Lab 5: Muscle Physiology

Pi

Pi

________ is released and power stroke occurs.

RyR

________ (ryanodine receptor)- gated Ca++ channel on terminal cisternae of sarcoplasmic reticulum.

DHP receptor

________ (dihydropyridine)- undergoes conformational change in response to action potential, physically attached to RyR.

Sarcoplasmic Reticulum

________- acts as Ca++ store, Ca++ sequestered inside at rest, Ca++ ATP- ase pump returns Ca++ to SR 3)

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-tubule)

invagination of sarcolemma

DHP receptor (dihydropyridine)

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

RyR (ryanodine receptor)

gated Ca++ channel on terminal cisternae of sarcoplasmic reticulum

Sarcoplasmic Reticulum

acts as Ca++ store, Ca++ sequestered inside at rest, Ca++ ATP-ase pump returns Ca++ to SR 3)

Sarcomere

functional unit of myofibril

Thin filament

composed of actin, troponin and tropomyosin

Actin

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

Tropomyosin

regulatory protein that blocks myosin binding site on actin at rest

Troponin

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

Myosin

motor protein of sarcomere that binds and breaks down ATP → ADP + Pi

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

Motor Unit

one motor neuron and the muscle cells it innervates

Fatigue

failure to generate or maintain output

Central

psychological, can chose to continue

Peripheral

physiological failure, no choice

What is released at the axon terminal in a neuromuscular junction?

ACh (acetylcholine)

At a neuromuscular junction, the motor end plated is lined with ___ receptors.

nicotinic

What binds to the nicotinic receptors?

ACh (acetylcholine)

When ACh binds to the nicotinic receptors, they open resulting in ___.

ion flow

What ion flows in quicker than K+ flows out?

Na+

What does ion flow initiate?

end-plate potential (EEP)

How does the end-plate potential initiate an action potential?

it pushes voltage gated channels outside of motor end plate to threshold

What ends the excitation at motor end plate?

AChE (acetylcholinesterase) breaks down ACh

What makes up the triad?

one t-tubule and 2 flanking terminal cisternae of sacroplasmic reticulum

What area is the triad closely associated with?

area of sarcomere where actin and myosin overlap

What is the function of transverse tubules (t-tubules)?

invagination (folding backwards) of sarcolemma

Transverse tubules (t-tubules) form a network within a cell that allows ___.

action potential to travel deep

What receptors line transverse tubules (t-tubules)?

DHP receptors

DHP receptor (dihydropyridine) will undergo a conformational change in response to ___.

action potential

DHP receptors are physically attached to ___.

RyR

RyR (ryanodine receptor) are gated ___ channel on terminal cisternae of sarcoplasmic reticulum.

Ca++

What is the function of sarcoplasmic reticulum?

acts as Ca++ store

At rest, Ca++ is inside or outside of cell?

inside

What pump returns Ca++ to SR?

ATP-ase pump

What is a functional unit of myofibril?

sacromere

What composes a sarcomere?

thin filament, myosin, titin, and nebulin

What composes a thin filament?

actin, troponin, and tropomyosin

What is actin?

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

What is tropomyosin?

regulatory protein that blocks myosin binding site on actin at rest

What is troponin?

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

What forms the thick filament?

myosin

What is myosin?

motor protein of sarcomere that binds and breaks down ATP -> ADP + Pi

Myosin isoforms varies between ___ and speed of contraction varies among isoforms.

muscle cell types

Binding and breakdown of ATP puts ___ into cocked position.

myosin head

When myosin head is in cocked position, it is ready to bind to __, while ___ and ___ remain bound.

actin; ADP and Pi

When binding site is available on myosin head, it binds to ___.

actin

When Pi is released at myosin head, a ___ occurs.

power stroke

What occurs during rigor state?

ADP is released but head still bound to actin

What must bind to myosin head again to release ADP and restart cycle?

ATP

What is titin?

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

What is nebulin?

inelastic protein associated with thin filament, helps maintain alignment

What is excitation-contraction coupling?

EEP -> AP -> 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 actin performing power stroke

What detects an AP along sarcolemma?

EMG

What is a motor unit?

one motor neuron and the muscle cells it innervates

Number of ___ varies in general relation to size of muscle.

myofibers

One motor unit can have multiple ___.

myofibers

What is fine control?

few motor units -> small amount of force added

What is more efficient force generation?

larger motor units -> large amount of force added

What occurs to motor units to avoid fatigue?

units cycle in and out during longer muscle contractions

What is fatigue?

failure to generate or maintain output

What is central fatigue?

physchological, person can chose to continue

What is peripheral fatigue?

physiological failure, no choice