Axonal Transmission

Axonal transmission • • Neurons communicate through electrochemical system which can flow from den to the soma and the axon high work If the overall depolarisation pass the spike threshold an action potential will be initiated here in the axon high look and will propagate through the axon all the way to the axon terminal which is part of the synapse. Synapses Synapse - A junction between a Neuron and another cell/muscle/gland that allows the neuron to transmit an electrical or chemical signal. E: can be found between glacial cell and certain types of neurons C: most common synapses between neurons Chemical Synapse • Is a synapse in which the information is transmitted if you add the release of the chemical agent that we call neuron transmitter. It is made up of: • Presynaptic site – The axon terminal of the presynaptic neuron. - Full of vesicles that are full of neuro transmitters. • Postsynaptic site – The dendrite (usually, but not always) of the postsynaptic cell - There is a field of receptors that can be activated by the neurotransmitter that is being released from the presynaptic nerve. There is a region that looks darker due to high density of receptors in this region. It is all PSD 95. • Synaptic cleft – The gap between the presynaptic and postsynaptic membranes • The acrostic process: This process can regulate the synaptic activity. - We look on synapses as tripartite synapse: which consists of pre and post and astro which encapsulates this synoptic region. The neuromuscular junction The neuromuscular junction is the synapse between a motor neuron and the muscle fibers it innervates • • It consists of a motor neuron axon terminal (boutons) as the presynaptic area and the sarcolemma (muscle fiber membrane) as the postsynaptic area The postsynaptic zone consists of many receptors to the neurotransmitter Acetylcholine (ACh). - And the neurotransmitter that is released via these vesicles from the pre axon is Ach. The neuromuscular junction: Acetylcholine • • • • Acetylcholine (ACh) is the first substance identified as neurotransmitter (1915, Henry Dale). It mostly has an excitatory impact on the target cell and expressed in both CNS and PNS. ACh is synthesized from Acetyl CoA and Choline by the enzyme Choline Acetyl transferase (CAT), and loaded to vesicles by the vesicular ACh transporter (VAChT). ACh action on the postsynaptic receptors is terminated by the enzyme acetylcholine esterase (AChE), which hydrolyze ACh in the synaptic cleft. ACh activate both ionotropic receptors (nicotinic acetylcholine receptors; nAChR) and metabotropic receptors (muscarinic acetylcholine receptors; mAChR) Neurotransmitters There are more than 100 neurotransmitters in the nervous system, which can be divided to two main categories: Small molecule neurotransmitters and neuropeptides • • Neuropeptides – large transmitter molecules (3-36 amino acids); synthesized in the Golgi apparatus and packaged into vesicles Small molecule neurotransmitters Usually an individual amino acid (Glutamate; GABA), synthesized and packaged locally at the synapse Synaptic release – the vesicular cycle • • • • • • • Allows the transfer of info from one cell to the next Reagrdless of the identity of the nt in pre synaptic cell, the synaptic machinery itself is quite similar. The synaptic activity starts long before an action potential arrives to the synapse. - It starts with vesicles that are formed in the Golgi apparatus and are then transferred to the axon terminal. - Only large neuropeptides are synthesised and packaged at the stoma level, whereas smaller ones are locally at the synapse. 3: the insertion of Ca into the cells triggers the fusion of the synaptic vessel. One the vesicle is fused with membrane, the nt transmitter is release to the synoptic left and diffused to the post-synoptic membrane where it can bind to its specific receptor. - This binding activates the receptor to create a posy synoptic signal, which is called post synaptic potential or post synoptic current which can propagate all the way to the soma and axon highland. The synoptic activity ends once the neurotransmitter is separated from the receptor and getting out from the synoptic left. It can go out either by: - Simple diffusion - Hydrolysis - Help of other transporters - Or just a simple re-obtate in the pre synoptic area where it can be packaged again for future use.