Transcript Nerve activates contraction

Essentials of Human Anatomy & Physiology
Elaine N. Marieb
Seventh Edition
The Nervous System
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Functions of the Nervous System
 Sensory input – gathering information
 Uses sensory receptors to monitor changes
occurring inside and outside the body
 Changes = stimuli
 Integration
 To process and interpret sensory input and
decide if action is needed
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Slide 7.1a
Functions of the Nervous System
Slide 7.1b
 Motor output
 A response to integrated stimuli
 The response activates muscles or glands
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Classification of the Nervous System
 Central nervous system (CNS)
 Brain & Spinal cord
 Integrative & control centers
 Peripheral nervous system (PNS)
 Cranial & Spinal Nerves outside the brain
and spinal cord
 Communication lines between the CNS and
the rest of the body
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Slide 7.2
Divisions of the NS

CNS



Brain
Spinal cord
PNS

Cranial & spinal
nerves
Distribution of Cranial Nerves
Figure 7.21
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Slide 7.59
Spinal Nerves
Figure 7.22a
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Slide 7.64
Functional Classification of the
Peripheral Nervous System
 Sensory (afferent) division
 Nerve fibers that carry information to the
central nervous system
 Somatic (body) & visceral (organ) sensory
neurons
Figure 7.1
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Functional Classification of the
Peripheral Nervous System
 Motor (efferent) division
 Nerve fibers that carry impulses away from
the central nervous system
 Motor neurons
 Conduct impulses from CNS to muscles &
glands
Figure 7.1
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Slide 7.3b
Functional Classification of the
Peripheral Nervous System
 Motor (efferent) division
 Two subdivisions
 Somatic nervous system = voluntary
Conducts impulses to skeletal
muscles
 Autonomic nervous system = involuntary
Conducts impulses to cardiac muscle,
smooth muscle, & glands
Figure 7.1
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Slide 7.3c
Functional Classification of the
Peripheral Nervous System
 Autonomic nervous system
 Has 2 subdivisions
 Sympathetic division
Fight or flight system
Speeds up HR, respiration rate,
increases cardiac output, deactivates
digestive system
 Parasympathetic division
Resting system
Activates digestive, slows other
systems
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Organization of the Nervous
System
Figure 7.2
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Slide 7.4
Neuroglia



“Cell Glue”
Assist, segregate, and insulate neurons
Neuroglia can replicate but cannot conduct
Nervous Tissue: Support Cells
(Neuroglia – non conducting)
 Astrocytes: CNS
 Abundant, star-shaped cells
 Brace & anchor neurons
 Control the chemical
environment of
the brain
Figure 7.3a
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Slide 7.5
Nervous Tissue: Support Cells
 Microglia: CNS
 Spider-like phagocytes
 Dispose of debris
 Engulf & destroy
invaders
 Ependymal cells:CNS
 Line cavities of the
brain and spinal cord
 Form & circulate
cerebrospinal
fluid
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Figure 7.3b, c
Slide 7.6
Nervous Tissue: Support Cells
 Oligodendrocytes
 CNS
 Produce myelin
sheath around
nerve fibers in the
central nervous
system
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Figure 7.3d
Slide 7.7a
Support Cells in the PNS
 Theodore Schwann
 Schwann cells
 Form myelin sheath in the peripheral
nervous system
Figure 7.3e
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Support Cells in the PNS
 Satellite cells
 Protect neuron cell bodies by cushioning &
controlling chemical environment
Figure 7.3e
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Slide 7.7b
Neurofibromatosis

Overproduction of
Schwann cells
Neuroglia vs. Neurons
Neuroglia divide. Neurons do not.
 Most brain tumors are “gliomas.”
 Most brain tumors involve the neuroglia cells,
not the neurons.
 Consider the role of cell division in cancer!
Nervous Tissue: Neurons
 Neurons = nerve cells
 Cells specialized to transmit messages –
can conduct but cannot replicate
 Have 3 specialized characteristics
 Longevity: with nutrition, can live as long
as you do
 Amitotic: unable to reproduce
themselves (so cannot be replaced)
 High metabolic rate: require continuous
oxygen & glucose (due to lots of activity)
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Slide 7.8
Neurolemma

Why is the plasma membrane of a neuron
so important?

It is the site of electrical signaling – plays a
crucial role in cell to cell interactions during
development as well
Major Regions of Neurons
 Cell body
 Contains the nucleus and is the
metabolic/biosynthetic center of the cell
 Does not contain centrioles (reflects
amitotic nature) but has the other
organelles
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Slide 7.8
Neuron Anatomy
 Cell bodycontains:
 Ribosomes –
protein makers
 Nissl substance –
specialized rough
ER
 Neurofibrils –
intermediate
cytoskeleton that
maintains cell shape
& help transport
Figure 7.4a
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Slide 7.9a
Neuron Anatomy
 Dendrites
 conduct
impulses toward
the cell body
 hundreds per
cell – diffusely
branched
 Receptive sites
 Immense
surface area for
reception
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Figure 7.4a
Slide 7.10
Neuron Anatomy
 Axons
 conduct impulses
away from the
cell body
 Single axon per
neuron arising
from axon hillock
 May have right
angle collateral
branches
 Vary in length
and diameter
Figure 7.4a
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Slide 7.10
Axons and Nerve Impulses
 Axons end in axonal terminals
10,000+ per neuron
 Contain vesicles with neurotransmitters
 Axonal terminals are separated from the
next neuron or effector by a gap
 Synaptic cleft – gap between adjacent
neurons
 Synapse – junction between nerves
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Slide 7.11
Label your neuron
diagram
Myelin Sheath
 Definition: whitish,
phospholipid
covering on axon
 Function:
 Protects & insulates
fibers
 Increases speed of
transmission
Figure 7.5
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Slide 7.12
Myelin Sheath in CNS
 Oligodendrite cells
 produce myelin
sheaths in jelly-roll
like fashion
 Coil around multiple
fibers not single axon
 Lack neurolemma which
plays a part in fiber
regeneration
Figure 7.5
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Slide 7.12
Myelin Sheath in PNS
 Schwann cells –
produce myelin sheaths
in jelly-roll like fashion
 Neurolemma –
nucleus and most of
cytoplasm just beneath
outermost plasma
membrane
 Nodes of Ranvier –
gaps in myelin sheath
along the axon
Figure 7.5
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Slide 7.12
Multiple Sclerosis, etc.

Multiple sclerosis – autoimmune disease –
myelin sheath converted to hardened
scleroses – current shortcircuited – muscle
control is lost
http://www.nationalmssociety.org/about%20
ms.asp

Demyelinating disorders
http://www.neuropat.dote.hu/myelin.htm
Take Quiz #1
CNS
 Nuclei – clusters of cell bodies within the
white matter of the central nervous system
 Tracts – bundles of nerve fibers/neurons
• Gray matter refers to cell bodies and
unmyelinated fiber while white matter refers to
the mylinated axons
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Slide 7.13
PNS


Ganglia – clusters of cell bodies found in
PNS
Nerves – bundles of nerve fibers
Functional Classification of
Neurons
 Sensory (afferent) neurons
 Carry impulses from the sensory receptors
 Cell bodies always found in ganglia in PNS
 Motor (efferent) neurons
 Carry impulses from the central nervous
system
 Cell bodies always found in CNS
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Slide
7.14a
Functional Classification of
Neurons
 Interneurons (association neurons)
 Integration & reflex
 Connect sensory and motor neurons
 Cell bodies always in CNS
 Make up 99% of neurons in body
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Slide
7.14b
Neuron Classification
Figure 7.6
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Slide 7.15
Structural Classification of Neurons
 Based on number of processes
extending from cell body
Figure 7.8a
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Slide
7.16a
Types of Neurons
Structural Classification of Neurons
 Multipolar neurons
 many extensions from the cell body
 Most common type
 All motor and association neurons
Figure 7.8a
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Slide
7.16a
Structural Classification of Neurons
 Bipolar neurons
 one axon and one dendrite
 Found in special sensory organs (retina
of eye, olfactory mucosa)
Figure 7.8b
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Slide
7.16b
Structural Classification of Neurons
 Unipolar neurons - diagrams
 short single process leaving the cell body
 Conduct to and from from cell body bidirectional
 Sensory neurons found in PNS
Figure 7.8c
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Slide
7.16c
Regeneration
 Mature neurons are incapable of
mitosis. However, PNS axons can
regenerate if cell body is not destroyed.
 Upon injury, an axon will begin to swell
& disintegrate in a process called
Wallerian degeneration.
 The uninjured cell body gets larger in
order to synthesize proteins needed for
regeneration
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Slide
7.14b
Repair
Regeneration
 Axons regenerate at a rate of 1.5
mm/day
 The greater the distance between
severed nerve endings, the less chance
of recovery. Surgical realignment can
help. Retraining may be necessary once
the connection is completed
 If distance is great, axonal sprouts may
grow into surrounding areas and form a
Slide
mass called a neuroma.
7.14b
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Regeneration
 PNS vs CNS
In PNS axon regeneration,
macrophages clean out the debris
from the injury.
Schwann cells will form a neurolemma
tunnel to guide severed nerve ending
together. A growth factor is also
released
In CNS – No Schwann cells to do this.Slide
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7.14b
Take Quiz #2
Functional Properties of Neurons
 Irritability
 Def: ability to respond to stimuli & convert it
into a nerve impulse
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Slide 7.17
Stages of electrical Event
 Resting Membrane Potential – INACTIVE
STATE
 The plasma membrane at rest is polarized
 The outer surface of the plasma
membrane is more positive than the inner
surface
 Neuron will be inactive in this condition
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Slide 7.17
Starting a Nerve Impulse
 A stimulus at threshold
causes a permeability
change
 which depolarizes the
neuron’s membrane
 A depolarized
membrane allows
sodium (Na+) to rush
into the membrane
 The reversing polarity
initiates an action
potential in the neuron
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Figure 7.9a–c
Slide 7.18
The Action Potential
 If the action potential (nerve impulse)
starts, it is propagated/conducted over
the entire axon. This is an all or none
response.
 During repolarization, potassium ions
rush out of the neuron which repolarizes
the membrane charge
 During the refractory period, the Na/K
pump restores the original ion balance
 This action requires ATP - Neuron cannot
conduct again until this happens
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Slide 7.19
Nerve Impulse Propagation
 Impulses travel faster in
myelinated fibers in a
process called saltatory
conduction.
 w/o myelin speed is less
(5 m/sec)
 w/myelin (100 m/sec or
200 mi/hr)
Figure 7.9c–e
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Slide 7.20
Functional Properties of Neurons
 Conductivity – ability to transmit an
impulse to other neurons, muscles, or
glands
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Slide 7.17
Stages of the Chemical Event
 The action potential reaches the axon
terminals
 Neurotransmitter is released into the synaptic
cleft when the vesicle fuses with the
membrane (presynaptic neuron)
 NT diffuses across the cleft and binds to the
receptors on the dendrite of the next neuron
(postsynaptic neuron)
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Slide 7.21
Pre & Post synaptic membranes
Stages of the Chemical Event
 An action potential is started in the next
neuron (or muscle or gland)
 In order to prevent continuous stimulation, NT
is removed from the synapse through:
 Re-uptake
 Enzymatic breakdown
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Slide 7.21
What are nuerotransmitters?
Definition:
Neurotransmitters are endogenous
chemicals which transmit signals from a neuron to a target
cell across a synapse.[1] Neurotransmitters are packaged
into synaptic vesicles clustered beneath the membrane on
the presynaptic side of a synapse, and are released into the
synaptic cleft, where they bind to receptors in the
membrane on the postsynaptic side of the synapse.
Release of neurotransmitters usually follows arrival of an
action potential at the synapse, but may also follow
graded electrical potentials. Low level "baseline" release
also occurs without electrical stimulation.
Neurotransmitters are synthesized from plentiful and
simple precursors, such as amino acids, which are readily
available from the diet and which require only a small
number of biosynthetic steps to convert.[2]
•Excitatory causes action while
inhibitory inhibits action
•Ionotropic: rapid response, shorter
action time
•Metabotropic: broader spectrum, longer
lasting effects
Neurotransmitters

Know the functional class & comments for
the following NT:






Acetylcholine
Norepinephrine
Dopamine
Serotonin
Histamine
Endorphins,enkephlins
Neurotransmitters
Group
Neurotransmitter
Region of Operation
Acetylcholine
Acetylcholine
Central Nervous System (CNS),
Peripheral Nervous System (PNS) and
Autonomic Nervous System (ANS)
Serotonin
Serotonin
CNS and PNS
Amino acids
Glutamate, Gamma Aminobutyric Acid (GABA), CNS
Glycine, Aspartate
Histamine
Histamine
Catecholamines
Hypothalamus
CNS and Sympathetic Nervous System
Norpinephrine, Epinephrine (Adrenalin)
Neuropeptides
Endorphins (Enkephalins and Dynorphins),
Substance P
CNS
Dopamine
Dopamine
CNS
Nucleotides
CNS, PNS and ANS
Adenosine, Adenosine Triphosphate (ATP)
Nitric oxide
Nitric oxide
CNS
Acetylcholine: Acetylcholine is widely
distributed that is known to trigger
muscle contraction excretion of the
central hormones are stimulated. It is a
‘Feel Good’ neurotransmitter that is
important for memory, alertness,
sexuality, anger to name a few.
Norepinephrine: In mood disorders like
manic depression, this neurotransmitter
plays a major role. The most important
features of norepinephrine are its
importance being connected to sleep,
dreams, emotions and learning. When
released into the blood circulation as a
hormone, results in the heart rate increase
by contracting the blood vessels.
Dopamine: Depending upon the location of
action, dopamine has varied functions.
Generally, dopamine acts as an inhibitory
neurotransmitter. Dopamine is the
neurotransmitter that is responsible for the
generation of feeling of pleasure, bliss,
control of appetite, feeling focussed and
control of movement. Dopamine also plays
a key role in modulating mood.
Serotonin: Regulation of body
temperature, mood, sleep, pain
and appetite are varied functions
that serotonin contributes.
Histamine triggers the inflammatory
response. As part of an immune response to
foreign pathogens, histamine is produced by
basophils and by mast cells found in nearby
connective tissues. Histamine increases the
permeability of the capillaries to white blood
cells and other proteins, in order to allow
them to engage foreign invaders in the
infected tissues.
Endorphins: Also called Opiods,
contributes for elevation and enhancing of
the mood. These are known as the naturally
occurring painkillers.
Enkephalins: An inhibitory
neurotransmitter that reduce depression,
help in restricting transmission of pain.
Electrical & Chemical synapses
The Brain From Top to Bottom
http://thebrain.mcgill.ca/flash/i/i_03/i_03
_m/i_03_m_par/i_03_m_par.html
How Neurons Communicate at
Synapses
Figure 7.10
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Slide 7.22