Neurotransmitters

Review the Synapse A synapse is the “gap” between the axon of one neuron and the dendrite of the next one. The average neuron has 1,000 synapses with other neurons.

1. Impulse from action potential opens ion channels for Ca++

2. The increased Ca++ concentration in the axon terminal initiates the release of the neurotransmitter (NT)

3. NT is released from its vesicle and crosses the “gap” or synaptic cleft and attaches to a protein receptor on the dendrite

4. Interaction of NT and protein receptor open post-synaptic membrane ion channel for Na+

5. After transmission the NT is either degraded by an enzyme or taken back into the pre-synaptic membrane by a transporter or reuptake pump

Neurotransmitters There are dozens of different neurotransmitters (NT) in the neurons of the body. NTs can be either excitatory (stimulate an action potential) or inhibitory (prevent an action potential by hyperpolarizing)

Acetylcholine (Ach) Excitatory Controls muscles and regulates memory, learning, attention used by the spinal cord neurons to control muscles and by many neurons in the brain to regulate memory

Dopamine Usually inhibitory Produced feelings of pleasure in the brain

Endorphins Reduces pain Tends to be released when in pain, during exercise or laughing. Name means “morphine-like substance produced inside the body

Epinephrine Regulates attention, mental focus, arousal, metabolism, and cognition Also called adrenaline Hormone and neurotransmitter

Gamma-aminobutyric acid (GABA) The major inhibitory neurotransmitter in the brain. Reduces excess stimulation, improves focus, lessens anxiety

Glutamate The most common excitatory neurotransmitter in the brain. Learning and memory

Norepinephrine Part of the flight-or-flight response in PNS. In the brain, affects attention Usually excitatory, but is inhibitory in a few brain areas. Neurotransmitter and hormone

Serotonin Involved in mood, appetite, and sensory perception. In the spinal cord, serotonin is inhibitory in pain pathways.

Drugs Interfere with Neuro-transmission

Drugs That Influence Neurotransmitters Change in Neurotransmission Effect on Neurotransmitter release or availability Drug that acts this way increase the number of impulses increased neurotransmitter release nicotine, alcohol, opiates release neurotransmitter from vesicles with or without impulses increased neurotransmitter release amphetamines methamphetamines release more neurotransmitter in response to an impulse nicotine block reuptake more neurotransmitter present in synaptic cleft cocaine amphetamine block receptor with another molecule no change in the amount of neurotransmitter released, or neurotransmitter cannot bind to its receptor on postsynaptic neuron LSD caffeine NIH Publication No. 00-4871