Transcript PowerPoint to accompany Hole’s Human Anatomy and

Hole’s Human Anatomy
and Physiology
Twelfth Edition
Shier w Butler w Lewis
Chapter
10
Nervous System I: Basic
Structure and Function
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1
10.1: Introduction
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Dendrites
• Cell types in neural tissue:
• Neurons
• Neuroglial cells (also
known as neuroglia, glia,
and glial)
Cell body
Nuclei of
neuroglia
Axon
2
© Ed Reschke
Divisions of the
Nervous System
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Brain
• Central Nervous System (CNS)
• Brain
• Spinal cord
Cranial
nerves
Spinal
cord
• Peripheral Nervous System (PNS)
• Cranial nerves
• Spinal nerves
Spinal
nerves
3
(a)
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
4
Divisions Nervous System
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Central Nervous System
(brain and spinal cord)
Brain
Peripheral Nervous System
(cranial and spinal nerves)
Cranial
nerves
Sensory division
Spinal
cord
Sensory receptors
Spinal
nerves
Motor division
Somatic
Nervous
System
Skeletal muscle
Autonomic
Nervous
System
Smooth muscle
Cardiac muscle
Glands
5
(a)
(b)
Functions of Nervous System
• Sensory Function (receiving • Integrative Function (deciding
information)
what to do about information)
• Sensory receptors gather
• Sensory information used to
information
create:
• Sensations
• Information is carried to the
• Memory
CNS
• Motor Function (acting
on information)
• Decisions are acted
upon
• Impulses are carried
to effectors
• Thoughts
• Decisions
6
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
7
Neuron Structure
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Chromatophilic
substance
(Nissl bodies)
Dendrites
Cell body
Nucleus
Nucleolus
Neurofibrils
Axonal
hillock
Impulse
Axon
Synaptic knob of
axon terminal
Nodes of Ranvier
Myelin (cut)
Axon
Nucleus of
Schwann cell
Schwann
cell
Portion of a
collateral
8
Myelination of Axons
• White Matter
• Contains myelinated
axons
• Considered fiber tracts
• Gray Matter
• Contains unmyelinated
structures
• Cell bodies, dendrites
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Dendrite
Unmyelinated
region of axon
Myelinated region of axon
Node of Ranvier
Axon
Neuron
Neuron
cell body nucleus
(a)
Enveloping
Schwann cell
Schwann
cell nucleus
Longitudinal
groove
Unmyelinated
axon
(c)
9
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
10
Classification of Neurons:
Structural Differences
• Multipolar neurons
• 99% of neurons
• Many processes
• Most neurons of
CNS
• Bipolar neurons
• Two processes
• Eyes, ears, nose
• Unipolar neurons
• One process
• Ganglia of PNS
• Sensory
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Dendrites
Peripheral
process
Axon
Direction
of impulse
Central
process
Axon
Axon
11
(a) Multipolar
(b) Bipolar
(c) Unipolar
Classification of Neurons:
Functional Differences
• Sensory Neurons
• Afferent (approach)
• Carry impulse to CNS
• Most are unipolar
• Some are bipolar
• Interneurons
• Link neurons in CNS
• Aka association neurons
• Multipolar
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Central nervous system
Peripheral nervous system
Cell body
Dendrites
Sensory
receptor
Cell body
Axon
(central process)
Axon
(peripheral process)
Sensory (afferent) neuron
Interneurons
• Motor Neurons
• Efferent (exit)
• Carry impulses away from CNS
to effectors
• Multipolar
Motor (efferent) neuron
Axon
Effector
(muscle or gland)
Axon
Axon
terminal
12
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)
13
Types of Neuroglial Cells
in the CNS
1) Microglia
• CNS
• Phagocytic cell
3) Oligodendrocytes
• CNS
• Myelinating cell
4) Ependyma or ependymal
2) Astrocytes
• CNS
• CNS
• Ciliated
• Scar tissue
• Line central canal of spinal
• Mop up excess ions, etc.
cord
• Induce synapse formation
• Line ventricles of brain
• Connect neurons to blood
• Keep CSF moving
vessels
14
Types of Neuroglial Cells
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Fluid-filled cavity
of the brain or
spinal cord
Neuron
Ependymal
cell
Oligodendrocyte
Astrocyte
Microglial cell
Axon
Myelin
sheath (cut)
Capillary
Node of
Ranvier
15
Regeneration of A Nerve Axon
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Skeletal
muscle fiber
Motor neuron
cell body
Changes
over time
Site of injury
Schwann cells
Axon
(a)
Distal portion of
axon degenerates
(b)
Proximal end of injured axon
regenerates into tube of sheath cells
(c)
Schwann cells
degenerate
(d)
Schwann cells
proliferate
(e)
Former connection
reestablished
16
16
10.5: The Synapse
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• Nerve impulses pass
from neuron to neuron at
synapses, moving from a
pre-synaptic neuron to a
post-synaptic neuron.
Synaptic
cleft
Impulse
Dendrites
Axon of
presynaptic
neuron
Axon of
postsynaptic
neuron
Axon of
presynaptic
neuron
Impulse
Cell body of
postsynaptic
neuron
Impulse
17
Synaptic Transmission
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Direction of
nerve impulse
• Neurotransmitters are
released when impulse
reaches synaptic knob
Axon
Ca+2
Synaptic knob
Synaptic
vesicles
Presynaptic neuron
Ca+2
Cell body or dendrite
of postsynaptic neuron
Mitochondrion
Ca+2
Synaptic
vesicle
Vesicle releasing
neurotransmitter
Axon
membrane
Neurotransmitter
Synaptic cleft
Polarized
membrane
Depolarized
membrane
(a)
18
Animation:
Chemical Synapse
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in
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19
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.
20
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 sodium ions out of the cell
and potassium ions into the cell.
21
Resting Potential
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• 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
High Na+
Low Na+
Impermeant
anions
High K+
Axon
Cell body
Low K+
Axon terminal
(a)
+
–
+
–
+
–
+
–
–
+
+
–
+
–
+ –
–
+
–
+
–
+
–
+
–
+
–
+
–70 mV
(b)
+
–
High Na+
Na+
Low K+
+
+
–
–
Low Na+
Pump
K+
High K+
+ –
–
+
+
–
+
–
+
–
–
+
–
+
–
+
–
+
+
–
–
+
+
–
–
+
–70 mV
(c)
22
+
–
–
+
+
–
–
+
Local Potential Changes
• Caused by various stimuli:
• Temperature changes
• Light
• Pressure
Gatelike mechanism
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Protein
Cell
membrane
(a) Channel closed
Fatty acid
tail
Phosphate
head
(b) Channel open
• Environmental changes affect the membrane
potential by opening a gated ion channel
• Channels are 1) chemically gated, 2) voltage gated,
or 3) mechanically gated
23
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
24
Local Potential Changes
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Na+
Na+
–62 mV
Neurotransmitter
(a)
Chemically-gated
Na+ channel
Presynaptic
neuron
Voltage-gated
Na+ channel
Trigger zone
Na+
Na+
Na+
Na+
Na+
–55 mV
25
(b)
Action Potentials
• At rest, the membrane is
polarized (RMP = -70)
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Na+
• Threshold stimulus
reached (-55)
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
Na+
Na+
Na+
Na+
–0
–70
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
(a)
• Sodium channels open
and membrane
depolarizes (toward 0)
K+
Na+
Na+
Na+
K+
K+
K+
K+
K+
K+
–0
K+
Na+ channels open
K+ channels closed
Threshold
stimulus
K+
K+
Na+
K+
Na+
K+
Na+
K+
K+
K+
K+
–70
• Potassium leaves
cytoplasm and
membrane repolarizes
(+30)
• Brief period of
hyperpolarization (-90)
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Region of depolarization
(b)
K+
K+
K+
K+
Na+
Na+
Na+
K+
K+
K+
K+
K+
K+
Na+
Na+
Na+
K+
K+
K+
K+
K+
K+
K+
K+
Region of repolarization
(c)
Na+
Na+
Na+
Na+
Na+
Na+
Na+
K+ channels open
Na+ channels closed
–0
–70
Na+
26
Action Potentials
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+40
Membrane potential (millivolts)
Action potential
+20
0
–20
Resting potential
reestablished
–40
Resting
potential
–60
–80
Hyperpolarization
0
1
2
3
4
5
Milliseconds
6
7
8
27
Action Potentials
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Region of
action potential
+
+
+
+
+
+
+
+
+
+
+
–
–
–
–
–
–
–
–
–
+
+
–
–
–
–
–
–
–
–
–
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
–
–
–
–
–
–
+
–
–
–
–
–
–
+
+
+
+
+
(a)
+
–
+
–
+
–
+
Direction of nerve impulse
–
–
–
+
+
+
+
+
+
+
+
+
+
+
+
(b)
+
–
–
–
–
–
–
–
+
+
–
–
–
–
–
–
–
–
–
+
+
–
–
+
(c)
+
+
+
+
+
+
+
+
+
28
Animation:
Action Potential Propagation
in Unmyelinated Neurons
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29
Animation:
Action Potential Propagation
in Myelinated Neurons
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30
All-or-None Response
• If a neuron responds at all, it responds completely
• 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
31
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
32
Impulse Conduction
33
Animation:
The Nerve Impulse
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34
10.7: Synaptic Transmission
• This is where released neurotransmitters cross the
synaptic cleft and reacts 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, making it more likely or
less likely for an action potential to occur.
35
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
36
Summation of
EPSPs and IPSPs
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• EPSPs and IPSPs are added
together in a process called
summation
• More EPSPs lead to greater
probability of an action
potential
• More IPSPs lead to lower
probability of an action
potential
Neuron
cell body
Nucleus
Presynaptic
knob
Presynaptic
axon
37
Neurotransmitters
38
Neurotransmitters
39
10.8: Impulse Processing
• The way the nervous system processes nerve impulses and
acts upon them.
• Neuronal pools of interneurons
• Convergence
• Divergence
40
Neuronal Pools
• Groups of interneurons that make synaptic connections
with each other
• Interneurons work together to perform a common function
– may be excitatory or inhibitory
• Each pool receives input from other neurons
• Each pool generates output to other neurons
41
Convergence
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• Neuron receives input from
several neurons
• Incoming impulses represent
information from different types
of sensory receptors
1
2
• Allows nervous system to
collect, process, and respond to
information
• Makes it possible for a neuron to
sum impulses from different
sources
3
(a)
42
Divergence
• One neuron sends impulses
to several neurons via its
branched axon
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• Can amplify an impulse
4
• Impulse from a single neuron
in CNS may be amplified to
activate enough motor units
needed for muscle contraction
or glandular secretion
6
5
43
(b)
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.
44
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.
45
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.
46