sarcolemma of the skeletal muscle fiber; contains ACh-receptors that bind to ACh
describe the synaptic cleft
space between synaptic end bulb of motor neuron & motor end plate of the skeletal muscle fiber
what are the 4 ways synaptic transmission occurs at the NMJ?
release of acetylcholine, activation of ACh receptors, production of muscle action potentials, termination of ACh activity
describe release of acetylcholine
nerve a.p. at endbulb of motor neuron causes synaptic vesicles to undergo exocytosis, synaptic vesicles fuse w/ motor neuron's plasma mem., releasing ACh into synaptic cleft, diffuses across synaptic cleft
describe activation of ACh receptors
binding of ACh to receptor on motor end plate opens an ion channel in ACh receptor, small cations (Na+) flow across mem.
describe production of muscle A.P.
inflow of Na+, makes inside of muscle fiber more (+), change triggers muscle A.P., then propagates along sarcolemma into T tubule system, causing muscle fiber to contract
describe termination of ACh activity
ACh no longer released when A.P. in motor neuron ceases, ACh is broken down by enzyme acetylcholinesterase(AChE), prevents formation of another A.P.
what is acetylcholinesterase (AChE)?
enzyme which breaks down the molecules of ACh into acetyl & choline
what is excitation-contraction coupling?
sequence of events connecting muscle A.P. to muscle contractions
what are the 3 ways muscle fibers obtain ATP?
transfer of phosphate from creatine phosphate to ADP to form ATP, anaerobic glycolysis, aerobic (cellular) respiration
describe transfer of phosphate from creatine phosphate to ADP to form ATP
immediate source of ATP, 15 seconds;
what is creatine?
small molecule similar to an amino acid in structure; found in skeletal muscle fibers & cardiac muscle fibers
what is creatine kinase (CK)?
transfers 1 of the phosphate groups of ATO to creatine to form creatine phosphate when ATP is in excess
what is creatinine?
break down of creatine, forming a nitrogenous waste product
describe anaerobic glycolysis
source of ATP when a skeletal muscle fiber lacks O2 or doesnt have enough O2 to meet metabolic needs (weight-lifting)- 2 min
describe aerobic (cellular) respiration
source of ATP when skeletal muscle fiber has plenty of O2 (resting, walking, moderately running on treadmill)- several min to hr or more