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45 terms

BIO259 - General Principles of Muscle Contraction (+ cardiac muscle from last unit)

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cardiac muscle: voluntary or involuntary?
involuntary
cardiac muscle: defining features
shorter fibers than striated that are fused together for added length; intercoalated discs at the point of attachment; branched; centrally located nucleus
cardiac muscle: contraction speed
slow
cardiac muscle: contraction
needs no stimulation; all fibers beat on their own at different frequencies, but because neighboring contractions pass it down, the fasted fiber dictates speed of all others; nervous system can override this natural beating
cardiac muscle: purkinje fibers
specialized fibers to control the rate of contraction among the 4 cardiac chambers
motor unit
a motor neuron and all of the muscle fibers it innervates
the basic unit of skeletal muscle contraction
motor unit
smallest unit of skeletal muscle contraction
motor unit
low innervation ratio motor units
fewer muscle fibers per motor unit, increasing amount of control
high innervation ratio motor units
more muscle fibers per motor unit, increasing amount of power
types of contraction
isotonic, isometric
isotonic contraction
same force; muscle fibers shorten against the resistance of a movable force/object
isometric contraction
same length; muscle fibers do not shorten against the resistance of an immovable force/object
types of contraction: which is more common in our daily lives?
a combination
muscle twitch
the mechanical response of muscle fibers to the received impulse
recording contractions: time 1 (first)
brain tells the fiber to contract, but nothing happens
recording contractions: time 2
electrical activity occurs at the nerve electrode, and then it dissipates
recording contractions: time 3
electrical activity at the muscle electrode along the sarcolemma and t-tubules, then dissipates
recording contractions: time 4
contraction in muscle fiber (muscle twitch)
recording contractions: time 5 (last)
everything is over, all is relaxed again
recording contractions: what accounts for the delay before step 4?
the time it takes to change the permeability of the SER to ca ions
recording contractions: what accounts for the delay before step 3?
the time it takes the electrical signal to travel from one cell to another
recording contractions: what accounts for the delay before step 2?
the time it takes for the signal to go from the brain to the distal end of the neuron
threshold
the minimum amount of strength required of the stimulus to generate a response from the motor unit
suprathreshold
a stimulus with enough strength to generate a response
subthreshold
a stimulus that lacks the strength to generate a response
organ level contraction
variable contraction of whole muscles based on recruitment of motor units taking place in the CNS
how is the contraction strength controlled?
the CNS fires more units at once for a stronger response; fewer at once for a weaker response
how is the contraction duration controlled?
twitch fusion and tonus
twitch fusion
the sending of multiple stimuli, staggered, to create a longer contraction
twitch fusion subtypes
single twitch, partial twitch fusion, complete twitch fusion
partial twitch fusion subtypes
summation, incomplete tetanus
complete twitch fusion subtypes
complete tetanus
summation
applying a stimulus and then a second (and third, fourth, etc.) before the first twitch has completely ended
incomplete tetanus
applying stimuli evenly spaced so that the amplitude remains the same at each jump up; never fully relaxes
complete tetanus
the muscle doesn't relax at all because the stimuli come so frequently
what is the drawback of twitch fusion?
it stops after the last stimulus ends, or muscles fatigue - which is after only 20 seconds
tonus
staggering the stimuli to different motor units so that some can be contracted while others are resting, allowing for a longer contraction
energetics of contraction
contraction requires ATP to be synthesized as quickly as it is being used (aka very fast), so while ATP is going to the relaxed muscles to contract them, ADP is going to getting a high energy P from phosphocreatine (ultimate energy source in the background is still glucose)
what happens if the PCr process doesn't provide enough energy/quickly enough?
the process finally goes anaerobic
muscle fiber types
red and white fibers
other names for muscle fiber types
slow and fast twitch fibers
red fibers
slow twitches with lots of mitochondria and a high consumption of oxygen
white fibers
fast and powerful twitches with fewer mitochondria, low consumption of oxygen (glycolytic)
the ratio of red:white fibers in a muscle is determined by
function and genetics