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Slide 1

Unit 2

Twitch Response of muscle to single threshold stimulus. It is an artificial condition not normally induced. It has three phases
Lag Phase Initial absence of response following the stimulus
Contraction Phase Muscle tension increases & peaks and causes movement if greater than resistance
Relaxation Phase Tension Decreases
Latent Period Interval between the AP and the initiation of tension
Motor Unit Single neuron and all fibers innervated by that neuron. Stronger stimuli activate more , increasing overall strength of contraction
Recruitment The progressive addition of efferent fibers and motor units in the contractile event with increasing strength of stimulus. It acts to increase the force of contraction
Asynchronous Recruitment Events are not occurring at the same time. Motor units are fired in an alternating pattern to minimize fatigue. It is only effective for sub-maximal contractions
Treppe Progressive increase in the force of muscle contraction in response to successive threshold stimuli of comparable intensity. There is complete relaxation happening here and it occurs in low frequency. It is evident in muscle that has undergone prolonged r
Summation Refers to the addition (or summing) of individual twitch contractions such that total muscle contraction is increased. It occurs in high frequency. It may occur as
Multiple Fiber Summation It is also known as Multiple Motor Unit Summation. Number of motor units contracting simultaneously is increased
Frequency Summation It is also known as Multiple Wave Summation. Successive contractions occur before the preceding contraction has ceased. This increases force of contraction. It occurs in very high frequency. There is no opportunity for the muscle to relax
Tetany It is a form of frequency summation. A stimulus occurring during the relaxation phase causes a twitch that is stronger than the initial twitch. As the rate of the stimulation is increased, the relaxation interval becomes shorter and shorter. Contractions
Incomplete Tetanus (Unfused) Partial relaxation of the muscle fibers between contractions
Complete Tetanus (Fused) The frequency of contraction precludes relaxation. There is no relaxation
Muscle Tone It is caused by muscle units within a muscle sporadically contracting. This sort of sustained tension prepares muscle for activity
Normal Tone It is important for posture. It also contributes to maintenance of body temperature
Contracture Shortening of muscle in the absence of ATP. The muscle becomes stuck and unable to release from its contracted condition. It may also refer to imbalanced atrophy of antagonistic muscle groups
Rigor Mortis Contracture occurring several hours after death. The muscle achieves contraction and rigidity in the absence of action potentials. The condition is attributable to a loss of ATP needed to separate cross bridges from actin during relaxation. It persists un
Created by: Skumar8