Nervous System
Worksheet 2.6
Supplemental Instruction
Iowa State University
Leader:
Course:
Instructor:
Date:
Hannah
A ECL 365
Dr. Waldman
10/12/15
1. The two major subdivisions of the nervous system are the _central__ and
_peripheral____ nervous system.
2. The basic cellular units of the nervous system are _neurons_. These cells possess two
different kinds of processes known as _dendrites___ and __axons___.
a. How do these compare in their function?
 Dendrites: branched, receive information
 Axons: long; carry info (impulses) away from the cell body
3. There are three main classes of neurons, what are they and their functions?
 Sensory (afferent) neurons sense the environment and take sensory
information to the CNS
 Interneurons (99% of all neurons) connect neurons together in CNS
(integrate info)
 Motor (efferent) neurons receive info from the CNS and takes it to effector
organs (e.g. muscles, glands) to elicit/trigger a response
4. Neurons communicate via nerve impulses. What are the characteristics of these impulses?
 Occur in response to a stimulus
 Produced by changes in membrane electrical potential
 All-or-none responses
 Stimulus intensity signaled by frequency of impulse (large stimulus = high
frequency—number of impulses increases, not 1 bigger action potential;
small stimulus = low frequency)
5. Describe how a nerve impulse is generated (e.g. changes from resting potential to an
action potential).
 Resting potential net positive charge outside and negative charge inside the
cell
o Membrane maintains high K+ inside axon and high Na+ outside axon
o At rest, membrane is more permeable to K+, less to Na+
o A Na+/K+ pump helps maintain membrane potential (2 K+ in, 3 Na+
out)
 Action potential rapid perturbation of the resting potential caused by a
stimulus
o Impulse started by opening Na+ permeable channels
o Na+ rushes into axon reversing polarity (depolarization)—now +
inside, - outside  then K+ moves out reestablishing the resting
potential
6. The bigger the axon, the ___faster__ (e.g. speed) the response.
7. Vertebrates increase the speed of impulse conduction by ___myelinating_____ axons.
In this way, charge propagates by __saltatory___ movement/conduction.
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8. A __synapse___ is a site where signals are transmitted from one cell to another (junction
sites). There are two kinds of these – name them and describe their function.
 1) Electrical charge flows across “gap-junctions” (between axon and
dendrite)
o No time lag (very fast)—good for escape reaction
 2) Chemical use neurotransmitters that diffuse from one membrane to the
other to propagate signal
9. Describe the sequence of signal transmission used in a chemical synapse.
 1) Action potential arrives at synapse
 2) Ca+ channels open and Ca+ rushes into cell
o Causes release of neurotransmitters into synaptic cleft
 3) Neurotransmitter binds to receptor in post-synaptic membrane (excites it)
 4) Postsynaptic action potential produced and propagated
 5) Neurotransmitter inactivated
 6) Resynthesized, returned, stored
10. Although brain size tends to _increase_ with body size, proportionally larger animals
tend to have relatively _smaller__ brains.
11. Certain parts of the brain are either reduced or well developed, depending on use. In
birds the ___optic____ lobes are enlarged (for great vision) while in mammals the
__olfactory____ lobe is very well developed.
12. True/False: Humans potentially have the ability to produce brain repair cells, as shown in
adult canaries and zebra finches.
13. Motor neurons can be part of two subdivisions, the __somatic___ nervous system
(skeletal muscles) or the __autonomic___ nervous system (other muscles and glands).
a. Most internal organs are innervated with two __antagonistic__ components of
the autonomic nervous system. If one speeds it up, the other slows it down. (Ex:
the control of the heart rate and respiratory rate in the parasympathetic—
decreases both—and sympathetic—increases both—nervous system)
14. __Reflex____ __arcs__ are critical for fast responses and use neurological feedback
loops to function. These involve only 2-3 neurons and by-pass the __brain__ for an even
faster result.
15. Different lobes of the brain are shown to have different functions in the body. Match the
following functions to the correct lobes. (May be more than one right answer)
Speech_A, B___
Motor cortex __A___
Hearing __D______
Taste _B___
Smell ___D__
Vision ___C____
Reading __B____
A) Frontal lobe
B) Parietal lobe
C) Occipital lobe
D) Temporal lobe
1060 Hixson-Lied Student Success Center  515-294-6624  sistaff@iastate.edu  http://www.si.iastate.edu