Download I. How Do Scientists Study the Nervous System?

Chapter Summary/Lecture Organizer
Chapter 4 — Neuroscience
I.
II.
How Do Scientists Study the Nervous System?
A.
Neuroscientists use several methods to learn about brain anatomy and brain function
1.
Examining autopsy tissue
2.
Testing patients with localized brain damage
3.
Using electroencephalograms (EEGs) to assess brain activity
4.
Animal research
5.
Leisioning (surgical destruction of tissue)
6.
Neuroimaging
B.
Each method has its utility and weakness. Neuroimaging allows us to study brain
structures and functioning in a living person.
What Cells Make Up the Nervous System?
A.
The two major types of brain cells are neurons and glial cells.
B.
Neurons communicate with other cells by producing and sending electrochemical
signals.
1.
Dendrites extend from the cell body toward other neurons, and collect inputs
(neurotransmitters) from other neurons.
2.
Axons extend from the cell body toward the axon terminal.
C.
Three types of glial cells are: astroglia or astrocytes, oligodendroglia, and microglia.
Glial cells are involved in various functions, such as forming the blood-brain barrier
(astroglia or astrocytes), producing myelin sheaths (oligodendroglia), and clearing
the brain of debris (microglia).
III. How Do Neurons Work?
A.
Communication within a neuron occurs electrically by means of the action potential,
whereas communication between neurons occurs at the synapse via chemical signals
called neurotransmitters.
B.
Neurotransmitter molecules are released by synaptic vesicles in the terminals of the
presynaptic neuron, diffuse across the synapse and bind to receptors on the
postsynaptic site.
1.
Action potentials follow an all-or-none principle.
2.
After firing, the axon is unable to fire again no matter how strong a stimulus is
provided to the neuron (absolute refractory period).
C.
The response of a receiving neuron to a neurotransmitter is determined by the
receptor on the postsynaptic, or receiving, neuron’s membrane. Depending on the
postsynaptic potential of the receptor (excitatory or inhibitory), the postsynaptic
neurons will fire or not. Collections of neurons that communicate with one another
are referred to as neural circuits or neural networks.
IV. How Is the Nervous System Organized?
V.
A.
Two major divisions of the nervous system are the:
1.
central nervous system—consists of the brain and spinal cord
2.
peripheral nervous system—consists of nerves that extend throughout the body
outside the central nervous system
B.
The peripheral nervous system has two divisions:
1.
somatic nervous system — gathers information about the senses and movement
2.
autonomic nervous system — controls involuntary functions and responses to
stress
C.
The autonomic nervous system is divided into:
1.
sympathetic nervous system—responds to potentially life-threatening situations
2.
parasympathetic nervous system—responsible for digestion and other processes
that occur when the body is at rest
The Structure of the Brain
A.
The brain can be subdivided into many regions, each of which serves one or more
specialized functions.
1.
The brainstem participates in movement and sensation of the head and neck as
well as in basic bodily functions, such as respiration and heart rate. The raphe
nuclei in the reticular formation are major brain sources of the neurotransmitter
serotonin. Neurons in the locus coeruleus use norepinephrine and are important
for arousal and attention.
2.
The cerebellum is involved in motor coordination and some types of learning.
3.
The midbrain includes the substantia nigra, an area producing dopamine and
important for movement. Parkinson’s disease is a neurological disorder
involving impairment of dopamine in the substantia nigra region.
B.
The thalamus serves as a relay station for sensory information on its way to the
cerebral cortex.
1.
2.
Lateral geniculate nucleus (LGN)—relays information about visual stimuli
Medial geniculate nucleus (MGN)—relays information about auditory stimuli
C.
The hypothalamus controls basic drives (food, drink, sex) and stimulates the pituitary
gland (endocrine system) to release hormones (chemical messengers important for
growth, reproduction, metabolism, and stress).
1. The hypothalamus signals the anterior pituitary to activate peptides (chemicals
that can act as hormones themselves or that can work to stimulate the release of
hormones from other endocrine glands).
a.
The anterior pituitary produces releasing factors that control encodrine
glands such as the ovaries, testes, thyroid, and adrenal glands.
b.
Hypothalamus–Pituitary–Adrenal (HPA) axis—the interactive pathway
involved in the stress response.
2.
Activation of posterior pituitary releases hormones called neuropeptides (such
as oxytocin and vasopression) into the blood stream.
D.
The amygdala is involved in recognizing, learning about, and responding to stimuli
that induce fear.
E.
The hippocampus is involved in learning and memory, including storage of episodic
memories and storage of spatial navigational information, and shows plasticity and
neurogenesis.
F.
The striatum is involved in certain types of learning and memory that do not rquire
conscious awareness.
G.
The nucleus accumbens is involvedd in motivation and reward learning.
H.
Many brain regions participate in different types of learning - the hippocampus is
important for spatial navigation learning and learning about life’s events; the
amygdala is important for fear learning; the cerebellum and striatum for motor
learning and the nucleus accumbens for reward learning.
I.
A large part of the brain consists of the neocortex, which is responsible for our most
complex behaviors including language and thought. The neocortex can be subdivided
into regions or lobes with specialized functions: frontal lobe (planning and
movement, speech production, working memory, moral reasoning, mood regulation),
parietal lobe (touch, somatosensory stimuli processing, spatial relations), temporal
lobe (audition, language comprehension, facial recognition) and occipital lobe (visual
processing). The cortex controls movement, integrates sensory information, and
serves numerous cognitive functions.
J.
The corpus callosum is a bundle of axons connecting and allowing communication
between the two hemispheres of the brain. The corpus callosum is sometimes severed
to treat epilepsy.
VI. Building the Brain How We Develop
A.
Cellular processes that build the brain include:
1.
During the embryo stage, a neural tube is formed from layers of the ectoderm
2.
During cellular differentiation, neurogenesis occurs, producing new neurons,
and neuronal migration occurs in which axons extend and dendrite connections
are made. Toxic events (teratogens) may interrupt this cellular maturation
process.
3.
Synaptogenesis is the formation of new synaptic connections with other neurons
B.
Cellular processes that sculpt or fine-tune the brain are programmed cell death, axon
retraction, and synapse elimination. Myelination in humans occurs mostly after we
are born. Research with animals show that dendrites and synapses change in shape,
size and number throughout adult life.
VII. Brain Side and Brain Size How We Differ
A.
The strong popular bias about hemispheric differences (“right brain” vs. “left brain”)
is overstated. Research shows that the two hemispheres are more similar than
different and that any differences are usually relative. For most right-handed people,
Wernicke’s and Broca’s areas related to speech and language are found on the left
hemisphere, but these language areas are often located on the right side of the brain in
left-handed people.
B.
Although women’s brains are smaller in size than men’s, there is no relationship
between brain size and intelligence. Brain size appears to be related to overall body
size and not to brain function.
VIII. Neurological Diseases When Things Go Wrong
A.
Neurological illnesses are often due to structural brain problems involving
degeneration of neurons. Some key neurological diseases are:
1.
Multiple sclerosis involves the loss or myelin on the axons of neurons resulting
in inefficient neural transmission.
2.
In amyotrophic lateral sclerosis (ALS or Lou Gehrig’s disease), the motor
neurons in the spinal cord degenerate for unknown reasons.
3.
Parkinson’s disease is primarily the result of dopamine neuronal destruction in
the substantia nigra.
4.
Huntington’s disease is inherited and results in neuronal death in the striatum.
B.
Some regeneration occurs in the brain after it is injured, but repair is typically not
complete and functional impairment often remains. Researchers believe
transplantation of brain tissue, particularly embryonic stem cells, may provide relief
for some neurological diseases.