Chapter 4.2: Neural Conduction and Synaptic Transmission

Axodendritic synapses

synapses of axon terminal buttons on dendrites.

Axosomatic synapses

synapses of axon terminal buttons on somas.

Axoaxonic synapses

mediate presynaptic facilitation and inhibition.

Directed synapses

synapses at which the site of neurotransmitter release and the site of neurotransmitter reception are in close distant.

Nondirected synapses

are synapses at which the site of release is at some distance from the site of reception.

Small molecule

• neurotransmitters are typically synthesized in the terminal button and packaged in synaptic vesicles by the button’s Golgi complex.

• Once filled with neurotransmitter, the vesicles are stored in clusters next to the presynaptic membrane.

Neuropeptides

• are assembled in the cytoplasm of the cell body.

• They are then packaged in vesicles by the cell body’s Golgi complex and transported by microtubules to the terminal buttons.

Coexistence

Many neurons contain two neurotransmitters—a situation generally referred to as

Exocytosis

the process of neurotransmitter release.

Receptors

Once released, neurotransmitter produce signals in postsynaptic neurons by binding to ___ in the postsynaptic membrane.

Receptor subtypes

• There is only one type of receptor for each neurotransmitter but this has not proved to be the case.

• Most neurotransmitters bind to several different types of receptors.

• The different types of receptors to which a particular neurotransmitter can bind are called the

Ionotropic receptors

• are associated with ion channels.

• When a neurotransmitter molecule binds to an ___, the associated ion channel usually opens or closes immediately, influence immediate postsynaptic potential.

Metabotropic receptors

• are associated with signal proteins and G proteins (guanosinetriphosphate − sensitive proteins).

• are slower to develop, longer-lasting, more diffuse, and more varied.

• is attached to a portion of the signal protein outside the neuron.

G protein

• is attached to a portion of the signal protein inside the neuron where it’s associated.

Auto-receptors

• metabotropic receptors that have two characteristics:

• They bind to their neuron’s own neurotransmitter molecules.

• They are located on the presynaptic, rather than the postsynaptic, membrane

• To monitor the number of neurotransmitter molecules in the synapse.

Reuptake

Neurotransmitters, once released, are almost immediately drawn back into the presynaptic buttons by transporter mechanisms.

Enzymatic Degradation

Other neurotransmitters are degraded (broken apart) in the synapse by the action of enzymes.

Example: Acetylcholinesterase - Acetylcholine

Triparte synapse

Synaptic transmission depends on communication among three cells (presynaptic neuron, postsynaptic neuron, and astrocyte). This is referred to as the

Amino acids, monoamines, Acetylcholine

Conventional Neurotransmitters examples

Amino Acids neurotransmitters

• Molecular building blocks of proteins.

• Fast-acting, directed synapses in the central nervous system.

glutamate, aspartate, glycine, and gamma-aminobutyric acid

The four most widely studied amino acid neurotransmitters

Excitatory Neurotransmitters

They increase the likelihood that the neuron will fire an action potential.

Inhibitory Neurotransmitters

They decrease the likelihood that the neuron will fire an action potential.

Aspartate

An amino acid that plays a role in spatial memory.

Glycine

Smallest of the amino acids. Is role is to process sensory and motor function.

High glycine

Observed to those without motivation. Waking up in the morning and tired and no energy in the afternoon.

Low Glycine

Anxious and has difficulty to sleep.

Glutamate

is the most prevalent excitatory neurotransmitter in the mammalian central nervous system.

GABA

• is the most prevalent inhibitory neurotransmitter.

• When you are relaxed or in control, it is high

• contributes to vision, motor control, and plays a role in the regulation of anxiety.

• simple modification of glutamate

Glutamate

• Plays a primary role in cognitive functions such as memory and learning.

• Excessive amounts can cause cellular death and is associated with Alzheimer's disease, stroke and epileptic seizures.

High glutamate

OCD such as uncontrollable washing of hands and ADHD.

Low glutamate

Schizophrenia and Autism and concentration problem.

Low GABA

Bipolar disorder and GAD

Benzodiazepines

which are used to help treat anxiety, function by increasing the efficiency of GABA neurotransmitters.

Monoamine

• From a single amino acid—hence

• are slightly larger than amino acid neurotransmitters, and their effects tend to be more diffuse.

• Present in small groups of neurons whose cell bodies are located in the brain stem.

Dopamine

• you are doing something pleasurable. It is involved in reward, motivation, and additions.

• “Pleasure neurotransmitter”

High dopamine

Schizophrenia, drug addiction, ADHD and impulsive behavior.

Low dopamine

Parkinson’s disease and depression.

Epinephrine

is released by the adrenal system – adrenalin. The role is increasing the heart rate, increasing blood pressure, expanding the air passages of the lungs, enlarging the pupil in the eye

Norepinephrine

role in physical arousal - alertness is involved in the body's fight or flight response and also in memory.

Serotonin

• “Mood neurotransmitter”

• Play a role in regulating and modulating mood, sleep, anxiety, sexuality, and appetite.

High serotonin

• Stress and ADHD.

Low serotonin

If you have difficulty going to sleep or have episodes of depression. If you also have suicidal thoughts and aggression.

Tryptophan

Serotonin is synthesized from the amino acid and is classified as an indolamine.

Noradrenergic

Neurons that release norepinephrine are called

Adrenergic

those that release epinephrine are called

Acetylcholine

• considered as the first discovered neurotransmitters associated with motor neurons.

• It plays a role in learning and memory and muscle contractions.

• Neurons that release it are said to be cholinergic.

High acetylcholine

Associated with depression.

Low acetylcholine

Associated with Alzheimer’s disease.

Unconventional Neurotransmitters

• They act in ways that are different from other neurotransmitters.

Nitric oxide and carbon monoxide

Class of unconventional neurotransmitters, the soluble-gas neurotransmitters, includes

Soluble-gas neurotransmitters

• are difficult to study because they exist for only a few seconds.

• At some synapses, they transmit signals from the postsynaptic neuron back to the presynaptic neuron.

Endocannabinoids

are neurotransmitters that are main psychoactive (producing psychological effects) constituent of marijuana.

Pituitary peptides

contains neuropeptides that were first identified as hormones released by the pituitary.

Hypothalamic peptides

contains neuropeptides that were first identified as hormones released by the hypothalamus

Brain-gut peptides

contains neuropeptides that were first discovered in the gut.

Opioid peptides

contains neuropeptides that are similar in structure to the active ingredients of opium.

Miscellaneous peptides

is a catch-all category that contains all of the neuropeptide transmitters that do not fit into one of the other four categories.

Agonist

Drugs that facilitate the effects of a particular neurotransmitter are said to be (increase the effect)

Antagonists

Drugs that inhibit the effects of a particular neurotransmitter are said to be its (block the effect)

Opium poppy

Opium, obtained from the seed pods of the ____, has been used by humans since prehistoric times for its pleasurable effects.

Morphine

its major psychoactive ingredient, is addictive. has its good side: it is an effective

analgesic (painkiller).

Dopamine agonists

• cocaine and amphetamines

• resembles schizophrenia. These findings - schizophrenia is caused by excessive activity of dopamine and that dopamine antagonists (blocking) would be effective in its treatment.

Presynaptic

refers to the neuron that sends a signal

Postsynaptic

refers to the neuron that receives the signal, at a synapse, the junction where these neurons communicate. 

Indolamine

an amino acid needed for normal growth in infants and production and maintenance of the body’s proteins muscles, enzymes, and neurotransmitter

Glutamate, Aspartate, Glycina, GABA

List the amino acids (GAGG)

Dopamine, Epinephrine, Norepinephrine

The monoamines under Catecholamines:

Serotonin

The monoamine under Indolamines

Nitric oxide and carbon monoxide

Unconventional neurotransmitters under soluble gases

Anandamide

Unconventional neurotransmitters under endocannaboids