7F: Synapses and Action Potentials Flashcards
3 types of synapses
- axosomatic synapses: axon terminals making contact with another cell body
- axodendritic synapses: axon terminals making contact with the synaptic shaft of spine synapses
- axo-axonic synapses: axon terminals making contact with another axon terminal
- rare. often used to make inhibitory synapses
electrical vs. chemical synapses
chemical synapses: 1. load neurotrasmitters into vesicles 2. action potential in presynaptic terminal 3. depolarization opens Ca2+ voltage gated ion channels
4. influx of Ca2+ through channels 5. vesicles fuse with presynaptic membrane 6. neurotransmitter released into the synaptic cleft 7. transmitters bind receptor molecules on postsynaptic membrane 8. opening or closing of postsynaptic channels 9. change in excitability of the postsynaptic neuron 10. endocytosis of vesicular membrane involving clathrin
electrical synapses: done by gap junctions. faster communication between cells. cannot regenerate action potentials as well as chemical synapses
how to synaptic vesicles fuse to the membrane?
synaptotagmin, a Ca2+ sensor, senses a rise in Ca2+ levels. Synaptobrevin, a SNARE protein, forms a complex with SNARE protein on the PM of the neuron and allow the vesicle to empty it’s contents
Myasthenia gravis
- autoantibodies again the postsynaptic acetylcholine receptor.
- Neurotransmission weakens and causes poor muscle function
Lamber-Eaton Syndrom
- autoantibodies to own Ca@+ channels, which block voltage gated Ca2+ channels from opening in presynaptic neuron
- reduction in transmitter release
Neurotransmitters and area of concentration
ACh: excitatory neruotransmitter for neuro-muscular junction. In LEMS and Myasthenic Gravis
Norepinepherin : Excitatory & Inhibitory. Autonomic nervous system
Serotonin : Excitatory & Inhibitory. Autonomic nervous system
Glutamate: wide distribution, excitotoxic cell death. In Seizures. Excitatory transmitter for the CNS
Dopamine: Parkinson’s Disease. Excitatory & Inhibitory transmitter
GABA : Epilepsy. Inhibitory transmitter
Glycine: only spinal cord. Inhibitory transmitter
How can one neurotransmitter be both excitatory and inhibitory?
because it can bind to two different kinds of receptors.
- AMPA receptors: ion channel. excitatory
- Metabotropic receptors: g-protein receptors in 3 classes. class I is excitatory. Class II and III are inhibitory
How do neurons keep a negative resting membrane potential?
- they have Na+/K+ pumps that pump 3Na+ out per 2K+ in
- also have resting open Na+ and K+ channels to let Na+ and K+ to flow down their concentration gradients
neurons have less resting Na+ channels than K+ channels, so more K+ flows out down it’s conc. gradient creating and overall negative charge in the cell
what is the resting membrane potential of a neuron
about -60mV
how are action potentials generated?
- voltage gated Na+ channels sense depolarization and open (fast)
- Na+ rushes into the cell making it very positive (action potential)
- Voltage gated K+ channels sense depolarization and open (slow)
- Na+ channels get inactivated and close (fast)
- K+ rushes out of the cell restoring negative membrane potential
- slow closing of the K+ channels over shoot the resting membrane potential
- K+ channels close (slow) and resting membrane potential is restored
Axon hillock
- initial segment of the axon
- where the action potential is generated
- high concentration of voltage-gated Na+ channels
How does an action potential only flow in one direction?
because the area of the axon that just propagated the action potential will be in a refractory period and be unable to perform another action potential. So it can only flow in one direction
Schwann cell vs. Oligodendrocyte
Schwann cell: wraps around one neuron
- but one neuron has many Schwann cells
Oligodendrocyte wraps around many neurons
They both also make different proteins
