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General Outcome:

Explain how the Nervous System
controls physiological processes
The Nervous System
A system of the body that coordinates & regulates
the activities of the body
Control System
Maintains homeostasis
 homeo/stasis (same/changing)

◦ changes in order to keep a balance
5 major components
Stimulus
receptor
-highly specific
-receive stimuli
Sensory Pathway
modulator/regulator
-Selects appropriate
Response (spinal cord
or brain)
Motor Pathway
effector
-carries out the response
(muscle or gland)
Action
The Nervous System & Homeostasis
◦ Organization of the Nervous
System
◦ Structure of a neuron
◦ Action Potential
◦ Synaptic Transmission
◦ Structure of the Brain
◦ Senses: The Eye & Ear
Nervous System
Organizational Tree!
Nervous System
Central Nervous System
(CNS)
Decision maker
Brain & Spinal Cord
Peripheral Nervous
System (PNS)
Feeds into & out of CNS
Sensory Pathway
Somatic Pathway
(Voluntary)
under conscious control
Examples?
NS Overview
Sympathetic
(Stimulatory)
Speeds you up!
Excites you!
Motor Pathway
Autonomic Pathway
(Involuntary)
unconscious control
Examples?
Parasympathetic
(Restores to normal)
Restores balance!
Restores Homeostasis!
Sympathetic vs. Parasympathetic
(to stimulate)
(to restore)
• Dilates Pupils
Constricts pupils
• Inhibits tears & salivation
Stimulates the same
• Increases heart rate
Decreases heart rate
• Increases respiration
Decreases respiration
• Inhibits digestion
Stimulates digestion
• Relaxes bladder & bowels
Contracts them(#1&2’s)
• Inhibits genitals
Stimulates genitals
• Initiates ejaculation
• Adrenaline Response
Anatomy of a Nerve Cell

Two different types of cells are found in
the nervous system:
◦ Glial Cells: non-conducting; important for
support and metabolism of nerve cells
◦ Neurons: functional units of the nervous
system (conduct nerve impulses)
The Neuron: Wires within a nerve!
See diagram on p.410 of text
Types of Neurons – see your handout!

Motor Neuron
◦ Connects the central nervous system to a
muscle or a gland (also called efferent neurons)

Sensory Neuron
◦ Connects a sensory receptor to the central
nervous system (also called afferent neurons)

Interneuron (or Association Neuron)
◦ Connect sensory neurons to motor neurons
◦ Connects two or more neurons
◦ Found in CNS
The Neuron
http://www.youtube.com/watch?v=36DSFSyxHw0
Dendrite – receives information from receptors or other neurons and conducts
nerve impulses toward the cell body.
Schwann Cells– special type of cell that produces the myelin sheath
Cell Body – contains nucleus and organelles
Nodes of Ranvier – gaps within the myelin sheath
Impulses jump from node-to-node therefore speeding
up the impulses
Neurillemma – delicate membrane that promotes regeneration of
damaged neurons
Only found in myelinated neurons
Myelin – a fatty protein that covers the axon
Insulate the axon allowing nerve impulses to travel faster
(Myelination is only found outside the brain and spinal
cord)
Axon – conducts nerve impulses away from the cell body
To Do:
Read p. 408-411 from text and Complete
66 word summary
 Complete Sections A thru C in your
Notes Package
 Color and Label Neuron Diagram

Structure of a Neuron
From Nelson Biology
The Job of Schwaan
cells = Wrap Axons!
Schwaan cells:
 Nourish the axon
 Provide insulation (myelin)
 Repair axon damage (neurilemma)
Neurilemma =
 Found mainly in PNS
•concentric rings around

axon
•created by the Schwaan cell
• makes the impulse fast
(insulated)
Job of Myelin!
Provide insulation
like the covering on
speaker wire
 Prevent loss of signal
down axon!
 Damaged myelin
results in a loss of
signal down the
axon! (Results in)
 Multiple Sclerosis
(MS)

Above is a map giving the geographical prevalence of Multiple Sclerosis (MS)
world-wide. It has long been established that MS is more likely to occur in
communities in the further Northern and Southern Lattitudes, possibly due
to less sunlight, environmental factors or dietary reasons.
http://www.msrc.co.uk/index.cfm?fuseaction=show&pageid=2325
A beauty of a neuron!
Types of Neurons
Sensory Neurons
(Afferent Neurons) –
conducts nerve impulse
from sense organs to the
brain and spinal cord
(CNS)
Interneuron
(Association Neuron) –
found within the CNS
No myelination
Intergrates and
interprets sensory
information and relays
information to
outgoing neurons
Motor Neuron
(Efferent Neurons) –
conducts nerve impulses
from CNS to muscle fiber
or glands (effectors)
To Do:
Textbook Questions pg. 410 #1-4
 Work on STS Assignment
 Remember:

◦ Purchase Key Booklet by next Friday
◦ Parent letter – if I don’t already have it
Returning involuntary body functions to
normal after a period of stress is the
function of which division of the nervous
system?
A.
B.
C.
D.
Central
Somatic
Sympathetic
Parasympathetic

Syphilis is a STI that affects the central
nervous system. The neurons damaged by
syphilis are
A.
B.
C.
D.
interneurons
sensory neurons
somatic motor neurons
autonomic motor neuron
Common Reflexes

Babinski reflex:
◦ a tickle of a babies foot causes the toes to curl

Pupillary reflex:
◦ iris diameter changes in response to light conditions

Cross extensor reflex:
◦ in a standing position, fatigue of one leg causes withdrawal of weight onto the other
leg

Stretch reflex:
◦ -the body senses the muscles shortening so the tendency is to stretch them out in
order to perform motor functions properly

Knee jerk reflex (patellar):
◦ a tap on the patellar tendon causes top leg muscles to contract & lower leg muscles to
relax simultaneously

Withdrawal reflex:
◦ defensive strategy in response to a painful stimuli like heat & cold or a cut or pinch of
some kind

Others include: Vomiting, coughing, defecation, & milk release some of
which are voluntary reflexes.
Reflexes:





Don’t need to write yet…
are well established neural circuits that are preprogrammed to allow motor responses to certain
stimuli
some may be instinctual as in newborns
some are learned as in repeated motor tasks involved in
sport
some are defensive to enhance survival
and other reflexes help your eye to move as you read
this page.
Reflex Arc
A reflex that does
not require the brain
 Reflexes may be
innate or acquired

Reflex Arc

Reflexes are autonomic responses to
certain stimuli
◦ Involuntary/automatic

They pathway that a nerve impulse takes
is called a reflex arc
Anatomy of a Reflex Arc
How the Reflex
Arc Functions:
1) Sensory organs
(receptors) detect
dangerous stimuli!
2) Impulse is passed
from the sensory
organ to a sensory
neuron!
3) Sensory Neuron
transfers the impulse
to the Association
neuron in the spinal
cord!
How the Reflex
Arc Functions…
4) The INTERNEURON
links the SENSORY
to the MOTOR
neuron!
5) The MOTOR neuron
takes the impulse to
the EFFECTOR!
6) The effector (usually
a muscle) reacts.
7) Simultaneously,
interneurons send
the signal up to the
BRAIN for
interpretation!
Reflex Arc Video
Learner Outcome:
Describe the composition and function of
reflex arcs
 Design and perform an experiment to
investigate the physiology of reflex arcs

To Do:
Reflex Lab
 Section E in your notes package

◦ P. 414 Questions # 2, 3, 5, 6
Action Potential
how do nerves work???

In 1900 Bernstein hypothesized that
nerve impulses where electrochemical in
nature.
◦ Future experimentation proved this.

Giant Squid Experiment:
◦ Cole and Curtis placed two tiny electrodes –
one inside the large axon of a squid and the
second across from the first outside the axon.
Giant Squid Experiment
Squid Axon
•Cole and Curtis measured the electrical potential
across the membrane.
•The resting potential was found to be about –
70mV.
When stimulated, the action potential
jumped to about +40 mV.
 The action potential only lasted for a few
milliseconds before the nerve cell returned
to the resting potential.

+40
threshold
mV
-70
1
2 ms
3
4
Definitions:

Action Potential:
◦ the voltage difference across a nerve cell
membrane when the nerve is excited
(~40 mV)

Resting Potential:
◦ Voltage difference across a nerve membrane
when it is NOT transmitting a nerve impulse
(almost always -70 mV)
Maintaining Resting Potential
Caused by an uneven distribution of positively
charged ions across the membrane
 Set up and maintained by a Sodium-Potassium
pump.
 3 Na+ are pumped out of the cell, 2 K+ ions are
pumped into the cell.

sodium/potassium ion pump
sodium/potassium pump 2
http://www.youtube.com/watch?v=9euDb4TN
3b0
http://www.youtube.com/watch?v=yQwQsEK21E
These positive ions want to move with
their concentration gradient by diffusion.
 More sodium moves out than potassium
moves in leaving a “relative” negative charge
inside the cell.
 The cell is polarized.


resting potential clip
Action Potential
A Nerve impulse is an Action Potential
 When a neuron receives a stimulus it becomes
more permeable to sodium than potassium

◦ When stimulated the ion gates for sodium open up.

Positive ions flood into the cell making it positive.
This rapid inflow is referred to as
depolarization.

After the impulse, the Na+ channels close
and the K+ channels open. This is called
repolarization.
◦ The flow of potassium ions out of the cell (with
their concentration gradient) restores the resting
potential.


The potassium gates close relatively slowly
which makes the inside of the neuron slightly
more negative then resting potential
(hyperpolarization)
The Na+/K+ pump continues to pump the
sodium and potassium across the membrane
against the concentration gradient to restore
the resting potential.
Diagram from Textbook
Summary of Impulse.
1. At rest – Na+/K+ pump moving
2. Stimulation – sodium gates open
3. The flood of sodium into the cytoplasm stimulates
adjacent areas
4. Refractory – potassium gates open – sodium gates
close
5. At rest – Na+/K+ pump moving ions
Action potential overview
Electropotential graph
Movement of Action Potential
Many action potentials are generated one after
another along the cell membrane, causing a wave
of depolarization (similar to falling dominos).
 When axons are myelinated, nerve impulses travel
by saltatory conduction

◦ Gated ion channels are concentrated at the nodes of
Ranvier
◦ Flow of ions across cell membrane can only happen at
the nodes so action potentials “jump” from node to
node
◦ This causes the signal to be transmitted down an
axon much faster.
myelinated vs. unmyelinated impuse
Refractory Period:

The time it takes (~0.001 s) for a
depolarized neuron to repolarize
◦ return to resting potential

During the refractory period another
impulse can NOT be sent along the
neuron.
Threshold
The amount of stimulus required to initiate an
action potential (or, to cause depolarization to
occur)
 Once threshold is reached the nerve impulse is
passed along


Draw diagram
All-or-None Response
A neuron will “fire” either 100%, or not at
all.
 There is no difference in strength of a
nerve impulse

To Do:
Read pages 415 – 419 in your textbook
 Complete Section D in your notes
package
 Nerve impulse coloring diagram (pg. 7
notes package)


Schwann Cell & Action Potential

http://www.mcgrawhill.ca/school/applets/abbio/ch11/actionpotential_action.swf
Synaptic Transmission
Neurons are not
directly connected to
each other.
 The electrochemical
action potential cannot
jump the synaptic cleft
(or synapse).
 Synaptic transmission
is entirely chemical in
nature.

1. http://www.youtube.com/watch?v=vGS7g
uM1Gw0
Synapse movie clip
Synapse
At the end of axons, tiny synaptic vesicles
contain neurotransmitters
 When an impulse reaches the end of an
axon, these synaptic vesicles migrate
toward the end of the axon
 They then release their neurotransmitter
and it diffuses across the synaptic cleft

Synapse
Neurotransmitters attach to specific
receptor sites and causes sodium
channels to open resulting in a
depolarization in the membrane.
 An action potential is created and the
impulse travels down the neuron.
 Diffusion takes time, so the more
synapses involved, the slower the
response.

Synapse



Synaptic transmission can only occur in one
direction.
Since only presynaptic neurons contain
synaptic vesicles, and only post synaptic
neurons have receptor sites for them, the
messages cant be sent in the other direction
This explains why impulses can only travel
from sensory neuron to interneuron to
motor neuron and never in the other
direction
Figure 10(b), pg. 420
Synaptic vesicles in the end
plate of the presynaptic
neuron release
neurotransmitters into the
synaptic cleft. The
neurotransmitters attach
themselves to receptors
on the postsynaptic
membrane, causing it to
depolarize. The action
potential continues along
the postsynaptic neuron.

Synapse action at muscular juction
Neurotransmitters

Acetylcholine (Ach):
(excitatory – passes message along)
◦ neurotransmitter produced in the presynaptic knob and stored in vesicles.
◦ when an action potential reaches the presynaptic knob the vesicles rupture releasing
their contents (acetylcholine) into the
synaptic cleft
◦ The acetylcholine diffuses across the synapse
and binds to receptor sites on the postsynaptic knob
Neurotransmitters

How do we stop the message?
◦ Before another message can cross the cleft, it
must be cleaned (remove the
neurotransmitter)
◦ The enzyme acetyl cholinesterase removes
acetylcholine from the receptor sites and
breaks it into acetic acid & choline
◦ the acetic acid & choline are reabsorbed into
the presynaptic knob to be reused
Neurotransmitters
• Not all neurons cause depolarization in the post
synaptic membrane. Some neurons are inhibitory.

Neurotransmitters can be:
◦ excitatory - passes along message to the next
neuron, or
◦ Inhibitory – binds to the next neuron and
inhibits the message from being passed on
See figure 11 p. 422
Neurotransmitters

Often it takes more than one neuron
releasing its neurotransmitter into the
synaptic cleft to elicit a response in the
post synaptic neuron.
◦ This is referred to as SUMMATION
Figure 11, pg. 422
Action potentials must occur
simultaneously in A and B to
reach the threshold in D.
Other Types of Neurotransmitters:
Serotonin
 Dopamine
 Norepinephrine
 GABA


You will fill in some information regarding these in your
notes package but do NOT have to memorize them. If used
on a diploma you will be told what you need to know about
them
13.2 Summary Electrochemical Impulse
• Nerves conduct electrochemical impulses from
the dendrites along the axon to the end plates of
the neuron.
• Active transport and diffusion of sodium and
potassium ions establish a polarized membrane.
• An action potential is caused by the inflow of
sodium ions.
• Nerve cells exhibit an all-or-none response.
• Neurotransmitters allow the nerve message to
move across synapses.
To Do:
Reflex/Synapse Worksheet
 Complete section F in your notes package
 Case Study “Drugs and the Synapse” p.
423-424 of text


For Extra Practice:
◦ Pg. 418 # 1-4
◦ Pg. 420 # 5-7
◦ Pg. 425 #3-7