Ex. Phys. Neuromuscular Physiology Flashcards
skeletal muscle general features
- attached to bones to produce movement
- comprised of long, multi-nucleated cells (fibers) arranged in series for maximum force production
- actin and myosin are the primary contractile filaments
- voluntarily controlled
skeletal muscle properties
- contractility: can generate tension
- irritability: responds to stimulation
- extensibility: can stretch
- elasticity: can return to original length
skeletal muscle structure (smallest to largest)
myofilament myofibril muscle cell/fiber fascicle whole muscle
myofilament
- composition
- filament relationship
- other important myofilaments
composition
-thin filaments
-thick filaments
filament relationship
-for every one thick filament there are six thin filaments surrounding it
other important myofilaments
-collagen
–structural myofilament
–arrangement and amount dictate how flexible or rigid the tissue is
-elastin
–stretchy protein that gives muscle its elastic property
-titin
–helps keep the myosin filaments aligned with one another inside the sarcomere
-nebulin
–protein that dictates the length of the actin filaments
thin filaments
actin
troponin
tropomyosin
thick filaments
myosin, which includes heavy and light chains
myofibril
- what is it?
- functional unit
bundle of myofilaments
functional unit
-sarcomere
sarcomere
- composition
- identifiable features
each sarcomere contains multiple thick and thin filaments identifiable features -Z-disk/line -M-line -I-band -H-zone -A-band
Z-disc/line
edges of the sarcomere
M-line
center “anchor” of the sarcomere
I-band
area where only actin filaments are present (no overlap with myosin)
H-zone
area where only myosin filaments are present (no overlap with actin)
A-band
area that spans the length of myosin filaments (includes areas of myosin and actin overlap)
muscle cell/fiber
-what is it
composition
bundle of myofibrils composition -sarcolemma -satellite cells -sarcoplasm -transverse tubules -sarcoplasmic reticulum -terminal cisternae -mitochondria -nuclei -myostatin -dystrophin
sarcolemma
-what is it?
cell membrane
satellite cells
-function
regulate growth & adaptation
sarcoplasm
- what is it?
- contains
fluid part contains -ATP-CrP -glycogen -fats -mitochondria
Transverse tubules (t-tubules) -function
propagate action potentials inward from sarcolemma to myofibrils
sarcoplasmic reticulum
- location
- function
SR
network of longitudinal tubules that surround myofibrils for Ca2+ storage and release
terminal cisternae
-function
enlarged portion of SR for Ca2+ storage and release
mitochondria
-function
aerobic factories that produce ATP
nuclei
-function
control centers for the muscle fiber
myostatin
-function
negatively regulates muscle growth
dystrophin
-function
links cytoskeleton of muscle fiber to the extracellular matrix
contractile fibers within a skeletal muscle
- known as
- innervated by
known as extrafusal muscle fibers
innervated by alpha motor neurons
fascicle
-what is it?
bundle of muscle fibers
whole muscle
-what is it?
bundle of fascicles
connective tissues
- types (deep to superficial)
- what does each tissue type do?
types -endomysium (surrounds fibers) -perimysium (surrounds fascicles) -epimysium (surrounds whole muscle) function -each tissue type connects to form bundles that ultimately fuse into the tendon
pennation
- what is it?
- types
the “architecture” of a muscle
types
-parallel
-pennate
parallel
- characteristics
- types
characteristics -long fibers arranged parallel along the length of a muscle to produce large ranges of motion types -flat -fusiform -strap -radiate -sphincter
pennate
- characteristics
- types
characteristics -fibers arranged obliquely to the central tendon to maximize cross-sectional area and force types -unipennate -bipennate -multipennate
fiber types (speed)
Type IIx (fast glycolytic)
Type IIa (fast oxidative glycolytic)
Type I (slow oxidative)
-all of the muscle fibers have the same stuff, just in different amounts
-there is shifting between Type IIx and Type IIa
-lower extremity and larger muscles have more Type II
Type IIx
-anatomical properties
-little myoglobin, mitochondria, and blood capillaries
-a lot of glycogen and
CrP in sarcoplasm
-fast form of myosin ATPase enzyme
Type IIx
-physiological/functional properties
- can anaerobically generate and hydrolize ATP at a high rate
- fatigue easily
- speed of contraction in 5-6x faster than Type I fibers
- contraction force is much higher than Type I fibers
- great for speed/power activities
Type IIa
-anatomical properties
- moderate amounts of myoglobin, mitochondria, and blood capillaries
- a lot of glycogen and CrP in sarcoplasm
- fast form of myosin ATPase enzyme
Type IIa
-physiological/functional properties
- decent capacity for generating ATP via anaerobic AND aerobic metabolism, therefore these fibers can hydrolyze ATP at a high rate (slower than Type IIx, but still fast)
- faster contraction velocity than Type I, but slower than Type IIx
- higher contraction force than Type I, bull tell than IIx
- more resistant to fatigue than Type IIx, but less resistant than Type I
- good compromise for all activities
Type I
-anatomical properties
- a LOT of myoglobin, mitochondria, and blood capillaries
- slow form of myosin ATPase enzyme
Type I
-physiological/functional properties
- can aerobically generate loads of ATP, but at a slow rate
- most resistant to fatigue
- slowest contraction velocity
- lowest contraction force
- great for endurance activities
muscle receptor types
muscle spindles
Golgi Tendon Organs (GTOs)
muscle spindles
- function
- knows as
- rapid lengthening of whole muscle…
function -provide feedback on muscle length and rateof change in length to the CNS known as -intrafusal muscle fibers, which are innervated by gamma motor neurons rapid lengthening of whole muscle (feedback sent to CNA) elicits the "stretch (myostatic) reflex" (response)
stretch reflex
- lengthening of the intrafusal fibers (muscle spinles) stimulate Ia efferent (sensory) neurons
- sensory feedback is received in the CNS and inhibits a-motor neuron for the antagonist muscle (reciprocal inhibition)
- motor feedback from A-motor neuron stimulates extrafusal muscle fiber contraction in the agonist muscle
muscle spindle note
gamma-motor neurons regulate the sensitivity of the muscle spindle by stimulating the intrafusal fibers to contract, thereby shortening the spindle
consequently, only a small stretch is required to activate the stretch reflex
Golgi Tendon Organs (GTO’s)
- function
- location
function
-provide feedback on muscle tension and rate of change in tension to the CNS
location
-located in tendinous connective tissue at ends of skeletal muscle
autogenic inhibition reflex
-what is it?
response elicited by tension placed on several motor units within a muscle (feedback sent to CNS)
autogenic inhibition reflex
-process
- deformation of 10-20 motor units (due to tension) within the GTO stimulates 1b afferent (sensory) neurons
- sensory feedback is received in the CNS and inhibits a-motor neuron for the agonist muscle and excites a-motor neuron for the antagonist muscle (reciprocal excitation)
- inhibited motor feedback from A-motor neuron for agonist muscle inhibits or reduces extrafusal muscle fiber contraction
autogenic inhibition and reciprocal excitation function
play critical roles in the timing of muscle activation during locomotion
two processes of skeletal muscle contraction
excitation-contraction coupling
sliding filament theory
excitation-contraction coupling steps
- nervous stimulus in the form of an action potential (AP) is delivered to muscle via a-motor neuron
- at the neuromuscular junction, acetlycholine (Ach) is released from the pre-synaptic membrane of the a-motor neuron into the synaptic cleft
- Ach binds to nicotinic receptors on the post-synaptic membrane of the muscle fiber
- an AP is generated across the sarcolemma of the muscle fiber and down the T tubules
- the AP activates DHP receptors, which transmit electrical signal through triadic feet to ryanodine receptors located in the SR
- ryanodine receptors signal CA2+ release from the SR into the muscle sarcoplasm
Sliding filament theory steps
- Ca2+ binds to troponin, pushing tropomyosin off from active binding sites on actin
- myosin heads bind to actin at a 45 degree angle
- ATP binds to myosin heads causing myosin to dissociate from actin
- ATP is hydrolyzed into ADP and Pi by myosin ATPase, which cocks the myosin heads
- myosin binds weakly to actin again, this time at 90 degrees
- Pi is released from myosin heads, which initiates the power stroke
- myosin ehads rotate back to a 45 degree position relative to actin, dragging actin closer to the M-line
- ADP is released after the power stroke and myosin remains bound to actin
- repeat… the resultant ratcheting movement of myosin head and repeated coupling and uncoupling with actin produces muscle shortening/lengthening under tension
what happens when muscular contraction is no longer desires?
Ca2+ is resequestered into the SR, tropomyosin covers binding sites and actin slides back to original resting position
types of muscle contraction
isotonic
isometric
isokinetic
isotonic
- what happens
- types of isotonic contractions
muscle produces force while moving at any velocity
types
-concentric
-eccentric
concentric
muscle produces force while shortening
eccentric
muscle produces force while lengthening
isometric
muscle produces force statically
isokinetic
muscle produces maximal force at a fixed velocity
motor unit
- what is it?
- types of movement
- what dictates muscle fiber type?
an a-motor neuron and all the muscle fibers it innervates
types
-gross: single neuron innervating several fibers
-fine; single neuron innervating a few fibers
motor neuron dictates muscle fiber type
three strategies for neuromuscular recruitment
All or None Principle
Size Principle
rate coding
All or None Principle
- what is the principle?
- application
when a motor unit is recruited, all innervated fibers contract to their full potential
application
-when few motor units are recruited little force is produced
-when lots of motor units are recruited lots of force is produced
size principle
- what is it?
- application
low threshold motor units recruited first and higher threshold motor units are recruited as more force is needed
application
-Type I motor units are easier to recruit, so they are recruited first
-Type II motor units are recruited later
rate coding
- what is it?
- types of stimulus
a motor unit can exert varying levels of force dependent on the frequency at which it is stimulated
types
-single stimulus = twitch (little force)
-repeated, rapid stimuli = summation (more force)
-continued stimulation = tetanus (max force)
additional factors that influence muscle force output
fiber cross-sectional area (CSA) muscle pennation muscle receptor sensitivity & feedback velocity of muscle contraction muscle length muscle elasticity type of muscle action concurrent-activation potentiation (CAP) post-activation potentiation (PAP)
velocity of muscle contraction
- faster means…
- note
the fast a muscle fiber contracts, the less force it can produce
muscle length
- sarcomere too short
- ideal sarcomere length
- note
when the sarcomere is too short or too long, the number of actin-myosin cross-bridges decreases, so force output is limited
the ideal sarcomere length maximizes the number of actin-myosin cross-bridges for maximum force output
note
-the effective use of levers and body position can overcome deficiencies in sarcomere length to maximize practical force output
muscle elasticity
there is an elastic component of force output that can be augmented when a muscle is stretched (like a rubber band)
type of muscle action
- concentric
- isometric
- eccentric
- note
concentric is typically the weakest due to dynamic cross-bridging and actin-myosin overlap at shorter muscle lengths
isometric action can produce more force than concentric action probably because of static cross-bridges
eccentric (strongest) action can produce the most force because of the additional contribution of stored elastic energy
note
-eccentric action followed immediately by concentric action can induce what’s knows as the Stretch Shortening Cycle
concurrent-activation potentiation (CAP)
remote voluntary contractions (RVC) or the H-reflex may induce a MOTOR OVERFLOW that excites target motor units, which in turn increases force output
-grit your teeth when lifting a heavy weight
post-activation potentiation (PAP)
30-sec to a few minutes after a high intensity muscle contraction, the activated motor units may be more easily excitable and, therefore, more easily recruited for greater force production
