Chapter 5 - Neurotransmitters Flashcards
acetylcholine (Ach)
activates skeletal muscles in the somatic nervous system, and excites or inhibits internal organs in the autonomic nervous system
epinephrine (EP)
- aka adrenaline
- speeds up the heartbeat in frog hearts in Loewi’s experiment
norepinephrine (NE)
chemical messenger that increases heart rate in mammals
neurotransmitters
chemical messengers that are released by a neuron on a target to cause an excitatory or inhibitatory effect
difference between neurotransmitters and hormones
hormones travel longer distances, so their effects are slower
structure of synapses
cell A is connected to cell B by a connection called the synapse
- cell A is the presynaptic cell (sender)
- cell B is the postsynaptic cell (receiver)
- synapse consists of the terminal button of the presynaptic axon, synaptic cleft (small gap between the 2 cells), and the postsynaptic membrane
- presynaptic neuron secretes a chemical into the synaptic cleft, a neurotransmitter, which then binds to the postsynaptic receptors on the postsynaptic membrane
synaptic vesicles
the neurotransmitters in the presynaptic cell
quantum
content of 1 synaptic vesicle
- there is the same number of neurotransmitters in each vesicle
five steps of neurotransmission
- synthesis
- packing + storage
- release
- receptor action at the postsynaptic membrane
- inactivation
synthesis
the neurotransmitter is synthesized somewhere in the neuron
- peptide transmitters are synthesized in the cell body (DNA, mRNA) through transcription and translation
- small-molecule transmitters are synthesized directly in the axon terminal, using food-derived substances
packing + storage
the synthesized neurotransmitters are packaged and stored in vesicles
release
the vesicles containing neurotransmitters dock near release sites on the presynaptic membrane
- amount of neurotransmitter released depends on the amount of Ca entering the axon terminal and the number of vesicles docked at the membrane
receptor action at the postsynaptic membrane
neurotransmitters that are released into the synaptic cleft reach the postsynaptic membrane, where they bind to its transmitter-activated receptors
inactivation
if neurotransmitters remained in the synaptic cleft indefinitely, they would continue to bind to receptors, so the cell could not respond to new signals
- thus, neurotransmitters must be inactivated after they have done their work
diffusion
neurotransmitters diffuse away from the synaptic cleft towards areas of lower concentration
degradation
neurotransmitters are broken down by enzymes in the synaptic cleft
reuptake
neurotransmitters (and/or the residues of their enzyme degradation) can return to the presynaptic cell, where they can be reused
astrocyte uptake
neurotransmitters can be taken up by astrocytes, which can then provide them once again to the presynaptic cell
axodendritic synapses
connect an axon (presynaptic) to a dendrite (postsynaptic)
axosomatic synapses
connect an axon (presynaptic) to a cell body (postsynaptic)