Skeletal Muscle sys Flashcards
What are the 3 concentric layers of connective tissue in the muscle in order from outermost to innermost?
Epimysium
- dense irregular
-separates muscles from other tissues
Perimysium
- divides muscles into compartments called fascicles
- collagen, elastic fibers, blood vessels and nerves go to each fascicle
Endomysium
- surrounds each individual fiber
-connects fibers together and to blood vessels
what is a fascicle?
a bundle of fibers
what are myosatelite cells?
stem cells. Considered totipotent: unlocked DNA
what are tendons? what is an aponeurosis
connect muscle to bone. flat tendon sheet.
where do nerves and blood vessels reside?
in the connective tissues
nerves are?
bundles of axons
what do nerves form with muscles?
neuromuscular junctions
embryonic myoblasts
muscle progenitor cells that proliferate and fuse together to form muscle fibers during embryonic development
What are transverse (t) tubules
deep indentations in sarcolemma that conduct electrical impulse to sarcoplasmic reticulum
myofibrils and myofilaments
give muscle striated appearance
hundreds/thousands of myofibrils per muscle
myofibrils:
myofilaments - thick and thin
myosin and actin
regulatory proteins: tropomyosin and troponin
accessory proteins: titin and nebulin
abundant mitochondria
What is the sarcoplasmic reticulum
storage site for Ca ions
t-tubules enlarge, fuse, and form expanded chambers
Different bands of the sarcomere?
A band: dark band (myosin concentrated)
I band: light band (actin concentrated)
M line: where the myosin meets and makes a straight line
z lines: ends of sarcomeres that move closer together when contraction
H band: lighter zone in A band
HAMIZ: initial of every band
thin filaments?
f-actin, nebulin, tropomyosin, troponin
what does nebulin do?
supports actin and maintains its form
thick filaments?
bundles of myosin
twisting tail binds to other myosin molecules
myosin heads project towards thin filaments
what does titin do?
structural component of myosin
loose when myosin is relaxed
tight when stretched
describe steps for a muscle contraction
…
motor units?
individual neurons and the muscle fibers they control
can be 1:1 or 1:100
smaller the ratio finer the movement
what produces tension?
frequency of stimulation
number of motor units recruited
what are singular contractions called?
muscle twitches
all or none principles
muscle fibers contract completely or not at all
all muscles in a motor unit contract at the same time
number of motor units recruited increases gradually
peak tension occurs at max rate of stimulation
Describe a t-tubule… how is it continuous? What role does it play in the activation of contraction?
…
What releases ACh? what does acetylcholine bind to on the muscle? what does it cause?
voltage gated Ca channel on neuron opens due to AP. nicotinic receptor. Opens Na channel on muscle causing an AP which allows calcium to be released by sarcoplasmic reticulum
what else can happen to acetylcholine
acetylcholinesterase breaks it up into acetyl and choline and choline gets reused
How does calcium affect muscle contractions at high and low concentrations?
…
What is troponin?
calcium activated troponin binds to 2 additional calcium (4Ca) which causes the troponin to change shape and move tropomyosin off of the myosin binding site.
What are the 3 methods for calcium clearance?
Ca-H+ exchangers which require ATP found on sarcolemma and sarcoplasmic reticulum
Na-Ca exchangers which are passive on sarcolemma
calsequestrin and calreticulin bind Ca to them and store them in reticulum
How do muscles respond to exercise?
increasing the amount of intracellular contractile proteins
what causes a muscle pump?
increased myofibrils and mitochondria
what causes the degeneration of muscle? characteristics?
lack of stimulation
is initially reversible, dying muscle fibers not replaced
skeletal muscle fiber types? how are they classified
by how they obtain atp
fast (white) fibers
- densely packed w myofibrils
-large glycogen storage, little mitochondria
-contract quickly and powerfully, energy sinks (anaerobic)
slow (red) fibers
-smaller and take 3x the time to contract
-extended contraction
-aerobic metabolism
-many mitochondria
intermediate fibers
-in between both
what are the 2 types of motor neurons?
slow-twitch fiber neurons
-small diameter
-conduction velocity is low
fast-twitch fiber neurons
-conduction velocity is high
-large diameter
Muscle fiber organization
parallel
-run whole length
- can be banded (abs) or wrap (supinator)
Convergent
-cover broad area and attach at same site
-pecs
pennate medicine
- pull at an angle
-unipennate (finger flexors)
-bipennate (quads)
-multipennate deltoids
circular
-asshole
smooth muscle?
involuntary
contractile filaments that connect at focal densities
cell is pulled inward from all angles
multiunit vs unitary
multiunit: each one has their own autonomic neurons
unitary: gap junctions permit coordinated contraction
Muscle twitch? 3 phases?
single, brief stimulus
latent: first few milliseconds, contraction coupling
contraction: cross bridging shortens
relaxation: calcium restoration
how long do muscles store atp for?
6 seconds of work
modes of ATP synthesis in muscles
hydrolysis in creatine phosphate (15s)
glycolysis (40s)
TCA and ETC (long term)
creatine phosphate hydrolysis
phosphate from creatine + ADP = ATP
fast
limited, rapidly depleted
glycolysis and sources of glucose
sources: blood, glycogen
glycolysis is aerobic or anaerobic
fairly fast, not long acting
fermentation
purpose: regen NADH and ATP
Citric acid cycle and ETC
long term energy, krebs cycle first then ETC
fats can be sent into krebs in long term exercise
Both fiber types use what metabolism? Specific?
creatine phosphate
glycolysis: fast twitch
etc and krebs: slow twitch
over time they use fats from adipocytes
Muscle fatigue? occurs when? what produces rapid fatigue? what restores ionic balance? what gets damaged, in turn what regulation is disrupted?
physiological inability to contract. Intense exercise? Na/K pumps. Sarcoplasmic reticulum gets damaged, regulation of Ca is disrupted.
What is oxygen debt? what causes dramatic changes in muscle chemistry? to return to a resting state:
amount of extra O2 needed for restorative processes
exercise
o2 reserves must be replenished
lactic acid conversion
glycogen regen
ATP and CP reserves
