University:
Western Sydney University
Course:
MEDI 2003 | Clinical Sciences 2
Academic year:

2024
Views:

107

Pages:

3
Author:

Mariam A. A.

What determine the synaptic nature? • 1. 2. • • • The nature can determine by to parameters: Identity of the nt The identity of the receptors it activates The nature of a synapse - excitatory or inhibitory - depends on the neurotransmitter as well as the receptor At most excitatory synapses the neurotransmitter (e.g., glutamate or ACh) causes an influx of Na+ into the cell and therefore depolarization of the postsynaptic membrane - These signals are called EPSPS At most inhibitory synapses the neurotransmitter (e.g., glycine or GABA) causes an influx of Cl- or efflux of K+ which result in hyperpolarization of the postsynaptic membrane - We call these signals IPSPS What determine the synaptic nature? Can a certain neurotransmitter be both inhibitory and excitatory? Yes. This is because the synoptic identity is not only determined by the identity of the nt but also based on the identity of the receptor. At the neuromuscular junction ACh is excitatory, acting on the ionotropic nicotinic receptors to cause an influx of Na+, but at the sinus node of the heart, ACh is inhibitory, acting on metabotropic muscarinic receptors to slow down the heart rate The quantal nature of synaptic transmission • Most of what we know about synaptic machinery comes from electro-physiological recordings from both pre synoptic and post synoptic cells. One way to study synaptic transmission is by recording the electrical activity at the postsynaptic side by inserting a recording electrode. These electrical signals called synaptic potentials (End plate potentials in the NMJ). • These happened without any stimuli. (for the pics below) - Because of spontaneous release of vesicles. Usually, it is one vesicle but in some cases it can be two or more vesicles. Using this technique, Bernard Katz found that ACh is released in packets of vesicles (quanta), (we need to take into account they did not really about the existence of vesicles back then), which can be measured by the small voltages they produce (Miniature End Plate Potentials) in the post-synaptic membrane. • Their conclusion is based on this experiment, we see here. They measured both e and s. - The e activity is measured following electrical stimulus and voltage followed by the activation if the stimulus. - S is measured randomly without stimulus. - The amplitude of e is either equal or a multiplication of that of s. - Thus, they hypothesised that neurotransmitters are released in quanta which is the size of the vesicle - And when they evoked the cell by applying stimuli, there was release several vesicles, which explains the multifaction factor. Katz also found that the release of ACh vesicles occur in a probabilistic fashion (hence the failures). Therefore, not every action potential will lead to synaptic release and different synapses will have different release probability