NEUR 2600 Lecture Notes - Lecture 5: Second Messenger System, Golgi Apparatus, Choline
CHAPTER 5: HOW DO NEURONS COMMUNICATE AND ADAPT
●A chemical message
○Otto Loewi (1921)
■Frog heart experiment
■Role of the vagus nerve and neurotransmitter acetylcholine (ACh) in
slowing heart rate
○Acetylcholine
■The first neurotransmitter discovered in the PNS and CNS; activates
skeletal muscles in the somatic nervous system and may excite or inhibit
internal organs in the ANS
○Otto Loewi’s subsequent research
■Epinephrine (EP, or adrenaline)
●Chemical messenger that acts as a hormone to mobilize the body
for fight or flight during times of stress and as a neurotransmitter in
the CNS
■Norepinephrine (NE, or noradrenaline)
●Neurotransmitter found in the brain and in the parasympathetic
division of the ANS; accelerates heart rate in mammals
○Neurotransmitter
■Chemical released by a neuron onto a target with an excitatory or
inhibitory effect
■Outside the CNS, many of these chemicals circulate in the bloodstream as
hormones (have distant targets, action slower than that of a
neurotransmitter)
■Hypothalamus to the pituitary gland to the hormones into blood and
finally to target organs and glands
●Structure of synapses
○Electron microscope
■Projects a beam of electrons through a very thin slice of tissue
■Varying structure of the tissue scatters the beam onto a reflective surface,
where it leaves an image, or shadow, of the tissue
■Much better resolution than the light microscope
■1950s: revealed the structure of a synapse for the first time
○Chemical synapse
■The junction where messenger molecules (neurotransmitters) are released
from one neuron to excite or inhibit the next neuron
■Most synapses in the mammalian nervous system are chemical
■
●Structure of chemical synapses
○Presynaptic membrane (axon terminal)
■Where the action potential terminates to release the chemical message
○Postsynaptic membrane (dendritic spine)
■The receiving side of the chemical message; EPSPs or IPSPs are generated
○Synaptic cleft
■Small gap where the chemical travels from presynaptic to postsynaptic
membrane
○Synaptic vesicle (presynaptic)
■Small membrane-bound spheres that contain one or more
neurotransmitters
○Storage granule (presynaptic)
■Membranous compartment that holds several vesicles containing
neurotransmitter(s)
○Postsynaptic receptor (postsynaptic)
■Site to which a neurotransmitter molecule binds
○Electrical synapses
■Gap function
●Fused presynaptic membrane that allows an action potential to pass
directly from one neuron to the next
■Electrical synapses are fast
■Chemical synapses are more flexible (amplify or diminish signal)
●Neurotransmission in four steps
○The neurotransmitter must be
■1. Synthesized and stored in the axon terminal
■2. Transported to the presynaptic membrane and released in response to an
action potential
■3. Able to bind to and activate receptors on the target cell on the
postsynaptic membrane
■4. Inactivated, or it will continue to work indefinitely
○Step 1: synthesis and storage
■Neurotransmitters are derived in two general ways
●Synthesized in the axon terminal
○Building blocks from food are pumped into cell via
transporters, protein molecules embedded in the cell
membrane
●Synthesized in the cell body
○According to instructions in the DNA
○Transported on microtubules to axon terminal
○Step 2: neurotransmitter release
■At the terminal, the action potential opens voltage-sensitive calcium
(Ca2+) channels
■Ca2+ enters the terminal and binds to the protein calmodulin, forming a
complex
■Complex causes some vesicles to empty their contents into the synapse
and others to get ready to empty their contents
○Step 3: receptor-site activation
■After release, the neurotransmitter diffuses across the synaptic cleft to
activate receptors on the postsynaptic membrane
■Transmitter-activated receptors
●Protein embedded in the membrane of a cell that has a binding site
for a specific neurotransmitter
■On postsynaptic side, neurotransmitter may
●1. Depolarize the postsynaptic membrane, causing excitatory
action on the postsynaptic neuron (EPSP)
Document Summary
Chapter 5: how do neurons communicate and adapt. Role of the vagus nerve and neurotransmitter acetylcholine (ach) in slowing heart rate. The first neurotransmitter discovered in the pns and cns; activates skeletal muscles in the somatic nervous system and may excite or inhibit internal organs in the ans. Chemical messenger that acts as a hormone to mobilize the body for fight or flight during times of stress and as a neurotransmitter in the cns. Neurotransmitter found in the brain and in the parasympathetic division of the ans; accelerates heart rate in mammals. Chemical released by a neuron onto a target with an excitatory or inhibitory effect. Outside the cns, many of these chemicals circulate in the bloodstream as hormones (have distant targets, action slower than that of a neurotransmitter) Hypothalamus to the pituitary gland to the hormones into blood and finally to target organs and glands. Projects a beam of electrons through a very thin slice of tissue.
