PSY-150//Withrows
September 7, 2003
Chapter Two Notes:
Neurons: Found in brain and
nervous system. Individual cells specialized to receive and transmit
information. Different from other cells by the tiny fibers that extend from the
cell body that are called dendrites. Dendrites pick up incoming messages from
other neurons and transmits them to the cell body. The axon is a single long
fiber that extends form the cell body that carries outgoing messages. A group
of axons bundled together make up a nerve. The myelin sheath is a white fatty
covering made up of glial cells found on some axons, which provides insulation
and also increases the speed at which signals are transmitted. Neurons that
collect messages from sense organs and carry those messages to the spinal cord
or brain are called sensory neurons or afferent neurons. Neurons that carry
messages from the spinal cord or brain to the muscles and glands are motor neurons
or association neurons.
When a neuron is
at rest, the membrane around the cell forms a partial barrier between the
fluids that are inside and outside of the cell. The resting potential of a
neuron is when an electrical charge across the membrane results from more
positive ions is on the outside and more negative ions are in the inside. A
neuron is polarized when the electric charge on the inside is negative relative
to the outside. To generate a neuron’s signal. The tension of polarization must
be released. When the membrane is depolarized, the incoming message is strong
enough to change the electrical imbalance, which is called action potential or
neural impulse, the firing of the nerve cell. Graded potential is a shift in
the electrical charge caused by incoming messages. The neuron’s threshold of
excitement is the level an impulse must exceed to cause a neuron to fire. The
all-or-none law is a principle that the action potential in a neuron does not
vary in strength. Either the neuron fires at full strength or it does not fire
at all. Neurons are separated by a tiny gap called a synaptic space. The
synapse is composed of the axon terminals of one neuron, the synaptic space,
the dendrites, and the cell body of the next neuron.
When a neuron fires, an impulse
travels down the axon and out of the axon terminals into the terminal button.
The terminal button is made up of tiny sacs that release chemicals into the
synapse. These chemicals are called neurotransmitters. Each neurotransmitter
goes to specific receptor sites to ensure that they do not stimulate other
neurons. Examples of neurotransmitters: Dopamine, Serotonin, and Endorphines.
Neurotransmitters affect a wide range of physical and emotional responses.
Neural plasticity is the
brain’s ability to change in response to experience.
The central nervous system
consists of the brain and the spinal cord. The peripheral nervous system
connects the central nervous system to the rest of the body.
Three Areas of the Brain
1. Hindbrain: Earliest part of the brain to evolve.
Contains the medulla, pons, and cerebellum. The medulla controls bodily
functions like blood pressure, breathing, heart rate. Pons regulate sleep-wake
cycles. Cerebellum controls certain reflexes and body movements. There is also
the midbrain region above the cerebellum that is responsible for hearing,
sight, and pain registration. The thalamus, in the forebrain, relays and
transmits messages from the sense receptors with the exception of smell. The
hypothalamus is the forebrain region that governs motivation and emotional
responses.
2. The cerebral cortex regulates the most complex
behavior, is the outer surface of the two cerebral hemispheres. The cerebral
cortex consists of four lobes: frontal lobe (coordinates messages from other
cerebral lobes, involved in complex problem-solving tasks), Parietal lobe
(receives sensory information from all over the body and also involved in
spatial abilities), temporal lobe (involved in complex visual tasks, balance,
emotions, and plays strong role in understanding language), and the occipital
lobe (receives and processes visual information.
3. The limbic system is a ring of structures that play a
role in learning and emotional behavior. Is fully developed only in mammals.
Includes hippocampus that is essential in formation of new memories. Also parts
of limbic system heightens experience of pleasure and coordinates nervous
system’s response to stress.
The primary connection
between the left and right hemispheres is a thick band of nerve fibers called
corpus callosum. It permits the exchange of information between the two
hemispheres. The left hemisphere controls writing and the right side of the
body, is dominant in language and tasks involving symbolic reasoning. The right
hemisphere controls touch and the movement of the left side of the body. It is
generally superior in nonverbal, visual, and spatial tasks.
Tools for studying the brain:
microelectrode techniques, macroelectrode techniques (EEG), structural imaging
(CT scanning, MRI), and functional imaging (EEG imaging, MEG, MSI).
The spinal cord is the body’s
information superhighway and connects the brain to most of the rest of the
body. Two major neural pathways in the spinal cord: One consists of motor
neurons, descending from the brain that controls internal organs and muscles
and help regulate the autonomic nervous system. The other pathway consists of
ascending, sensory neurons that carry information from the extremities and
internal organs to the brain.
The Peripheral Nervous
System: Links the brain and the spinal cord to the rest of the body. It
consists of afferent neurons (carries messages from sense organs to spinal cord
or brain) and efferent neurons (carries message from spinal cord or brain to
muscles and glands). The somatic nervous system is part of the PNS that carries
messages from the senses to the central nervous system and between the central
nervous system and the skeletal muscles. The autonomic nervous system is part
of the PNS that carries messages between the central nervous system and the
internal organs and is also has important role in emotions.
The autonomic nervous system
is divided into two parts. The sympathetic division prepares the body for quick
action in an emergency connecting its nerve fibers to every internal organ. The
parasympathetic division calms and relaxes the body. These nerve fibers are
connected to the same internal organs and calm the body once the threat has
passed.
The Endocrine System:
Endocrine glands release
chemical substances called hormones that are carried through the body via the
bloodstream. Hormones help regulate bodily activities similar to
neurotransmitters. At first stages of development, hormones organize the
nervous system and body tissues. Hormones activate behaviors.
The thyroid gland is located
below the voice box and produces the hormone thyroxin that regulates the body’s
metabolism. Parathyroids are four tiny glands embedded in the thyroid that
secretes parathormone, influencing levels of excitability. The pineal gland is
located roughly in the center of the brain and appears to regulate activity
levels (sleep-wake cycles) over the course of the day with the hormone,
melatonin. The pancreas is an organ that lies between the stomach and the small
intestine that secretes insulin and glucagon to regulate blood-sugar levels.
The pituitary gland is located on the underside of the brain that produces the
largest number of the body’s hormones having the largest effect on the body’s
functions. Gonads are the reproductive glands. Gonads secrete the hormones
androgens and estrogen (produced in both male and female but at different
levels) which play an number of important organizing roles in human
development. There are two adrenal glands located just above the kidneys that
affect the body’s reaction to stress. The adrenal glands are composed of two
parts, the outer covering called the adrenal cortex and the inner core called
the adrenal medulla. The hormone epinephrine is secreted by the adrenal glands
which amplifies the effects of the sympathetic nervous system.
Behavior genetics is the
study of the relationship between hereditary and behavior. Evolutionary
psychology is a subfield of psychology concerned with the origins of behavior
and mental processes, the adaptive value, and the purposes they continue to
serve. Genetics is the study of how traits are transmitted from one generation
to the next. Genes are elements that control the transmission of traits and are
found on chromosomes. Chromosomes are pairs of threadlike bodies within the
cell nucleus that contains genes. DNA, or deoxyribonucleic acid, is a complex
molecule in a double-helix configuration that is the main ingredient of
chromosomes and genes and that forms the code for all genetic information. The
human genome is the fill complement of genes within a human cell. A dominant
gene is a member of a gene pair that controls the appearance of a certain
trait. A recessive gene is a member of a gene pair that can control the
appearance of a certain trait only if it is paired with another recessive gene.
The process by which several genes interact to produce a certain trait is
called polygenic influence and is responsible for our most important traits.
Behavior genetics is the
study of the relationship between genetics and behavior. There are a number of
ways to study behavioral techniques indirectly:
·
Family studies: Studies
of heritability in humans based on the assumption that genes influence a
certain trait, close relatives should be more similar in traits than distant
relatives.
·
Twin studies: Studies of
identical and fraternal twins to determine the relative influence of heredity
and environment on human behavior.
·
Adoption studies:
Research carried out on children, adopted at birth by parents not related to
them, to determine the relative influence of heredity and environment on human
behavior.
Molecular genetics: The human
genome is the complete set of genes within a human cell that defines a human
being.
Natural Selection: The key to
explain the behavioral traits that people have in common. The mechanism
proposed by Charles Darwin in his theory of evolution, which states that
organisms best adapted to their environment tend to survive, transmitting their
genetic characteristics to succeeding generations, whereas organisms with less
adaptive characteristics tend to vanish from earth.
