The Muscle Twitch and the Latent Period

PhysioEx Lab Report Exercise 2: Skeletal Muscle Physiology Activity 1: The Muscle Twitch and the Latent Period Name: Date: 15 September 2020 Pre-lab Quiz Results You scored 100% by answering 5 out of 5 questions correctly. 1 Skeletal muscles are connected to bones by You correctly answered: tendons. 2 Skeletal muscles are composed of hundreds to thousands of individual cells called You correctly answered: fibers. 3 The term motor unit refers to You correctly answered: one motor neuron and all of the skeletal muscle fibers it innervates. 4 The motor neuron and muscle fiber intersect at what is called You correctly answered: the neuromuscular junction. 5 A twitch is You correctly answered: one contractile response to a single action potential. Experiment Results Predict Question 1 Predict Question: Will changes to the stimulus voltage alter the duration of the latent period? Your answer: Yes, changing the stimulus voltage will change the latent period duration proportionately. Stop & Think Questions 1 What is the period of time that elapses between the generation of an action potential and the start of muscle tension development in a muscle fiber? You correctly answered: The latent period. 2 What occurs during the latent period of these isometric contractions? You correctly answered: All the steps of excitation-contraction coupling occur. Experiment Data Voltage (v) Length (mm) Active Force Passive Force Total Force Latent Period (msec) 0 75 0 0 0 3 75 1.04 0 1.04 ---- ---- 4 75 1.32 0 1.32 4.00 2 75 0.66 0 0.66 3.20 4 75 1.32 0 1.32 3.20 6 75 1.65 0 1.65 3.20 8 75 1.81 0 1.81 3.20 10 75 1.82 0 1.82 3.20 Voltage = 0 V Voltage = 3 V Voltage = 4 V Voltage = 2 V Voltage = 4 V Voltage = 6 V Voltage = 8 V Voltage = 10 V Post-lab Quiz Results You scored 100% by answering 6 out of 6 questions correctly. An action potential in a motor neuron triggers the release of which neurotransmitter? You correctly answered: acetylcholine. 2 The term skeletal muscle fiber refers to You correctly answered: an individual skeletal muscle cell. 3 The graded depolarization in the skeletal muscle fiber that is elicited in response to one action potential from the motor neuron is called You correctly answered: an EPP (end-plate potential). 4 Which of the following is not a phase of a skeletal muscle twitch? You correctly answered: hyperpolarization phase. 5 A skeletal muscle twitch is You correctly answered: one contractile response to a single action potential. 6 Which of the following correctly matches the twitch phase with its definition? You correctly answered: the contraction phase: the time between the end of the latent period and peak muscle tension. Review Sheet Results 1 Define the terms skeletal muscle fiber, motor unit, skeletal muscle twitch, electrical stimulus, and latent period. Your answer: Skeletal muscle fiber: the mechanical response to a single action potential motor unit: one motor neuron and all the muscle fibers skeletal muscle twist:mechanical response to a single action potential. electrical stimulus: stimulus that activates the end plate potential latent period: the time period between a action in a muscle cell and when the muscle starts to contract. 2 What is the role of acetylcholine in a skeletal muscle contraction? Your answer: Acetylcholine is released in the end plate potential. It binds receptors to the motor and initiates the change in ion permeability. 3 Describe the process of excitation-contraction coupling in skeletal muscle fibers. Your answer: Converts an electrical stimulus to a mechanical response. It is the link between action potential and the start of muscle contraction. 4 Describe the three phases of a skeletal muscle twitch. Your answer: latent period: the time between action potential and the start of muscle contraction contraction phase: starts at the muscle contraction (end of latent period) and ends when the muscle tension peaks relaxation phase: the time elapsed between muscle tension peak and the end of the muscle contraction. 5 Does the duration of the latent period change with different stimulus voltages? How well did the results compare with your prediction? Your answer: Stimulus voltage increases while the active force of muscle increases. The latent period is the time between the potential and the muscle contraction, and I found that the latent period changed (increased) in time when the stimulus voltage was increased. 6 At the threshold stimulus, do sodium ions start to move into or out of the cell to bring about the membrane depolarization? Your answer: At the threshold stimulus, sodium ions start to move into the cell.