lab 4

Question 1

what is an electromyogram?

Answer 1

it records the deplorization of skeletal muscles

Question 2

why is an electrocardiogram discrete while an electromyogram is irregular?

Answer 2

an electrocardiogram records cardiac muscle, which have junctions and act together to coordinate; the skeletal muscle cells are composed of multiple motor units and don’t depolarize all together

Question 3

what are the physiological events that occur between the delivery of a stimulus and the start of a recorded response?

Answer 3

the nerve axon is stimulated, when the stimulus reaches threshold, the action potential is propagated along the nerve; once the action potential reaches the motor end plate, it will cause voltage gated calcium channels. calcium influx causes vesicles to fuse to the presynaptic membrane releasing acetylcholine
acetylcholine diffuses across the neuromuscular junction and binds to ionotropic acetylcholine receptors on the post-synaptic membrane. the acetylcholine causes the opening of a sodium channel and will cause another action potential to propagate in the muscle cell. calcium influx will occur, causing contraction of the muscle

Question 4

what is the latent period between stimulation and muscle activity due to?

Answer 4

the length of axon that has to be travelled

Question 5

at what frequency of action potentials does tetanus occur?

Answer 5

> 75ms

Question 6

what is recruitment?

Answer 6

the increase in number of motor axons firing to increase the motor units that are functioning

Question 7

what is summation?

Answer 7

an increase frequency of stimulation increases the strength of contraction. with rapid stimulation the muscle fiber is restimulated while there is still some contractile force

Question 8

give an example of coactivation

Answer 8

e.g. when the biceps is activated there is mild activation of the triceps