Download File - Mr. Downing Biology 30

Biology 30
The Nervous System
Chapter 11 and 12
Intro Animation
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• In the Biology 20 course, you studied some of
the major body systems in the context of
achieving homeostasis.
• Homeostasis: the process by which a constant internal
environment is maintained despite changes in the
environment.
• Examples?
• The current unit builds on that knowledge by
investigating the control mechanisms that keep
all of these systems working together in
balance.
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The Nervous & Endocrine System
• Though many organ systems play a role in
regulating the body, the two main systems are
the endocrine system and the nervous
system.
• The endocrine and the nervous system
sometimes determine how other systems do
their jobs.
– Endocrine System: hormones
– Nervous System: electrical messages
The Nervous System
-an elaborate communication system that contains
more than 100 billion nerve cells in brain alone
-monitors the internal and external environment,
integrates all of these inputs, and orchestrates a
coordinated response to any changes.
For Example:
• nerve cells detect external environmental stimuli
(smells, light intensity, pressure, etc.) and relays
the information to the brain.
• internal nerve cells also tell the brain about breathing
rate, heart rate, blood pressure
-if environmental conditions change, the nervous
system quickly lets the body adjust to those
changes
-complex nerve connections in the brain allow us to
think, reason, remember, show various emotions, etc.
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See p. 367
Central Nervous System-
Peripheral Nervous System• Somatic Nervous System:
• Autonomic Nervous System:
Nervous System Function
• to maintain homeostasis
• it controls all of the bodies
activities
• 3 major functions:
1. Sensory input – moves signals
form our various sense organs to
the brain
2. Integration – interpretation of
those signals and the formation
of an appropriate response.
3. Motor output – conduction of
signals to the body’s muscles and
glands
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Neuron Types
Caption: Wearable computing. Male researcher using the prototype fingernail touch sensor he has developed. This affective
computer detects each touch of the finger by the change it causes in the colour of the blood capillaries below the nail. Such a
system could be used for buttonless controls, for example for a computer. By resting on the fingernails, the sensors do not
interfere with the natural sense of touch. Affective computers provide feedback about the wearer's physical state or behaviour.
This sensor was created at the Media Lab of the Massachusetts Institute of Technology (MIT), USA.
3 Types of Neurons
• 1. Sensory neurons : Carry information from the environment to the
CNS for processing (ex. Eyes responding to light).
• 2. Interneurons : Link or connect neurons together in the CNS. They
carry impulses within the CNS (found predominantly in the brain and
spinal cord). They interpret the sensory information and connect
neurons to outgoing motor neurons.
• 3. Motor neurons : Carry information from the CNS to the body
effectors (muscles and glands because they are what cause things to
happen)
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Anatomy of a Nerve Cell
• 2 Types of cells found in the
nervous system:
– Neurons and Glial Cells
• Neuron (nerve cell) - the
fundamental structural unit of
the nervous system that enables
us to receive information, process
it, and produce action.
– a “bundle” of neurons forms a
nerve
• Glial cells - (“glue”) are nonconducting cells that help the
neurons out, tying them together
and providing support (nourish
and remove wastes).
– Largest concentration found in the
brain
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Nerves are composed of
neurons
Individual neurons
Nerve
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Neuron Structure
dendrites - the branching
axon - the long extension
of a neuron that carries
nerve impulses away from
the body of the cell.
myelin sheath - the
fatty substance that
surrounds and
protects some nerve
fibers made up of
many cells
structure of a neuron that
receives messages
(attached to the cell body)
axon terminals the hair-like ends
of the axon
cell body - the cell body
of the neuron; it contains
the nucleus (also called
the soma)
Node of Ranvier - one of
the many gaps in the
myelin sheath - this is
where the action potential
occurs during saltatory
conduction along the axon
Schwann's cells - cells that
produce myelin - they are
located within the myelin
sheath.
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The Basic Neuron
The 3 basic parts to a neuron: cell body, axon, and dendrites.
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Glial Cells
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Myelin Sheath
-a white fatty, protein covering on the axon
-formed by special glial cells called Schwann cells
-acts as insulation for neurons to prevent loss of charged ions from the
nerve cell
-in between parts of the myelin sheath are nodes of Ranvier
-nerve impulses “jump” from node to node, speeding up nerve impulse
Transmission; therefore, nerve impulses move faster along a myelinated
nerve.
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Myelinated vs. Unmyelinated Nerve transmission
Types of Nerves
1. Myelinated Nerves
• are covered with a myelin sheath
• make up the white matter of the brain and spinal cord
• the myelinated neurons located outside the central nervous system are
covered with a membrane called a neurilemma
• the neurilemma promotes regeneration of damaged axons or dendrites
2. Unmyelinated Nerves
• have no myelin sheath
• make up the grey matter in the brain and spinal cord
• Lack neurilemma resulting in permanent damage
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Multiple Sclerosis
• An auto-immune disease in which the immune system attacks
and destroys the myelin sheath around surrounding axons.
• Results in a progressive loss of signal, muscle control, and brain
Function
• What it is like to have MS
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The Reflex Arc
Reflex arc- a neural pathway
through the spinal cord that
provides the framework for a
reflex action
(an involuntary, unconscious action)
•A reflex arc does not require
coordination by the brain
•Contains 5 essential components:
--Stimulus
1. the sensory receptor
2. the sensory neuron
3. the interneuron
4. the motor neuron
5. the effector (muscle or gland etc)
--Response
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•
When the patellar tendon
is tapped, (1)sensory
neurons detect the
stretching and send a
signal (2) to the CNS (in
this case, the spinal cord).
•
The information goes to a
motor neuron (3) and to
an interneuron (4).
•
The motor neuron
stimulates the contraction
of the quadriceps muscle
which extends the leg,
while the interneuron
sends an inhibitory signal
to the flexor muscle.
•
Reflexes are a protective
mechanism for the body
Draw Reflex arc
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Examples of Reflexes
1. Knee jerk
2. Pupillary – a light shone in one eye sends a nerve impulse to the CNS (brain
in this case). A connection is made with interneurons and then motor neurons,
one going to each eye. The motor neurons stimulate the pupillary muscles to
contract, and the pupils get smaller.
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Reflexes
• In general the following characteristics are
used to describe reflex actions. They are:
– involuntary – mostly unaware of them until after the brain
has registered what has occurred
– purposeful and adaptive – most are essential to our
survival
– predictable – a specific given stimulus will continue to
produce the same result
– have a measurable reaction time – although extremely
quick, do not occur instantaneously
• The more complex the reaction, the longer the reaction time
• Physiological conditions can affect reaction time (fatigue, drugs)
• Occur more rapidly in different people
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Check Your Understanding
• Differentiate between the PNS and the CNS.
• Describe the function of the following parts of a neuron:
dendrites, myelin sheath, Schwann cells, cell body, and axon.
• What is the relationship between the speed of a nerve
impulse and the size of the axon along which it travels?
• What is the difference between gray and white matter?
• Name the essential components of a reflex arc and the
function of each.
• What are the nodes of Ranvier?
• What the benefit of having an axon covered by neurillemma?
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