Synaptic Transmission (E1)

Synaptic Transmission

the transfer of information from one synapse to another

Neurotransmitters

chemicals that act at the postsynaptic terminal

Electrical Synapse (Gap Junction)

Allow direct transfer of ionic current from one cell to the next via gap junctions

Heart (Cardiac Muscle):

Currents pass through cardiac myocytes to maintain synchrony

Brainstem (Respiratory Neurons)

maintain steady breathing

Retina

fast visual processing

Chemical Synapse

Use chemicals to bridge the space—chemical neurotransmission

Synaptic vesicles

small membrane-closed spheres that store neurotransmitters

Active zone

presynaptic membrane, site of neurotransmitter release

Presynaptic

Axon terminal of Neuron 1

Postsynaptic

Dendrite of Neuron 2

Types of Chemical Synapses (CNS)

axodendritic, axosomatic, axoaxonic

Gray’s type 1 synapses

Asymmetrical membrane differentiation (excitatory)

Gray’s type 2 synapses

symmetrical membrane differentiations (inhibitory)

Neuromuscular Junction

Chemical synapse between a spinal motor neuron and a skeletal muscle fiber

Motor end-plate

postsynaptic membrane

Types of Neurotransmitters

Amino acids

Amines

Peptides

vesicle

membrane-bound space which may appear empty (light)

granule

membrane-bound but its content is electron-dense (darker)

Glutamate and Glycine

amino acids

GABA and Amines

made primarily by neurons that release them

Substance P

a peptide composed of a chain of 11 amino acid residues

Transporters

specialized proteins embedded in the vesicle membrane that allow

uptake of neurotransmitters

Neurotransmitter release is triggered by

action potential

Depolarization of terminal membrane

voltage-gated Ca2+ channels open

Exocytosis

release of neurotransmitter from an intracellular

vesicle into the extracellular space by fusion of the vesicles

membrane by the cells membrane

Endocytosis

process where a bit of the cell membrane is pinched off, internalized, and converted to an intracellular vesicle

Arrival of an action potential

voltage-gated calcium channels open, calcium floods pre-synapse

triggers exocytosis and release of neurotransmitter

Calcium

are recycled by endocytosis

Vescicles

Ligand-gated channel

opens when a ligand binds to a receptor

Voltage-gated channel

opens when the electrical potential across the membrane is altered

7 transmembrane domains

GPCRs weave through the cell membrane seven times

Activate G proteins

ligand binding causes the receptor to activate G protein

Amplify signals

one activated receptor can activate many G proteins, which can activate many downstream molecules

Modulation

neurotransmitters bind to a G-protein coupled receptor, they can have an overall excitatory or inhibitory effect depending on the molecules that are activated downstream

Depolarize

Membrane potential moves closer to

zero (less negative)

Polarized

Resting membrane potential

Hyperpolarize

Membrane potential moves away from zero (more negative