Pt 14
Action potential is caused by what?
changes in electrical charges
Axon branches end on muscle fiber, forming
neuromuscular junction or motor end plate
Synaptic vesicles contain what?
neurotransmitter acetylcholine (ACh)
Resting sarcolemma is what?
polarized
muscle fiber cannot be stimulated for a specific amount of time, until repolarization is complete
refractory period
Restoration of resting conditions
repolarization
Skeletal muscles are stimulated by what?
somatic motor neurons
if end plate potential causes enough change in membrane voltage to reach critical level called threshold, what will open ?
voltage gated Na+ channels in membrane will open
Action potential across sarcolemma occurs in three steps
1. End plate potential 2. Depolarization 3. Repolarization
What the sarcolemma is polarized what does it mean?
A voltage exists across the membrane
Junctional folds contain millions of what?
ACh receptors
Nerve impulse arrives at axon terminal causing what to be released into what?
ACh to be released into synaptic cleft
When there is a change or depolarization that is conducted along the membrane it is called a what?
Action potential
What is the third step that has to happen for skeletal muscles to contract
Action potential must be propagated along sarcolemma
ACh binding leads to electrical events that untimely generate a what?
Action potential through muscle fiber
What is the second step that has to happen for skeletal muscles to contract
An action potential and electrical current must be generated in the sarcolemma
Neuromuscular junction consists of what three things?
Axon terminals, synaptic cleft, and Junctional folds
Axons (long, threadlike extensions of motor neurons travel form where to where?
Central nervous system to skeletal muscle
The ACh released from motor neurons causes what to open?
Chemically gated ion channels on sarcolemma
AP spreads across sarcolemma from one Voltage-gated Na+ channels to the next one. In adjacent areas causing what?
Depolarization
Because the sarcolemma because less negative this results in what?
End plate potential
Steps 3 and 4 for skeletal muscle contraction like electrical signals to the contraction so they are referred to as what?
Excitation-contracting coupling
What is the fourth and final step that has to happen for skeletal muscles to contract
Intracellular Ca2+ levels must rise briefly
In reference to cells the oppositely charged particles are what?
Ions
Unfolding of sarcolemma is called what?
Junctional folds
What separates ions?
Plasma membrane
In their resting state all cells have a voltage across their membrane, called the
Membrane potential
Each muscle fiber has one neuromuscular junction with one what?
Motor neuron
large influx of Na+ through channels into cell triggers AP that is unstoppable and will lead to what?
Muscle fiber contraction
Ion conditions of resting state are restored by what?
Na+ - K+ pump
After the gated ion channels open what diffuses into the muscle fiber
Na+ and some k+
____ voltage gated channels close and voltage gated ____ open
Na+, K+
transports Na+ ions out of cell and K+ ions into cell
Na+/K+ pump
Inside of the resting sarcolemma is what compared to the outside?
Negative
What is the first step that has to happen for skeletal muscles to contract
Nerve stimulation
Step one and two for skeletal muscle contraction occur where?
Neuromuscular junction
K+ effluvia out of cell rapidly brings cell back to initial what?
Resting membrane voltage
ACh released from motor neuron binds to ACh receptors on what?
Sarcolemma
What separates fibers
Sarcolemma
A plasma membrane is more permeable to some particles than others depending on their what?
Size, solubility, or charge
Axon terminal (end of axon) and muscle fiber are deprecated by gel-filled space called what?
Synaptic cleft
Stored within axon terminals are membrane-bound what?
Synaptic vesicles
Each axon branches divided into many branches as it enters what?
The muscle
ACh diffuses across the cleft and binds with receptors on what?
The sacolemma
Electrical potential energy that is due to the separation of oppositely charged particles
Voltage
Generation and propagation of an action potential
depolarization
The process during the action potential when sodium is rushing into the cell causing the interior to become more positive
depolarization
What happens in end plate potential
initial depolarization of motor end plate
Because Na+ diffuses in, interior of sarcolemma becomes
less negative (more positive)