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Biol 221 Worksheet
Nervous System I
Organization, Cells, & Physiology
I. Nervous System Functions
List the three basic functions carried out within the nervous system
1. _____________________________________
2. _____________________________________
3. _____________________________________
Which of these functions controls muscles & glands?
_________________________________________
Which monitors the environment?
_________________________________________
Which makes decisions regarding appropriate responses to sensory
information?
_________________________________________
II. Nervous System Structural Subdivisions (based on location &
structure)
The brain and the spinal cord belong to the ________________(CNS/PNS).
Nerves belong to the _________________(CNS/PNS). Sensory and motor
functions are carried out by the _______________(CNS/PNS). Integration
of sensory and motor functions occurs in the ______________(CNS/PNS).
III. Peripheral Nervous System (PNS)
A. Two Functional Divisions of the PNS
The PNS can be subdivided into two functional divisions;
_______________________ (Sensory/Motor) that carries information
towards the CNS, and ________________________(Sensory/Motor) that
carries commands away from the CNS. Sensory information is
carried toward the CNS by ____________________(afferent/efferent)
fibers (i.e. axons). Motor commands are carried away from the
CNS by ____________________(afferent/efferent) fibers.
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B. Sensory/Afferent Division of the PNS
The sensory division of the PNS is further subdivided into Somatic
Sensory and Visceral Sensory. Both of these sensory divisions of
the PNS are ________________ (afferent/efferent). The Somatic
Sensory division carries information to the CNS from
________________________________________________________________________.
The Visceral Sensory division of the PNS carries information to
the CNS from ____________________________________________________________.
C. Motor/Efferent Division of the PNS
The motor division of the PNS is further subdivided into the
Somatic Nervous System (SNS) and the Autonomic Nervous
System (ANS). Both of these motor divisions of the PNS are
__________________(afferent/efferent). The Somatic Nervous System
________________________ (voluntarily/involuntarily) controls
____________________ muscles. The Autonomic Nervous System
________________________ (voluntarily/involuntarily) controls
_________________ muscle, ________________ muscle, and _________________.
D. Autonomic Nervous System Branches
Both branches of the ANS are motor/efferent in function and
involuntarily control the same organs but with opposite effects;
therefore, they are ___________________________ to one another.
Also known as the housekeeping branch, the _______________________
(Sympathetic/Parasympathetic) branch maximizes growth,
healing, and digestion. This branch of the ANS originates from
_____________________________ regions of the CNS, and is relative
energy _______________________________(costly/conservative).
Commonly referred to as the fight or flight branch, the
_______________________ (Sympathetic/Parasympathetic) branch
readies the body to respond to an immediate and serious threat.
This branch of the ANS originates from _____________________________
regions of the spinal cord, and is relative energy
____________________________ (costly/conservative).
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IV. Neurons
Neurons are the basic functional cell of the nervous system, and are
highly specialized to conduct nerve impulses.
A. Neuron Anatomy
There are three basic parts to a neuron. The ___________________ is
where the nucleus and many other organelles are found.
___________________ (dendrites/axons) are numerous, shorter and
highly branched _____________________ (afferent/efferent) processes
that arise from the cell body. ________________(dendrites/axons) are
singular, long __________________(afferent/efferent) processes that
originate at the axon hillock of the cell body. Axons may have
branches called _________________________, but all axons have
numerous branches at their ends called ______________
_____________________________. Changes in organelles reflect the special
needs of these cells, for example ___________________ help reinforce
from within, and _____________ bodies are specialized forms of
rough endoplasmic reticula.
B. Structural Classification of Neurons
The structural approach to classifying (naming) neurons is based
on simply counting the total number of processes that arise
directly from the cell body (sum of dendrites and axon). A neuron
with just one attached process is called ______________________________;
a neuron with two attached processes is called
__________________________, and a neuron with more than two total
processes is called __________________________________________________.
C. Functional Classification of Neurons
The functional approach to classifying neurons is based on the
direction in which the cell transmits relative to the CNS.
Neurons that carry information from receptors toward the CNS
are __________________________ sensory/motor neurons, and are also
known as _____________________________ (afferent/efferent) neurons.
Neurons that carry information away from the CNS to effectors are
__________________________ sensory/motor neurons, and are also
known as _____________________________ (afferent/efferent) neurons.
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V. Neuroglia
Neuroglia are diverse cells of the nervous system that retain the
ability to mitotically divide.
Match the glial cell to its location and function(s). Each organelle will
have more than one correct answer, and locations may apply to more
than one type of glial cell.
_____________Astrocyte
_____________Ependymal cell
_____________Microglial cell
_____________Oligodendrocyte
_____________Satellite cell
_____________Schwann cell
a. PNS
b. CNS
c. Myelinates part of one
axon
d. Myelinates multiple axons
e. phagocyte
f. helps form the blood-brain
barrier
g. lines ventricles
h. protects & cushions
ganglia
i. links blood vessels &
neurons
j. derived from white blood
cells
k. derived from epithelial
cells
l. produces & helps circulate
CSF
VI. Neuron Physiology
A. Myelination
A ________________ sheath forms when a Schwann cell or part of an
oligodendrocyte repeatedly wraps an ____________ (axon/dendrite).
Myelinated axons conduct _________________________ (faster/slower)
than non-myelinated axons. Most axons are
___________________________(myelinated/non-myelinated).
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Oligodendrocytes myelinate axons in the ______________ (PNS/CNS),
and Schwann cells myelinate axons in the ______________ (PNS/CNS).
Nodes of Ranvier (also called neurofibril nodes) are locations
along a myelinated axon where there is no ______________________.
Because the entire cell wraps the axon when Schwann cells are
involved, a ___________________________ forms external to the myelin
sheath.
B. Resting Membrane Potential
Prior to carrying a nerve impulse, a neuron’s cell membrane must
first be ______________________(polarized/depolarized). This is caused
by the sodium potassium pump forcing high numbers of sodium
ions _________________ (outside/inside) the neuron and large
numbers of potassium ions _______________________(outside/inside)
the neuron. The resultant measureable difference in charge across
the resting neuron’s cell membrane is called its’ _____________________
__________________________ ___________________________.
C. Conduction of a Nerve Impulse along a Neuron
First, an appropriate _________________________ stimulus opens ________
(Na+/K+) channels in the neuron’s cell membrane. The cell
membrane ______________________________ (depolarizes/repolarizes)
as ___________ (Na+/K+) flows __________________ (into/out of) the
neuron, along its entire length from __________________________
(dendrite/axon) to ___________________(dendrite/axon).
Shortly after they open, ______________(Na+/K+) channels close and
________________(Na+/K+) channels ______________(open/close). The
cell membrane then ________________________________________
(depolarizes/repolarizes) as ___________ (Na+/K+) flows
__________________ (into/out of) the neuron, along its entire length
from _______________________ (dendrite/axon) to __________________
(dendrite/axon).
Neurons must repolarize before they can be successfully restimulated to conduct. The time required to repolarize a neuron
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before it can generate another action potential is called the
__________________________________ period.
Neurons will either respond to a stimulus by first depolarizing
then repolarizing (this is a nerve impulse, also called an action
potential), or by not responding with an action potential. There is
no partial action potential. This is called the __________ or _________
Principle.
D. Types of Conduction
When successfully stimulated, unmyelinated neurons are capable
of ___________________________(continuous/saltatory) conduction. In
this type of conduction all of the ions channels for first Na+ then K+
must open then close in sequence along the entire length of the
cell membrane. This results in a relative ________________
(slower/faster) rate of conduction.
In contract, myelinated neurons are capable of
___________________________(continuous/saltatory) conduction. In this
type of conduction only ions channels for first Na+ then K+ must
open then close at nodes of Ranvier. In this type of conduction, the
action potential seems to leap from node-to-node; this is a much
________________ (slower/faster) rate of conduction.
E. Synaptic Transmission
Once an action potential arrives at the end of a presynaptic axon,
the axon terminals (or synaptic knobs if present)
_______________________ (depolarize/repolarize).
This change triggers opening of ion channels that allow
______________(Ca2+/Na+/K+) to _____________ (enter/exit) the
presynaptic neuron. The influx of this ion causes
______________________________ (endocytosis/exocytosis) of synaptic
vesicles, releasing neurotransmitter molecules.
The Neurotransmitters diffuse across the ___________________
______________ and bind to _______________________________ on the
postsynaptic cell membrane, opening _____________ (Na+/K+)
channels. If enough ____________ (Na+/K+) flows ________________
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(into/out of) the neuron, then it will __________________________________
(depolarize/repolarize), and an action potential will occur.
F. Neurotransmitters
Neurotransmitters that raise the threshold of a neuron, making it
more difficult to stimulate a neuron to generate an action
potential, are called _________________ (excitatory/inhibitory)
neurotransmitters. For example, if a neurotransmitter opens a K+
channel, then K+ will flow out of the cell, making it even more
_____________(positive/negative) outside, thereby raising the resting
membrane potential. This is called hyperpolarization. Likewise, if
a neurotransmitter opens a Cl- channel then Cl- will flow into the
cell, making it more _____________(positive/negative) inside, thereby
hyperpolarizing the membrane.
In contrast, neurotransmitters that open Na+ channels in the
membrane, may cause the membrane to depolarize.
Neurotransmitters that do this are called _________________________
(excitatory/inhibitory).
List the three ways that neurotransmitters are removed from the
synapse:
1. __________________________________________
2. __________________________________________
3. __________________________________________
G. Sensory Receptors
Receptors are always located in the ______(CNS/PNS), always
perform a __________________(sensory/motor) function, and respond
only to specific stimuli.
List the three basic types of receptors (based on structural
complexity) and either give examples of the various stimuli to
which they respond, or give an example of their name.
1. ________________________________________________________________________
2. ________________________________________________________________________
3. ________________________________________________________________________
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H. Where are neuron cell bodies located in the nervous system?
A group of neuron cell bodies in the __________(CNS/PNS) is called a
ganglion.
A cluster of neuron cell bodies in the ___________ (CNS/PNS) is
called a nucleus.
The cell bodies of sensory/afferent neurons are always located in
the (CNS/PNS) and are found in ___________________ (ganglia/nuclei),
or in special sense organs.
The cell bodies of interneurons are always located in the _________
(CNS/PNS) in either gray matter or in nuclei.
The cell bodies of some motor neurons are located in gray matter
in the ________ (CNS/PNS), while the cell bodies of other motor
neurons may be found in ganglia in the (CNS/PNS).
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