Transcript Nerve activates contraction

Functions of the Nervous System
1. Sensory input – gathering information
 To monitor changes (stimuli) occurring inside
and outside the body
2. Integration
 To process and interpret sensory input and
decide if action is needed
3. Motor Output
 A response to the integrated stimuli
 The response activates muscles or
glands
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Slide 7.1a
Functions of the Central Nervous
System (CNS)
Example: As you’re driving you see a red
light and automatically move your foot to the
brake.
Figure 7.1
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Slide 7.3b
Structural Classification of the
Nervous System
 Central nervous system (CNS)
 Brain
 Spinal cord
 Peripheral nervous system (PNS)
 Nerves outside the brain (cranial) and
spinal cord (spinal)
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Slide 7.2
Functional Classification of the
Peripheral Nervous System
1. Sensory (afferent) division
 Nerve fibers that carry information to the
central nervous system
2. Motor (efferent) division
 Nerve fibers that carry impulses away
from the central nervous system
Figure 7.1
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Slide 7.3a
Functional Classification of the
Peripheral Nervous System
 Motor (efferent) division – has two
subdivisions
1. Somatic nervous system
 Voluntary
 Allows us to control our skeletal muscles
2. Autonomic nervous system
 Involuntary
 Automatically controls our cardiac and
smooth muscles
Figure 7.1
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Slide 7.3c
Organization of the Nervous System
Figure 7.2
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Slide 7.4
Types of Nervous Tissue
 There are only 2 types of nervous
tissue:
1. Neuroglia – support cells; name means
nerve glue
2. Neurons – the actual nerve cells
Figure 7.3a
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Slide 7.5
Neuroglia or Support Cells
 They can not transmit a nerve impulse
 They never lose their ability to divide
(most neurons do)
 This means most brain tumors are
formed by these cells (gliomas)
 4 kinds of neuroglia support the CNS:
astrocytes, microglia, ependymal cells,
and oligodendrocytes
 2 kinds of neuroglia support the PNS;
Schwann cells and satellite cells
Figure 7.3a
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Slide 7.5
CNS Support Cells (Neuroglia)
1. Astrocytes
 Abundant, star-shaped cells
 Brace or support neurons
 Form barrier
between capillaries
and neurons
 Control the chemical
environment of
the brain
Figure 7.3a
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Slide 7.5
CNS Support Cells (Neuroglia)
2. Microglia
 Spider-like phagocytes
 Dispose of debris
3. Ependymal cells
 Line cavities of the
brain and spinal cord
 Cilia help to circulate
the cerebrospinal
fluid
Figure 7.3b, c
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Slide 7.6
CNS Support Cells (Neuroglia)
4. Oligodendrocytes
 Produce myelin
sheath (a fatty
layer of insulation)
around nerve fibers
in the central
nervous system
Figure 7.3d
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Slide 7.7a
PNS Support Cells (Neuroglia)
1. Satellite cells
 Protect neuron cell bodies
2. Schwann cells
 Form myelin sheath in the peripheral
nervous system
Figure 7.3e
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Slide 7.7b
Nervous Tissue: Neurons
 Neurons = nerve cells
 Cells specialized to transmit messages
 All neurons have a:
 Cell body – nucleus and metabolic center
of the cell
 Processes – fibers that extend from the
cell body
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Slide 7.8
Neuron Anatomy
 Cell body &
extensions
outside the cell
body
 Dendrites –
conduct impulses
toward the cell
body
 Axons – conduct
impulses away
from the cell body
Figure 7.4a
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Slide 7.10
Axons and Nerve Impulses
 One axon ends in many axonal
terminals (hundreds to thousands)
 Axonal terminals contain hundreds of
tiny vesicles with neurotransmitters
 Axonal terminals are separated from the
next neuron by a gap
 This gap is called the synaptic cleft or
synapse
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Slide 7.11
Neuron Anatomy
 Most long neurons are covered with myelin
(white, fatty substance)
 This forms the myelin sheath
 In the PNS, Schwann cells form it while in
the CNS, oligodendrocytes form it
 In the CNS, myelinated neurons are called
the white matter and unmyelinated neurons
are called the gray matter
Figure 7.4a
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Slide 7.10
Multiple Sclerosis
 In this disease, the myelin sheath is slowly
destroyed and hardened (called scleroses)
 This short circuits the nerve transmissions
and the person loses the ability to control
muscles
 It’s an autoimmune disease which means
the body attacks the protein in the sheath
for some unknown reason
 There’s no cure but it’s treated with
interferon and bovine myelin
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Figure 7.4a
Slide 7.10
Classification of Neurons
 Can classify neurons by their function:
1. Sensory (afferent) neurons – toward
CNS
2. Motor (efferent) neurons – away from
CNS
3. Interneurons (association) neurons –
connect sensory & motor neurons
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Slide 7.14a
Neuron Classification
Figure 7.6
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Slide 7.15
Classification of Neurons
 Can classify neurons by their structure
or number of processes they have:
1. Multipolar neurons– many
extensions; by far the most common
2. Bipolar neurons – 2 extensions
3. Unipolar neurons – 1 extension
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Slide 7.14a
Structural Classification of Neurons
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Slide 7.16a
2 Functional Properties of Neurons
1. Irritability – ability to respond to stimuli
and convert it to an impulse
2. Conductivity – ability to transmit an
impulse to other neurons, muscles or
glands
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Slide 7.17
Starting a Nerve Impulse
1. Polarized membrane – at
rest a neuron has fewer
+ ions inside than
outside = no activity
2. Depolarization – a
stimulus depolarizes the
neuron’s membrane
which allows sodium
(Na+) to flow inside the
membrane
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Figure 7.9a–c
Slide 7.18
Starting a Nerve Impulse
3. The build up of + sodium
ions inside initiates an
action potential in the
neuron = nerve impulse
4. The nerve impulse is all
or none – it travels down
the entire axon
5. Repolarization – almost
immediately the extra +
ions are moved back out
of the neuron and it
becomes polarized again
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Figure 7.9a–c
Slide 7.18
Nerve Impulse Propagation
 Impulses travel
faster when fibers
have a myelin
sheath
 Impulses cross the
synapse to the next
neuron by release of
a neurotransmitter
Figure 7.9c–e
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Slide 7.20
How Neurons Communicate at
Synapses
Figure 7.10
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Slide 7.22
Things that affect the conduction of
impulses
 Alcohol, sedatives and anesthetics all block
nerve impulses by not allowing sodium into
the neuron.
 No sodium means no action potential or
nerve impulse
 Cold and continuous pressure also impair
nerve impulses because they disrupt blood
flow
 Examples: can’t write your name if hands are
cold or your foot “falling asleep”
Figure 7.10
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Slide 7.22
The Reflexes
 Reflex – rapid, predictable, and
involuntary responses to stimuli
 Reflex – like a one way street; always
go the same direction
 Reflex arc – direct route from a sensory
neuron, to an interneuron, to an effector
Figure 7.11a
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Simple Reflex Arc
Figure 7.11b, c
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Types of Reflexes
1. Autonomic reflexes
 Regulates smooth & cardiac muscle
plus glands
 Regulates body functions: digestion,
elimination, blood pressure & sweating
 Also includes salivating & pupil dilation
2. Somatic reflexes
 Involves the skeletal muscles – pulling
away from a hot object
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