The study of the effects of chemicals on the body, both _____________________ (made in the body) and _________________ (made outside the body) is called PHARMACOLOGY.

The chemicals that travel across the ____________________ between neuron to neuron or from neuron to muscle are called ____________________.

Acetylcholine (ACh) - An Excitatory Neurotransmitter

A neurotransmitter released by a _____synaptic neuron onto either a _______synaptic neuron or onto _______________ causing them to ________________ (ie. respiratory muscles).

Structure of ACh:

Ach binds to _____________________ on the muscle to open ion channels which allow entry of positive ions (_______) which depolarizes the muscle cell to threshold. When an AP fires in the muscle, the muscle contracts. Shortly after binding, the ACh drops off of the _________________ and is broken down (degraded) by an enzyme in the synapse called _______________________________. This terminates the contraction of muscle.

ACh on Muscle:

Curare - A Nervous System Poison

South American arrow poison.

Curare ______________________ with ACh for the receptors on muscle. When curare binds instead of ACh it simply ___________ the receptors without activating them and there is loss of muscle function, paralysis, and possibly death.

Curare on Muscle:

To treat curare poisoning:

If it is diagnosed quickly, a drug called _______________________ can be administered. This drug inhibits acetylcholinesterase (enzyme) so that it cannot break down ____________. As a result, ACh concentration increases in the synapse and can out-compete curare.

GABA - An Inhibitory Neurotransmitter

GABA is found in many locations in the nervous system. It acts to ______________ neurons from firing. Thus, it can cause a muscle to relax or reduce activity in the central nervous system causing a sedating effect.

GABA is believed to bind to post-synaptic receptors opening __________ channels. The entry of ____________ ions then _______polarizes the neuron or muscle reducing the likelihood of "firing" AP's. Some drugs such as barbiturates, alcohol (and others) enhance the action of GABA to cause sedation.

Cocaine - A Stimulant Drug

Cocaine blocks the re-uptake of _________________________ (NE), or other neurotransmitters, from the synapse. As a result, NE builds up and continually stimulates the post-synaptic neuron. This leads to repeated "firing" of the postsynaptic neuron and consequent central nervous system excitation.

After continual use of cocaine, the presynaptic neuron can become depleted of ACh reserves resulting in reduced "firing" of the postsynaptic neuron which may be associated with a feeling of tiredness or depression.


Many other chemicals (endogenous and exogenous) alter neurotransmission by blocking or promoting presynaptic neurotransmitter release or blocking or promoting postsynaptic excitation or inhibition. Examples of such chemicals are: