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I.
Composed of neural tissue, blood vessels, and connective tissue
A. The central nervous system is made up of the brain and spinal
cord
B. The Peripheral nervous system is made up of the nerves
C. Nerve tissue is made up of NEURONS(nerve cells) and
NEUROGLIA (supporting cells)
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2. Read General Functions of the Nervous System and take
notes.
B. Functional differences of neurons
1. SENSORY neurons carry impulses from body to the
brain via spinal cord.
2. INTERNEURONS form links between neurons by
directing sensory neurons to appropriate processing
regions or transferring impulses to motor neurons.
a. Found in brain and spinal cord
3. MOTOR neurons (efferent neurons) carry impulses
to EFFECTERS (muscles and glands).
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C. SCHWANN cells (neuroglia) surround
peripheral nerves fiber to make
MYELIN SHEATH (speeds up impulse
conduction).
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D. Astrocytes (neuroglia) are often
found between neurons and blood vessels. They support and
hold structures together, help metabolism of certain
substances, regulate ion concentrations, form scar tissue to
fill gaps in the brain caused by injury, and may
have a nutritive function.
E. OLIGODENDROCYTES form
myelin in the brain and spinal
cord. Unlike Schwann cells,
oligodendrocytes can myelinate
more than one axon.
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F. MICROGLIA are found in the CNS and help phagocytize
bacterial cells and cellular debris.
G. EPENDYMAL cells are ciliated and form the inner lining of
the central canal of the spinal cord. They also cover the
VENTRICLES of the brain. They help to circulate
cerebrospinal fluid.
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III. After injury, peripheral nerves are much more capable of
regeneration than nerves in the CNS.
IV. Cell membrane potential (potential
difference in charges)
A. Cell membranes are polarized
(charged) with a more positive
outside and negative inside.
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B. Results from Na+/K+ pump
C. K+ found intracellularly and Na+ found extracellularly.
V.
Resting potential (non-stimulated neuron)
A. Na+ and K+ diffuse. The outside is slightly positive because
the membrane is more permeable to Na+
B. ATP is used to pump Na+ and K+ (further charge separation)
C. Local potential changes
1.
Neurons get excited by stimuli, causing membrane gates
to open and ions to flow
a. HYPERPOLARIZATION (inside becomes more
negative)
or
b. DEPOLARIZATION (becomes more positive)
Changes depend on the intensity of the stimulus
2. If neurons depolarize enough, the membrane potential
reaches a THRESHOLD POTENTIAL and an ACTION
POTENTIAL will begin
a. Oftentimes SUMMATION (combined effects from
more than one stimulus) is needed for an action
potential.
VI. Action potential
A.
At resting, Na+ channels are closed. They open briefly
when the threshold is reached and increase Na+
permeability. Na+ rushes inward and intracellular fluid
becomes more positive (DEPOLARIZATION).
B.
Once a particular voltage is reached, gated Na+ ions close.
C. At the same time, slower gated K+ channels open. K+
diffuses outward and the neuron becomes negative
again (REPOLARIZATION).
D. Neuron remains in resting
potential until it is
stimulated again.
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E. Action potentials happen at the
axons, but not at the dendrites.
F. An action potential in one neuron
can stimulates the adjacent
neurons to its
threshold level.
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VII. Nerve impulses are all or none.
VIII. After a nerve impulse, there is a REFRACTORY period when
when a threshold stimulus will not trigger another impulse.
A. During the ABSOLUTE REFRACTORY PERIOD (last 1/12500
of a second) the membrane is changing in Na+ permeability
and cannot be stimulated.
B. A RELATIVE REFRACTORY PERIOD follows in which the
membrane is is finishing repolarization. Only a high intensity
stimulus will trigger an impulse.
IX. Speed of nerve impulses
A. Myelinated axons send messages more quickly than nonmyelinated ones.
B. Axons with greater diameter send impulses more quickly.
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X.
Nerve impulses pass from one neuron to the next at the
synapse.
A. There are SYNAPTIC KNOBS at the AXON TERMINALS full
of SYNAPTIC VESICLES.
1. Synaptic vesicles are full of
NEUROTRANSMITTER chemicals
that send signals from one neuron
to the next.
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A. When a nerve impulse reaches a synaptic
knob, voltage sensitive Ca+ channels
open as Ca+ flows inward. This causes synaptic vesicles to fuse
with the membrane and release neurtotransmitters that bind
with receptors on adjacent neurons.
B. Endocytosis eventually returns neurotransmitters to the
cytoplasm.
1. Enzymes may break down neurotransmitters to stop
signal transmission.
2. Some neurotransmitters are taken back to the synaptic
knob in a process called reuptake.
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I.
The central nervous system - brain and spinal cord
connected by brainstem.
A. The organs of the central
nervous system are surrounded
by bones, membranes, and fluid
that offer protection.
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II., The spinal cord is continuous with the brain.
A.
III.
Each of its 31 segments gives rise to a pair of spinal nerves
(communication).
The CEREBRUM
A. Largest part of the brain.
B. Made of two CEREBRAL
HEMISPHERES connected by a bridge of nerve fibers called
the CORPUS
CALLOSUM
C. The cerebrum provides higher brain
functions: interpreting impulses from
sense organs, initiating voluntary
muscular movements, storing information
as memory, and retrieving this
information in reasoning.
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D. Lobes of the cerebral hemispheres are named for the
underling bones (FRONTAL, PARIETAL, TEMPORAL,
OCCIPITAL, INSULA)
1. In the frontal lobe: concentrating, planning, complex
problem solving, emotional behavior and realization
of consequences.
2. In the parietal lobes: understand speech and reading,
store memories of visual scenes, music, and other
complex sensory patterns.
3. In the occipital lobes: analysis of visual patterns and
recognition.
4. The WERNICKE’S AREA, where the parietal, temporal,
and occipital association areas join, plays the primary role
in complex thought processes
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1. Although both cerebral hemispheres participate in basic
functions, most people have a dominant hemisphere.
IV. The BASAL NUCLEI deep in the cerebral hemisphere inhibits
dopamine to inhibit muscular functions.
V.
The DIENCEPHALON is located between the cerebrum and the
brainstem and is made up of the THALAMUS,
HYPOTHALAMUS, and the PINEAL and PITUITARY gland.
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A. The thalamus is a selective gateway for sensory impulses. It
acts as both a messenger and an editor.
B. The hypothalamus maintains homeostasis by regulating heart
rate and blood pressure, body temperature, water and
electrolyte balance, control of hunger and body weight,
control of movements and secretions of the intestines and
stomach, sleep and wakefulness, and production of
substances that stimulate the pituitary gland.
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VI. The LIMBIC SYSTEM is made of parts of
the diencephalon, hypothalamus, thalamus,
basal nuclei, and cerebrum and controls
emotional experiences and expression.
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VII. The BRAINSTEM connects the brain to
the spinal cord and is made of the
MIDBRAIN, PONS, and MEDULLA OBLONGATA.
A. The midbrain has reflex centers.
B. The pons transmits impulses from the cerebrum to centers
within the CEREBELLUM.
C. The medulla oblongata controls heart
rate, regulation of smooth muscles,
and rate, rhythm, and depth of
breathing.
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X.
A complex network of nerves called the RETICULAR
FORMATION extends throughout the medeulla oblongata,
pons, and midbrain. When it gets stimulated, it cause the
cerebral cortex to “wakeup”.
XI. The cerebellum coordinates skeletal muscles and maintains
balance.
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