What's the purpose of acetylcholine in the CNS?
Are all acetylcholine receptors nicotinic or muscarinic?
- 1 decade agoFavorite Answer
In the central nervous system, ACh has a variety of effects as a neuromodulator upon plasticity, arousal and reward. ACh has an important role in the enhancement of sensory perceptions when we wake up and sustained attention.
Damage to the cholinergic system in the brain has been suggested to play a role in the memory deficits associated with Alzheimer's disease.
Acetylcholine and the associated neurons form a neurotransmitter system, the cholinergic system from the brainstem and basal forebrain that projects axons to mainly areas of the brain. In the brainstem it originates from the Pedunculopontine nucleus and dorsolateral tegmental nuclei collectively known as the mesopontine tegmentum area or pontomesencephalotegmental complex. In the basal forebrain, it originates from the basal optic nucleus of Meynert and medial septal nucleus,:
* The pontomesencephalotegmental complex acts mainly on M1 receptors in the brainstem, deep cerebellar nuclei, pontine nuclei, locus ceruleus, raphe nucleus, lateral reticular nucleus and inferior olive. It also projects to the thalamus, tectum, basal ganglia and basal forebrain
* Basal optic nucleus of Meynert acts mainly on M1 receptors in the neocortex.
* Medial septal nucleus acts mainly on M1 receptors in the hippocampus and neocortex.
In addition, ACh acts as an important "internal" transmitter in the striatum, which is part of the basal ganglia. It is released by a large set of interneurons with smooth dendrites, known as tonically active neurons or TANs.
ACh is involved with synaptic plasticity, specifically in learning and short-term memory.
Acetylcholine has been shown to enhance the amplitude of synaptic potentials following long-term potentiation in many regions, including the dentate gyrus, CA1, piriform cortex, and neocortex. This effect most likely occurs either through enhancing currents through NMDA receptors or indirectly by suppressing adaptation. The suppression of adaptation has been shown in brain slices of regions CA1, cingulate cortex, and piriform cortex, as well as in vivo in cat somatosensory and motor cortex by decreasing the conductance of voltage-dependent M currents and Ca2+-dependent K+ currents.
Acetylcholine also has other effects on neurons. One effect is to cause a slow depolarization by blocking a tonically-active K+ current, which increases neuronal excitability. Another upon postsynaptic M4-muscarinic ACH receptors is to open inward-rectifier potassium ion channel (Kir) and cause inhibition.
These two effects happen upon neurons in different neuron layers. For instance, the excitation effect acts on intrinsic and associational fibers in layer Ib of piriform cortex, but has no effect on afferent fibers in layer Ia. Similar laminar selectivity has been shown in dentate gyrus and region CA1 of the hippocampus.
In the cerebral cortex, ACH inhibits layer 4 medium spiny neurons, the main targets of thalamocortical inputs while excitating of pyramidal cells in layers 2/3 and layer 5. This filters out weak sensory inputs in layer 4 and amplifies inputs that reach the layers 2/3 and layer L5 excitatory microcircuits. As a result, these layer-specific effects of ACH might function to improve the signal noise ratio of cortical processing.
Another theory interprets acetylcholine neuromodulation in the neocortex as modulating the estimate of expected uncertainty, acting counter to norepinephrine (NE) signals for unexpected uncertainty. Both modulations would then decrease synaptic transition strength, but ACh would then be needed to counter the effects of NE in learning, a signal understood to be 'noisy'.
- MaryLv 44 years ago
My breed was created just to keep me waiting on them!!!. Seriously, they are considered one of the oldest, if not the oldest ancient breed. They have DNA of the same era as the wolf and coyote.(30,000 to 150,000 years ago) They appear to be a 'natural dog' and are called by the natives of their origins, as Noah's dog, as they have been around as long as their known history. So, what were they bred for? Well, they were used to hunt. I'm not sure that they were officially 'bred'. They hunted gazelle and leopard.. They were also herding dogs, and still have strong herding instincts. They were never fed by their masters, but set loose to hunt at night, for their own sustenance. They were sheared each year, at the same time as the flocks, and their hair was used to make headwear and underwear, as it was softer than wool, and had no odor when wet. An interesting fact, that has kept the breed pure over the many generations. The females will rarely breed with another breed. Other breeds don't recognize their pheromones, and the females show no interest in any other male dog. Many females are loyal to their first mate, and won't mate with a dog who is a stranger. The only time you get a mixed breed, is if the two were raised together ( pack) or an occasional wondering male. Currently, they are used for predator control and the sport of lurecoursing...and teaching their owners patience!
- Anonymous1 decade ago
acetylcholine is a neural transmitter. Some substances act as mediators and others, including acetylcholine, simulate or active the next nerve cell as impulses pass down the a nerve. Once it has performed this action by passing across the synapse (neural junction between two nerve cells) it is broken down by an enzyme called acetylcholine esterase into an acetyl group and choline. Acetylcholine also passes across the neural muscular junction, similar to the synapse between neurons (nerve cells) and also between nerve endings and muscle cells stimulating them and thus causing your muscles to move.
Acetylcholine is also involved in memory and learning and is in particularly short supply in people with Alzheimer's disease. A recently released drug helps Alzheimers sufferers by inhibiting the action of acetylcholine esterase.Source(s): Me! =)