Animal Physio LT1 Reviewer (Lab)

LAB Exercise 1 Dissolution ● ●

Results ○ Which substance(s) dissolved? ○ Which substance(s) did not? ○ How can you tell?

Filtration ● ●

Results ○ Which substances passed through the selectively permeable disk? ○ Which substances did not? ○ Why do some substances pass through the filter paper while other substances do not?

Diffusion ● Methodology ● Prepared 5% agar and poured onto 6 petri dishes in equivalent amounds ● After agar was set, a well was created in the center of each petri dish ● Prepared dyes ○ methylene blue ■ 100% ■ 50% ○ Congo red ■ 100% ■ 50% ● Filled wells with dye ○ A ■ Petri dish 1: 100% methylene blue ■ Petri dish 2: 100% Congo red ○ B ■ Petri dish 3: 100% methylene blue ■ Petri dish 4: 100% Congo red ○ C ■ Petri dish 5: 50% methylene blue ■ Petri dish 6: 50% Congo red ● Setup ○ A ■ Petri dish 1: Room temperature ■ Petri dish 2: Room temperature ○ B ■ Petri dish 3: Refrigerated ■ Petri dish 4: Refrigerated ○ C ■ Petri dish 5: Room temperature ■ Petri dish 6: Room temperature ● After finishing set-up, time was recorded ● Petri dishes were checked 10 times within 3 days to observe for diffusion and the following were done in a table: ○ time and date were recorded ○ measured distance from the edge of well to the distance of the edge of diffusion (in mm) ● Calculations and Analysis ○ Rate of linear diffusion was computed in mm per hour ○ Created line graph comparing the three setups ■ X-axis: time in hours

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■ Y-axi: rate of linear diffusion Results ○ Factors affecting diffusion ■ Temperature ● increasing temperature increases movement, allowing diffusion to take place ● all forms of motion is influenced by heat energy ● heat has the ability to cause random motion in microscopic particles such as atoms and molecules ● increase in temperature, increases rate of diffusion ■ Molecular Weight/Particle Size ● Congo red (696.68) diffused faster than methylene blue (319.86) ● methylene blue should have diffused faster because of its smaller molecular weight and particle size ● results reflect that factors other than molecular weight had more bearing on diffusion (see membrane permeability) ● increase in molecular weight, decreases rate of diffusion ■ Membrane Permeability ● agar = 5% agar + 95% water ● Congo red is water soluble ● methylene blue is slightly soluble in water ● Since agar is mostly water, and methylene is more hydrophobic, it would diffuse slower despite having a smaller molecular weight ● increase in membrane permeability, increases rate of diffusion ○ in this case, increase in water solubility, increases rate of diffusion ■ Concentration ● 100% concentrated dyes diffuse faster than less concentrated ones ○ 100% concentrations of methylene blue and congo red have 0% water ○ 5% agar has 95% water ○ dyes are more concentrated than agar (agar has more water) ○ well containing dye is concentrated so dye moved to regions with less concentration and more water (moved away from the well and toward the agar) ● 50% concentrated dyes contain 50% water ○ diffused slower into the 5% agar containing 95% water ● increasing concentration, increases rate of diffusion

Osmosis ● Concept of osmosis ○ diffusion of water through a semi-permeable membrane ○ water moves from lower solute concentration to higher solute concentration ○ water moves from higher solvent concentration to solvent water concentration ○ movement occurs until equilibrium is reached ○ solutions ■ hypotonic ● solute concentration is higher outside ● results in cell bursting ■ hypertonic ● solute concentration is higher inside ● results in cell shrinking ■ isotonic ● solute concentration is equal ● equilibrium ● Methodology ○ cellophane represented the semipermeable membrane ● Results ○ increase in solute concentratation, increases fluid displacement ■ increase in solute concentration is equivalent to the increase in concentration gradient ■ higher concentration gradient, slows down equilibrium

Hemolysis ● Concepts ○ hypotonicity ■ higher concentration of solute outside cell, a lot of water inside cell ■ cell tends to burst ■ principle behind hemolysis ○ hemolysis ■ clear solution = complete hemolysis ○ isotonic coefficient ■ molarity at which non-electrolyte (glucose) completely hemolyzed rbc ÷ molarity at which electrolyte (sodium chloride) completely hemolyzed rbc ■ amount of salts to be added to distilled water to make the solution isotonic for rbc ○ degree of dissociation ■ the fraction of the original solute that has dissociated ● Methodology ● Results ○ hemolysis was observed in setups with: ■ calcium chloride (CaCl2) ■ potassium chloride (KCl) ○ hemolysis decreases as dilution decreases ■ increase in dilution causes increase in hypotonicity, increasing hemolysis ○ 2 ions completely dissociated when the isotonic coefficient is 3 Fermentation Concept: The formation of gas by fermentation produces pressure in the tubes causing the liquid to be pushed. Methods: · Fermentation tubes were given mixtures: o A - 15 ml of 10% glucose solution o B - 7.5 ml of 10% glucose solution and 7.5 ml yeast suspension o C - 15 ml sucrose solution o D - 7.5 ml of 10% sucrose solution and 7.5 ml yeast suspension o E - 15 ml yeast suspension · The rate of fermentation was measured as the amount of gas displaced in the tube (measured by cm using ruler) and were measured at different time intervals of 10 mins, 15 mins, 30 mins, 1 hr, 2 hrs, and 24 hrs. o A and C did not ferment as there was no yeast o Change in the pressure of the tubes results when yeast ferments sugars. Production of carbon dioxide pushes the solution. Foaming was also produced due to carbon dioxide. o E should not have fermented since supposedly no sugars should be found. *Error: Residual sugars were found. Tubes were not cleaned properly o B (containing glucose) fermented faster than D (containing sucrose) because yeast fermentation converts simple sugars (glucose) to ethanol and carbon dioxide. A disaccharide, has to be first degraded into its monosaccharide units before it proceeds to fermentation. o The fast rate of fermentation of E must have occurred since E contained the most amount of yeast. · Additional test for acidity. 5 drops of phenol red was added then gently shook. The color change of the solution was: o A - Transparent yellow o B - More opaque yellow separated from a darker brown liquid o C - Transparent yellow o D – Most opaque yellow

o E - More opaque yellow separated from a darker brown liquid Phenol red is a pH indicator that turns red at or above pH 7 (alkaline) and turns yellow at a pH lower than 7 (acidic). All setups produced a yellow color indicating their acidic nature. Carbon dioxide from fermentation reacted to components of the solution which yield to acids such as carbonic acid.

Exercise 2 Brainstem Reflexes ● Methodology ○ Pupillary Reflex ■ shine light on one eye and observe pupil of that eye ○ Consensual Pupillary Reflex ■ shine light on one eye and observe pupil of that other eye ○ Ciliospinal Reflex ■ pinch neck and observe reaction of eyes ○ Corneal Reflex ■ suddenly touch cornea of eye and see what happens ○ Orbicularis Oculi Reflex ■ surprise person by flashing light on their eyes and observe reaction ○ Auditocephalogyric Reflex ■ surprise person with loud sound and observe reaction ○ Gag Reflex ■ prod pharyngeal region of neck and see what happens ● Results ○ Pupillary Reflex ■ result: pupil constriction ● pupil‟s role is to allow light to enter retina ● constriction happens when there is too much light to protect photoreceptors ■ anatomic components ● CN II ○ Optic nerve ○ sensory nerve for eye region: responsible for detecting stimuli ● CN III ○ Oculomotor nerve ○ motor nerve: responsible for effector ○ Consensual Pupillary Reflex ■ result: pupil constriction ● though unexposed to light, also constricts so response is consensual ● optic tract conducts visual information from both eyes and the pretectal area projects bilaterally to both Edinger-Westphal nuclei ○ pretectal area ■ narrow, transversely oriented rostral zone of the mesencephalic tectum ■ contains several nuclei that receive fibers from the optic tract ■ has bilateral efferent connections with the Edinger-Westphal nucleus of the oculomotor nuclear complex by way of which it mediates the pupillary light reflex ○ Edinger-Westphal nuclei ■ contains preganglionic parasympathetic (visceromotor) neurons whose axons end in the ciliary ganglion ■ Input to the Edinger-Westphal nucleus arises from a cell group called the pretectum, a cell complex that receives retinal input and is part of the pathway involved in reducing the size of the pupil upon light stimulation of the retina ■ anatomic components ● CN II

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Optic nerve sensory nerve for eye region: responsible for detecting stimuli Oculomotor nerve motor nerve: responsible for effector

Ciliospinal Reflex ■ result: pupil dilation ● eyes dilate in response to pain: defense against noxious stimuli ● person becomes alert to sensations of pain in neck ■ anatomic components ● CN II ○ Optic nerve ○ sensory nerve for eye region: responsible for detecting stimuli ● CN III ○ Oculomotor nerve ○ motor nerve: responsible for effector Corneal Reflex ■ result: blinked ● blinked in response to tactile stimulation as defense mechanism ■ anatomic components ● CN II ○ Optic nerve ○ sensory nerve for eye region: responsible for detecting stimuli ● CN III ○ Oculomotor nerve ○ motor nerve: responsible for effector Orbicularis Oculi Reflex ■ result: blinked ● defense to noxious stimuli ■ anatomic components ● CN II ○ Optic nerve ○ sensory nerve for eye region: responsible for detecting stimuli ● CN III ○ Oculomotor nerve ○ motor nerve: responsible for effector Auditocephalogyric Reflex ■ result: head and eyes turned toward direction of stimulus ● defense mechanism: concept of „arousal‟ from psychology ● arousal: type of bodily energy which primes or prepares us for emergency action ■ anatomic components ● CN IV ○ Trochlear nerve ○ motor nerve: responsible for eye movement ○ directed eye to seek stimulus (loud sound) ● CN VIII ○ Vestibulocochlear nerve ○ sensory nerve: for hearing and balance ● CN XI ○ Spinal accessory nerve ○ motor nerve: responsible for head movement Gag Reflex ■ result: gagged ● defense mechanism: discourage organism from eating incompatible substances (allergenic, toxigenic) ■ anatomic components ● CN IX ○ Glossopharyngeal nerve ○ sensory nerve: responsible for detecting stimuli in pharyngeal area ● CN X ○ Vagus nerve ○ sensorimotor nerve: responsible for sensory and motor functions in

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viscera triggers regurgitation

Stretch (Deep Tendon) Reflexes Spinal Cord Reflexes Reflex ● ●

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basic unit for behavior is the reflex generally occur quickly and are the result of excitation of ○ sensory receptors ○ afferent nerve fibers ○ integration by the central nervous system ○ transmission of motor impulses over efferent (motor) nerve fibers ○ excitation of an effector organ /tissue. spinal cord may act as the primary integrator and source of a motor nerve response (spinal reflex) or as a modulator of motor responses when the brain or higher regions of the spinal cord are involved integrating and modulating activity on reflex activity is observed best when the controlling influences of the brain are removed (why pithing is needed)

Single pithing ● ablation of brain ● insert the scissors so they are back against the joint between the upper and lower jaws before cutting ● effectively breaks all connections between the brain and the spinal cord, it therefore eliminates any influence the brain could have on reflex activity Double pithing ● ablation of spinal cord and brain ● destroy the spinal cord by insertion of a mental dissection probe/needle into the open vertebral canal by the single pith

Muscle Tonus Electroencephalography (EEG) Reflex and Reaction Time Compound Action Potentials in Frog Sciatic Nerve large peripheral nerves ● bundles of thousands of individual axons encolosed in epinerium ● ex. vagus, sciatic, ulnar nerves epinerium ● loose connective tissue sheath fascicles ● smaller bundles of axons within epinerium ● each of which is also encased in perineurium perineurium ● more structured epithelial sheath endoneurium ● each individual axon is surrounded by a very thin individual connective tissue sheath

toad‟s sciatic nerve ● consists of only a single bundle of fibers, surrounded by the perineurium and loose epineurium Compound nerve ● ex. sciatic nerve ● typically contains efferent (α and γ motor axons, and post-ganglionic autonomic axons) and afferent (sensory) axons ● individual axons vary in diameter, myelination, excitability, threshold and conduction speed. Compound Action Potential ● algebraic sum of many individual “all-or-none” action potentials arising more or less simultaneously in a large number of individual axons in a large compound nerve does not occur naturally ● elicited experimentally or clinically by stimulating the whole nerve with extracellular stimulating electrodes and is recorded by means of extracellular recording electrodes, which measure the summed electrical response of all the excited axons in the nerve ● properties of the CAP: threshold, amplitude, duration, conduction velocity are determined by the type and number of individual axons which are recruited (excited) by the stimulus ○ number and type of axons excited depend on the intensity of the stimulus ● demonstrated by extracellular recording from many axons, is a graded response whose magnitude increases with the intensity of stimulation because different axons have different thresholds of excitation ● largest axons have the lowest threshold of excitation i.e., they are the most excitable. (Thus, in terms of excitability, Aα axons>Aβ>Aγ>Aδ>B>C) ● at low stimulus intensities, only the largest axons are activated, but as the stimulus intensity is raised in steps, more and more smaller axons are progressively recruited ● shape has the biphasic and unsymmetrical characteristics ● biphasic: each has a positive and negative component ○ biphasic nature of the CAP is due to the fact that the CAP is recorded with a pair of extracellular electrodes (bipolar recording) ○ when the nerve is inactive, there is no potential difference between the electrodes, and the trace is at baseline ○ When the CAP arrives at the indifferent electrode (1), the electrode becomes transiently negative to the recording electrode (2), the potential difference between the two is detected and amplified by the differential amplifier, and the polarity is stated in terms of the sign of charges in the recording electrode (3), and the trace is displayed as an upward deflection on the screen ○ When the CAP lies between the indifferent and recording electrodes there is no potential difference between the two electrodes and the trace returns to baseline ○ As the CAP moves down the nerve, the recording electrode becomes relatively negative and the potential difference between the electrodes is now seen as a downward deflection on the screen. Single Action Potential ● demonstrated by intracellular recording from a single axon ● “all-or-none” response: that is, under normal circumstances, the amplitude of the response does not change with stimulus intensity (above threshold) ● biphasic: each has a positive and negative component ○ The classic biphasic action potential recorded inside a single axon with a single intracellular electrode consists of an initial (positive) depolarization due to a transient increase in Na+ permeability, followed by a negative phase of hyperpolarization ○ hyperpolarization is due to a prolonged increase in K+ permeability ○ positive and negative phases of the intracellular action potential are thus generated by a sequence of selective membrane permeability changes, which result in depolarization and hyperpolarization of the cell membrane. ● conduction velocity of individual action potentials increases with the axon diameter ● action potentials of the largest axons will reach the recording electrodes first Stimulus artifact ● display initially will show only a brief biphasic deflection. ● results from the instantaneous spread of passive electrical current from stimulating to recording electrodes by the electrolyte on the surface of the nerve Initially, at low stimulating voltages, there will be no CAP. CAP: as stimulus strength (voltage) is gradually increased a small deflection appears to the right of the SA

Threshold Stimulus Voltage ● by carefully raising and lowering the stimulating voltage, find the smallest discernable deflection Maximal Stimulus Voltage ● Continue to increase the stimulating voltage, observing the changes in shape and magnitude of the CAP until further voltage increase no longer increases the amplitude of the CAP Refractory Period ● during the action potential, a second stimulus will not produce a second action potential. ● we can give the sciatic nerve two stimuli successively, and the intensity of the two stimuli is identical ● If the first stimulus can produce an action potential, then the second stimulus can also produce action potential, if the interval of the two stimuli exceeds the refractory period of the action potential arising from the first stimulus ○ At the beginning, the interval of the tow stimuli is very long and exceeds the refractory period of the first action potential arising from the first stimulus considerably. Under this circumstance, both the two stimuli can produce action potential ○ Then, we minish the interval gradually, at first, we can record two action potential ○ When the internal is short enough that it equals the refractory period of the first action potential, the second stimulus can‟t produce action potential, and the interval of this two stimuli is the refractory period of the action potential. Conduction Velocity ● d/t --where d = the conduction distance; --and t = the conduction time.

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Study Questions How does a CAP differ from a single action potential? A compound action potential is the sum of multiple axons in a nerve firing, while a single action potential is generated by just one axon. single action potential (recording from a single axon) is an “all or none” response ○ under normal circumstances, the amplitude of the response does not change with stimulus intensity ○ conduction velocity of individual action potentials increases with axon diameter ■ action potentials of the largest axons will reach the recording electrodes first ○ compound action potential (recording from many axons) is a graded response ○ magnitude increases with intensity of stimulation ○ this is because different axons have different thresholds of excitation ■ largest axons have the lowest thresholds of excitation and are the most excitable ○ at low stimulus intensities, only the largest axons are activated ○ as stimulus intensity is raised in steps, more and more smaller axons are progressively recruited

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Action potentials are said to be all or none responses. Why does the frog sciatic nerve give a graded response? The frog sciatic nerve is made up of different axons, each with their own threshold. Some are higher than others while some are lower. Therefore, as you increase the voltage, more and more of them fire, giving a seemingly graded response This graded response phenomenon illustrates the differences in threshold that exists among the different sizes of fibers that make up the nerve. Remember, you are recording from a nerve, a large bundle of neurons, each with a different threshold. If the stimulus voltage is increased slowly and smoothly, you may observe discrete jumps in the amplitude of the compound action potential as different threshold classes of nerve fibers are “recruited”. As you increase the amplitude more neurons reach their threshold and contribute to the increase in size of the compound action potential. Eventually, as the stimulus voltage is increased, a point will be reached when the wave form of the action potential stops changing. At this point all

the fibers in the nerve able to respond to the stimulus are being stimulated. This is a maximal response. 3. ● ●

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In this exercise, you examined the effect of increasing stimulus intensity on the nerve. What other stimulus parameter might also affect the nerve‟s tendency to generate a CAP? Frequency and duration can affect the nerve‟s tendency to generate a CAP; frequency in that if there‟s the right amount of time between them, their effects can be additive and trigger a CAP; duration in that even a weak stimulus can potentially trigger a CAP if kept up long enough

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Explain the difference between the relative and absolute refractory periods. No action potentials can be fired during the absolute refractory period since too many Na+ channels are voltage inactivated from the last action potential being fired. However, during the relative refractory period, enough Na+ channels have opened back up to allow another action potential to be fired, though a stronger stimulus than normal will be required.

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Briefly describe the cellular events responsible for the refractory period. (Hint: Discuss the mechanism of repolarization.) After an action potential is fired, a large fraction of the cell‟s Na+ channels are voltage inactivated, preventing a second action potential from being fired. This is the absolute refractory period. The cell then releases K+, repolarizing the membrane and causing the Na+ channels to open back up. Between the absolute refractory period and reaching the normal resting membrane potential comes the relative refractory period, which is explained above.

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What was the smallest voltage required to produce the maximum (largest) CAP? What proportion of the nerve fibers were excited to produce this maximal response? To produce a maximum response, the whole nerve must be stimulated. If the stimulus voltage is increased slowly and smoothly, you may observe discrete jumps in the amplitude of the compound action potential as different threshold classes of nerve fibers are “recruited”. As you increase the amplitude more neurons reach their threshold and contribute to the increase in size of the compound action potential. Eventually, as the stimulus voltage is increased, a point will be reached when the wave form of the action potential stops changing. At this point all the fibers in the nerve able to respond to the stimulus are being stimulated. This is a maximal response.

Based on your calculation for CAP conduction velocity, how long would it take the CAP to travel the length of the sciatic nerve? Assume a total length of 10 cm. The conduction velocity of the action potential is determined by measuring the distance traveled (length of the nerve in m) and dividing by the time (sec) taken to complete the reflex arc, also called the latency. Conduction velocity = distance (m)/time (sec). 0.1 m / t = 155.4 m/s -4 t = 0.1 m / 155.4 m/s = 6.44x10 seconds

Exercise 3 Prelab Study Questions 1. Where is the gastrocnemius muscle and sciatic nerve in the frog and in you? ● Gastrocnemius ○ largest and most superficial of calf muscles ○ part of Triceps Surae ○ main propellant in walking and running ○ Location in Human

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Location in Frog

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Sciatic Nerve ○ main nerve traveling down the leg ○ major branch of sacral plexus ○ innervates most of the hind limb ○ mixed-function nerve: made up of axons of sensory and motor neurons ○ Location in Human

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Location in Frog

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How does an action potential move in a bundle of neurons like the sciatic nerve? compound action potential (recording from many axons) is a graded response ○ magnitude increases with intensity of stimulation ○ this is because different axons have different thresholds of excitation ■ largest axons have the lowest thresholds of excitation and are the most excitable ○ at low stimulus intensities, only the largest axons are activated ○ as stimulus intensity is raised in steps, more and more smaller axons are progressively recruited

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What is the function of the PowerLab hardware and software? Components of the PowerLab recording system. ○ Hardware ■ Transducer ● Transforms the energy of a physiological event into electrical energy. ■ Amplifier ● Amplifies the electrical signals from the transducer. ■ Data acquisition unit ● Converts analog signals from the transducer or amplifier into digital information. ■ Computer ● Records, displays, stores, and analyzes data. ● Chart resembles a chart recording device.

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● Scope resembles an oscilloscope. Software ■ LabTutor software ● offers complete life science experiments, in one easy-to-follow web browser interface including: ○ experiment background information ○ set up protocols ○ real-time data acquisition ○ laboratory reports

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What type of signal does the Powerlab hardware receive?

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What is tetanus? infection of the nervous system with the potentially deadly bacteria Clostridium tetani (C. tetani) infection begins when the spores enter the body through an injury or wound often begins with mild spasms in the jaw muscles (lockjaw) tetany: sudden, powerful, and painful contractions of muscle groups caused by prolonged muscular action; may lead to muscle tears and fractures

Physiology of the amphibian skeletal muscle ● Graded Response ● Effect of Load on Contraction Force ● Effect of Pulse Frequency on Contraction Force Tetanus Relationship between stimulus voltage and contraction strength effect of stimulus strength ● threshold stimulus, and maximal response at the lowest stimulus strength that results in some contraction (i.e. Threshold), only a few motor units are stimulated ● by increasing the strength of stimulus, an increased number of motor units can be "recruited" to increase contraction force, and a greater displacement (muscle contraction) is recorded on the graph. effect of stimulus frequency on skeletal contraction muscle contraction ● results in development of tension or force usually measured in grams ● muscles will shorten if they develop more force than the force that is opposing them ● ex: contracting muscles in our arm will shorten and allow us to lift a book if the force developed by the muscles is greater than the weight (force) of the book. no tetanus ● stimuli are applied at a frequency where the time interval between stimuli is longer than the time it takes for the muscle fibers to completely contract and relax, then no tetanus (no temporal summation) is observed partial/incomplete tetanus ● stimulus frequency was increased until the muscle fibers no longer had time to completely relax ● partial relaxation between muscle twitches ● most sustained voluntary skeletal muscle contractions are incomplete tetanic contractions with different motor units stimulated at different times (asynchronous contractions) ● asynchronous contractions delay muscle fatigue, which is an inability to contract caused by long periods of muscle contraction ● stimuli is applied at a frequency where the time interval between stimuli is shorter than the time it takes for the muscle fibers to completely relax, then partial (incomplete) tetanus is observed ● type of wave summation with partial relaxation observed between twitches

fused/complete tetanus ● stimulus frequency was increased further so that the muscle fiber could not even begin to relax ● sustained contraction with no relaxation observed between twitches ● stimuli are applied at a frequency where the time interval is shorter than the time it takes for the muscle fibers to even begin to relax, then fused (complete) tetanus is observed ● type of wave summation with no observable relaxation between twitches twitch contraction ● type of muscle contraction, but not normal muscle contractions ● single, brief stimulus is applied to a muscle fiber, either naturally in the form of a nerve impulse, or artificially in the form of an electrical stimulus ● quick shortening observed in a skeletal muscle when a single action potential traveling down a motor neuron stimulates the skeletal muscle fibers of the motor unit to contract ● single contractile event in response to single action potential

three phases of twitch contraction latent period ● lasts about 2 msec (milliseconds) ● time between stimulation of muscle cells and force generation contraction period ● lasts about 10–100 msec ● period during which force (measured in grams) is increasing relaxation period ● which lasts 10–100 msec ● period when force is decreasing ● phase of contraction; period during which more crossbridges detach than reattach to thin filaments normal muscle contractions ● not twitch contractions ● sustained contractions of varying force threshold stimulus ● minimal stimulus that results in a muscle twitch maximal stimulus ● stimulus that produces maximal force is called the maximal stimulus ● stimulus to the muscle greater than maximal does not produce a greater force wave summation ● if the muscle fibers of a motor unit are stimulated before the relaxation phase of a muscle twitch is complete, then the next contraction will produce a greater force ● how to increase force generated ● increasing the frequency of muscle stimulation produces sustained force generation ● increasing the number of motor units contracting at the same time, motor unit recruitment increases force generated maximal force development ● occurs when all motor units of a muscle are stimulated and all muscle fibers are contracting fatigue ● an inability to contract caused by long periods of muscle contraction wave/temporal summation ● force of contraction seems to increase like the sum of the individual contraction waves

load ●

force that the muscle is contracting against.

displacement ● strength of contraction ● sum of the force exerted by all the motor units that are excited recruitment ● multiple motor unit summation ● increasing the number of motor units that are stimulated to contract motor unit ● motor neuron and all the muscle fibers it innervate

Fatigue Electromyography Smooth muscle Postlab Study Questions 1. In light of the “all or none” law of muscle contraction, how can you explain the graded response? ● The frog sciatic nerve is made up of different axons, each with their own threshold. Some are higher than others while some are lower. Therefore, as you increase the voltage, more and more of them fire, giving a seemingly graded response ● This graded response phenomenon illustrates the differences in threshold that exists among the different sizes of fibers that make up the nerve. Remember, you are recording from a nerve, a large bundle of neurons, each with a different threshold. If the stimulus voltage is increased slowly and smoothly, you may observe discrete jumps in the amplitude of the compound action potential as different threshold classes of nerve fibers are “recruited”. As you increase the amplitude more neurons reach their threshold and contribute to the increase in size of the compound action potential. Eventually, as the stimulus voltage is increased, a point will be reached when the wave form of the action potential stops changing. At this point all the fibers in the nerve able to respond to the stimulus are being stimulated. This is a maximal response. 2.

What effect does stretching the muscle have on contraction strength? Is this effect linear? What preload force resulted in the highest contraction force?

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What effect does varying the stimulation frequency have on contraction force? Which stimulus interval caused the greatest contraction force?

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Define tetanus. At which stimulus interval did you observe tetanus? Definition ○ infection of the nervous system with the potentially deadly bacteria Clostridium tetani (C. tetani) ○ infection begins when the spores enter the body through an injury or wound ○ often begins with mild spasms in the jaw muscles (lockjaw) ○ tetany: sudden, powerful, and painful contractions of muscle groups caused by prolonged muscular action; may lead to muscle tears and fractures what stimulus interval ○ partial stimulus ■ stimulus frequency was increased until muscle had no time to completely relax ■ partial relaxation between muscle twitches

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stimuli are applied at a frequency where the time interval between stimuli is shorter than the time it takes for the muscle fibers to completely relax fused/complete tetanus ■ stimulus frequency was increased further until muscle could not even begin to relax ■ sustained contraction wherein no relaxation observed between twitches ■ stimuli are applied at a frequency where the time interval is shorter than the time it takes for the muscle fibers to even begin to relax

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At what time point did your muscle begin to fatigue? Calculate the % decrease in contraction force by comparing the force at the end of the experiment with the maximal contraction force.

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In your own words, explain a possible mechanism for why the muscle was unable to maintain a prolonged contraction in this experiment. .