Electromyography

EMG• Measures a muscle’s electric

potential– Surface EMG – Intramuscular EMG

Muscles!!!• Motor Unit: – A motor neuron and all the muscle fibers

it innervates.

Muscles!!!• Contraction– State of mechanical activity.– Either isotonic or isometric.– Triggered when a nerve impulse at

neuromuscular junction causes acetylcholine to spread over the muscle surface/sarcolemma as an electrical depolarization.

Neuromuscular Junctions (my favorite!... Seriously.)

Video

• http://highered.mcgraw-hill.com/olc/dl/120107/bio_c.swf

Muscle Types• Cardiac– Striated– Involuntary

• Skeletal– Striated– Voluntary

• Smooth– Non-striated– Involuntary

Fatigue• 2 Types:–Muscle Fatigue:• Exercising muscle can no longer respond to

stimulation with the same degree of contractile activity.

– Central or Psychological Fatigue:• CNS no longer adequately activates the

motor neurons supplying the working muscles.

EMG• Shape Indicates:– Composition of motor units, number of

muscle fibers innervated by a motor unit, muscle type, health, etc.

• Used to diagnose neuropathies and myopathies

EMG• Neuropathy:

– An AP amplitude 2x normal due to increase # of fibers/motor unit because of re-innervation of de-innervated fibers.

– Increase in duration of AP.– Decrease # of motor units in muscle.

• Myopathy:– Decrease duration of AP.– Reduction in area to amplitude ratio of AP.– Decrease # of motor units in muscle.

Myotonia Congenita• Fainting goats• Abnormality of Cl- channels.

They can’t act as buffers against APs; muscles relax slowly.

• Cold makes condition worse.

• Cl- channels don’t open fast enough after AP to get membrane potential back to negative.

Methods

• Should be in PAST tense!• Should be DETAILED. How many trials did you

run? How long was each? How did you measure the cues? What are the data you collected?

• DATA IS A PLURAL WORD!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!– These data were recorded using the labscribe

program.

A GREAT answer!• Reflexes to auditory stimuli occur faster than reflexes

to visual stimuli. This is due to the neural pathways for visual and auditory systems being different. Auditory receptors are ionotropic in that the stimulus is translated into an electrical signal, while the visual receptors are metabotropic, which translates the stimulus into a chemical signal (Hill 2008). – DO NOT CITE ME!!!!

HOMEWORK!!!!• Answer all questions.• Write a methods and results section.• Make sure to check my rubric (Will be

posted on the website!). I will use it to grade assignments from this point forward.

• Be thorough. My grading gets harder, not easier as the semester progresses.