Transcript Chapter 14-Nervous Tissuex

Chapter 14
Nervous Tissue
• Neuron = single cell
• Nerve = bundle of cells targeting
same muscle, organ, gland, etc.
2
Fig. 14.1
Nervous System
Organization
• Structural organization
• Central nervous system
• Peripheral nervous
system
• cranial nerves extend
from brain
• spinal nerves extend
from spinal cord
• ganglia are clusters of
neuron cell bodies
outside CNS
Brain
Spinal
cord
Central
nervous
system (CNS)
Cranial
nerves
Peripheral
Spinal
nerves nervous
Ganglia system
(PNS)
Nervous System
Organization
• Functional organization
• Sensory nervous system
• receives sensory
information and sends
to brain
• afferent
• Motor nervous system
• transmits motor
impulses from CNS to
muscles or glands
• efferent
• SAME DAVE
Fig. 14.1
Brain
Spinal
cord
Central
nervous
system (CNS)
Cranial
nerves
Peripheral
Spinal
nerves nervous
Ganglia system
(PNS)
Fig. 14.1
Nervous System
Organization
• Sensory nervous system
divisions
• Somatic sensory receives info
from skin, joints, skeletal muscles,
eyes, ears, nose
• Visceral sensory receives info
from organs, glands, etc.
• Changes in neuron’s
environment are called stimuli
Fig. 14.1
Nervous System
Organization
• Motor nervous system
divisions
• somatic motor division
• under voluntary (conscious and
unconscious) control
• controls skeletal muscles
• autonomic motor division
• the involuntary nervous system
• controls cardiac and smooth
muscles, and glands
Fig. 14.2
Functional Organization of the Nervous System
Nervous system
Sensory nervous system
Contains receptors
Transmits information from
receptors to the CNS
Somatic sensory
Receives sensory
information
from skin, fascia,
joints, skeletal
muscles,
special senses
Motor nervous system
Transmits information from
CNS to the rest of the body
Sends motor information
to effectors
Visceral sensory
Somatic motor
Autonomic motor
Receives sensory
information
from viscera
“Voluntary”
nervous system:
innervates
skeletal muscle
“Involuntary”
nervous system:
innervates
cardiac muscle,
smooth muscle,
glands
Dendritic spines
Direction of nerve
impulse ("input")
Dendrites
Nucleus
Cell body
Axon hillock
Axon
Neurolemmocyte/
Schwann
cell
Direction
of nerve impulse
("output")
Axon collateral
Neurofibril
node
Myelin sheath
Axon terminals
• Axon collateral =
side branch of neuron
• Neurolemmocyte =
Schwann cell = cell
that wraps around
and supports axon
Synaptic knobs
Input
Output
Fig. 14.3
Dendrites
Nucleus
Cell body
Axon hillock
Axon
LM 100x
Fig. 14.4
Types of neurons
• Unipolar have one process connecting axon to cell body
• most sensory neurons in PNS
Dendrites
Cell body
Short single process
Peripheral
process
Central
process
Axon
(a) Unipolar neuron
Fig. 14.4
Types of neurons
• Bipolar have two processes from cell body
• Present in olfactory epithelium of nose and retina of eye
Cell body
Dendrite
Axon
(b) Bipolar neuron
Fig. 14.4
Types of neurons
• Multipolar have many dendrites and one axon
• most common in human body
• motor neurons that innervate muscles and glands
Dendrites
Dendrites
Cell body
Cell body
Axon
Axon
(c) Multipolar neurons
Input
Output
Fig. 14.5
• Interneurons integrate response to sensory input
• communication between sensory and motor neurons
• lie entirely within CNS
• multipolar structures
Cell body
Afferent
of sensory
(input)
transmission neuron
Posterior root
ganglion
Spinal cord
Dendrites
Sensory neuron
Skin receptors
Skeletal muscle
Axon
Interneuron
Efferent
(output)
transmission
Motor neuron
Glial cells
•
•
•
•
AKA neuroglia
occur within CNS and PNS
smaller than neurons; capable of mitosis
assist neurons with functions; protect and nourish
neurons
• 4 types
– distinguished by size, intracellular organization, presence of
specific cytoplasmic processes
14
Fig. 14.6
Neuron
Microglial cell
Astrocyte
Oligodendrocyte
Myelinated axon
Myelin sheath (cut)
Capillary
Ependymal
cells
Ventricle of
brain
Fig. 14.7
Astrocytes
• Most abundant glial cells
in CNS
Perivascular
feet
Astrocyte
• >90% of nervous tissue
in some
areas of brain
• Lots of projection from
surface
• Touch capillary walls
and neurons
Neuron
Capillary
(a) Astrocyte
Fig. 14.7
Astrocytes
• Functions
• Help form blood-brain barrier
(prevent unwanted materials
from entering brain)
• Regulate chemical
composition of fluid within the
brain
• Help regulate synaptic
transmission
• Strengthen and organize
nervous tissue in CNS
• Replace damaged neurons
• Assist with neuronal
development
Neuron
Perivascular
feet
Astrocyte
Capillary
(a) Astrocyte
Fig. 14.7
Ependymal cells
• in CNS
• Line spinal cord and brain
vesicles
• Secrete cerebrospinal fluid
• One side covered by cilia to
create current to move fluid
Central canal of
Cilia spinal cord
Ependymal
cells
Spinal cord
(b) Ependymal cells
Fig. 14.7
Microglial cells
• In CNS
Microglial cell
Neuron
• Fewest in CNS
• Small with slender branches
• Travel through CNS
• Replicate in response to
infection
• Remove debris
(c) Microglial cell
Fig. 14.7
Oligodendrocytes
Oligodendrocyte
• Have many processes
extending from plasma
membrane
• Wrap plasma membrane around
neighboring axons = myelin
• Provides insulation,
Axons
increases speed of signals
in neurons
(d) Oligodendrocyte
Myelin
sheath
Fig. 14.7
PNS Glial Cells
Posterior root ganglion
Satellite cells
Satellite cells
• Surround cell body of
neurons in ganglia
• Provide protection, support,
nutrition
Axon
• Separate cell bodies from
each other inside ganglia
Cell body of Posterior root
sensory neuron
Fig. 14.7
PNS Glial Cells
Neurolemmocytes/
Schwann cells
Neurofibril nodes
Axon
• Similar to oligodendrocytes of
CNS
• Each wraps itself around ONE
axon
• one axon myelinated by many
Schwann cells
Neurolemmocyte
Myelin sheath
• Provide insulation, speed
signals carried by neuron
Page 422
An MRI shows a glioma (arrow).
© Simon Fraser/Science Source
Fig. 14.8
1. Neurolemmocyte
starts to wrap around
a portion of an axon.
Formation of Myelin
Sheath
Copyright © McGraw-Hill Education. Permission required for reproduction or display.
Axon
Neurolemmocyte
Direction of
wrapping
Fig. 14.8
1. Neurolemmocyte
starts to wrap around
a portion of an axon.
Axon
Neurolemmocyte
2. Neurolemmocyte
cytoplasm and
plasma membrane
begin to form
consecutive layers
around axon.
Copyright © McGraw-Hill Education. Permission required for reproduction or display.
Direction of
wrapping
Fig. 14.8
1. Neurolemmocyte
starts to wrap around
a portion of an axon.
Axon
Neurolemmocyte
2. Neurolemmocyte
cytoplasm and
plasma membrane
begin to form
consecutive layers
around axon.
3. The overlapping
inner layers of the
neurolemmocyte
plasma membrane
form the myelin
sheath.
Copyright © McGraw-Hill Education. Permission required for reproduction or display.
Direction of
wrapping
Cytoplasm of the
neurolemmocyte
Myelin sheath
1. Neurolemmocyte
starts to wrap around
a portion of an axon.
2. Neurolemmocyte
cytoplasm and plasma
membrane begin to
form consecutive
layers around axon.
3. The overlapping
inner layers of the
neurolemmocyte
plasma membrane
form the myelin
sheath.
4. Eventually, the neurolemmocyte
cytoplasm and nucleus are pushed
to the periphery of the cell as the
myelin sheath is formed.
Axon
Neurolemmocyte
Direction of
wrapping
Cytoplasm of the
neurolemmocyte
Myelin sheath
Myelin sheath
Neurolemmocyte
nucleus
Copyright © McGraw-Hill Education. Permission required for reproduction or display.
Oligodendrocytes
Fig. 14.9
Neurofibril
node
Axons
Myelin sheath
(a) CNS
Neurolemmocytes
(forming myelin sheath)
Neuron
cell body
Neurofibril
node
Axon
(b) PNS
Fig. 14.10
Unmyelinated axons
Neurolemmocyte
1 Neurolemmocyte starts to
envelop multiple axons.
2 The unmyelinated axons are
enveloped by the neurolemmocyte,
but there are no myelin sheath
wraps around each axon.
Unmyelinated
axon
Neurolemmocyte
Axons
Neurolemmocyte
nucleus
Fig. 14.10
Unmyelinated axons
Unmyelinated axons
Myelin sheath
Myelinated axon
TEM 60,000x
Myelin and Signal Conduction
• With myelin, signal in neuron appears to “jump” from one
node to another
– called “saltatory conduction”
• Signals travel faster
along neuron
Neurofibril
nodes
Fig. 14.11
Neuron regeneration
Endoneurium Neurilemma
1 Trauma severs axon.
Skeletal muscle fibers
2 The proximal portion of each severed
axon seals off and swells. The distal
portion of axon and myelin sheath
disintegrate; the neurolemma survives.
Endoneurium
Sealed, swollen
end of axon
Fig. 14.11
Neuron regeneration
Endoneurium
Neurilemma
1 Trauma severs axon.
Skeletal muscle fibers
2
The proximal portion of each severed
axon seals off and swells. The distal
portion of axon and myelin sheath
disintegrate; the neurilemma survives.
3
Endoneurium Sealed, swollen
end of axon
Neurilemma and endoneurium
form a regeneration tube.
Fig. 14.11
Neuron regeneration
Endoneurium
Neurilemma
1 Trauma severs axon.
Skeletal muscle fibers
2
The proximal portion of each severed
axon seals off and swells. The distal
portion of axon and myelin sheath
disintegrate; the neurilemma survives.
3
Endoneurium Sealed, swollen
end of axon
Neurilemma and endoneurium
form a regeneration tube.
4 Axon regenerates and
remyelination occurs.
Fig. 14.11
Neuron regeneration
1
Endoneurium
Neurilemma
Trauma severs axon.
Skeletal muscle fibers
2
The proximal portion of each severed
axon seals off and swells. The distal
portion of axon and myelin sheath
disintegrate; the neurilemma survives.
3
Neurilemma and endoneurium
form a regeneration tube.
4
5
Endoneurium Sealed, swollen
end of axon
Axon regenerates and
remyelination occurs.
Innervation to effector
is restored.
Page 427
Actor Christopher
Reeve was a pioneer in
challenging previous
conceptions about
neuron regeneration.
© Kenneth Lambert/AP Photo
Rob Smets
Bullfighter, Professional Bull Riding
Broke his neck 3 times,
suffered same break as
Christopher Reeve.
Sustained only limited
mobility in his neck
37
Fig. 14.12
Axon
Myelin sheath
Endoneurium
Fascicle
Perineurium
Epineurium
Blood vessels
Fig. 14.12
Perineurium
Fascicle
Myelin sheath
Axon
Nucleus
Endoneurium
Neurofibril node
Axon
LM 550x
Myelin sheath
Blood vessels
SEM 450x
Fig. 14.14
Electrical
synapse
Smooth
muscle cells
Presynaptic
cell
Gap junction
Local current
++
+ +
+
+
+
+
+
+
+
+
Positively
charged ions
Plasma
membrane
(a) Electrical synapse
Postsynaptic
cell
++
++
+++
++
Connexons
Inner surface
of plasma
membrane
Fig. 14.14
Nerve impulse
Axon
Synaptic
vesicles
containing
acetylcholine
(ACh)
Calcium
(Ca2+) ions
Voltage-regulated
calcium (Ca2+)
channel
Synaptic
cleft
Acetylcholine binds
to receptor protein,
causing ion gates
to open
Presynaptic neuron
Acetylcholine
Sodium
(Na+) ions
Postsynaptic neuron
Postsynaptic
membrane
Receptor protein
Fig. 14.15
Input Output
Input
Input
Input
Input
Input
Input
Input
Output
Outputs
(a) Converging
circuit
(b) Diverging
circuit
Output
Output
(c) Reverberating (d) Parallel-after-discharge
circuit
circuit
Page 431
(a)
Individuals with neurodegenerative
diseases must overcome physical
challenges to carry on the activities of
daily life. (a) Amyotrophic lateral
sclerosis (scientist and writer
Stephen Hawking).
(b) Multiple sclerosis.
(b)