Skeletal Muscle Flashcards
Muscle Fasciculus are
the individual bundles of muscle fibers in a skeletal muscle
Muscle Fibers consist of
a single muscle cell
Myofibrils are made up of
thick and thin myofilaments giving muscle its striped appearance
Myofilaments consist of
thick fillaments (myosin), thin filaments (actin) and elastic filaments (titans)
Skeletal muscle fiber size
extends the tntire lenght of a muscle, 10-80 micrometers in diameter
How many muscles does one nerve innervate?
One, usuall in the midele of the fiber
What encapsulates a muscle fiber?
the sarcolemma
What is a muscle fiber made up of?
contains 100s to 1000s of myofibrils
Myofibrils contain more of what than what?
More actin than myosin
What does the Sarcoplasma contain?
Glycosomes (membrane-enclosed organelle that contains glycolytic enzymes), Myoglobin-Oxygen, Mitochondria, Calcium
What type of proteins are myofilaments?
Polymerized proteins
Actin:
3000 filaments, Thin filaments, Light I bands
Myosin:
1500 filaments, Thick filaments, Dark A bands
What is a sarcomere
the portion of myofibril between 2 consecutive Z-discs (gets smaller and larger depending on contraction)
What are Z-discs made of?
structural proteins
Wehre do Z-discs attach
to the ends of actin
What do Z-discs interdigate with
myosin
Puropose of Z-discs
attach myofibrils together along the entire muscle fiber
What does a Titan do?
keeps actin and myosin in place
Titan size
BIG protein - molecular weight of 3 million
How does a titan work?
Titans are springy, the elastic end attaches to the Z-disc and the other end is tethered to myosin thick filament
what are A bands?
mysin (thick filament) + ends of actin (thin filament)
what are I bands?
actin (thin filament)
what is the H zone?
just myosin, middle / zero interaction with actin
what is a Z-disk?
structure of the myofibril (ends of actin/interdigitates myosin)
What is the M line
within the H zone; M = “mittelscheibe” = “middle” of sarcomere
What is a Titan
springy framework holding myosin in place
How many polypeptide chains does a myosin molecule have?
6
How many heavy chains does a myosin molecule have?
2 (MW = 200,000)
How many light chains does a myosin molecule have?
4 (MW = 20,000)
What configuration are myosin heavy chins in?
double helix (tail, ends fold bilaterally into globulare polypeptide structures = heads)
Describe the myosin light chains
4 light chains are part of the myosin heads (2 per head)
What does Calsequestrin do
Binds with Ca++ in the sarcoplasmic reticulum attracting it towards the channels for quick exit when needed
What are two things the myosin light chains do
*#1: help control the function of the head during contraction
*#2: functions as an ATP enzyme
How many molecules make up myosin?
200+
How long is myosin filament
1.6 micrometers in length
Muscle from big to small
Muscle - muscle fascicles - muscle fibers - myofibrils (made of many sarcomeres) - myofilaments (made of actin, myosin, titan)
What are myofilaments made of?
actin, myosin, and titans
What are myofibrils made of?
many sarcomeres
What is Actin made up of?
2 F-actin molecules twisted like a helix - have G-actin molecules “active sites”
What does tropomyosin do?
Spirals around F-actin covering the “active sites” (G-actin molecules “G sites”)
Troponin I has an affinity for:
Actin
Troponin T has an affinity for:
Tropomyosin
Troponin C has an affinity for:
Calcium
3 sources of energy
*1: Rephosphorylation of ATP (phosphocreatine-donates phosphate group to convert ADP to ATP)
*2: Glycolysis (restores phosphocreatinine, direct energy for contraction in absence of O2, 2.5x faster than “foodstuff method”
*3: Oxidative Metabolism (O2 + foodstuff = ATP)
One motor uniti is innervated by a single nerve fiber, how many muscle fibers are in each motor unit?
80-100 muscle fibers/motor unit
What is the motor end plate coverd by?
Schwann Cells (protection from surrounding enviornment)
What is the Synaptic Gutter?
Invagination caused by the nerve ending on the membrane layer
What is a Synaptic Cleft?
Space between terminal & fiber membrane (25 nanometers)
How does Choline enter the axon?
Via the Choline Transporter (CHT), sodium also enters with it
What is needed to synthesize (ACh)?
Acetyl CoA + Choline (and an enzyme)
What enzyme catalyzes synthesis of ACh?
Choline Acetyltransferase (CAT)
What moves ACh vesicles to the nerve terminal?
Vesicular Acetylcholine Transporter (VAT)
When ACh is released, what 2 things can happen?
*1: It attaches to a receptor
*2: It is degraded
What degrades ACh in the synaptic cleft?
Acetylcholinesterase cleaves ACh into Choline + Acetate
What degrades ACh in plasma
Pseudocholinesterase
How are new vesicles formed?
After AP, “coated pits” appear in the nerve terminal and clathrin protein contracts forming new vesicles in the terminal
What are ACh vesicles attracted too in the nerve terminal?
Dense Bars
What allows ACh vesicles to attach to the pre-synaptic cleft and exocitose?
Ca++/Calmodulin dependent protein kinase that has beeen activated by calcium
How many ACh attach to an ACh receptor to create a conformational change (activation)
2
What charge does the ACh receptor have and what does it do?
Negative charge - repels negative ions and attracts positive such as Na+ (VIP)
Adult ACh is comprised of what subunits?
2x alpha
1 beta
1delta
1episilon
Fetal ACh is comprised of what subunits?
2x alpha
1 beta
1 delta
1 gamma
What allows action potentials depolarize the entire muscle?
Transverse tubules (T-tubuels)
What sections is the Sarcoplasmic reticulum divided into?
Terminal Cisternae and
Longitudinal Tubules
An important voltage gated channel often targeted by calcium channel blockers:
Dihydropyridine receptor (DHP)
Receptor on the SR targeted by Dantrolene:
Ryanodine receptor
Two receptors that work together to release calcium from the SR in skeletal muscle:
Dihydropyridine receptor
Ryanodien receptor
What do Desmosomes do?
Prevent sheering of cell connections
What do Connexins do?
Form intercellular gap junctions (channels that mediate direct signaling between cells)
What causes muscle fatigue?
glycogen depletion, bloodflow interruption
What causes Rigor Mortis?
ATP is all utilized. No more present to trigger release of myosin
How long until Rigor Mortis relaxes?
15-25 hours due to protien deterioration (myosin no longer connected)
How long is an AP in skeletal muscle?
1 - 5 milliseconds (5x longer than large myelinated nerves)
