Exam 3 (Muscles) Flashcards
What is the M line?
where myosin strands bind
What is the I band?
area of actin not bound to myosin
What is the relaxation period in a muscle contraction?
Ca++ is pumped back into sarcoplasmic reticulum
time varies across muscle type
What does connective tissue do?
matrix for nerve and blood cells; attaches tendons to bones
What are the features of nebulin?
inelastic; aligns actin
What controls skeletal muscle?
neurotransmitters from somatic neuron
What controls cardiac muscle?
autorhythmic; some hormones
What controls smooth muscle?
Ach; epinephrine; paracrines (NO)
What causes cramps?
low muscle K+ → Ca++ stays out of sarcoplasmic reticulum → muscle stays contracted
What is the latent period in a muscle contraction?
pause between ACh stimulus and the actual muscle contraction
standard across muscle type
What is the muscle equivalent of the cell membrane?
sarcolemma
What causes parasthesia?
constricted blood flow to nerve → nerve can’t respond until O2/glucose restored
What is the Z disc?
where actin strands bind
What are the forms of troponin?
- TN-I: binds actin
- TN-T: binds TM
- TN-C: binds Ca++ → TN conformational change → TM move → stronger actin/myosin bond → power stroke
What are the factors involved in peripheral muscle fatigue?
- inadequate ACh synthesis
- increased local [Pi]
- calcium phosphate → Ca++ can’t bind to TN
- reduced muscle glycogen stores
What is the function of tropomyosin (TM)?
covers actin; blocks actin-myosin binding sites
What causes benign muscle fasciculations (twitching)?
low blood Ca++ → somatic motor neuron vgNa+ channels open easily → neuron depolarizes randomly
What is the H zone?
area of myosin not bound to actin
What are the features of titin?
largest protein; elastic; returns stretched muscle to resting length
What are the steps of triggering a muscle contraction?
- ACh released from neuron
- ACh binds to lg-Na+ channels → Na+ influx
- depolarization down t-tubule → conformational change in DHPR (protein plug)
- RyR (protein pore) opened → Ca++ release
- Ca++ binds to TN → muscle contraction
How is muscle contraction regulated?
- acetylcholinesterase hydrolyzes ACh → terminates action potential
- Ca++ ATPase pumps Ca++ back into sarcoplasmic reticulum
What happens when myosin binds to actin?
Pi is released; power stroke
What does botulism do?
blocks ACh release
What happens when ATP is hydrolyzed by myosin ATPase?
myosin cocks and binds to actin (cross-bridge)
What are the two types of muscle fatigue?
central (only in brain)
peripheral (in muscle)
What happens when ATP binds to myosin?
myosin dissociates from actin
