powerpoint to accompany hole’s human anatomy and physiology 12e
TRANSCRIPT
1
10.1: Introduction
• Cell types in neural tissue:
• Neurons
• Neuroglial cells (also
known as neuroglia, glia,
and glial cells)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Dendrites
Cell body
Axon
Nuclei of
neuroglia
© Ed Reschke
2
10.2: General Functions of
the Nervous System
• The three general functions of the nervous system:
• Receiving stimuli = sensory function
• Deciding about stimuli = integrative function
• Reacting to stimuli = motor function
3
Functions of Nervous System
• Sensory Function
• Sensory receptors gather information
• Information is carried to the CNS
• Integrative Function
• Sensory information used to create: • Sensations
• Memory
• Thoughts
• Decisions
• Motor Function
• Decisions are acted upon
• Impulses are carried to effectors
4
Divisions of the
Nervous System
• Central Nervous System (CNS)
• Brain
• Spinal cord
• Peripheral Nervous System (PNS)
• Cranial nerves
• Spinal nerves
5
Divisions of Peripheral
Nervous System
• Sensory Division
• Picks up sensory information and delivers it to the CNS
• Motor Division
• Carries information to muscles and glands
• Divisions of the Motor Division:
• Somatic – carries information to skeletal muscle
• Autonomic – carries information to smooth muscle,
cardiac muscle, and glands
6
Divisions Nervous System
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Sensory division Sensory receptors
Motor division
Skeletal muscle
Brain
(a) (b)
Spinal
cord Spinal
nerves
Cranial
nerves
Central Nervous System
(brain and spinal cord)
Peripheral Nervous System
(cranial and spinal nerves)
Smooth muscle
Cardiac muscle
Glands
Autonomic
Nervous
System
Somatic
Nervous
System
7
10.3: Description of Cells of
the Nervous System
• Neurons vary in size and shape
• They may differ in length and size of their axons and dendrites
• Neurons share certain features:
• Dendrites
• A cell body
• An axon
8
Neuron Structure Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Cell body
Neurofibrils
Nucleus Nucleolus
Dendrites
Impulse
Nodes of Ranvier
Myelin (cut)
Axon
Axon
Chromatophilic
substance
(Nissl bodies)
Axonal
hillock
Portion of a
collateral
Schwann
cell
Nucleus of
Schwann cell
Synaptic knob of
axon terminal
9
Myelination of Axons
• White Matter
• Contains myelinated
axons
• Considered fiber tracts
• Gray Matter
• Contains unmyelinated
structures
• Cell bodies, dendrites
Dendrite
Node of Ranvier
Myelinated region of axon
Axon
(a)
Unmyelinated
region of axon
Neuron
cell body
Neuron
nucleus
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
(c)
Enveloping
Schwann cell Schwann
cell nucleus
Unmyelinated
axon
Longitudinal
groove
10
Types of Neuroglial Cells
in the PNS
1) Schwann Cells
• Produce myelin found on peripheral myelinated neurons
• Speed up neurotransmission
2) Satellite Cells
• Support clusters of neuron cell bodies (ganglia)
11
Types of Neuroglial Cells
in the CNS
2) Astrocytes
• CNS
• Scar tissue
• Mop up excess ions, etc.
• Induce synapse formation
• Connect neurons to blood vessels
• Part of Blood Brain Barrier
3) Oligodendrocytes
• CNS
• Myelinating cell
4) Ependyma or ependymal
• CNS
• Ciliated
• Line central canal of spinal
cord
• Line ventricles of brain
•Produce CSF
1) Microglia
• CNS
• Phagocytic cell
12
Types of Neuroglial Cells Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Microglial cell
Axon
Oligodendrocyte
Astrocyte
Capillary
Neuron
Myelin
sheath (cut)
Node of
Ranvier
Ependymal
cell
Fluid-filled cavity
of the brain or
spinal cord
13
10.4: Classification of Neurons
and Neuroglia
• Neurons vary in function
• They can be sensory, motor, or integrative neurons
• Neurons vary in size and shape, and in the number of axons
and dendrites that they may have
• Due to structural differences, neurons can be classified into
three (3) major groups:
• Bipolar neurons
• Unipolar neurons
• Multipolar neurons
14
Classification of Neurons:
Structural Differences
• Bipolar neurons • dendrite, axon, cb in middle
• Eyes, ears, nose
• Unipolar neurons
• Two ax process
• Ganglia of PNS
• Sensory
• Multipolar neurons
• 99% of neurons
• Many processes
• Most neurons of
CNS
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Dendrites
Axon Axon
Axon Direction
of impulse
(a) Multipolar
Central
process
Peripheral
process
(c) Unipolar (b) Bipolar
15
Classification of Neurons:
Functional Differences
• Sensory Neurons
• Afferent
• Carry impulse to CNS
• Most are unipolar
• Some are bipolar
• Interneurons
• Link neurons
• Aka association neurons
or internuncial neurons
• Multipolar
• Located in CNS
• Motor Neurons
• Multipolar
• Carry impulses away from CNS
• Carry impulses to effectors
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Central nervous system Peripheral nervous system
Cell body
Interneurons
Dendrites
Axon
Axon
Sensory (afferent) neuron
Motor (efferent) neuron
Cell body
Axon
(central process)
Axon
(peripheral process)
Sensory
receptor
Effector
(muscle or gland)
Axon
terminal
16
Regeneration of A Nerve Axon Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Axon Site of injury Schwann cells
(a)
(b)
(c)
(d)
(e)
Changes
over time
Motor neuron
cell body
Former connection
reestablished
Schwann cells
proliferate
Schwann cells
degenerate
Proximal end of injured axon
regenerates into tube of sheath cells
Distal portion of
axon degenerates
Skeletal
muscle fiber
17
10.5: The Synapse
• Nerve impulses pass
from neuron to neuron at
synapses, moving from a
pre-synaptic neuron to a
post-synaptic neuron.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Dendrites
Impulse
Impulse
Impulse
Synaptic
cleft
Axon of
presynaptic
neuron
Cell body of
postsynaptic
neuron
Axon hillock of
Postsynaptic neuron
Axon of
presynaptic
neuron
18
Synaptic Transmission
• Neurotransmitters are
released when impulse
reaches synaptic knob
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Mitochondrion
Synaptic knob
(a)
Synaptic cleft
Neurotransmitter
Axon
Ca+2
Presynaptic neuron
Direction of
nerve impulse
Synaptic
vesicles
Cell body or dendrite
of postsynaptic neuron
Synaptic
vesicle
Vesicle releasing
neurotransmitter
Axon
membrane
Polarized
membrane
Depolarized
membrane
Ca+2 Ca+2
19
Animation: Chemical Synapse
Please note that due to differing
operating systems, some animations
will not appear until the presentation is
viewed in Presentation Mode (Slide
Show view). You may see blank slides
in the “Normal” or “Slide Sorter” views.
All animations will appear after viewing
in Presentation Mode and playing each
animation. Most animations will require
the latest version of the Flash Player,
which is available at
http://get.adobe.com/flashplayer.
Please note that due to differing
operating systems, some animations
will not appear until the presentation is
viewed in Presentation Mode (Slide
Show view). You may see blank slides
in the “Normal” or “Slide Sorter” views.
All animations will appear after viewing
in Presentation Mode and playing each
animation. Most animations will require
the latest version of the Flash Player,
which is available at
http://get.adobe.com/flashplayer.
20
10.6: Cell Membrane Potential
• A cell membrane is usually electrically charged, or
polarized, so that the inside of the membrane is negatively
charged with respect to the outside of the membrane (which is
then positively charged).
• This is as a result of unequal distribution of ions on the
inside and the outside of the membrane.
21
Distribution of Ions
• Potassium (K+) ions are the major intracellular positive ions (cations).
• Sodium (Na+) ions are the major extracellular positive ions (cations).
• This distribution is largely created by the Sodium/Potassium Pump
(Na+/K+ pump).
• This pump actively transports 3 sodium ions out of the cell and 2
potassium ions into the cell.
22
Resting Potential
• Resting Membrane Potential
(RMP):
• 70 mV difference from
inside to outside of cell
• It is a polarized
membrane
• Inside of cell is negative
relative to the outside of
the cell
• RMP = -70 mV
• Due to distribution of
ions inside vs. outside
• Na+/K+ pump restores
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Axon Cell body
Low Na+
Axon terminal Low K+
High K+
High Na+
(a)
+
+ – –
+
+ – –
+
+
– + –
– + – +
–
+ –
+ –
+ – +
–
+ –
+ –
+ –
+ –
+ –
–70 mV
(b)
+
+ – –
+
+ – –
+
+
– + –
– + – +
–
+ –
+ –
+ –
+ –
+ –
+ –
+ –
–70 mV
Low Na+
Low K+ High K+
High Na+
Na+
K+
(c)
Pump
Impermeant
anions
23
Local Potential Changes
• Caused by various stimuli: • Temperature changes
• Light
• Pressure
• Environmental changes affect the membrane
potential by opening a gated ion channel
• Channels are 1) chemically gated, 2) voltage gated,
or 3) mechanically gated
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Gate-like mechanism Protein
(b) Channel open (a) Channel closed
Cell
membrane
Fatty acid
tail
Phosphate
head
24
Local Potential Changes
• If membrane potential becomes more negative, it has hyperpolarized
• If membrane potential becomes less negative, it has depolarized
• Graded (or proportional) to intensity of stimulation reaching
threshold potential
• Reaching threshold potential results in a nerve impulse, starting an
action potential
25
Local Potential Changes Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
–62 mV
Na+
Na+
Neurotransmitter
(a)
–55 mV
Na+
Na+
Na+ Na+
Na+
Trigger zone (axon hillock)
(b)
Chemically-gated
Na+ channel
Presynaptic
neuron
Voltage-gated
Na+ channel
26
Action Potentials
• At rest, the membrane is
polarized (RMP = -70)
• Sodium channels open
and membrane
depolarizes (toward 0)
• Potassium leaves
cytoplasm and
membrane repolarizes
(+30)
• Threshold stimulus
reached (-55)
• Brief period of
hyperpolarization (-90)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
(a)
Region of depolarization (b)
Region of repolarization (c)
–70
–0
–70
–0
–70
–0 K+
Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+
K+ K+ K+ K+ K+ K+ K+
Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+
K+ K+ K+ K+ K+ K+ K+ K+
Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+
K+ K+ K+ K+ K+
Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+
K+ K+ K+ K+ K+
K+
K+
K+ K+
K+ K+
Na+ Na+ Na+
Na+ Na+ Na+
Threshold
stimulus
Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+
Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+
K+ K+ K+ K+ K+
K+ K+ K+ K+ K+
Na+ Na+ Na+
Na+ Na+ Na+
K+
K+
K+ K+ K+
K+ K+ K+
Na+ channels open
K+ channels closed
K+ channels open
Na+ channels closed
27
Action Potentials
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Milliseconds
1 0
0
+20
+40
2 3 4 5 6 7 8
Me
mb
ran
e p
ote
nti
al (m
illi
vo
lts
)
Action potential
Hyperpolarization
–40
–20
–60
–80
Resting
potential
Resting potential
reestablished
28
Action Potentials Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
(a)
Direction of nerve impulse
+ +
+ +
+
– – – – – – – – –
– – – – – – – – –
– – – – – – – – –
– – – – – – – – –
– – – – – – – – –
– – – – – – – – –
+ + + + + + + +
+ + + + + + + + +
(b)
+ +
+ +
+ + + + + + + + +
+ + + + + + + + +
(c)
+ +
+ +
+ + + + + + + + +
+ + + + + + + + +
Region of
action potential
29
Animation: Action Potential
Propagation in Myelinated Neurons
Please note that due to differing
operating systems, some animations
will not appear until the presentation is
viewed in Presentation Mode (Slide
Show view). You may see blank slides
in the “Normal” or “Slide Sorter” views.
All animations will appear after viewing
in Presentation Mode and playing each
animation. Most animations will require
the latest version of the Flash Player,
which is available at
http://get.adobe.com/flashplayer.
30
Animation: Action Potential
Propagation in Unmyelinated Neurons
Please note that due to differing
operating systems, some animations
will not appear until the presentation is
viewed in Presentation Mode (Slide
Show view). You may see blank slides
in the “Normal” or “Slide Sorter” views.
All animations will appear after viewing
in Presentation Mode and playing each
animation. Most animations will require
the latest version of the Flash Player,
which is available at
http://get.adobe.com/flashplayer.
31
All-or-None Response
• If a neuron axon responds at all, it responds completely –
with an action potential (nerve impulse)
• A nerve impulse is conducted whenever a stimulus of
threshold intensity or above is applied to an axon
• All impulses carried on an axon are the same strength
32
Refractory Period
• Absolute Refractory Period • Time when threshold stimulus does not start another
action potential
• Relative Refractory Period • Time when stronger threshold stimulus can start another
action potential
33
Impulse Conduction
34
Animation: The Nerve Impulse
Please note that due to differing
operating systems, some animations
will not appear until the presentation is
viewed in Presentation Mode (Slide
Show view). You may see blank slides
in the “Normal” or “Slide Sorter” views.
All animations will appear after viewing
in Presentation Mode and playing each
animation. Most animations will require
the latest version of the Flash Player,
which is available at
http://get.adobe.com/flashplayer.
Please note that due to differing
operating systems, some animations
will not appear until the presentation is
viewed in Presentation Mode (Slide
Show view). You may see blank slides
in the “Normal” or “Slide Sorter” views.
All animations will appear after viewing
in Presentation Mode and playing each
animation. Most animations will require
the latest version of the Flash Player,
which is available at
http://get.adobe.com/flashplayer.
35
10.3 Clinical Application
Factors Affecting Impulse Conduction
36
10.7: Synaptic Transmission
• This is where released neurotransmitters cross the
synaptic cleft and react with specific molecules called
receptors in the postsynaptic neuron membrane.
• Effects of neurotransmitters vary.
• Some neurotransmitters may open ion channels and
others may close ion channels.
37
Synaptic Potentials
• EPSP
• Excitatory postsynaptic potential
• Graded
• Depolarizes membrane of postsynaptic neuron
• Action potential of postsynaptic neuron becomes more likely
• IPSP
• Inhibitory postsynaptic potential
• Graded
• Hyperpolarizes membrane of postsynaptic neuron
• Action potential of postsynaptic neuron becomes less likely
38
Summation of
EPSPs and IPSPs
• EPSPs and IPSPs are added
together in a process called
summation
• More EPSPs lead to greater
probability of an action
potential
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Nucleus
Neuron
cell body
Presynaptic
knob
Presynaptic
axon
Neurotransmitters
39
40
Neurotransmitters
41
Neuropeptides
• Neurons in the brain or spinal cord synthesize neuropeptides.
• These neuropeptides act as neurotransmitters.
• Examples include:
• Enkephalins
• Beta endorphin
• Substance P
42
10.4 Clinical Application
Opiates in the Human Body
43
10.8: Impulse Processing
• Way the nervous system processes nerve impulses and acts
upon them
• Neuronal Pools
• Interneurons
• Work together to perform a common function
• May excite or inhibit
• Convergence
• Various sensory receptors
• Can allow for summation of impulses
• Divergence
• Branching axon
• Stimulation of many neurons ultimately
44
Neuronal Pools
• Groups of interneurons that make synaptic connections
with each other
• Interneurons work together to perform a common function
• Each pool receives input from other neurons
• Each pool generates output to other neurons
45
Convergence
• Neuron receives input from several
neurons
• Incoming impulses represent
information from different types of
sensory receptors
• Allows nervous system to collect,
process, and respond to information
• Makes it possible for a neuron to
sum impulses from different sources
1 2
3
(a)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
46
Divergence
• One neuron sends impulses
to several neurons
• Can amplify an impulse
• Impulse from a single neuron
in CNS may be amplified to
activate enough motor units
needed for muscle contraction
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
(b)
4
5
6
47
Important Points in Chapter 10:
Outcomes to be Assessed
10.1: Introduction
Describe the general functions of the nervous system.
Identify the two types of cells that comprise nervous tissue.
Identify the two major groups of nervous system organs.
10.2: General Functions of the Nervous System
List the functions of sensory receptors.
Describe how the nervous system responds to stimuli.
10.3: Description of Cells of the Nervous System
Describe the three major parts of a neuron.
Define neurofibrils and chromatophilic substance.
48
Important Points in Chapter 10:
Outcomes to be Assessed
Describe the relationship among myelin, the neurilemma, and the
nodes of Ranvier.
Distinguish between the sources of white matter and gray matter.
10.4: Classification of Neurons and Neuroglia
Identify structural and functional differences among neurons.
Identify the types of neuroglia in the central nervous system and their
functions.
Describe the Schwann cells of the peripheral nervous system.
10.5: The Synapse
Define presynaptic and postsynaptic.
Explain how information passes from a presynaptic to a postsynaptic
neuron.
49
Important Points in Chapter 10:
Outcomes to be Assessed
10.6: Cell Membrane Potential
Explain how a cell membrane becomes polarized.
Define resting potential, local potential, and action potential.
Describe the events leading to the conduction of a nerve impulse.
Compare nerve impulse conduction in myelinated and unmyelinated
neurons.
10.7: Synaptic Transmission
Identify the changes in membrane potential associated with excitatory
and inhibitory neurotransmitters.
10.8: Impulse Processing
Describe the basic ways in which the nervous system processes
information.
50
Quiz 10
Complete Quiz 10 now!
Read Chapter 11.