Synapses and Neuromuscular Junction Flashcards
Synapse
Point of connection and communciation between two cells
Synaptic Transmission
Process of communication between two cells
Electrical Synapse
Synapse which communicates via electrical currents
Chemical Synapse
Synapse that communicates via chemical movement, found in CNS
Gap Junctions
Point of electrical transmission. Tiny spaces between neurons filled with connexins. Allow cells to be highly synchronised, common in early development
Connexin
Made of 6 subunits to create a channel between two cells that ions can flow through
Electrically Coupled
Cells where the electrical current can pass from one cell to another
Post synaptic potential
temporary change in the electric polarization of the membrane of a nerve cell, caused by transmission from a neighbouring cell
Synaptic Vesicles
Vesicles about 50 nm filled with Neurotransmitters
Secretory Granules
Vesicles about 100 nm, filled with soluble proteins
membrane differentiation
Dense accumultions of proteins on either side of the synaptic celft
Active Zones
Sites of Neurotransmitter release
Postsynaptic Density
Proteins thickly layered around post synaptic membrane
axodendritic
axon to dendrite
axosomatic
axon to soma
axoaxonic
axon to axon
axospinous
Axon to dendritic spine
dendodendritic
dendrite to dendrite (rare9
Gray’s Type 1 synapse
Post synaptic cell is bigger than pre synaptic cell, also called asymmetric synapses
Usually excitatory
Gray’s type 2 synapse
Cells are same size or symmetrical
Usually inhibitory
Neuromuscular Junction
the point of communication between a nerve fibre and the end plate of the muscle fibre
Motor end plate
innervated tissue in Neuromuscular junction
Neurotransmitters
Chemically Messengers used by the brain at he synapse, divided into three subtypes, amines, amino acids, and peptides.
Amines
Small Neurotransmitters stored in vesicles include:
Acetylcholine (ACh)
Dopamine (DA)
Epinephrine
Histamine
Norepinephrine (NE)
Serotonin (5-HT)
Amino Acids
Small Neurotransmitters stored in vesicles include:
GABA
Glutamate (Glu)
Glycine (Gly)
Petides
Large soluble Neurotransmitters stored in secretory granules include:
Cholecystokinin (CCK)
Dynorphin
Enkephalins (Enk)
N-acetylaspartylglutamate (NAAG)
Neuropeptide-Y
Somatostatin
Substance P
Thyrotropin releasing hormone
Vasoactive intestinal polypeptide (VIP)
Transporters
Get Neurotransmitters into the vesicle
Voltage Gated Calcium Channels
Open when AP reaches terminal, triggering Ca2+ influx. Ca2+ triggers vesicle release
Exocytosis
How vesicles are released
Endocytosis
How vesicle membrane is recaptured to be recycled
SNARE proteins
Proteins on membranes that allow the vesicles to dock into place before being released, when Ca2+ enters they cleave and the Vesicle merges with the cell membrane inducing exocytosis
V-snares
Snares on vesicles
T-snares
Snares on membrane
Secretory Granule Release
Need a very high AP to be released, otherwise system is similar to vesicles
Transmitter gated ion channels
Form of neurotransmitter receptors.
4-5 subunits make up the channel
when a set number of transmitter molecules bind to receptor sites the channel will open allowing specific ions to channel through creating a PSP
AChR
Acetylcholine receptors,
consist of 5 subunits and 2 receptor sites
2α,1β, 1𝛾, 1δ
Permeable to Na+ and K+
Excitatory Post synpatic potentials
EPSPs
Positive influx of ions in post synaptic cell
G-protein coupled receptors
Neurotransmitter binds to receptor proteins, proteins activate G-proteins, that move along postsynaptic membrane, Activate effector proteins (which can cause widespread metabolic changes in the receptor cell)
Much slower and long lasting system than traditional receptors
Autoreceptors
Recpetors on presynaptic cell (usually g-proteins)
Effects vary but commonly: inhibit Nt release, or induce synthesis
Helps autoregulation
Synaptic enzymes
enzymes that break down excess neurotransmitter in the cleft
Eg Acteylcholineesterase
Densentization
Receptors becoming desensitised to transmitters and closing
Neuropharmacology
Study effects of drugs on the nervous system
Neuropharmacology
Study effects of drugs on the nervous system
Inhibitors
Inhibit normal function of proteins in transmission
Receptor Antagonist
Block receptors
Receptor Agonist
Bind to receptors and increase activation
nicotinic ACh receptors
ACh receptors in muscles
Synaptic Integration
How multiples post synaptic potentials combine within post synaptic cell
Quanta
Number of neurotransmitters in one vesicle
Mini post synaptic potential
1 quanta of neurotransmitters
Quantal Analysis
Analysing quanta released
EPSP summation
includes both spatial summation and temporal summation, is the process that determines whether or not an action potential will be generated by the combined effects of excitatory and inhibitory signals, both from multiple simultaneous inputs, and from repeated inputs
Spatial Summation
Adding all PSPs from multiple sites in the cell at the same time
Temporal Summation
adding PSPs at the same synapse when in quick succession
cable theory
cable theory uses mathematical models to calculate the electric current (and accompanying voltage) along passive[a] neurites, particularly the dendrites that receive synaptic inputs at different sites and times
inhibitory synapse
synapse that lowers membrane potential of the post synaptic cell
IPSPs
making it harder for EPSPs to reach a high enough level via shunting inhibition
Modulation
Receptors that do not produce EPSPs or IPSPs, but alter the efficacy of EPSPs
Permeability of K+ and Na+ at AChR
Depends on membrane potential (linear R)
Vesicles formation
Budding
Docking
SNARE
Synaptogenesis
Clathrin
Budding
Dynamin
Repeat
Evidence for Chemical Transmission at NMJ
Electron Micrograph w/vesicles
time between release
ACh released when nerves excitated
Muscles contract when ACh exposed
Efficacy of drugs and toxins at NMJ
not protected by BBB, thus uniquely susceptible to many
Sarin
AChE inhibitor, thus it is not broken down and overwhelms synapse. Used as a nerve agent and pesticide. Can be used to treat Alzheimer’s and Myasthenia Gravis
Curare and Bungarotoxin
Block receptors to prevent muscle contraction.
Curare used medically, because it prevents cleavage of SNARE proteins
Bungarotoxin was used in the amazon as a tranquilizer, now commonly used as Botox
