Summary and Key Terms

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 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.

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.

Different neurotransmitters are associated with different functions. Often, psychological disorders involve imbalances in a given neurotransmitter system. Therefore, psychotropic drugs are prescribed in an attempt to bring the neurotransmitters back into balance. Drugs can act either as agonists or as antagonists for a given neurotransmitter system.

Parts of the Nervous System

The brain and spinal cord make up the central nervous system. The peripheral nervous system is comprised of the somatic and autonomic nervous systems. The somatic nervous system transmits sensory and motor signals to and from the central nervous system. The autonomic nervous system controls the function of our organs and glands, and can be divided into the sympathetic and parasympathetic divisions. Sympathetic activation prepares us for fight or flight, while parasympathetic activation is associated with normal functioning under relaxed conditions.

The Brain and Spinal Cord

The brain consists of two hemispheres, each controlling the opposite side of the body. Each hemisphere can be subdivided into different lobes: frontal, parietal, temporal, and occipital. In addition to the lobes of the cerebral cortex, the forebrain includes the thalamus (sensory relay) and limbic system (emotion and memory circuit). The midbrain contains the reticular formation, which is important for sleep and arousal, as well as the substantia nigra and ventral tegmental area. These structures are important for movement, reward, and addictive processes. The hindbrain contains the structures of the brainstem (medulla, pons, and midbrain), which control automatic functions like breathing and blood pressure. The hindbrain also contains the cerebellum, which helps coordinate movement and certain types of memories.

Individuals with brain damage have been studied extensively to provide information about the role of different areas of the brain, and recent advances in technology allow us to glean similar information by imaging brain structure and function. These techniques include CT, PET, MRI, fMRI, and EEG.

The Endocrine System

The glands of the endocrine system secrete hormones to regulate normal body functions. The hypothalamus serves as the interface between the nervous system and the endocrine system, and it controls the secretions of the pituitary. The pituitary serves as the master gland, controlling the secretions of all other glands. The thyroid secretes thyroxine, which is important for basic metabolic processes and growth; the adrenal glands secrete hormones involved in the stress response; the pancreas secretes hormones that regulate blood sugar levels; and the ovaries and testes produce sex hormones that regulate sexual motivation and behaviour.

Key Terms

action potential
electrical signal that moves down the neuron’s axon
adrenal gland
sits atop our kidneys and secretes hormones involved in the stress response
drug that mimics or strengthens the effects of a neurotransmitter
phenomenon that incoming signal from another neuron is either sufficient or insufficient to reach the threshold of excitation
specific version of a gene
structure in the limbic system involved in our experience of emotion and tying emotional meaning to our memories
drug that blocks or impedes the normal activity of a given neurotransmitter
auditory cortex
strip of cortex in the temporal lobe that is responsible for processing auditory information
autonomic nervous system
controls our internal organs and glands
major extension of the soma
biological perspective
view that psychological disorders like depression and schizophrenia are associated with imbalances in one or more neurotransmitter systems
Broca’s area
region in the left hemisphere that is essential for language production
central nervous system (CNS)
brain and spinal cord
hindbrain structure that controls our balance, coordination, movement, and motor skills, and it is thought to be important in processing some types of memory
cerebral cortex
surface of the brain that is associated with our highest mental capabilities
long strand of genetic information
computerized tomography (CT) scan
imaging technique in which a computer coordinates and integrates multiple x-rays of a given area
corpus callosum
thick band of neural fibers connecting the brain’s two hemispheres
branch-like extension of the soma that receives incoming signals from other neurons
deoxyribonucleic acid (DNA)
helix-shaped molecule made of nucleotide base pairs
disease related to insufficient insulin production
dominant allele
allele whose phenotype will be expressed in an individual that possesses that allele
electroencephalography (EEG)
recording the electrical activity of the brain via electrodes on the scalp
endocrine system
series of glands that produce chemical substances known as hormones
study of gene-environment interactions, such as how the same genotype leads to different phenotypes
fight or flight response
activation of the sympathetic division of the autonomic nervous system, allowing access to energy reserves and heightened sensory capacity so that we might fight off a given threat or run away to safety
largest part of the brain, containing the cerebral cortex, the thalamus, and the limbic system, among other structures
fraternal twins
twins who develop from two different eggs fertilized by different sperm, so their genetic material varies the same as in non-twin siblings
frontal lobe
part of the cerebral cortex involved in reasoning, motor control, emotion, and language; contains motor cortex
functional magnetic resonance imaging (fMRI)
MRI that shows changes in metabolic activity over time
sequence of DNA that controls or partially controls physical characteristics
genetic environmental correlation
view of gene-environment interaction that asserts our genes affect our environment, and our environment influences the expression of our genes
genetic makeup of an individual
glial cell
nervous system cell that provides physical and metabolic support to neurons, including neuronal insulation and communication, and nutrient and waste transport
secretes sexual hormones, which are important for successful reproduction, and mediate both sexual motivation and behaviour
(plural: gyri) bump or ridge on the cerebral cortex
left or right half of the brain
consisting of two different alleles
division of the brain containing the medulla, pons, and cerebellum
structure in the temporal lobe associated with learning and memory
state of equilibrium—biological conditions, such as body temperature, are maintained at optimal levels
consisting of two identical alleles
chemical messenger released by endocrine glands
forebrain structure that regulates sexual motivation and behaviour and a number of homeostatic processes; serves as an interface between the nervous system and the endocrine system
identical twins
twins that develop from the same sperm and egg
concept that each hemisphere of the brain is associated with specialized functions
limbic system
collection of structures involved in processing emotion and memory
longitudinal fissure
deep groove in the brain’s cortex
magnetic resonance imaging (MRI)
magnetic fields used to produce a picture of the tissue being imaged
hindbrain structure that controls automated processes like breathing, blood pressure, and heart rate
membrane potential
difference in charge across the neuronal membrane
division of the brain located between the forebrain and the hindbrain; contains the reticular formation
motor cortex
strip of cortex involved in planning and coordinating movement
sudden, permanent change in a gene
myelin sheath
fatty substance that insulates axons
cells in the nervous system that act as interconnected information processors, which are essential for all of the tasks of the nervous system
nervous system’s ability to change
chemical messenger of the nervous system
Nodes of Ranvier
open spaces that are found in the myelin sheath that encases the axon
occipital lobe
part of the cerebral cortex associated with visual processing; contains the primary visual cortex
secretes hormones that regulate blood sugar
parasympathetic nervous system
associated with routine, day-to-day operations of the body
parietal lobe
part of the cerebral cortex involved in processing various sensory and perceptual information; contains the primary somatosensory cortex
peripheral nervous system (PNS)
connects the brain and spinal cord to the muscles, organs and senses in the periphery of the body
individual’s inheritable physical characteristics
pituitary gland
secretes a number of key hormones, which regulate fluid levels in the body, and a number of messenger hormones, which direct the activity of other glands in the endocrine system
multiple genes affecting a given trait
hindbrain structure that connects the brain and spinal cord; involved in regulating brain activity during sleep
positron emission tomography (PET) scan
involves injecting individuals with a mildly radioactive substance and monitoring changes in blood flow to different regions of the brain
prefrontal cortex
area in the frontal lobe responsible for higher-level cognitive functioning
psychotropic medication
drugs that treat psychiatric symptoms by restoring neurotransmitter balance
range of reaction
asserts our genes set the boundaries within which we can operate, and our environment interacts with the genes to determine where in that range we will fall
protein on the cell surface where neurotransmitters attach
recessive allele
allele whose phenotype will be expressed only if an individual is homozygous for that allele
resting potential
the state of readiness of a neuron membrane’s potential between signals
reticular formation
midbrain structure important in regulating the sleep/wake cycle, arousal, alertness, and motor activity
neurotransmitter is pumped back into the neuron that released it
semipermeable membrane
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
somatic nervous system
relays sensory and motor information to and from the CNS
somatosensory cortex
essential for processing sensory information from across the body, such as touch, temperature, and pain
substantia nigra
midbrain structure where dopamine is produced; involved in control of movement
(plural: sulci) depressions or grooves in the cerebral cortex
sympathetic nervous system
involved in stress-related activities and functions
synaptic cleft
small gap between two neurons where communication occurs
synaptic vesicle
storage site for neurotransmitters
temporal lobe
part of cerebral cortex associated with hearing, memory, emotion, and some aspects of language; contains primary auditory cortex
terminal button
axon terminal containing synaptic vesicles
sensory relay for the brain
theory of evolution by natural selection
states that organisms that are better suited for their environments will survive and reproduce compared to those that are poorly suited for their environments
threshold of excitation
level of charge in the membrane that causes the neuron to become active
secretes hormones that regulate growth, metabolism, and appetite
ventral tegmental area (VTA)
midbrain structure where dopamine is produced: associated with mood, reward, and addiction
Wernicke’s area
important for speech comprehension


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Introduction to Psychology Copyright © 2021 by Southern Alberta Institution of Technology (SAIT) is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

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