AP 1 (9-4)
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What is shivering thermogenesis?
when body temperature drops muscles are stimulated by nervous system to spastically contract breaking down ATP and giving off heat
Minimum stimulus that causes a contraction
Any voltage lower than threshold?
How are muscle fibers in a motor unit stimulated?
by an all-or-none response, once threshold is reached all fibers will contract
Do stimulations greater than threshold cause stronger contractions?
Why do whole muscles not have a all-or-none response mechanism to stimulation?
whole muscles are comprised of motor units which all have different thresholds
What is motor unit recruitment?
motor units of low thresholds contract first followed by other motor units with steadily increasing thresholds
What does motor unit recruitment result in?
Graded contractions, contractions of different strength that range from weak to strong
Where do twitch contractions occur?
one single muscle cell or the whole muscle
What is a twitch contraction?
a single contraction caused by a single stimulus at threshold or above
Three phases of a myogram
latent period- from time of stimulation to time of contraction
contraction period- muscle shortens
relaxation period- muscle returns to original length
What two factors determine the amount of tension produced by a muscle?
amount of tension produced by each muscle fiber
total number of muscle fibers stimulated
What is a tetanic contraction?
sustained contractions that are caused by rapid series of stimuli of the same strength to a muscle (>30/second)
What causes tetanic contractions?
adding twitches together so that the contraction periods occur so close to one another no relaxation periods can occur
Can single cells or motor units participate in tetanic contraction?
What is the process of recurring stimulation to a muscle?
Does summation cause stronger contractions than the twitch of a single cell?
Two types of tetanic contraction
Contraction involving body movement; how does it work?
isotonic tetanic contraction - muscle shortens and load muscle is pulling against moves
Contraction involves balance and posture and muscle tone; how does it work?
isometric tetanic contraction - lifting an object too heavy which causes one to stand still
AP 1 (9-4)
Lecture Exam 4