Muscle Activation, Excitation, Contraction Coupling

what must happen for a skeletal muscle to contract?

activation at neuromuscular junction, excitation-contraction coupling

what is activation?

nervous system stimulation

what is generated during activation?

action potential in sarcolemma

what is increased during activation?

intracellular calcium levels

what happens during excitation-contraction coupling?

action potential spreads along sarcolemma, cross bridge cycling

what is the first phase of skeletal muscle contraction?

activation , motor neuron stimulates muscle fiber

what is the first step of activation?

action potential arrives at axon terminal

what happens once the action potential arrives at the axon terminal at a neuromuscular junction?

calcium channels open, calcium moves into axon terminal

what happens when calcium moves into the axon terminal during activation?

ACh releases into synaptic cleft

what happens once ACh is released into the synaptic cleft?

ACh binds to receptors on the sarcolemma

what does the binding of ACh to receptors on the sarcolemma result in?

sodium and potassium channels open

what happens after ACh binds to receptors and opens the Na+ and K+ channels?

ion movement causes depolarization; action potential in sarcolemma

what is A?

dendrites

what is B?

cell body

what is C?

nucleus

what is D?

nucleolus 

what is E?

nasal bodies

what is F?

axon hillock

what is G?

axon

what is H?

myelin sheath

what is I?

schwann cell

What is J?

terminal branches

what is K?

node of ranvier 

what is L?

axon terminal

what is found in the axon terminal?

synaptic vesicles of neurotransmitters (ACh)

what is the space between axon terminals and muscle fibers?

synaptic cleft

what are the junctional folds of sarcolemma for?

increasing surface area for binding of ACh

what is the resting membrane potential?

-70 mV (more negative inside than outside)

what is the resting membrane potential maintained by?

sodium potassium pump

what is it called when Na+ moves in to a cell?

depolarization

what is it called when K+ moves out of a cell?

repolarization

what happens during depolarization?

inside of membrane becomes more positive than RMP

what happens during repolarization?

membrane returns to RMP from a depolarized state

what happens during hyperpolarization?

inside of membrane becomes more negative than RMP

what is the minimum stimulus required to initiate an electrical event in muscle fiber that will result in contraction?

threshold 

what is the required membrane potential for a muscle cell to depolarize?

-55mV

what happens once a threshold is met?

an action potential will fire and travel through entire muscle

what is happening at A?

depolarization due to sodium entry

what is happening at B?

sodium channels open

what is happening at C?

sodium channels close, potassium channels open

what is happening at D?

repolarization due to potassium exit

what is happening at E?

potassium channels open

what is the second phase of muscle contraction?

excitation

what is the first step of excitation?

action potential travels across the sarcolemma

what happens after the action potential travels across the sarcolemma?

action potential travels down t tubules

what happens after the action potential travels down t tubules?

sarcoplasmic reticulum releases calcium

what happens after the sarcoplasmic reticulum releases calcium?

calcium binds to troponin and moves tropomyosin from myosin binding sites on actin

what happens after tropomyosin moves from myosin binding sites on actin?

myosin heads bind to actin, contraction begins

how many ATP’s are needed during contraction: cross bridge cycling

2

what happens after myosin head binds actin in phase 3: contraction?

power stroke

when is the second ATP used during phase 3: contraction

myosin heads detach from actin

what is the last step in muscle contraction?

myosin head resets

what will cause the cycle of muscle contraction to continue?

available ATP, calcium bound to troponin

what does exposure to botulinum toxin cause?

botulism 

what does the botulinum toxin do?

blocks release of ACh from synaptic vesicles, paralyzing affected muscle