2.2 Synaptic Transmission

Question 1

chemical transmission

Answer 1

1. Action potential depolarizes the terminal membrane, which causes Ca2+ (Calcium) to flow into the cell.
2. Ca2+ causes vesicles to bind with a cell membrane. These vesicles contains a neurotransmitter.
3. Neurotransmitter is released by exocytosis into the synaptic cleft.
4. Transmitter binds with receptor

Question 2

ligand-gated ion channels

Answer 2

These receptors are directly activated by the binding of a specific ligand (chemical messenger) to the receptor. The binding causes a conformational change in the receptor, leading to the opening of an ion channel and the subsequent flow of ions across the cell membrane.
Activation of ligand-gated ion channels results in a rapid and direct response, as the ions flow through the channel and quickly change the membrane potential of the cell.
These receptors primarily mediate fast synaptic transmission between neurons or muscle contraction. The opening or closing of ion channels changes the membrane potential and can lead to depolarization (excitation) or hyperpolarization (inhibition) of the cell.
These receptors are relatively less diverse in terms of the types of ligands they can bind to. They are often specific to neurotransmitters or ions.

Question 3

G protein-coupled receptors (GPCRs)

Answer 3

These receptors are indirectly activated by the binding of a ligand, which triggers the activation of a G protein associated with the receptor. The activated G protein then initiates a signaling cascade within the cell, leading to various cellular responses.
Activation of GPCRs initiates a relatively slower and more complex signaling cascade involving multiple steps, which can take longer to elicit a cellular response.
GPCRs regulate a wide range of cellular processes, including neurotransmitter release, hormone secretion, cell proliferation, sensory perception, and immune responses. The downstream signaling pathways activated by GPCRs can involve second messengers, such as cyclic AMP (cAMP), calcium ions, or phospholipase C (PLC).
GPCRs exhibit high diversity in ligand specificity and can respond to a wide variety of ligands, including hormones, neurotransmitters, and sensory stimuli.

Question 4

Neurotransmitter

Answer 4

• Synthesized by and localized within the presynaptic neuron, and stored in the presynaptic terminal before release
• It is released by the presynaptic neuron when action potentials depolarize the terminal (mediated primarily by Ca2+)
• The postsynaptic neuron contains receptors specific for it.
• When artificially applied to a postsynaptic cell, it elicits the same response that stimulating the presynaptic neuron would

Question 5

neurotransmitters that usually have an excitatory effect

Answer 5

ACh, catecholamines, glutamate, histamine, serotonin, and some other neuropeptides

Question 6

neurotransmitters that usually have inhibitory effect

Answer 6

GABA, glycine and some of the neuropeptides

Question 7

Glutamate

Answer 7

is released by the pyramidal cells of the cortex, therefor it is the most prevalent neurotransmitter and is found in most of the fast excitatory synapses in the brain and spinal cord.

Question 8

GABA

Answer 8

is synthesized from glutamate. It is found in most of the fast inhibitory synapses across the brain.

Question 9

Acetylcholine (ACh)

Answer 9

is present in the synapses between neurons and between neurons and muscles, where it has an excitatory effect and activates muscles.

Question 10

Dopamine

Answer 10

The primary sites of dopamine production are the adrenal glands and a few small areas of the brain. This include the striatum, substantia nigra and hypothalamus. There are several dopaminergic pathways, each sprouting from one of the small brain areas and is involved in several functions including cognitive and motor control, motivation, arousal, reinforcement, reward etc.

Question 11

Serotonin

Answer 11

Is released largely by the neurons of the raphe nuclei, in the brainstem. The serotonergic pathways are involved in the regulation of mood, temperature, appetite, behavior, muscle contraction, sleep and the cardiovascular and endocrine systems.

Question 12

Norepinephrine (NE) / Noradrenaline

Answer 12

is the sympathic nervous system’s go-to neurotransmitter. It is produced by neurons with cell bodies in the locus coerculeus - area in the brain involved in physiological reactions to stress and located in the brainstem, more precisely the pons. Outside the brain NE is released by the adrenal glands. There are two types of receptors for NE: alpha-1 and alpha-2, and beta. The alpha-2 receptors tend to have excitatory effects, the alpha-1 and beta receptors tend to have inhibitory effects.

Question 13

Neurosteroids

Answer 13

steroids synthesized within the brain and modulate neuronal excitability by rapid non-genomic actions.

Question 14

Inactivation of neurotransmitters after release

Answer 14

This removal can be accomplished by active reuptake of the substance back into the presynaptic terminal, by enzymatic breakdown of the transmitter in the synaptic cleft, or merely by diffusion of the neurotransmitter away from the region of the synapse or site of action.

Question 15

Electrical Neurotransmission

Answer 15

There is no synaptic cleft that separates the neurons. The neuronal membranes touch at specializations called gap junctions, and the cytoplasms of the two neurons are essentially continuous. As a result, the two neurons are isopotential, meaning that electrical changes in one are reflected instantaneously in the other.