BY 409L Module 5

In the neuromuscular junction, the axon terminal releases...

Acetylcholine (Ach)

The motor end plate is lined with...

nicotinic receptors

______________ breaks does Ach, ending excitation at motor end plate.

Acetylcholinesterase (AChE)

triad

one t-tubule and 2 flanking terminal cisternae of sarcoplasmic reticulum, closely associated with area of sarcomere where actin and myosin overlap

transverse tubules (t-tubules)

invaginations of sarcolemma that form a network within the cell, which allows action potentials to travel deep

T-tubules are lined with...

DHP receptors

DHP receptor (dihydropyridine)

undergoes a conformational change in response to an action potential, physically attached to RyR

RyR (ryanodine receptor)

a gated Ca++ channel on terminal cisternae of sarcoplasmic reticulum

sarcoplasmic reticulum

stores calcium

The Ca++ ATP-ase pump returns Ca++ to the...

sarcoplasmic reticulum

sarcomere

functional unit of myofibril

thin filament

actin, troponin, tropomyosin

actin

a globular protein with an active binding site for myosin head, two chains of actin twisted together form the main part of thin filament

tropomyosin

a regulatory protein that blocks the myosin binding site on actin at rest

troponin

a regulatory protein with a binding site of Ca++, undergoes conformational change to move tropomyosin when Ca++ is bound

myosin

motor protein of sarcomere that binds and breaks down ATP into ADP and Pi; forms thick filament

The binding and breakdown of ATP puts the myosin head into...

a cocked position

The myosin head binds to __________ when the active site is available.

actin

power stroke

action of myosin pulling actin inward (toward the M line)

What is released when myosin binds to actin?

inorganic phosphate (Pi); ADP is released but head is still bound to actin (rigor state)

titin

elastic protein connecting Z disk to M line, helps align filaments and passively shorten stretched muscle

nebulin

inelastic protein associated with thin filament, helps maintain alignment

excitation-contraction coupling

end-plate potential --> action potential --> DHP receptor conformational change --> RyR opening allowing Ca++ into sarcoplasm as secondary messenger --> Ca++ binds to troponin --> troponin moves tropomyosin, exposing myosin binding site on actin --> myosin binds to actin, performs power stroke

EMG (electromyography)

a measurement technique that records the electrical activity of a muscle or group of muscles

EMG detects...

action potentials along sarcolemma

motor unit

one motor neuron and the muscle cells it innervates

A few motor units will add...

a small amount of force for fine control

Large motor units will add...

large amounts of force for a more efficient force generation

Units cycle in and out during longer muscle contractions to avoid...

fatigue

fatigue

failure to generate or maintain output

central fatigue

psychological, can choose to continue

peripheral fatigue

physiological failure, no choice