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Bio 12: Nervous System: Lesson 1
Neurons to Reflex Arc
Inquiry into Life – pg. 319-325
Today’s Objectives:
 Analyse the transmission of nerve impulses, including:
 Identify and give functions for: dendrite, cell body, axon, axoplasm, axomembrane
 Differentiate among sensory, motor, and inter-neurons with respect to structure and function
 Explain the transmission of a nerve impulse through a neuron, using applicable terminology
(see handout)
 Relate the structure of a myelinated nerve fibre to the speed of impulse conduction, with
reference to applicable structures (see handout)
 Identify the major components of a synapse (see handout)
 Explain the process by which impulses travel across a synapse
 Describe how neurotransmitters are broken down in the synaptic cleft
 Describe the structure of a reflex arc (see handout), and relate its structure to how it functions
Structures and Functions
1. Dendrites
-___________________________________________________________________.
-Many dendrites enter a cell body.
2. Cell Body
-Contains the nucleus and cell organelles needed to keep the cell alive.
-Only a _____________________________________________________________.
-Relays impulse from __________________________________________________.
3. Axons
-Conduct a nerve impulse ______________________________________________.
4. Myelin Sheath
-Protective coating of Schwann Cells around larger Axons and Dendrites.
5. Nodes of Ranvier
-_______________________________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.
Bio 12: Nervous System: Lesson 1
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Types of Neurons
1. Motor Neuron
-_______________________: Moving toward a central organ or point.
-Relays messages from the ___________________________ to the muscles and
organs.
2. Sensory Neuron
-_______________________________: Moving away from a central organ or point.
-Relays messages from _________________________________________________
3. Interneuron (associated neuron or Connector Neuron)
-Relays message from ___________________________________________________.
-Make up the brain and spinal cord.
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Bio 12: Nervous System: Lesson 1
Bases of
Comparison
Length of Fibers
Sensory Neuron
Interneuron
Motor Neuron
Location
Function
***A nerve is composed of long fibers of a number of Neurons***
Impulse Generation (Action Potential)
Nerve impulses are _____________________________. If we measure the
______________ _____________________ a voltmeter, we will see a reading of
___________________. Voltage is a comparison of electrical charge between two
points.
When the neuron is __________________________, the charge changes briefly to
____________________ (mv), then back to __________________.
(-60mv means that the inside is 60 mv _________________________________).
If we hook up our voltmeter to a machine called an oscilloscope, we can see the change in
voltage over a period of time.
There is a difference in ________________________ on either side of
the membrane of a neuron.
At Rest-___________________________________
-______________________________________
molecules inside the neuron.
Bio 12: Nervous System: Lesson 1
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The concentration of sodium ions Na+ is __________________________________________.
The concentration of potassium ions K+ ___________________________________________.
This unequal distribution is due to the ________________________________________ which actively
transports Na+ out and K+ into the axon
The membrane is more permeable to K+ ions, and some _____________________________________
This ___________________________________________, along with of the large negative
molecules, causes the ________________________________________________________.
This situation is called _______________________________. -60mv
When the axon or dendrite is stimulated, ______________________________which allows some Na+
to enter the _____________________ (interior). Now, the inside becomes more positive than the
outside by 40 mv.
This is called the ___________________________________ of the _____________________. The
charge changes from –60 mv to +40 mv. The change is called _________________________.
After the sodium gates have opened, then potassium gates open. K+ _____________________.
This is called the _______________________________ of the action potential. The charge returns
to –60mv. The change is called ___________________________________.
**Note: Charge is back to normal, but ions are reversed
Finally, there is a ________________________ in which the ___________________________
(ACTIVE TRANSPORT) returns ______________________________________to the inside. This is
called the _________________________________. During the refractory period, another action
potential ____________________________
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So far we have only been looking at one point on the Axon or Dendrite. The opening of the
sodium gates in one area _______________________________________________________. We get
a _____________________________________________________ down the nerve fiber.
Na+
+ + + + + + + +++ +
- - - - - - - - - - K+
- - - - - - - - - - - - -
+ + + + + + +++ + +
Na+
K+
+++ -- + + +++ +
- - - ++- - - - - - Na+
- - - - - ++ - - - - - - - -
+ + + - - + + + + + + +
K+
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Bio 12: Nervous System: Lesson 1
Summary of an Action Potential
1. RESTING POTENTIAL
-Charge is _________________
- ________________________
- ________________________
2. UPSWING OF ACTION POTENTIAL
-_________________________
-_____________________________________
- _____________________________________
-(_____________________________________
3. DOWNSWING OF ACTION POTENTIAL
-_____________________________
-_______________________________________
- _______________________________________
-(______________________________________)
4. RECOVERY PHASE
-_______________________________________
-_______________________________________
-_______________________________________
****NOW NEURON CAN BE RESTIMULATED****
****REMEMBER THIS IS A WAVE MOTION DOWN THE NEURON****
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Bio 12: Nervous System: Lesson 1
Myelinated Vs Unmyelinated Fibers
__________________________
____________________
____________________________________
In vertebrates, where most long nerve fibres have myelin sheath around them, the Schwann cells
restrict ion movement across the axomembrane and the impulse “jumps” between successive nodes
of Ranvier, thus __________________________________________.
This type of “jumping” transmission is called __________________________________
It is ________________________ that wrap around the nerve fiber. When it is __________________,
it is covered by Schwann cells. Impulse ___________________ from node to node.
UnMyelinated Neuron
Each action potential starts the next action potential, causing a wave along the entire neuron. In
myelinated axons and dendrites, the ____________________________________________.
In unmyelinated fibers, the impulse ______________________________________.
This difference in speed is because the action potential is ______________________________.
Depolarization only occurs at the _________________________.
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Synapse
Each axon branches off and ends with a swelled tip or
__________________that 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 ______________________
is carried out by chemicals called _________________________________ .
These substances are stored in vesicles at the end of the axon.
__________________________ (speeds up activity) and ________________________ (slows down
activity) 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 Ca+2 as well since _____________________
____________________________________. This
calcium binds with contractile proteins that pull the
___________________________________.
The vesicles join with the cell membrane, forcing the
neurotransmitter into the cleft
(___________________).
**Ca+2 causes the microfilaments to contract and pull the synaptic vesicles to the presynaptic
membrane*
Neurotransmitter’s job is to increase the ______________________________________ on
the postsynaptic membrane.
The Neurotransmitter binds to ____________________________ on the dendrite of the next
neuron. If enough transmitter substance is received, the _____________________ and continue the
impulse.
A neurotransmitter only has a _____________________ once it has been released into the
____________________. ____________ rapidly break down the transmitter substance to clear the
synapse so the next impulse can be transmitted. ____________________________ breaks down
____________________ and _______________________breaks down ___________________.
Pain killers such as Tylenol act as an enzyme to break down the neurotransmitter to decrease
the pain impulse. A natural painkiller in the body is __________________________.
An impulse can only travel across a synapse in one direction. Only the axon contains
______________________________________, so the impulse can only travel
AXON  DENDRITE across a synapse.
**** ALL OR NONE LAW (threshold): If enough neurotransmitter is received by the postsynaptic fiber,
it will fire ________________. (all). If not enough substance is received, it will ____________
____________________________. (none)
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Bio 12: Nervous System: Lesson 1
There are ________________________________________ neurotransmitters in the body. When two
excitatory neurotransmitters work together to cause an action potential, it is called
________________.
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 by passing the brain.
Stages of Reflex Arc
1. ________________________________________________________________. ie. nerve impulse
2. _______________________________________________________________________________.
(spinal cord)
3. _______________________________________________________________________________.
4. _______________________________________________________________________________.
(muscle/organ)
5. _______________________________________________________________________________.
Bio 12: Nervous System: Lesson 1
***The brain finds out later what
had happened***
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