PSYC-2900 Chapter 2.3

synaptic transmission

communication between neurons using a chemical signal carried by neurotransmitters released from the terminal buttons of the presynaptic neuron. neurotransmitters move by diffusion across the synapse, and attach to a binding site/receptor on the postsynaptic neuron

ligand

anything that attached to the binding site/receptor on the postsynaptic neuron

excitatory postsynaptic potential (EPSP)

a change in a neuron's membrane voltage that increases the likelihood of an action potential. occurs when a neurotransmitter binds to a receptor on the postsynaptic membrane, causing positively charged ions to flow into the cell (depolarization)

inhibitory postsynaptic potential (IPSP)

a synaptic response that decreases the likelihood of a neuron firing caused by hyperpolarization of the postsynaptic membrane by allowing negatively charged ions to enter. this causes the membrane potential to become more negative and inhibits the neuron and its’ signal transmission

synaptic vesicles

small organelles made of membrane that store and release neurotransmitters in neurons

small vesicles

a type of synaptic vesicle found in all terminal buttons and contain neurotransmitters. they are produced in the soma and carried by the axoplasmic transport to the terminal buttons

exocytosis

the process by which neurotransmitters are released:

1. synaptic vesicles dock at proteins in the release zone

2. action potential opens calcium channels, allowing calcium ions to enter and bind with protein embedded in membrane of docked vesicles

3. fusion pores open, and the neurotransmitter is released into the synaptic cleft

release-ready vesicles

synaptic vesicles that are few in number, and are docked and ready for release (less than a second)

recycling pool

where some vesicles are found, they are merged and recycle to be released again (a few seconds)

reserve pool

where most vesicles are found, produced through bulk endocytosis, a process that moves large amounts of membrane into a cell, forming a vacuole and releasing synaptic vesicles ( a few minutes)

ionotropic receptors

direct receptor proteins that bind neurotransmitters and open ion channels, allowing ions to pass through the cell membrane

metabotropic receptors

indirect receptor proteins located close to a g protein that causes a chain of chemical events to indirect open an ion channel. the changes made take longer to begin, but last longer

postsynaptic potentials

a change in the membrane potential of the postsynaptic neuron determined by characteristics of postsynaptic receptors

(i.e. the type of ion channel they open)

2 types exist: excitatory postsynaptic potential (EPSP), and inhibitory postsynaptic potential (IPSP)

rate of neuron firing

determines the number of vesicle pools that open, and controlled by excitatory and inhibitory input to its dendrites and soma.

• ↑ excitatory synapse activity = ↑ rate of firing

• ↑ inhibitory synapse activity = ↓ rate of firing

reuptake

a mechanism of ending postsynaptic potentials by the rapid removal of neurotransmitters from the synaptic cleft by the terminal button

enzymatic deactivation

a mechanism of ending postsynaptic potentials by enzymes breaking down the neurotransmitter into inactive components

(e.g. acetylcholinesterase (AChE) deactivates acetylcholine (ACh))

autoreceptors

inhibitory receptors on nerve cells (located on the membrane of any cell part) that respond to the neurotransmitters released by the same cell. they are part of a negative feedback loop in order to regulate internal processes of the cell (e.g. synthesis, release of neurotransmitters)

axoaxonic synapses

synapses found on the axon that alter the amount of neurotransmitters released by the terminal buttons, and can produce presynaptic modulation (i.e. presynaptic inhibition or presynaptic facilitation)

presynaptic facilitation

a mechanism that can be produced by axoaxonic synapses that increases the release of neurotransmitters from axons

dendrodendritic synapses

connections between the dendrites of two different neurons that can be either chemical or electrical

presynaptic inhibition

a mechanism that can be produced by axoaxonic synapses that reduces the likelihood of a neuron firing an action potential

chemical dendrodendritic synapses

connections between two neurons' dendrites that use chemical neurotransmitters to pass signals by an incoming action potential allowing the release of neurotransmitters to send the signal to the post synaptic cell

electrical dendrodendritic synapses

connections joined by a gap junction that allow electrical signals to pass between dendrites. the membranes of the connecting cells meet and almost touch, and contain channels that permit ions to diffuse

(common in invertebrates)

neuromodulators

a type of non-synaptic communication that are chemicals (mostly peptides) released by neurons that travel farther and are dispersed more widely than neurotransmitters

hormones

a type of non-synaptic communication that are secreted by endocrine glands or cells in various organs, and are distributed through the bloodstream to reach target cells that contain particular receptors

steroid hormones

a type of non-synaptic communication that are secreted by endocrine glands or cells in various organs, and are distributed through the bloodstream to reach target cells that contain particular receptors