BCLN BIOLOGY 12 – Rev July 2014
Unit 12 ~ Learning Guide
Name:________________
INSTRUCTIONS
Complete the following notes and questions as you work through the related lessons.
You are required to have this package completed BEFORE you write your unit test. Do
your best and ask questions about anything that you don't understand BEFORE you
write the unit test.
U12 NOTES: NERVOUS SYSTEM (web notes and video)
Structures and Functions
1. Dendrites
 ______________________
______________________
______________________
______________________
 Many dendrites enter a cell
body.

2. Cell Body
 Contains the nucleus and
cell organelles __________
______________________
______________________
 Only a single axon leaves a
cell body.
 Relays impulse from
______________________
______________________
3. Axons
 Conducts a nerve impulse ___________________________________
_______________________.
4. Myelin Sheath
 Protective coating of Schwann Cells around larger axons and dendrites
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BCLN BIOLOGY 12 – Rev July 2014
5. Nodes of Ranvier
 ______________________________(not coated) on the Myelin Sheath.
 ______________________ transmission of impulse.
6. Motor End Plates
 In close proximity to muscles and organs.
 From here the impulse is chemically transported to the organs.
7. Ganglia
 A collection of cell bodies outside of the Central Nervous System.
Types of Neurons
1. Motor Neuron
 ___________________________: Moving toward a central organ or point.
 Relays messages from the _____________________________________
____________________ to the _________________________________.
2. Sensory Neuron
 ______________________________: Moving away from a central organ
or point.
 Relays messages from _______________________________________
__________________________________________________________.
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3. Interneuron (associated neuron or Connector Neuron)
 Relays message from _________________________________________
__________________________________________________________.
 Make up the brain and spinal cord.
**A Nerve is composed of long fibers of a number of Neurons**
YOU SHOULD WATCH THE TYPES OF NEURONS
VIDEO BEFORE PROCEEDING ANY FURTHER!
Impulse Generation
Nerve impulses are ______________
__________________. If we measure
the voltage of a resting neuron using
a voltmeter, we will see a reading of
__________________. Voltage is a
comparison of electrical charge
between two points.
When the neuron is stimulated, the
charge
changes
briefly
to
__________ (mv), then back to
____________ (mv).
If we hook up our voltmeter to a
machine
called
an
_______________________, we can see the change in voltage over a period of time.
There is a difference in ion distribution on either side of the membrane of a neuron.
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BCLN BIOLOGY 12 – Rev July 2014
At rest


____________________________________________________________
____________________________________________________________
____________________________________________________________
Because of the large negative molecules, the inside is more negative than the outside.
(-65mv means that the inside is -65mv more negative than outside). This situation is
called Resting Potential. -65mv
When the axon or dendrite is stimulated,
___________________________________ which
allows some ______________________________
____________________ (interior). Now, the inside
becomes more positive than the outside by
___________.
This is called the ________________________ of
the
action
potential.
The
charge
is
called___________________________. After the
sodium gates have opened, the _____________
_____________________ and _____________
______________________.
This is called the _________________________
of the action potential. The charge returns to
_________.
The
change
is
called
___________________________.
***Note: Charge is back to normal, but there is a problem, the Na+ and K+
_______________________________.***
Finally, there is a ______________________________________________ in which the
____________________________________ (ACTIVE TRANSPORT) ____________
__________________________________________________________ of the neuron.
The neuron is at now at rest and ready to fire again. The concentration gradient in a
neuron at rest must be continually maintained by the sodium potassium pump since
there is continuous leakage of sodium and potassium down their concentration
gradients.
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BCLN BIOLOGY 12 – Rev July 2014
So far we have only been
looking at one point on the
Axon or Dendrite. The
depolarization of one point
in a neuron starts a chain
reaction down the length of
the neuron and the sodium
gates in the next area open.
We get a wave motion
(chain reaction) moving
down the nerve fiber.
YOU SHOULD WATCH THE IMPULSE GENERATION
VIDEO BEFORE PROCEEDING ANY FURTHER!
Summary
1. RESTING POTENTIAL
 Charge is ______________
 __________________________________
 __________________________________
2. UPSWING OF ACTION POTENTIAL
 ___________________________________________________________
 ___________________________________________________________
 ___________________________________________________________
 ___________________________________________________________
3. DOWNSWING OF ACTION POTENTIAL
 ___________________________________________________________
 ___________________________________________________________
 ___________________________________________________________
 ___________________________________________________________
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BCLN BIOLOGY 12 – Rev July 2014
4. RECOVERY PHASE
 ___________________________________________________________
___________________________________________________________
 ___________________________________________________________
___________________________________________________________
 ___________________________________________________________
___________________________________________________________
***NOW NEURON CAN BE RESTIMULATED***
**REMEMBER THIS IS A WAVE MOTION DOWN THE NEURON**
Myelinated versos Unmyelinated
Fibers
____________________________ wrap
around the nerve fibers when they are
myelinated. This results in the impulse
skipping from node to node.
In myelinated axons and dendrites, the
impulse can travel up to 200m/s. In
unmyelinated fibers, the impulse can be
as slow as 0.5 m/s.
This difference in speed is because the
action potential is able to jump over the
myelin sheath. Depolarization only occurs
at the nodes of Ranvier.
Synapse
Each axon branches off and ends with a
swelled tip or ______________________
which lies close to but not touching the
dendrite of another neuron (or an organ). The
entire region is called a __________________.
Transmission of nerve impulses across a
Synaptic clef is carried out by chemicals called
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BCLN BIOLOGY 12 – Rev July 2014
_____________________________________. These substances are stored in vesicles
at the end of the axon. ___________________________________________________
___________________ and ____________________________________________
_________________________ are examples of neurotransmitters.
When an impulse reaches the end of the axon like it usually would, not only does Na+
come into the axon but _______ as well. This calcium bind with
_________________________________ that _________________________________
____________________________________________________. The vesicles join with
the
cell membrane, forcing the neurotransmitter into
the cleft by
__________________________. The neurotransmitter _________________________
___________________________________________.
The neurotransmitter's job is to increase the _________________________
___________________________ on the ____________________________________.
The Neurotransmitter binds to ___________________________________ on the
dendrite of the next neuron. If enough transmitter substance is received, the
_________________________________________________ and continue the impulse.
A _______________________ only has a ____________________________________
once it has been released into the ______________________________.
__________________ rapidly ____________________________________________
_____________________ substance to _________________________________ so
the next impulse can be transmitted. _______________________________ breaks
down _____________________________ and _____________________________
breaks down ________________________________.
Painkillers such as Tylenol act as an enzyme to break down the neurotransmitter to
decrease the pain impulse.
***ALL OR NONE RESPONSE (Threshold)***.
If enough neurotransmitter is received by the postsynaptic fiber, it will fire _________
(ALL) If not enough substance is received, it will _______________________________
(NOTHING).
There are excitatory and inhibitory neurotransmitters in the body. When two excitatory
neurotransmitters work together to cause an action potential, it is called summation.
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BCLN BIOLOGY 12 – Rev July 2014
YOU SHOULD WATCH THE SYNAPSE
VIDEO BEFORE PROCEEDING ANY FURTHER!
Reflex Arc
Reflexes are _____________
_______________________
______________ to changes
occurring inside or outside
the body. Some involve the
________________ (such as
blinking the eye), while
others do not (such as
moving your hand away from
a hot object). Why does the
brain not have to be
involved? If it were, by the
time the impulse traveled to
the brain, the brain figured
out what was happening, and
sent a response to the body,
____________________________________________________.
So the body evolved a method of bypassing the brain
1. ________________________________________________________________
___________________________________ i.e., nerve impulse
2. ________________________________________________________________
__________________________________ (spinal cord).
3. ________________________________________________________________
__________________________________
4. ________________________________________________________________
_________________________________ (muscle/organ).
5. ________________________________________________________________
_________________________________.
***The brain finds out later what had happened***
***Reflexes, however can be controlled.***
YOU SHOULD WATCH THE REFLEX
VIDEO BEFORE PROCEEDING ANY FURTHER!
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BCLN BIOLOGY 12 – Rev July 2014
U12 PRACTICE: NERVOUS SYSTEM
1. Draw and label a myelinated neuron showing the cell body, dendrite, axon, axon
terminal, Schwann cells and Nodes of Ranvier. Provide a brief description of the
function of each labeled structure beside its label. Please be neat! (12 marks)
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BCLN BIOLOGY 12 – Rev July 2014
2. Below is a diagram of a reflex arc:
a. Label each cell as either an interneuron, motor neuron or sensory neuron.
(3 marks)
b. Using arrows, indicate the direction of nerve impulse through each neuron.
(1 mark)
c. Label the receptor end of the sensory neuron, the dendrite and axon. (2
marks)
d. Label the effector (muscle/organ) of the motor neuron, the dendrite and
the axon. (2 marks)
Neuron
Neuron
Neuron
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BCLN BIOLOGY 12 – Rev July 2014
3. What is the purpose of a reflex arc? (2 marks)
4. Compare and contrast the functions of sensory neurons, motor neurons and
interneurons. (4 marks)
5. Identify the similarities and differences between the sensory neuron and motor
neuron. (2 marks)
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BCLN BIOLOGY 12 – Rev July 2014
6. What is meant when it is said that the electrical impulse of a neuron is an "all-ornothing" event? Please include the term "threshold" in your explanation. (2
marks)
7. Label the following diagram of an Action Potential. (8 marks):
o repolarization
o depolarization
o resting potential (label
twice)
o threshold potential
o recovery
o membrane Potential
(mV)
o time (mS)
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BCLN BIOLOGY 12 – Rev July 2014
8. When a neuron is not sending an electrical signal it is said to be at rest.
a. How is a resting potential created and maintained? (2 marks)
b. How does the concentration of sodium ions compare inside the neuron
versus outside the neuron during rest? (1 mark)
c. How does the concentration of potassium ions compare inside the neuron
versus outside the neuron during rest? (1 mark)
d. Explain how the relative concentrations (inside versus outside) of sodium
and potassium ion are exploited to create an action potential. Be sure to
explain how the ions move (which move in which direction) during the
depolarization, repolarization, and recover phases. (7 marks)
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BCLN BIOLOGY 12 – Rev July 2014
9. Draw a synapse. Label and briefly describe the function, in relation to a synapse,
of the following (20 marks): (Be sure to use the terms exocytosis and diffusion
where applicable)
o
o
o
o
o
synaptic vesicle
neurotransmitter
mitochondria
presynaptic membrane
synaptic gap
o postsynaptic membrane
o
Ca2+
o axon terminal
o dendrite
o contractile proteins
~ END OF BIOLOGY 12 UNIT 12 LEARNING GUIDE ~
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BCLN BIOLOGY 12 – Rev July 2014
UNIT 12 ANSWER KEY
1. Draw and label a myelinated neuron showing the cell body, dendrite, axon, axon terminal,
Schwann cells and Nodes of Ranvier. Provide a brief description of the function of each labeled
structure beside its label. Please be neat! (12 marks)
cell body = performs housekeeping functions
of the cell
dendrite = receives chemical signals from
other neurons
axon = transmits electrical signals from
dendrite to axon terminal
axon terminal = converts electrical signal back
to chemical signal
Schwann cells = myelinates the axon so that
the electrical signal travels faster
Nodes of Ranvier = gaps along the axon
between myelinating cells where saltotory
conduction ("signal jumping") occurs
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BCLN BIOLOGY 12 – Rev July 2014
2. Below is a diagram of a reflex arc:
a. Label each cell as either an interneuron, motor neuron or sensory neuron. (3 marks)
b. Using arrows, indicate the direction of nerve impulse through each neuron. (1 mark)
c. Label the receptor end of the sensory neuron, the dendrite and axon. (2 marks)
d. Label the effector (muscle/organ) of the motor neuron, the dendrite and the axon. (2
marks)
Neuron
Neuron
Neuron
3. What is the purpose of a reflex arc? (2 marks)
= reflex arcs signal independent of the brain to ensure the fastest possible reaction
time and are generally associated with involuntary reflexes that prevent us from
harm such as blinking, pulling limbs away from sharp or hot objects
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BCLN BIOLOGY 12 – Rev July 2014
4. Compare and contrast the functions of sensory neurons, motor neurons and interneurons. (4
marks)
= sensory neurons detect stimuli from internal or external environment and transmit
signals from peripheral nervous system towards central nervous system
= motor neurons transmit signals from central nervous system to peripheral nervous
system and a variety of effectors to ensure an appropriate response to external or
internal stimuli
= interneurons connect sensory neurons to motor neurons within the central nervous
system and provide a site for signal integration
5. Identify the similarities and differences between the sensory neuron and motor neuron. (2 marks)
= sensory neurons and motor neurons both have myelinated axons and the vast
majority of their structure located within the peripheral nervous system but
sensory neurons carry signals from peripheral nervous system to central nervous
system whereas motor neurons carry signals from central nervous system to
peripheral nervous system
6. What is meant when it is said that the electrical impulse of a neuron is an "all-or-nothing" event?
Please include the term "threshold" in your explanation. (2 marks)
= an electrical signal will not be initiated along an axon unless the threshold potential
is met at the dendrite, if threshold is met it will initiate a domino effect of sodium
channel openings such that the electrical signal progresses along the axon in an
unstoppable or "all-or-nothing" fashion
7. Label the following diagram of an Action Potential. (8 marks):
o
o
o
o
repolarization
depolarization
resting potential (label
twice)
threshold potential
o
o
o
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recovery
membrane Potential (mV)
time (mS)
BCLN BIOLOGY 12 – Rev July 2014
8. When a neuron is not sending an electrical signal it is said to be at rest.
a. How is a resting potential created and maintained? (2 marks)
= Sodium/Potassium (Na+/K+) pumps pump 3 sodium ions (Na+) out of cell for every 2
potassium ions (K+) it pumps into the cell resulting in a net negative charge on the
inside of the cell relative to the outside of the cell
b. How does the concentration of sodium ions compare inside the neuron versus outside
the neuron during rest? (1 mark)
= lower Na+ inside cell than outside the cell
c. How does the concentration of potassium ions compare inside the neuron versus outside
the neuron during rest? (1 mark)
= higher K+ inside cell than outside the cell
d. Explain how the relative concentrations (inside versus outside) of sodium and potassium
ion are exploited to create an action potential. Be sure to explain how the ions move
(which move in which direction) during the depolarization, repolarization, and recover
phases. (7 marks)
= during depolarization voltage-gated sodium channels open at -40 mV
(threshold potential) and sodium ions rush down their concentration gradient
into the cell causing it to become more positive on the inside relative to the
outside (+40 mV)
= during repolarization voltage-gated potassium channels open at +40 mV and
potassium ions rush down their concentration gradient out of the cell to
cause it to become negative on the inside relative to the outside (below -65
mV)
= during the recovery phase both voltage-gated sodium channels and voltagegated potassium channels are closed and the sodium/potassium pumps can
restore the balance of sodium and potassium ions such that the neuron is set
to signal again
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BCLN BIOLOGY 12 – Rev July 2014
9. Draw a synapse. Label and briefly describe the function, in relation to a synapse, of the following
(20 marks): (Be sure to use the terms exocytosis and diffusion where applicable)
o
o
o
o
o
synaptic vesicle
neurotransmitter
mitochondria
presynaptic membrane
synaptic gap
o
o
o
o
o
postsynaptic membrane
Ca2+
axon terminal
dendrite
contractile proteins
Synaptic vesicle = contains neurotransmitter
Neurotransmitter =chemical messenger that diffuses across synaptic cleft
Mitochondria = provides energy from ATP to power sodium/potassium pumps and
vesicle movement
Presynaptic membrane = before synapse = axon terminal
Post synaptic membrane = after synapse = dendrite
Synaptic cleft = space between two adjacent neurons
Ca2+ = ion that binds to contractile proteins causing synaptic vesicles to move to and
fuse with presynaptic membrane
Axon terminal = converts electrical signal to chemical signal
Dendrite = receives chemical signals with potential to convert to electrical signal
Contractile proteins = enable synaptic vesicles to move
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