LAB TIME/DATE _______________________
Skeletal Muscle Physiology
The Muscle Twitch and the Latent Period
1. Define the terms skeletal muscle fiber, motor unit, skeletal muscle twitch, electrical stimulus, and latent period. Motor unit- single α-motor neuron and all of the corresponding muscle fibers it innervates; all of these fibers will be of the same type Skeletal muscle fiber- long and narrow cells that often span the entire length of a muscle Skeletal muscle twitch- an activation of a muscle by firing a motor neuron Electrical stimulus- the application of an electric current by means of a prosthesis to stimulate and restore partial function to a muscle disabled by neurologic lesions Latent period-a seemingly inactive period, as that between exposure to an infection and subsequent illness, or that between the instant of stimulation and the beginning of response. 2. What is the role of acetylcholine in a skeletal muscle contraction? Acetylcholine is the chemical signal the nerve sends to the muscle to cause contraction
3. Describe the process of excitation-contraction coupling in skeletal muscle fibers. ACH is released at the end-plate potential. ACH diffuses into the sarcolemma, attaches to the receptors in the motor end plate and causes a change in the ions permeability that creates graded depolarization of the end-plate potential. Basically, it attaches to the receptors in the motor-end plate and creates the beginning process of triggering muscle contractions.
4. Describe the three phases of a skeletal muscle twitch. Latent Phase: During this phase there is no muscle contraction. This phase is the period of time prior to muscle contractions. The latent phase, chemical changes in the cells occur in preparation for muscle contractions. Contraction Phase: Is the period in which the muscle tension is at it's highest. This is the time where the greatest amount of muscle force is generated. It begins at the end of the latent period and ends when tension peaks at it's highest. Relaxation Phase: The period of contraction after the contraction phase, and ends at end of muscle contraction.
5. Does the duration of the latent period change with different stimulus voltages? How well did the results compare with your prediction? No. The latent period remained the same
6. At the threshold stimulus, do sodium ions start to move into or out of the cell to bring about the membrane depolarization? The threshold is the time at which the sodium ions start moving into the cell to bring about the membrane depolarization.
A C T I V I T Y 2
The Effect of Stimulus Voltage on Skeletal Muscle Contraction 1. Describe the effect of increasing stimulus voltage on isolated skeletal muscle. Specifically, what happened to the muscle force generated with stronger electrical stimulations and why did this change occur? How well did the results compare with your prediction? As the stimulus voltage is increased past the muscle's threshold voltage, the amount of force in the entire muscle increases. Each time the voltage was increased the force generated from the muscle also increased. This occurs because as the voltage increases, and is delivered to the whole muscle
2. How is this change in whole-muscle force achieved in vivo? The increase of electrical current causes a progressive increase in the amount of muscle force based on the amount of the electrical current.
3. What happened in the isolated skeletal muscle when the maximal voltage was applied? All of the muscle fibers in the isolated skeletal muscle became depolarized and all developed active force. T Y 3
The Effect of Stimulus Frequency on Skeletal Muscle Contraction 1. What is the difference between stimulus intensity and stimulus frequency? Stimulus intensity describes the amount of force generated to administer the stimulus and stimulus frequency refers to the rate of delivered stimulus to the muscle.
2. In this...