Biomedical Science - Synapses, Muscles and Neuromuscular junctions

synapse

-location where axon terminal of 1 neuron communicates with a dendrite of another neuron

OR

-where axon terminal communicates with muscle tissue

Synaptic cleft

a tiny gap between the bouton of the axon terminal and dendrite of nearby neuron/muscle cells

^400nm wide - prevents activation of nearby neurons

where neurotransmitter diffuses across

release of neurotransmitters

The axon terminal has voltage gated calcium ion channels in the membrane, these open when the wave of depolarisation reaches them, Ca2+ then enters the axon and this causes the release of vesicles containing a chemical neurotransmitter into the synaptic cleft

binding of neurotransmitter

Neurotransmitter receptors are called ligand gated ion channels, they open in response to a molecule binding into a receptor shape, the channel opens and this causes ions to rush into the cell

activation of post synaptic neuron

-post synaptic channels are either Na+ channels or Cl- channels

-if sodium channels are opened by the neurotransmitter binding, sodium enters the cell to produce a positive voltage and make depolarisation more likely (stimulation/excitation)

-if chloride channels are opened, chloride enters the cell to produce a more negative voltage and make depolarisation less likely

key neurotransmitters

-Noradrenaline: used between postsynaptic neurons and targets tissues in sympathetic neuros system - EPSP (excitatory)

-Acetylcholine (ACh): used between post synaptoc neurons and target organs in PNS (excitatory)

-Glycine: inhibitory in CNS

-Glutamate: excitatory in CNS

-Gamma amino butyric acid (GABA): most common inhibitory in CNS

removing neurotransmitters from synaptic cleft

-to prevent repeated transmission, neurotransmitters are rapidly removed so that their effect on the post synaptic receptors are short lived

Neurotransmitters are usually inactivated by:

ENZYMES THAT DESTROY THE NEUROTRANSMITTER or

REUPTAKE INTO PRESYNAPTIC BY A TRANSPORTER

convergence

if several presynaptic nerves synapse on the same post synaptic nerve, information is received from many neurons

divergence

if a presynaptic axon contacts several post synaptic neurons information is spread

neuromuscular junction

-motor neurons form a synapse/neuromuscular junction with a muscle cell to cause them to contract

-each branch of the axon terminal will synapse with a motor end plate on the muscle tissue

contraction

The motor neuron must release ACh from its synaptic vesicles into the synaptic cleft to initiate voluntary muscle contraction