Lesson 20 Flashcards
muscle means literally…
little mouse
muscular system refers only to…
skeletal muscle
myology
the study of the muscular system
excitability (responsiveness)
respond to chemical signals, stetch, and electrical changes across the plasma membrane
conductivity
local electrical excitation sets off a wave of excitation that travels along the muscle fiber
contractility
shorten when stimulated
extensibility
capable of being stretched between contractions
elasticity
returns to its original rest length after being stretch
striations
alternating light and dark transverse bands; results from arrangement of internal contractile proteins
voluntary
usually subject to conscious control
skeletal muscle cells are also called _____ _____ or _____
muscle fibers, myofibers
six functions of skeletal muscle
- produce skeletal movement
- maintain posture and body position
- support soft tissues
- guard entrances and exits
- maintain body temperature
- store nutrients
endomysium
fibrous connective tissues that surrounds each muscle fiber
perimysium
bundles muscle fibers into fascicles
epimysium
surrounds entire muscle
collagen (4)
- stretches slightly under tension and recoils when released
- resists excessive stretching to protect muscle from injury
- returns muscle to original length
- contributes power output and muscle efficiency
fascicles
bundles of muscle fibers wrapped together
fascia
sheet of connective tissue between muscles or muscle groups
what does the endomysium allow room for?
capillaries and nerve fibers
what type of cells does the endomysium contain?
myosatellite cells (stem cells) that repair damage to muscle cells
CANNOT DEVELOP INTO A WHOLE MUSCLE
what does the perimysium contain? (3)
nerves, blood vessels, and stretch receptors
tendon
when the endomysium, perimysium, and epimysium come together to form a connective tissue attachment to bone
sarcolemma
plasma membrane for a muscle fiber (cell)
sarcoplasm
cytoplasm of a muscle fiber
myofibrils
long protein cords occupying most of the sarcoplasm
glycogen
carbohydrate store to provide energy for exercise
myoglobin
red pigmented protein that binds oxygen and provides some needed for muscle activity
sarcoplasmic reticulum (SR)
smooth ER that forms a network around each myofibril, that stores calcium in the cell
terminal cisterns
dilated end-sacs of SR which cross the muscle fiber from one side to the other
transverse (T) tubules (2)
tubular infoldings of the sarcolemma which penetrate through the cell and emerge on the other side
- funnels action potentials generated in the muscle cell towards the terminal cisterns of the SR
triad
a T tubule and its two associated terminal cisterns
myoblasts
stem cells that fuse to form each muscle fiber early in development, each contributing one nucleus
myosatellite cells
unspecialized myoblasts remaining between the muscle fiber and endomysium
three kinds of myofilaments
- thick filaments
- thin filaments
- elastic filaments (titin)
thick filaments
made of several hundred myosin molecules
myosin structure (3)
- two chains intertwined to form a shaft-like tail and a double globular head
- heads directed outward in a helical array around the bundle
- heads on one half angle to the left, while heads on the other half are to the right
bare zone
middle zone with no heads
fibrous (F) actin
two intertwined strands of globular (G) actin subunits, each with an active site that can binds myosin
F actin is held together by a protein called _____ that runs along the length of the F actin strand
nebulin
tropomyosin
regulatory protein that blocks the active sites of G actin subunits
troponin
small, calcium-binding protein on each tropomyosin molecule
elastic filaments
made of a huge, springy protein called titin
what do elastic filaments do? (2)
- help stabilize and position the thick filament
- prevent overstretching and provide recoil
where is titin located?
they run through the core of the thick filament and anchor it to Z disc and M line
contractile proteins
myofilaments, myosin, and actin
regulatory proteins
tropomyosin and troponin
how is contraction activated?
by the release of calcium from the SR into the sarcoplasm, binding to troponin
A band
dark band
H band
at the middle of the A band, thick filaments only
M line
dark, transverse protein in the middle of the H band
I band
light band, only thin filaments
Z line
protein complex that provides anchorage for thin and elastic filaments
sarcomere
smallest functional unit of muscles
- segment from Z line to Z line
zone of overlap
area of the A band minus the H band
skeletal muscle cannot contract unless.
stimulated by a nerve
denervation atrophy
shrinkage of paralyzed muscle when nerve remains disconnected; motor neuron no longer stimulating the muscle cell
skeletal muscles are served by _____ _____ _____
somatic motor neurons
somatic motor neurons
nerve cells whose cell bodies are in the brainstem and spinal cord that serve skeletal muscles
somatic motor fibers
axons of somatic motor neurons
motor unit
one nerve fiber and all the muscle fibers innervated by it; they behave as a functional unit
muscle fibers of one motor unit….. (4)
- are dispersed throughout muscle
- contract in unison
- produce weak contraction over wide area
- provide ability to sustain long-term contraction as motor units take turns contracting
effective contraction usually requires contraction of …..
several motor units at once
small motor units
provide fine degree of control
large motor units
provide more strength than control
neuromuscular junction (NMJ)
aka motor end plate
- when a nerve fiber meets its muscle fiber target at a synapse
muscle cell sarcolemma have millions of what kind of receptor?
acetylcholine
postsynaptic membrane folds (junctional folds)
folds of the sarcolemma that increase the surface area, maximizing the number of ACh receptors
myasthenia gravis
a lack….
a lack of ACh receptors in muscle cells causing weakness
acetylcholinesterase
enzyme that breaks down ACh, allowing for relaxation
muscle fibers and nerve cells are what kind of cell?
electrically excitable cells
electrophysiology
study of the electrical activity of cells
electrical activity depends the concentration differences of ions in what two places?
intracellular fluid and extracellular fluid
polarized
contains a net negative charge
electrical potential/voltage
any difference in charge between two points
cholinesterase inhibitors
bind acetylcholinesterase and prevents it from degrading ACh
spastic paralysis
a state of continual contraction of the muscles; possible suffocation
tetanus (lockjaw)
a form of spastic paralysis caused by toxin Clostridium tetani
_____ in the spinal cord normally stops motor neurons from producing unwanted muscle contractions
glycine
what does tetanus toxin do?
blocks glycine release in the spinal cord and causes overstimulation and spastic paralysis of muscles
flaccid paralysis
a state in which the muscles are limp and cannot contract
curare
competes with ACh for receptor sites, but does not stimulate muscles
botulism
type of food poisoning caused by neuromuscular toxin secreted by the bacterium Clostridium botulinum
what does botulism toxin do?
blocks release of ACh causing flaccid paralysis
botox is really just
Clostridium botulinum toxin
