SMT
Nerve and Muscle
Dr. Loay Abu Dalu .MD, MSc (UK)
Key points
Action potential
Simple Muscle Twitch
Summation
Tetanization
Effect of temperature on S.M.T
Muscle fatigue
Resting membrane state
, it’s the state in which there is no stimulus.
The charges in side the cells is negative in comparing with outside the cell
Resting membrane potential
Action Potential
Simple Muscle Twitch
Summation of Muscle
Definition of summation :
• It means the adding together of individual twitch contractions to increase the intensity of overall contraction.
• Because the contractile mechanism has no refractory period,
• repeated stimulation (i.e. increase the frequency) before relaxation can produce additional activation of the contractile elements and a response will be added to that already present, this is called "summation of contraction".
Types of Summation
Clinical value
Widespread and long lasting pain are characteristics of many chronic pain syndromes. This suggests that both spatial and temporal summations are important in chronic pain conditions.
Tetanization
• Frequency summation and tetanization, with rapid repeated stimulation,
• activation of the contractile mechanism occurs repeatedly before any relaxation occurs and the response fuses into one continuous contraction and the whole contraction appears to be smooth called Tetanus
• During tetanus the tension developed is 4 times than the individual contraction
Types of
Tetanus:
Unfused Tetanus: at a low stimulus frequency, the force at the plateau oscillates
Fused Tetanus: at high stimulus frequencies, the force plateau is smooth
Tetanization
Effect of Temperature on Simple Muscle Twitch
Hot Temperature
• When warm ringer solution is applied to the muscle nerve preparation and a simple muscle twitch is recorded then we notice that
• All the durations are shortened
(latent period, contraction period,& relaxation period).
• The height of contraction has increased.
Cold Temperature
• When cold ringer solution is applied to the muscle nerve preparation and a simple muscle twitch is recorded then we notice that
• All the durations are prolonged (latent period, contraction period,and relaxation period).
• The height of contraction has decreased.
Em
Effect of Temperature on Simple Muscle Twitch
Time
Muscle Fatigue
• A fatigue curve is obtained when the nerve muscle preparation is stimulated repeatedly till a fatigue curve is obtained.
• A fatigue curve has a prolonged refractory period, low height of contraction no point of
• complete relaxation (contracture remainder).
• Fatigue is a reversible phenomenon.
