NMJ And Synapses Flashcards
What are special senses
sight
Smell
hearing
Taste
Electrical synapse?
Gap junctions
Fastest and most primitive
Allows synchronous activity
Common between glial cells and neurones/ glial-glial and cardiomyocytes
Direct transfer of ions
Bi directional
Chemical synapse?
Release of NT from presynaptic terminal
Diffuses
Interacts with receptor on post synaptic
What is presynaptic area with vesicles known as
Active zone
How is signal terminated
Enzymatic breakdown
Features of NT receptors
Transmembrane spanning proteins
Binding causes conformational change
Specific
One NT - several receptor subtypes
Ionotropic receptor signalling mechanism?
(Receptor operated/ ligand gated channel)
Transmitter binds
Conformational change
Channel opening
Ion movement
Metabotropic receptor signalling mechanism?
(G protein coupled)
Transmitter binding
conformational change
activates G-protein
activates ‘effector systems’
indirect effects: e.g. open or close ion channels; stimulate or inhibit enzymes/ secondary messenger systems
Indirect effects of G coupled protein receptors
Open or close ion channels
Stimulate or inhibit enzymes/ secondary messenger systems
Spatial summation
Summing of post synaptic potentials generated at separate synapses to reach threshold value
Temporal summation
Summing of post synaptic potentials generated at same synapse, if they occur in rapid succession
Single synapse repeatedly stimulating the cell
Axon hillock?
Region where an action potential is generated and then propagated along the axon
Between soma and axon
An input closer to axon hilllock will have a much larger effect on excitability of cell compared to input at dendritic tree
What is gap junction?
An electrical synapse
Gap junction is a physical point of contact between adjacent cells via their cell membrane
Which type of myocytes are connected via gap junctions?
Cardiac myocytes
Allows cardiac muscle to depolarise to cause contraction
Two ways of termination of signal
- Enzymatic breakdown and Reuptake of NT
Specific re-uptake sites. NT hydrolysed by enzymes in presynaptic membrane/ repackaged into vesicles - Enzymatic breakdown in extracellular fluid
Without uptake. Mitochondria in extracellular fluid. e.g. acetylcholine
Types of monoamine NT
Noradrenaline (adrenal medulla)
Dopamine
Serotonin
Mixed synapse?
Both inhibitory and excitatory synaptic inputs
GABA?
Inhibitory NT
Promotes anti-stress and calmness
What is in white matter?
Axons of neurones
How is muscle contraction guaranteed ?
- Many NMJ along the length of the muscle to ensure muscle fibres contract simultaneously
- Many vesicles in pre synaptic membrane
- Many post synaptic receptors
Description of ligand gated ion channel for ACh?
5 protein subunits
Two binding sites for ACh. Two need to bind for conformational change.
Junctional folds on post synaptic neurone
Invaginations in the Sarcolemma (cell membrane of muscle fibre) at NMJ
Increases surface area
High density of ACh receptors and voltage gated Na channels
What is EPP?
End plate potential
Separate event to AP and occurs first
Voltage produced solely by ACh binding to nAChR on motor end plate
Generated by ligand gated channels
How is AP generated?
Generated by voltage gated Na channels
