Synaptic Transmission

Question 1

Define Gap Junctions

Answer 1

made up of connexons that allow passage of small water-soluble molecules and ions. (LOW SELECTIVITY)

• Bidirectional electrical synapse
• rapid transmission with little or no delay

Question 2

Define Neuromodulator

Answer 2

chemical messenger that can affect release of neurotransmitter or the receptor function of a neurotransmitter

Question 3

Describe the presynaptic events of NT release

Answer 3

1) AP depolarizes membrane of presympatic terminal
2) Voltage gated Calcium channels open and Calcium flows INTO cell leading to LOCALIZED increase in Ca Conc.
3) Increase Ca conc increases probability that synaptic vessels at active zone fuse with presynaptic membrane and release NT (exocytosis)
4) NT release via full fusion or kiss and run

Question 4

Describe the Postsynaptic events of NT release

Answer 4

1) binding of transmitters to postsynaptic receptors
2) activation of receptors elicit postsynaptic response (excitatory/inhibitory)
3) May induce AP

Question 5

Describe Recovery Phase of NT release

Answer 5

1) repolarization of the presynaptic terminal via Potassium EFFLUX
2) Voltage gated Calcium channels close
3) removal of Calcium from cytoplasm
4) synaptic vesicles membrane is removed from terminal membrane by Clathrin dependent-endocytosis and recycled into new synaptic vesicles

Question 6

Describe the mechanisms of removing calcium from cytoplasm

Answer 6

• Diffusion
• sequesterd by cytoplasmic calcium binding proteins
• pumped into smooth endoplasmic reticulum cisterns
• pumped out of the cell into the extracellular fluid by Na/Ca exchange transporters

Question 7

Define Ionotropic receptors

Answer 7

Ligand-gated ion channel receptor

• one macromolecule may bind transmitter and form channel
• bidning of NT DIRECTLY changes channel’s permeability to ions
• responsible for FAST chemical synaptic transmissino

Question 8

Define Metabotropic receptors

Answer 8

G-protein coupled receptors

• Slower acting on membrane potential
• Binding of NT causes a G-protein-mediated signaling event
• 2nd messenger

Question 9

Describe the major inhibitory NT

Answer 9

GABA causes influx of Chloride which hyperpolarizes the membrane

Question 10

Define Acetylcholine

Answer 10

Small molecule transmitter

- released in NMJ and acts on nicotinic acetylcholine receptors

Question 11

Define Catecholamines

Answer 11

Share a common biosynthetic pathway which starts with tyrosine.

• Dopamine = all metabotropic receptors
• Norepinephrine = bind to adrenergic/noradrenergic receptors
• Epinephrine = bind to adrenergic/noradrenergic Receptors

Question 12

Define Serotonin

Answer 12

• biogenic amine
• binds to several different types of 5-HT receptors
• SSRI are selective serotonin re-uptake inhibitors that are used to treat depression

Question 13

Define Histamine

Answer 13

• a diamine
• several different histamine receptors subtypes (all are metabotropic
• Antihistamines such as diphenhydramine which readily penetrate the Blood brain barrier are sedating

Question 14

Define GABA

Answer 14

amino acid transmitter
- major CNS inhibitory transmitter
Two types of receptors:
GABAa = directly gated channel for chloride (ionotropic
GABAb = metabotropic receptor which has an inhibitory effect by opening potassium channels or suppression of calcium channels

Question 15

Define Glycine

Answer 15

Binds to ionotopic receptor and opens the directly gated chloride channels (inhibitory)
- Tetanus toxin targets Glycine in inhibitory interneurons.