CNS 10 3/4/25

Miniature endplate potentials

spontaneous depolarizations due to release of large numbers of Ach from presynaptic termina

. Quanta hypothesis

epp is due to simultaneous release of many quanta of Ach

Qunata hypo EX

Each quantum produces one mepp (the amount of transmitter in a signle vesicle). How to study this? Bathe muscle in low Calcium solution and stimulate neuron. Epps produced were small and increased in steps

Vesicle hypothesis

high concentration of synaptic vesicles contained in nerve terminals which contain transmitters. P.S. a. Vesucles are recycled; fuse with membrane

Calcium hypothesis

Ca in extracellular fluid is needed alongside nerve stimulation to produce an epp: Ca promotes fusion of vesicle to membrane

Ca What IF

a. If Ca is delivered to junction the same time as nerve is stimulated, a large epp will form b. No epp with only Ca c. Small epp with only stimulation d. Small epp if Ca delivered to junction a long time before stimulation

Active zone

region from which synaptic vesicles release transmitters. i. Vesicles are docked when in active zone, but have not yet released transmitters

Synapsin

ound to vesicle membranehu

Synaptotagmin

triggers fusion of docked vesicles to membrane when activated by Ca+

SNARE

causes docking in vesicles when V SNARE (vesicle) forms complex w A SNARE (membrane)

Tetanus and Botulinum –

cleaves SNARE complexes

Calmodulin

calcium binding protein; triggers vesicles in waiting to dissociate from actin anchors and move toward active zone( triggered by CA influx)

Kiss and run

vesicle and membrane fuse to open a small pore and release transmitter, then the pore closes and the vesicle is reformed

. 2nd hypothesis –

entire vesicle fuses with membrane and must be reformed

Clathrin

coats the budding portion of the membrane and binds to adaptins

Adaptins –

associate with proteins in axonal membrane 1. Binding of clathrin causes sphere to form

Dynamin

wraps around stalk and pinches it off, freeing the vesicle. Coated vesicle sheds protein coats and becomes naked, then is refilled and goes to reserve pool k`1

V-Snares

on vesicle membrane

A-SNARE

on presynaptic membrane