neuromuscular system Flashcards
What are voltage-gated ion channels?
Channels that open or close in response to changes in membrane potential.
What are chemically-gated ion channels?
Channels that open in response to the binding of a neurotransmitter.
What do the ventral horns of the grey matter contain?
Cell bodies of somatic motor neurons.
What do descending tracts in the white matter do?
Carry information down the spinal cord.
What is the neuromuscular junction?
The region where a motor neuron contacts the skeletal muscle.
What triggers a muscle action potential?
A nerve signal delivered by a motor neuron.
What is a motor unit?
A neuron plus the fibers it triggers.
What are synaptic end bulbs?
Structures at the neuron terminal that release neurotransmitters.
What is the motor end plate?
The area of the muscle where ACh receptors are located.
What is the synaptic cleft?
The gap between the synaptic end bulbs and the motor end plate.
What happens when an action potential arrives at the motor neuron terminal?
Voltage-gated Ca2+ channels open, allowing Ca2+ to enter the axon terminal.
What is acetylcholine (ACh)?
A neurotransmitter released by exocytosis that binds to receptors on the sarcolemma.
What is the end plate potential?
A local change in the membrane potential that spreads to the adjacent sarcolemma.
What is the threshold value for firing an action potential?
-55mV.
What are T tubules?
Invaginations of the sarcolemma at the A-I junction that allow action potentials to reach all sarcomeres.
What is the role of the sarcoplasmic reticulum (SR)?
Stores calcium ions in resting muscle and releases them during contraction.
What is excitation-contraction coupling?
The sequence of events by which transmission of an AP leads to the sliding of myofilaments.
What happens when Ca2+ binds to troponin?
It moves tropomyosin off actin sites, allowing myosin to bind to actin.
What initiates the contraction cycle?
Myosin bound to ADP + Pi attaches to actin myofilaments, forming a cross-bridge.
What is the power-stroke in the contraction cycle?
Myosin head pivots and bends, pulling the actin filament towards the M line.
What occurs when ATP attaches to myosin?
Myosin releases actin and the cross-bridge breaks.
What causes rigor mortis?
Lack of ATP prevents myosin from releasing actin.
What happens during muscle relaxation?
ACh is broken down by acetylcholinesterase, Ca2+ ions are transported back into the SR.
What is the role of tropomyosin during relaxation?
Covers actin binding sites, preventing contraction.
True or False: Muscle tone is maintained by motor neuron activity even at rest.
True.
