2.2 pt 1 - Neurotransmitters

What are the two basic categories of neurotransmitters?

Large and small

What is the Large category of neurotransmitters?

Neuropeptides and is synthesized in soma and transported by microtubules to pre-synaptic terminal

What is the Small category of neurotransmitters?

Amino acids, Monoamines, Acetylcholine and they’re synthesized in pre-synaptic terminal

What are the major classes of neurotransmitters?

Amino Acid, Monoamines, Acetylcholine, Neuropeptides, and Soluble Gases

True or False: Most neurons release more than one kind of neurotransmitter

True, they also typically receive more types of neurotransmitters than they can release

True or False: Neurotransmitters can have time-limited or extended effects

True

True or False: Neurotransmitters do not have spatially focused or systemic effects

False, they do

Why do different regions of the brain have different receptor subtypes for a particular neurotransmitter?

Because the action of neurotransmitters depends on their context

True or False: Depending on the region and the receptor subtype, the same neurotransmitter can serve very different functions

True

What does an ionotropic receptor function as?

As a ligand-gated ion channel

What can binding cause in an ionotropic receptor?

Is the response fast or slow in an ionotropic receptor

It is considered fast

Are the effects short or long-lasting in ionotropic receptors?

They are short-lasting

Binding in an ionotropic receptor can cause ____ or _____.

Depolarization (excitatory response) or Hyperpolarization (inhibitory response)

Which post-synaptic receptor causes G-protein to be released activating an effector enzyme or an ion channel?

Metabotropic Receptor

Is the response is a metabotropic receptor fast or slow?

It is considered slow

Are the effects in a metabotropic receptor short or long-lasting?

They’re long-lasting

A second messenger regarding a metabotropic receptor can cause _____ or ______

An EPSP (excitatory post-synaptic potential) or IPSP (inhibitory post-synaptic potential)

What breaks apart neurotransmitters in the synapse?

Enzyme

True or False: Neurotransmitters detach from receptors but remain active

True

What happens to neurotransmitters once they detach from a receptor?

Transporters being them back into pre-synaptic cell where they are re-used

What is negative feedback within a cell?

It tells the pre-synaptic cell to stop releasing neurotransmitters

What are some of the most common neurotransmitters in the brain?

Glutamate and GABA

True or False: Glutamate in the principle of inhibitory (hyperpolarizing) neurotransmitters

False, they’re exitatory (depolarizing) neurotransmitters

Is GABA the principle inhibitory (hyperpolarizing) or excitatory (depolarizing) neurotransmitter?

It is the principle inhibitory (hyperpolarizing) neurotransmitter

What can the imbalance of glutamate and GABA cause?

It can result in seizures (excitation wins out) or loss of consciousness (inhibition wins out)

Where does glutamate come from?

It comes from glutamic acid in our diet (essentially every protein)

What are some of the complicated processes that glutamate is involved with?

Leaning and memory

What receptors does glutamate act on?

1. AMPA (excitatory ionotropic receptor (Na^+))

2. Kainate (excitatory ionotropic receptor (Na^+))

3. NMDA (excitatory ionotropic receptor (Na^+, Ca²+)/both ligand-gated and voltage-gated)

4. Metabotropic (many subtypes)

True or False: Too much stimulation of glutamate receptors can be bad

True

What happens if there is too much glutamate receptor stimulation?

It can lead to cell death, meaning it must be tightly controlled

What happens once glutamate binds to a receptor?

Astrocytes surrounding the synapse cause it to inactivate

What is excitatory influence of glutamate balanced by?

Inhibitory influence of GABA

What does GABA stand for?

Gamma - AminoButyric Acid

What transforms glutamate into GABA?

An enzymatic reaction

Which two receptors does GABA act on?

1. GABA-A (isotropic (Cl^-)/Rapid inhibitory action)

2. GABA-B (metabotropic/second messenger ultimately affects ion channels, leading to inhibitory action)

What are monoamines?

Neurons that synthesize monoamines are relatively few in number, and reside in small nuclei in the brain stem

How many receptor subtypes does dopamine have?

5 receptors (D1-D5)

• all g-protein coupled (metabotropic)

• widely distributed in the brain

True or False: Variety in receptor subtypes allows dopamine to play a varied role in behavior and cognition

True

What are some of the roles does dopamine play in behavior and cognition?

• Movement

• Reinforcement/Reward

• Working memory, planning, attention, cognitive control

What happens when there is a death of dopaminergic neurons?

Individuals often form Parkinson’s Disease

What are the primary symptoms of Parkinson’s Disease?

• Tremors and trembling

• Rigidity in the limbs and trunk

• Slowness of movement

• Impaired balance

True or False: Dopamine plays a large role in rewarding aspects of drugs

True

What are some naturally occurring genetic variations in the D4 receptor in dopamine leading to interesting phenotypes related to reward?

• novelty seeking

• sensation seeking

• extroversion

• substance abuse

• ADHD

Why is the pre-frontal cortex so important regarding receiving dopamine?

It is the area of the brain that’s important in working memory, planning, and organization

True or False: Dopaminergic neurons project (among other places) to the pre-frontal cortex

True

What happens if the pre-frontal cortex is damaged?

It can lead to impaired working memory and distractibility

What is working memory?

A cognitive brain system that temporarily holds and actively manipulates information needed for complex tasks like reasoning, learning, and comprehension

What is norepinephrine linked to?

• arousal and vigilance

• emotional enhancement of memory

Where does norepinephrine come from?

It is synthesized from dopamine in the brainstem (locus coeruleus)

What is another name for norepinephrine?

Noradrenaline

True or False: Norepinephrine sends widespread projections to brain and spinal cord

True

Where does epinephrine come from?

It is synthesized from norepinephrine

What does epinephrine play a crucial role in?

Fight-or-Flight response

What is epinephrine also known as?

Adrenaline

What is epinephrine used for medically?

Epi-pen —> epinephrine narrows blood vessels, limiting the effect of the allergen

Where does serotonin come from?

It is synthesized from tryptophan by neurons in the brain stem (raphe nuclei)

What does serotonin control?

• Feeding/satiety

• sleep-wake cycle

• mood

What is the Monoamine hypothesis of depression?

Deficiency of monoamines are responsible for symptoms of depression

What could low levels of serotonin in depression cause?

It could cause these neurotransmitter systems to behave unusually

True or False: Serotonin is thought to regulate the activitiy of other monoamines

True

True or False: Drugs which alter serotonin levels are often used to treat depression

True

Where does acetylcholine come from?

Synthesized from acetate and choline by neurons in the brain stem (modified amino acid)

What happens to acetylcholine after binding?

It is broken down and recycled

Where is choline found?

In milk, eggs, and peanuts

How does acetylcholine affect the central nervous system?

It is involved in aspects of cognition like learning and memory

How does acetylcholine affect the peripheral nervous system?

It is involved in communication between motor neurons and muscles

Where do motor neurons in the spinal cord send their axons?

To the muscles

What is it called when there are synapses between motor neuron axons and muscles fibers?

Neuromuscular junctions

What happens when motor neuron fires an action potential?

Acetylcholine is released into the synapse

What leads to the contraction of the muscle?

Acetylcholine binds to nicotinic receptors

What is myasthenia gravis?

Autoimmune disorder that attacks nicotinic receptors

What can myasthenia gravis cause?

The muscles become progressively weaker, trouble speaking, swallowing, vision problems

What are neuropeptides commonly considered?

Neuromodulators

Where are neuropeptides synthesized?

In the soma rather than the pre-synaptic terminals

How are neuropeptides released?

They’re released mainly by dendrites rather than pre-synaptic terminals —> release requires repeated stimulation rather than a single action potential

What are some of the effects neuropeptides produce once released?

• Diffuse widely and prime other neurons to release neuropeptides as well

• Many exert their effects by altering gene activity, so effects are long-lasting

• involved in hunger, thirst, pain, and longer-term sensations

What are some types of neuropeptides?

• Endorphins (endogenous opioids produced during exercise, excitement, pain, etc/ produce analgesia [relief from pain], sedation, euphoria/ drugs like heroin [an opiate] minic endogenous opioids)

• Substance P (important in transmission of pain information)

What is nitric oxide?

A soluble gas synthesized and released by neurons as needed (diffuses passively through the membrane)

What does nitric oxide do?

Relaxes and widens blood vessels, increasing blood flow to active neurons

How does nitric oxide help regarding MRIs?

The increased blood flow during neural activity enables imaging techniques like functional MRI