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allele whose phenotype will be expressed only if an individual is homozygous for that allele

the state of readiness of a neuron membrane’s potential between signals

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midbrain structure important in regulating the sleep/wake cycle, arousal, alertness, and motor activity

neurotransmitter is pumped back into the neuron that released it

cell membrane that allows smaller molecules or molecules without an electrical charge to pass through it, while stopping larger or highly charged molecules

cell body

relays sensory and motor information to and from the CNS

essential for processing sensory information from across the body, such as touch, temperature, and pain

midbrain structure where dopamine is produced; involved in control of movement

(plural: sulci) depressions or grooves in the cerebral cortex

involved in stress-related activities and functions

small gap between two neurons where communication occurs

storage site for neurotransmitters

part of cerebral cortex associated with hearing, memory, emotion, and some aspects of language; contains primary auditory cortex

axon terminal containing synaptic vesicles

sensory relay for the brain

states that organisms that are better suited for their environments will survive and reproduce compared to those that are poorly suited for their environments

level of charge in the membrane that causes the neuron to become active

secretes hormones that regulate growth, metabolism, and appetite

midbrain structure where dopamine is produced: associated with mood, reward, and addiction

important for speech comprehension


3.1 Human Genetics Genes are sequences of DNA that code for a particular trait. Different versions of a gene are called alleles—sometimes alleles can be classified as dominant or recessive. A dominant allele always results in the dominant phenotype. In order to exhibit a recessive phenotype, an individual must be homozygous

110 Chapter 3 | Biopsychology

This OpenStax book is available for free at http://cnx.org/content/col31502/1.4



for the recessive allele. Genes affect both physical and psychological characteristics. Ultimately, how and when a gene is expressed, and what the outcome will be—in terms of both physical and psychological characteristics—is a function of the interaction between our genes and our environments.

3.2 Cells of the Nervous System Glia and neurons are the two cell types that make up the nervous system. While glia generally play supporting roles, the communication between neurons is fundamental to all of the functions associated with the nervous system. Neuronal communication is made possible by the neuron’s specialized structures. The soma contains the cell nucleus, and the dendrites extend from the soma in tree-like branches. The axon is another major extension of the cell body; axons are often covered by a myelin sheath, which increases the speed of transmission of neural impulses. At the end of the axon are terminal buttons that contain synaptic vesicles filled with neurotransmitters.

Neuronal communication is an electrochemical event. The dendrites contain receptors for neurotransmitters released by nearby neurons. If the signals received from other neurons are sufficiently strong, an action potential will travel down the length of the axon to the terminal buttons, resulting in the release of neurotransmitters into the synaptic cleft. Action potentials operate on the all-or-none principle and involve the movement of Na+ and K+ across the neuronal membrane.

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