Twin-Pulse Facilitation Measured as Twitch Ratios in the Frog Sciatic Nerve/Gastrocnemius Muscle Preparation

Neuromyotonia is an extremely unusual disorder, where impulsive motor unit are constantly firing and activating the muscle fibers. Neuromyotonia has several symptoms but the most common ones are muscle pains and twitching. The condition affects the voltage-gated potassium channels, by reducing the number of voltage gated potassium-complex resulting in prolonged depolarization of the motor nerve terminal and excessive acetylcholine release. Treatment depends on the varying symptoms from person to person but usually people are prescribed with medication or undergo a plasma exchange.

Pinnington, N., Elliott, A., Sciences, F. of L., Manchester and Kingdom, U. (2007) Proceedings of the physiological society. Available at: http://www.physoc.org/proceedings/abstract/Proc%20Physiol%20Soc%208PC39 (Accessed: 3 March 2016).

3. Increasing frequency of stimulation to the trigger zone: DOES NOT increase the production of action potentials.

Muscle contraction can be understood as the consequence of a process of transmission of action potentials from one neuron to another. A chemical called acetylcholine is the neurotransmitter released from the presynaptic neuron. As the postsynaptic cells on the muscle cell membrane receive the acetylcholine, the channels for the cations sodium and potassium are opened. These cations produce a net depolarization of the cell membrane and this electrical signal travels along the muscle fibers. Through the movement of calcium ions, the muscle action potential is taken into actual muscle contraction with the interaction of two types of proteins, actin and myosin.

5. Now take each stage in turn and discuss how sustained neural activity could create a dysfunction and result in a decrease in muscle response during repetitive motor nerve stimulation.

As a result of the contractions in the Muscle- Skeletal Longitudinal Section cells and the Muscle- Skeletal Cross Section cells, it allows your muscle to be able to contract in response to nerve stimuli. This means that the movements of most of these muscles are not involuntary, you can control them. Therefore, once the stimulation stops, the muscles relax.

Next with a stimulation duration of 50us, the stimulus amplitude should be set to the maximal tolerable stimulus intensity. With stimulus frequency of 2Hz, observe and record the leg movement, increase it by 5Hz but should not exceed 50Hz. With the electrodes connected to the analogy output channel and ground of the DAQ board. With the corresponding LabVIEW program, the frequency and amplitude (voltage) of the stimulation supplied to the leg can be controlled. With this the “sweet spot” of the lowest amplitude and best frequency to cause evoked movement can be found and recorded. Now the stimulation frequency should be set to 10Hz and the duration of stimulation pulse to 5ms or less. The range if leg movement changes can be observed as amplitude changes. Electrical stimulation in increments of 0.01V should be delivered and the minimal voltage required to generate muscle twitch should be recorded. The pulse duration should then be increased by durations of 10ms and the minimum voltage should be recorded this should be repeated for a variety of pulse

In this exercise, you examined the effect of increasing stimulus intensity on the nerve. What other stimulus parameter

Neurons can fire efficiently or it can also work too hard or too little. These patterns can in

() who stated that stimulation of dMT axonal fibers with brief light pulses did not evoke fast synaptic inputs in CeL neurons. Only small, slow inward currents were reported following high frequency light stimulation. The diverging results may be the consequence of differing viral transduction efficiency or stimulation conditions. Interestingly, the apparent connectivity of dMT and BA was substantially greater as compared to dMT and CeL. Furthermore, synaptic responses evoked in BA PNs were larger as compared to those in CeL neurons regarding absolute amplitudes of AMPAR- and NMDAR-mediated currents under similar stimulation conditions. The effect may be due to stronger innervation of the BA by dMT efferents, to increased presynaptic transmitter release or to increased postsynaptic receptor expression. The AMPAR/NMDAR ratio, which may give an indication of input-independent basal synaptic strength based on postsynaptic AMPAR occupancy, did not reveal any differences dMT-BA and dMT-CeL synapses. Interestingly, AMPAR silent synapses were discovered in the CeL. These synapses may be recruited during periods of increased synaptic input and facilitate

A simple spinal reflex is a reflex—involuntary, graded, patterned response to a stimulus—that is produced via a single synapse between sensory axons and motor neurons and confined to the spinal cord. In this experiment, two simple spinal reflexes—the myotactic reflex and the H-reflex—were stimulated. We compared a) the latency period—the amount of time between a stimulus and the effector response— and the amplitude—magnitude of an electrical signal—of each reflex; then, b) the effect of the Jendrassik Maneuver (JM) upon the latency period and amplitude of each respective reflex. For the myotactic response, a mechanical stimulus, a sharp strike of the patellar tendon, was utilized to elicit a signal in stretch receptors; however, to trigger the H-reflex, an electrical impulse was applied. These reflexes originate from an action potential produced by a sensory neuron when a stimulus is applied. Sensory neurons transmit the action potentials to an integrating center—the spinal cord—where a response is determined. Then, this response is taken back to the effector organ via motor neurons. The reflex occurs while the brain is becoming aware of the stimulus. Furthermore, the myotactic reflex is

4. 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?

2. What occurs in the muscle during this apparent lack of activity? Ca++ is being released from the sacroplasmic reticulum and filament movement is taking up slack.

Exercise 2: Skeletal Muscle Physiology: Activity 3: The Effect of Stimulus Frequency on Skeletal Muscle Contraction Lab Report Pre-lab Quiz Results You scored 100% by answering 4 out of 4 questions correctly. 1. During a single twitch of a skeletal muscle You correctly answered: b. maximal force is never achieved. 2. When a skeletal muscle is repetitively stimulated, twitches can overlap each other and result in a stronger muscle contraction than a stand-alone twitch. This phenomenon is known as You correctly answered: c. wave summation. 3. Wave summation is achieved by You correctly answered: a. increasing the stimulus frequency (the rate of stimulus delivery to the muscle). 4. Wave summation increases the force produced in the muscle.

The compound action potential adds up all the action potentials that each individual neuron experiences in the sciatic nerve. Different stimulus amplitudes cause different neurons to fire an action potential; this is due to the fact that each neuron has a different threshold potential, or the minimum voltage the neuron needs to fire an action potential. The individual neuron action potential is an ‘all-or-nothing’ event, but the CAP, as a summation of different individual neurons, is not. The CAP amplitude will increase with larger stimulus potentials because more neurons with higher individual thresholds will be recruited. For this frog sciatic nerve, there are three fiber types, A, B, and C. A fibers are further divided, in the order of decreasing diameter, into α, β, γ, and δ fibers. There is an inverse relationship between the diameter of the nerve fiber and the threshold potential: the larger the diameter, the lower the threshold. Thus, as the largest fibers, the Aα neurons will be the first to be stimulated at a low stimulus potential, and the Aδ neuron fibers will be the last to be recruited. Because the sciatic nerve is mostly composed of A fibers, the recruitment of A-subtype nerve fibers are more readily distinguishable from the data. The minimum potential required to stimulate the Aα fibers was between 75 mV and 80 mV. Once the stimulus potential reached 90 mV, Aβ neurons were recruited and contributed to the increase in amplitude of the CAP. At a stimulus