Bilaterally symmetrical animals exhibit ____: clustering of
sensory organs at the front end of the body. Even
relatively simple cephalized animals, such as flat worms, have a ___
___ ___. Annelids and arthropods have segmentally arranged
clusters of neurons called ___.
cephalization
central nervous system
ganglia
The ____ division correlates with the
"fight-or-flight" response. The ____ division
promotes a return to "rest and digest". The ____
division controls activity of the digestive tract, pancreas, and
gallbladder.
sympathetic
parasympathetic
enteric
The ___ ___ carries signals to skeletal muscles and is
voluntary. The ___ ___ ___ regulates internal environment in
an involuntary manner.
motor system
autonomic nervous system
____ ____: originates in the brain and generally terminate in organs
of the head and upper body.
____ ____: originates in the spinal cord and extends to body parts
below the head.
cranial nerves
spinal nerves
The simplest animals with nervous systems, cnidarians, have
neurons arranged in ____ ____ (interconnected nerve cells).
More complex animals have ____, which are bundles of axons.
nerve nets
nerves
A neuron can produce ___ of action potentials per second.
Although each action potential is all-or-none, the frequency of
action potentials can reflect strength of a ___.
hundreds
stimulas
The presynaptic neuron synthesizes and packages the
neurotransmitter in ____ ____ located in the ____ terminal.
The action potential causes the release of the
neurotransmitter. The neurotransmitter diffuses across the
____ ____ and is received by the postsynaptic cell.
synaptic vesicles
synaptic
synaptic cleft
The PNS transmits information to and from the CNS, and
regulates movement and internal environment. ____ neurons
transmit information to the CNS, while ____ neurons transmit
information away from the CNS.
afferent
efferent
If a stimulus causes the membrane voltage to cross a critical
____, a huge spike in membrane voltage results. An action
potential is this brief all-or-none major depolarization of a
neuron's plasma membrane. Once generated, an action
potential moves along an axon from hillock to terminal(s),
constituting a signal from one place to another.
threshold
Other stimuli trigger a ____, a reduction in the magnitude of
the membrane potential. This brings the neuron closer to
the threshold at which a nerve impulse is generated.
depolarization
Neurons contain ____ ____ ____ that open or close in response
to stimuli. This is ____, which moves the membrane
potential further away from the threshold (less ready to generate an
impulse).
gated ion channels
hyperpolarization
____-____ ____ use the energy of ATP to maintain these K+ and
Na+ gradients across the plasma membrane. These
concentration gradients represent chemical ____ ____.
sodium-potassium pumps
potential energy
A ____ is a junction between an axon and another cell.
The ____ ____ of one axon passes information across the synapse
in the form of chemical messengers called ____.
synapse
synaptic terminal
neurotransmitters
Most of a neuron's organelles are in the ____ ____.
Most neurons have ____, highly branched extensions that receive
signals from other neurons. The ____ is typically a much
longer extension that transmits signals to other cells at
synapses. An axon joins the cell body at the ____.
cell body
dendrites
axon
axon hillock
____ are nerve cells that transfer information within the
body. ____ use two types of signals to communicate: ____
signals (long-distance) and ____ signals (short-distance).
neurons
electrical
chemical
At ____ ____, the electrical current flows from one neuron to
another. At ____ ____, a chemical neurotransmitter carries
information across the gap junction.
electrical synapses
chemical synapses
Axons of vertebrates are insulated by a ____ ____, which causes
an action potential's speed to increase. Action potentials
are formed only at ____ of ____, gaps in the myelin sheath where
voltage-gated Na+ channels are found. Action potentials in
myelinated axons jump between the nodes of Ranvier in a process
called ____ ____.
myelin sheath
nodes of Ranvier
saltatory conduction
An action-potential can travel long distances by regenerating
itself along the ____. Once generated, the action potential
depolarizes neighboring regions of the axon membrane, causing it to
spread like a wave. However, action potentials travel only
one way: toward the ____ terminals, due to the ____ ____.
axon
synaptic
refractory period
During the very brief ____ ____ after an action potential, a second
action potential cannot be initiated.
refractory period
The brain and spinal cord contain,
- ____ ____: consists of neuron cell bodies, dendrites, and
unmyelinated axons.
- ____ ____: consists of bundles of myelinated axons.
gray matter
white matter
The ____ ____ of the spinal cord and the ____ of the ____ are
hollow and filled with ____ fluid. The ____ fluid is
filtered from blood, and functions to cushion the brain and spinal
cord.
central canal
ventricles of the brain
cerebrospinal
cerebrospinal
The spinal cord conveys information from the brain to the ____
____ ____. A ____ is the body's automatic response to
stimulus.
peripheral nervous system
reflex