human anatomy ch.10: how muscles work

what are the structures that form the neuromuscular junction?

synaptic knob, synaptic vesicles, synaptic cleft, motor end plate, ACh receptors, acetylcholinesterase (AChE)

what is the synaptic knob?

expanded tip of neuron axon

what are the synaptic vesicles and what are they filled with?

membrane sacs in synaptic knob filled with acetylcholine (ACh) which is a neurotransmitter

what is the synaptic cleft?

narrow space separating the synaptic knob and motor end plate

what is the motor end plate?

region of the sarcolemma with many folds (increased surface area) under the synaptic knob

what are the ACh receptors?

proteins that bind ACh on the motor end plate

what is acetylcholinesterase (AChE) ?

enzyme in the synaptic cleft that breaks down ACh (regulatory component that prevents continuous stimulation of the muscle)

are skeletal muscles voluntary or involuntary and what is each muscle fiber controlled by?

skeletal muscles are voluntary, meaning they do not contract until a signal from the motor neuron, and each muscle fiber is controlled by one motor neuron

when does contraction begin?

when a motor neuron impulse stimulates an impulse in a muscle fiber

what is the first step in muscle contraction?

a nerve impulse causes acetylcholine (ACh) release into the synaptic cleft. ACh binds to the receptors on the motor end plate initiating a muscle fiber impulse

what is the second step in muscle contraction?

spread of the impulse down the T-tubules which causes calcium to leak into the sarcoplasm

what is the 3rd step in muscle contraction and has ATP been used up to this point?

calcium will bind to troponin, causing troponin to change shape and pull tropomyosin out of the way, revealing actin binding sites. myosin heads will then bind at actin binding site, forming cross-bridges. 0 ATP has been used up to this point.

what is the 4th step in muscle contraction and does it require ATP?

myosin pulls actin towards the center of the sarcomere in a powerstroke. this repeats and shortens the sarcomere. ADP is released in order to grab more ATP in crossbridge cycling. this requires ATP.

what is step 5 of muscle contraction?

the signal stops. calcium ions are sucked back up into the sarcoplasmic reticulum, tropomyosin recovers actin binding sites, and filaments slide back into place

define the term “motor unit”

a singular motor neuron and all of the muscle fibers its controls

what is a motor unit’s role in muscle function?

when a motor neuron is stimulated, ALL of the muscle fibers it contains activate. the more power a movement requires, the more motor units that will be recruited. in movements like planks, activation of motor units is rotated

what are the three types of muscle fibers?

slow oxidative (SO) fibers- type I, fast oxidative (FO) fibers- type IIa, and fast glycolytic (FG) fibers- type IIb

what are slow oxidative fibers in regards to size, energy use, and fatiguability?

small, aerobic, and fatigue-resistant

what are fast oxidative fibers in regards to size, energy use, and fatiguability?

intermediate, aerobic, and generate tension fast

what are fast glycolytic fibers in regards to size, energy use, and fatiguability?

large, anaerobic, use glycolysis to generate tension super fast for short burts