AP 1 (9-4)

when body temperature drops muscles are stimulated by nervous system to spastically contract breaking down ATP and giving off heat

threshold stimulus

subthreshold stimulus

by an all-or-none response, once threshold is reached all fibers will contract

no

whole muscles are comprised of motor units which all have different thresholds

motor units of low thresholds contract first followed by other motor units with steadily increasing thresholds

Graded contractions, contractions of different strength that range from weak to strong

one single muscle cell or the whole muscle

a single contraction caused by a single stimulus at threshold or above

• latent period- from time of stimulation to time of contraction
• contraction period- muscle shortens
• relaxation period- muscle returns to original length

• amount of tension produced by each muscle fiber
• total number of muscle fibers stimulated

sustained contractions that are caused by rapid series of stimuli of the same strength to a muscle (>30/second)

adding twitches together so that the contraction periods occur so close to one another no relaxation periods can occur

yes

summation

yes

• isotonic
• isometric

isotonic tetanic contraction - muscle shortens and load muscle is pulling against moves

isometric tetanic contraction - lifting an object too heavy which causes one to stand still