IPSP – If the total inhibitory effects are greater than the excitatory effects, the membrane hyperpolarizes (IPSP). The result is inhibition of the postsynaptic neuron and the inability to generate an AP.
Neurotransmitters
A neurotransmitter is a chemical that travels from presynaptic to postsynaptic neurons across synaptic clefts to relay electrical impulses. There are about 100 known NTs. Some bind to receptors opening or closing ion channels in the membrane while others act more slowly to influence chemical reactions within a cell. NTs can be either excitatory or inhibitory on postsynaptic neurons. Many NTs are also hormones released in the bloodstream by endocrine cells in organs throughout the body. NTs are divided into 2 classes based on size: small molecule neurotransmitters and neuropeptides.
A. Small Molecule Neurotransmitters
Acetylcholine (ACh)
Released by many PNS neurons and some CNS neurons Excitatory (ex: NMJ) & Inhibitory (ex: heart rate)
Inactivated by Acetylcholinesterase (AChE)
Amino Acids
Several act as NTs in the CNS
Glutamate (glutamic acid) & Aspartate (aspartic acid) both excitatory Most excitatory neurons in the CNS and ~ ½ synapses in the brain communicate with glutamate.
Gamma Aminobutyric Acid (GABA): the most common inhibitory NT in the CNS (~1/3 of brain synapses) & Glycine are both inhibitory. In the spinal cord the ~ ½ use Glycine and ½ use GABA.
Biogenic Amines
Include: norepinephrine, epinephrine, dopamine, and serotonin
Excitatory or Inhibitory
Norepinephrine (NE): roles in arousal (awakening), dreaming, regulating mood. Both norepinephrine and epinephrine also act as hormones being released into the blood from the adrenal gland.
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