Cognitive Aspects

A neuron is a specific type of cell. A neuron is made up of dendrites which are like little tree branches reaching outward from the cell body. The nucleus of the cell is at the center of the cell body. Neurons have a type of tail that is called the axon. At the other end of the axon are axon terminals or axon endings. The space just outside of the axon terminals is known as the synapse. Neurons can link themselves to other neurons to create a chain of neurons. Messages are able to traverse chains of neurons and this is how signals are sent in the brain. Messages are sent by either chemical or electrical means. If the message is chemical based, then this means that at the axon terminal, a specific type of neurotransmitter (chemical) is released into the synapse to either connect to or block the connection of the next neuron in the chain. If the message is electrical based then there is a channel through which ions can directly pass from one neuron to the next neuron in the chain.

The Neuron

Action Potential:

1. Begins by an outside stimulus causing a potential electrical difference across the cell membrane. The cell switches from negative (within the cell membrane) to positive (within the cell membrane) back to negative again.

2. This causes a cascading effect where the positive ions within the cell are pushed down the axon of the neuron.

3. Once when the positive ions reach the axon terminals, either a neurotransmitter is released into the synapse or the ions jump directly to the next neuron.

4. This ion jump or release of neurotransmitters acts as the stimulus for the next neuron and thereby leads to a message being sent down a link of neurons.

Resting Potential:

Resting potential increases the polarization of a cell membrane to allow for an action potential to occur. Resting potential functions on the basis of concentration gradients. The concentration of sodium, potassium, chloride, and organic ions differs across the cell membrane. The sodium potassium pump takes the positively charged potassium ions out of the cell while it brings the negatively charged sodium ions into the cell, creating a electrical polarization across the cell membrane.

Maintenance of Resting Potential:

1. Active pump takes potassium into cell and sodium out of cell

2. Maintains concentration gradients

3. Passive leak currents:

   A) Potassium passes down concentration gradient out of cell.

   B) Sodium passes down concentration, electrical gradient into cell.

   C) Potassium moves more than sodium.

   D) Makes inside of cell more negative and outside more positive.

   E) Increases polarization of membrane.

Importance of Leak Currents:

1. Need polarized membrane to send neural message (action potential).

2. Membrane too polarized cannot send message.

3. Membrane less polarized more likely to send message.

Cognition and Drugs

Below are the two different types of neuron receptors and the different types of neurotransmitters associated with either type of receptor.

Ionotropic Receptors:

Ionotropic receptors are ligand-gated, as opposed to voltage-gated channels in action potential. These receptors permit the flow of ions and neurotransmitters determine whether the channel is opened or closed. If sodium channels are open, then that means the the neurotransmitter is excitatory. If the potassium channels are open, then this means the neurotransmitter is inhibitory. This type of receptor are fast and short acting.

Ionotropic Neurotransmitters:

Some example ionotropic neurotransmitters are glutamate (the primary excitatory signaling), GABA (the primary inhibitory signaling), acetylcholine (which nicotine mimics), 5HT3 (subtype of serotonin), glycine, and ATP (adenosine triphosphate).

Metabotropic Receptors:

Metabotropic receptors are a class of G-protein-coupled receptors and functions as a molecular switch in the cell. Metabotropic receptors can have an effect on ion channels and second messengers (can alter DNA expression, having effects on cell functioning). These type of receptors are slow and long acting.

Metabotropic Neurotransmitters:

Example metabotropic neurotransmitters are monoamines which are neurotransmitters such as norepinephrine, dopamine, most forms of serotonin, and histamine. Acetylcholine, opioid, cannabinoid, and adenosine are also example metabotropic neurotransmitters.

Drugs act at the synapse, aiding or impeding normal synaptic transmission

Note: Some drugs may also act within the interior of the cell. Such as, anesthetics may disrupt function of microtubules.

Below are substances and groups of substances that have an effect on the brain. Things listed with these substances or groups of substances are things such as which neurotransmitter the substance(s) inhibit or mimic, what type of neurotransmitter receptor the substance binds to, what one experiences while using the substance(s), and what the substance(s) may be classified as.

Alcohol, benzodiazepine, anxiolytics, hypnotics, and barbiturates:

1. Agonist for GABA

2. Bind to ionotropic GABA receptor

Alcohol, benzodiazepines, barbiturates:

1. Enhance inhibitory effects of GABA when it binds

Nicotine:

1. Agonist for acetylcholine

2. Bind to ionotropic nicotinic receptors

3. stimulant/anxiolytic

Cocaine and amphetamines:

1. Agonists of metabotropic dopamine and norepinephrine

2. Block reuptake of a neurotransmitter (cocaine)

3. Cause leakage of neurotransmitter from uptake site (amphetamines)

4. Stimulant

Caffeine:

1. Antagonist of adenosine, an inhibitory neurotransmitter

2. Blocks metabotropic adenosine receptor

3. Stimulant

Theobromine:

1. Works in similar way to caffeine

2. Found in chocolate

Opiates:

1. Agonists of endogenous opiates

2. Bind to their metabotropic receptors

3. Analgesics (relieves pain)

Atropine:

1. Antagonist for acetylcholine

2. Block metabotropic muscarinic receptors

3. Found in belladonna (deadly nightshade)

4. Impedes parasympathetic system

5. Dilates pupils

6. Deliriant

Ketamine:

1. Antagonist for glutamate

2. Binds to ionotropic NMDA receptor

3. Dissociative anesthetic; fosters loss of bodily awareness

Psychedelics:

1. Sensory alterations such as warping of surfaces, shape suggestibility, and color variations

2. Intense colors not previously experienced

3. Repetitive geometric shapes

4. Synesthesia (one sensation causes another sensation such as hearing a sound causes a visual sensation)

5. Experience of additional spatial or temporal dimension

Cannabis:

1. Agonist of endocannabinoids

2. Bind to their metabotropic receptors

3. Mind altering

4. Endocannabinoids generated by postsynaptic dendrites

5. Presynaptic receptor, most abundant metabotropic receptor

6. Adjusts synaptic strength

7. Impedes learning and memory

MDMA:

1. Primarily agonist for serotonin

2. Causes leakage of serotonin from uptake site

3. Alters and intensifies thoughts and feelings

4. Enhanced feelings of connection

5. Euphoria

6. Related to methamphetamine

Awareness

Awareness is mediated by thalamocortical connections:

1. Sensory input to thalamus

2. Thalamus passes sensory information to cortex

3. Re-entrant feedback messages from cortex to thalamus

4. Attentional regulation messages from cortex to thalamus

5. Neuromodulators from brain stem support thalamus and cortex

If this process gets interrupted than an individuals awareness is then affected. For example, substances such as anesthetics are thought to disrupt step 3 and thereby inhibit one’s awareness. If someone ingests a substance such as anesthetics or some other drug and it affects their awareness, then this process has more than likely been disrupted somehow.

The Brain and Emotions

There are basic emotions that have certain areas in the brain that support them. Some of these brain areas may overlap for several different emotions, but different combinations of these brain areas mostly results in a distinct basic emotion. The following are the basic emotions with their brain areas listed:

Fear:

1. Amygdala

2. Hypothalamus

3. Periaqueductal gray (PAG)

Rage:

1. Amygdala

2. Hypothalamus

3. Bed nucleus of stria terminalis (BNST)

4. Periaqueductal gray (PAG)

Lust:

1. Amygdala

2. Hypothalamus

3. Bed nucleus of stria terminalis (BNST)

4. Periaqueductal gray (PAG)

**Note the similarity between the emotions rage and lust. Suggests there is a connection between the two emotions which is evidenced by the behavior of the two emotions.

Panic:

1. Anterior cingulate

2. Hypothalamus

3. Bed nucleus of stria terminalis (BNST)

4. Thalamus

5. Periaqueductal gray (PAG)

Disgust:

1. Insula

Seeking:

1. Nucleus accumbens (NA)

2. Ventral tegmental area (VTA)

3. Hypothalamus

4. Periaqueductal gray (PAG)

Care:

1. Anterior cingulate

2. Hypothalamus

3. Bed nucleus of stria terminalis (BNST)

4. Ventral tegmental area (VTA)

5. Periaqueductal gray (PAG)

Play:

1. Dorsomedial thalamus

2. Parafascicular area (thalamus)

3. Periaqueductal gray (PAG)

Happiness:

1. Premotor cortex

Sadness:

1. Basal ganglia

**Note: Both happiness and sadness are associated with predominantly motor areas of the brain which suggest movement plays a role in happiness and sadness levels.

Further reading can be found from the Queensland Brain Institute