Synapses and Neurotransmitter

Where do nerve impulses start and end

Presynaptic cleft; Postsynaptic cleft

What are the two types of synaptic transmission and which is most common

Electrical and chemical; chemical most common

Describe electrical transmission

Ionic current flow directly between pre and post synaptic

Describe chemical transmission

Neurotransmitters are released from axon terminals and rapidly diffuse across the synaptic cleft binding receptions on postsynaptic cleft to elicit a response

What must take place in the presynaptic cell for neurotransmitter release

Depolarization

How do Post synaptic potentials differ

Chemical can be excitatory or inhibitory while electrical are excitatory

How does directionality of synapses differ

Chemical is unidirectional an electrical is bidirectional

What is the neurotransmitter in the neuromuscular junction

Acetylcholine

What mediates signal reception in the neuromuscular junction

Nicotinic acetylcholine receptor

Where is ACh synthesized

Axon terminal

What enzyme catalyzes the production of ACh

Choline acetyltransferase CHaT

Where is ACh stored

Synaptic vesicles in axon terminals

Why are neurotransmitters like ACh stored in synaptic vesicles

Prevents degradation and helps regulate release

What stimulates the release of ACh

Ca2+ influx via voltage gated sodium channels

What stimulates the opening of calcium channels

Propagation of AP from the axon to the axon terminals

Why does calcium move into the cell

Wants to move down it’s concentration gradient and electrical gradient

What proteins mediate synaptic vesicle docking at the presynaptic membrane and where are they located

Synaptobrevin: vesicle membrane

SNAP 25 and syntaxin: on the inner surface of the plasma membrane

How does Calcium stimulate the release of neurotransmitters (process)

Calcium influx via voltage gated calcium channels, calcium binds synaptotagmin, stimulates fusion, vesicle releases neurotransmitters into cleft

Describe junctional folds

Invaginations in the post synaptic membrane that increase surface area for acetylcholine receptors

Which receptor receives the signal on the myocyte

Nicotinic acetylcholine receptors

What does AChRs bind and what kind of receptor is it

Binds both acetylcholine and nicotine; ionotropic receptor

How is ACh inactivated

Acetylcholinesterase binds ACh in the synaptic cleft inactivating it

What happens to acetic acid and choline after inactivation of ACh

Choline is transported from the synaptic cleft into the axon terminal and acetic acid diffuses away

What is the postsynaptic muscle cell response to ACh binding

Ligand gated channels open, sodium diffuses into cell, membrane depolarizes, graded potentials start, voltage gated sodium channels open at TP, AP is generated

What does botulinum toxin prevent

Presunaptic release of ACh which leads to skeletal muscle paralysis

What do Nicotinic ACh receptor inhibitors do

Bind but done activate Nicotinic ACh receptors; induces muscle relaxation

How is an action potential generated at a neron-neruon synapsse

Requires summation of PSPs

What is the effect of increase AP frequency

Increase neurotransmitter release and increased types of neurotransmitters

What happens with excessive or prolonged ligand present

Desensitization(binding affinity) or downregulation( decrease in number of receptors)

What are the two types of receptors

Ionotropic and metabotripic

Describe ionotropic receptors

Function by directly opening ion channels

Describe metabotriopic receptors

Function by causing a change in a serious of metabolic chains

What does NMDA bind and cause

Glutamate; transpires sodium an calcium in and potassium out, resulting in depolarization and EPSP

What do GABA-A receptors bind and transport and their effect on cell

GABA, Cl-, and stimulate hyperpolarization

What G protein and secondary messengers are utilized by Muscarinic acetylcholine receptors

Gq proteins, DAG and IP3 are produced form PIP2 and activate PKC, resulting in membrane hyperpolarization via potassium efflux

What kind of G proteins and secondary messengers are utilized by Beta adrenergic receptors

Gs proteins activates adenylate cyclase, cAMP produced from ATP activates PKA and calcium channels will open, calcium influx, membrane demoralizes