Synapse Formation and Structure

describe a chemical synapse

a chemical synapse is where the ap occurs which causes the calcium to flow into the presynaptic neuron and then synthesizes NT which then forms synaptic vesicles, and then the NT flow in the synaptic cleft which is about 20-40 nm long, and then binds to ionotropic receptors and metabotropic receptors, this all takes 1-2 ms, and then causes a change in both membrane potential and gene expression and causes biocehmical cascades in the post synaptic neuron

electrical synapse

it is where the ap in the form of an electrical signal flows through the gap junction (low resis bridges), and has the ability to go in both directions

what are the 3 types of synapses a neuron can make

axon with bloodstream, axon with axon, axon with dendrite, axon with extracellular, axon with soma

what is myasthenia gravis

Myasthenia Gravis - autoimmune disease which causes affects the NMJ, causing muscle weakness, some symptoms = weakness of eyes, blurred vision, impaired speech, some treatments include anticholinestrase drugs, immunosuppresants etc.

describe epilepsy

imbalance between exictatory and inhibitory signals in brain results in hyperexcitation and seizures, to treat = antiepileptic drugs

tripartite synapse

Presynapse, postsynapse and the astrocyte, which has k channels, and buffering for k, and glutamate transporters, and the gliotransmitter release, and the metabotropic glutamate receptors

how does axon decide if it is an axon not dendrite

neurons are polarized with dendrite and axon side, axons express Tau and dendrites express MAP2, actin filaments allow for cytoskeletal components, while dendrites do not

semaphorins - dendrite formation, axon guidance cues - axon formation

formation of synapse

first axons find a target, then they make the necessary synaptic components, both presynaptic and postsynaptic, and then they will rearrange based on need and activity

immunoglobulin superfam

calcium independent proteins = adhere to each other, involve with cell adhesion molecules = short range axon guidance

cadherins

calcium dpendent proteins that adhere to each other, cams involved in short range

integrins

mediate interactions between neurons and extracellular matrix, cam involved in short range

receptor tyrosine kinases

located on axons and bind to growth factors, long range axon guidance

netrins

secreted, diffusable proteins that bind to receptors on axons, long range axon guidance

semaphorins

secreted or cell surface bound proteins, long - range axon guidance

what is the first axon to extend to its target

pioneer axon

what is pioneer axon useful for

additional axons can migrate along pioneer axon through fasciculation

chemoaffinity hypothesis

topographic info eocnded by chemical gradients which are detected by complementary gradients of axon receptors

describe synaptogenesis in three steps

axons find target to connect with, axons develop both presynaptic components while target makes postsynaptic components, then synapses mature and constantly rearrange, (strengthen, weaken, eliminate) based on env stimuli and activity, cells meant to connect = cues like CAMS

what is the role of glial cells in synapse formation

Schwann cells in the PNS and Astrocytes in CNS envelope in the pre and post synapse appears to be involved with synapse formation, additionally cultured neurons tend to form less synapse

synaptic pruning how does it work

multiple axons = meet at one site to ensure a connection is made, only strong connections remain, therefore target cell = neurotrophic factors = support for neurons (essential)

neurotrophic factor hypothesis - neurons recieving neurotrophic factor from target survive, and other degenerate by programmed cell death = apoptosis