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TRANSCRIPT
Physiology Lab: Week 7 – Muscle Phys
MUSCLE PHYSIOLOGY
ELECTROMYOGRAPHY
Physiology Lab: Week 7 – Muscle Phys
Anatomy of Skeletal Muscles
• Levels of Organization
• Skeletal muscles consist of muscle fascicles
• Muscle fascicles consist of muscle fibers
• Muscle fibers consist of myofibrils
• Myofibrils consist of sarcomeres
• Sarcomeres consist of myofilaments
• Myofilaments are made of actin and myosin
Physiology Lab: Week 7 – Muscle Phys
NOTE: Each muscle fiber is innervated by only ONE neuron
I. Introduction
Physiology Lab: Week 7 – Muscle Phys
Defined as…One motor neuron and all the muscle fibers it innervates
Motor Unit
I. Introduction
Asynchronous recruitment…occurs when motor units alternate, allowing some to relax while others contract – only works for submaximal contractions.
Physiology Lab: Week 7 – Muscle Phys
• The number of muscle fibers in a motor unit varies from one
muscle to another
• Eye muscles vs. leg muscles
Precise movement – 6 fibers per nerve
vs.
More strength – 1,000 fibers per nerve
Motor Units vary in size
I. Introduction
Question: How do muscles control the force of contraction?
Physiology Lab: Week 7 – Muscle Phys
Answer: Graded contractions are achieved by:
1. Changing the strength (voltage) of the stimulus
(motor unit recruitment)
2. Changing the frequency of stimulation
(summation)
I. Introduction Graded Responses
Question: How do muscles control the force of contraction?
Physiology Lab: Week 7 – Muscle Phys
• The “activation of additional motor units” results
in an increased force of contraction
FEWER
MOTOR UNITS
MORE
MOTOR UNITS
Motor Unit Recruitment
I. Introduction
Physiology Lab: Week 7 – Muscle Phys
• Muscle twitch response is all-or-none
• Single twitches do not accomplish anything useful in the body
• Increasing the frequency of the stimulus increases the force of contraction
I. Introduction Summation
Increasing frequency
Physiology Lab: Week 7 – Muscle Phys
THRESHOLD AND MAXIMAL
RESPONSE
Experiment 1
Physiology Lab: Week 7 – Muscle Phys
II. Threshold and Maximal Response Maximum stimulus
Figure on p 146
Threshold
stimulus
Maximum contraction
Fo
rce
The minimum stimulus that
will cause a muscle twitch
The lowest voltage
that results in a
maximum contraction
Supramaximal
stimuli
All muscle fibers are active
Physiology Lab: Week 7 – Muscle Phys
II. Threshold and Maximal Response
• Phases of a SINGLE twitch contraction
– latent period
• first few milliseconds after stimulation
– contraction phase
• muscle shortens
– relaxation phase
• return to resting length
Figure on p 148
Physiology Lab: Week 7 – Muscle Phys
A. B. C.
Physiology Lab: Week 7 – Muscle Phys
SUMMATION, TETANUS AND
FATIGUE
Experiment 2
Physiology Lab: Week 7 – Muscle Phys
II. Summation, Tetanus and Fatigue Increasing Frequency of Stimulus
• Single Twitch – not useful
• Wave summation – one twitch is added to another
• Complete tetanus – relaxation phase is eliminated
• Fatigue – (next)
Physiology Lab: Week 7 – Muscle Phys Figure on p 147
• Wave summation – one twitch is added to another
• Complete tetanus – relaxation phase is eliminated
• Fatigue – decrease in the muscle’s ability to generate force
II. Summation, Tetanus and Fatigue Increasing Frequency of Stimulus
Tetanus
Physiology Lab: Week 7 – Muscle Phys
• Decrease in the muscle’s ability to generate force
• All motor units being used – none alternating
Due to:
• Energy sources used faster than ATP can be
generated
• Reduced blood flow
• Lactic acid build up (? New research says no)
Psychological vs. Physiological Fatigue
II. Summation, Tetanus and Fatigue
Physiology Lab: Week 7 – Muscle Phys
You should understand these terms:
• Motor unit
• Motor unit recruitment
• Threshold
• Summation
• Tetanus
• Fatigue
• What are some factors that increase the
strength of a contraction?
• What are some factors that lead to fatigue?
Physiology Lab: Week 7 – Muscle Phys
Electromyography
• Recording of electrical activity
of the muscle =
electromyogram (EMG)
• Measurement of Power =
Dynamometry
• Resting skeletal muscles exhibit
“tonus” (readiness)
- the detection, amplification, and recording of changes in skin
voltage produced by underlying skeletal muscle contraction
Physiology Lab: Week 7 – Muscle Phys
EMG Data
electromyogram
Force (Kg)
EMG (mV)
IEMG (mV)
Force = actual measurement of the strength of clench
EMG = actual recording of the mV
IEMG = absolute intensity of the mV
Physiology Lab: Week 7 – Muscle Phys
• Q1: Which gender is stronger
• Q2: Which arm is stronger (dominant vs. non-dominant)
• Q3: Which gender fatigues faster
Muscle Physiology
Experimentation
Physiology Lab: Week 7 – Muscle Phys
Test your force…
• Measure Maximum clench force • Max. ÷ 5 (ex. 30kg/5 = 6kg)
• Measure fatigue
• Repeat for 2nd arm
• Data analysis to fill in Tables
• Put values on excel
• Homework: perform t-tests on all 3
• Write a report: support/refute Hypothesis, t- values, conclusion etc.
Physiology Lab: Week 7 – Muscle Phys
Let’s get started…
• Place electrodes on Dominant forearm as shown
• Attach colored leads to electrodes as shown