference between summation and tetatnus?
-summation is as a result of two stimuli at different intervals -tetanus is as a result of many stimuli over a prolonged period of time -must have prolonged summation to reach tetanus
What happens to the EMG signal when contraction strength increases?
-the amplitude of the signal increases
What is resting membrane potential determined by?
-the difference in ion concentrations of the IC and EC fluids -relative permeability of the cell membrane to the different ion species
Why is the inside of a cell negative compared to the outside?
-the excess negative charge on the inside->large immobile organic anions -excess of positive ions(Na+) outside
What happens if your motor units are paralyzed? What would a normal EMG trace look like?
-the poison paralyzed his motor unit, the muscles won't contract with the same force as shown by the EMG trace. -Brett's normal EMG would have had a higher amplitude.
What is the maximum excitation voltage?
-the stimulus voltage at which the contractile response no longer increases supramaximal stimulus=max excitation voltage x 1.5
Compare the graphs of the conduction velocity experiment. How do the AP differ when you moved the recording electrodes further down the axon.
-the two action potentials had a longer latency period
What tension is generated at a long sarcomere length?
-thick and thin filaments barely overlap and form few cross bridges -can't generate any tension/force
What tension is generated at a short sarcomere length?
-thick and thin filaments have too much overlap before contraction -thick filaments can move thin filaments very little before thin filaments begin to overlap -can't generate any tension/force
Explain how to find the threshold voltage to conduct an earthworm AP.
-threshold: minimum stimulating voltage 1. Median Giant Fiber generates AP(Red arrow): -Start with a stimulus high enough to fire an AP(2v) -Halve the stimulus, if you still get a response -Decrease it again by a half, until you don't see anything -Then increase the final value by 0.05 V until you find the threshold 2. Further, increase stimulation voltage/higher threshold, you might see a second action potential generated by lateral axon
What is the functional unit of the thyroid gland and what are the structures?
-thyroid follicles(functional unit)->hight pink bubbles -follicular cells->surround the follicle -follicular colloid->fluid of the lumen -parafollicular cells/C Cells->located in between follicles of the thyroid gland(produce calcitonin to reduce calcium levels)
What is complete tetanus?
-when muscle reaches maximum contraction
During reciprocal activation, why is the antagonist muscle not completely silent?
-when the biceps muscle is activated forcefully, there is a minor increase in the activity in the triceps
Where is the parathyroid gland located?
-within the thyroid gland
Explain the set up of the cockroach experiment.
1. At the base of each spine is a single sensory neuron -As the spine moves, the sensory neuron associated with it creates a receptor potential that may ultimately trigger AP 2. Connect recording pins to leg-> immediately see AP or spontaneous recordings
Formulare a hypothesis on how Batratoxin works.
1. Batrachotoxin could prevent voltage-gated Na+ channels from closing resulting in a continuous depolarization and action potential of the cell. 2. Batrachotoxin could prevent the opening of the K+ channels which would prevent the cell from repolarizing after an action potential. In this case, the Na+ channels might open and close as normal, but if the K+ channels can't open and bring the membrane potential back in the negative direction(repolarization) so the neuron will remain depolarized as shown above.
What are the different thyroid levels administered to the mice to observe the rate of oxygen consumption?
1. Control Group 2. PTU Group Thyroid Hormone Group-
What is the difference method?
1. Distance: first stimulating electrode to first recording electrode 2. Latency: formed from beginning of stimulating artifact to beginning of AP -Move recording electrodes closer or further from stimulating electrodes -Move further->AP generated happens much later than previously seen 3. V=(D2-D1)/(LP2-LP1)
What are hormones secreted by?
1. Endocrine glands -pancreas -parathyroid -pituitary -thyroid -adrenal -gonads -placenta 2. Endocrine tissues with other glands -heart -liver -kidney -GI
What does the endocrine tissue in the pancreas consist of?
1. Islet of Langerhans->two big circles that secrete insulin and glucagon 2. Venules of Pancreas->drains secretions from the islet of Langerhans and provides the blood supplies to acinic cells in the pancreas
What are the functions of the cockroach spines?
1. Locomotive->movement 2. Sensory receptors: For tactile, auditory and vibratory stimuli
Explain the structures of the cerebellum.
1. Molecular Layer->close to surface contains axons -dendrites of Purkinje layer extend here 2. Purkinje layer->somas of the Purkinje cells are located here 3. Granule layer->cell bodies of axons in molecular layer are located here
Explain spontaneous firing of tactile neurons in cockroaches.
1. Observed in a small population of axons 2. Variable amplitude: a. Some vertical lines are larger than others-> different action potential amplitudes are generated by different axons b. Larger action potentials are produced by larger sensory neurons c. Position of electrodes placed on cockroach influences the action potential amplitude
How can you differentiate action potentials from noise? What kind of waveforms will you observe from spontaneous recordings?
1. Place ground electrode in coxa, and the positive electrode in the femur, observe a neg then pos waveform b/c extracellular recording 2. AP duration is 100 microsecond 3. Many axons are within the spatial detection limits of the recording electrodes placed in the femur-> many different potential amplitudes are generally visible -each is related to the size or number of sensory axons displaying spontaneous electrical activity -AP from same nerve should have similar amplitude -Amplitude: distance from top of peak to valley of the peak -Make sure leg is in natural position, is elevated on petri dish(spine is not compressed)
Explain the procedure to create co-contraction:
1. Place your elbow unsupported and bent in 90° 2. Add a small weight and record the in the EMG 3. Remove the weight and add increasing weights and measure
Explain the steps for EMG Data Acquisition?
1. Raw input(from biological or physical sources) is converted to an analog voltage by a transducer->this signal's amplitude varies over time 2. Raw signal enters PowerLab and undergoes: a. signal conditioning->amplification and filtering b. analgo voltage is sampled at regular intervals and converted from analgo->digital 3. Digital signal is transmitted to the computer
What is the difference between intracellular and extracellular recordings?
1. Size is reduced 2. Shape of wave form depends on where you place the electrodes and does not reflect different phases of the action potential 3. Intracellular recording-accurate recordings of electrical activity of single cell 4. Extracellular Recording->easier to operate and better for when you want to know that action potential has occurred and record activity of entire population of cells
Explain the procedure to create reciprocal activation:
1. Slowly flex and extend your forearm with resistant applied 2. This activates the biceps and triceps alternately 3. Perform this alternating pattern of activation for 20-30 seconds
Explain how to find the threshold value for the median giant axon in the earthworm.
1. Stimulate the earthworm at 2V to see an AP from the median giant axon 2. Reduce the stimulus voltage by half->if you see an AP response 3. Reduce the stimulus voltage by half again until you see NO AP 4. Increase the stimulus voltage by 0.05V until an AP is seen 5. threshold->stimulus voltage at which a response for the median giant fiber is first seen 6. latency-measure the time from the stimulus artifact to the start of the AP at that threshold
Explain the refractory period experiment.
1. Stimulate the earthworm at the threshold to just excite the median giant fiber 2. set the frequency to 10 ms->nerve will stimulate twice at this time -you should see two stimulus artifacts and 2 responses 3. decrease the frequency to 9ms and observe the response 4. continue to decrease the frequency until the second response disappears
What is the neuroanatomy of an earthworm?
1. Ventral nerve cord runs the length of the worm, and contains 3 giants axons with some smaller nerve fibers: a. median giant axon b. 2 lateral giant nerve fibers lying on each side of the medium one->function as single fiber due to cross connection
Explain the extracellular recording mechanism for the earthworm experiment and how the positive and negative deflections are created.
1. What is recorded: The electrical potential difference between two electrodes that are placed along the axons 2. Bipolar electrodes->one is pos and neg 3. Before stimulus is delivered both wires should be measured basically at an equal or similar voltage so there is no deflection recorded 4. Action Potential Propagates: 1st Negative electrode measures the negative EC potential=POSITIVE deflection on screen 5. Action potential progress between both recording electrodes and the recorded potential return to baseline level at the 1st electrode->no voltage differences between two recording electrodes 6. Action Potential Propagates: 2nd Positive electrode measures negative EC potential=NEGATIVE deflection on the screen 7. Once AP passes both electrodes it return to baseline
What are a few key characteristics of action potentials
1. brief and regenerative 2. all or none 3. refractory period 4. directional conductance of signals over long distances
What are the main cells of the PARAthyroid gland?
1. chief cells 2. oxyphil cells
When conductance is shown on the graph, why are both ionic traces positive? Conversely, when ionic currents are shown, why is the [K+] ionic current trace positive while the [Na+] ionic current trace is negative?
1. conductance=permeability so the ionic traces for conductance are positive because there are a lot of K+ and Na+ channels open. This would show the max current possible when all channels are open to allow max flux of permeable ions. 2. The ionic currents trace shows a positive K+ current so channels are open and K+ is flowing out in the action potential. At the same time, Na+ channels are open and Na+ flows in shown by the negative trace.
Explain the anatomy of the Femoral Tactile Spine.
1. contains a singular bipolar sensory neuron 2. Dendrite(spine wall) a. Mechanosensitive dendrites of sensory neuron in the wall of the spine lead through the spine lumen to the cell body, then the axon that proceeds along the femur b. Dendrite have consistent shapes 3. Cell body(varies in size depending on lumen diameter) a. Size of the body and nucleus increase almost linearly with the axonal diameter of the tactile spine b. Bigger the spine, the bigger the neuron cell body 4. Trachea passes through lumen of the spine
What are the functions and structures of the Posterior Pituitary gland/Hypophysis?
1. contains terminals of hypothalamic axons 2. Hormones synthesized in the hypothalamus and released in the posterior pituitary gland for storage and release into the capillary bed a. vasopressin(ADH) b. oxytocin 3. Contains specialized glial cells->pituicytes 4. Extensive Capillary networks
What are the two ways that recruiting more motor units will increase contractile strength?
1. higher amplitude stimuli can recruit MORE motor units->summation of amplitudes and stronger contractile force 2. motor units of LARGER SIZE will summate for larger contractile force
Describe major structural differences between sheep and human brain.
1. olfactory bulb of the sheep is much larger in size than that of the human olfactory bulb. 2. the sheep has a much smaller frontal lobe compared to the human brain. 3. there are more gyri and sulci in the cerebrum of the human than the sheep cerebrum. 4. the sensory nerves(ex.trigeminal nerves) in the sheep are larger and more developed in the sheep brain than in the human brain. 5. the human brain stem is towards the backbone and downwards, because the human body is vertical, while in the sheep its projected outwards because the backbone is horizontal.
What is the experimental setup for the muscle contraction experiment?
1. secure the femur in the femur clamp 2. adjust the height of the transducer so the thread connecting the muscle to the transducer has slight tension on it and is vertical 3. position the stimulating electrode so the two electrodes press into the belly of the gastrocnemius muscle
Explain the conduction velocity experiment.
1. stimulate the earthworm at a threshold for the lateral giant fibers to ensure both median and lateral are stimulated->observe AP 2. record the distance 1 from the first stimulating electrode to the first recording electrode 3. Move the recording electrodes further toward the tail end 4. stimulate the earthworm at a threshold for the lateral giant fibers to ensure both median and lateral are stimulated->observe AP 5. record the distance 2 between the first stimulating electrode and the first recording electrode 6. measure the latency period for the AP generated for both the median and lateral giant fibers at both distance 1 and distance 2
Explain what different parts of a histogram means?
1. x-axis represents the range of values 2. y-axis represents the incidence -Large bin number is associated with small bin width->get more detailed information -Must pick optimized number to show overall trend
What trends in the action potential do you notice as the temperature begins to decrease?
As temperature decreases, the time it takes for the action potential to generate increases.
Describe how the isolated muscle responded as the stimulus interval was decreased progressively
As the stimuli interval was decreased progressively, the stimuli summated and recruited a greater force from the muscle as shown by higher amplitude. At a larger stimulus interval, the individual stimuli recruited two separate contractions shown by two contractions of relatively smaller amplitude. At a shorter stimulus interval, the two stimuli summated to cause a single contraction of much higher amplitude.
As you increase voltage to the muscle, describe how it responds to the increased stimulus.
As you increase the voltage delivered to the muscle, the force increases as shown by a greater amplitude.
The IC and EC concentrations are the same for cation A. The resting membrane potential is -70mV. What is the net driving force for A during the resting stage? a. Move from IC to EC b. no net driving force c. Move from EC to IC
C
The amplitude of action potential recorded in this week's lab can be affected by A. the size of the nerve B. proximity of the nerve to the recording electrodes C. Both A and B.
C. both the size of the nerve and the proximity of the nerve to the recording electrodes
What are the types of tissues in the pancreas?
Exocrine and Endocrine Tissue
A single twitch represents the max force that a muscle can contract. True False
False
During the refractory period experiment, Action Potential generated from the first stimulus always appears before the stimulus artifact generated by the second stimulus in your recording. True or False
False
One motor unit can respond with multiple twitches per stimuli? True False
False
Spines found on cockroaches' leg contain receptors for tactile and audiovibratory stimuli. Each spine contains 2-3 sensory neurons. True or False
False
To anesthetize the worm, you can place it in a beaker filled with Worm Ringer's with 10% ethanol. True or False
False
From the MetaNeuron program, what is the final cell resting membrane potential (R.P. or Vrest) in mV? From your calculations on the previous page, what is the final cell resting membrane potential? What are the reasons for the differences between the 2 values? Hint: How many ions are being taken into account?
From the MetaNeuron Program, the final cell resting membrane potential is -64mV. From our previous calculations, the final cell resting membrane potential is -73.06mV. In the MetaNeuron simulation, the resting membrane potential is only taking K+ and Na+ permeabilities into account. In our calculations, K+. Na+, and Cl- permeabilities are taken into account so the V rest will also include the equilibrium potential of Cl- which is a negative value so it will make the resting membrane potential more negative than if only K+ and Na+ are considered like in MetaNeuron.
In the anterior pituitary region, do you see multiple cell types in each follicle or does each follicle contain a single cell type? What is the most abundant cell type? Which is the least prevalent?
In the anterior pituitary region, you see multiple cell types for each follicle, which is distinguished by the type of hormone it secretes. There are somatotropes, prolactins, gonadotropes, corticotropes and thyrotropes. The most abundant are the somatotropes which secrete growth hormone, and the least abundant cell are gonadotrophs which secrete FSH and LH.
Describe what happened to the recorded action potentials when you applied the press-and-hold stimulus to each spine. Consider amplitude, density, frequency, and any other differences in the action potentials. What is the evidence showing the spines became adapted to the stimulus?
In the press and hold experiment, the action potential amplitudes increased at first and the density or number of action potentials was much greater at the beginning of the hold compared to as time went on. As time goes on, the spines eventually adapt to the pressure and the frequency and density of the action potentials decrease. If you look at the filtered action potential screen you see action potentials with consistently high amplitudes and as time goes on the amplitudes become smaller and more spaced out demonstrating that the spine becomes adapted to the stimulus and stops firing action potentials.
The purpose of this week's lab is to a. Investigate the sensory responses by recording action potentials from a cockroach. b. Record from cockroach ventral nerve cord to investigate the conduction properties. c. Study behavior changes in cockroach after different sensory stimuli are applied. d. Use cockroach as a model to study central nervous system.
Investigate the sensory responses by recording action potentials from a cockroach.
What is conduction failure?
MUSCLE FATIGUE DUE TO TETANUS -AP repeatedly fire, EC K+ concentration in T Tubules increases from the repeated depolarization upsetting usual ion concentrations balance->can lead to failure of AP conduction
What is inhibition of cross-bridge cycling?
MUSCLE FATIGUE DUE TO TETANUS -buildup of ADP and inorganic phosphate as ATP is consumed will delay cross-bridge formation
What is acid buildup?
MUSCLE FATIGUE DUE TO TETANUS -due to lactic acid buildup can alter proteins involved with Ca2+ release
From your data, the theoretical maximum frequency at which nerve impulses can be generated by the median giant fiber was calculated. Do you think that the nerve fiber would be able to generate impulses continuously at this rate?
No. Eventually, ATP would be depleted which is needed for the pumps to move ions back to the original concentration to establish resting potential.
How do you calculate the normalized O2 consumption rate?
O2 consumption rate/grams of mouse
What causes the bubbles to move through the pipette during the experiment?
O2 is consumer by the mouse and the generated CO2 is absorbed in the set up
An intracellularly recorded nerve action potential approximates 80 mV. Why is your recorded action potential so much smaller?
Our recorded action potential is smaller because we are measuring an extracellular recording of an action potential as opposed to intracellular. As an action potential propagates, the depolarization makes the outside of the cell more negative compared to the inside of the cell, which is more positive. The extracellular recording measures the more negative outside of the cell while the intracellular recording would measure the more positive inside the cell. Therefore the intracellular recording is 80mV while the extracellular recording is more negative or a smaller value.
Compare the size of sheep olfactory bulbs to humans.
Sheep olfactory bulbs are bigger than those of humans because the smell is an important trait.
The biphasic nature of the action potential recorded extracellularly is a consequence of: the use of two extracellular electrodes spaced some distance apart to record the potential
T
The earthworm giant axon: is composed of individual cells, one in each segment, linked through gap junctions
T
The two lateral giant nerve fibers: behave as a single fiber because of extensive cross-connections between them
T
What does stretch measure?
TENSION
Define tetanus. At which stimulus interval did you observe tetanus? Explain the mechanism behind this phenomenon.
Tetanus is when the average muscle contraction is constant and prolonged when initiated by an increase in stimulus frequency. We observed tetanus at 20 ms stimulus interval. During tetanus, each muscle fiber does not have time to relax between each administered stimuli so the contraction becomes one. Nearing 20 ms stimulus interval you see a single high amplitude contraction force, while at higher stimulus intervals(so not at tetanus yet), you see multiple separate contractions.
In light of the "all or none" law of muscle contraction, how can you explain the graded response?
The "all or none" law of muscle contraction states that when the stimulus applied exceeds the threshold, the neuron will send an action potential at full force which will result in a response/action in the muscle fibers-contraction. However, graded responses depend on recruitment in which higher amplitude stimuli can recruit many motor units for a stronger contractile force with a higher amplitude. Additionally, if the motor units recruited are of greater size, there will be a stronger force of contraction.
What stretch resulted in the highest contraction force? What happens to the muscle at the highest stretch levels?
The 5mm stretch resulted in the highest contraction force of 2316mV during the twitch. As the stretch increased, the resting force increased and the contracting/twitch force increased as well. However, the muscle at the highest stretch level has a twitch force that is almost equal to the resting force since the muscle has no time to relax or rest so the peaks or net force decreased.
What is the affect of TTX?
The TTX inhibits most of the voltage gated Na+ channels that are required for an action potential to occur. Therefore, when the stimulus is applied, there will be a very small depolarization, as shown by a lower amplitude, because very few Na+ channels, if any, remain open for an action potential to occur
The typical shape of the action potential is biphasic with two peaks of opposite sign. Can you explain why this is?
The action potential is biphasic with two peaks of opposite sign because the outside of the cell becomes more negative relative to the inside of the cell. The first negative electrode is extracellular and picks up the negative charge as the action potential propagates. The double negative charge of the first electrode and the earthworm is demonstrated with a positive deflection/signal on the display. The second positive electrode picks up the negative charge as the action potential propagates showing a negative deflection/signal on the display.
Describe in detail the cellular events responsible for the absolute refractory period AND the relative refractory period
The period from the start of the action potential to immediately after the peak from depolarization is the absolute refractory period-when a second action potential cannot be initiated by a second stimulus. This is because Na+ channels are becoming inactivated and can't be depolarized by another stimulus. After, is the relative refractory period when Na+ channels begin to recover from inactivation and if a strong enough stimulus is applied, an action potential CAN be stimulated. The stimuli, however, must be stronger than the stimuli needed at rest. Eventually all the Na+ channels will come out of inactivation and an action potential can be generated.
You have seen that an action potential generated very soon after a preceding one is not full-size. Explain this observation.
The reason that an action potential generated very soon after a preceding one is not of full size is that the cell did not get to "recover". After depolarization, a cell hyperpolarizes as K+ leaves the cell and the Na+ channels become inactive. The refractory period is when the cell is hyperpolarizing and cannot trigger an action potential until all the Na+ channels become unblocked and can be stimulated and trigger the depolarization. If the stimulus is given too soon/at a short interval, this is during the absolute refractory period and no action potential will occur. If the stimulus is given during the relative refractory period, the Na+channels are slowly coming out of inactivation so the action potential will be of a smaller amplitude since not all Na+channels are ready for the depolarization yet.
Does your trace roughly match with a typical length tension curve? If not, could you provide some explanations?
The trace does match a typical length-tension curve. When you compare the net force for each stretch length, the max net force was at a length of 2mm. The lowest net force values in mN was found at the 0mm stretch length and the 5 mm stretch length which were the minimum and maximum values we tested. Therefore by looking at the shape of our line for Net Force, our trace does match the typical length-tension curve.
It is usually assumed that an action potential starts immediately at the cathode. If this were true, both methods for calculating conduction velocity would provide the same answer. However, when a strong stimulus intensity is used, the action potential may begin some distance away from the cathode. Under these conditions, the difference method would be more accurate. 5. Explain why there is a difference in the conduction velocity values produced by the two calculation methods for the median nerve. Which method is more accurate?
There is a difference in the conduction velocity values produced by the two calculation methods for the median nerves because you remove any uncertainties when it comes to measuring latencies. For this exercise, we are applying a strong stimulus and the action potential begins a distance away from the cathode. The absolute method results in much larger values for the median nerve because you just calculate the distance over latency, while the difference method results in smaller values for the median nerve because you measure the difference of distance over a difference of latencies so the difference method would be more accurate.
There was an increase in the number of fibers responding as the stimulus strength was increased. What is this type of behavior called? Is this of physiological significance to the earthworm?
This process is called recruitment when an increase in stimulus strength recruit more fibers through the activation/recruitment of additional motor units to increase the overall contractile strength. This behavior doesn't have a physiological significance to the earthworm as the median giant fibers and lateral giant fibers have different functions.
How should the normalized O2 consumption rates relate to each other?
Thyroid hormone will have the highest O2 consumption due to increased metabolic activity followed by the control, followed by the PTU treated mice who would have the lowest O2 consumption due to decreased metabolic activity.
After placing recording electrodes as instructed in the tactile spine cockroach experiment, you should always be able to observe action potentials that are firing instantaneously. True or False
True
Ground electrode should be pinned through the worm somewhere between the stimulating electrodes and the recording electrodes. True or False
True
In general, large action potentials are produced by axons with large diameters. True or False
True
Explain how the EMG trace changes when you add weights to your arm. What can you infer is happening to the muscles as weight is added?
When you added more weights to you arm, the EMG trace had higher amplitude because more motor units are being recruited to generate and support the added force.
Is there any relationship between the position of the spine and the amplitude of the stimulated action potentials? Suggest factors other than the position on the leg that could influence the amplitude of action potentials.
Yes, there is a relationship between the position of the spine and the amplitude of the action potential because the spine was closest to the recording electrode. Another factor that could affect the amplitude of the action potential is the size of the axon-larger diameter axons produce greater action potential amplitudes. If there are more axons stimulated, more than 1 neuron is firing, and if the neuron is larger, a larger amplitude would be seen.
Given a typical neuron with ENa+=+50mV and Vm=-70mV, predict the direction of Na+ flow when the membrane is forcibly set to 0mv a. flow inside of the cell b. flow outside of the cell c. no net flow
a.
Recruitment refers to: a. twitches in all the fibers of several motor units b. multiple twitches in one fiber of one motor unit c. one twitch in multiple fibers of one motor unit
a. recruitment involves stimulating more and larger motor units
Which of the following correctly describe bin number? (Choose all that apply.) a. A large bin number will allow us to see more detailed information about the data. b. A large bin number will allow us to better see the general trend of the data. c. When plotting a histogram, increase in bin number will result in a decrease bin width. d. When plotting a histogram, increase in bin number will result in an increased bin width.
a. A large bin number will allow us to see more detailed information about the data. c. When plotting a histogram, increase in bin number will result in a decrease bin width.
Given a typical neuron with Ek=-90mV and Vm=-70mV determine the direction of K+ flow when the membrane is forcibly set to the following voltages? a.Vm=0mV b. Vm=-70mV c. Vm=-90mV d. Vm=-120mV
a. OUT b. OUT c. at equilibrium potential d. IN
The primary function of three stainless steel pins serve as the a. recording electrodes. b. stabilizer. c. stimulator. d. antenna.
a. recording electrodes
As the mouse breathes inside the metabolic chamber, the soap bubble seal moves because CO2 is generated as a result and absorbed by the soda lime placed at the bottom of the chamber. The rate of this change is: a. CO2 generation and absorption rate b. can be converted to air consumption rate if divided by 21% c. O2 consumption rate
all of the above
The bubbles that are placed into the pipetted are to a. keep the system air-tight b. indicate the oxygen/air consumption
all of the above
Which of the following could result in no signal or poor signal? (Choose all that apply.) a. Worms were drowned. b. The recording pan is filled with Worm's Ringers when ensuring the worm is fully anesthetized. c. The contact between the recording pins and the worm is poor (e.g., dirty pins, electrodes are not pinned through the worm, etc.). d. The head of the earthworm is not touching both stimulating electrodes.
all of the above
Describe how the muscle responded to high frequency stimulation?
as the stimulus frequency continues, the force generated by the muscle decreases over time
The strength of a single skeletal muscle fiber twitch: a. is unaffected by stimulus frequency b. is increased with fiber stretch up to some optimal length c. is increased by stimulus magnitude up to some maximum
b.
Which of the following statements about electromyography (EMG) recording is NOT true? a. Attaching electrodes to hairy or bony area on the skin will give bad electrical contact. b. EMG is a technique that measures the contractile force of the muscles. c. The signal recorded by EMG is from multiple muscle fibers. d. In our experiment, integrated instead of raw data is used for value measurement.
b. EMG measures electrical activity NOT contractile strength
To avoid excessive amounts of background noise, you need to make sure that the cockroach leg is (Choose all that apply.) a. leg is pressed against the surface of the Petri dish. b. in a natural position. c. leg is elevated from the surface of the Petri dish. d. in a bended position.
b. in a natural position. c. leg is elevated from the surface of the Petri dish.
Which of the following is NOT a mechanism of fatigue? a. acid accumulation b. neurotransmitter release c. conduction failure d. cross-bridge inhibition
b. neurotransmitter breakdown
What is the difference between reciprocal contraction and co-contraction?
co-contraction involves the continued activation of both agonist and antagonist muscle to maintain a joint or posture
After being subjected to PTU for a period of time, the metabolic rate of a mouse will: increase/decrease
decrease
The cockroach experimental setup is an [A]__________ (extracellular, intracellular) recording. A recording collected from this setup contains action potential from [B]__________(a single, multiple) sensory axon(s).
extracellular, multiple
What does seeing broad peaks in a histogram represent
multiple action potentials at that same amplitude by the same axon
What does seeing more than 1 peak in a histogram represent?
multiple axons are firing
How do you calculate air consumption rate
normalized consumption rate/.21
What is the absolute method?
of AP 3. V=distance/latency period
Where does the display of the digital signal for an EMGoccur?
on the computer
What is the percent decline in force?
the maximal force generated due to tetanus compared to the force at the end of stimulation due to fatigue
What is the sampling rate?
the number of digital samples per second -digital samples are each of the data points that give you a smooth voltage signal
