5 Steps to a 5 AP Psychology, 2014-2015 Edition

nucleus, which directs synthesis of such substances as neurotransmitters. The dendritesare
branching tubular processes capable of receiving information. The axonemerges from the
cyton as a single conducting fiber (longer than a dendrite) which branches and ends in tips
calledterminal buttons, axon terminals, or synaptic knobs. The axon is usually covered by
an insulating myelin sheath(formed by glial cells). Neurogenesis, the growth of new neu-
rons, takes place throughout life.
Neurotransmittersare chemicals stored in structures of the terminal buttons called
synaptic vesicles. Different neurotransmitters have different chemical structures and per-
form different functions. For example, acetylcholine (ACh)causes contraction of skeletal
muscles, helps regulate heart muscles, is involved in memory, and also transmits messages
between the brain and spinal cord. Lack of ACh is associated with Alzheimer’s disease.
Dopaminestimulates the hypothalamus to synthesize hormones and affects alertness and
movement. Lack of dopamine is associated with Parkinson’s disease; too much dopamine is
associated with schizophrenia. Glutamateis a major excitatory neurotransmitter involved
in information processing throughout the cortex and especially memory formation in the
hippocampus. Both schizophrenia and Alzheimer’s may involve glutamate receptors.

Biological Bases of Behavior  71

node of

Ranvier

axon terminal

or

terminal button

or

synaptic knob

synaptic gap

synaptic vesicle with

neurotransmitters

enlargement of

terminal button of

presynaptic neuron

and membrane of

dendrite of postsynaptic

neuron at synapse

Figure 7.3 Typical neurons.