muscles 2 Flashcards
Motor Neuron
nerve cell that controls muscle contraction
neuromuscular junction
synapse between motor neuron and muscle cell
how is action potential initiated?
- travels through motor neuron and arrives at synaptic terminal
- initiated in motor neuron in response to CNS commands
Where does control of skeletal muscle activity occur?
neuromuscular junction
How does AP in motor neuron cause ACh to be released?
- ACh diffuses across synaptic gap
- ACh binds to receptors on chemically gated sodium channels in muscle membrane
what happens before and after sodium ions flow into muscle cell?
Before: ACh binds to receptors on chemically gated sodium channels in muscle membrane
After: depolarizes the muscle cell membrane and starts an action potential in the muscle cell
How long do chemically regulated gates stay open?
As long as ACh is present
What does Acetylcholine Esterase (AChE) do and where is it located?
located: synaptic gap
rapidly breaks down Acetyl Choline
Excitation of muscle cell causes the action potential to spread where?
Across the entire muscle cell membrane including the T tubules
Action potential along T-tubule causes what?
release of Ca from citernae of SR
List the steps of the contraction cycle
1) Ca binds to troponin, moving tropomyosin
2) attachment of myosin head to actin
3) pivot of myosin head pulls on actin
4) detachment of myosin head w/ binding of ATP
How does Ca ion concentration return to resting level?
AP depolarization ends, voltage gated Ca channels in SR close
-Ca ion flow into sarcoplasm stops
How is Ca transported out of sarcoplasm?
- across sarcolemma to outside of cell
- across sarcoplasmic reticulum membrane into SR
- requires ATP
Duration of contraction depends on?
1) Duration of stimulation at nerve-muscle synapse (neuromuscular junction)=continued release of ACh and multiple AP in muscle fiber
2) Presence of Ca ions in sarcoplasm till Ca returns to resting level
3) Availability of ATP, needed to power myosin head
Contraction ends and relaxation occurs when?
- Action potentials stop in motor neuron
- AChE breaks down ACh in neuromuscular synaptic gap
- ACh gated channels close, sodium ion influx stops
- AP stop occurring in sarcolemma and T-tubules
Why does relaxation require ATP?
- ATP needed to pump Ca into the SR
- ATP needed to disconnect myosin heads from actin
- Rigor mortis- lack of ATP after death
What does Ca ion resting levels do during relaxation?
Tropomyosin covers actin sites and no new myosin cross bridges can form
botulism
blockage of release of ACh
myasthenia gravis
interference w/ binding of ACh to receptors
polio
loss of motor neuron
peripheral nerve damage
Muscular system disorder
loss of motor neuron axon
MS
reduction of AP efficiency, damage to myelin
tetanus
excessive stimulation of motor neuron
Tension depends on
- tension that develops in individual muscle cells during contraction
- number of muscle cells that contract
What causes sarcomere shortening?
The sliding of actin and myosin filaments
What causes muscle cells to shorten?
all sarcomeres shortening
Amount of shortening depends on?
tension and resistance
Tension produced in individual muscle fibers can vary due to?
- length-tension relationship
- frequency of stimulation by motor neuron
Tension produced by entire muscle depends on?
- # of muscle cells receiving nerve stimulation, commanding them to contract
- muscle cells are grouped in motor units
skeletal muscle contracts most forcefully over?
A narrow ranges of resting lengths
Tension and the number of cross bridges formed depends on?
Degree of overlap of actin and myosin filaments
What is a twitch?
- cycle of contaction, relaxation produced by a single AP in a muscle cell
- not typical in normal muscle activity
Twitch, Latent phase
Action potential occurs
-no contraction until Ca is released from SR
Twitch, Contraction phase
Tension rises to peak
- Ca moves tropomyosin off of actin sites
- myosin cross bridges form,actin is pulled
Twitch, Relaxation phase
Tension falls to resting levels
- Ca is pumped back into SR
- Actin sites covered by tropomyosin
- No cross bridges remain
Sustained muscular contractions are produced by?
- high frequency of action potentials in muscle cell
- produced in response to high frequency of acton potentials in motor neuron (high frequency of stimulation)
complete tetanus
maximum tension production in a muscle cell-maximum cross bridge formation
“Tetanus” disease
- caused by Clostridium tetani bacteria
- bacterial toxin causes high frequency of action potentials in motor neurons
