Synapses and Neuromuscular Control

Flashcards on Synapses, Neuromuscular Control, and Nervous System Disorders

Electrical Synapses

Electric current passes directly from pre- to postsynaptic cell through gap junctions.

Chemical Synapses

Electrical signal is converted into a chemical signal that is released from the presynaptic cell and acts on receptors on the postsynaptic cell.

Gap Junctions

Intercellular channel formed by the docking of two hemichannels composed of connexin or innexin proteins.

Classical Neurotransmitter Example

Acetylcholine

Biogenic Amines

Noradrenaline, dopamine, serotonin, histamine

Amino Acid Neurotransmitters

Glutamate, GABA, glycine

Peptide Neurotransmitters

Substance P, Opioids (endorphins, enkephalins)

Unconventional Neurotransmitters

Nitric oxide (NO), adenosine triphosphate (ATP), cannabinoids

Excitatory Neurotransmitter

Excites the postsynaptic cell by depolarizing the membrane.

Inhibitory Neurotransmitter

Inhibits the postsynaptic cell by hyperpolarizing the membrane.

Neurotransmitter Release - Regulated Exocytosis

Action potential depolarizes axon terminal, Ca2+ enters, exocytosis of synaptic vesicle contents, neurotransmitter binds to postsynaptic receptors, postsynaptic cell response.

Acetylcholine Synthesis Enzyme

Choline acetyltransferase catalyzes transfer of acetyl group from acetyl CoA to choline to make acetylcholine.

Acetylcholine Degradation Enzyme

Acetylcholinesterase degrades ACh into acetic acid and choline.

Ionotropic Receptors

Open (chemically-gated) ion channels.

Metabotropic Receptors

Activate second messenger pathways.

Nicotinic Acetylcholine Receptor (nAChR)

Allows cations to enter the neuron upon transmitter binding; ionotropic receptor.

Muscarinic Acetylcholine Receptor (mAChR)

Coupled via G-proteins to different effectors; metabotropic receptor.

Adrenergic receptor subtypes: α1

Activates phospholipase C, producing IP3 and DAG.

Adrenergic receptor subtypes: α2

Inhibits adenylate cyclase, decreasing cAMP.

Adrenergic receptor subtypes: β1- β3

Activates adenylate cyclase, increasing cAMP.

Somatic Motor Pathway

Control skeletal muscle.

Neurotransmitter at Neuromuscular Junction

ACh acts on nicotinic ACh receptors on skeletal muscle.

Autonomic Nervous System

Controls involuntary actions.

Somatic Nervous System

Controls voluntary actions.

Autonomic Nervous System Transmitters

ACh and NA primary transmitters.

Somatic Nervous System Transmitters

Mainly ACh primary transmitter.

Myasthenic Disorders

A broad group of disorders of neuromuscular transmission; muscular weakness and fatigability.

Myasthenia Gravis (MG)

Auto-antibodies attack protein subunits of the nicotinic ACh receptor.

Lambert-Eaton Myasthenia (LEMS)

Auto-antibodies attack voltage gated Ca++ channels in the motor neuron presynaptic terminal.

ACh Receptor Deficiency

Mutations in genes encoding nicotinic ACh receptor subunits.

Congenital Myasthenic Syndrome with Episodic Apnea (CMSEA)

Mutations in choline acetyltransferase, the ACh synthetic enzyme.

End Plate Acetylcholinesterase Deficiency

Mutations in acetylcholinesterase.

Neurotransmitter Imbalance in Depression

Associated with imbalances in activity of central monoaminergic and cholinergic pathways in limbic system.

Drug Treatments for Depression

Tricyclic antidepressants, SSRIs, MAO inhibitors