acetylcholine - a neurotransmitter that carries nerve impulses across a synapse from one neuron to another or from a neuron to a muscle.
afferent - carrying something (like a nerve impulse) toward the central part.
amygdala - a part of the brain (and part of the limbic system) that is used in emotion.
anterior - towards the front.
anterior commissure - a small fiber that connects the right and left cerebral hemispheres of the brain.
arachnoid - one of the three membranes that protects the brain and spinal cord. The space between the arachnoid and the pia (another membrane) is filled with cerebrospinal fluid, protecting the brain from physical blows and providing the brain with nutrients.
association cortex - any part of the cortex in which information is analyzed, processed, or stored.
astroglia or astrocyte - a type of glial cell that supports neurons.
autonomic nervous system - controls our life support systems that we
don't consciously control, like breathing, digesting food, blood circulation, etc.
axon - the long extension of a neuron that carries nerve impulses away from the body of the cell.
axodendritic synapse - a synapse formed by contact between a presynaptic axon and a postsynaptic dendrite.
basal ganglia - groups of hundreds of thousands of neurons at the base of the cerebrum and in the upper brainstem; they help control well-learned movements (like walking) and sensation.
blood-brain barrier - the blood-brain barrier protects the brain from chemical intrusion from the rest of the body. Blood flowing into the brain is filtered so that many harmful chemicals cannot enter the brain.
brainstem or brain stem - the base of the brain. This part of the brain connects the brain's cerebrum to the spinal cord. The brain stem controls many automatic and motor functions. The brain stem is composed of the medulla oblongata, the pons, the midbrain, and the reticular formation.