When acetylcholine reaches receptors on the membranes of muscle fibers,
membrane channels open
and the process that contracts a relaxed muscle fibers begins: Open channels allow an influx of sodium ions into the cytoplasm of the muscle fiber.
What happens to the acetylcholine after the muscle contracts?
After it is packaged, transported, and released, it binds to the acetylcholine receptor on the motor end-plate;
it is degraded in the synaptic cleft by the enzyme acetylcholinesterase (AChE) into acetate
(and acetic acid) and choline. The choline is recycled back into the neuron.
What is the relationship between acetylcholine and muscle contraction?
Muscle contraction is controlled by receptors in the muscle cell membranes that respond to the neurotransmitter acetylcholine when it is released from
motor
neurons. Acetylcholine receptors are also found on neurons, where they perform a variety of important functions, including modulating cognition and addiction.
What happens after acetylcholine binds to its receptors?
At the synapse of a motor neuron and striated muscle cell, binding of acetylcholine to nicotinic acetylcholine receptors triggers
a rapid increase in permeability of the membrane to both Na
+
and K
+
ions, leading to depolarization, an action potential, and then contraction
(see Figure 21-37).
What triggers the release of acetylcholine from a synaptic terminal?
The release of acetylcholine occurs when an action potential is relayed and reaches the axon terminus in which depolarization
causes voltage-gated calcium channels to open and conduct an influx of calcium
, which will allow the vesicles containing acetylcholine for release into the synaptic cleft.
How does curare interact with acetylcholine?
In modern medicine, curare is classified as a neuromuscular blocking agent—it produces flaccidity in skeletal muscle by competing with the
neurotransmitter acetylcholine at the neuromuscular junction
(the site of chemical communication between a nerve fibre and a muscle cell).
What are the effects of acetylcholine?
Acetylcholine is the chief neurotransmitter of the parasympathetic nervous system, the part of the autonomic nervous system (a branch of the peripheral nervous system) that contracts smooth muscles, dilates blood vessels,
increases bodily secretions, and slows heart rate
.
What happens if you have too much acetylcholine?
Excessive accumulation of acetylcholine (ACh) at the neuromuscular junctions and synapses causes symptoms of both muscarinic and nicotinic toxicity. These include cramps,
increased salivation, lacrimation, muscular weakness, paralysis, muscular fasciculation, diarrhea, and blurry vision
.
What causes a decrease in acetylcholine?
Acetylcholine is a chemical messenger, or neurotransmitter, that plays an important role in brain and muscle function. Imbalances in acetylcholine are linked with chronic conditions, such as
Alzheimer’s disease
and Parkinson’s disease.
What happens if you block acetylcholine?
Acetylcholine and
myasthenia gravis
Myasthenia gravis causes the immune system to block or destroy acetylcholine receptors. Then, the muscles do not receive the neurotransmitter and cannot function normally. Specifically, without acetylcholine, muscles cannot contract.
What would happen if the receptors for acetylcholine were blocked?
The acetylcholine receptor is an essential link between the brain and the muscles, so it is a sensitive location for attack. Many organisms make poisons that block the acetylcholine receptor,
causing paralysis
.
What foods help produce acetylcholine?
Choline is an essential nutrient and a building block of acetylcholine. Foods that are naturally high in choline include
whole eggs, meats and fish, and whole grains
. Studies in laboratory animals and humans suggest that consuming foods or supplements rich in choline may elevate levels of acetylcholine in the brain.
What part of the brain produces acetylcholine?
Acetylcholine is synthesized in certain neurons by the enzyme choline acetyltransferase from the compounds choline and acetyl-CoA. Cholinergic neurons are capable of producing ACh. An example of a central cholinergic area is
the nucleus basalis of Meynert in the basal forebrain
.
What ion causes the release of acetylcholine?
Extracellular
calcium ions
enter the axon terminal via the voltage-gated calcium channels. These calcium ions then attach to the vesicles that contain ACh. The attachment of the calcium ions to the vesicles causes the release of ACh in the synaptic cleft.
How do you trigger acetylcholine?
One of the easiest ways to raise acetylcholine levels is
to consume foods or take dietary supplements that are high in choline
— an essential nutrient that can be converted into acetylcholine ( 1 ). Choline is present in many foods, including ( 6 ): Beef liver: 3 ounces (85 grams) contain 65% of the Daily Value (DV).
Is there an antidote to curare?
The antidote for curare poisoning is
an acetylcholinesterase (AChE) inhibitor (anti-cholinesterase)
, such as physostigmine or neostigmine.
