Contraction of Skeletal Muscle Flashcards
Define Motor Neuron
nerve cell that controls muscle contraction
Define Neuromuscular junction
synapse between motor neuron and muscle cell
Action potentials are initiated in response to CNS and travel
through motor neuron and arrive at synaptic terminal
ACh is released from a motor neuron terminal in response to
an action potential in the motor neuron
When ACh is released following an action potential
ACh diffuses across synaptic gap
ACh binds to receptors on chemically gated sodium channels
Sodium ions flow in
Muscle cell membrane depolarizes
When do Chemically regulated channels close?
When ACh is no longer present
What is AChE
Acetylcholine Esterase
Located in synaptic gap
Rapidly breaks down Acetylcholine
Action potentials in the muscle cell membrane are conducted into the interior of the muscle via ____ and cause Ca 2+ ions to be released from the ____
Transverse Tubules
SR
Action potential along T-tubule causes release of calcium to initiate contraction cycle:
- Ca2+ binds to troponin and moves tropomyosin
- Myosin head attaches to actin
- Myosin head pivots and pulls on actin
- Myosin head detaches with binding of ATP, breaking cross brdige
When does the contraction cycle stop?
When calcium ion concentration falls to resting level
What happens when AP depolarization ends and voltage gated Ca 2+ channels close?
Calcium ion flow stops
Ca2+ actively pumped out of sarcoplasm
What does the duration of contraction depend on?
Duration of stimulation at nerve-muscle synapse
Presence of calcium ions in sarcoplasm
Availability of ATP
Contraction ends and relaxation occurs when
AP stop in motor neuron
ACh Esterase breaks down ACh
ACh gated channels close
AP stop in sarcolemma and T tubules
When do calcium ion levels in sarcoplasm return to resting levels?
Tropomyosin covers actin sites and no new myosin cross bridges can form
True or false: Relaxation requires ATP
True
Why does relaxation require ATP?
Needed to pump Ca2+ into SR and to disconnect myosin heads from actin
What is rigor mortis?
Lack of ATP after death
Define botulism
Blockage of release of ACh
Define myasthenia gravis
Interference with binding of ACh to receptors
Define polio
Loss of motor neuron
Define peripheral nerve damage
Loss of motor neuron axon
Define MS
Reduction of AP efficiency and damage to myelin
Define tetanus
Excessive stimulation of motor neuron
If you interfere with ACh Esterase activity, what would happen
Your heart would stop
What is tension
Pulling strength
Tension in a muscle depends on
- Tension in individual muscle cells during contraction
- Number of muscle cells that contract
The amount of shortening of a muscle depends on
Tension and resistance
How is tension produced
sarcomeres shorten, muscle cells shorten
Tension can vary due to
length-tension relationship
Frequency of stimulation by motor neuron
Amount of cross bridges form
What is the length tension relationship?
Idea that depending on how stretched or compressed a muscle might be, it will effect how much tension that muscle will produce
What is a motor unit?
Collection of muscle cells that contract together at the same time, because they are all innervated by the same motor neuron
Skeletal muscle contracts most forcefully over a
narrow range of resting legnths
What is a twitch
cycle of contraction, relaxation produced by a single action potential in a muscle cell
What are the 3 phases of a twitch?
- latent phase
- contraction phase
- relaxation phase
Describe the latent phase of a twitch
Action potential occurs
No contraction until Ca 2+ released from SR
Describe the contraction phase of a twitch
Tension rises to peak
Ca2+ moves tropomyosin off actin sites
Myosin cross bridges form
Describe the relaxation phase of a twitch
tension falls to resting levels
Ca2+ pumps 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 or motor neurons
Summation of tension produces
Greater tension
Define Complete tetanus
You can hold something that maximum tension with a sustained contraction
Define incomplete tetanus
You sustain a contraction without reaching maximum tension
Summation occurs when
You have repeated stimulation produced before relaxation phase has been completed (build up of ca2+ ions in sarcoplasm)
What is Tetanus disease
Clostridium tetani bacterial toxin causes high frequency of action potentials in motor neurons
