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)