Synaptic transmission

• Synapses: small spaces between 2 neurons or neuron or effector
• Presynaptic neuron: transmits nerve impulse to the synapse, has ending called axon terminal
• Axon terminal contains mitochondria and synaptic vesicles filled with neurotransmitters
• Neurons are able to release more than one type of neurotransmitter
• Postsynaptic neuron: Carrie’s nerve impulse away from synapse, contains receptor protein.
• when the action potential reaches the axon terminal it releases Ca+ which binds to synaptic vesicles (neurotransmitters) and causes vesicle to move to the membrane.
• Na+ needs to reach axon terminal for Ca+ to come in
• Synaptic vesicles release their neurotransmitters into synaptic cleft by exocytosis.
• excitatory neurotransmitters: cause an action potential.
• inhibitory neurotransmitters don’t cause an action potential and makes the membrane become negative.
• Acetylcholine is an excitatory neurotransmitter to skeletal muscle but inhibitory to cardiac muscle
• Acetylcholine diffuses through the synaptic cleft and bind to ligand-gated ion channel and only open up in presence of acetylcholine.
• Excitatory neurotransmitters bind to receptors on postsynaptic membrane causing Na+ to open, creating an excitatory postsynaptic potential (EPSP)
• Postsynaptic membrane releases enzyme (cholinesterase) that breaks down acetylcholine. Enzyme degradation.
• Cholinesterase is specific to acetylcholine
• Acetylcholine may be packed back into synaptic neuron.
• Gliol cells help clean out neurotransmitter out of synaptic cleft (diffusion away from synaptic cleft) gliol cells absorb it and repackage it.
• Once neurotransmitter is gone from postsynaptic receptor, ion channels in postsynaptic neurons close. stimulus disappears and membrane will go back to resting membrane potential
• GABA is an inhibitory neurotransmitte.
• Inhibitory neurotransmitters bind to receptors and cause K+ channels in postsynaptic membrane to open, causing a hyperpolarization creating an inhibitory postsynaptic potential (IPSP)
• IPSP will not allow membrane to ever hit threshold potential and no action potential is generated.
• summation: combination of graded potentials in the postsynaptic neuron. If combination of potentials received reached threshold potential, action potential is triggered.
• Axon hillock will determine information, excitatory and inhibitory will cancel out.
• 2-3 or more neurotransmitters at same time cause a threshold potential (summation)
• Temporal summation: 1 presynaptic neuron but happen so quickly it can cause a threshold potential.
• Inhibitory transmitters help us determine which information is important.
• Nerve gas: blocks cholinesterase (enzyme) and if a person exhales it muscle contraction happens but relaxation won’t. This happens because acetylcholine isn’t removed
• Botox: blocks neurotransmitters by blocking presynaptic vesicles causing the message not to be delivered, can cause death because of a stop in breathing, produced by anaerobic bacteria.
• glutamate: excitatory neurotransmitter