The Nervous System Flashcards

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 ___.

central nervous system

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


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

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 ___.


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 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.


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.


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.


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

gated ion channels

____-____ ____ 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 ____.

synaptic terminal

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
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).


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 ____ ____.

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

central canal
ventricles of the brain

The spinal cord conveys information from the brain to the ____
____ ____. A ____ is the body's automatic response to

peripheral nervous system