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Marijuana is a fascinating drug, because it's effects varies from one person to another, it has effects that falls under 3 drug categories(Depressant, Narcotics, Hallucinogen)


As a Depressant, it can put a person in a parasympathetic nervous system state or a resting state, characterized by shallow breathing, dilated pupils, increased appetite and slower reaction time, behaviors usually observed upon people, who are resting or relaxed. This improves appetite in people with HIV/AIDS.

As a Narcotic, it can inhibit or prevents the feeling of pain, it can treat chronic pain and muscle spasms in people, who had experience major accidents or Epilepsy.

As a Hallucinogen, it can produce illusions/mental images. People report using hallucinogenic drugs for more social or recreational purposes, including to have fun, help them deal with stress, or enable them to enter into what they perceive as a more enlightened sense of thinking or being. Hallucinogens have also been investigated as therapeutic agents to treat diseases associated with perceptual distortions, such as schizophrenia, obsessive-compulsive disorder, bipolar disorder, and dementia.

Marijuana, has different varieties, each variety has different major effects, upon the body. And how the body respond to Marijuana differ from one person to another. That's why we have different classifications for Pot-smokers.


The action potential (electrical impulse) is pulled along the cell by positive ions entering and attracting it before leaving again.


An action potential is the electrical signal that travels down the neuron cell.

The electrical signal is negatively charged, because it is, obviously, electrical. It is drawn along the neuron by a series of positive ions appearing in front of it and pulling it forward. Imagine if you tied a string to a ten pound note and pulled it along the street with a cartoon character chasing after it - that's how I like to think of it.

The inside of the neuron cell is normally negatively charged relative to the outside. Ion channels open when the electrical signal enters the cell and pump #Na^+# ions inside, which attracts the electrical signal along the cell.

Since the cell is normally negative, or polar, the influx of positive ions is known as a depolarisation, because it turns the cell more positive in that area. However, once the cell has reached a certain level of depolarisation, the #Na^+# supply cuts off and the cell begins pumping #K^+# ions out of the cell instead. This turns the cell back to negative, causing a repolarisation.

While this is happening, some of the #Na^+# spreads out and changes the charge slightly further along the cell, which activates more sodium gates and lets sodium flow in further along, which depolarises that segment of the axon and pulls the electrical signal even further along.

The series of depolarisation and repolarisation along the cell makes the action potential move down the axon.

When an electrical impulse reaches the synapse, it opens calcium channels. The calcium enters and causes vesicles (bubbles) of neurotransmitters to bind to the membrane and release the chemicals. The neurotransmitter molecules drift across the synapse and bond to receptors on the next neuron, which initiates the electrical signal and the process of de- and repolarisations repeats.


Perceptual set is a tendency to perceive or notice some aspects of the available sensory data and ignore others.


Our bodies are magnificent machines. One of the ways they demonstrate this is by taking repetitive motions and actions and reducing the resources needed to perform them. For instance, when a baby is learning to walk, each step is planned and performed. But after a relatively short period of time, they are running without giving it a thought - they just run (and run and run and run...)

Our brains do the same thing. The world is full of information that continually enters our senses. In order to speed up processing time and reduce the energy needed to perform those functions, it operates largely on what is expected and not necessarily on what is actually there.

And that is what Perception Set Theory gets into - how the brain "perceives" - or as the below link describes it - "Perceptual set theory stresses the idea of perception as an active process involving selection, inference and interpretation."

Perceptual set is a tendency to perceive or notice some aspects of the available sensory data and ignore others. For instance, have you ever seen this:

Aoccdrnig to a rscheearch at Cmabrigde Uinervtisy, it deosn't mttaer in waht oredr the ltteers in a wrod are, the olny iprmoetnt tihng is taht the frist and lsat ltteer be at the rghit pclae. The rset can be a toatl mses and you can sitll raed it wouthit porbelm. Tihs is bcuseae the huamn mnid deos not raed ervey lteter by istlef, but the wrod as a wlohe.

The brain doesn't read every word but instead selects out important bits and teases out the rest based on expectation and inference.

Another kind of perceptual set is when we have a fear of snakes, to automatically assume that every suspicious looking thing in the grass is a snake - even though most times we're looking at a garden hose.

There are a number of ways perception sets can change. If we're hungry, the perception set will tend to look for food over other things.

The link has a great article about perception sets.



They come from tyrosine and tryptophan, respectively.


Both are formed by enzymatically controlled hydroxylation and decarboxylation reactions.


Dopamine is formed by the metabolism of tyrosine.

#"Tyrosine" → "L-DOPA" → "Dopamine"#

The enzyme tyrosine hydroxylase first hydroxylates tyrosine to L-3,4-dihydroxyphenylalanine (L-DOPA).


In a second step, the enzyme L-DOPA decarboxylase decarboxylates L-DOPA to form dopamine.


Serotonin is formed by the metabolism of tryptophan.

#"Tryptophan" → "5-hydroxytryptophan" → "serotonin"#

In the first step, the enzyme tryptophan hydroxylase hydroxylates tryptophan to form 5-hydroxy tryptophan (5-HTP).


In a second step, the enzyme aromatic L-amino acid decarboxylase decarboxylates 5-HTP to form serotonin.


I'm presuming your question is related to sensation.


Absolute Threshold is the point where some sensory input becomes just noticeable to our senses. It is the softest sound we can hear or the slightest touch we can feel. Anything less than this goes unnoticed.

Once a stimulus becomes detectable, how much must it change by for the change to become noticeable by us? The Difference Threshold is the amount of change needed for us to recognize that a change has occurred. This change is referred to as the Just Noticeable Difference .

This difference however is not absolute. Imagine you have an empty hand, and someone puts a 1 g weight in it. You would notice this weight.
Now imagine that you have a 1 kg weight, and someone adds a 1g weight to that. You would not notice this at all.
This is referred to as Weber’s Law .

Ever wonder why it is that we notice certain smells or sounds right away and then after a while they fade into the background? Once we adapt to the smell of a perfume or the ticking of the clock, we stop recognizing it. This process of becoming less sensitive to unchanging stimulus is referred to as sensory adaptation, after all, if a stimulus doesn’t change, why do we need to constantly sense it?

Source: http://allpsych.com/psychology101/sensation/


An action potential is generated in the following steps: depolarization, repolarization, hyperpolarization and a refactory period.


Assuming you are referring to depolarization (as to how it's caused!):
Receptor cells (cells which detect change) act as transducers (which means, they can convert, for eg. light into energy in an electrical impulse!). These initiate action potentials.

When there no arrival of an impulse/action potential, the neuron is at it's resting potential . They have a high amount of potassium ions in the axon and a high amount of sodium ions outside ( potential difference ). However, the amount of sodium ions outside are much greater than the potassium ions inside - thus results in an electrochemical gradient. This is maintained by sodium-potassium pumps.

www.s-cool.co.uk (the first part of the axon is at it's resting potential)

  • Depolarization: when an electric current stimulates the axon, voltage-gated channels open in the membrane to allow sodium ions to pass through. It diffuses down the electrochemical gradient. This causes the potential different to become less negative inside the axon (as there is an inflow of sodium ions!). Resulting in depolarization. (the second part in the diagram!)

( I'll include explanations of the other steps as well, just incase.. )

  • Repolarization: due to depolarization, the axon becomes positive (because of the inflow of postassium ions). Thus, voltage-gated channels for sodium close and potassium ion channels open, so that potassium diffuses out. This is to restore the initial potential difference.

  • Hyperpolarization: during repolarization, potassium ions tend to diffuse out toooo much. Causing, hyperpolarization briefly.

  • Finally, the refractory period: at this stage, the axon is not responsive. It is recovering from the action potential to restore its resting potential. (aka back to the resting potential where the axon has a high amount of potassium and outside, there's a high amount of sodium!)

Check out this youtube video for more about action potentials!:

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